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Title: Handbook of Medical Entomology

Author: William Albert Riley
        Oskar Augustus Johanssen

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Language: English

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[Illustration: Some early medical entomology. Athanasius Kircher's
illustration of the Italian tarantula and the music prescribed as an
antidote for the poison of its bite. (1643).]




HANDBOOK OF MEDICAL

ENTOMOLOGY

WM. A. RILEY, PH.D.

Professor of Insect Morphology and Parasitology, Cornell University

and

O. A. JOHANNSEN, PH.D.

Professor of Biology, Cornell University

[Illustration]

ITHACA, NEW YORK

THE COMSTOCK PUBLISHING COMPANY

1915


COPYRIGHT, 1915

BY THE COMSTOCK PUBLISHING COMPANY,

ITHACA, N. Y.


Press of W. F. Humphrey
Geneva, N. Y.




PREFACE


The Handbook of Medical Entomology is the outgrowth of a course of
lectures along the lines of insect transmission and dissemination of
diseases of man given by the senior author in the Department of
Entomology of Cornell University during the past six years. More
specifically it is an illustrated revision and elaboration of his "Notes
on the Relation of Insects to Disease" published January, 1912.

Its object is to afford a general survey of the field, and primarily to
put the student of medicine and entomology in touch with the discoveries
and theories which underlie some of the most important modern work in
preventive medicine. At the same time the older phases of the
subject--the consideration of poisonous and parasitic forms--have not
been ignored.

Considering the rapid shifts in viewpoint, and the development of the
subject within recent years, the authors do not indulge in any hopes
that the present text will exactly meet the needs of every one
specializing in the field,--still less do they regard it as complete or
final. The fact that the enormous literature of isolated articles is to
be found principally in foreign periodicals and is therefore difficult
of access to many American workers, has led the authors to hope that a
summary of the important advances, in the form of a reference book may
not prove unwelcome to physicians, sanitarians and working
entomologists, and to teachers as a text supplementing lecture work in
the subject.

Lengthy as is the bibliography, it covers but a very small fraction of
the important contributions to the subject. It will serve only to put
those interested in touch with original sources and to open up the
field. Of the more general works, special acknowledgment should be made
to those of Banks, Brumpt, Castellani and Chalmers, Comstock, Hewitt,
Howard, Manson, Mense, Neveau-Lemaire, Nuttall, and Stiles.

To the many who have aided the authors in the years past, by suggestions
and by sending specimens and other materials, sincerest thanks is
tendered. This is especially due to their colleagues in the Department
of Entomology of Cornell University, and to Professor Charles W. Howard,
Dr. John Uri Lloyd, Mr. A. H. Ritchie, Dr. I. M. Unger, and Dr. Luzerne
Coville.

They wish to express indebtedness to the authors and publishers who have
so willingly given permission to use certain illustrations. Especially
is this acknowledgment due to Professor John Henry Comstock, Dr. L. O.
Howard, Dr. Graham-Smith, and Professor G. H. T. Nuttall. Professor
Comstock not only authorized the use of departmental negatives by the
late Professor M. V. Slingerland (credited as M. V. S.), but generously
put at their disposal the illustrations from the MANUAL FOR THE STUDY OF
INSECTS and from the SPIDER BOOK. Figures 5 and 111 are from Peter's
"Der Arzt und die Heilkunst in der deutschen Vergangenheit." It should
be noted that on examining the original, it is found that Gottfried's
figure relates to an event antedating the typical epidemic of dancing
mania.

                                                  WM. A. RILEY.
                                                  O. A. JOHANNSEN.

  CORNELL UNIVERSITY,
  January, 1915.




ADDITIONS AND CORRECTIONS

vi line 11, for Heilkunft read Heilkunst.

18 line 2, for tarsi read tarsus.

32 line 21, and legend under fig. 23, for C. (Conorhinus) abdominalis
      read Melanolestes abdominalis.

47 legend under figure for 33c read 34.

92 line 22 and 25, for sangiusugus read sanguisugus.

116 legend under fig. 83, for Graham-Smith read Manson.

136 line 10, from bottom, insert "ring" after "chitin".

137 line 3, for meditatunda read meditabunda.

145 line 7, from bottom, for Rs read R_5.

158 line 20, for have read has.

212 after the chapter heading insert "continued".

219 line 10, from bottom, for Cornohinus read Conorhinus.

266 line 1, fig. 158j refers to the female.

272 line 5, insert "palpus" before "and leg".

281 line 6, for discodial read discoidal.

281 last line, insert "from" before "the".

284 line 5, for "tubercle of" read "tubercle or".

305 lines 19, 28, 44, page 306 lines 1, 9, 22, 27, 30, page 307 line 7,
      page 309 lines 8, 11, for R_{4+5} read M_{1+2}.

309 legend under fig. 168 add Bureau of Entomology.

312 line 36, for "near apex" read "of M_{1+2}".

313 running head, for Muscidæ read Muscoidea.

314 line 29, for "distal section" read "distally M_{1+2}".

315 legend under fig. 172, for Pseudopyrellia read Orthellia, for
      Lyperosia read Hæmatobia, for Umbana read urbana.

323 and 325 legends under the figures, add "After Dr. J. H. Stokes".

328 line 7 from bottom for Apiochæta read Aphiochæta.




CONTENTS


CHAPTER I

INTRODUCTION                                                  1-5

  Early suggestions regarding the transmission of disease by
    insects.
  The ways in which arthropods may affect the health of man.


CHAPTER II

ARTHROPODS WHICH ARE DIRECTLY POISONOUS                       6-56

  The Araneida, or Spiders.
    The tarantulas. Bird spiders. Spiders of the genus
      Latrodectus. Other venomous spiders. Summary.
  The Pedipalpida, or whip-scorpions.
  The Scorpionida, or true scorpions.
  The Solpugida, or solpugids.
  The Acarina, or mites and ticks.
  The Myriapoda, or centipedes and millipedes.
  The Hexapoda, or true insects.
    Piercing or biting insects poisonous to man.
      Hemiptera, or true bugs.
        The Notonectidæ or back-swimmers. Belostomidæ or giant
          water-bugs. Reduviidæ, or assassin bugs. Other
          Hemiptera reported as poisonous to man.
      Diptera; the midges, mosquitoes and flies.
    Stinging insects.
      Apis mellifica, the honey bee. Other stinging forms.
    Nettling insects.
      Lepidoptera, or butterflies and moths. Relief from
        poisoning by nettling larvæ.
    Vescicating insects and those possessing other poisons
      in their blood plasma. The blister beetles. Other
      cryptotoxic insects.


CHAPTER III

PARASITIC ARTHROPODS AFFECTING MAN                            57-130

  Acarina, or mites.
    The Trombidiidæ, or harvest mites.
    The Ixodoidea, or ticks.
      Argasidæ. Ixodidæ. Treatment of tick bites.
    The mites.
      Dermanyssidæ. Tarsonemidæ. Sarcoptidæ, the itch mites.
        Demodecidæ, the follicle mites.
  Hexapoda, or true insects.
    Siphunculata, or sucking lice.
    Hemiptera.
    The bed-bug. Other bed-bugs.
  Parasitic Diptera, or flies.
    Psychodidæ, or moth flies. Phlebotominæ. Culicidæ, or
      mosquitoes. Simuliidæ, or black-flies. Chironomidæ, or
      midges. Tabanidæ, or horse-flies. Leptidæ or
      snipe-flies. Oestridæ, or bot-flies. Muscidæ, the
      stable-fly and others.
  Siphonaptera, or fleas.
    The fleas affecting man, the dog, cat, and rat.
    The true chiggers, or chigoes.

CHAPTER IV

ACCIDENTAL OR FACULTATIVE PARASITES                           131-143

  Acarina, or mites.
  Myriapoda, or centipedes and millipedes.
  Lepidopterous larvæ.
  Coleoptera, or beetles.
  Dipterous larvæ causing myiasis.
    Piophila casei, the cheese skipper. Chrysomyia macellaria,
      the screw-worm fly. Calliphorinæ, the bluebottles.
      Muscinæ, the house or typhoid fly, and others.
      Anthomyiidæ, the lesser house-fly and others.
      Sarcophagidæ, the flesh-flies.


CHAPTER V

ARTHROPODS AS SIMPLE CARRIERS OF DISEASE                      144-163

  The house or typhoid fly as a carrier of disease.
  Stomoxys calcitrans, the stable-fly.
  Other arthropods which may serve as simple carriers of
    pathogenic organisms.


CHAPTER VI

ARTHROPODS AS DIRECT INOCULATORS OF DISEASE GERMS             164-174

  Some illustrations of direct inoculations of disease germs
    by arthropods.
  The rôle of fleas in the transmission of the plague.


CHAPTER VII

ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC ORGANISMS         175-185

  Insects as intermediate hosts of tape-worms.
  Arthropods as intermediate hosts of nematode worms.
    Filariasis and mosquitoes.
  Other nematode parasites of man and animals.


CHAPTER VIII

ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA          186-211

  Mosquitoes and malaria.
  Mosquitoes and yellow fever.


CHAPTER IX

ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA          212-229

  Insects and trypanosomiases.
    Fleas and lice as carriers of Trypanosoma lewisi.
    Tsetse-flies and nagana.
    Tsetse-flies and sleeping sickness in man.
    South American trypanosomiasis.
    Leishmanioses and insects.
  Ticks and diseases of man and animals.
    Cattle tick and Texas fever.
    Ticks and Rocky Mountain Spotted fever of man.


CHAPTER X

ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA
(CONTINUED)                                                   230-240

  Arthropods and Spirochætoses of man and animals.
    African relapsing fever of man.
    European relapsing fever.
    North African relapsing fever of man.
    Other types of relapsing fever of man.
    Spirochætosis of fowls.
    Other spirochæte diseases of animals.
  Typhus fever and lice.


CHAPTER XI

SOME POSSIBLE, BUT IMPERFECTLY KNOWN CASES OF
ARTHROPOD TRANSMISSION OF DISEASE                             241-256

  Infantile paralysis, or acute anterior poliomyelitis.
  Pellagra. Leprosy. Verruga peruviana. Cancer.


CHAPTER XII

KEYS TO THE ARTHROPODS NOXIOUS TO MAN                         257-317

  Crustacea.
  Myriapoda, or centipedes and millipedes.
  Arachnida (Orders of).
    Acarina or ticks.
  Hexapoda (Insecta).
    Siphunculata and Hemiptera (lice and true bugs).
    Diptera (mosquitoes, midges, and flies).
    Siphonaptera (fleas).


APPENDIX

Hydrocyanic acid gas against household insects                318-320
  Proportion of ingredients. A single room as an example.
    Fumigating a large house. Precautions.

Lesions produced by the bite of the black-fly                 321-326


BIBLIOGRAPHY                                                  327-340


INDEX                                                         341-348




CHAPTER I.

INTRODUCTION

EARLY SUGGESTIONS REGARDING THE TRANSMISSION OF DISEASE BY INSECTS


Until very recent years insects and their allies have been considered as
of economic importance merely in so far as they are an annoyance or
direct menace to man, or his flocks and herds, or are injurious to his
crops. It is only within the past fifteen years that there has sprung
into prominence the knowledge that in another and much more insiduous
manner, they may be the enemy of mankind, that they may be among the
most important of the disseminators of disease. In this brief period,
such knowledge has completely revolutionized our methods of control of
certain diseases, and has become an important weapon in the fight for
the conservation of health.

It is nowhere truer than in the case under consideration that however
abrupt may be their coming into prominence, great movements and great
discoveries do not arise suddenly. Centuries ago there was suggested the
possibility that insects were concerned with the spread of disease, and
from time to time there have appeared keen suggestions and logical
hypotheses along this line, that lead us to marvel that the
establishment of the truths should have been so long delayed.

One of the earliest of these references is by the Italian physician,
Mercurialis, who lived from 1530 to 1607, during a period when Europe
was being ravaged by the dread "black death", or plague. Concerning its
transmission he wrote: "There can be no doubt that flies feed on the
internal secretions of the diseased and dying, then, flying away, they
deposit their excretions on the food in neighboring dwellings, and
persons who eat of it are thus infected."

It would be difficult to formulate more clearly this aspect of the facts
as we know them to-day, though it must always be borne in mind that we
are prone to interpret such statements in the light of present-day
knowledge. Mercurialis had no conception of the animate nature of
contagion, and his statement was little more than a lucky guess.

Much more worthy of consideration is the approval which was given to his
view by the German Jesuit, Athanasius Kircher in 1658. One cannot read
carefully his works without believing that long before Leeuwenhook's
discovery, Kircher had seen the larger species of bacteria. Moreover, he
attributed the production of disease to these organisms and formulated,
vaguely, to be sure, a theory of the animate nature of contagion. It has
taken two and a half centuries to accumulate the facts to prove his
hypothesis.

The theory of Mercurialis was not wholly lost sight of, for in the
medical literature of the eighteenth century there are scattered
references to flies as carriers of disease. Such a view seems even to
have been more or less popularly accepted, in some cases. Gudger (1910),
has pointed out that, as far back as 1769, Edward Bancroft, in "An Essay
on the Natural History of Guiana in South America," wrote concerning the
contagious skin-disease known as "Yaws": "It is usually believed that
this disorder is communicated by the flies who have been feasting on a
diseased object, to those persons who have sores, or scratches, which
are uncovered; and from many observations, I think this is not
improbable, as none ever receive this disorder whose skins are whole."

Approaching more closely the present epoch, we find that in 1848, Dr.
Josiah Nott, of Mobile, Alabama, published a remarkable article on the
cause of yellow fever, in which he presented "reasons for supposing its
specific cause to exist in some form of insect life." As a matter of
fact, the bearing of Nott's work on present day ideas of the insect
transmission of disease has been very curiously overrated. The common
interpretation of his theory has been deduced from a few isolated
sentences, but his argument appears quite differently when the entire
article is studied. It must be remembered that he wrote at a period
before the epoch-making discoveries of Pasteur and before the
recognition of micro-organisms as factors in the cause of disease. His
article is a masterly refutation of the theory of "malarial" origin of
"all the fevers of hot climates," but he uses the term "insect" as
applicable to the lower forms of life, and specific references to
"mosquitoes," "aphids," "cotton-worms," and others, are merely in the
way of similes.

But, while Nott's ideas regarding the relation of insects to yellow
fever were vague and indefinite, it was almost contemporaneously that
the French physician, Louis Daniel Beauperthuy argued in the most
explicit possible manner, that yellow fever and various others are
transmitted by mosquitoes. In the light of the data which were available
when he wrote, in 1853, it is not surprising that he erred by thinking
that the source of the virus was decomposing matter which the mosquito
took up and accidentally inoculated into man. Beauperthuy not only
discussed the rôle of mosquitoes in the transmission of disease, but he
taught, less clearly, that house-flies scatter pathogenic organisms. It
seems that Boyce (1909) who quotes extensively from this pioneer work,
does not go too far when he says "It is Dr. Beauperthuy whom we must
regard as the father of the doctrine of insect-borne disease."

In this connection, mention must be made of the scholarly article by the
American physician, A. F. A. King who, in 1883, brought together an all
but conclusive mass of argument in support of his belief that malaria
was caused by mosquitoes. At about the same time, Finley, of Havana, was
forcefully presenting his view that the mosquito played the chief rôle
in the spread of yellow fever.

To enter more fully into the general historical discussion is beyond the
scope of this book. We shall have occasion to make more explicit
references in considering various insect-borne diseases. Enough has been
said here to emphasize that the recognition of insects as factors in the
spread of disease was long presaged, and that there were not wanting
keen thinkers who, with a background of present-day conceptions of the
nature of disease, might have been in the front rank of investigators
along these lines.


THE WAYS IN WHICH ARTHROPODS MAY AFFECT THE HEALTH OF MAN

When we consider the ways in which insects and their allies may affect
the health of man, we find that we may treat them under three main
groups:

A. They may be directly poisonous. Such, for example, are the scorpions,
certain spiders and mites, some of the predaceous bugs, and stinging
insects. Even such forms as the mosquito deserve some consideration from
this viewpoint.

B. They may be parasitic, living more or less permanently on or in the
body and deriving their sustenance from it.

Of the parasitic arthropods we may distinguish, first, the _true
parasites_, those which have adopted and become confirmed in the
parasitic habit. Such are the itch mites, the lice, fleas, and the
majority of the forms to be considered as parasitic.

In addition to these, we may distinguish a group of _accidental_, or
_facultative parasites_, species which are normally free-living, feeding
on decaying substances, but which when accidentally introduced into the
alimentary canal or other cavities of man, may exist there for a greater
or less period. For example, certain fly larvæ, or maggots, normally
feeding in putrifying meat, have been known to occur as accidental or
facultative parasites in the stomach of man.

C. Finally, and most important, arthropods may be transmitters and
disseminators of disease. In this capacity they may function in one of
three ways; as _simple carriers_, as _direct inoculators_, or as
_essential hosts_ of disease germs.

As simple carriers, they may, in a wholly incidental manner, transport
from the diseased to the healthy, or from filth to food, pathogenic
germs which cling to their bodies or appendages. Such, for instance, is
the relation of the house-fly to the dissemination of typhoid.

As direct inoculators, biting or piercing species may take up from a
diseased man or animal, germs which, clinging to the mouth parts, are
inoculated directly into the blood of the insect's next victim. It it
thus that horse-flies may occasionally transmit anthrax. Similarly,
species of spiders and other forms which are ordinarily perfectly
harmless, may accidentally convey and inoculate pyogenic bacteria.

It is as essential hosts of disease germs that arthropods play their
most important rôle. In such cases an essential part of the life cycle
of the pathogenic organism is undergone in the insect. In other words,
without the arthropod host the disease-producing organism cannot
complete its development. As illustrations may be cited the relation of
the Anopheles mosquito to the malarial parasite, and the relation of the
cattle tick to Texas fever.

A little consideration will show that this is the most important of the
group. Typhoid fever is carried by water or by contaminated milk, and in
various other ways, as well as by the house-fly. Kill all the
house-flies and typhoid would still exist. On the other hand, malaria is
carried only by the mosquito, because an essential part of the
development of the malarial parasite is undergone in this insect.
Exterminate all of the mosquitoes of certain species and the
dissemination of human malaria is absolutely prevented.

Once an arthropod becomes an essential host for a given parasite it may
disseminate infection in three different ways:

1. By infecting man or animals who ingest it. It is thus, for example,
that man, dog, or cat, becomes infected with the double-pored dog
tapeworm, _Dipylidium caninum_. The cysticercoid stage occurs in the
dog louse, or in the dog or cat fleas, and by accidentally ingesting the
infested insect the vertebrate becomes infested. Similarly, _Hymenolepis
diminuta_, a common tapeworm of rats and mice, and occasional in man,
undergoes part of its life cycle in various meal-infesting insects, and
is accidentally taken up by its definitive host. It is very probable
that man becomes infested with _Dracunculus (Filaria) medinensis_
through swallowing in drinking water, the crustacean, _Cyclops_,
containing the larvæ of this worm.

2. By infecting man or animals on whose skin or mucous membranes the
insect host may be crushed or may deposit its excrement. The pathogenic
organism may then actively penetrate, or may be inoculated by
scratching. The causative organism of typhus fever is thus transmitted
by the body louse.

3. By direct inoculation by its bite, the insect host may transfer the
parasite which has undergone development within it. The malarial
parasite is thus transferred by mosquitoes; the Texas fever parasite by
cattle ticks.




CHAPTER II.

ARTHROPODS WHICH ARE DIRECTLY POISONOUS


Of all the myriads of insects and related forms, a very few are of
direct use to man, some few others have forced his approbation on
account of their wonderful beauty, but the great hordes of them are
loathed or regarded as directly dangerous. As a matter of fact, only a
very small number are in the slightest degree poisonous to man or to the
higher animals. The result is that entomologists and lovers of nature,
intent upon dissipating the foolish dread of insects, are sometimes
inclined to go to the extreme of discrediting all statements of serious
injury from the bites or stings of any species.

Nevertheless, it must not be overlooked that poisonous forms do exist,
and they must receive attention in a consideration of the ways in which
arthropods may affect the health of man. Moreover, it must be recognized
that "what is one man's meat, is another man's poison," and that in
considering the possibilities of injury we must not ignore individual
idiosyncrasies. Just as certain individuals may be poisoned by what, for
others, are common articles of food, so some persons may be abnormally
susceptible to insect poison. Thus, the poison of a bee sting may be of
varying severity, but there are individuals who are made seriously sick
by a single sting, regardless of the point of entry. Some individuals
scarcely notice a mosquito bite, others find it very painful, and so
illustrations of this difference in individuals might be multiplied.

In considering the poisonous arthropods, we shall take them up by
groups. The reader who is unacquainted with the systematic relationship
of insects and their allies is referred to Chapter XII. No attempt will
be made to make the lists under the various headings exhaustive, but
typical forms will be discussed.


ARANEIDA OR SPIDERS

Of all the arthropods there are none which are more universally feared
than are the spiders. It is commonly supposed that the majority, if not
all the species are poisonous and that they are aggressive enemies of
man and the higher animals, as well as of lower forms.

That they really secrete a poison may be readily inferred from the
effect of their bite upon insects and other small forms. Moreover, the
presence of definite and well-developed poison glands can easily be
shown. They occur as a pair of pouches (fig. 1) lying within the
cephalothorax and connected by a delicate duct with a pore on the claw
of the chelicera, or so-called "mandible" on the convex surface of the
claw in such a position that it is not plugged and closed by the flesh
of the victim.

[Illustration: 1. Head of a spider showing poison gland (_c_) and its
relation to the chelicera (_a_).]

The glands may be demonstrated by slowly and carefully twisting off a
chelicera and pushing aside the stumps of muscles at its base. By
exercising care, the chitinous wall of the chelicera and its claw may be
broken away and the duct traced from the gland to its outlet. The inner
lining of the sac is constituted by a highly developed glandular
epithelium, supported by a basement membrane of connective tissue and
covered by a muscular layer, (fig. 2). The muscles, which are striated,
are spirally arranged (fig. 1), and are doubtless under control of the
spider, so that the amount of poison to be injected into a wound may be
varied.

[Illustration: 2. Section through a venom gland of Latrodectus
13-guttatus showing the peritoneal, muscular and epithelial layers.
After Bordas.]

The poison itself, according to Kobert (1901), is a clear, colorless
fluid, of oily consistency, acid reaction, and very bitter taste. After
the spider has bitten two or three times, its supply is exhausted and
therefore, as in the case of snakes, the poison of the bite decreases
quickly with use, until it is null. To what extent the content of the
poison sacs may contain blood serum or, at least, active principles of
serum, in addition to a specific poison formed by the poison glands
themselves, Kobert regards as an open question. He believes that the
acid part of the poison, if really present, is formed by the glands and
that, in the case of some spiders, the ferment-like, or better, active
toxine, comes from the blood.

[Illustration: 3. Chelicera of a spider.]

But there is a wide difference between a poison which may kill an insect
and one which is harmful to men. Certain it is that there is no lack of
popular belief and newspaper records of fatal cases, but the evidence
regarding the possibility of fatal or even very serious results for man
is most contradictory. For some years, we have attempted to trace the
more circumstantial newspaper accounts, which have come to our notice,
of injury by North American species. The results have served, mainly, to
emphasize the straits to which reporters are sometimes driven when there
is a dearth of news. The accounts are usually vague and lacking in any
definite clue for locating the supposed victim. In the comparatively few
cases where the patient, or his physician, could be located, there was
either no claim that the injury was due to spider venom, or there was no
evidence to support the belief. Rarely, there was evidence that a
secondary blood poisoning, such as might be brought about by the prick
of a pin, or by any mechanical injury, had followed the bite of a
spider. Such instances have no bearing on the question of the venomous
nature of these forms.

[Illustration: 4. The Italian tarantula (Lycosa tarantula). After
Kobert.]

The extreme to which unreasonable fear of the bites of spiders
influenced the popular mind was evidenced by the accepted explanation of
the remarkable dancing mania, or tarantism, of Italy during the Middle
Ages. This was a nervous disorder, supposed to be due to the bite of a
spider, the European tarantula (fig. 4), though it was also, at times,
attributed to the bite of the scorpion. In its typical form, it was
characterized by so great a sensibility to music that under its
influence the victims indulged in the wildest and most frenzied dancing,
until they sank to the ground utterly exhausted and almost lifeless. The
profuse perspiring resulting from these exertions was supposed to be the
only efficacious remedy for the disease. Certain forms of music were
regarded as of especial value in treating this tarantism, and hence the
name of "tarantella" was applied to them. Our frontispiece, taken from
Athanasius Kircher's _Magnes sive de Arte Magnetica_, 1643 ed.,
represents the most commonly implicated spider and illustrates some of
what Fabre has aptly designated as "medical choreography."

The disease was, in reality, a form of hysteria, spreading by sympathy
until whole communities were involved, and was paralleled by the
outbreaks of the so-called St. Vitus's or St. John's dance, which swept
Germany at about the same time (fig. 5). The evidence that the spider
was the cause of the first is about as conclusive as is that of the
demoniacal origin of the latter. The true explanation of the outbreaks
is doubtless to be found in the depleted physical and mental condition
of the people, resulting from the wars and the frightful plagues which
devastated all Europe previous to, and during these times. An
interesting discussion of these aspects of the question is to be found
in Hecker.

[Illustration: 5. Dancing mania. Illustration from Johann Ludwig
Gottfried's Chronik. 1632.]

So gross has been the exaggeration and so baseless the popular fear
regarding spiders that entomologists have been inclined to discredit all
accounts of serious injury from their bites. Not only have the most
circumstantial of newspaper accounts proved to be without foundation but
there are on record a number of cases where the bite of many of the
commoner species have been intentionally provoked and where the effect
has been insignificant. Some years ago the senior author personally
experimented with a number of the largest of our northern species, and
with unexpected results. The first surprise was that the spiders were
very unwilling to bite and that it required a considerable effort to get
them to attempt to do so. In the second place, most of those
experimented with were unable to pierce the skin of the palm or the back
of the hand, but had to be applied to the thin skin between the fingers
before they were able to draw blood. Unfortunately, no special attempt
was made to determine, at the time, the species experimented with, but
among them were _Theridion tepidariorum_, _Miranda aurantia_
(_Argiopa_), _Metargiope trifasciata_, _Marxia stellata_, _Aranea
trifolium_, _Misumena vatia_, and _Agelena nævia_. In no case was the
bite more severe than a pin prick and though in some cases the sensation
seemed to last longer, it was probably due to the fact that the mind was
intent upon the experiment.

[Illustration: 6. An American tarantula (Eurypelma hentzii). Natural
size. After Comstock.]

Similar experiments were carried out by Blackwell (1855), who believed
that in the case of insects bitten, death did not result any more
promptly than it would have from a purely mechanical injury of equal
extent. He was inclined to regard all accounts of serious injury to man
as baseless. The question cannot be so summarily dismissed, and we shall
now consider some of the groups which have been more explicitly
implicated.


THE TARANTULAS.--In popular usage, the term "tarantula" is loosely
applied to any one of a number of large spiders. The famous tarantulas
of southern Europe, whose bites were supposed to cause the dancing
mania, were Lycosidæ, or wolf-spiders. Though various species of this
group were doubtless so designated, the one which seems to have been
most implicated was _Lycosa tarantula_ (L.), (fig. 4). On the other
hand, in this country, though there are many Lycosidæ, the term
"tarantula" has been applied to members of the superfamily Avicularoidea
(fig. 6), including the bird-spiders.

Of the Old World Lycosidæ there is no doubt that several species were
implicated as the supposed cause of the tarantism. In fact, as we have
already noted, the blame was sometimes attached to a scorpion. However,
there seems to be no doubt that most of the accounts refer to the spider
known as _Lycosa tarantula_.

There is no need to enter into further details here regarding the
supposed virulence of these forms, popular and the older medical
literature abound in circumstantial accounts of the terrible effects of
the bite. Fortunately, there is direct experimental evidence which bears
on the question.

Fabre induced a common south European wolf-spider, _Lycosa narbonensis_,
to bite the leg of a young sparrow, ready to leave the nest. The leg
seemed paralyzed as a result of the bite, and though the bird seemed
lively and clamored for food the next day, on the third day it died. A
mole, bitten on the nose, succumbed after thirty-six hours. From these
experiments Fabre seemed justified in his conclusion that the bite of
this spider is not an accident which man can afford to treat lightly.
Unfortunately, there is nothing in the experiments, or in the symptoms
detailed, to exclude the probability that the death of the animals was
the result of secondary infection.

As far back as 1693, as we learn from the valuable account of Kobert,
(1901), the Italian physician, Sanguinetti allowed himself to be bitten
on the arm by two tarantulas, in the presence of witnesses. The
sensation was equivalent to that from an ant or a mosquito bite and
there were no other phenomena the first day. On the second day the wound
was inflamed and there was slight ulceration. It is clear that these
later symptoms were due to a secondary infection. These experiments have
been repeated by various observers, among whom may be mentioned Leon
Dufour, Josef Erker and Heinzel, and with the similar conclusion that
the bite of the Italian tarantula ordinarily causes no severe symptoms.
In this conclusion, Kobert, though firmly convinced of the poisonous
nature of some spiders, coincides. He also believes that striking
symptoms may be simulated or artificially induced by patients in order
to attract interest, or because they have been assured that the bite,
under all circumstances, caused tarantism.

The so-called Russian tarantula, _Trochosa singoriensis_ (fig. 7), is
much larger than the Italian species, and is much feared. Kobert carried
out a series of careful experiments with this species and his results
have such an important bearing on the question of the venomous nature of
the tarantula that we quote his summary. Experimenting first on nearly a
hundred living specimens of _Trochosa singoriensis_ from Crimea he says
that:

"The tarantulas, no matter how often they were placed on the skin,
handled, and irritated, could not be induced to bite either myself, the
janitor, or the ordinary experimental animals. The objection that the
tarantulas were weak and indifferent cannot stand, for as soon as I
placed two of them on the shaved skin of a rabbit, instead of an attack
on the animal, there began a furious battle between the two spiders,
which did not cease until one of the two was killed."

[Illustration: 7. Trochosa singoriensis. After Kobert.]

"Since the spiders would not bite, I carefully ground up the fresh
animals in physiological salt solution, preparing an extract which must
have contained, in solution, all of the poisonous substance of their
bodies. While in the case of _Latrodectus_, as we shall see, less than
one specimen sufficed to yield an active extract, I have injected the
filtered extract of six fresh Russian tarantulas, of which each one was
much heavier than an average _Latrodectus_, subcutaneously and into the
jugular vein of various cats without the animals dying or showing any
special symptoms. On the basis of my experiments I can therefore only
say that the quantity of the poison soluble in physiological salt
solution, even when the spiders are perfectly fresh and well nourished,
is very insignificant. That the poison of the Russian tarantula is not
soluble in physiological salt solution, is exceedingly improbable.
Moreover, I have prepared alcoholic extracts and was unable to find them
active. Since the Russian spider exceeds the Italian in size and in
intensity of the bite, it seems very improbable to me that the
pharmacological test of the Italian tarantula would yield essentially
other results than those from the Russian species."

To the AVICULAROIDEA belong the largest and most formidable appearing of
the spiders and it is not strange that in the New World they have fallen
heir to the bad reputation, as well as to the name of the tarantula of
Europe. In this country they occur only in the South or in the far West,
but occasionally living specimens are brought to our northern ports in
shipments of bananas and other tropical produce, and are the source of
much alarm. It should be mentioned, however, that the large spider most
frequently found under such circumstances is not a tarantula at all, but
one of the Heteropodidæ, or giant crab-spiders, (fig. 8).

[Illustration: 8. The giant crab-spider or banana spider (Heteropoda
venatoria). Natural size. After Comstock.]

In spite of their prominence and the fear which they arouse there are
few accurate data regarding these American tarantulas. It has often been
shown experimentally that they can kill small birds and mammals, though
it is doubtful if these form the normal prey of any of the species, as
has been claimed. There is no question but that the mere mechanical
injury which they may inflict, and the consequent chances of secondary
infection, justify, in part, their bad reputation. In addition to the
injury from their bite, it is claimed that the body hairs of several of
the South American species are readily detached and are urticating.

Recently, Phisalix (1912) has made a study of the physiological effects
of the venom of two Avicularoidea, _Phormictopus carcerides_ Pocock,
from Haiti and _Cteniza sauvagei_ Rossi, from Corsica. The glands were
removed aseptically and ground up with fine, sterilized sand in
distilled water. The resultant liquid was somewhat viscid, colorless,
and feebly alkaline. Injected into sparrows and mice the extract of
_Phormictopus_ proved very actively poisonous, that from a single spider
being sufficient to kill ten sparrows or twenty mice. It manifested
itself first and, above all, as a narcotic, slightly lowering the
temperature and paralyzing the respiration. Muscular and cardiac
weakening, loss of general sensibility, and the disappearance of
reflexes did not occur until near the end. The extract from _Cteniza_
was less active and, curiously enough, the comparative effect on
sparrows and on mice was just reversed.


SPIDERS OF THE GENUS LATRODECTUS.--While most of the popular accounts of
evil effects from the bites of spiders will not stand investigation, it
is a significant fact that, the world over, the best authenticated
records refer to a group of small and comparatively insignificant
spiders belonging to the genus _Latrodectus_, of the family Theridiidæ.
The dread "Malmigniatte" of Corsica and South Europe, the "Karakurte" of
southeastern Russia, the "Katipo" of New Zealand, the "Mena-vodi" and
"Vancoho" of Madagascar, and our own _Latrodectus mactans_, all belong
to this genus, and concerning all of these the most circumstantial
accounts of their venomous nature are given. These accounts are not mere
fantastic stories by uneducated natives but in many cases are reports
from thoroughly trained medical men.

The symptoms produced are general, rather than local. As summarized by
Kobert (1901) from a study of twenty-two cases treated in 1888, in the
Kherson (Russia) Government Hospital and Berislaw (Kherson) District
Hospital the typical case, aside from complications, exhibits the
following symptoms. The victim suddenly feels the bite, like the sting
of a bee. Swelling of the barely reddened spot seldom follows. The
shooting pains, which quickly set in, are not manifested at the point of
injury but localized at the joints of the lower limb and in the region
of the hip. The severity of the pain forces the victim to the hospital,
in spite of the fact that they otherwise have a great abhorrence of it.
The patient is unable to reach the hospital afoot, or, at least, not
without help, for there is usually inability to walk. The patient, even
if he has ridden, reaches the hospital covered with cold sweat and
continues to perspire for a considerable period. His expression
indicates great suffering. The respiration may be somewhat dyspnoeic,
and a feeling of oppression in the region of the heart is common. There
is great aversion to solid food, but increasing thirst for milk and tea.
Retention of urine, and constipation occur. Cathartics and, at night,
strong narcotics are desired. Warm baths give great relief. After three
days, there is marked improvement and usually the patient is dismissed
after the fifth. This summary of symptoms agrees well with other
trustworthy records.

It would seem, then, that Riley and Howard (1889), who discussed a
number of accounts in the entomological literature, were fully justified
in their statement that "It must be admitted that certain spiders of the
genus _Latrodectus_ have the power to inflict poisonous bites, which may
(probably exceptionally and depending upon exceptional conditions) bring
about the death of a human being."

And yet, until recently the evidence bearing on the question has been
most conflicting. The eminent arachnologist, Lucas, (1843) states that
he himself, had been repeatedly bitten by the Malmigniatte without any
bad effects. Dr. Marx, in 1890, gave before the Entomological Society of
Washington, an account of a series of experiments to determine whether
the bite of _Latrodectus mactans_ is poisonous or not. He described the
poison glands as remarkably small[A] and stated that he had introduced
the poison in various ways into guinea-pigs and rabbits without
obtaining any satisfactory results. Obviously, carefully conducted
experiments with the supposed venom were needed and fortunately they
have been carried out in the greatest detail by Kobert (1901).

This investigator pointed out that there were two factors which might
account for the discrepancies in the earlier experiments. In the first
place, the poison of spiders, as of snakes, might be so exhausted after
two or three bites that further bites, following directly, might be
without visible effect. Secondly, the application of the poison by means
of the bite, is exceedingly inexact, since even after the most careful
selection of the point of application, the poison might in one instance
enter a little vein or lymph vessel, and in another case fail to do so.
Besides, there would always remain an incalculable and very large amount
externally, in the nonabsorptive epithelium. While all of these factors
enter into the question of the effect of the bite in specific instances,
they must be as nearly as possible obviated in considering the question
of whether the spiders really secrete a venom harmful to man.

Kobert therefore sought to prepare extracts which would contain the
active principles of the poison and which could be injected in definite
quantities directly into the blood of the experimental animal. For this
purpose various parts of the spiders were rubbed up in a mortar with
distilled water, or physiological salt solution, allowed to stand for an
hour, filtered, and then carefully washed, by adding water drop by drop
for twenty-four hours. The filtrate and the wash-water were then united,
well mixed and, if necessary, cleared by centrifuging or by exposure to
cold. The mixture was again filtered, measured, and used, in part, for
injection and, in part, for the determination of the organic materials.

Such an extract was prepared from the cephalothoraces of eight dried
specimens of the Russian _Latrodectus_ and three cubic centimeters of
this, containing 4.29 mg. of organic material, were injected into the
jugular vein of a cat weighing 2450 grams. The previously very active
animal was paralyzed and lay in whatever position it was placed. The
sensibility of the skin of the extremities and the rump was so reduced
that there was no reaction from cutting or sticking. There quickly
followed dyspnoea, convulsions, paralysis of the respiratory muscles
and of the heart. In twenty-eight minutes the cat was dead, after having
exhibited exactly the symptoms observed in severe cases of poisoning of
man from the bite of this spider.

These experiments were continued on cats, dogs, guinea pigs and various
other animals. Not only extracts from the cephalothorax, but from other
parts of the body, from newly hatched spiders, and from the eggs were
used and all showed a similar virulence. Every effort was made to avoid
sources of error and the experiments, conducted by such a recognized
authority in the field of toxicology, must be accepted as conclusively
showing that this spider and, presumably, other species of the genus
_Latrodectus_ against which the clinical evidence is quite parallel,
possess a poison which paralyzes the heart and central nervous system,
with or without preliminary stimulus of the motor center. If the
quantity of the poison which comes into direct contact with the blood is
large, there may occur hæmolysis and thrombosis of the vessels.

On the other hand, check experiments were carried out, using similar
extracts of many common European spiders of the genera _Tegenaria_,
_Drassus_, _Agelena_, _Eucharia_ and _Argyroneta_, as well as the
Russian tarantula, _Lycosa singoriensis_. In no other case was the
effect on experimental animals comparable to the _Latrodectus_ extract.

Kobert concludes that in its chemical nature the poison is neither an
alkaloid, nor a glycoside, nor an acid, but a toxalbumen, or poisonous
enzyme which is very similar to certain other animal poisons, notably
that of the scorpion.

[Illustration: 9. Latrodectus mactans; (_a_) female, x 3; (_b_) venter
of female; (_c_) dorsum of male. After Comstock.]

The genus _Latrodectus_ is represented in the United States by at least
two species, _L. mactans_ and _L. geometricus_. Concerning _L. mactans_
there are very circumstantial accounts of serious injury and even death
in man[B]. _Latrodectus mactans_ is coal black, marked with red or
yellow or both. It has eight eyes, which are dissimilar in color and
are distinctly in front of the middle of the thorax, the lateral eyes of
each side widely separate. The tarsus of the fourth pair of legs has a
number of curved setæ in a single series. It has on the ventral side of
its abdomen an hour-glass shaped spot. The full-grown female is about
half an inch in length. Its globose abdomen is usually marked with one
or more red spots dorsally along the middle line. The male is about half
as long but has in addition to the dorsal spots, four pairs of stripes
along the sides. Immature females resemble the male in coloring (fig.
9).

Regarding the distribution of _Latrodectus mactans_, Comstock states
that: "Although it is essentially a Southern species, it occurs in
Indiana, Ohio, Pennsylvania, New Hampshire, and doubtless other of the
Northern States." _L. geometricus_ has been reported from California.


OTHER VENOMOUS SPIDERS--While conclusive evidence regarding the venomous
nature of spiders is meager and relates almost wholly to that of the
genus _Latrodectus_, the group is a large one and we are not justified
in dismissing arbitrarily, all accounts of injury from their bites.
Several species stand out as especially needing more detailed
investigation.

_Chiracanthium nutrix_ is a common European species of the family
Clubionidæ, concerning which there is much conflicting testimony. Among
the reports are two by distinguished scientists whose accounts of
personal experiences cannot be ignored. A. Forel allowed a spider of
this species to bite him and not only was the pain extreme, but the
general symptoms were so severe that he had to be helped to his house.
The distinguished arachnologist, Bertkau reports that he, himself, was
bitten and that an extreme, burning pain spread almost instantaneously
over the arm and into the breast. There were slight chills the same day
and throbbing pain at the wound lasted for days. While this particular
species is not found in the United States, there are two other
representatives of the genus and it is possible that they possess the
same properties. We are unaware of any direct experimental work on the
poison.

_Epeira diadema_, of Europe, belongs to a wholly different group, that
of the orb-weavers, but has long been reputed venomous. Kobert was able
to prepare from it an extract whose effects were very similar to that
prepared from _Latrodectus_, though feebler in its action. Under
ordinary circumstances this spider is unable to pierce the skin of man
and though Kobert's results seem conclusive, the spider is little to be
feared.

_Phidippus audax_ (_P. tripunctatus_) is one of our largest Attids, or
jumping spiders. The late Dr. O. Lugger describes a case of severe
poisoning from the bite of this spider and though details are lacking,
it is quite possible that this and other large species of the same
group, which stalk their prey, may possess a more active poison than
that of web-building species.


SUMMARY--It is clearly established that our common spiders are not to be
feared and that the stories regarding their virulence are almost wholly
without foundation. On the other hand, the chances of secondary
infection from the bites of some of the more powerful species are not to
be ignored.

Probably all species possess a toxin secreted by the poison gland,
virulent for insects and other normal prey of the spiders, but with
little or no effect on man.

There are a very few species, notably of the genus _Latrodectus_, and
possibly including the European _Chiracanthium nutrix_ and _Epeira
diadema_, which possess, in addition, a toxalbumen derived from the
general body tissue, which is of great virulence and may even cause
death in man and the higher animals.

[Illustration: 10. A whip-scorpion (Mastigoproctus giganteus). Half
natural size. After Comstock.]


THE PEDIPALPIDA OR WHIP-SCORPIONS

The tailed whip-scorpions, belonging to the family Thelyphonidæ, are
represented in the United States by the giant whip-scorpion
_Mastigoproctus giganteus_ (fig. 10), which is common in Florida, Texas
and some other parts of the South. In Florida, it is locally known as
the "grampus" or "mule-killer" and is very greatly feared. There is no
evidence that these fears have any foundation, and Dr. Marx states that
there is neither a poison gland nor a pore in the claw of the
chelicera.


THE SCORPIONIDA, OR TRUE SCORPIONS

The true scorpions are widely distributed throughout warm countries and
everywhere bear an evil reputation. According to Comstock (1912), about
a score of species occur in the Southern United States. These are
comparatively small forms but in the tropics members of this group may
reach a length of seven or eight inches. They are pre-eminently
predaceous forms, which lie hidden during the day and seek their prey by
night.

[Illustration: 11. A true scorpion. After Comstock.]

The scorpions (fig. 11) possess large pedipalpi, terminated by strongly
developed claws, or chelæ. They may be distinguished from all other
Arachnids by the fact that the distinctly segmented abdomen is divided
into a broad basal region of seven segments and a terminal, slender,
tail-like division of five distinct segments.

The last segment of the abdomen, or telson, terminates in a
ventrally-directed, sharp spine, and contains a pair of highly developed
poison glands. These glands open by two small pores near the tip of the
spine. Most of the species when running carry the tip of the abdomen
bent upward over the back, and the prey, caught and held by the
pedipalpi, is stung by inserting the spine of the telson and allowing it
to remain for a time in the wound.

The glands themselves have been studied in _Prionurus citrinus_ by
Wilson (1904). He found that each gland is covered by a sheet of muscle
on its mesal and dorsal aspects, which may be described as the
_compressor muscle_. The muscle of each side is inserted by its edge
along the ventral inner surface of the chitinous wall of the telson,
close to the middle line, and by a broader insertion laterally. A layer
of fine connective tissue completely envelops each gland and forms the
basis upon which the secreting cells rest. The secreting epithelium is
columnar; and apparently of three different types of cells.

1. The most numerous have the appearance of mucous cells, resembling the
goblet cells of columnar mucous membranes. The nucleus, surrounded by a
small quantity of protoplasm staining with hæmatoxylin, lies close to
the base of the cell.

2. Cells present in considerable numbers, the peripheral portions of
which are filled with very numerous fine granules, staining with acid
dyes such as methyl orange.

3. Cells few in number, filled with very large granules, or irregular
masses of a substance staining with hæmatoxylin.

The poison, according to Kobert (1893), is a limpid, acid-reacting
fluid, soluble in water but insoluble in absolute alcohol and ether.
There are few data relative to its chemical nature. Wilson (1901) states
that a common Egyptian species, _Buthus quinquestriatus_, has a specific
gravity of 1.092, and contains 20.3% of solids and 8.4% ash.

The venom of different species appears to differ not only quantitatively
but qualitatively. The effects of the bite of the smaller species of the
Southern United States may be painful but there is no satisfactory
evidence that it is ever fatal. On the other hand, certain tropical
species are exceedingly virulent and cases of death of man from the bite
are common.

In the case of _Buthus quinquestriatus_, Wilson (1904) found the
symptoms in animals to be hypersecretion, salivation and lachrymation,
especially marked, convulsions followed by prolonged muscular spasm;
death from asphyxia. The temperature shows a slight, rarely
considerable, rise. Rapid and considerable increase of blood-pressure
(observed in dogs) is followed by a gradual fall with slowing of the
heart-beat. The coagulability of the blood is not affected.

An interesting phase of Wilson's work was the experiments on desert
mammals. The condition under which these animals exist must frequently
bring them in contact with scorpions, and he found that they possess a
degree of immunity to the venom sufficient at least to protect them from
the fatal effects of the sting.

As far as concerns its effect on man, Wilson found that much depended
upon the age. As high as 60 per cent of the cases of children under
five, resulted fatally. Caroroz (1865), states that in a Mexican state
of 15,000 inhabitants, the scorpions were so abundant and so much feared
that the authorities offered a bounty for their destruction. A result
was a large number of fatalities, over two hundred per year. Most of the
victims were children who had attempted to collect the scorpions.

The treatment usually employed in the case of bites by the more
poisonous forms is similar to that for the bite of venomous snakes.
First, a tight ligature is applied above the wound so as to stop the
flow of blood and lymph from that region. The wound is then freely
excised and treated with a strong solution of permanganate of potash, or
with lead and opium lotion.

In recent years there have been many attempts to prepare an antivenom,
or antiserum comparable to what has been used so effectively in the case
of snake bites. The most promising of these is that of Todd (1909),
produced by the immunization of suitable animals. This antivenom proved
capable of neutralizing the venom when mixed _in vitro_ and also acts
both prophylactically and curatively in animals. Employed curatively in
man, it appears to have a very marked effect on the intense pain
following the sting, and the evidence so far indicates that its prompt
use greatly reduces the chance of fatal results.


THE SOLPUGIDA, OR SOLPUGIDS

The SOLPUGIDA are peculiar spider-like forms which are distinguished
from nearly all other arachnids by the fact that they possess no true
cephalothorax, the last two leg-bearing segments being distinct,
resembling those of the abdomen in this respect. The first pair of legs
is not used in locomotion but seemingly functions as a second pair of
pedipalpi. Figure 12 illustrates the striking peculiarities of the
group. They are primarily desert forms and occur in the warm zones of
all countries. Of the two hundred or more species, Comstock lists twelve
as occurring in our fauna. These occur primarily in the southwest.

[Illustration: 12. A solpugid (Eremobates cinerea). After Comstock.]

The Solpugida have long borne a bad reputation and, regarding virulence,
have been classed with the scorpions. Among the effects of their bites
have been described painful swelling, gangrene, loss of speech, cramps,
delirium, unconsciousness and even death. Opposed to the numerous loose
accounts of poisoning, there are a number of careful records by
physicians and zoölogists which indicate clearly that the effects are
local and though they may be severe, they show not the slightest symptom
of direct poisoning.

More important in the consideration of the question is the fact that
there are neither poison glands nor pores in the fangs for the exit of
any poisonous secretion. This is the testimony of a number of prominent
zoölogists, among whom is Dr. A. Walter, who wrote to Kobert at length
on the subject and whose conclusions are presented by him.

However, it should be noted that the fangs are very powerful and are
used in such a manner that they may inflict especially severe wounds.
Thus, there may be more opportunity for secondary infection than is
usual in the case of insect wounds.

The treatment of the bite of the Solpugida is, therefore, a matter of
preventing infection. The wound should be allowed to bleed freely and
then washed out with a 1:3000 solution of corrosive sublimate, and, if
severe, a wet dressing of this should be applied. If infection takes
place, it should be treated in the usual manner, regardless of its
origin.


THE ACARINA, OR MITES AND TICKS

A number of the parasitic Acarina evidently secrete a specific poison,
presumably carried by the saliva, but in most cases its effect on man is
insignificant. There is an abundant literature dealing with the
poisonous effect of the bite of these forms, especially the ticks, but
until recently it has been confused by failure to recognize that various
species may transmit diseases of man, rather than produce injury through
direct poisoning. We shall therefore discuss the Acarina more especially
in subsequent chapters, dealing with parasitism and with disease
transmission.

Nevertheless, after the evidence is sifted, there can be no doubt that
the bites of certain ticks may occasionally be followed by a direct
poisoning, which may be either local or general in its effects. Nuttall
(1908) was unable to determine the cause of the toxic effect, for, in
_Argas persicus_, the species most often implicated, he failed to get
the slightest local or general effect on experimental animals, from the
injection of an emulsion prepared by crushing three of the ticks.

It seems clearly established that the bite of certain ticks may cause a
temporary paralysis, or even complete paralysis, involving the organs of
respiration or the heart, and causing death. In 1912, Dr. I. U. Temple,
of Pendleton, Oregon, reported several cases of what he called "acute
ascending paralysis" associated with the occurrence of ticks on the head
or the back of the neck. A typical severe case was that of a six year
old child, who had retired in her usual normal health. The following
morning upon arising she was unable to stand on her feet. She exhibited
paralysis extending to the knees, slight temperature, no pain, sensory
nerves normal, motor nerves completely paralyzed, reflexes absent. The
following day the paralysis had extended to the upper limbs, and before
night of the third day the nerves of the throat (hypoglossal) were
affected. The thorax and larynx were involved, breathing was labored,
she was unable to swallow liquids, phonation was impossible and she
could only make low, guttural sounds. At this stage, two ticks, fully
distended with blood, were found over the junction of the spinal column
with the occipital bones in the hollow depression. They were removed by
the application of undiluted creoline. Though the child's life was
despaired of, by the following morning she was very much improved. By
evening she was able to speak. The paralysis gradually receded,
remaining longest in the feet, and at the end of one week the patient
was able to go home.

There was some doubt as to the exact species of tick implicated in the
cases which Dr. Temple reported, although the evidence pointed strongly
to _Dermacentor venustus_.[C] Somewhat later, Hadwen (1913) reported
that "tick paralysis" occurs in British Columbia, where it affects not
only man, but sheep and probably other animals. It is caused by the
bites of _Dermacentor venustus_ and was experimentally produced in lambs
and a dog (Hadwen and Nuttall, 1913). It is only when the tick begins to
engorge or feed rapidly, some days after it has become attached, that
its saliva produces pathogenic effects.

Ulceration following tick bite is not uncommon. In many of the instances
it is due to the file-like hypostome, with its recurved teeth, being
left in the wound when the tick is forcibly pulled off.


THE MYRIAPODA, OR CENTIPEDES AND MILLIPEDES

The old class, Myriapoda includes the DIPLOPODA, or millipedes, and the
CHILOPODA, or centipedes. The present tendency is to raise these groups
to the rank of classes.


The Diplopoda

The DIPLOPODA, or millipedes (fig. 13), are characterized by the
presence of two pairs of legs to a segment. The largest of our local
myriapods belong to this group. They live in moist places, feeding
primarily on decaying vegetable matter, though a few species
occasionally attack growing plants.

[Illustration: 13. A millipede. After Comstock.]

The millipedes are inoffensive and harmless. _Julus terrestris_, and
related species, when irritated pour out over the entire body a
yellowish secretion which escapes from cutaneous glands. It is volatile,
with a pungent odor, and Phisalix (1900) has shown that it is an active
poison when injected into the blood of experimental animals. This,
however, does not entitle them to be considered as poisonous arthropods,
in the sense of this chapter, any more than the toad can be considered
poisonous to man because it secretes a venom from its cutaneous glands.


The Chilopoda

[Illustration: 14. Two common centipedes.

(_a_) Lithobius forficatus. After Comstock.

(_b_) Scutigera forceps. Natural size; after Howard.]

The CHILOPODA, or centipedes (fig. 14), unlike the millipedes, are
predaceous forms, and possess well developed poison glands for killing
their prey. These glands are at the base of the first pair of legs
(fig. 15), which are bent forward so as to be used in holding their
prey. The legs terminate in a powerful claw, at the tip of which is the
outlet of the poison glands.

The poison is a limpid, homogeneous, slightly acid fluid, which
precipitates in distilled water. Briot (1904) extracted it from the
glands of _Scolopendra morsitans_, a species common in central France,
and found that it was actively venomous for the ordinary experimental
animals. A rabbit of two kilograms weight received an injection of three
cubic centimeters in the vein of the ear and died in a minute. A white
rat, weighing forty-eight grams, received one and a half cubic
centimeters in the hind leg. There was an almost immediate paralysis of
the leg and marked necrosis of the tissues.

[Illustration: 15. Mandible of Scolopendra cingulata showing venom
gland. After Dubosq.]

As for the effect on man, there is little foundation for the fear with
which centipedes are regarded. Our native species produce, at most,
local symptoms,--sometimes severe local pain and swelling,--but there is
no authentic record of fatal results. In the tropics, some of the
species attain a large size, _Scolopendra gigantea_ reaching a length of
nearly a foot. These forms are justly feared, and there is good evidence
that death sometimes, though rarely, results from their bite.

One of the most careful accounts of death from the sting of the scorpion
is that of Linnell, (1914), which relates to a comparatively small
Malayan species, unfortunately undetermined. The patient, a coolie, aged
twenty, was admitted to a hospital after having been stung two days
previously on the left heel. For cure, the other coolies had made him
eat the head of the scorpion. On admission, the patient complained of
"things creeping all over the body". Temp. 102.8°. On the fourth day he
had paralysis of the legs, and on the fifth day motor paralysis to the
umbilicus, sensation being unaltered. On the sixth day there was
retention of the urine and on the ninth day (first test after third day)
sugar was present. On the thirteenth day the patient became comatose,
but could be roused to eat and drink. The temperature on the following
day fell below 95° and the patient was still comatose. Death fifteenth
day.

Examination of the spinal (lumbar) cord showed acute disseminated
myelitis. In one part there was an acute destruction of the anterior
horn and an infiltration of round cells. In another portion Clarke's
column had been destroyed. The perivascular sheaths were crowded with
small round cells and the meninges were congested. Some of the cells of
the anterior horn were swollen and the nuclei eccentric; chromatolysis
had occurred in many of them.

As for treatment, Castellani and Chalmers (1910), recommend bathing the
part well with a solution of ammonia (one in five, or one in ten). After
bathing, apply a dressing of the same alkali or, if there is much
swelling and redness, an ice-bag. If necessary, hypodermic injections of
morphine may be given to relieve the pain. At a later period
fomentations may be required to reduce the local inflammation.


THE HEXAPODA OR TRUE INSECTS

There are a number of HEXAPODA, or true insects, which are, in one way
or another, poisonous to man. These belong primarily to the orders
Hemiptera, or true bugs; Lepidoptera, or butterflies and moths (larval
forms); Diptera, or flies; Coleoptera, or beetles; and Hymenoptera, or
ants, bees, and wasps. There are various ways in which they may be
poisonous.

1. _Piercing_ or _biting_ forms may inject an irritating or poisonous
saliva into the wound caused by their mouth-parts.

2. _Stinging forms_ may inject a poison, from glands at the caudal end
of the abdomen, into wounds produced by a specially modified ovipositer,
the _sting_.

3. _Nettling_ properties may be possessed by the hairs of the insect.

4. _Vescicating_, or _poisonous blood plasma_, or _body fluids_ are
known to exist in a large number of species and may, under exceptional
circumstances, affect man.

For convenience of discussion, we shall consider poisonous insects under
these various headings. In this, as in the preceding discussion, no
attempt will be made to give an exhaustive list of the poisonous forms.
Typical instances will be selected and these will be chosen largely from
North American species.


PIERCING OR BITING INSECTS POISONOUS TO MAN


HEMIPTERA

Several families of the true bugs include forms which, while normally
inoffensive, are capable of inflicting painful wounds on man. In these,
as in all of the Hemiptera, the mouth-parts are modified to form an
organ for piercing and sucking. This is well shown by the accompanying
illustration (fig. 16).

The upper lip, or _labrum_, is much reduced and immovable, the lower
lip, or _labium_, is elongated to form a jointed sheath, within which
the lance-like mandibles and maxillæ are enclosed. The mandibles are
more or less deeply serrate, depending on the species concerned.

[Illustration: 16. Beak of hemipteron.]

The poison is elaborated by the salivary glands, excepting, possibly, in
_Belostoma_ where Locy is inclined to believe that it is secreted by the
maxillary glands. The salivary glands of the Hemiptera have been the
subject of much study but the most recent, comprehensive work has been
done by Bugnion and Popoff, (1908 and 1910) to whose text the reader is
referred for details.

The Hemiptera have two pairs of salivary glands: the _primary gland_, of
which the efferent duct leads to the salivary syringe, and the
_accessory gland_, of which the very long and flexuous duct empties into
the primary duct at its point of insertion. Thus, when one observes the
isolated primary gland it appears as though it had efferent ducts
inserted at the same point. In _Nepa_ and the _Fulgoridæ_ there are two
accessory glands and therefore apparently three ducts at the same point
on the primary gland. The _ensemble_ differs greatly in appearance in
different species but we shall show here Bugnion and Popoff's figure of
the apparatus of _Notonecta maculata_, a species capable of inflicting a
painful bite on man (fig. 17).

[Illustration: 17. Salivary glands of Notonecta maculata. After Bugnion
and Popoff.]

[Illustration: 18. Pharyngeal syringe or salivary pump of Fulgora
maculata. After Bugnion and Popoff.]

[Illustration: 19. Heteroptera, (_a_) Melanolestes picipes; (_b_)
Notonecta undulata; (_c_, _d_) Aradus robustus (_c_) adult, (_d_) nymph,
much enlarged; (_e_) Arilus cristatus; (_f_) Belostoma americana; (_g_)
Nabis (Coriscus) subcoleoptratus, enlarged; (_h_) Cimex lectularius,
(_i_) Oeciacus vicarius, much enlarged; (_j_) Lyctocoris fitchii, much
enlarged. After Lugger.]

Accessory to the salivary apparatus there is on the ventral side of the
head, underneath the pharynx, a peculiar organ which the Germans have
called the "Wanzenspritze," or syringe. The accompanying figure of the
structure in _Fulgora maculata_ (fig. 18) shows its relation to the
ducts of the salivary glands and to the beak. It is made up of a
dilatation forming the body of the pump, in which there is a chitinous
piston. Attached to the piston is a strong retractor muscle. The
function of the salivary pump is to suck up the saliva from the salivary
ducts and to force it out through the beak.

Of the Hemiptera reported as attacking man, we shall consider briefly
the forms most frequently noted.


The NOTONECTIDÆ, or _back swimmers_, (fig. 19_b_) are small, aquatic
bugs that differ from all others in that they always swim on their
backs. They are predaceous; feeding on insects and other small forms.
When handled carelessly they are able to inflict a painful bite, which
is sometimes as severe as the sting of a bee. In fact, they are known in
Germany as "Wasserbienen."


The BELOSTOMATIDÆ, or _giant water bugs_, (fig. 19_f_) include the
largest living Hemiptera. They are attracted to lights and on account of
the large numbers which swarm about the electric street lamps in some
localities they have received the popular name "electric light bugs."
Our largest representatives in the northern United States belong to the
two genera _Belostoma_ and _Banacus_, distinguished from each other by
the fact that _Belostoma_ has a groove on the under side of the femur of
the front leg, for the reception of the tibia.

The salivary glands of Belostoma were figured by Leidy (1847) and later
were studied in more detail by Locy (1884). There are two pairs of the
glands, those of one pair being long and extending back as far as the
beginning of the abdomen, while the others are about one-fourth as long.
They lie on either side of the oesophagus. On each side of the
oesophagus there is a slender tube with a sigmoid swelling which may
serve as a poison reservoir. In addition to this salivary system, there
is a pair of very prominent glands on the ventral side of the head,
opening just above the base of the beak. These Locy has called the
"cephalic glands" and he suggests that they are the source of the
poison. They are the homologues of the maxillary glands described for
other Hemiptera, and it is by no means clear that they are concerned
with the production of venom. It seems more probable that in
_Belostoma_, as in other Hemiptera, it is produced by the salivary
glands, though the question is an open one.

The Belostomatidæ feed not only on insects, but on small frogs, fish,
salamanders and the like. Matheson (1907) has recorded the killing of a
good-sized bird by _Belostoma americana_. A woodpecker, or flicker, was
heard to utter cries of distress, and fluttered and fell from a tree. On
examination it was found that a bug of this species had inserted its
beak into the back part of the skull and was apparently busily engaged
in sucking the blood or brains of the bird. Various species of
_Belostoma_ have been cited as causing painful bites in man. We can
testify from personal experience that the bite of _Belostoma americana_
may almost immediately cause severe, shooting pains that may extend
throughout the arm and that they may be felt for several days.

[Illustration: 20. Reduvius (Opsicoetus) personatus. (×2).]

Relief from the pain may be obtained by the use of dilute ammonia, or a
menthol ointment. In the not uncommon case of secondary infection the
usual treatment for that should be adopted.

[Illustration: 21. (_a_) Reduvius personatus, nymph. Photograph by M. V.
S.]


The REDUVIIDÆ, or _assassin-bugs_ are capable of inflicting very painful
wounds, as most collectors of Hemiptera know to their sorrow. Some
species are frequently to be found in houses and outhouses and Dr.
Howard suggests that many of the stories of painful spider bites relate
to the attack of these forms.

[Illustration: 21. (_b_) Reduvius personatus, adult (×2) Photograph by
M. V. S.]

An interesting psychological study was afforded in the summer of 1899,
by the "kissing-bug" scare which swept over the country. It was reported
in the daily papers that a new and deadly bug had made its appearance,
which had the unpleasant habit of choosing the lips or cheeks for its
point of attack on man. So widespread were the stories regarding this
supposedly new insect that station entomologists all over the country
began to receive suspected specimens for identification. At Cornell
there were received, among others, specimens of stone-flies, may-flies
and even small moths, with inquiries as to whether they were
"kissing-bugs."

[Illustration: 22. Rasahus biguttatus. (×2). After Howard.]

Dr. L. O. Howard has shown that the scare had its origin in newspaper
reports of some instances of bites by either _Melanolestes picipes_
(fig. 19a) or _Opsicoetes personatus_ (fig. 20), in the vicinity of
Washington, D. C. He then discusses in considerable detail the more
prominent of the Reduviidæ which, with greater or less frequency pierce
the skin of human beings. These are _Opsicoetes personatus_,
_Melanolestes picipes_, _Coriscus subcoleoptratus_ (fig. 19_g_),
_Rasahus thoracicus_, _Rasahus biguttatus_ (fig. 22), _Conorhinus
sanguisugus_ (fig. 71), and _Melanolestes abdominalis_ (fig. 23).

[Illustration: 23. Melanolestes abdominalis (×2). After Marlatt.]

One of the most interesting of these species is _Reduvius personatus_,
(= _Opsicoetus personatus_), which is popularly known as the "masked
bed-bug hunter." It owes this name to the fact that the immature nymphs
(fig. 21) have their bodies and legs completely covered by dust and
lint, and that they are supposed to prey upon bed-bugs. LeConte is
quoted by Howard as stating that "This species is remarkable for the
intense pain caused by its bite. I do not know whether it ever willingly
plunges its rostrum into any person, but when caught, or unskilfully
handled it always stings. In this case the pain is almost equal to the
bite of a snake, and the swelling and irritation which result from it
will sometimes last for a week."

A species which very commonly attacks man is _Conorhinus sanguisugus_,
the so-called "big bed-bug" of the south and southern United States. It
is frequently found in houses and is known to inflict an exceedingly
painful bite. As in the case of a number of other predaceous Hemiptera,
the salivary glands of these forms are highly developed. The effect of
the bite on their prey and, as Marlatt has pointed out, the constant and
uniform character of the symptoms in nearly all cases of bites in man,
clearly indicate that their saliva contains a specific substance. No
satisfactory studies of the secretions have been made. On the other
hand, Dr. Howard is doubtless right in maintaining that the very serious
results which sometimes follow the bite are due to the introduction of
extraneous poison germs. This is borne out by the symptoms of most of
the cases cited in literature and also by the fact that treatment with
corrosive sublimate, locally applied to the wound, has yielded favorable
results.


OTHER HEMIPTERA REPORTED AS POISONOUS TO MAN--A large number of other
Hemiptera have been reported as attacking man. Of these, there are
several species of Lygæidæ, Coreidæ, and Capsidæ. Of the latter, _Lygus
pratensis_, the tarnished plant-bug, is reported by Professor Crosby as
sucking blood. _Orthotylus flavosparsus_ is another Capsid which has
been implicated. _Empoasca mali_ and _Platymetopius acutus_ of the
Jassidæ have also been reported as having similar habits.

Whenever the periodical cicada or "seventeen-year locust" becomes
abundant, the newspapers contain accounts of serious results from its
bites. The senior author has made scores of attempts to induce this
species to bite and only once successfully. At that time the bite was in
no wise more severe than a pin-prick. A student in our department
reports a similar experience. There is no case on record which bears
evidence of being worthy of any credence, whatsoever.

Under the heading of poisonous Hemiptera we might consider the bed-bugs
and the lice. These will be discussed later, as parasites and as
carriers of disease, and therefore need only be mentioned here.


DIPTERA

Several species of blood-sucking Diptera undoubtedly secrete a saliva
possessing poisonous properties. Chief among these are the Culicidæ, or
mosquitoes, and the Simuliidæ, or black-flies. As we shall consider
these forms in detail under the heading of parasitic species and
insects transmitting disease, we shall discuss here only the poison of
the mosquitoes.

It is well known that mosquitoes, when they bite, inject into the wound
a minute quantity of poison. The effect of this varies according to the
species of mosquito and also depends very much on the susceptibility of
the individual. Soon after the bite a sensation of itching is noticed
and often a wheal, or eminence, is produced on the skin, which may
increase to a considerable swelling. The scratching which is induced may
cause a secondary infection and thus lead to serious results. Some
people seem to acquire an immunity against the poison.

The purpose of this irritating fluid may be, as Reaumur suggested, to
prevent the coagulation of the blood and thus not only to cause it to
flow freely when the insect bites but to prevent its rapid coagulation
in the stomach. Obviously, it is not developed as a protective fluid,
and its presence subjects the group to the additional handicap of the
vengeance of man.

[Illustration: 24. Diagram of a longitudinal section of a mosquito.]

As to the origin of the poison, there has been little question, until
recent years, that it was a secretion from the salivary glands.
Macloskie (1888) showed that each gland is subdivided into three lobes,
the middle of which differs from the others in having evenly granulated
contents and staining more deeply than the others (fig. 24). This middle
lobe he regarded as the source of the poison. Bruck, (1911), by the use
of water, glycerine, chloroform, and other fluids, extracted from the
bodies of a large number of mosquitoes a toxine which he calls
_culicin_. This he assumes comes from the salivary glands. Animal
experimentation showed that this extract possessed hemolytic powers.
Inoculated into the experimenter's own skin it produced lesions which
behaved exactly as do those of mosquito bites.

Similarly, most writers on the subject have concurred with the view that
the salivary glands are the source of the poison. However, recent work,
especially that of Nuttall and Shipley (1903), and Schaudinn (1904), has
shown that the evidence is by no means conclusive. Nuttall dissected out
six sets (thirty-six acini) of glands from freshly killed _Culex
pipiens_ and placed them in a drop of salt solution. The drop was
allowed to dry, it being thought that the salt crystals would facilitate
the grinding up of the glands with the end of a small glass rod, this
being done under microscopic control. After grinding up, a small drop of
water was added of the size of the original drop of saline, and an equal
volume of human blood taken from the clean finger-tip was quickly mixed
therewith, and the whole drawn up into a capillary tube. Clotting was
not prevented and no hemolysis occurred. Salivary gland emulsion added
to a dilute suspension of corpuscles did not lead to hemolysis. This
experiment was repeated a number of times, with slight modification, but
with similar results. The data obtained from the series "do not support
the hypothesis that the salivary glands, at any rate in _Culex pipiens_,
contain a substance which prevents coagulation."

Much more detailed, and the more important experiments made along this
line, are those of Schaudinn (1904). The results of these experiments
were published in connection with a technical paper on the alternation
of generations and of hosts in _Trypanosoma_ and _Spirochæta_, and for
this reason seem to have largely escaped the notice of entomologists.
They are so suggestive that we shall refer to them in some detail.

Schaudinn observed that the three oesophageal diverticula (commonly,
but incorrectly, known as the "sucking stomach") (fig. 24) usually
contain large bubbles of gas and in addition, he always found yeast
cells. On the ground of numerous observations, Schaudinn was convinced
that these yeast plants are normal and constant commensals of the
insect. He regarded them as the cause of the gas bubbles to be found in
diverticula. It was found that as the insect fed, from time to time the
abdomen underwent convulsive contractions which resulted in the emptying
of the oesophageal diverticula and the salivary glands through blood
pressure.

In order to test the supposed toxic action of the salivary glands,
Schaudinn repeatedly introduced them under his skin and that of his
assistant, in a drop of salt solution, and never obtained a suggestion
of the irritation following a bite of the insect, even though the glands
were carefully rubbed to fragments after their implantation. Like
Nuttall, he failed to get satisfactory evidence that the secretion of
the salivary glands retarded coagulation of the blood.

He then carefully removed the oesophageal diverticula with their
content of yeast and introduced them into an opening in the skin of the
hand. Within a few seconds there was noticeable the characteristic
itching irritation of the mosquito bite; and in a short time there
appeared reddening and typical swelling. This was usually much more
severe than after the usual mosquito bite, and the swelling persisted
and itched longer. This was because by the ordinary bite of the mosquito
most of the yeast cells are again sucked up, while in these experiments
they remained in the wound. These experiments were repeated a number of
times on himself, his assistant and others, and always with the same
result. From them Schaudinn decided that the poisonous action of the
mosquito bite is caused by an enzyme from a commensal fungus. These
conclusions have not, as yet, been satisfactorily tested.

Relief from the effect of the mosquito bite may be obtained by bathing
the swellings with weak ammonia or, according to Howard, by using moist
soap. The latter is to be rubbed gently on the puncture and is said to
speedily allay the irritation. Howard also quotes from the _Journal of
Tropical Medicine and Hygiene_ to the effect that a few drops of a
solution of thirty to forty grains of iodine to an ounce of saponated
petroleum rubbed into the mosquito bite, or wasp sting, allay the pain
instantaneously.

Methods of mosquito control will be discussed later, in considering
these insects as parasites and as carriers of disease.


STINGING INSECTS

The stinging insects all belong to the order HYMENOPTERA. In a number of
families of this group the ovipositor is modified to form a sting and is
connected with poison-secreting glands. We shall consider the apparatus
of the honey-bee and then make briefer reference to that of other forms.


APIS MELLIFICA, THE HONEY BEE--The sting of the worker honey-bee is
situated within a so-called sting chamber at the end of the abdomen.
This chamber is produced by the infolding of the greatly reduced and
modified eighth, ninth and tenth abdominal segments into the seventh.[D]
From it the dart-like sting can be quickly exserted.

The sting (fig. 25) is made up of a central shaft, ventro-laterad of
which are the paired _lancets_, or darts, which are provided with sharp,
recurved teeth. Still further laterad lie the paired whitish,
finger-like _sting palpi_. Comparative morphological as well as
embryological studies have clearly established that these three parts
correspond to the three pairs of gonopophyses of the ovipositor of more
generalized insects.

[Illustration: 25. Sting of a honey bee. _Psn Sc_, base of acid poison
gland; _B Gl_, alkaline poison gland; _Stn Plp_, sting palpi; _Sh B_,
bulb of sting; _Sh A_, basal arm; _Lct_, lancets or darts; _Sh s_, shaft
of sting. Modified from Snodgrass.]

[Illustration: 26. Poison apparatus of a honey bee. Modified from
Snodgrass.]

An examination of the internal structures (fig. 26) reveals two distinct
types of poison glands, the acid-secreting and the alkaline-secreting
glands, and a prominent poison reservoir. In addition, there is a small
pair of accessory structures which have been called lubricating glands,
on account of the supposed function of their product. The acid-secreting
gland empties into the distal end of the poison reservoir which in turn
pours the secretion into the muscular bulb-like enlargement at the base
of the shaft. The alkaline secreting gland empties into the bulb ventrad
of the narrow neck of the reservoir.

The poison is usually referred to as formic acid. That it is not so
easily explained has been repeatedly shown and is evidenced by the
presence of the two types of glands. Carlet maintains that the product
of either gland is in itself innocent,--it is only when they are
combined that the toxic properties appear.

The most detailed study of the poison of the honey-bee is that of Josef
Langer (1897), who in the course of his work used some 25,000 bees.
Various methods of obtaining the active poison for experimental purposes
were used. For obtaining the pure secretion, bees were held in the
fingers and compressed until the sting was exserted, when a clear drop
of the poison was visible at its tip. This was then taken up in a
capillary tube or dilute solutions obtained by dipping the tip of the
sting into a definite amount of distilled water.

An aqueous solution of the poison was more readily obtained by pulling
out the sting and poison sacs by means of forceps, and grinding them up
in water. The somewhat clouded fluid was then filtered one or more
times. For obtaining still greater quantities, advantage was taken of
the fact that while alcohol coagulates the poison, the active principle
remains soluble in water. Hence the stings with the annexed glands where
collected in 96 per cent alcohol, after filtering off of the alcohol
were dried at 40° C., then rubbed to a fine powder and this was
repeatedly extracted with water. Through filtering of this aqueous
extract there was obtained a yellowish-brown fluid which produced the
typical reactions, according to concentration of the poison.

The freshly expelled drop of poison is limpid, of distinct acid
reaction, tastes bitter and has a delicate aromatic odor. On
evaporation, it leaves a sticky residue, which at 100 degrees becomes
fissured, and suggests dried gum arabic. The poison is readily soluble
in water and possesses a specific gravity of 1.1313. On drying at room
temperature, it leaves a residue of 30 per cent, which has not lost in
poisonous action or in solubility. In spite of extended experiments,
Langer was unable to determine the nature of the active principle. He
showed that it was not, as had been supposed, an albuminous body, but
rather an organic base.

The pure poison, or the two per cent aqueous solution, placed on the
uninjured skin showed absolutely no irritating effect, though it
produced a marked reaction on the mucus membrane of the nose or eye. A
single drop of one-tenth per cent aqueous solution of the poison brought
about a typical irritation in the conjunctiva of the rabbit's eye. On
the other hand, the application of a drop of the poison, or its
solution, to the slightest break in the skin, or by means of a needle
piercing the skin, produced typical effects. There is produced a local
necrosis, in the neighborhood of which there is infiltration of
lymphocytes, oedema, and hyperæmia.

The effect of the sting on man (fig. 27) is usually transitory but there
are some individuals who are made sick for hours, by a single sting.
Much depends, too, on the place struck. It is a common experience that
an angry bee will attempt to reach the eye of its victim and a sting on
the lid may result in severe and prolonged swelling. In the case of a
man stung on the cheek, Legiehn observed complete aphonia and a breaking
out of red blotches all over the body. A sting on the tongue has been
known to cause such collateral oedema as to endanger life through
suffocation. Cases of death of man from the attacks of bees are rare but
are not unknown. Such results are usually from a number of stings but,
rarely, death has been known to follow a single sting, entering a blood
vessel of a particularly susceptible individual.

[Illustration: Effect of bee stings. After Root.]

It is clearly established that partial immunity from the effects of the
poison may be acquired. By repeated injections of the venom, mice have
been rendered capable of bearing doses that certainly would have killed
them at first. It is a well-known fact that most bee-keepers become
gradually hardened to the stings, so that the irritation and the
swelling become less and less. Some individuals have found this immunity
a temporary one, to be reacquired each season. A striking case of
acquired immunity is related by the Roots in their "A B C and X Y Z of
Bee Culture." The evidence in the case is so clear that it should be
made more widely available and hence we quote it here.

A young man who was determined to become a bee-keeper, was so
susceptible to the poison that he was most seriously affected by a
single sting, his body breaking out with red blotches, breathing growing
difficult, and his heart action being painfully accelerated. "We finally
suggested taking a live bee and pressing it on the back of his hand
until it merely pierced his skin with the sting, then immediately
brushing off both bee and sting. This was done and since no serious
effect followed, it was repeated inside of four or five days. This was
continued for some three or four weeks, when the patient began to have a
sort of itching sensation all over his body. The hypodermic injections
of bee-sting poison were then discontinued. At the end of a month they
were repeated at intervals of four or five days. Again, after two or
three weeks the itching sensation came on, but it was less pronounced.
The patient was given a rest of about a month, when the doses were
repeated as before." By this course of treatment the young man became so
thoroughly immunized that neither unpleasant results nor swelling
followed the attacks of the insects and he is able to handle bees with
the same freedom that any experienced bee-keeper does.

In an interesting article in the _Entomological News_ for November,
1914, J. H. Lovell calls attention to the fact that "There has been a
widespread belief among apiarists that a beekeeper will receive more
stings when dressed in black than when wearing white clothing. A large
amount of evidence has been published in the various bee journals
showing beyond question that honey-bees under certain conditions
discriminate against black. A few instances may be cited in
illustration. Of a flock of twelve chickens running in a bee-yard seven
black ones were stung to death, while five light colored ones escaped
uninjured. A white dog ran among the bee-hives without attracting much
attention, while at the same time a black dog was furiously assailed by
the bees. Mr. J. D. Byer, a prominent Canadian beekeeper, relates that a
black and white cow, tethered about forty feet from an apiary, was one
afternoon attacked and badly stung by bees. On examination it was found
that the black spots had five or six stings to one on the white. All
noticed this fact, although no one was able to offer any explanation. A
white horse is in much less danger of being stung, when driven near an
apiary, than a black one. It has, indeed, been observed repeatedly that
domestic animals of all kinds, if wholly or partially black, are much
more liable to be attacked by bees, if they wander among the hives, than
those which are entirely white."

In order to test the matter experimentally, the following series of
experiments was performed. In the language of the investigator:

"On a clear, warm day in August I dressed wholly in white with the
exception of a black veil. Midway on the sleeve of my right arm there
was sewed a band of black cloth ten inches wide. I then entered the
bee-yard and, removing the cover from one of the hives, lifted a piece
of comb with both hands and gently shook it. Instantly many of the bees
flew to the black band, which they continued to attack as long as they
were disturbed. Not a single bee attempted to sting the left sleeve,
which was of course entirely white, and very few even alighted upon it."

"This experiment was repeated a second, third and fourth time; in each
instance with similar results. I estimated the number of bees on the
band of black cloth at various moments was from thirty to forty; it was
evident from their behavior that they were extremely irritable. To the
left white sleeve and other portions of my clothing they paid very
little attention; but the black veil was very frequently attacked."

"A few days later the experiments were repeated, but the band of black
cloth, ten inches wide, was sewed around my left arm instead of around
the right arm as before. When the bees were disturbed, after the hive
cover had been removed, they fiercely attacked the band of black cloth
as in the previous experiences; but the right white sleeve and the white
suit were scarcely noticed. At one time a part of the black cloth was
almost literally covered with furiously stinging bees, and the black
veil was assailed by hundreds. The bees behaved in a similar manner when
a second hive on the opposite side of the apiary was opened."

"A white veil which had been procured for this purpose, was next
substituted for the black veil. The result was most surprising, for,
whereas in the previous experiments hundreds of bees had attacked the
black veil, so few flew against the white veil as to cause me no
inconvenience. Undoubtedly beekeepers will find it greatly to their
advantage to wear white clothing when working among their colonies of
bees and manipulating the frames of the hives."

When a honey-bee stings, the tip of the abdomen, with the entire sting
apparatus, is torn off and remains in the wound. Here the muscles
continue to contract, for some minutes, forcing the barbs deeper and
deeper into the skin, and forcing out additional poison from the
reservoir.

Treatment, therefore, first consists in removing the sting without
squeezing out additional poison. This is accomplished by lifting and
scraping it out with a knife-blade or the fingernail instead of grasping
and pulling it out. Local application of alkalines, such as weak
ammonia, are often recommended on the assumption that the poison is an
acid to be neutralized on this manner, but these are of little or no
avail. They should certainly not be rubbed in, as that would only
accelerate the absorption of the poison. The use of cloths wrung out in
hot water and applied as hot as can be borne, affords much relief in the
case of severe stings. The application of wet clay, or of the end of a
freshly cut potato is sometimes helpful.

In extreme cases, where there is great susceptibility, or where there
may have been many stings, a physician should be called. He may find
strychnine injections or other treatment necessary, if general symptoms
develop.

[Illustration: 28. The poison apparatus of Formica. Wheeler, after
Forel.]


OTHER STINGING FORMS--Of the five thousand, or more, species of bees,
most possess a sting and poison apparatus and some of the larger forms
are capable of inflicting a much more painful sting than that of the
common honey-bee. In fact, some, like the bumble bees, possess the
advantage that they do not lose the sting from once using it, but are
capable of driving it in repeatedly. In the tropics there are found many
species of stingless bees but these are noted for their united efforts
to drive away intruders by biting. Certain species possess a very
irritating saliva which they inject into the wounds.

The ants are not ordinarily regarded as worthy of consideration under
the heading of "stinging insects" but as a matter of fact, most of them
possess well developed stings and some of them, especially in the
tropics, are very justly feared. Even those which lack the sting possess
well-developed poison glands and the parts of the entire stinging
apparatus, in so far as it is developed in the various species, may
readily be homologized with those of the honey-bee.

The ants lacking a sting are those of the subfamily CAMPONOTINÆ, which
includes the largest of our local species. It is an interesting fact
that some of these species possess the largest poison glands and
reservoir (fig. 28) and it is found that when they attack an enemy they
bring the tip of the abdomen forward and spray the poison in such a way
that it is introduced into the wound made by the powerful mandibles.

[Illustration: 29. A harmless, but much feared larva, the "tomato worm."
Natural size. Photograph by M. V. S.]

More feared than any of the other Hymenoptera are the hornets and wasps.
Of these there are many species, some of which attain a large size and
are truly formidable. Phisalix (1897), has made a study of the venom of
the common hornet and finds that, like the poison of the honey-bee, it
is neither an albuminoid nor an alkaloid. Its toxic properties are
destroyed at 120° C. Phisalix also says that the venom is soluble in
alcohol. If this be true, it differs in this respect from that of the
bee. An interesting phase of the work of Phisalix is that several of her
experiments go to show that the venom of hornets acts as a vaccine
against that of vipers.


NETTLING INSECTS

So far, we have considered insects which possess poison glands connected
with the mouth-parts or a special sting and which actively inject their
poison into man. There remain to be considered those insects which
possess poisonous hairs or body fluids which, under favorable
circumstances, may act as poisons. To the first of these belong
primarily the larvæ of certain Lepidoptera.


LEPIDOPTERA

[Illustration: 30. Another innocent but much maligned caterpillar, the
larva of the Regal moth. Photograph by M. V. S.]

When we consider the reputedly poisonous larvæ of moths and butterflies,
one of the first things to impress us is that we cannot judge by mere
appearance. Various species of Sphingid, or hawk-moth larvæ, bear at the
end of the body a chitinous horn, which is often referred to as a
"sting" and regarded as capable of inflicting dangerous wounds. It would
seem unnecessary to refer to this absurd belief if it were not that each
summer the newspapers contain supposed accounts of injury from the
"tomato worm" (fig. 29) and others of this group. The grotesque, spiny
larva (fig. 30) of one of our largest moths, _Citheronia regalis_ is
much feared though perfectly harmless, and similar instances could be
multiplied.

[Illustration: 31. The flannel moth (Lagoa crispata). (_a_) Poisonous
larva.]

[Illustration: 31. (_b_) Adult. Enlarged. Photographs by M. V. S.]

But if the larvæ are often misjudged on account of their ferocious
appearance, the reverse may be true. A group of most innocent looking
and attractive caterpillars is that of the flannel-moth larvæ, of which
_Lagoa crispata_ may be taken as an example. Its larva (fig. 31) has a
very short and thick body, which is fleshy and completely covered and
hidden by long silken hairs of a tawny or brown color, giving a convex
form to the upper side. Interspersed among these long hairs are
numerous short spines connected with underlying hypodermal poison
glands. These hairs are capable of producing a marked nettling effect
when they come in contact with the skin. This species is found in our
Atlantic and Southern States. Satisfactory studies of its poisonous
hairs and their glands have not yet been made.

[Illustration: 32 The poisonous saddle back caterpillar. Empretia
(Sibine) stimulea. Photograph by M. V. S.]

[Illustration: 33_a_. Io moth larvæ on willow. Photograph by M. V. S.]

_Sibine stimulea (Empretia stimulea)_, or the saddle-back caterpillar
(fig. 32), is another which possesses nettling hairs. This species
belongs to the group of Eucleidæ, or slug caterpillars. It can be
readily recognized by its flattened form, lateral, bristling spines and
by the large green patch on the back resembling a saddle-cloth, while
the saddle is represented by an oval, purplish-brown spot. The small
spines are venomous and affect some persons very painfully. The larva
feeds on the leaves of a large variety of forest trees and also on
cherry, plum, and even corn leaves. It is to be found throughout the
Eastern and Southern United States.

[Illustration: 33_b_. Io moth. Full grown larva. Photograph by M. V. S.]

[Illustration: 34. Io moth. Adult. Photograph by M. V. S.]

_Automeris io_ is the best known of the nettling caterpillars. It is the
larva of the Io moth, one of the Saturniidæ. The mature caterpillar,
(fig. 33), which reaches a length of two and one-half inches, is of a
beautiful pale green with sublateral stripes of cream and red color and
a few black spines among the green ones. The green radiating spines give
the body a mossy appearance. They are tipped with a slender chitinous
hair whose tip is readily broken off in the skin and whose poisonous
content causes great irritation. Some individuals are very susceptible
to the poison, while others are able to handle the larvæ freely without
any discomfort. The larvæ feed on a wide range of food plants. They are
most commonly encountered on corn and on willow, because of the
opportunities for coming in contact with them.

[Illustration: 35. Larva of brown-tail moth. (Natural size). Photograph
by M. V. S.]

The larvæ of the brown-tail moth (_Euproctis chrysorrhoea_) (fig. 35
and 36), where they occur in this country, are, on account of their
great numbers, the most serious of all poisonous caterpillars. It is not
necessary here, to go into details regarding the introduction of this
species from Europe into the New England States. This is all available
in the literature from the United States Bureau of Entomology and from
that of the various states which are fighting the species. Suffice to
say, there is every prospect that the pest will continue to spread
throughout the Eastern United States and Canada and that wherever it
goes it will prove a direct pest to man as well as to his plants.

Very soon after the introduction of the species there occurred in the
region where it had gained a foothold, a mysterious dermatitis of man.
The breaking out which usually occurred on the neck or other exposed
part of the body was always accompanied by an intense itching. It was
soon found that this dermatitis was caused by certain short, barbed
hairs of the brown-tail caterpillars and that not only the caterpillars
but their cocoons and even the adult female moths might harbor these
nettling hairs and thus give rise to the irritation. In many cases the
hairs were wafted to clothing on the line and when this was worn it
might cause the same trouble. Still worse, it was found that very
serious internal injury was often caused by breathing or swallowing the
poisonous hairs.

[Illustration: 36. Browntail moths. One male and two females. Photograph
by M. V. S.]

The earlier studies seemed to indicate that the irritation was purely
mechanical in origin, the result of the minute barbed hairs working into
the skin in large numbers. Subsequently, however, Dr. Tyzzer (1907)
demonstrated beyond question that the trouble was due to a poison
contained in the hairs. In the first place, it is only the peculiar
short barbed hairs which will produce the dermatitis when rubbed on the
skin, although most of the other hairs are sharply barbed. Moreover, it
was found that in various ways the nettling properties could be
destroyed without modifying the structure of the hairs. This was
accomplished by baking for one hour at 110° C, by warming to 60° C in
distilled water, or by soaking in one per cent. or in one-tenth per
cent. of potassium hydrate or sodium hydrate. The most significant part
of his work was the demonstration of the fact that if the nettling
hairs are mingled with blood, they immediately produce a change in the
red corpuscles. These at once become coarsely crenated, and the roleaux
are broken up in the vicinity of the hair (fig. 37_b_). The corpuscles
decrease in size, the coarse crenations are transformed into slender
spines which rapidly disappear, leaving the corpuscles in the form of
spheres, the light refraction of which contrasts them sharply with the
normal corpuscles. The reaction always begins at the basal sharp point
of the hair. It could not be produced by purely mechanical means, such
as the mingling of minute particles of glass wool, the barbed hairs of a
tussock moth, or the other coarser hairs of the brown-tail, with the
blood.

[Illustration: 37. (_a_) Ordinary hairs and three poison hairs of
subdorsal and lateral tubercles of the larva of the browntail moth.
Drawing by Miss Kephart.]

The question of the source of the poison has been studied in our
laboratory by Miss Cornelia Kephart. She first confirmed Dr. Tyzzer's
general results and then studied carefully fixed specimens of the larvæ
to determine the distribution of the hairs and their relation to the
underlying tissues.

[Illustration: 37. (_b_) Effect of the poison on the blood corpuscles of
man. After Tyzzer.]

The poison hairs (fig. 37), are found on the subdorsal and lateral
tubercles (fig. 38), in bunches of from three to twelve on the minute
papillæ with which the tubercles are thickly covered. The underlying
hypodermis is very greatly thickened, the cells being three or four
times the length of the ordinary hypodermal cells and being closely
crowded together. Instead of a pore canal through the cuticula for each
individual hair, there is a single pore for each papillæ on a tubercle,
all the hairs of the papilla being connected with the underlying cells
through the same pore canal, (figs. 39 and 40).

[Illustration: 38. Cross section of the larva of the browntail moth
showing the tubercles bearing the poison hairs. Drawing by Miss
Kephart.]

The hypodermis of this region is of two distinct types of cells. First,
there is a group of slender fusiform cells, one for each poison hair on
the papilla, which are the trichogen, or hair-formative cells. They are
crowded to one side and towards the basement membrane by a series of
much larger, and more prominent cells (fig. 40), of which there is a
single one for each papilla. These larger cells have a granular
protoplasm with large nuclei and are obviously actively secreting. They
are so characteristic in appearance as to leave no question but that
they are the true poison glands.

[Illustration: 39. Epithelium underlying poison hairs of the larva of
the browntail moth. Drawing by Miss Kephart.]

Poisonous larvæ of many other species have been reported from Europe and
especially from the tropics but the above-mentioned species are the more
important of those occurring in the United States and will serve as
types. It should be noted in this connection that through some curious
misunderstanding Goeldi (1913) has featured the larva of _Orgyia
leucostigma_, the white-marked tussock moth, as the most important of
the poisonous caterpillars of this country. Though there are occasional
reports of irritation from its hairs such cases are rare and there is no
evidence that there is any poison present. Indeed, subcutaneous
implantation of the hairs leads to no poisoning, but merely to temporary
irritation.

[Illustration: 40. Same as figure 39, on larger scale.]

Occasionally, the hairs of certain species of caterpillars find
lodgement in the conjunctiva, cornea, or iris of the eye of man and give
rise to the condition known as _opthalmia nodosa_. The essential feature
of this trouble is a nodular conjunctivitis which simulates tuberculosis
of the conjunctiva and hence has been called _pseudo-tubercular_. It may
be distinguished microscopically by the presence of the hairs.

[Illustration: 41. (_a_) Nodular conjunctivitis in the eye of a child.
De Schweinitz and Shumway.]

Numerous cases of opthalmia nodosa are on record. Of those from this
country, one of the most interesting is reported by de Schweinitz and
Shumway (1904). It is that of a child of fifteen years whose eye had
become inflamed owing to the presence of some foreign body. Downward and
inward on the bulbar conjunctiva were a number of flattened,
grayish-yellow nodules, between which was a marked congestion of the
conjunctival and episcleral vessels (fig. 41_a_). Twenty-seven nodules
could be differentiated, those directly in the center of the collection
being somewhat confluent and assuming a crescentic and circular
appearance. The nodules were excised and, on sectioning, were found to
be composed of a layer of spindle cells and round cells, outside of
which the tissue was condensed into a capsule. The interior consisted of
epithelioid cells, between which was a considerable intercellular
substance. Directly in the center of a certain number of nodules was
found the section of a hair (fig. 41_b_). The evidence indicated that
the injury had resulted from playing with caterpillars of one of the
Arctiid moths, _Spilosoma virginica_. Other reported cases have been
caused by the hairs of larvæ of _Lasiocampa rubi_, _L. pini_,
_Porthetria dispar_, _Psilura monacha_ and _Cnethocampa processionea_.

[Illustration: 41_b_. Section through one of the nodules showing the
caterpillar hair. De Schweinitz and Shumway.]


RELIEF FROM POISONING BY NETTLING LARVÆ--The irritation from nettling
larvæ is often severe and, especially in regions where the brown-tail
abounds, inquiries as to treatment arise. In general, it may be said
that cooling lotions afford relief, and that scratching, with the
possibilities of secondary infection, should be avoided, in so far as
possible.

Among the remedies usually at hand, weak solutions of ammonia, or a
paste of ordinary baking soda are helpful. Castellani and Chalmers
recommend cleaning away the hairs by bathing the region with an alkaline
lotion, such as two per cent solution of bicarbonate of soda, and then
applying an ointment of ichthyol (10%).

In the brown-tail district, there are many proprietary remedies of which
the best ones are essentially the following, as recommended by Kirkland
(1907):

    Carbolic acid    œ drachm.
    Zinc oxide       œ oz.
    Lime water       8 oz.

Shake thoroughly and rub well into the affected parts.

In some cases, and especially where there is danger of secondary
infection, the use of a weak solution of creoline (one teaspoonful to a
quart of water), is to be advised.


VESCICATING INSECTS AND THOSE POSSESSING OTHER POISONS IN THEIR BLOOD
PLASMA

We have seen that certain forms, for example, the poisonous spiders, not
only secrete a toxine in their poison glands, but that such a substance
may be extracted from other parts of their body, or even their eggs.
There are many insects which likewise possess a poisonous blood plasma.
Such forms have been well designated by Taschenberg as _cryptotoxic_
([Greek: kryptos] = hidden). We shall consider a few representative
forms.

[Illustration: 42_a_. Blister beetle.]

[Illustration: 42_b_. An American blister beetle. Meloe angusticollis.
Photograph by M. V. S.]


THE BLISTER BEETLES--Foremost among the cryptotoxic insects are the
_Meloidæ_ or "blister beetles," to which the well-known "Spanish fly"
(fig. 42_a_), formerly very generally used in medical practice, belongs.
The vescicating property is due to the presence in the blood plasma of a
peculiar, volatile, crystalline substance known as _cantharidin_, which
is especially abundant in the reproductive organs of the beetle.
According to Kobert, the amount of this varies in different species from
.4 or .5% to 2.57% of the dry weight of the beetle.

While blister beetles have been especially used for external
application, they are also at times used internally as a stimulant and a
diuretic. The powder or extract was formerly much in vogue as an
aphrodisiac, and formed the essential constituent of various philters,
or "love powders". It is now known that its effects on the reproductive
organs appear primarily after the kidneys have been affected to such an
extent as to endanger life, and that many cases of fatal poison have
been due to its ignorant use.

There are many cases on record of poisoning and death due to internal
use, and in some instances from merely external application. There are
not rarely cases of poisoning of cattle from feeding on herbage bearing
a large number of the beetles and authentic cases are known of human
beings who have been poisoned by eating the flesh of such cattle. Kobert
states that the beetles are not poisonous to birds but that the flesh of
birds which have fed on them is poisonous to man, and that if the flesh
of chickens or frogs which have fed on the cantharidin be fed to cats it
causes in them the same symptoms as does the cantharidin.

Treatment of cases of cantharidin poison is a matter for a skilled
physician. Until he can be obtained, emetics should be administered and
these should be followed by white of egg in water. Oils should be
avoided, as they hasten the absorption of the poison.


OTHER CRYPTOTOXIC INSECTS--Though the blister beetles are the best known
of the insects with poisonous blood plasma, various others have been
reported and we shall refer to a few of the best authenticated.

One of the most famous is the Chrysomelid beetle, _Diamphidia simplex_,
the body fluids of whose larvæ are used by certain South African bushmen
as an arrow poison. Its action is due to the presence of a toxalbumin
which exerts a hæmolytic action on the blood, and produces inflammation
of the subcutaneous connective tissue and mucous membranes. Death
results from general paralysis. Krause (1907) has surmised that the
active principle may be a bacterial toxin arising from decomposition of
the tissues of the larva, but he presents no support of this view and it
is opposed by all the available evidence.

In China, a bug, _Heuchis sanguinea_, belonging to the family Cicadidæ,
is used like the Meloidæ, to produce blistering, and often causes
poisoning. It has been assumed that its vescicating properties are due
to cantharidin, but the presence of this substance has not been
demonstrated.

Certain Aphididæ contain a strongly irritating substance which produces,
not merely on mucous membranes but on outer skin, a characteristic
inflammation.

It has been frequently reported that the larvæ of the European cabbage
butterfly, _Pieris brassicæ_, accidentally eaten by cows, horses, ducks,
and other domestic animals, cause severe colic, attempts to vomit,
paralysis of the hind legs, salivation, and stomatitis. On _postmortem_
there are to be found hæmorrhagic gastro-enteritis, splenitis, and
nephritis. Kobert has recently investigated the subject and has found a
poisonous substance in the blood of not only the larvæ but also the
pupæ.


FOOTNOTES:

[A] This is diametrically opposed to the findings of Bordas (1905) in
the case of the European _Latrodectus 13-guttatus_, whose glands are
"much larger than those of other spiders." From a considerable
comparative study, we should also unhesitatingly make this statement
regarding the glands of our American species, _L. mactans_.

[B] Dr. E. H. Coleman (Kellogg, 1915) has demonstrated its virulence by
a series of experiments comparable with those of Kobert.

[C] According to Stiles, the species occurring in the Northwest which is
commonly identified as _D. venustus_ should be called _D. andersoni_
(see footnote, chapter 12).

[D] It should be remembered that in all the higher Hymenoptera the first
abdominal segment is fused with the thorax and that what is apparently
the sixth segment is, in reality, the seventh.




CHAPTER III

PARASITIC ARTHROPODA AFFECTING MAN


The relation of insects to man as simple parasites has long been
studied, and until very recent years the bulk of the literature of
medical entomology referred to this phase of the subject. This is now
completely overshadowed by the fact that so many of these parasitic
forms are more than simple parasites, they are transmitters of other
microscopic parasites which are pathogenic to man. Yet the importance of
insects as parasites still remains and must be considered in a
discussion of the relation of insects to the health of man. In taking up
the subject we shall first consider some general features of the
phenomenon of animal parasitism.

Parasitism is an adaptation which has originated very often among living
organisms and in widely separated groups. It would seem simple to define
what is meant by a "parasite" but, in reality, the term is not easily
limited. It is often stated that a parasite is "An organism which lives
at the expense of another," but this definition is applicable to a
predatory species or, in its broadest sense, to all organisms. For our
purpose we may say with Braun: "A parasite is an organism which, for the
purpose of obtaining food, takes up its abode, temporarily or
permanently, on or within another living organism".

Thus, parasitism is a phase of the broad biological phenomenon of
_symbiosis_, or living together of organisms. It is distinguished from
_mutualism_, or symbiosis in the narrow sense, by the fact that only one
party to the arrangement obtains any advantage, while the other is to a
greater or less extent injured.

Of parasites we may distinguish on the basis of their location on or in
the host, _ecto-parasites_, which live outside of the body; and
_endoparasites_, which live within the body. On account of their method
of breathing the parasitic arthropods belong almost exclusively to the
first of these groups.

On the basis of relation to their host, we find _temporary parasites_,
those which seek the host only occasionally, to obtain food; and the
_stationary_ or _permanent_ parasites which, at least during certain
stages, do not leave their host.

_Facultative parasites_ are forms which are not normally parasitic, but
which, when accidentally ingested, or otherwise brought into the body,
are able to exist for a greater or less period of time in their unusual
environment. These are generally called in the medical literature
"pseudoparasites" but the term is an unfortunate one.

We shall now take up the different groups of arthropods, discussing the
more important of the parasitic forms attacking man. The systematic
relationship of these forms, and key for determining important species
will be found in Chapter XII.


ACARINA OR MITES

The ACARINA, or _mites_, form a fairly natural group of arachnids,
characterized, in general, by a sac-like, unsegmented body which is
generally fused with the cephalothorax. The mouth-parts have been united
to form a beak or rostrum.

The representatives of this group undergo a marked metamorphosis.
Commonly, the larvæ on hatching from the egg, possess but three pairs of
legs, and hence are called _hexapod larvæ_. After a molt, they transform
into nymphs which, like the adult, have four pairs of legs and are
called _octopod nymphs_. These after a period of growth, molt one or
more times and, acquiring external sexual organs, become adult.

Most of the mites are free-living, but there are many parasitic species
and as these have originated in widely separated families, the Acarina
form an especially favorable group for study of the origin of
parasitism. Such a study has been made by Ewing (1911), who has reached
the following conclusions:

"We have strong evidence indicating that the parasitic habit has
originated independently at least eleven times in the phylogeny of the
Ararina. Among the zoophagous parasites, the parasitic habit has been
developed from three different types of free-living Acarina: (a)
predaceous forms, (b) scavengers, (c) forms living upon the juices of
plants."

Ewing also showed that among the living forms of Acarina we can trace
out all the stages of advancing parasitism, semiparasitism, facultative
parasitism, even to the fixed and permanent type, and finally to
endoparasitism.

Of the many parasitic forms, there are several species which are serious
parasites of man and we shall consider the more important of these.
Infestation by mites is technically known as _acariasis_.

[Illustration: 43. Effect of the harvest mites on the skin of man.
Photograph by J. C. Bradley.]


The Trombidiidæ, or Harvest Mites

In many parts of this country it is impossible for a visitor to go into
the fields and, particularly, into berry patches and among tall weeds
and grass in the summer or early fall without being affected by an
intolerable itching, which is followed, later, by a breaking out of
wheals, or papules, surrounded by a bright red or violaceous aureola,
(fig. 43). It is often regarded as a urticaria or eczema, produced by
change of climate, an error in diet, or some condition of general
health.

Sooner or later, the victim finds that it is due to none of these, but
to the attacks of an almost microscopic red mite, usually called
"jigger" or "chigger" in this country. As the term "chigger" is applied
to one of the true fleas, _Dermatophilus penetrans_, of the tropics,
these forms are more correctly known as "harvest mites." Natives of an
infested region may be so immune or accustomed to its attacks as to be
unaware of its presence, though such immunity is by no means possessed
by all who have been long exposed to the annoyance.

[Illustration: 44. Harvest mites. (Larvæ of Trombidium). After C. V.
Riley.]

The harvest mites, or chiggers, attacking man are larval forms,
possessing three pairs of legs (fig. 44). Their systematic position was
at first unknown and they were classed under a special genus _Leptus_, a
name which is very commonly still retained in the medical literature. It
is now known that they are the larval forms of various species of the
genus _Trombidium_, a group of predaceous forms, the adults of which
feed primarily on insects and their eggs. In this country the species
best known are those to be found late in summer, as larvæ at the base of
the wings of houseflies or grasshoppers.

There is much uncertainty as to the species of the larvæ attacking man
but it is clear that several are implicated. Bruyant has shown that in
France the larvæ _Trombidium inapinatum_ and _Trombidium holosericeum_
are those most frequently found. The habit of attacking man is abnormal
and the larvæ die after entering the skin. Normally they are parasitic
on various insects.

Most recent writers agree that, on man, they do not bore into the skin,
as is generally supposed, but enter a hair follicle or sebaceous gland
and from the bottom of this, pierce the cutis with their elongate
hypopharynx. According to Braun, there arises about the inserted
hypopharynx a fibrous secretion--the so-called "beak" which is, in
reality, a product of the host. Dr. J. C. Bradley, however, has made
careful observations on their method of attack, and he assures us that
the mite ordinarily remains for a long time feeding on the surface of
the skin, where it produces the erythema above described. During this
time it is not buried in the skin but is able to retreat rapidly into it
through a hair follicle or sweat gland. The irritation from the mites
ceases after a few days, but not infrequently the intolerable itching
leads to so much scratching that secondary infection follows.

Relief from the irritation may be afforded by taking a warm salt bath as
soon as possible after exposure or by killing the mites by application
of benzine, sulphur ointment or carbolized vaseline. When they are few
in number, they can be picked out with a sterile needle.

Much may be done in the way of warding off their attacks by wearing
gaiters or close-woven stockings extending from ankle to the knee. Still
more efficacious is the sprinkling of flowers of sulphur in the
stockings and the underclothes from a little above the knee, down. The
writers have known this to make it possible for persons who were
especially susceptible to work with perfect comfort in badly infested
regions. Powdered naphthalene is successfully used in the same way and
as Chittenden (1906) points out, is a safeguard against various forms of
man-infesting tropical insect pests.

The question of the destruction of the mites in the field is sometimes
an important one, and under some conditions, is feasible. Chittenden
states that much can be accomplished by keeping the grass, weeds, and
useless herbage mowed closely, so as to expose the mites to the sun. He
believes that in some cases good may be done by dusting the grass and
other plants, after cutting, with flowers of sulphur or by spraying with
dilute kerosene emulsion in which sulphur has been mixed. More recently
(1914) he calls attention to the value of cattle, and more especially
sheep, in destroying the pests by tramping on them and by keeping the
grass and herbage closely cropped.


IXODOIDEA OR TICKS

Until recently, the ticks attracted comparatively little attention from
entomologists. Since their importance as carriers of disease has been
established, interest in the group has been enormously stimulated and
now they rank second only to the mosquitoes in the amount of detailed
study that has been devoted to them.

[Illustration: 45_a_. Argus persicus. Capitulum of male. After Nuttall
and Warburton.]

The ticks are the largest of the Acarina. They are characterized by the
fact that the hypostome, or "tongue" (fig. 45) is large and file-like,
roughened by sharp teeth. They possess a breathing pore on each side of
the body, above the third or fourth coxæ (fig. 45_b_).

[Illustration: 45_b_. Left spiracle of nymph of _Argas persicus_. After
Nuttall and Warburton.]

There are two distinct families of the IXODOIDEA, differing greatly in
structure, life-history and habits. These are the ARGASIDÆ and the
IXODIDÆ. We shall follow Nuttall (1908) in characterizing these two
families and in pointing out their biological differences, and shall
discuss briefly the more important species which attack man. The
consideration of the ticks as carriers of disease will be reserved for a
later chapter.


Argasidæ

In the ticks belonging to the family ARGASIDÆ, there is comparatively
little sexual dimorphism, while this is very marked in the Ixodidæ. The
capitulum, or so-called "head" is ventral, instead of terminal; the
palpi are leg-like, with the segments subequal; the scutum, or dorsal
shield, is absent; eyes, when present, are lateral, on supracoxal folds.
The spiracles are very small; coxæ unarmed; tarsi without ventral
spurs, and the pulvilli are absent or rudimentary.

In habits and life history the Argasidæ present striking
characteristics. In the first place, they are long-lived, a factor which
counts for much in the maintenance of the species. They are intermittent
feeders, being comparable with the bed-bug in this respect. There are
two or more nymphal stages, and they may molt after attaining maturity.
The female lays comparatively few eggs in several small batches.

Nuttall (1911) concludes that "The Argasidæ represent the relatively
primitive type of ticks because they are less constantly parasitic than
are the Ixodidæ. Their nymphs and adults are rapid feeders and chiefly
infest the habitat of their hosts. * * * Owing to the Argasidæ infesting
the habitats of their hosts, their resistance to prolonged starvation
and their rapid feeding habits, they do not need to bring forth a large
progeny, because there is less loss of life in the various stages, as
compared with the Ixodidæ, prior to their attaining maturity."

[Illustration: 46. Argus persicus. Dorsal and ventral aspects. (×4).
After Hassell.]

Of the Argasidæ, we have in the United States, several species which
have been reported as attacking man.

_Argas persicus_, the famous "Miana bug" (fig. 46), is a very widely
distributed species, being reported from Europe, Asia, Africa, and
Australia. It is everywhere preeminently a parasite of fowls. According
to Nuttall it is specifically identical with _Argas americanus_ Packard
or _Argas miniatus_ Koch, which is commonly found on fowls in the United
States, in the South and Southwest. Its habits are comparable to those
of the bed-bug. It feeds intermittently, primarily at night, and instead
of remaining on its host, it then retreats to cracks and crevices.
Hunter and Hooker (1908) record that they have found the larva to remain
attached for five or eight days before dropping. Unlike the Ixodidæ, the
adults oviposit frequently.

[Illustration: 47. Otiobius (Ornithodoros) megnini, head of nymph. After
Stiles.]

[Illustration: 48. Otiobius (Ornithodoros) megnini, male. (_a_) dorsal,
(_b_) ventral aspect. After Nuttall and Warburton.]

The most remarkable feature of the biology of this species is the great
longevity, especially of the adult. Hunter and Hooker report keeping
larvæ confined in summer in pill boxes immediately after hatching for
about two months while under similar conditions those of the Ixodid,
_Boophilus annulatus_ lived for but two or three days. Many writers have
recorded keeping adults for long periods without food. We have kept
specimens in a tin box for over a year and a half and at the end of that
time a number were still alive. Laboulliene kept unfed adults for over
three years. In view of the effectiveness of sulphur in warding off the
attacks of Trombidiidæ, it is astonishing to find that Lounsbury has
kept adults of _Argas persicus_ for three months in a box nearly filled
with flowers of sulphur, with no apparent effect on them.

We have already called attention to the occasional serious effects of
the bites of this species. While such reports have been frequently
discredited there can be no doubt that they have foundation in fact. The
readiness with which this tick attacks man, and the extent to which old
huts may be infested makes it especially troublesome.

_Otiobius (Ornithodoros) megnini_, the "spinose ear-tick" (figs. 47,
48), first described from Mexico, as occurring in the ears of horses, is
a common species in our Southwestern States and is recorded by Banks as
occurring as far north as Iowa.

The species is remarkable for the great difference between the spiny
nymph stage and the adult. The life history has been worked out by
Hooker (1908). Seed ticks, having gained entrance to the ear, attach
deeply down in the folds, engorge, and in about five days, molt; as
nymphs with their spinose body they appear entirely unlike the larvæ. As
nymphs they continue feeding sometimes for months. Finally the nymph
leaves the host, molts to form the unspined adult, and without further
feeding is fertilized and commences oviposition.

The common name is due to the fact that in the young stage the ticks
occur in the ear of their hosts, usually horses or cattle. Not
uncommonly it has been reported as occurring in the ear of man and
causing very severe pain. Stiles recommends that it be removed by
pouring some bland oil into the ear.

Banks (1908) reports three species of _Ornithodoros_--_O. turicata_,
_coriaceus_ and _talaje_--as occurring in the United States. All of these
attack man and are capable of inflicting very painful bites.


Ixodidæ

The ticks belonging to the family IXODIDÆ (figs. 49 and 50) exhibit a
marked sexual dimorphism. The capitulum is anterior, terminal, instead
of ventral as in the Argasidæ; the palpi are relatively rigid (except in
the subfamily Ixodinæ), with rudimentary fourth segment; scutum present;
eyes, when present, dorsal, on side of scutum. The spiracles are
generally large, situated well behind the fourth coxæ; coxæ generally
with spurs; pulvilli always present.

In habits and life history the typical Ixodidæ differ greatly from the
Argasidæ. They are relatively short-lived, though some recent work
indicates that their longevity has been considerably under-estimated.
Typically, they are permanent feeders, remaining on the host, or hosts,
during the greater part of their life. They molt twice only, on leaving
the larval and the nymphal stages. The adult female deposits a single,
large batch of eggs. Contrasting the habits of the Ixodidæ to those of
the Argasidæ, Nuttall (1911) emphasizes that the Ixodidæ are more highly
specialized parasites. "The majority are parasitic on hosts having no
fixed habitat and consequently all stages, as a rule, occur upon the
host."

[Illustration: 49. Ixodes ricinus; male, ventral aspect. After Braun and
Luehe.]

As mere parasites of man, apart from their power to transmit disease,
the Ixodidæ are much less important than the Argasidæ. Many are reported
as occasionally attacking man and of these the following native species
may be mentioned.

[Illustration: 50. Ixodes ricinus, var. scapularis, female. Capitulum
and scutum; ventral aspect of capitulum; coxæ; tarsus 4; spiracle;
genital and anal grooves. After Nuttall and Warburton.]

_Ixodes ricinus_, the European castor bean tick (figs. 49, 50), is a
species which has been often reported from this country but Banks (1908)
has shown that, though it does occur, practically all of the records
apply to _Ixodes scapularis_ or _Ixodes cookei_. In Europe, _Ixodes
ricinus_ is very abundant and very commonly attacks man. At the point
of penetration of the hypostome there is more or less inflammation but
serious injury does not occur unless there have been introduced
pathogenic bacteria or, unless the tick has been abruptly removed,
leaving the capitulum in the wound. Under the latter circumstances,
there may be an abscess formed about the foreign body and occasionally,
serious results have followed. Under certain conditions the tick, in
various stages, may penetrate under the skin and produce a tumor, within
which it may survive for a considerable period of time.

_Ixodes cookei_ is given by Banks as "common on mammals in the Eastern
States as far west as the Rockies." It is said to affect man severely.

_Amblyomma americanum_, (fig. 158c), the "lone star tick," is widely
distributed in the United States. Its common name is derived from the
single silvery spot on the scutum of the female. Hunter and Hooker
regard this species as, next to _Boophilus annulatus_, the most
important tick in the United States. Though more common on cattle, it
appears to attack mammals generally, and "in portions of Louisiana and
Texas it becomes a pest of considerable importance to moss gatherers and
other persons who spend much time in the forests."

_Amblyomma cajennense_, noted as a pest of man in central and tropical
America, is reported from various places in the south and southwestern
United States.

_Dermacentor variabilis_ is a common dog tick of the eastern United
States. It frequently attacks man, but the direct effects of its bite
are negligible.

The "Rocky Mountain spotted fever tick" (_Dermacentor andersoni_
according to Stiles, _D. venustus_ according to Banks) is, from the
viewpoint of its effects on man, the most important of the ticks of the
United States. This is because, as has been clearly established, it
transmits the so-called "spotted fever" of man in our northwestern
states. This phase of the subject will be discussed later and it need
merely be mentioned here, that this species has been reported as causing
painful injuries by its bites. Dr. Stiles states that he has seen cases
of rather severe lymphangitis and various sores and swellings developing
from this cause. In one case, of an individual bitten near the elbow,
the arm became very much swollen and the patient was confined in bed for
several days. The so-called tick paralysis produced by this species is
discussed in a preceding chapter.

There are many other records of various species of ticks attacking man,
but the above-mentioned will serve as typical and it is not necessary to
enter into greater detail.


TREATMENT OF TICK BITES--When a tick attaches to man the first thing to
be done is to remove it without leaving the hypostome in the wound to
fester and bring about secondary effects. This is best accomplished by
applying to the tick's body some substance which will cause it to more
readily loosen its hold. Gasoline or petroleum, oil or vaseline will
serve. For removing the spinose ear-tick, Stiles recommends pouring some
bland oil into the ear. Others have used effectively a pledget of cotton
soaked in chloroform.

In general, the treatment recommended by Wellman for the bites of
_Ornithodoros moubata_ will prove helpful. It consists of prolonged
bathing in very hot water, followed by the application of a strong
solution of bicarbonate of soda, which is allowed to dry upon the skin.
He states that this treatment is comforting. For severe itching he
advises smearing the bites with vaseline, which is slightly impregnated
with camphor or menthol. Medical aid should be sought when complications
arise.

The DERMANYSSIDÆ are Gamasid mites which differ from others of the group
in that they are parasitic on vertebrates. None of the species normally
attack man, but certain of them, especially the poultry mite, may be
accidental annoyances.

[Illustration: 51. Dermanyssus gallinæ, female. After Delafond.]

_Dermanyssus gallinæ_ (fig. 51), the red mite of poultry, is an
exceedingly common and widespread parasite of fowls. During the day it
lives in cracks and crevices of poultry houses, under supports of
roosts, and in litter of the food and nests, coming out at night to
feed. They often attack people working in poultry houses or handling
and plucking infested fowls. They may cause an intense pruritis, but
they do not produce a true dermatosis, for they do not find conditions
favorable for multiplication on the skin of man.


Tarsonemidæ

The representatives of the family TARSONEMIDÆ are minute mites, with the
body divided into cephalothorax and abdomen. There is marked sexual
dimorphism. The females possess stigmata at the anterior part of the
body, at the base of the rostrum, and differ from all other mites in
having on each side, a prominent clavate organ between the first and
second legs. The larva, when it exists, is hexapodous and resembles the
adult. A number of the species are true parasites on insects, while
others attack plants. Several of them may be accidental parasites of
man.

[Illustration: 52. Pediculoides ventricosus, female. After Webster.]

[Illustration: 53. Pediculoides ventricosus, gravid female. (×80).
After Webster.]

_Pediculoides ventricosus_ (fig. 52 and 53) is, of all the Tarsonemidæ
reported, the one which has proved most troublesome to man. It is a
predaceous species which attacks a large number of insects but which has
most commonly been met with by man through its fondness for certain
grain-infesting insects, notably the Angoumois grain moth, _Sitotroga
cerealella_, and the wheat straw-worm, _Isosoma grande_. In recent years
it has attracted much attention in the United States and its
distribution and habits have been the object of detailed study by
Webster (1901).

[Illustration: 54. Pediculoides ventricosus, male. After Braun.]

There is a very striking sexual dimorphism in this species. The
non-gravid female is elongate, about 200µ by 70µ (fig. 52), with the
abdomen slightly striated longitudinally. The gravid female (fig. 53)
has the abdomen enormously swollen, so that it is from twenty to a
hundred times greater than the rest of the body. The species is
viviparous and the larvæ undergo their entire growth in the body of the
mother. They emerge as sexually mature males and females which soon
pair. The male (fig. 54) is much smaller, reaching a length of only 320µ
but is relatively broad, 80µ, and angular. Its abdomen is very greatly
reduced.

As far back as 1850 it was noted as causing serious outbreaks of
peculiar dermatitis among men handling infested grain. For some time the
true source of the difficulty was unknown and it was even believed that
the grain had been poisoned. Webster has shown that in this country (and
probably in Europe as well) its attacks have been mistaken for those of
the red bugs or "chiggers" (larval Trombiidæ). More recently a number of
outbreaks of a mysterious "skin disease" were traced to the use of straw
mattresses, which were found to be swarming with these almost
microscopic forms which had turned their attentions to the occupants of
the beds. Other cases cited were those of farmers running wheat through
a fanning mill, and of thrashers engaged in feeding unthrashed grain
into the cylinder of the machine.

[Illustration: 55. Lesions produced by the attacks of Pediculoides
ventricosus. After Webster.]

The medical aspects of the question have been studied especially by
Schamberg and Goldberger and from the latter's summary (1910) we derive
the following data. Within twelve to sixteen hours after exposure,
itching appears and in severe cases, especially where exposure is
continued night after night by sleeping on an infested bed, the itching
may become almost intolerable. Simultaneously, there appears an eruption
which characteristically consists of wheals surrounded by a vesicle
(fig. 55). The vesicle as a rule does not exceed a pin head in size but
may become as large as a pea. Its contents rapidly become turbid and in
a few hours it is converted into a pustule. The eruption is most
abundant on the trunk, slight on the face and extremities and almost
absent on the feet and hands. In severe cases there may be
constitutional disturbances marked, at the outset, by chilliness,
nausea, and vomiting, followed for a few days by a slight elevation of
temperature, with the appearance of albumin in the urine. In some cases
the eruption may simulate that of chicken-pox or small-pox.

Treatment for the purpose of killing the mites is hardly necessary as
they attach feebly to the surface and are readily brushed off by
friction of the clothes. "Antipruritic treatment is always called for;
warm, mildly alkaline baths or some soothing ointment, such as zinc
oxide will be found to fulfil this indication." Of course, reinfestation
must be guarded against, by discarding, or thoroughly fumigating
infested mattresses, or by avoiding other sources. Goldberger suggests
that farm laborers who must work with infested wheat or straw might
protect themselves by anointing the body freely with some bland oil or
grease, followed by a change of clothes and bath as soon as their work
is done. We are not aware of any experiments to determine the effect of
flowers of sulphur, but their efficiency in the case of "red bugs"
suggests that they are worth a trial against _Pediculoides_.

Various species of TYROGLYPHIDÆ (fig. 150_f_) may abound on dried fruits
and other products and attacking persons handling them, may cause a
severe dermatitis, comparable to that described above for _Pediculoides
ventricosus_. Many instances of their occurrence as such temporary
ectoparasites are on record. Thus, workers who handle vanilla pods are
subject to a severe dermatitis, known as vanillism, which is due to the
attacks of _Tyroglyphus siro_, or a closely related species. The
so-called "grocer's itch" is similarly caused by mites infesting various
products. Castellani has shown that in Ceylon, workers employed in the
copra mills, where dried cocoanut is ground up for export, are much
annoyed by mites, which produce the so-called "copra itch." The skin of
the hands, arms and legs, and sometimes of the whole body, except the
face, is covered by fairly numerous, very pruriginous papules, often
covered by small, bloody crusts due to scratching. The condition is
readily mistaken for scabies. It is due to the attacks of _Tyroglyphus
longior castellanii_ which occur in enormous numbers in some samples of
the copra.


Sarcoptidæ

The SARCOPTIDÆ are minute whitish mites, semi-globular in shape, with a
delicate transversely striated cuticula. They lack eyes and tracheæ. The
mouth-parts are fused at the base to form a cone which is usually
designated as the head. The legs are short and stout, and composed of
five segments. The tarsi may or may not possess a claw and may terminate
in a pedunculated sucker, or simple long bristle, or both. The presence
or absence of these structures and their distribution are much used in
classification. The mites live on or under the skin of mammals and
birds, where they produce the disease known as scabies, mange, or itch.
Several species of the Sarcoptidæ attack man but the most important of
these, and the one pre-eminent as the "itch mite" is _Sarcoptes
scabiei_.

The female of _Sarcoptes scabiei_, of man, is oval and yellowish white;
the male more rounded and of a somewhat reddish tinge, and much smaller.
The body is marked by transverse striæ which are partly interrupted on
the back. There are transverse rows of scales, or pointed spines, and
scattered bristles on the dorsum.

[Illustration: 56_a_. Sarcoptes scabiei, male. (×100). After
Fürstenberg.]

The male (fig. 56) which is from 200-240µ in length, and 150-200µ in
breadth, possesses pedunculated suckers on each pair of legs except the
third, which bears, instead, a long bristle. The female (fig. 56)
300-450µ in length and 250-350µ in breadth, has the pedunculated suckers
on the first and second pairs of legs, only, the third and fourth
terminating in bristles.

[Illustration: 56_b_. Sarcoptes scabiei, female. (×100.) After
Fürstenberg.]

The mite lives in irregular galleries from a few millimeters to several
centimeters in length, which it excavates in the epidermis (fig. 57). It
works especially where the skin is thin, such as between the fingers, in
the bend of the elbows and knees, and in the groin, but it is by no
means restricted to these localities. The female, alone, tunnels into
the skin; the males remain under the superficial epidermal scales, and
seldom are found, as they die soon after mating.

As she burrows into the skin the female deposits her eggs, which measure
about 150 × 100µ. Fürstenberg says that each deposits an average of
twenty-two to twenty-four eggs, though Gudden reports a single burrow as
containing fifty-one. From these there develop after about seven days,
the hexapod larvæ. These molt on the sixteenth day to form an octopod
nymph, which molts again the twenty-first day. At the end of the fourth
week the nymphs molt to form the sexually mature males and the so-called
pubescent females. These pair, the males die, and the females again cast
their skin, and become the oviparous females. Thus the life cycle is
completed in about twenty-eight days.

The external temperature exercises a great influence on the development
of the mites and thus, during the winter, the areas of infestation not
only do not spread, but they become restricted. As soon as the
temperature rises, the mites increase and the infestation becomes much
more extensive.

[Illustration: 57. Sarcoptes scabiei. Diagrammatic representation of the
course in the skin of man.]

In considering the possible sources of infestation, and the chances of
reinfestation after treatment, the question of the ability of the mite
to live apart from its host is a very important one. Unfortunately there
are few reliable data on this subject. Gerlach found that, exposed in
the dry, warm air of a room they became very inactive within twenty-four
hours, that after two days they showed only slight movement, and that
after three or four days they could not be revived by moisture and
warming. The important fact was brought out that in moist air, in folded
soiled underwear, they survived as long as ten days. Bourguignon found
that under the most favorable conditions the mites of _Sarcoptes scabiei
equi_ would live for sixteen days.

The disease designated the "itch" or "scabies," in man has been known
from time immemorial, but until within less than a hundred years it was
almost universally attributed to malnutrition, errors of diet, or "bad
blood." This was in spite of the fact that the mite was known to Mouffet
and that Bonomo had figured both the adult and the egg and had declared
the mite the sole cause of the disease. In 1834 the Corsican medical
student, Francis Renucci, demonstrated the mite before a clinic in Saint
Louis Hospital in Paris and soon thereafter there followed detailed
studies of the life history of the various itch mites of man and
animals.

[Illustration: 58. Scabies on the hand. From portfolio of Dermochromes
by permission of Rebman & Co., of New York. Publishers.]

The disease is a cosmopolitan one, being exceedingly abundant in some
localities. Its spread is much favored where large numbers of people are
crowded together under insanitary conditions and hence it increases
greatly during wars and is widely disseminated and abundant immediately
afterwards. Though more commonly to be met with among the lower classes,
it not infrequently appears among those of the most cleanly, careful
habits, and it is such cases that are most liable to wrong diagnosis by
the physician.

Infection occurs solely through the passage, direct or indirect, of the
young fertilized females to the skin of a healthy individual. The adult,
oviparous females do not quit their galleries and hence do not serve to
spread the disease. The young females move about more or less at night
and thus the principal source of infestation is through sleeping in the
same bed with an infested person, or indirectly through bedclothes, or
even towels or clothing. Diurnal infestation through contact or clothing
is exceptional. Many cases are known of the disease being contracted
from animals suffering from scabies, or mange.

When a person is exposed to infestation, the trouble manifests itself
after eight or ten days, though there usually elapses a period of twenty
to thirty days before there is a suspicion of anything serious. The
first symptom is an intense itching which increases when the patient is
in bed. When the point of irritation is examined the galleries may
usually be seen as characteristic sinuous lines, at first whitish in
color but soon becoming blackish because of the contained eggs and
excrement. The galleries, which may not be very distinct in some cases,
may measure as much as four centimeters in length. Little vesicles, of
the size of a pin head are produced by the secretions of the feeding
mite; they are firm, and projecting, and contain a limpid fluid. Figures
58 and 59 show the typical appearance of scabies on the hands, while
figure 60 shows a severe general infestation. The intolerable itching
induces scratching and through this various complications may arise. The
lesions are not normally found on the face and scalp, and are rare on
the back.

[Illustration: 59. Scabies on the hand. After Duhring.]

[Illustration: 60. Generalized infection of Scabies. After Morrow.]

Formerly, scabies was considered a very serious disease, for its cause
and method of treatment were unknown, and potentially it may continue
indefinitely. Generation after generation of the mites may develop and
finally their number become so great that the general health of the
individual is seriously affected. Now that the true cause of the disease
is known, it is easily controlled.

Treatment usually consists in softening the skin by friction with soap
and warm water, followed by a warm bath, and then applying some
substance to kill the mites. Stiles gives the following directions,
modified from Bourguignon's, as "a rather radical guide, to be modified
according to facilities and according to the delicacy of the skin or
condition of the patient":

1. The patient, stripped naked, is energetically rubbed all over (except
the head) for twenty minutes, with green soap and warm water. 2. He is
then placed in a warm bath for thirty minutes, during which time the
rubbing is continued. 3. The parasiticide is next rubbed in for twenty
minutes and is allowed to remain on the body for four or five hours; in
the meantime the patient's clothes are sterilized, to kill the eggs or
mites attached to them. 4. A final bath is taken to remove the
parasiticide.

The parasiticide usually relied on is the officinal sulphur ointment of
the United States pharmacopoeia. When infestation is severe it is
necessary to repeat treatment after three or four days in order to kill
mites which have hatched from the eggs.

The above treatment is too severe for some individuals and may, of
itself, produce a troublesome dermatitis. We have seen cases where the
treatment was persisted in and aggravated the condition because it was
supposed to be due to the parasite. For delicate-skinned patients the
use of balsam of Peru is very satisfactory, and usually causes no
irritation whatever. Of course, sources of reinfection should be
carefully guarded against.

_Sarcoptes scabiei crustosæ_, which is a distinct variety, if not
species, of the human itch mite, is the cause of so-called Norwegian
itch. This disease is very contagious, and is much more resistant than
the ordinary scabies. Unlike the latter, it may occur on the face and
scalp.

_Sarcoptes scabiei_ not only attacks man but also occurs on a large
number of mammals. Many species, based on choice of host, and minute
differences in size and secondary characters, have been established, but
most students of the subject relegate these to varietal rank. Many of
them readily attack man, but they have become sufficiently adapted to
their normal host so that they are usually less persistent on man.

_Notoedres cati_ (usually known as _Sarcoptes minor_) is a species of
itch mites which produce an often fatal disease of cats. The body is
rounded and it is considerably smaller than _Sarcoptes scabiei_, the
female (fig. 61) measuring 215-230µ long and 165-175µ wide; the males
145-150µ by 120-125µ. The most important character separating
_Notoedres_ from _Sarcoptes_ is the position of the anus, which is
dorsal instead of terminal. The mite readily transfers to man but does
not persist, the infestation usually disappearing spontaneously in about
two weeks. Infested cats are very difficult to cure, unless treatment is
begun at the very inception of the outbreak, and under ordinary
circumstances it is better to kill them promptly, to avoid spread of the
disease to children and others who may be exposed.

[Illustration: 61. Notoedres cati, male and female. After Railliet.]


Demodecidæ

The DEMODECIDÆ are small, elongate, vermiform mites which live in the
hair follicles of mammals. The family characteristics will be brought
out in the discussion of the species infesting man, _Demodex
folliculorum_.

[Illustration: 62. Demodex folliculorum. (×200) After Blanchard.]

_Demodex folliculorum_ (fig. 62) is to be found very commonly in the
hair follicles and sebaceous glands of man. It is vermiform in
appearance, and with the elongate abdomen transversely striated so as to
give it the appearance of segmentation. The female is 380-400µ long by
45µ; the male 300µ by 40µ. The three-jointed legs, eight in number, are
reduced to mere stubs in the adult. The larval form is hexopod. These
mites thus show in their form a striking adaptation to their
environment. In the sebaceous glands and hair follicles they lie with
their heads down (fig. 63). Usually there are only a few in a gland, but
Gruby has counted as many as two hundred.

[Illustration: 63. Demodex folliculorum. Section through skin showing
the mites in situ. Magnification of Nos. 1, 2, 6 and 7, ×150; Nos, 3,
4, 5, ×450. After Megnin.]

The frequency with which they occur in man is surprising. According to
European statistics they are found in 50 per cent to 60 per cent or even
more. Gruby found them in forty out of sixty persons examined. These
figures are very commonly quoted, but reliable data for the United
States seem to be lacking. Our studies indicate that it is very much
less common in this country than is generally assumed.

The Demodex in man does not, as a rule, cause the slightest
inconvenience to its host. It is often stated that they give rise to
comedons or "black-heads" but there is no clear evidence that they are
ever implicated. Certain it is that they are not the usual cause. A
variety of the same, or a very closely related species of _Demodex_, on
the dog gives rise to the very resistant and often fatal follicular
mange.


HEXAPODA OR TRUE INSECTS

The HEXAPODA, or true insects, are characterized by the fact that the
adult possesses three pairs of legs. The body is distinctly segmented
and is divided into head, thorax, and abdomen.

The mouth-parts in a generalized form, consist of an upper lip, or
_labrum_, which is a part of the head capsule, and a central unpaired
_hypopharynx_, two _mandibles_, two _maxillæ_ and a lower lip, or
_labium_, made up of the fused pair of second maxillæ. These parts may
be greatly modified, dependent upon whether they are used for biting,
sucking, piercing and sucking, or a combination of biting and sucking.

Roughly speaking, insects may be grouped into those which undergo
_complete metamorphosis_ and those which have _incomplete
metamorphosis_. They are said to undergo complete metamorphosis when the
young form, as it leaves the egg, bears no resemblance to the adult. For
example, the maggot changes to a quiescent pupa and from this emerges
the winged active fly. They undergo incomplete metamorphosis, when the
young insect, as it leaves the egg, resembles the adult to a greater or
less extent, and after undergoing a certain number of molts becomes
sexually mature.

Representatives of several orders have been reported as accidental or
faculative parasites of man, but the true parasites are restricted to
four orders. These are the Siphunculata; the Hemiptera, the Diptera and
the Siphonaptera.


SIPHUNCULATA

The order SIPHUNCULATA was established by Meinert to include the true
sucking lice. These are small wingless insects, with reduced
mouth-parts, adapted for sucking; thorax apparently a single piece due
to indistinct separation of its three segments: the compound eyes
reduced to a single ommatidium on each side. The short, powerful legs
are terminated by a single long claw. Metamorphosis incomplete.

There has been a great deal of discussion regarding the structure of the
mouth-parts, and the relationships of the sucking lice, and the
questions cannot yet be regarded as settled. The conflicting views are
well represented by Cholodkovsky (1904 and 1905) and by Enderlein
(1904).

[Illustration: 64. Pediculus showing the blind sac (_b_) containing the
mouth parts (_a_) beneath the alimentary canal (_p_). After Pawlowsky.]

Following Graber, it is generally stated that the mouth-parts consist of
a short tube furnished with hooks in front, which constitutes the lower
lip, and that within this is a delicate sucking tube derived from the
fusion of the labrum and the mandibles. Opposed to this, Cholodkovsky
and, more recently, Pawlowsky, (1906), have shown that the piercing
apparatus lies in a blind sac under the pharynx and opening into the
mouth cavity (fig. 64). It does not form a true tube but a furrow with
its open surface uppermost. Eysell has shown that, in addition, there is
a pair of chitinous rods which he regards as the homologues of the
maxillæ.

When the louse feeds, it everts the anterior part of the mouth cavity,
with its circle of hooks. The latter serve for anchoring the bug, and
the piercing apparatus is then pushed out.

[Illustration: 65. Pediculus humanus, ventral aspect of male. (×10)]

Most writers have classed the sucking lice as a sub-order of the
Hemiptera, but the more recent anatomical and developmental studies
render this grouping untenable. An important fact, bearing on the
question, is that, as shown by Gross, (1905), the structure of the
ovaries is radically different from that of the Hemiptera.

Lice infestation and its effects are known medically as _pediculosis_.
Though their continued presence is the result of the grossest neglect
and filthiness, the original infestation may be innocently obtained and
by people of the most careful habits.

Three species commonly attack man. Strangely enough, there are very few
accurate data regarding their life history.

_Pediculus humanus_ (fig. 65), the head louse, is the most widely
distributed. It is usually referred to in medical literature as
_Pediculus capitis_, but the Linnean specific name has priority. In
color it is of a pale gray, blackish on the margins. It is claimed by
some authors that the color varies according to the color of the skin of
the host. The abdomen is composed of seven distinct segments, bearing
spiracles laterally. There is considerable variation in size. The males
average 1.8 mm. and the females 2.7 mm. in length.

The eggs, fifty to sixty in number, stick firmly to the hairs of the
host and are known as nits. They are large and conspicuous, especially
on dark hair and are provided with an operculum, or cap, at the free
end, where the nymphs emerge. They hatch in about six days and about the
eighteenth day the young lice are sexually mature.

[Illustration: 66. Pediculosis of the head. The illustration shows the
characteristic indications of the presence of lice, viz: the occipital
eczema gluing the hairs together, the swollen cervical glands, and the
porrigo, or eruption of contagious pustules upon the neck. After Fox.]

The head lice live by preference on the scalp of their host but
occasionally they are found on the eyelashes and beard, or in the pubic
region. They may also occur elsewhere on the body. The penetration of
the rostrum into the skin and the discharge of an irritating saliva
produce a severe itching, accompanied by the formation of an eczema-like
eruption (fig. 66). When the infestation is severe, the discharge from
the pustules mats down the hair, and scabs are formed, under which the
insects swarm. "If allowed to run, a regular carapace may form, called
_trichoma_, and the head exudes a foetid odor. Various low plants may
grow in the trichoma, the whole being known as _plica
palonica_."--Stiles.

Sources of infestation are various. School children may obtain the lice
from seatmates, by wearing the hats or caps of infested mates, or by the
use, in common, of brushes and combs. They may be obtained from infested
beds or sleeper berths. Stiles reports an instance in which a large
number of girls in a fashionable boarding school developed lousiness a
short time after traveling in a sleeping car.

Treatment is simple, for the parasites may readily be controlled by
cleanliness and washing the head with a two per cent solution of
carbolic acid or even kerosene. The latter is better used mixed with
equal parts of olive oil, to avoid irritation. The treatment should be
applied at night and followed the next morning by a shampoo with soap
and warm water. It is necessary to repeat the operation in a few days.
Xylol, used pure, or with the addition of five per cent of vaseline, is
also very efficacious. Of course, the patient must be cautioned to stay
away from a lighted lamp or fire while using either the kerosene or
xylol. While these treatments will kill the eggs or nits, they will not
remove them from the hairs. Pusey recommends repeated washings with
vinegar or 25 per cent of acetic acid in water, for the purpose of
loosening and removing the nits.

Treatment of severe infestations in females is often troublesome on
account of long hair. For such cases the following method recommended by
Whitfield (1912) is especially applicable:

The patient is laid on her back on the bed with her head over the edge,
and beneath the head is placed a basin on a chair so that the hair lies
in the basin. A solution of 1 in 40 carbolic acid is then poured over
the hair into the basin and sluiced backwards and forwards until the
whole of the hair is thoroughly soaked with it. It is especially
necessary that care should be taken to secure thorough saturation of the
hair over the ears and at the nape of the neck, since these parts are
not only the sites of predilection of the parasites but they are apt to
escape the solution. This sluicing is carried out for ten minutes by the
clock. At the end of ten minutes the hair is lifted from the basin and
allowed to drain, but is not dried or even thoroughly wrung out. The
whole head is then swathed with a thick towel or better, a large piece
of common house flannel, which is fastened up to form a sort of turban,
and is allowed to remain thus for an hour. It can then be washed or
simply allowed to dry, as the carbolic quickly disperses. At the end of
this period every pediculus and what is better, every ovum is dead and
no relapse will occur unless there is exposure to fresh contagion.
Whitfield states that there seem to be no disadvantages in this method,
which he has used for years. He has never seen carboluria result from
it, but would advise first cutting the hair of children under five years
of age.

_Pediculus corporis_ (= _P. vestimenti_) the body louse, is larger than
the preceding species, the female measuring 3.3 mm., and the male 3 mm.
in length. The color is a dirty white, or grayish. _P. corporis_ has
been regarded by some authorities as merely a variety of _P. humanus_
but Piaget maintains there are good characters separating the two
species.

The body louse lives in the folds and seams of the clothing of its host,
passing to the skin only when it wishes to feed. Brumpt states that he
has found enormous numbers of them in the collars of glass-ware or
grains worn by certain naked tribes in Africa.

Exact data regarding the life-history of this species have been
supplied, in part, by the work of Warburton (1910), cited by Nuttall. He
found that _Pediculus corporis_ lives longer than _P. humanus_ under
adverse conditions. This is doubtless due to its living habitually on
the clothing, whereas _humanus_ lives upon the head, where it has more
frequent opportunities of feeding. He reared a single female upon his
own person, keeping the louse enclosed in a cotton-plugged tube with a
particle of cloth to which it could cling. The tube was kept next to his
body, thus simulating the natural conditions of warmth and moisture
under which the lice thrive. The specimen was fed twice daily, while it
clung to the cloth upon which it rested. Under these conditions she
lived for one month. Copulation commenced five days after the female had
hatched and was repeated a number of times, sexual union lasting for
hours. The female laid one hundred and twenty-four eggs within
twenty-five days.

The eggs hatched after eight days, under favorable conditions, such as
those under which the female was kept. They did not hatch in the cold.
Eggs kept near the person during the day and hung in clothing by the
bedside at night, during the winter, in a cold room, did not hatch until
the thirty-fifth day. When the nymphs emerge from the eggs, they feed at
once, if given a chance to do so. They are prone to scatter about the
person and abandon the fragment of cloth to which the adult clings.

The adult stage is reached on the eleventh day, after three molts, about
four days apart. Adults enter into copulation about the fifth day and as
the eggs require eight days for development, the total cycle, under
favorable conditions, is about twenty-four days. Warburton's data differ
considerably from those commonly quoted and serve to emphasize the
necessity for detailed studies of some of the commonest of parasitic
insects.

Body lice are voracious feeders, producing by their bites and the
irritating saliva which they inject, rosy elevations and papules which
become covered with a brownish crust. The intense itching provokes
scratching, and characteristic white scars (fig. 67) surrounded by
brownish pigment (fig. 68) are formed. The skin may become thickened and
take on a bronze tinge. This melanoderma is especially marked in the
region between the shoulders but it may become generalized, a prominent
characteristic of "vagabond's disease." According to Dubre and Beille,
this melanoderma is due to a toxic substance secreted by the lice, which
indirectly provokes the formation of pigment.

[Illustration: 67. Pediculosis in man caused by the body louse. After
Morrow.]

Control measures, in the case of the body louse, consist in boiling or
steaming the clothes or in some cases, sterilizing by dry heat. The
dermatitis may be relieved by the use of zinc-oxide ointment, to which
Pusey recommends that there be added, on account of their parasiticidal
properties, sulphur and balsam of Peru, equal parts, 15 to 30 grains to
the ounce.

_Phthirius pubis_ (= _P. inguinalis_), the pubic louse, or so-called
"crab louse," differs greatly from the preceding in appearance. It is
characterized by its relatively short head which fits into a broad
depression in the thorax. The latter is broad and flat and merges into
the abdomen. The first pair of legs is slender and terminated by a
straight claw. The second and third pairs of legs are thicker and are
provided with powerful claws fitted for clinging to hairs. The females
(fig. 69) measure 1.5 to 2 mm. in length by 1.5 mm. in breadth. The male
averages a little over half as large. The eggs, or nits, are fixed at
the base of the hairs. Only a few, ten to fifteen are deposited by a
single female, and they hatch in about a week's time. The young lice
mature in two weeks.

The pubic louse usually infests the hairs of the pubis and the perineal
region. It may pass to the arm pits or even to the beard or moustache.
Rarely, it occurs on the eyelids, and it has even been found, in a very
few instances, occurring in all stages, on the scalp. Infestation may be
contracted from beds or even from badly infested persons in a crowd. We
have seen several cases which undoubtedly were due to the use of public
water closets. It produces papular eruption and an intense pruritis.
When abundant, there occurs a grayish discoloration of the skin which
Duguet has shown is due to a poisonous saliva injected by the louse, as
is the melanoderma caused by the body louse.

[Illustration: 68. Melanoderma caused by the body louse. From Portfolio
of Dermochromes, by permission of Rebman & Co., New York, Publishers.]

The pubic louse may be exterminated by the measures recommended for the
head louse, or by the use of officinal mercurial ointment.

[Illustration: 69. Phthirius pubis. Ventral aspect of female. (×12).]


HEMIPTERA

Several species of HEMIPTERA-HETEROPTERA are habitual parasites of man,
and others occur as occasional or accidental parasites. Of all these,
the most important and widespread are the bed-bugs, belonging to the
genus _Cimex_ (= _Acanthia_).


THE BED-BUGS--The bed-bugs are characterized by a much flattened oval
body, with the short, broad head unconstricted behind, and fitting into
the strongly excavated anterior margin of the thorax. The compound eyes
are prominent, simple eyes lacking. Antennæ four-jointed, the first
segment short, the second long and thick, and the third and fourth
slender. The tarsi are short and three segmented.

It is often assumed in the literature of the subject that there is but a
single species of _Cimex_ attacking man, but several such species are to
be recognized. These are distinguishable by the characters given in
Chapter XII. We shall consider especially _Cimex lectularius_, the most
common and widespread species.

_Cimex lectularius_ (= _Acanthia lectularia_, _Clinocoris
lectularius_), is one of the most cosmopolitan of human parasites but,
like the lice, it has been comparatively little studied until recent
years, when the possibility that it may be concerned with the
transmission of various diseases has awakened interest in the details of
its life-history and habits.

[Illustration: 70. Cimex lectularius adult and eggs. Photograph by M. V.
S.]

The adult insect (fig. 70) is 4-5 mm. long by 3 mm. broad, reddish brown
in color, with the beak and body appendages lighter in color. The short,
broad and somewhat rectangular head has no neck-like constriction but
fits into the broadly semilunar prothorax. The four segmented labium or
proboscis encloses the lancet-like maxillæ and mandibles. The distal of
the four antennal segments is slightly club-shaped. The prothorax is
characteristic of the species, being deeply incised anteriorly and with
its thin lateral margins somewhat turned up. The mesothorax is
triangular, with the apex posteriorly, and bears the greatly atrophied
first pair of wings. There is no trace of the metathoracic pair. The
greatly flattened abdomen has eight visible segments, though in reality
the first is greatly reduced and has been disregarded by most writers.
The body is densely covered with short bristles and hairs, the former
being peculiarly saber-shaped structures sharply toothed at the apex and
along the convex side (fig. 159_b_).

The peculiar disagreeable odor of the adult bed-bug is due to the
secretion of the stink glands which lie on the inner surface of the
mesosternum and open by a pair of orifices in front of the metacoxæ,
near the middle line. In the nymphs, the thoracic glands are not
developed but in the abdomen there are to be found three unpaired dorsal
stink glands, which persist until the fifth molt, when they become
atrophied and replaced by the thoracic glands. The nymphal glands occupy
the median dorsal portion of the abdomen, opening by paired pores at the
anterior margin of the fourth, fifth and sixth segments. The secretion
is a clear, oily, volatile fluid, strongly acid in reaction. Similar
glands are to be found in most of the Hemiptera-Heteroptera and their
secretion is doubtless protective, through being disagreeable to the
birds. In the bed-bug, as Marlatt points out, "it is probably an
illustration of a very common phenomenon among animals, i.e., the
persistence of a characteristic which is no longer of any special value
to the possessor." In fact, its possession is a distinct disadvantage to
the bed-bug, as the odor frequently reveals the presence of the bugs,
before they are seen.

The eggs of the bed-bug (fig. 70) are pearly white, oval in outline,
about a millimeter long, and possess a small operculum or cap at one
end, which is pushed off when the young hatches. They are laid
intermittently, for a long period, in cracks and crevices of beds and
furniture, under seams of mattresses, under loose wall paper, and
similar places of concealment of the adult bugs. Girault (1905) observed
a well-fed female deposit one hundred and eleven eggs during the
sixty-one days that she was kept in captivity. She had apparently
deposited some of her eggs before being captured.

The eggs hatch in six to ten days, the newly emerged nymphs being about
1.5 mm. in length and of a pale yellowish white color. They grow slowly,
molting five times. At the last molt the mesathoracic wing pads appear,
characteristic of the adult. The total length of the nymphal stage
varies greatly, depending upon conditions of food supply, temperature
and possibly other factors. Marlatt (1907) found under most favorable
conditions a period averaging eight days between molting which, added to
an equal egg period, gave a total of about seven weeks from egg to adult
insect. Girault (1912) found the postembryonic period as low as
twenty-nine days and as high as seventy days under apparently similar
and normal conditions of food supply. Under optimum and normal
conditions of food supply, beginning August 27, the average nymphal life
was 69.9 days; average number of meals 8.75 and the molts 5. Under
conditions allowing about half the normal food supply the average
nymphal life was from 116.9 to 139 days. Nymphs starved from birth lived
up to 42 days. We have kept unfed nymphs, of the first stage, alive in a
bottle for 75 days. The interesting fact was brought out that under
these conditions of minimum food supply there were sometimes six molts
instead of the normal number.

The adults are remarkable for their longevity, a factor which is of
importance in considering the spread of the insect and methods of
control. Dufour (1833) (not De Geer, as often stated) kept specimens for
a year, in a closed vial, without food. This ability, coupled with their
willingness to feed upon mice, bats, and other small mammals, and even
upon birds, accounts for the long periods that deserted houses and camps
may remain infested. There is no evidence that under such conditions
they are able to subsist on the starch of the wall paper, juices of
moistened wood, or the moisture in the accumulations of dust, as is
often stated.

There are three or four generations a year, as Girault's breeding
experiments have conclusively shown. He found that the bed-bug does not
hibernate where the conditions are such as to allow it to breed and that
breeding is continuous unless interrupted by the lack of food or, during
the winter, by low temperature.

Bed-bugs ordinarily crawl from their hiding places and attack the face
and neck or uncovered parts of the legs and arms of their victims. If
undisturbed, they will feed to repletion. We have found that the young
nymph would glut itself in about six minutes, though some individuals
fed continuously for nine minutes, while the adult required ten to
fifteen minutes for a full meal. When gorged, it quickly retreats to a
crack or crevice to digest its meal, a process which requires two or
three days. The effect of the bite depends very greatly on the
susceptibility of the individual attacked. Some persons are so little
affected that they may be wholly ignorant of the presence of a large
number of bugs. Usually the bite produces a small hard swelling, or
wheal, whitish in color. It may even be accompanied by an edema and a
disagreeable inflammation, and in such susceptible individuals the
restlessness and loss of sleep due to the presence of the insects may be
a matter of considerable importance. Stiles (1907) records the case of a
young man who underwent treatment for neurasthenia, the diagnosis being
agreed upon by several prominent physicians; all symptoms promptly
disappeared, however, immediately following a thorough fumigation of
his rooms, where nearly a pint of bed-bugs were collected.

It is natural to suppose that an insect which throughout its whole life
is in such intimate relationship with man should play an important rôle
in the transmission of disease. Yet comparatively little is definitely
known regarding the importance of the bed-bug in this respect. It has
been shown that it is capable of transmitting the bubonic plague, and
South American trypanosomiasis. Nuttall succeeded in transmitting
European relapsing fever from mouse to mouse by its bite. It has been
claimed that Oriental sore, tuberculosis, and even syphilis may be so
carried. These phases of the subject will be considered later.

The sources of infestation are many, and the invasion of a house is not
necessarily due to neglect, though the continued presence of the pests
is quite another matter. In apartments and closely placed houses they
are known to invade new quarters by migration. They are frequently to be
met with in boat and sleeper berths, and even the plush seats of day
coaches, whence a nucleus may be carried in baggage to residences. They
may be brought in the laundry or in clothes of servants.

Usually they are a great scourge in frontier settlements and it is
generally believed that they live in nature under the bark of trees, in
lumber, and under similar conditions. This belief is founded upon the
common occurrence of bugs resembling the bed-bug, in such places. As a
matter of fact, they are no relation to bed-bugs but belong to
plant-feeding forms alone (fig. 19 _c_, _d_).

It is also often stated that bed-bugs live in poultry houses, in
swallows nests, and on bats, and that it is from these sources that they
gain access to dwellings. These bugs are specifically distinct from the
true bed-bug, but any of them may, rarely, invade houses. Moreover,
chicken houses are sometimes thoroughly infested with the true _Cimex
lectularius_.

Control measures consist in the use of iron bedsteads and the reduction
of hiding places for the bugs. If the infestation is slight they may be
exterminated by a vigilant and systematic hunt, and by squirting
gasoline or alcohol into cracks and crevices of the beds, and furniture.
Fumigation must be resorted to in more general infestations.

The simplest and safest method of fumigation is by the use of flowers of
sulphur at the rate of two pounds to each one thousand cubic feet of
room space. The sulphur should be placed in a pan, a well made in the
top of the pile and a little alcohol poured in, to facilitate burning.
The whole should be placed in a larger pan and surrounded by water so as
to avoid all danger of fire. Windows should be tightly closed, beds,
closets and drawers opened, and bedding spread out over chairs in order
to expose them fully to the fumes. As metal is tarnished by the sulphur
fumes, ornaments, clocks, instruments, and the like should be removed.
When all is ready the sulphur should be fired, the room tightly closed
and left for twelve to twenty-four hours. Still more efficient in large
houses, or where many hiding places favor the bugs, is fumigation with
hydrocyanic acid gas. This is a deadly poison and must be used under
rigid precautions. Through the courtesy of Professor Herrick, who has
had much experience with this method, we give in the Appendix, the clear
and detailed directions taken from his bulletin on "Household Insects."

Fumigation with formaldehyde gas, either from the liquid or "solid"
formalin, so efficient in the case of contagious diseases, is useless
against bed-bugs and most other insects.


OTHER BED-BUGS--_Cimex hemipterus_ (= _C. rotundatus_) is a tropical and
subtropical species, occurring in both the old and new world. Patton and
Cragg state that it is distributed throughout India, Burma, Assam, the
Malay Peninsula, Aden, the Island of Mauritius, Reunion, St. Vincent and
Porto Rico. "It is widely distributed in Africa, and is probably the
common species associated there with man." Brumpt also records it for
Cuba, the Antilles, Brazil, and Venezuela.

This species, which is sometimes called the Indian bed-bug, differs from
_C. lectularius_ in being darker and in having a more elongate abdomen.
The head also is shorter and narrower, and the prothorax has rounded
borders.

It has the same habits and practically the same life cycle as _Cimex
lectularius_. Mackie, in India, has found that it is capable of
transmitting the Asiatic type of recurrent fever. Roger suggested that
it was also capable of transmitting Kala-azar and Patton has described
in detail the developmental stages of _Leishmania_, the causative
organism of Kala-azar, in the stomach of this bug, but Brumpt declares
that the forms described are those of a common, non-pathogenic
flagellate to be found in the bug, and have nothing to do with the
human disease. Brumpt has shown experimentally that _Cimex hemipterus_
may transmit _Trypanosoma cruzi_ in its excrement.

_Cimex boueti_, occurring in French Guinea, is another species attacking
man. Its habits and general life history are the same as for the above
species. It is 3 to 4.5 mm. in length, has vestigial elytra, and much
elongated antennæ and legs. The extended hind legs are about as long as
the body.

_Cimex columbarius_, a widely distributed species normally living in
poultry houses and dove cotes, _C. inodorus_, infesting poultry in
Mexico, _C. hirundinis_, occurring in the nests of swallows in Europe
and _Oeciacus vicarius_ (fig. 19i) occurring in swallows' nests in this
country, are species which occasionally infest houses and attack man.

[Illustration: 71. Conorhinus sanguisugus.]

_Conorhinus sanguisugus_, the cone-nosed bed-bug. We have seen in our
consideration of poisonous insects, that various species of Reduviid
bugs readily attack man. Certain of these are nocturnal and are so
commonly found in houses that they have gained the name, of "big
bed-bugs." The most noted of these, in the United States, is _Conorhinus
sanguisugus_ (fig. 71), which is widely distributed in our Southern
States.

Like its near relatives, _Conorhinus sanguisugus_ is carnivorous in
habit and feeds upon insects as well as upon mammalian and human blood.
It is reported as often occurring in poultry houses and as attacking
horses in barns. The life history has been worked out in considerable
detail by Marlatt, (1902), from whose account we extract the following.

[Illustration: 72. Beak of Conorhinus sanguisugus. After Marlatt.]

The eggs are white, changing to yellow and pink before hatching. The
young hatch within twenty days and there are four nymphal stages. In all
these stages the insect is active and predaceous, the mouth-parts (fig.
72) being powerfully developed. The eggs are normally deposited, and the
early stages are undoubtedly passed, out of doors, the food of the
immature forms being other insects. Immature specimens are rarely found
indoors. It winters both in the partly grown and adult stage, often
under the bark of trees or in any similar protection, and only in its
nocturnal spring and early summer flights does it attack men. Marlatt
states that this insect seems to be decidedly on the increase in the
region which it particularly infests,--the plains region from Texas
northward and westward. In California a closely related species of
similar habits is known locally as the "monitor bug."

The effect of the bite of the giant bed-bug on man is often very severe,
a poisonous saliva apparently being injected into the wound. We have
discussed this phase of the subject more fully under the head of
poisonous insects.

_Conorhinus megistus_ is a Brazilian species very commonly attacking
man, and of special interest since Chagas has shown that it is the
carrier of a trypanosomiasis of man. Its habits and life history have
been studied in detail by Neiva, (1910).

This species is now pre-eminently a household insect, depositing its
eggs in cracks and crevices in houses, though this is a relatively
recent adaptation. The nymphs emerge in from twenty to forty days,
depending upon the temperature. There are five nymphal stages, and as in
the case of true bed-bugs, the duration of these is very greatly
influenced by the availability of food and by temperature. Neiva reckons
the entire life cycle, from egg to egg, as requiring a minimum of three
hundred and twenty-four days.

The nymphs begin to suck blood in three to five days after hatching.
They usually feed at night and in the dark, attacking especially the
face of sleeping individuals. The bite occasions but little pain. The
immature insects live in cracks and crevices in houses and invade the
beds which are in contact with walls, but the adults are active flyers
and attack people sleeping in hammocks. The males as well as the females
are blood suckers.

Like many blood-sucking forms, _Conorhinus megistus_ can endure for long
periods without food. Neiva received a female specimen which had been
for fifty-seven days alive in a tightly closed box. They rarely feed on
two consecutive days, even on small quantities of blood, and were never
seen to feed on three consecutive days.

Methods of control consist in screening against the adult bugs, and the
elimination of crevices and such hiding places of the nymphs. Where the
infestation is considerable, fumigation with sulphur is advisable.


PARASITIC DIPTERA OR FLIES

Of the DIPTERA or two-winged flies, many species occasionally attack
man. Of these, a few are outstanding pests, many of them may also serve
to disseminate disease, a phase of our subject which will be considered
later. We shall now consider the most important of the group from the
viewpoint of their direct attacks on man.


Psychodidæ or Moth-Flies

The PSYCHODIDÆ or Moth-flies, include a few species which attack man,
and at least one species, _Phlebotomus papatasii_, is known to transmit
the so-called "three-day fever" of man. Another species is supposed to
be the vector of Peruvian verruga.

The family is made up of small, sometimes very small, nematocerous
Diptera, which are densely covered with hairs, giving them a moth-like
appearance. The wings are relatively large, oval or lanceolate in shape,
and when at rest are held in a sloping manner over the abdomen, or are
held horizontally in such a way as to give the insect a triangular
outline. Not only is the moth-like appearance characteristic, but the
venation of the wings (fig. 163, d) is very peculiar and, according to
Comstock, presents an extremely generalized form. All of the
longitudinal veins separate near the base of the wing except veins R_2
and R_3 and veins M_1 and M_2. Cross veins are wanting in most cases.

Comparatively little is known regarding the life-history and habits of
the Psychodidæ, but one genus, _Phlebotomus_, contains minute,
blood-sucking species, commonly known as sand-flies. The family is
divided into two subfamilies, the PSYCHODINÆ and the PHLEBOTOMINÆ. The
second of these, the PHLEBOTOMINÆ, is of interest to us.


THE PHLEBOTOMINÆ--The Phlebotominæ differ from the Psychodinæ in that
the radical sector branches well out into the wing rather than at the
base of the wing. They are usually less hairy than the Psychodinæ. The
ovipositor is hidden and less strongly chitinized. The species attacking
man belong to the genus _Phlebotomus_, small forms with relatively
large, hairy wings which are held upright, and with elongate proboscis.
The mandibles and maxillæ are serrated and fitted for biting.

According to Miss Summers (1913) there are twenty-nine known species of
the genus _Phlebotomus_, five European, eleven Asiatic, seven African
and six American. One species only, _Phlebotomus vexator_, has been
reported for the United States. This was described by Coquillett,
(1907), from species taken on Plummer's Island, Maryland. It measures
only 1.5 mm. in length. As it is very probable that this species is much
more widely distributed, and that other species of these minute flies
will be found to occur in our fauna, we quote Coquillett's description.

_Phlebotomus vexator_, Coq.: Yellow, the mesonotum brown, hairs chiefly
brown; legs in certain lights appear brown, but are covered with a white
tomentum; wings hyaline, unmarked; the first vein (R_1) terminates
opposite one-fifth of the length of the first submarginal cell (cell
R_2); this cell is slightly over twice as long as its petiole; terminal,
horny portion of male claspers slender, bearing many long hairs; the
apex terminated by two curved spines which are more than one-half as
long as the preceding part, and just in front of these are two similar
spines, while near the middle of the length of this portion is a fifth
spine similar to the others. Length 1.5 mm.

The life-history of the Phlebotomus flies has been best worked out for
the European _Phlebotomus papatasii_ and we shall briefly summarize the
account of Doerr and Russ (1913) based primarily on work on this
species. The European Phlebotomus flies appear at the beginning of the
warm season, a few weeks after the cessation of the heavy rains and
storms of springtime. They gradually become more abundant until they
reach their first maximum, which in Italy is near the end of July
(Grassi). They then become scarcer but reach a second maximum in
September. At the beginning of winter they vanish completely,
hibernating individuals not being found.

After fertilization there is a period of eight to ten days before
oviposition. The eggs are then deposited, the majority in a single mass
covered by a slimy secretion from the sebaceous glands. The larvæ emerge
in fourteen to twenty days. There is uncertainty as to the length of
larval life, specimens kept in captivity remaining fifty or more days
without transforming. Growth may be much more rapid in nature. The larvæ
do not live in fluid media but in moist detritus in dark places. Marett
believes that they live chiefly on the excrement of pill-bugs (Oniscidæ)
and lizards. Pupation always occurs during the night. The remnants of
the larval skin remain attached to the last two segments of the
quiescent pupa and serve to attach it to the stone on which it lives.
The pupal stage lasts eleven to sixteen days, the adult escaping at
night.

Only the females suck blood. They attack not only man but all
warm-blooded animals and, according to recent workers, also cold-blooded
forms, such as frogs, lizards, and larvæ. Indeed, Townsend (1914)
believes that there is an intimate relation between _Phlebotomus_ and
lizards, or other reptiles the world over. The Phlebotomus passes the
daylight hours within the darkened recesses of the loose stone walls and
piles of rock in order to escape wind and strong light. Lizards inhabit
the same places, and the flies, always ready to suck blood in the
absence of light and wind, have been found more prone to suck reptilian
than mammalian blood.

On hot summer nights, when the wind is not stirring, the Phlebotomus
flies, or sand-flies, as they are popularly called, invade houses and
sleeping rooms in swarms and attack the inmates. As soon as light begins
to break the flies either escape to the breeding places, or cool, dark
places protected from the wind, or a part of them remain in the rooms,
hiding behind pictures, under garments, and in similar places. Wherever
the Phlebotomus flies occur they are an intolerable nuisance. On account
of their small size they can easily pass through the meshes of ordinary
screens and mosquito curtains. They attack silently and inflict a very
painful, stinging bite, followed by itching. The ankles, dorsum of the
feet, wrists, inner elbow, knee joint and similar places are favorite
places of attack, possibly on account of their more delicate skin.

Special interest has been attracted to these little pests in recent
years, since it has been shown that they transmit the European
"pappatici fever" or "three day fever." More recently yet, it appears
that they are the carriers of the virus of the Peruvian "verruga." This
phase of the subject will be discussed later.

Control measures have not been worked out. As Newstead says, "In
consideration of the facts which have so far been brought to light
regarding the economy of Phlebotomus, it is clearly evident that the
task of suppressing these insects is an almost insurmountable one. Had
we to deal with insects as large and as accessible as mosquitoes, the
adoption of prophylactic measures would be comparatively easy, but owing
to the extremely minute size and almost flea-like habits of the adult
insects, and the enormous area over which the breeding-places may occur,
we are faced with a problem which is most difficult of solution." For
these reasons, Newstead considers that the only really prophylactic
measures which can at present be taken, are those which are considered
as precautionary against the bites of the insects.

Of repellents, he cites as one of the best a salve composed of the
following:

  Ol. Anisi                                                    3 grs.
  Ol. Eucalypti                                                3 grs.
  Ol. Terebenth                                                3 grs.
  Unq. Acid Borac.

Of sprays he recommends as the least objectionable and at the same time
one of the most effective, formalin. "The dark portions and angles of
sleeping apartments should be sprayed with a one per cent. solution of
this substance every day during the season in which the flies are
prevalent. A fine spraying apparatus is necessary for its application
and an excessive amount must not be applied. It is considered an
excellent plan also to spray the mosquito curtains regularly every day
towards sunset; nets thus treated are claimed to repel the attacks of
these insects." This effectiveness of formalin is very surprising for,
as we have seen, it is almost wholly ineffective against bed-bugs,
mosquitoes, house flies and other insects, where it has been tried.

A measure which promises to be very effective, where it can be adopted,
is the use of electric fans so placed as to produce a current of air in
the direction of the windows of sleeping apartments. On account of the
inability of the Phlebotomus flies to withstand even slight breezes, it
seems very probable that they would be unable to enter a room so
protected.


Culicidæ or Mosquitoes

From the medical viewpoint, probably the most interesting and important
of the blood-sucking insects are the mosquitoes. Certainly this is true
of temperate zones, such as those of the United States. The result is
that no other group of insects has aroused such widespread interest, or
has been subjected to more detailed study than have the mosquitoes,
since their rôle as carriers of disease was made known. There is an
enormous literature dealing with the group, but fortunately for the
general student, this has been well summarized by a number of workers.
The most important and helpful of the general works are those of Howard
(1901), Smith (1904), Blanchard (1905), Mitchell (1907), and especially
of Howard, Dyar, and Knab, whose magnificent monograph is still in
course of publication.

Aside from their importance as carriers of disease, mosquitoes are
notorious as pests of man, and the earlier literature on the group is
largely devoted to references to their enormous numbers and their
blood-thirstiness in certain regions. They are to be found in all parts
of the world, from the equator to the Arctic and Antarctic regions.
Linnæus, in the "Flora Lapponica," according to Howard, Dyar and Knab,
"dwells at some length upon the great abundance of mosquitoes in Lapland
and the torments they inflicted upon man and beast. He states that he
believes that nowhere else on earth are they found in such abundance and
he compares their numbers to the dust of the earth. Even in the open,
you cannot draw your breath without having your mouth and nostrils
filled with them; and ointments of tar and cream or of fish grease are
scarcely sufficient to protect even the case-hardened cuticle of the
Laplander from their bite. Even in their cabins, the natives cannot take
a mouthful of food or lie down to sleep unless they are fumigated almost
to suffocation." In some parts of the Northwestern and Southwestern
United States it is necessary to protect horses working in the fields by
the use of sheets or burlaps, against the ferocious attacks of these
insects. It is a surprising fact that even in the dry deserts of the
western United States they sometimes occur in enormous numbers.

Until comparatively recent years, but few species of mosquitoes were
known and most of the statements regarding their life-history were based
upon the classic work of Reaumur (1738) on the biology of the rain
barrel mosquito, _Culex pipiens_. In 1896, Dr. Howard refers to
twenty-one species in the United States, now over fifty are known;
Giles, in 1900, gives a total of two hundred and forty-two for the world
fauna, now over seven hundred species are known. We have found eighteen
species at Ithaca, N. Y.

All of the known species of mosquitoes are aquatic in the larval stage,
but in their life-histories and habits such great differences occur that
we now know that it is not possible to select any one species as typical
of the group. For our present purpose we shall first discuss the general
characteristics and structure of mosquitoes, and shall then give the
life-history of a common species, following this by a brief
consideration of some of the more striking departures from what have
been supposed to be the typical condition.

The CULICIDÆ are slender, nematocerous Diptera with narrow wings,
antennæ plumose in the males, and usually with the proboscis much longer
than the head, slender, firm and adapted for piercing in the female.
The most characteristic feature is that the margins of the wings and, in
most cases, the wing veins possess a fringe of scale-like hairs. These
may also cover in part, or entirely, the head, thorax, abdomen and legs.
The females, only, suck blood.

On account of the importance of the group in this country and the
desirability of the student being able to determine material in various
stages, we show in the accompanying figures the characters most used in
classification.

The larvæ (fig. 73) are elongate, with the head and thorax sharply
distinct. The larval antennæ are prominent, consisting of a single
cylindrical and sometimes curved segment. The outer third is often
narrower and bears at its base a fan-shaped tuft of hairs, the
arrangement and abundance of which is of systematic importance. About
the mouth are the so-called rotary mouth brushes, dense masses of long
hairs borne by the labrum and having the function of sweeping food into
the mouth. The form and arrangement of thoracic, abdominal, and anal
tufts of hair vary in different species and present characteristics of
value. On either side of the eighth abdominal segment is a patch of
scales varying greatly in arrangement and number and of much value in
separating species. Respiration is by means of tracheæ which open at the
apex of the so-called anal siphon, when it is present. In addition,
there are also one or two pairs of tracheal gills which vary much in
appearance in different species. On the ventral side of the anal siphon
is a double row of flattened, toothed spines whose number and shape are
likewise of some value in separating species. They constitute the comb
or pecten.

[Illustration: 73. Culex larva showing details of external structure.]

The pupa (fig. 139, b) unlike that of most insects, is active, though it
takes no food. The head and thorax are not distinctly separated, but the
slender flexible abdomen in sharply marked off. The antennæ,
mouth-parts, legs, and wings of the future adult are now external, but
enclosed in chitinous cases. On the upper surface, near the base of the
wings are two trumpets, or breathing tubes, for the pupal spiracles are
towards the anterior end instead of at the caudal end, as in the larva.
At the tip of the abdomen is a pair of large chitinous swimming paddles.

As illustrative of the life cycle of a mosquito we shall discuss the
development of a common house mosquito, _Culex pipiens_, often referred
to in the Northern United States as the rain barrel mosquito. Its life
cycle is often given as typical for the entire group, but, as we have
already emphasized, no one species can serve this purpose.

The adults of _Culex pipiens_ hibernate throughout the winter in
cellars, buildings, hollow trees, or similar dark shelters. Early in the
spring they emerge and deposit their eggs in a raft-like mass. The
number of eggs in a single mass is in the neighborhood of two hundred,
recorded counts varying considerably. A single female may deposit
several masses during her life time. The duration of the egg stage is
dependent upon temperature. In the warm summer time the larvæ may emerge
within a day. The larvæ undergo four molts and under optimum conditions
may transform into pupæ in about a week's time. Under the same favorable
conditions, the pupal stage may be completed in a day's time. The total
life cycle of _Culex pipiens_, under optimum conditions, may thus be
completed in a week to ten days. This period may be considerably
extended under less favorable conditions of temperature and food supply.

_Culex pipiens_ breeds continuously throughout the summer, developing in
rain barrels, horse troughs, tin cans, or indeed in any standing water
about houses, which lasts for a week or more. The catch basins of sewers
furnish an abundant supply of the pests under some conditions. Such
places, the tin gutters on residences, and all possible breeding places
must be considered in attempts to exterminate this species.

Other species of mosquitoes may exhibit radical departures from _Culex
pipiens_ in life-history and habits. To control them it is essential
that the biological details be thoroughly worked out for, as Howard,
Dyar, and Knab have emphasized, "much useless labor and expense can be
avoided by an accurate knowledge of the habits of the species." For a
critical discussion of the known facts the reader is referred to their
monograph. We shall confine ourselves to a few illustrations.

The majority of mosquitoes in temperate climates hibernate in the egg
stage, hatching in the spring or even mild winter days in water from
melting snow. It is such single-brooded species which appear in
astounding numbers in the far North. Similarly, in dry regions the eggs
may stand thorough dessication, and yet hatch out with great promptness
when submerged by the rains. "Another provision to insure the species
against destruction in such a case, exists in the fact * * * that not
all the eggs hatch, a part of them lying over until again submerged by
subsequent rains." In temperate North America, a few species pass the
winter in the larval state. An interesting illustration of this is
afforded by _Wyeomia smithii_, whose larvæ live in pitcher plants and
are to be found on the coldest winter days imbedded in the solid ice.
Late in the spring, the adults emerge and produce several broods during
the summer.

In the United States, one of the most important facts which has been
brought out by the intensive studies of recent years is that certain
species are migratory and that they can travel long distances and become
an intolerable pest many miles from their breeding places. This was
forcibly emphasized in Dr. Smith's work in New Jersey, when he found
that migratory mosquitoes, developing in the salt marshes along the
coast, are the dominant species largely responsible for the fame of the
New Jersey mosquito. The species concerned are _Aedes sollicitans_, _A.
cantator_ and _A. tæniorhynchus_. Dr. Smith decided that the first of
these might migrate at least forty miles inland. It is obvious that
where such species are the dominant pest, local control measures are a
useless waste of time and money. Such migratory habits are rare,
however, and it is probable that the majority of mosquitoes do not fly
any great distance from their breeding places.

While mosquitoes are thought of primarily as a pest of man, there are
many species which have never been known to feed upon human or mammalian
blood, no matter how favorable the opportunity. According to Howard,
Dyar, and Knab, this is true of _Culex territans_, one of the common
mosquitoes in the summer months in the Northern United States. There are
some species, probably many, in which the females, like the males, are
plant feeders. In experimental work, both sexes are often kept alive for
long periods by feeding them upon ripe banana, dried fig, raisins, and
the like, and in spite of sweeping assertions that mosquitoes must have
a meal of blood in order to stimulate the ovaries to development, some
of the common blood-sucking species, notably _Culex pipiens_, have been
bred repeatedly without opportunity to feed upon blood.

The effect of the bite varies greatly with different species and depends
upon the susceptibility of the individual bitten. Some persons are
driven almost frantic by the attacks of the pests when their companions
seem almost unconscious of any inconvenience. Usually, irritation and
some degree of inflammation appear shortly following the bite. Not
infrequently a hardened wheal or even a nodule forms, and sometimes
scratching leads to secondary infection and serious results.

The source of the poison is usually supposed to be the salivary glands
of the insect. As we have already pointed out, (p. 34), Macloskie
believed that one lobe of the gland, on each side, was specialized for
forming the poison, while a radically different view is that of
Schaudinn, who believed that the irritation is due to the expelled
contents of the oesophageal diverticula, which contain a gas and a
peculiar type of fungi or bacteria. In numerous attempts, Schaudinn was
unable to produce any irritation by applying the triturated salivary
glands to a wound, but obtained the typical result when he used the
isolated diverticula.

The irritation of the bite may be relieved to some extent by using
ammonia water, a one per cent. alcoholic solution of menthol, or
preparations of cresol, or carbolic acid. Dr. Howard recommends rubbing
the bite gently with a piece of moist toilet soap. Castellani and
Chalmers recommend cleansing inflamed bites with one in forty carbolic
lotion, followed by dressing with boracic ointment. Of course,
scratching should be avoided as much as possible.

Repellents of various kinds are used, for warding off the attacks of the
insects. We have often used a mixture of equal parts of oil of
pennyroyal and kerosene, applied to the hands and face. Oil of
citronella is much used and is less objectionable to some persons. A
recommended formula is, oil of citronella one ounce, spirits of camphor
one ounce, oil of cedar one-half ounce. A last resort would seem to be
the following mixture recommended by Howard, Dyar, and Knab for use by
hunters and fishermen in badly infested regions, against mosquitoes and
blackflies.

Take 2Œ lbs. of mutton tallow and strain it. While still hot add œ
lb. black tar (Canadian tar). Stir thoroughly and pour into the
receptacle in which it is to be contained. When nearly cool stir in
three ounces of oil of citronella and 1Πoz. of pennyroyal.

At night the surest protection is a good bed net. There are many types
of these in use, but in order to be serviceable and at the same time
comfortable it should be roomy and hung in such a way as to be stretched
tightly in every direction. We prefer one suspended from a broad, square
frame, supported by a right-angled standard which is fastened to the
head of the bed. It must be absolutely free from rents or holes and
tucked in securely under the mattress or it will serve merely as a
convenient cage to retain mosquitoes which gain an entrance. While such
nets are a convenience in any mosquito ridden community, they are
essential in regions where disease-carrying species abound. Screening of
doors, windows and porches, against the pests is so commonly practiced
in this country that its importance and convenience need hardly be
urged.

Destruction of mosquitoes and prevention of breeding are of fundamental
importance. Such measures demand first, as we have seen, the correct
determination of the species which is to be dealt with, and a knowledge
of its life-history and habits. If it prove to be one of the migratory
forms, it is beyond mere local effort and becomes a problem demanding
careful organization and state control. An excellent illustration of the
importance and effectiveness of work along these lines is afforded by
that in New Jersey, begun by the late Dr. John B. Smith and being pushed
with vigor by his successor, Dr. Headlee.

In any case, there is necessity for community action. Even near the
coast, where the migratory species are dominant, there are the local
species which demand attention and which cannot be reached by any
measures directed against the species of the salt marshes. The most
important of local measures consist in the destruction of breeding
places by filling or draining ponds and pools, clearing up of more
temporary breeding places, such as cans, pails, water barrels and the
like. Under conditions where complete drainage of swamps is
impracticable or undesirable, judicious dredging may result in a pool or
series of steep-sided pools deep enough to maintain a supply of fish,
which will keep down the mosquito larvæ. Where water receptacles are
needed for storage of rain water, they should be protected by careful
screening or a film of kerosene over the top of the water, renewed every
two weeks or so, so as to prevent mosquitoes from depositing their eggs.
When kerosene is used, Water drawn from the bottom of the receptacle
will not be contaminated by it to any injurious extent. Where ponds
cannot be drained much good will be accomplished by spraying kerosene
oil on the surface of the water, or by the introduction of fish which
will feed on the larvæ.

Detailed consideration of the most efficient measures for controlling
mosquitoes is to be found in Dr. Howard's Bulletin No. 88 of the Bureau
of Entomology, "Preventive and remedial work against mosquitoes" or, in
more summarized form, in Farmers' Bulletin No. 444. One of these should
be obtained by any person interested in the problems of mosquito control
and public health.

[Illustration: 74. Mouth parts of Simulium. After Grünberg.]


The Simuliidæ, or Black Flies

The SIMULIIDÆ, or black flies, are small, dark, or black flies, with a
stout body and a hump-back appearance. The antennæ are short but
eleven-segmented, the wings broad, without scales or hairs, and with the
anterior veins stout but the others very weak. The mouth-parts (fig. 74)
are fitted for biting.

The larvæ of the Simuliidæ (fig. 75) are aquatic and, unlike those of
mosquitoes, require a well ærated, or swiftly running water. Here they
attach to stones, logs, or vegetation and feed upon various
micro-organisms. They pupate in silken cocoons open at the top. Detailed
life-histories have not been worked out for most of the species. We
shall consider as typical that of _Simulium pictipes_, an inoffensive
species widely distributed in the Eastern United States, which has been
studied especially at Ithaca, N.Y. (Johannsen, 1903).

[Illustration: 75. Larva of Simulium, (×8). After Garman.]

The eggs are deposited in a compact yellowish layer on the surface of
rock, on the brinks of falls and rapids where the water is flowing
swiftly. They are elongate ellipsoidal in shape, about .4 by .18 mm. As
myriads of females deposit in the same place the egg patches may be
conspicuous coatings of a foot or much more in diameter. When first laid
they are enveloped in a yellowish white slime, which becomes darker,
until finally it becomes black just before the emerging of the larvæ.
The egg stage lasts a week.

The larvæ (fig. 75) are black, soft skinned, somewhat cylindrical in
shape, enlarged at both ends and attenuated in the middle. The posterior
half is much stouter than the anterior part and almost club-shaped. The
head bears two large fan-shaped organs which aid in procuring food.
Respiration is accomplished by means of three so-called blood gills
which are pushed out from the dorsal part of the rectum. The larvæ occur
in enormous numbers, in moss-like patches. If removed from their natural
habitat and placed in quiet water they die within three or four hours.
Fastened to the rock by means of a disk-like sucker at the caudal end of
the body, they ordinarily assume an erect position. They move about on
the surface of the rocks, to a limited extent, with a looping gait
similar to that of a measuring worm, and a web is secreted which
prevents their being washed away by the swiftly flowing water. They feed
chiefly upon algæ and diatoms.

The complete larval stage during the summer months occupies about four
weeks, varying somewhat with the temperature and velocity of the water.
At the end of this period they spin from cephalic glands, boot-shaped
silken cocoons within which they pupate. The cocoon when spun is firmly
attached to the rock and also to adjacent cocoons. Clustered
continuously over a large area and sometimes one above another, they
form a compact, carpet-like covering on the rocks, the reddish-brown
color of which is easily distinguishable from the jet-black appearance
of the larvæ. The pupal stage lasts about three weeks. The adult fly,
surrounded by a bubble of air, quickly rises to the surface of the water
and escapes. The adults (fig. 76) are apparently short lived and thus
the entire life cycle, from egg to egg is completed in approximately
eight weeks.

[Illustration: 76. Simulium venustum, (×8). After Garman.]

In the case of _Simulium pictipes_ at Ithaca, N. Y., the first brood of
adults emerges early in May and successive generations are produced
throughout the summer and early autumn. This species winters in the
larval condition. Most of the other species of _Simulium_ which have
been studied seem to be single brooded.

While _Simulium pictipes_ does not attack man, there are a number of the
species which are blood-sucking and in some regions they are a veritable
scourge. In recent years the greatest interest in the group has been
aroused by Sambon's hypothesis that they transmit pellagra from man to
man. This has not been established, and, indeed, seems very doubtful,
but the importance of these insects as pests and the possibility that
they may carry disease make it urgent that detailed life-histories of
the hominoxious species be worked out.

As pests a vivid account of their attacks is in Agassiz's "Lake
Superior" (p. 61), quoted by Forbes (1912).

"Neither the love of the picturesque, however, nor the interests of
science, could tempt us into the woods, so terrible were the black
flies. This pest of flies which all the way hither had confined our
ramblings on shore pretty closely to the rocks and the beach, and had
been growing constantly worse, here reached its climax. Although
detained nearly two days, * * * we could only sit with folded hands, or
employ ourselves in arranging specimens, and such other operations as
could be pursued in camp, and under the protection of a 'smudge.' One,
whom scientific ardor tempted a little way up the river in a canoe,
after water plants, came back a frightful spectacle, with blood-red
rings round his eyes, his face bloody, and covered with punctures. The
next morning his head and neck were swollen as if from an attack of
erysipelas."

There are even well authenticated accounts on record of death of humans
from the attacks of large swarms of these gnats. In some regions, and
especially in the Mississippi Valley in this country, certain species of
black flies have been the cause of enormous losses to farmers and
stockmen, through their attacks on poultry and domestic animals. C. V.
Riley states that in 1874 the loss occasioned in one county in Tennessee
was estimated at $500,000.

The measures of prevention and protection against these insects have
been well summarized by Forbes (1912). They are of two kinds: "the use
of repellents intended to drive away the winged flies, and measures for
the local destruction of the aquatic larvæ. The repellents used are
either smudges, or surface applications made to keep the flies from
biting. The black-fly will not endure a dense smoke, and the well-known
mosquito smudge seems to be ordinarily sufficient for the protection of
man. In the South, leather, cloth, and other materials which will make
the densest and most stifling smoke, are often preserved for this use in
the spring. Smudges are built in pastures for the protection of stock,
and are kept burning before the doors of barns and stables. As the
black-flies do not readily enter a dark room, light is excluded from
stables as much as possible during the gnat season. If teams must be
used in the open field while gnats are abroad, they may be protected
against the attacks of the gnats by applying cotton-seed oil or axle
grease to the surface, especially to the less hairy parts of the
animals, at least twice a day. A mixture of oil and tar and, indeed,
several other preventives, are of practical use in badly infested
regions; but no definite test or exact comparison has been made with any
them in a way to give a record of the precise results."

"It is easy to drive the flies from houses or tents by burning pyrethrum
powder inside; this either kills the flies or stupifies them so that
they do not bite for some time thereafter." * * * "Oil of tar is
commonly applied to the exposed parts of the body for the purpose of
repelling the insects, and this preparation is supplied by the Hudson
Bay Company to its employees. Minnesota fishermen frequently grease
their faces and hands with a mixture of kerosene and mutton tallow for
the same purpose." We have found a mixture of equal parts of kerosene
and oil of pennyroyal efficient.

Under most circumstances very little can be done to destroy this insect
in its early stage, but occasionally conditions are such that a
larvicide can be used effectively. Weed (1904), and Sanderson (1910)
both report excellent results from the use of phinotas oil, a
proprietary compound. The first-mentioned also found that in some places
the larvæ could be removed by sweeping them loose in masses with stiff
stable brooms and then catching them downstream on wire netting
stretched in the water.


Chironomidæ or Midges

The flies of this family, commonly known as midges, resemble mosquitoes
in form and size but are usually more delicate, and the wing-veins,
though sometimes hairy, are not fringed with scales. The venation is
simpler than in the mosquitoes and the veins are usually less distinct.

These midges, especially in spring or autumn, are often seen in immense
swarms arising like smoke over swamps and producing a humming noise
which can be heard for a considerable distance. At these seasons they
are frequently to be found upon the windows of dwellings, where they are
often mistaken for mosquitoes.

The larvæ are worm-like, but vary somewhat in form in the different
genera. Most of them are aquatic, but a few live in the earth, in
manure, decaying wood, under bark, or in the sap of trees, especially in
the sap which collects in wounds.

[Illustration: 77. Culicoides guttipennis; (_a_) adult, (×15); (_b_)
head of same; (_c_) larva; (_d_) head; (_e_) pupa. After Pratt.]

Of the many species of CHIRONOMIDÆ, (over eight hundred known), the vast
majority are inoffensive. The sub-family Ceratopogoninæ, however, forms
an exception, for some of the members of this group, known as sandflies,
or punkies, suck blood and are particularly troublesome in the
mountains, along streams, and at the seashore. Most of these have been
classed under the genus _Ceratopogon_, but the group has been broken up
into a number of genera and _Ceratopogon_, in the strict sense, is not
known to contain any species which sucks the blood of vertebrates.

THE CERATOPOGONINÆ--The Ceratopogoninæ are among the smallest of the
Diptera, many of them being hardly a millimeter long and some not even
so large. They are Chironomidæ in which the thorax is not prolonged over
the head. The antennæ are filiform with fourteen (rarely thirteen)
segments in both sexes, those of the male being brush-like. The basal
segment is enlarged, the last segment never longer than the two
preceding combined, while the last five are sub-equal to, or longer than
the preceding segment. The legs are relatively stouter than in the other
Chironomidæ. The following three genera of this subfamily are best known
as blood suckers in this country.

Of the genus _Culicoides_ there are many species occurring in various
parts of the world. A number are known to bite man and animals and it is
probable that all are capable of inflicting injury. In some localities
they are called punkies, in others, sand-flies, a name sometimes also
applied to the species of _Simulium_ and _Phlebotomus_. Owing to their
very small size they are known by some tribes of Indians as No-see-ums.
The larvæ are found in ponds, pools, water standing in hollow tree
stumps, and the like. Though probably living chiefly in fresh water, we
have found a species occurring in salt water. The larvæ are small,
slender, legless, worm-like creatures (fig. 77_c_) with small brown head
and twelve body segments. The pupæ (fig. 77_e_) are slender, more
swollen at the anterior end and terminating in a forked process. They
float nearly motionless in a vertical position, the respiratory tubes in
contact with the surface film. The adults are all small, rarely
exceeding 2Πmm. in length. The wings are more or less covered with
erect setulæ or hairs and in many species variously spotted and marked
with iridescent blotches. The antennæ have fourteen segments, the palpi
usually five. The wing venation and mouth-parts are shown in figures 77
and 78. Of the twenty or more species of this genus occurring in the
United States the following are known to bite: _C. cinctus_, _C.
guttipennis_, _C. sanguisuga_, _C. stellifer_, _C. variipennis_, _C.
unicolor_.

[Illustration: 78. Culicoides guttipennis; mouth parts of adult. After
Pratt.]

One of the most widely distributed and commonest species in the Eastern
States is _C. guttipennis_ (fig. 77a). It is black with brown legs, a
whitish ring before the apex of each femur and both ends of each tibia;
tarsi yellow, knobs of halteres yellow. Mesonotum opaque, brown, two
vittæ in the middle, enlarging into a large spot on the posterior half,
also a curved row of three spots in front of each wing, and the narrow
lateral margins, light gray pruinose. Wings nearly wholly covered with
brown hairs, gray, with markings as shown in the figure. Length one mm.

_Johannseniella_ Will. is a wide-spread genus related to the foregoing.
Its mouth-parts are well adapted for piercing and it is said to be a
persistent blood sucker, particularly in Greenland. This genus is
distinguished from _Culicoides_ by its bare wings, the venation (fig.
163, c), and the longer tarsal claws. There are over twenty North
American species.

[Illustration: 79. Chrysops univittatus, (×4). After Osborn.]

In the Southwestern United States, _Tersesthes torrens_ Towns. occurs, a
little gnat which annoys horses, and perhaps man also, by its bite. It
is related to _Culicoides_ but differs in the number of antennal
segments and in its wing venation (fig. 163, e). The fly measures but
two mm. in length and is blackish in color. The antennæ of the female
have thirteen segments, the palpi but three, of which the second is
enlarged and swollen.


Tabanidæ or Horse-Flies

The TABANIDÆ,--horse-flies, ear-flies, and deer-flies,--are well-known
pests of cattle and horses and are often extremely annoying to man. The
characteristics of the family and of the principal North American genera
are given in the keys of Chapter XII. There are over 2500 recorded
species. As in the mosquitoes, the females alone are blood suckers. The
males are flower feeders or live on plant juices. This is apparently
true also of the females of some of the genera.

The eggs are deposited in masses on water plants or grasses and sedges
growing in marshy or wet ground. Those of a common species of _Tabanus_
are illustrated in figure 80, _a_. They are placed in masses of several
hundred, light colored when first deposited but turning black. In a week
or so the cylindrical larvæ, tapering at both ends (fig. 80, _b_),
escape to the water, or damp earth, and lead an active, carnivorous
life, feeding mainly on insect larvæ, and worms. In the forms which have
been best studied the larval life is a long one, lasting for months or
even for more than a year. Until recently, little was known concerning
the life-histories of this group, but the studies of Hart (1895), and
Hine (1903 +) have added greatly to the knowledge concerning North
American forms.

Many of the species attack man with avidity and are able to inflict
painful bites, which may smart for hours. In some instances the wound is
so considerable that blood will continue to flow after the fly has left.
We have seen several cases of secondary infection following such bites.

[Illustration: 80. (_a_) Eggs of Tabanus. Photograph by J. T. Lloyd.]

[Illustration: 80. (_b_) Larva of Tabanus. Photograph by M. V. S.]

The horse-flies have been definitely convicted of transferring the
trypanosome of surra from diseased to healthy animals and there is good
evidence that they transfer anthrax. The possibility of their being
important agents in the conveyal of human diseases should not be
overlooked. Indeed, Leiper has recently determined that a species of
_Chrysops_ transfers the blood parasite _Filaria diurna_.


Leptidæ or Snipe-Flies

The family LEPTIDÆ is made up of moderate or large sized flies,
predaceous in habit. They are sufficiently characterized in the keys of
Chapter XII. Four blood-sucking species belonging to three genera have
been reported. Of these _Symphoromyia pachyceras_ is a western species.
Dr. J. C. Bradley, from personal experience, reports it as a vicious
biter.

[Illustration: 80. (_c_) Mouth parts of Tabanus. After Grünberg.]


Oestridæ or Bot-flies

To the family OESTRIDÆ belong the bot and warble-flies so frequently
injurious to animals. The adults are large, or of medium size, heavy
bodied, rather hairy, and usually resemble bees in appearance.

The larvæ live parasitically in various parts of the body of mammals,
such as the stomach (horse bot-fly), the subcutaneous connective tissue
(warble-fly of cattle), or the nasal passage (sheep bot-fly or head
maggot).

There are on record many cases of the occurrence of the larvæ of
Oestridæ as occasional parasites of man. A number of these have been
collected and reviewed in a thesis by Mme. Pètrovskaia (1910). The
majority of them relate to the following species.

_Gastrophilus hæmorrhoidalis_, the red tailed bot-fly, is one of the
species whose larvæ are most commonly found in the stomach of the horse.
Schoch (1877) cites the case of a woman who suffered from a severe case
of chronic catarrh of the stomach, and who vomited, and also passed from
the anus, larvæ which apparently belonged to this species. Such cases
are exceedingly rare but instances of subcutaneous infestation are
fairly numerous. In the latter type these larvæ are sometimes the cause
of the peculiar "creeping myasis." This is characterized at its
beginning by a very painful swelling which gradually migrates, producing
a narrow raised line four to twenty-five millimeters broad. When the
larva is mature, sometimes after several months, it becomes stationary
and a tumor is formed which opens and discharges the larva along with
pus and serum.

_Gastrophilus equi_ is the most widespread and common of the horse
bot-flies. Portschinsky reports it as commonly causing subcutaneous
myasis of man in Russia.

_Hypoderma bovis_ (= _Oestrus bovis_), and _Hypoderma lineata_ are the
so-called warble-flies of cattle. The latter species is the more common
in North America but Dr. C. G. Hewitt has recently shown that _H. bovis_
also occurs. Though warbles are very common in cattle in this country,
the adult flies are very rarely seen. They are about half an inch in
length, very hairy, dark, and closely resemble common honey-bees.

They deposit their eggs on the hairs of cattle and the animals in
licking themselves take in the young larvæ. These pass out through the
walls of the oesophagus and migrate through the tissues of the animal,
to finally settle down in the subcutaneous tissue of the back. The
possibility of their entering directly through the skin, especially in
case of infestation of man, is not absolutely precluded, although it is
doubtful.

For both species of _Hypoderma_ there are numerous cases on record of
their occurrence in man. Hamilton (1893) saw a boy, six years of age,
who had been suffering for some months from the glands on one side of
his neck being swollen and from a fetid ulceration around the back teeth
of the lower jaw of the same side. Three months' treatment was of no
avail and the end seemed near; one day a white object, which was seen to
move, was observed in the ulcer at the root of the tongue, and on being
extracted was recognized as a full grown larva of _Hypoderma_. It was of
usual tawny color, about half an inch long when contracted, about one
third that thickness, and quite lively. The case resulted fatally. The
boy had been on a dairy farm the previous fall, where probably the egg
(or larva) was in some way taken into his mouth, and the larva found
between the base of the tongue and the jaw suitable tissue in which to
develop.

Topsent (1901) reports a case of "creeping myasis" caused by _H.
lineata_ in the skin of the neck and shoulders of a girl eight years of
age. The larva travelled a distance of nearly six and a half inches. The
little patient suffered excruciating pain in the place occupied by the
larva.

_Hypoderma diana_ infests deer, and has been known to occur in man.

_Oestris ovis_, the sheep bot-fly, or head maggot, is widely distributed
in all parts of the world. In mid-summer the flies deposit living
maggots in the nostrils of sheep. These larvæ promptly pass up the nasal
passages into the frontal and maxillary sinuses, where they feed on the
mucous to be found there. In their migrations they cause great
irritation to their host, and when present in numbers may cause vertigo,
paroxysms, and even death. Portschinsky in an important monograph on
this species, has discussed in detail its relation to man. He shows that
it is not uncommon for the fly to attack man and that the minute living
larvæ are deposited in the eyes, nostrils, lips, or mouth. A typical
case in which the larvæ were deposited in the eye was described by a
German oculist Kayser, in 1905. A woman brought her six year old
daughter to him and said that the day before, about noontime, a flying
insect struck the eye of the child and that since then she had felt a
pain which increased towards evening. In the morning the pain ceased but
the eye was very red. She was examined at about noon, at which time she
was quiet and felt no pain. She was not sensitive to light, and the only
thing noticed was a slight congestion and accumulation of secretion in
the corner of the right eye. A careful examination of the eye disclosed
small, active, white larvæ that crawled out from the folds of the
conjunctiva and then back and disappeared. Five of these larvæ were
removed and although an uncomfortable feeling persisted for a while, the
eye became normal in about three weeks.

Some of the other recorded cases have not resulted so favorably, for the
eyesight has been seriously affected or even lost.

According to Edmund and Etienne Sergent (1907), myasis caused by the
larvæ of _Oestris ovis_ is very common among the shepherds in Algeria.
The natives say that the fly deposits its larvæ quickly, while on the
wing, without pause. The greatest pain is caused when these larvæ
establish themselves in the nasal cavities. They then produce severe
frontal headaches, making sleep impossible. This is accompanied by
continuous secretion from the nasal cavities and itching pains in the
sinuses. If the larvæ happen to get into the mouth, the throat becomes
inflamed, swallowing is painful, and sometimes vomiting results. The
diseased condition may last for from three to ten days or in the case of
nasal infection, longer, but recovery always follows. The natives remove
the larvæ from the eye mechanically by means of a small rag. When the
nose is infested, tobacco fumigations are applied, and in case of throat
infestation gargles of pepper, onion, or garlic extracts are used.

_Rhinoestrus nasalis_, the Russian gad-fly, parasitizes the
nasopharyngeal region of the horse. According to Portschinsky, it not
infrequently attacks man and then, in all the known cases deposits its
larvæ in the eye, only. This is generally done while the person is
quiet, but not during sleep. The fly strikes without stopping and
deposits its larva instantaneously. Immediately after, the victim
experiences lancinating pains which without intermission increase in
violence. There is an intense conjunctivitis and if the larvæ are not
removed promptly the envelopes of the eye are gradually destroyed and
the organ lost.

[Illustration: 81. Larvæ of Dermatobia cyaniventris. After Blanchard.]

[Illustration: 82. Young larva of Dermatobia cyaniventris. After
Surcouf.]

_Dermatobia cyaniventris_--This fly (fig. 83) is widely distributed
throughout tropical America, and in its larval stage is well known as a
parasite of man. The larvæ (figs. 81 and 82) which are known as the "ver
macaque," "torcel," "ver moyocuil" or by several other local names,
enter the skin and give rise to a boil-like swelling, open at the top,
and comparable with the swelling produced by the warble fly larvæ, in
cattle. They cause itching and occasional excruciating pain. When
mature, nearly an inch in length, they voluntarily leave their host,
drop to the ground and complete their development. The adult female is
about 12 mm. in length. The face is yellow, the frons black with a
grayish bloom; antennæ yellow, the third segment four times as long as
the second, the arista pectinate. The thorax is bluish black with
grayish bloom; the abdomen depressed, brilliant metallescent blue with
violet tinge. The legs are yellowish, the squamæ and wings brownish.

The different types of larvæ represented in figure 81 were formerly
supposed to belong to different species but Blanchard regards them as
merely various stages of the same species. It is only very recently that
the early stage and the method by which man becomes infested were made
known.

[Illustration: 83. Dermatobia cyaniventris (×1Ÿ). After Manson.]

[Illustration: 84. Mosquito carrying eggs of Dermatobia cyaniventris.
After Surcouf.]

About 1900, Blanchard observed the presence of packets of large-sized
eggs under the abdomen of certain mosquitoes from Central America; and
in 1910, Dr. Moralès, of Costa Rica, declared that the Dermatobia
deposited its eggs directly under the abdomen of the mosquito and that
they were thus carried to vertebrates. Dr. Nunez Tovar observed the
mosquito carriers of the eggs and placing larvæ from this source on
animals, produced typical tumors and reared the adult flies. It remained
for Surcouf (1913) to work out the full details. He found that the
Dermatobia deposits its eggs in packets covered by a very viscid
substance, on leaves. These become attached to mosquitoes of the species
_Janthinosoma lutzi_ (fig. 84) which walk over the leaves. The eggs
which adhere to the abdomen, remain attached and are thus transported.
The embryo develops, but the young larva (fig. 82) remains in the egg
until it has opportunity to drop upon a vertebrate fed upon by the
mosquito.


Muscidæ

The following MUSCIDÆ, characterized elsewhere, deserve special mention
under our present grouping of parasitic species. Other important species
will be considered as facultative parasites.

_Stomoxys calcitrans_, the stable-fly, or the biting house-fly, is often
confused with _Musca domestica_ and therefore is discussed especially in
our consideration of the latter species as an accidental carrier of
disease. Its possible relation to the spread of infantile paralysis is
also considered later.

The _tsetse flies_, belonging to the genus _Glossina_, are African
species of blood-sucking Muscidæ which have attracted much attention
because of their rôle in transmitting various trypanosome diseases of
man and animals. They are characterized in Chapter XII and are also
discussed in connection with the diseases which they convey.

_Chrysomyia macellaria_, (= _Compsomyia_), the "screw worm"-fly is one
of the most important species of flies directly affecting man, in North
America. It is not normally parasitic, however, and hence will be
considered with other facultative parasites in Chapter IV.

[Illustration: 85. Larva of Auchmeromyia luteola. After Graham-Smith.]

[Illustration: 86. Auchmeromyia luteola (×4). After Graham-Smith.]

_Auchmeromyia luteola_, the Congo floor maggot. This is a muscid of
grewsome habits, which has a wide distribution throughout Africa. The
fly (fig. 86) deposits its eggs on the ground of the huts of the
natives. The whitish larvæ (fig. 85) on hatching are slightly flattened
ventrally, and each segment bears posteriorly three foot-pads
transversely arranged. At night the larvæ find their way into the low
beds or couches of the natives and suck their blood. The adult flies do
not bite man and, as far as known, the larvæ do not play any rôle in the
transmission of sleeping sickness or other diseases.

This habit of blood-sucking by muscid larvæ is usually referred to as
peculiar to _Auchmeromyia luteola_ but it should be noted that the larvæ
of _Protocalliphora_ frequent the nests of birds and feed upon the
young. Mr. A. F. Coutant has studied especially the life-history and
habits of _P. azurea_, whose larvæ he found attacking young crows at
Ithaca, N.Y. He was unable to induce the larvæ to feed on man.

[Illustration: 87. Cordylobia anthropophaga (×3). After Fülleborn.]

[Illustration: 88. Larva of Cordylobia anthropophaga. After Blanchard.]

_Cordylobia anthropophaga_, (_Ochromyia anthropophaga_), or Tumbu-fly
(fig. 87) is an African species whose larvæ affect man much as do those
of _Dermatobia cyniventris_, of Central and South America. The larva
(fig. 88), which is known as "ver du Cayor" because it was first
observed in Cayor, in Senegambia, develops in the skin of man and of
various animals, such as dogs, cats, and monkeys. It is about 12 mm. in
length, and of the form of the larvæ of other muscids. Upon the
intermediate segments are minute, brownish recurved spines which give to
the larva its characteristic appearance. The life-history is not
satisfactorily worked out, but Fuller (1914), after reviewing the
evidence believes that, as a rule, it deposits its young in the sleeping
places of man and animals, whether such be a bed, a board, the floor, or
the bare ground. In the case of babies, the maggots may be deposited on
the scalp. The minute maggots bore their way painlessly into the skin.
As many as forty parasites have been found in one individual and one
author has reported finding more than three hundred in a spaniel puppy.
Though their attacks are at times extremely painful, it is seldom that
any serious results follow.


THE SIPHONAPTERA OR FLEAS

The SIPHONAPTERA, or fleas (fig. 89) are wingless insects, with highly
chitinized and laterally compressed bodies. The mouth-parts are formed
for piercing and sucking. Compound eyes are lacking but some species
possess ocelli. The metamorphosis is complete.

This group of parasites, concerning which little was known until
recently, has assumed a very great importance since it was learned that
fleas are the carriers of bubonic plague. Now over four hundred species
are known. Of these, several species commonly attack man. The most
common hominoxious species are _Pulex irritans_, _Xenopsylla cheopis_,
_Ctenocephalus canis_, _Ctenocephalus felis_, _Ceratophyllus fasciatus_
and _Dermatophilus penetrans_, but many others will feed readily on
human blood if occasion arises.

[Illustration: 89. Xenopsylla cheopis, male (×25). After Jordan and
Rothschild.]

We shall treat in this place of the general biology and habits of the
hominoxious forms and reserve for the systematic section the discussion
of the characteristics of the different genera.

The most common fleas infesting houses in the Eastern United States are
the cosmopolitan dog and cat fleas, _Ctenocephalus canis_ (fig. 90) and
_C. felis_. Their life cycles will serve as typical. These two species
have until recently been considered as one, under the name _Pulex
serraticeps_. See figure 92.

[Illustration: 90. Dog flea (×15). After Howard.]

The eggs are oval, slightly translucent or pearly white, and measure
about .5 mm. in their long diameter. They are deposited loosely in the
hairs of the host and readily drop off as the animal moves around.
Howard found that these eggs hatch in one to two days. The larvæ are
elongate, legless, white, worm-like creatures. They are exceedingly
active, and avoid the light in every way possible. They cast their first
skin in from three to seven days and their second in from three to four
days. They commenced spinning in from seven to fourteen days after
hatching and the imago appeared five days later. Thus in summer, at
Washington, the entire life cycle may be completed in about two weeks.
(cf. fig. 91, 92).

Strickland's (1914) studies on the biology of the rat flea,
_Ceratophyllus fasciatus_, have so important a general bearing that we
shall cite them in considerable detail.

[Illustration: 91. Larva of Xenopsylla cheopis. After Bacot and
Ridewood.]

He found, to begin with, that there is a marked inherent range in the
rate of development. Thus, of a batch of seventy-three eggs, all laid in
the same day and kept together under the same conditions, one hatched in
ten days; four in eleven days; twenty-five in twelve days; thirty-one in
thirteen days; ten in fourteen days; one in fifteen days; and one in
sixteen days. Within these limits the duration of the egg period seems
to depend mainly on the degree of humidity. The incubation period is
never abnormally prolonged as in the case of lice, (Warburton) and
varying conditions of temperature and humidity have practically no
effect on the percentage of eggs which ultimately hatch.

The same investigator found that the most favorable condition for the
larva is a low temperature, combined with a high degree of humidity; and
that the presence of rubbish in which the larva may bury itself is
essential to its successful development. When larvæ are placed in a
bottle containing either wood-wool soiled by excrement, or with feathers
or filter paper covered with dried blood they will thrive readily and
pupate. They seem to have no choice between dried blood and powdered rat
feces for food, and also feed readily on flea excrement. They possess
the curious habit of always devouring their molted skins.

[Illustration: 92. Head and pronotum of (_a_) dog flea; (_b_) of cat
flea; (_c_) of hen flea. After Rothschild. (_d_) Nycteridiphilus
(Ischnopsyllus) hexactenus. After Oudemans.]

An important part of Strickland's experiments dealt with the question of
duration of the pupal stage under the influence of temperature and with
the longevity and habits of the adult. In October, he placed a batch of
freshly formed cocoons in a small dish that was kept near a white rat in
a deep glass jar in the laboratory. Two months later one small and
feeble flea had emerged, but no more until February, four months after
the beginning of the experiment. Eight cocoons were then dissected and
seven more found to contain the imago fully formed but in a resting
state. The remainder of the batch was then placed at 70° F. for one
night, near a white rat. The next day all the cocoons were empty and the
fleas were found on the white rat.

Thus, temperature greatly influences the duration of the pupal period,
which in _Ceratophyllus fasciatus_ averages seventeen days. Moreover,
when metamorphosis is complete a low temperature will cause the imago to
remain within the cocoon.

Sexually mature and ovipositing fleas, he fed at intervals and kept
alive for two months, when the experiment was discontinued. In the
presence of rubbish in which they could bury themselves, unfed rat fleas
were kept alive for many months, whereas in the absence of any such
substratum they rarely lived a month. In the former case, it was found
that the length of life is influenced to some degree by the temperature
and humidity. In an experiment carried out at 70° F. and 45 per cent
humidity, the fleas did not live for more than four months, while in an
experiment at 60° F. and 70 per cent humidity they lived for at least
seventeen months. There was no indication that fleas kept under these
conditions sucked moisture from surrounding objects, and those kept in
bell jars, with an extract of flea-rubbish on filter paper, did not live
any longer than those which were not so supplied.

Curiously enough, although the rat is the normal host of _Ceratophyllus
fasciatus_, it was found that when given the choice these fleas would
feed upon man in preference to rats. However, none of the fleas laid
eggs unless they fed on rat blood.

The experiments of Strickland on copulation and oviposition in the rat
flea showed that fleas do not copulate until they are sexually mature
and that, at least in the case of _Ceratophyllus fasciatus_, the
reproductive organs are imperfectly developed for some time (more than a
week) after emerging from the pupa. When mature, copulation takes place
soon after the fleas have fed on their true host--the rat--but not if
they have fed on a facultative host only, such as man. Copulation is
always followed by oviposition within a very short time.

The effect of the rat's blood on the female with regard to egg-laying,
Strickland concludes, is stimulating rather than nutritive, as fleas
that were without food for many months were observed to lay eggs
immediately after one feed. Similarly, the male requires the stimulus of
a meal of rat's blood before it displays any copulatory activity.

Mitzmain (1910) has described in detail the act of biting on man, as
observed in the squirrel flea, _Ceratophyllus acutus_. "The flea when
permitted to walk freely on the arm selects a suitable hairy space where
it ceases abruptly in its locomotion, takes a firm hold with the tarsi,
projects its proboscis, and prepares to puncture the skin. A puncture is
drilled by the pricking epipharynx, the saw-tooth mandibles
supplementing the movement by lacerating the cavity formed. The two
organs of the rostrum work alternately, the middle piece boring, while
the two lateral elements execute a sawing movement. The mandibles, owing
to their basal attachments, are, as is expressed by the advisory
committee on plague investigations in India (_Journal of Hygiene_, vol.
6, No. 4, p. 499), 'capable of independent action, sliding up and down
but maintaining their relative positions and preserving the lumen of the
aspiratory channel.' The labium doubles back, the V-shaped groove of
this organ guiding the mandibles on either side."

"The action of the proboscis is executed with a forward movement of the
head and a lateral and downward thrust of the entire body. As the
mouth-parts are sharply inserted, the abdomen rises simultaneously. The
hind and middle legs are elevated, resembling oars. The forelegs are
doubled under the thorax, the tibia and tarsi resting firmly on the
epidermis serve as a support for the body during the feeding. The
maxillary palpi are retracted beneath the head and thorax. The labium
continues to bend, at first acting as a sheath for the sawing mandibles,
and as these are more deeply inserted, it bends beneath the head with
the elasticity of a bow, forcing the mandibles into the wound until the
maxillæ are embedded in the skin of the victim. When the proboscis is
fully inserted, the abdomen ceases for a time its lateral swinging."

"The acute pain of biting is first felt when the mandibles have not
quite penetrated and subsequently during each distinct movement of the
abdomen. The swinging of the abdomen gradually ceases as it becomes
filled with blood. The sting of the biting gradually becomes duller and
less sensitive as feeding progresses. The movements of the elevated
abdomen grow noticeably feebler as the downward thrusts of the springy
bow-like labium becomes less frequent."

"As the feeding process advances one can discern through the translucent
walls of the abdomen a constant flow of blood, caudally from the
pharynx, accompanied by a peristaltic movement. The end of the meal is
signified in an abrupt manner. The flea shakes its entire body, and
gradually withdraws its proboscis by lowering the abdomen and legs and
violently twisting the head."

"When starved for several days the feeding of the rat fleas is conducted
in a rather vigorous manner. As soon as the proboscis is buried to the
full length the abdomen is raised and there ensues a gradual lateral
swaying motion, increasing the altitude of the raised end of the abdomen
until it assumes the perpendicular. The flea is observed at this point
to gain a better foothold by advancing the fore tarsi, and then,
gradually doubling back the abdomen, it turns with extreme agility,
nearly touching with its dorsal side the skin of the hand upon which it
is feeding. Meanwhile, the hungry parasite feeds ravenously."

"It is interesting to note the peculiar nervous action which the rodent
fleas exhibit immediately when the feeding process is completed or when
disturbed during the biting. Even while the rostrum is inserted to the
fullest the parasite shakes its head spasmodically; in a twinkling the
mouth is withdrawn and then the flea hops away."

A habit of fleas which we shall see is of significance in considering
their agency in the spread of bubonic plague, is that of ejecting blood
from the anus as they feed.

Fleas are famous for their jumping powers, and in control measures it is
of importance to determine their ability along this line. It is often
stated that they can jump about four inches, or, according to the Indian
Plague Commission _Xenopsylla cheopis_ cannot hop farther than five
inches. Mitzmain (1910) conducted some careful experiments in which he
found that the human flea, _Pulex irritans_, was able to jump as far as
thirteen inches on a horizontal plane. The mean average of five
specimens permitted to jump at will was seven and three-tenths inches.
The same species was observed to jump perpendicularly to a height of at
least seven and three-fourths inches. Other species were not able to
equal this record.

The effect of the bite of fleas on man varies considerably according to
the individual susceptibility. According to Patton and Cragg, this was
borne out in a curious manner by the experiments of Chick and Martin.
"In these, eight human hosts were tried; in seven, little or no
irritation was produced, while in one quite severe inflammation was set
up around each bite." Of two individuals, equally accustomed to the
insects, going into an infested room, one may be literally tormented by
them while the other will not notice them. Indeed it is not altogether
a question of susceptibility, for fleas seem to have a special
predilection for certain individuals. The typical itching wheals
produced by the bites are sometimes followed, especially after
scratching, by inflammatory papules.

The itching can be relieved by the use of lotions of carbolic acid (2-3
per cent), camphor, menthol lotion, or carbolated vaseline. If forced to
sleep in an infested room, protection from attacks can be in a large
measure gained by sprinkling pyrethrum, bubach, or California insect
powder between the sheets. The use of camphor, menthol, or oil of
eucalyptus, or oil of pennyroyal is also said to afford protection to a
certain extent.

In the Eastern United States the occurrence of fleas as household pests
is usually due to infested cats and dogs which have the run of the
house. We have seen that the eggs are not attached to the host but drop
to the floor when they are laid. Verrill, cited by Osborn, states that
on one occasion he was able to collect fully a teaspoonful of eggs from
the dress of a lady in whose lap a half-grown kitten had been held for a
short time. Patton and Cragg record seeing the inside of a hat in which
a kitten had spent the night, so covered with flea eggs that it looked
"as if it had been sprinkled with sugar from a sifter." It is no wonder
that houses in which pets live become overrun with the fleas.

One of the first control measures, then, consists in keeping such
animals out of the house or in rigorously keeping them free from fleas.
The latter can best be accomplished by the use of strong tar soap or
Armour's "Flesope," which may be obtained from most druggists. The use
of a three per cent solution of creolin, approximately four teaspoonfuls
to a quart of warm water, has also been recommended. While this is
satisfactory in the case of dogs, it is liable to sicken cats, who will
lick their fur in an effort to dry themselves. Howard recommends
thoroughly rubbing into the fur a quantity of pyrethrum powder. This
partially stupifies the fleas which should be promptly swept up and
burned.

He also recommends providing a rug for the dog or cat to sleep on and
giving this rug a frequent shaking and brushing, afterwards sweeping up
and burning the dust thus removed.

Since the larvæ of fleas are very susceptible to exposure, the use of
bare floors, with few rugs, instead of carpets or matting, is to be
recommended. Thorough sweeping, so as to allow no accumulation of dust
in cracks and crevices will prove efficient. If a house is once
infested it may be necessary to thoroughly scrub the floors with hot
soapsuds, or to spray them with gasoline. If the latter method is
adopted, care must be taken to avoid the possibility of fire.

To clear a house of fleas Skinner recommends the use of flake
naphthalene. In a badly infested house he took one room at a time,
scattering on the floor five pounds of flake naphthalene, and closed it
for twenty-four hours. It proved to be a perfect and effectual remedy
and very inexpensive, as the naphthalene could be swept up and
transferred to other rooms. Dr. Skinner adds, "so far as I am concerned,
the flea question is solved and if I have further trouble I know the
remedy. I intend to keep the dog and cat."

The late Professor Slingerland very effectively used hydrocyanic acid
gas fumigation in exterminating fleas in houses. In one case, where
failure was reported, he found on investigation that the house had
become thoroughly reinfested from pet cats, which had been left
untreated. Fumigation with sulphur is likewise efficient.

The fact that adult fleas are usually to be found on the floor, when not
on their hosts, was ingeniously taken advantage of by Professor S. H.
Gage in ridding an animal room at Cornell University of the pests. He
swathed the legs of a janitor with sticky fly-paper and had him walk
back and forth in the room. Large numbers of the fleas were collected in
this manner.

In some parts of the southern United States hogs are commonly infested
and in turn infest sheds, barns and even houses. Mr. H. E. Vick informs
us that it is a common practice to turn sheep into barn-lots and sheds
in the spring of the year to collect in their wool, the fleas which
abound in these places after the hogs have been turned out.

It is a common belief that adult fleas are attracted to fresh meat and
that advantage of this can be taken in trapping them. Various workers,
notably Mitzman (1910), have shown that there is no basis for such a
belief.


THE TRUE CHIGGERS--The chigoes, or true chiggers, are the most
completely parasitic of any of the fleas. Of the dozen or more known
species, one commonly attacks man. This is _Dermatophilus penetrans_,
more commonly known as _Sarcopsylla penetrans_ or _Pulex penetrans_.

This species occurs in Mexico, the West Indies, Central and South
America. There are no authentic records of its occurrence in the United
States although, as Baker has pointed out, there is no reason why it
should not become established in Florida and Texas. It is usually
believed that Brazil was its original home. Sometime about the middle of
the nineteenth century it was introduced into West Africa and has spread
across that continent.

The males and the immature females of _Dermatophilus penetrans_ (fig.
93) closely resemble those of other fleas. They are very active little
brown insects about 1-1.2 mm. in size, which live in the dust of native
huts and stables, and in dry, sandy soil. In such places they often
occur in enormous numbers and become a veritable plague.

[Illustration: 93. Dermatophilus penetrans. Much enlarged. After
Karsten.]

They attack not only man but various animals. According to Castellani
and Chalmers, "Perhaps the most noted feature is the way in which it
attacks pigs. On the Gold Coast it appeared to be largely kept in
existence by these animals. It is very easily captured in the free state
by taking a little pig with a pale abdomen, and placing it on its back
on the ground on which infected pigs are living. After watching a few
moments, a black speck will appear on the pig's abdomen, and quickly
another and another. These black specks are jiggers which can easily be
transferred to a test tube. On examination they will be found to be
males and females in about equal numbers."

Both the males and females suck blood. That which characterizes this
species as distinguished from other fleas attacking man is that when the
impregnated female attacks she burrows into the skin and there swells
until in a few days she has the size and appearance of a small pea (fig.
94). Where they are abundant, hundreds of the pests may attack a single
individual (fig. 95). Here they lie with the apex of the abdomen
blocking the opening. According to Fülleborn (1908) they do not
penetrate beneath the epidermis. The eggs are not laid in the flesh of
the victim, as is sometimes stated, but are expelled through this
opening. The female then dies, withers and falls away or is expelled by
ulceration. According to Brumpt, she first quits the skin and then,
falling to the ground, deposits her eggs. The subsequent development in
so far as known, is like that of other fleas.

[Illustration: 94. Dermatophilus penetrans, gravid female. After
Moniez.]

[Illustration: 95. Chiggers in the sole of foot of man. Manson's
Tropical Diseases. Permission of Cassell and Co.]

The chigoe usually enters between the toes, the skin about the roots of
the nails, or the soles of the feet, although it may attack other parts
of the body. Mense records the occurrence in folds of the epidermis, as
in the neighborhood of the anus. They give rise to irritation and unless
promptly and aseptically removed there often occurs pus formation and
the development of a more or less serious abscess. Gangrene and even
tetanus may ensue.

Treatment consists in the careful removal of the insect, an operation
more easily accomplished a day or two after its entrance, than at first,
when it is unswollen. The ulcerated point should then be treated with
weak carbolic acid, or tincture of iodine, or dusted thoroughly with an
antiseptic powder.

[Illustration: 96. Echidnophaga gallinacea.]

[Illustration: 97. Echidnophaga gallinacea infesting head of chicken.
After Enderlein.]

Castellani and Chalmers recommend as prophylactic measures, keeping the
house clean and keeping pigs, poultry, and cattle away therefrom. "High
boots should be used, and especial care should be taken not to go to a
ground floor bathroom with bare feet. The feet, especially the toes, and
under the nails, should be carefully examined every morning to see if
any black dots can be discovered, when the jigger should be at once
removed, and in this way suppuration will be prevented. It is
advisable, also, to sprinkle the floors with carbolic lotion, Jeyes'
fluid, or with pyrethrum powder, or with a strong infusion of native
tobacco, as recommended by Law and Castellani."

_Echidnophaga gallinacea_ (fig. 96) is a widely distributed Hectopsyllid
attacking poultry (fig. 97). It occurs in the Southern and Southwestern
United States and has been occasionally reported as attacking man,
especially children. It is less highly specialized than _Dermatophilus
penetrans_, and does not ordinarily cause serious trouble in man.




CHAPTER IV

ACCIDENTAL OR FACULTATIVE PARASITES


In addition to the many species of Arthropods which are normally
parasitic on man and animals, there is a considerable number of those
which may be classed as _accidental_ or _facultative_ parasites.

Accidental or facultative parasites are species which are normally
free-living, but which are able to exist as parasites when accidentally
introduced into the body of man or other animal. A wide range of forms
is included under this grouping.


ACARINA

A considerable number of mites have been reported as accidental or even
normal, endoparasites of man, but the authentic cases are comparatively
few.

In considering such reports it is well to keep in mind von Siebold's
warning that in view of the universal distribution of mites one should
be on his guard. In vessels in which animal and other organic fluids and
moist substances gradually dry out, mites are very abundantly found. If
such vessels are used without very careful preliminary cleaning, for the
reception of evacuations of the sick, or for the reception of parts
removed from the body, such things may be readily contaminated by mites,
which have no other relation whatever to them.

Nevertheless, there is no doubt but that certain mites, normally
free-living, have occurred as accidental parasites of man. Of these the
most commonly met with is _Tyroglyphus siro_, the cheese-mite.

_Tyroglyphus siro_ is a small mite of a whitish color. The male measures
about 500µ long by 250µ wide, the female slightly larger. They live in
cheese of almost any kind, especially such as is a little decayed. "The
individuals gather together in winter in groups or heaps in the hollows
and chinks of the cheese and there remain motionless. As soon as the
temperature rises a little, they gnaw away at the cheese and reduce it
to a powder. The powder is composed of excrement having the appearance
of little grayish microscopic balls; eggs, old and new, cracked and
empty; larvæ, nymphs, and perfect mites, cast skins and fragments of
cheese, to which must be added numerous spores of microscopic
fungi."--Murray.

_Tyroglyphus siro_, and related species, have been found many times in
human feces, under conditions which preclude the explanation that the
contamination occurred outside of the body. They have been supposed to
be the cause of dysentery, or diarrhoea, and it is probable that the
_Acarus dysenteriæ_ of Linnæus, and Latreille, was this species.
However, there is little evidence that the mites cause any noteworthy
symptoms, even when taken into the body in large numbers.

_Histiogaster spermaticus_ (fig. 152) is a Tyroglyphid mite which was
reported by Trouessart (1902) as having been found in a cyst in the
groin, adherent to the testis. When the cyst was punctured, it yielded
about two ounces of opalescent fluid containing spermatozoa and numerous
mites in all stages of development. The evidence indicated that a
fecundated female mite had been introduced into the urethra by means of
an unclean catheter. Though Trouessart reported the case as that of a
Sarcoptid, Banks places the genus _Histiogaster_ with the Tyroglyphidæ.
He states that our species feeds on the oyster-shell bark louse,
possibly only after the latter is dead, and that in England a species
feeds within decaying reeds.

_Nephrophages sanguinarius_ is a peculiarly-shaped, angular mite which
was found by Miyake and Scriba (1893) for eight successive days in the
urine of a Japanese suffering from fibrinuria. Males, .117 mm. long by
.079 mm. wide, females .36 mm. by. 12 mm., and eggs were found both in
the spontaneously emitted urine and in that drawn by means of a
catheter. All the mites found were dead. The describers regarded this
mite as a true endoparasite, but it is more probable that it should be
classed as an accidental parasite.


MYRIAPODA

There are on record a number of cases of myriapods occurring as
accidental parasites of man. The subject has been treated in detail by
Blanchard (1898 and 1902), who discussed forty cases. Since then at
least eight additions have been made to the list.

Neveau-Lamaire (1908) lists thirteen species implicated, representing
eight different genera. Of the _Chilognatha_ there are three, _Julus
terrestris_, _J. londinensis_ and _Polydesmus complanatus_. The
remainder are _Chilopoda_, namely, _Lithobius forficatus_, _L.
malenops_, _Geophilus carpophagus_, _G. electricus_, _G. similis_, _G.
cephalicus_, _Scutigera coleoptrata_, _Himantarium gervaisi_,
_Chætechelyne vesuviana_ and _Stigmatogaster subterraneus_.

The majority of the cases relate to infestation of the nasal fossæ, or
the frontal sinus, but intestinal infestation also occurs and there is
one recorded case of the presence of a species in _Julus_ (fig. 13) in
the auditory canal of a child.

In the nose, the myriapods have been known to live for months and
according to some records, even for years. The symptoms caused by their
presence are inflammation, with or without increased flow of mucus,
itching, more or less intense headache, and at times general symptoms
such as vertigo, delirium, convulsions, and the like. These symptoms
disappear suddenly when the parasites are expelled.

In the intestine of man, myriapods give rise to obscure symptoms
suggestive of infestation by parasitic worms. In a case reported by
Verdun and Bruyant (1912), a child twenty months of age had been
affected for fifteen days by digestive disturbances characterized by
loss of appetite, nausea and vomiting. The latter had been particularly
pronounced for three days, when there was discovered in the midst of the
material expelled a living myriapod of the species _Chætechelyne
vesuviana_. Anthelminthics had been administered without result. In some
of the other cases, the administration of such drugs had resulted in the
expulsion of the parasite through the anus.

One of the extreme cases on record is that reported by Shipley (1914).
Specimens of _Geophilus gorizensis_ (= _G. subterraneus_) "were vomited
and passed by a woman of 68 years of age. Some of the centipedes emerged
through the patient's nose, and it must be mentioned that she was also
suffering from a round worm. One of her doctors was of the opinion that
the centipedes were certainly breeding inside the lady's intestines, and
as many as seven or eight, sometimes more, were daily leaving the
alimentary canal."

"According to her attendant's statements those centipedes had left the
body in some hundreds during a period of twelve or eighteen months.
Their presence produced vomiting and some hæmatemesis, and treatment
with thymol, male-fern and turpentine had no effect in removing the
creatures."

The clinical details, as supplied by Dr. Theodore Thompson were as
follows:

"Examined by me July, 1912, her tongue was dry and glazed. There was
bleeding taking place from the nose and I saw a living centipede she had
just extracted from her nostril. Her heart, lungs and abdomen appeared
normal. She was not very wasted, and did not think she had lost much
flesh, nor was there any marked degree of anemia."

Shipley gives the following reasons for believing it impossible that
these centipedes could have multiplied in the patient's intestine. "The
breeding habits of the genus _Geophilus_ are peculiar, and ill adapted
for reproducing in such a habitat. The male builds a small web or nest,
in which he places his sperm, and the female fertilizes herself from
this nest or web, and when the eggs are fertilized they are again laid
in a nest or web in which they incubate and in two or three weeks hatch
out. The young _Geophilus_ differ but very little from the adult, except
in size. It is just possible, but improbable, that a clutch of eggs had
been swallowed by the host when eating some vegetables or fruit, but
against this is the fact that the _Geophilus_ does not lay its eggs upon
vegetables or fruit, but upon dry wood or earth. The egg-shell is very
tough and if the eggs had been swallowed the egg-shells could certainly
have been detected if the dejecta were examined. The specimens of the
centipede showed very little signs of being digested, and it is almost
impossible to reconcile the story of the patient with what one knows of
the habits of the centipedes."

In none of the observed cases have there been any clear indications as
to the manner of infestation. It is possible that the myriapods have
been taken up in uncooked fruit or vegetables.


LEPIDOPTEROUS LARVÆ

SCHOLECIASIS--Hope (1837) brought together six records of infestation of
man by lepidopterous larvæ and proposed to apply the name scholeciasis
to this type of parasitism. The clearest case was that of a young boy
who had repeatedly eaten raw cabbage and who vomited larvæ of the
cabbage butterfly, _Pieris brassicæ_. Such cases are extremely rare, and
there are few reliable data relative to the subject. In this connection
it may be noted that Spuler (1906) has described a moth whose larvæ live
as ectoparasites of the sloth.


COLEOPTERA

CANTHARIASIS--By this term Hope designated instances of accidental
parasitism by the larvæ or adults of beetles. Reports of such cases are
usually scouted by parasitologists but there seems no good basis for
wholly rejecting them. Cobbold refers to a half dozen cases of
accidental parasitism by the larvæ of _Blaps mortisaga_. In one of
these cases upwards of 1200 larvæ and several perfect insects were said
to have been passed _per annum_. French (1905) reports the case of a man
who for a considerable period voided adult living beetles of the species
_Nitidula bipustulata_. Most of the other cases on record relate to the
larvæ of _Dermestidæ_ (larder beetles _et al._) or _Tenebrionidæ_ (meal
infesting species). Infestation probably occurs through eating raw or
imperfectly cooked foods containing eggs or minute larvæ of these
insects.

[Illustration: 98. Larva of Piophila casei. Caudal aspect of larva.
Posterior stigmata.]

Brumpt cites a curious case of accidental parasitism by a coleopterous
larva belonging to the genus _Necrobia_. This larva was extracted from a
small tumor, several millimeters long, on the surface of the conjunctiva
of the eye. The larvæ of this genus ordinarily live in decomposing flesh
and cadavers.


DIPTEROUS LARVÆ

[Illustration: 99. Piophila casei. After Graham-Smith.]

MYASIS--By this term (spelled also myiasis, and myiosis), is meant
parasitism by dipterous larvæ. Such parasitism may be normal, as in the
cases already described under the heading parasitic Diptera, or it may
be facultative, due to free-living larvæ being accidentally introduced
into wounds or the body-cavities of man. Of this latter type, there is a
multitude of cases on record, relating to comparatively few species. The
literature of the subject, like that relating to facultative parasitism
in general, is unsatisfactory, for most of the determinations of species
have been very loose. Indeed, so little has been known regarding the
characteristics of the larvæ concerned that in many instances they could
not be exactly determined. Fortunately, several workers have undertaken
comparative studies along this line. The most comprehensive publication
is that of Banks (1912), entitled "The structure of certain dipterous
larvæ, with particular reference to those in human food."

Without attempting an exhaustive list, we shall discuss here the more
important species of Diptera whose larvæ are known to cause myasis,
either external or internal. The following key will serve to determine
those most likely to be encountered. The writers would be glad to
examine specimens not readily identifiable, if accompanied by exact data
relative to occurrence.

_a._ Body more or less flattened, depressed; broadest in the middle,
    each segment with dorsal, lateral, and ventral fleshy processes, of
    which the laterals, at least, are more or less spiniferous (fig.
    101). _Fannia_ (= _Homalomyia_).

  In _F. canicularis_ the dorsal processes are nearly as long as the
      laterals; in _F. scalaris_ the dorsal processes are short spinose
      tubercles.

_aa._ Body cylindrical, or slender conical tapering toward the head;
    without fleshy lateral processes (fig. 105).

_b._ With the posterior stigmata at the end of shorter or longer
    tubercles, or if not placed upon tubercles, then not in pit; usually
    without a "marginal button" and without a chitinous ring surrounding
    the three slits; the slits narrowly or broadly oval, not bent (fig.
    171 i). _Acalyptrate muscidæ_ and some species of _Anthomyiidæ_. To
    this group belong the cheese skipper (_Piophila casei_, figs. 98,
    99), the pomace-fly (_Drosophila ampelophila_), the apple maggot
    (_Rhagoletis pomonella_), the cherry fruit fly (_Rhagoletis
    cingulata_), the small dung fly (_Sepsis violacea_, fig. 170), the
    beet leaf-miner (_Pegomyia vicina_, fig. 171 i), the cabbage, bean
    and onion maggots (_Phorbia_ spp.) et. al.

_bb._ Posterior stigmata of various forms, if the slits are narrowly
    oval (fig. 171) then they are surrounded by a chitin ring which may
    be open ventro-mesally.

_c._ Integument leathery and usually strongly spinulose; larvæ
    hypodermatic or endoparasitic. Bot flies (fig. 171, f, g,
    k).--_Oestridæ_

_cc._ Integument not leathery and (except in _Protocalliphora_) spinulæ
    restricted to transverse patches near the incisures of the segments.

_d._ The stigmal plates in a pit; the lip-like margin of the pit with a
    number of fleshy tubercles; chitin ring of the stigma not complete;
    open ventro-mesally, button absent (fig. 171 e). Flesh
    flies.--_Sarcophaga_

_dd._ Stigmata not in a pit.

_e._ The chitin ring open ventra-mesally; button absent (fig. 171 c).
    Screw-worm fly. _Chrysomyia_

_ee._ The chitin ring closed.

_f._ Slits of the posterior stigmata straight; marginal "button" present
    (fig. 171 b); two distinct mouth hooks, fleshy tubercles around the
    anal area. _Phormia_ (fig. 171 f), _Lucilia_ and _Calliphora_ (fig.
    172, a, b), _Protocalliphora_ (fig. 171, j), _Cynomyia_ (fig. 171,
    a). Blow flies, bluebottle flies. _Calliphorinæ_

_ff._ Slits of the posterior stigmata sinuous or bent. Subfamily
    Muscinæ.

_g._ Slits of the posterior stigmata bent; usually two mouth hooks.
    _Muscina stabulans_ (fig. 171, l), _Muscina similis_, _Myiospila
    meditabunda_ (fig. 172, i), and some of the higher _Anthomyiidæ_.

_gg._ Slits of the posterior stigmata sinuous; mouth hooks usually
    consolidated into one. The house-fly (_Musca domestica_ fig. 171,
    d), the stable fly (_Stomoxys calcitrans_), the horn fly (_Lyperosia
    irritans_), _Pyrellia_, _Pseudopyrellia_, _Morellia_, _Mesembrina_.
    _Polietes_, et. al. (fig. 172 in part).

_Eristalis_--The larvæ of _Eristalis_ are the so-called rat-tailed
maggots, which develop in foul water. In a few instances these larvæ
have been known to pass through the human alimentary canal uninjured.
Hall and Muir (1913) report the case of a boy five years of age, who had
been ailing for ten weeks and who was under treatment for indigestion
and chronic constipation. For some time he had vomited everything he
ate. On administration of a vermifuge he voided one of the rat-tailed
maggots of _Eristalis_. He admitted having drunk water from a ditch full
of all manner of rotting matter. It was doubtless through this that he
became infested. It is worth noting that the above described symptoms
may have been due to other organisms or substances in the filthy water.

_Piophila casei_, the cheese-fly (fig. 99), deposits its eggs not only
in old cheeses, but on ham, bacon, and other fats. The larvæ (fig. 98)
are the well-known cheese skippers, which sometimes occur in great
abundance on certain kinds of cheese. Indeed, some people have a
comfortable theory that such infested cheese is especially good. Such
being the case, it is small wonder that this species has been repeatedly
reported as causing intestinal myasis. Thebault (1901) describes the
case of a girl who, shortly after consuming a large piece of badly
infested cheese, became ill and experienced severe pains in the region
of the navel. Later these extended through the entire alimentary canal,
the excrement was mixed with blood and she suffered from vertigo and
severe headaches. During the four following days the girl felt no
change, although the excretion of the blood gradually diminished and
stopped. On the fourth day she voided two half-digested larvæ and,
later, seven or eight, of which two were alive and moving.

That these symptoms may be directly attributed to the larvæ, or
"skippers," has been abundantly shown by experimental evidence.
Portschinsky cites the case of a dog fed on cheese containing the larvæ.
The animal suffered much pain and its excrement contained blood. On
_post mortem_ it was found that the small intestine throughout almost
its entire length was marked by bloody bruises. The papillæ on these
places were destroyed, although the walls were not entirely perforated.
In the appendix were found two or three dead larvæ. Alessandri (1910)
has likewise shown that the larvæ cause intestinal lesions.

According to Graham-Smith, Austen (1912) has recorded a case of myasis
of the nose, attended with a profuse watery discharge of several weeks
duration and pain, due to the larvæ of _Piophila casei_.


ANTHYOMYIIDÆ--The characteristic larvæ of two species of _Fannia_ (=
_Homalomyia_ or _Anthomyia_, in part) (fig. 101) are the most commonly
reported of dipterous larvæ causing intestinal myasis. Hewitt (1912) has
presented a valuable study of the bionomics and of the larvæ of these
flies, a type of what is needed for all the species concerned in myasis.
We have seen two cases of their having been passed in stools, without
having caused any special symptoms. In other instances their presence in
the alimentary canal has given rise to symptoms vaguely described as
those of tapeworm infestation, or helminthiasis. More specifically, they
have been described as causing vertigo, severe headache, nausea and
vomiting, severe abdominal pains, and in some instances, bloody
diarrhoea.

[Illustration: 100. Fannia canicularis (×4). After Graham-Smith.]

One of the most striking cases is that reported by Blankmeyer (1914), of
a woman whose illness began fourteen years previously with nausea and
vomiting. After several months of illness she began passing larvæ and
was compelled to resort to enemas. Three years previous to the report,
she noticed frequent shooting pains in the rectal region and at times
abdominal tenderness was marked. There was much mucus in the stools and
she "experienced the sensation of larvæ crawling in the intestine."
Occipital headaches were marked, with remissions, and constipation
became chronic. The appetite was variable, there was a bad taste in the
mouth, tongue furred and ridged, and red at the edges. Her complexion
was sallow, and general nervousness was marked. As treatment, there were
given doses of magnesium sulphate before breakfast and at 4 P. M., with
five grain doses of salol four times a day. The customary parasiticides
yielded no marked benefit. At the time of the report the patient passed
from four to fifty larvæ per day, and was showing some signs of
improvement. The nausea had disappeared, her nervousness was less
evident, and there was a slight gain in weight.

The case was complicated by various other disorders, but the symptoms
given above seem to be in large part attributable to the myasis. There
is nothing in the case to justify the assumption that larvæ were
continuously present, for years. It seems more reasonable to suppose
that something in the habits of the patient favored repeated
infestation. Nevertheless, a study of the various cases of intestinal
myasis caused by these and other species of dipterous larvæ seems to
indicate that the normal life cycle may be considerably prolonged under
the unusual conditions.

The best authenticated cases of myasis of the urinary passage have been
due to larvæ of _Fannia_. Chevril (1909) collected and described twenty
cases, of which seven seemed beyond doubt. One of these was that of a
woman of fifty-five who suffered from albuminuria, and urinated with
much difficulty, and finally passed thirty to forty larvæ of _Fannia
canicularis_.

It is probable that infestation usually occurs through eating partially
decayed fruit or vegetables on which the flies have deposited their
eggs. Wellman points out that the flies may deposit their eggs in or
about the anus of persons using outside privies and Hewitt believes that
this latter method of infection is probably the common one in the case
of infants belonging to careless mothers. "Such infants are sometimes
left about in an exposed and not very clean condition, in consequence of
which flies are readily attracted to them and deposit their eggs."

[Illustration: 101. Larva of Fannia scalaris.]


MUSCINÆ--The larvæ of the common house-fly, _Musca domestica_, are
occasionally recorded as having been passed with the feces or vomit of
man. While such cases may occur, it is probable that in most instances
similar appearing larvæ of other insects have been mistakenly
identified.

_Muscina stabulans_ is regarded by Portschinsky (1913) as responsible
for many of the cases of intestinal myasis attributed to other species.
He records the case of a peasant who suffered from pains in the lower
part of the breast and intestines, and whose stools were mixed with
blood. From November until March he had felt particularly ill, being
troubled with nausea and vomiting in addition to the pain in his
intestines. In March, his physician prescribed injections of a
concentrated solution of tannin, which resulted in the expulsion of
fifty living larvæ of _Muscina stabulans_. Thereafter the patient felt
much better, although he suffered from intestinal catarrh in a less
severe form.

[Illustration: 102 Muscina stabulans (×4). After Graham-Smith.]


CALLIPHORINÆ--Closely related to the Sarcophagidæ are the
_Calliphorinæ_, to which group belong many of the so-called "blue
bottle" flies. Their larvæ feed upon dead animals, and upon fresh and
cooked meat. Those of _Protocalliphora_, already mentioned, are
ectoparasitic on living nestling birds. Larva of _Lucilia_, we have
taken from tumors on living turtles. To this sub-family belongs also
_Aucheromyia luteola_, the Congo floor maggot. Some of these, and at
least the last mentioned, are confirmed, rather than faculative
parasites. Various species of Calliphorinæ are occasionally met with as
facultative parasites of man.

[Illustration: 103. Lucilia cæsar, (×3). After Howard.]

_Chrysomyia macellaria_, the screw worm fly (fig. 107), is the fly which
is responsible for the most serious cases of human myasis in the United
States. It is widely distributed in the United States but is especially
abundant in the south. While the larvæ breed in decaying matter in
general, they so commonly breed in the living flesh of animals that they
merit rank as true parasites. The females are attracted to open wounds
of all kinds on cattle and other animals and quickly deposit large
numbers of eggs. Animals which have been recently castrated, dehorned,
or branded, injured by barbed wire, or even by the attacks of ticks are
promptly attacked in the regions where the fly abounds. Even the navel
of young calves or discharges from the vulva of cows may attract the
insect.

[Illustration: 104. Calliphora erythrocephala, (×6). After
Graham-Smith.]

Not infrequently the fly attacks man, being attracted by an offensive
breath, a chronic catarrh, or a purulent discharge from the ears. Most
common are the cases where the eggs are deposited in the nostrils. The
larvæ, which are hatched in a day or two, are provided with strong
spines and proceed to bore into the tissues of the nose, even down into
or through the bone, into the frontal sinus, the pharynx, larynx, and
neighboring parts.

Osborn (1896) quotes a number of detailed accounts of the attacks of the
_Chrysomyia_ on man. A vivid picture of the symptomology of rhinal
myasis caused by the larvæ of this fly is given by Castellani and
Chalmers: "Some couple of days after a person suffering from a chronic
catarrh, foul breath, or ozæna, has slept in the open or has been
attacked by a fly when riding or driving,--_i.e._, when the hands are
engaged--signs of severe catarrh appear, accompanied with inordinate
sneezing and severe pain over the root of the nose or the frontal bone.
Quickly the nose becomes swollen, and later the face also may swell,
while examination of the nose may show the presence of the larvæ. Left
untreated, the patient rapidly becomes worse, and pus and blood are
discharged from the nose, from which an offensive odor issues. Cough
appears as well as fever, and often some delirium. If the patient lives
long enough, the septum of the nose may fall in, the soft and hard
palates may be pierced, the wall of the pharynx may be destroyed. By
this time, however, the course of the disease will have become quite
evident by the larvæ dropping out of the nose, and if the patient
continues to live all the larvæ may come away naturally."

For treatment of rhinal myasis these writers recommend douching the nose
with chloroform water or a solution of chloroform in sweet milk (10-20
per cent), followed by douches of mild antiseptics. Surgical treatment
may be necessary.

[Illustration: 105. Larva of a flesh fly (Sarcophaga). Caudal aspect.
Anterior stigmata. Pharyngeal skeleton.]


SARCOPHAGIDÆ--The larvæ (fig. 105) of flies of this family usually feed
upon meats, but have been found in cheese, oleomargerine, pickled
herring, dead and living insects, cow dung and human feces. Certain
species are parasitic in insects. Higgins (1890) reported an instance of
"hundreds" of larvæ of _Sarcophaga_ being vomited by a child eighteen
months of age. There was no doubt as to their origin for they were
voided while the physician was in the room. There are many other reports
of their occurrence in the alimentary canal. We have recorded elsewhere
(Riley, 1906) a case in which some ten or twelve larvæ of _Sarcophaga_
were found feeding on the diseased tissues of a malignant tumor. The
tumor, a melanotic sarcoma, was about the size of a small walnut, and
located in the small of the back of an elderly lady. Although they had
irritated and caused a slight hæmorrhage, neither the patient nor others
of the family knew of their presence. Any discomfort which they had
caused had been attributed to the sarcomatous growth. The infestation
occurred in mid-summer. It is probable that the adult was attracted by
the odor of the discharges and deposited the living maggots upon the
diseased tissues.

[Illustration: 106. A flesh fly (Sarcophaga), (×4). After Graham-Smith.]

According to Küchenmeister, _Sarcophaga carnaria_ (fig. 106), attracted
by the odor, deposits its eggs and larvæ in the vagina of girls and
women when they lie naked in hot summer days upon dirty clothes, or when
they have a discharge from the vagina. In malignant inflammations of the
eyes the larvæ even nestle under the eyelids and in Egypt, for example,
produce a very serious addition to the effects of small-pox upon the
cornea, as according to Pruner, in such cases perforation of the cornea
usually takes place.

[Illustration: 107. Chrysomyia macellaria, (×3).]

_Wohlfartia magnifica_ is another Sarcophagid which commonly infests man
in the regions where it is abundant. It is found in all Europe but is
especially common in Russia, where Portschinsky has devoted much
attention to its ravages. It deposits living larvæ in wounds, the nasal
fossæ, the ears and the eyes, causing injuries even more revolting than
those described for _Chrysomyia_.




CHAPTER V

ARTHROPODS AS SIMPLE CARRIERS OF DISEASE


The fact that certain arthropods are poisonous, or may affect the health
of man as direct parasites has always received attention in the medical
literature. We come now to the more modern aspect of our subject,--the
consideration of insects and other arthropods as transmitters and
disseminators of disease.

The simplest way in which arthropods may function in this capacity is as
_simple carriers_ of pathogenic organisms. It is conceivable that any
insect which has access to, and comes in contact with such organisms and
then passes to the food, or drink, or to the body of man, may in a
wholly accidental and incidental manner convey infection. That this
occurs is abundantly proved by the work of recent years. We shall
consider as typical the case against the house-fly, which has attracted
so much attention, both popular and scientific. The excellent general
treatises of Hewitt (1910), Howard (1911), and Graham-Smith (1913), and
the flood of bulletins and popular literature render it unnecessary to
consider the topic in any great detail.


THE HOUSE-FLY AS A CARRIER OF DISEASE

Up to the past decade the house-fly has usually been regarded as a mere
pest. Repeatedly, however, it had been suggested that it might
disseminate disease. We have seen that as far back as the sixteenth
century, Mercurialis suggested that it was the agent in the spread of
bubonic plague, and in 1658, Kircher reiterated this view. In 1871,
Leidy expressed the opinion that flies were probably a means of
communicating contagious diseases to a greater degree than was generally
suspected. From what he had observed regarding gangrene in hospitals, he
thought flies should be carefully excluded from wounds. In the same
year, the editor of the _London Lancet_, referring to the belief that
they play a useful rôle in purifying the air said, "Far from looking
upon them as dipterous angels dancing attendance on Hygeia, regard them
rather in the light of winged sponges spreading hither and thither to
carry out the foul behests of Contagion."

These suggestions attracted little attention from medical men, for it is
only within very recent years that the charges have been supported by
direct evidence. Before considering this evidence, it is necessary that
we define what is meant by "house-fly" and that we then consider the
life-history of the insect.

There are many flies which are occasionally to be found in houses, but
according to various counts, from 95 per cent to 99 per cent of these in
warm weather in the Eastern United States belong to the one species
_Musca domestica_ (fig. 108). This is the dominant house-fly the world
over and is the one which merits the name. It has been well
characterized by Schiner (1864), whose description has been freely
translated by Hewitt, as follows:

"Frons of male occupying a fourth part of the breadth of the head.
Frontal stripe of female narrow in front, so broad behind that it
entirely fills up the width of the frons. The dorsal region of the
thorax dusty grey in color with four equally broad longitudinal stripes.
Scutellum gray with black sides. The light regions of the abdomen
yellowish, transparent, the darkest parts at least at the base of the
ventral side yellow. The last segment and a dorsal line blackish brown.
Seen from behind and against the light, the whole abdomen shimmering
yellow, and only on each side of the dorsal line on each segment a dull
transverse band. The lower part of the face silky yellow, shot with
blackish brown. Median stripe velvety black. Antennæ brown. Palpi black.
Legs blackish brown. Wings tinged with pale gray with yellowish base.
The female has a broad velvety back, often reddishly shimmering frontal
stripe, which is not broader at the anterior end than at the bases of
the antennæ, but become so very much broader above that the light
dustiness of the sides is entirely obliterated. The abdomen gradually
becoming darker. The shimmering areas on the separate segments generally
brownish. All the other parts are the same as in the male."

The other species of flies found in houses in the Eastern United States
which are frequently mistaken for the house or typhoid fly may readily
be distinguished by the characters of the following key:

_a._ Apical cell (R_5) of the wide wing open, i.e., the bounding veins
    parallel or divergent (fig. 100). Their larvæ are flattened, the
    intermediate body segments each fringed with fleshy, more or less
    spinose, processes. _Fannia_

  b. Male with the sides of the second and third abdominal segments
      translucent yellowish. The larva with three pairs of nearly equal
      spiniferous appendages on each segment, arranged in a
      longitudinal series and in addition two pairs of series of smaller
      processes (fig. 100) _F. canicularis_

  bb. Male with blackish abdomen, middle tibia with a tubercle beyond
      the middle. The larva with spiniferous appendages of which the
      dorsal and ventral series are short, the lateral series long and
      feathered (fig. 101) _F. scalaris_

aa. Apical cell (R) of the wing more or less narrowed in the margin; i.
    e., the bounding veins more or less converging (fig. 108).

  b. The mouth-parts produced and pointed, fitted for piercing.

    c. Palpi much shorter than the proboscis; a brownish gray fly, its
        thorax with three rather broad whitish stripes; on each border
        of the middle stripe and on the mesal borders of the lateral
        stripes is a blackish brown line. Abdomen yellowish brown; on
        the second, third and fourth segments are three brown spots
        which may be faint or even absent. The larvæ live in dung. The
        stable-fly (fig. 110) _Stomoxys calcitrans_

    cc. Palpi nearly as long as the proboscis. Smaller species than the
        house-fly. The horn-fly (fig. 167) _Hæmatobia irritans_

  bb. Mouth-parts blunt, fitted for lapping.

    c. Thorax, particularly on the sides and near the base of the wings
        with soft golden yellow hairs among the bristles. This fly is
        often found in the house in very early spring or even in the
        winter. The cluster-fly, _Pollenia rudis_

    cc. Thorax without golden yellow hairs among the bristles.

      d. The last segment of the vein M with an abrupt angle. (fig.
          108). The larvæ live in manure, etc. House-fly, _Musca
          domestica_

      dd. The last segment of vein M with a broad, gentle curve (fig.
          102).

        e. Eyes microscopically hairy; each abdominal segment with two
            spots. Larvæ in dung. _Myiospila meditabunda_

        ee. Eyes bare; abdomen gray and brown marbled. _Muscina_

          f. With black legs and palpi. _M. assimilis_

          ff. With legs more or less yellowish; palpi yellow. Larvæ in
              decaying vegetable substances, dung, etc. _M. stabulans_

It is almost universally believed that the adults of _Musca domestica_
hibernate, remaining dormant throughout the winter in attics, around
chimneys, and in sheltered but cold situations. This belief has been
challenged by Skinner (1913), who maintains that all the adult flies die
off during the fall and early winter and that the species is carried
over in the pupal stage, and in no other way. The cluster-fly, _Pollenia
rudis_, undoubtedly does hibernate in attics and similar situations and
is often mistaken for the house-fly. In so far as concerns _Musca
domestica_, the important question as to hibernation in the adult stage
is an open one. Many observations by one of the writers (Johannsen) tend
to confirm Dr. Skinner's conclusion, in so far as it applies to
conditions in the latitude of New York State. Opposed, is the fact that
various experimenters, notably Hewitt (1910) and Jepson (1909) wholly
failed to carry pupæ through the winter.

[Illustration: 108. The house or typhoid fly (Musca domestica (×4)).
After Howard.]

The house-fly breeds by preference in horse manure. Indeed, Dr. Howard,
whose extensive studies of the species especially qualify him for
expressing an opinion on the subject, has estimated that under ordinary
city and town conditions, more than ninety per cent of the flies present
in houses have come from horse stables or their vicinity. They are not
limited to such localities, by any means, for it has been found that
they would develop in almost any fermenting organic substance. Thus,
they have been bred from pig, chicken, and cow manure, dirty waste
paper, decaying vegetation, decaying meat, slaughter-house refuse,
sawdust-sweepings, and many other sources. A fact which makes them
especially dangerous as disease-carriers is that they breed readily in
human excrement.

The eggs are pure white, elongate ovoid, somewhat broader at the
anterior end. They measure about one millimeter (1-25 inch) in length.
They are deposited in small, irregular clusters, one hundred and twenty
to one hundred and fifty from a single fly. A female may deposit as many
as four batches in her life time. The eggs hatch in from eight to
twenty-four hours.

The newly hatched larva, or maggot (fig. 108), measures about two
millimeters (1-12 inch) in length. It is pointed at the head end and
blunt at the opposite end, where the spiracular openings are borne. It
grows rapidly, molts three times and reaches maturity in from six to
seven days, under favorable conditions.

The pupal stage, like that of related flies, is passed in the old larval
skin which, instead of being molted, becomes contracted and heavily
chitinized, forming the so-called _puparium_ (fig. 108). The pupal stage
may be completed in from three to six days.

Thus during the warm summer months a generation of flies may be produced
in ten to twelve days. Hewitt at Manchester, England, found the minimum
to be eight days but states that larvæ bred in the open air in horse
manure which had an average daily temperature of 22.5° C., occupied
fourteen to twenty days in their development, according to the air
temperature.

After emergence, a period of time must elapse before the fly is capable
of depositing eggs. This period has been tuned the _preoviposition_
period. Unfortunately we have few exact data regarding this period.
Hewitt found that the flies became sexually mature in ten to fourteen
days after their emergence from the pupal state and four days after
copulation they began to deposit their eggs; in other words the
preoviposition stage was fourteen days or longer. Griffith (1908) found
this period to be ten days. Dr. Howard believes that the time "must
surely be shorter, and perhaps much shorter, under midsummer conditions,
and in the freedom of the open air." He emphasizes that the point is of
great practical importance, since it is during this period that the
trapping and other methods of destroying the adult flies, will prove
most useful.

Howard estimates that there may be nine generations of flies a year
under outdoor conditions in places comparable in climate to Washington.
The number may be considerably increased in warmer climates.

The rate at which flies may increase under favorable conditions is
astounding. Various writers have given estimates of the numbers of flies
which may develop as the progeny of a single individual, providing all
the eggs and all the individual flies survived. Thus, Howard estimates
that from a single female, depositing one hundred and twenty eggs on
April 15th, there may be by September 10th, 5,598,720,000,000 adults.
Fortunately, living forms do not produce in any such mathematical manner
and the chief value of the figures is to illustrate the enormous
struggle for existence which is constantly taking place in nature.

Flies may travel for a considerable distance to reach food and shelter,
though normally they pass to dwellings and other sources of food supply
in the immediate neighborhood of their breeding places. Copeman, Howlett
and Merriman (1911) marked flies by shaking them in a bag containing
colored chalk. Such flies were repeatedly recovered at distances of
eight to one thousand yards and even at a distance of seventeen hundred
yards, nearly a mile.

Hindle and Merriman (1914) continued these experiments on a large scale
at Cambridge, England. They "do not think it likely that, as a rule,
flies travel more than a quarter of a mile in thickly-housed areas." In
one case a single fly was recovered at a distance of 770 yards but a
part of this distance was across open fen-land. The surprising fact was
brought out that flies tend to travel either _against_ or across the
wind. The actual direction followed may be determined either directly by
the action of the wind (positive anemotropism), or indirectly owing to
the flies being attracted by any odor that it may convey from a source
of food. They conclude that it is likely that the chief conditions
favoring the disposal of flies are fine weather and a warm temperature.
The nature of the locality is another considerable factor. Hodge (1913)
has shown that when aided by the wind they may fly to much greater
distances over the water. He reports that at Cleveland, Ohio, the cribs
of the water works, situated a mile and a quarter, five miles, and six
miles out in Lake Erie are invaded by a regular plague of flies when the
wind blows from the city. Investigation showed that there was absolutely
nothing of any kind in which flies could breed on the crib.

The omnivorous habits of the house-fly are matters of everyday
observation. From our view point, it is sufficient to emphasize that
from feeding on excrement, on sputum, on open sores, or on putrifying
matter, the flies may pass to the food or milk upon the table or to
healthy mucous membranes, or uncontaminated wounds. There is nothing in
its appearance to tell whether the fly that comes blithely to sup with
you is merely unclean, or whether it has just finished feeding upon
dejecta teeming with typhoid bacilli.

[Illustration: 100. Pulvillus of foot of house-fly, showing glandular
hairs.]

The method of feeding of the house-fly has an important bearing on the
question of its ability to transmit pathogenic organisms. Graham-Smith
(1910) has shown that when feeding, flies frequently moisten soluble
substances with "vomit" which is regurgitated from the crop. This is, of
course, loaded with bacteria from previous food. When not sucked up
again these drops of liquid dry, and produce round marks with an opaque
center and rim and an intervening less opaque area. Fly-specks, then,
consist of both vomit spots and feces. Graham-Smith shows a photograph
of a cupboard window where, on an area six inches square, there were
counted eleven hundred and two vomit marks and nine fecal deposits.

From a bacteriologist's viewpoint a discussion of the possibility of a
fly's carrying bacteria would seem superfluous. Any exposed object,
animate or inanimate, is contaminated by bacteria and will transfer them
if brought into contact with suitable culture media, whether such
substance be food, or drink, open wounds, or the sterile culture media
of the laboratory. A needle point may convey enough germs to produce
disease. Much more readily may the house-fly with its covering of hairs
and its sponge-like pulvilli (fig. 109) pick up and transfer bits of
filth and other contaminated material.

For popular instruction this inevitable transfer of germs by the
house-fly is strikingly demonstrated by the oft copied illustration of
the tracks of a fly on a sterile culture plate. Two plates of gelatine
or, better, agar medium are prepared. Over one of these a fly (with
wings clipped) is allowed to walk, the other is kept as a check. Both
are put aside at room temperature, to be examined after twenty-four to
forty-eight hours. At the end of that time, the check plate is as clear
as ever, the one which the fly has walked is dotted with colonies of
bacteria and fungi. The value in the experiment consists in emphasizing
that by this method we merely render visible what is constantly
occurring in nature.

A comparable experiment which we use in our elementary laboratory work
is to take three samples of _clean_ (preferably, sterile) fresh milk in
sterile bottles. One of them is plugged with a pledget of cotton, into
the second is dropped a fly from the laboratory and into the third is
dropped a fly which has been caught feeding upon garbage or other filth.
After a minute or two the flies are removed and the vials plugged as was
number one. The three are then set aside at room temperature. When
examined after twenty-four hours the milk in the first vial is either
still sweet or has a "clean" sour odor; that of the remaining two is
very different, for it has a putrid odor, which is usually more
pronounced in the case of sample number three.

Several workers have carried out experiments to determine the number of
bacteria carried by flies under natural conditions. One of the most
extended and best known of these is the series by Esten and Mason
(1908). These workers caught flies from various sources in a sterilized
net, placed them in a sterile bottle and poured over them a known
quantity of sterilized water, in which they were shaken so as to wash
the bacteria from their bodies. They found the number of bacteria on a
single fly to range from 550 to 6,600,000. Early in the fly season the
numbers of bacteria on flies are comparatively small, while later the
numbers are comparatively very large. The place where flies live also
determines largely the numbers that they carry. The lowest number, 550,
was from a fly caught in the bacteriological laboratory, the highest
number, 6,600,000 was the average from eighteen swill-barrel flies.
Torrey (1912) made examination of "wild" flies from a tenement house
district of New York City. He found "that the surface contamination of
these 'wild' flies may vary from 570 to 4,400,000 bacteria per insect,
and the intestinal bacterial content from 16,000 to 28,000,000."

Less well known in this country is the work of Cox, Lewis, and Glynn
(1912). They examined over four hundred and fifty naturally infected
house-flies in Liverpool during September and early October. Instead of
washing the flies they were allowed to swim on the surface of sterile
water for five, fifteen, or thirty minutes, thus giving natural
conditions, where infection occurs from vomit and dejecta of the flies,
as well as from their bodies. They found, as might be expected, that
flies from either insanitary or congested areas of the city contain far
more bacteria than those from the more sanitary, less congested, or
suburban areas. The number of aerobic bacteria from the former varied
from 800,000 to 500,000,000 per fly and from the latter from 21,000 to
100,000. The number of intestinal forms conveyed by flies from
insanitary or congested areas was from 10,000 to 333,000,000 as compared
with from 100 to 10,000 carried by flies from the more sanitary areas.

Pathogenic bacteria and those allied to the food poisoning group were
only obtained from the congested or moderately congested areas and not
from the suburban areas, where the chances of infestation were less.

The interesting fact was brought out that flies caught in milk shops
apparently carry and obtain more bacteria than those from other shops
with exposed food in a similar neighborhood. The writers explained this
as probably due to the fact that milk when accessible, especially during
the summer months, is suitable culture medium for bacteria, and the
flies first inoculate the milk and later reinoculate themselves, and
then more of the milk, so establishing a vicious circle.

They conclude that in cities where food is plentiful flies rarely
migrate from the locality in which they are bred, and consequently the
number of bacteria which they carry depends upon the general standard
of cleanliness in that locality. Flies caught in a street of modern,
fairly high class, workmen's dwellings forming a sanitary oasis in the
midst of a slum area, carried far less bacteria than those caught in the
adjacent neighborhood.

Thus, as the amount of dirt carried by flies in any particular locality,
measured in the terms of bacteria, bears a definite relation to the
habits of the people and to the state of the streets, it demonstrates
the necessity of efficient municipal and domestic cleanliness, if the
food of the inhabitants is to escape pollution, not only with harmless
but also with occasional pathogenic bacteria.

The above cited work is of a general nature, but, especially in recent
years, many attempts have been made to determine more specifically the
ability of flies to transmit pathogenic organisms. The critical reviews
of Nuttall and Jepson (1909), Howard (1911), and Graham-Smith (1913)
should be consulted by the student of the subject. We can only cite here
a few of the more striking experiments.

Celli (1888) fed flies on pure cultures of _Bacillus typhosus_ and
declared that he was able to recover these organisms from the intestinal
contents and excrement.

Firth and Horrocks (1902), cited by Nuttall and Jepson, "kept _Musca
domestica_ (also bluebottles) in a large box measuring 4 × 3 × 3 feet,
with one side made of glass. They were fed on material contaminated with
cultures of _B. typhosus_. Agar plates, litmus, glucose broth and a
sheet of clean paper were at the same time exposed in the box. After a
few days the plates and broth were removed and incubated with a positive
result." Graham-Smith (1910) "carried out experiments with large numbers
of flies kept in gauze cages and fed for eight hours on emulsions of _B.
typhosus_ in syrup. After that time the infested syrup was removed and
the flies were fed on plain syrup. _B. typhosus_ was isolated up to 48
hours (but not later) from emulsions of their feces and from plates over
which they walked."

Several other workers, notably Hamilton (1903), Ficker (1903),
Bertarelli (1910) Faichnie (1909), and Cochrane (1912), have isolated
_B. typhosus_ from "wild" flies, naturally infected. The papers of
Faichnie and of Cochrane we have not seen, but they are quoted in
_extenso_ by Graham-Smith (1913).

On the whole, the evidence is conclusive that typhoid germs not only may
be accidentally carried on the bodies of house-flies but may pass
through their bodies and be scattered in a viable condition in the feces
of the fly for at least two days after feeding. Similar, results have
been reached in experiments with cholera, tuberculosis and yaws, the
last-mentioned being a spirochæte disease. Darling (1913) has shown that
murrina, a trypanosome disease of horses and mules in the Canal zone is
transmitted by house-flies which feed upon excoriated patches of
diseased animals and then pass to cuts and galls of healthy animals.

Since it is clear that flies are abundantly able to disseminate viable
pathogenic bacteria, it is important to consider whether they have
access to such organisms in nature. A consideration of the method of
spread of typhoid will serve to illustrate the way in which flies may
play an important rôle.

Typhoid fever is a specific disease caused by _Bacillus typhosus_, and
by it alone. The causative organism is to be found in the excrement and
urine of patients suffering from the disease. More than that, it is
often present in the dejecta for days, weeks, or even months and years,
after the individual has recovered from the disease. Individuals so
infested are known as "typhoid carriers" and they, together with those
suffering from mild cases, or "walking typhoid," are a constant menace
to the health of the community in which they are found.

Human excrement is greedily visited by flies, both for feeding and for
ovipositing. The discharges of typhoid patients, or of chronic
"carriers," when passed in the open, in box privies, or camp latrines,
or the like, serve to contaminate myriads of the insects which may then
spread the germ to human food and drink. Other intestinal diseases may
be similarly spread. There is abundant epidæmiological evidence that
infantile diarrhoea, dysentery, and cholera may be so spread.

Stiles and Keister (1913) have shown that spores of _Lamblia
intestinalis_, a flagellate protozoan living in the human intestine, may
be carried by house-flies. Though this species is not normally
pathogenic, one or more species of _Entamoeba_ are the cause of a type
of a highly fatal tropical dysentery. Concerning it, and another
protozoan parasite of man, they say, "If flies can carry _Lamblia_
spores measuring 10 to 7µ, and bacteria that are much smaller, and
particles of lime that are much larger, there is no ground to assume
that flies may not carry _Entamoeba_ and _Trichomonas_ spores."

Tuberculosis is one of the diseases which it is quite conceivable may be
carried occasionally. The sputum of tubercular patients is very
attractive to flies, and various workers, notably Graham-Smith, have
found that _Musca domestica_ may distribute the bacillus for several
days after feeding on infected material.

A type of purulent opthalmia which is very prevalent in Egypt is often
said to be carried by flies. Nuttall and Jepson (1909) consider that the
evidence regarding the spread of this disease by flies is conclusive and
that the possibility of gonorrhoeal secretions being likewise conveyed
cannot be denied.

Many studies have been published, showing a marked agreement between the
occurrence of typhoid and other intestinal diseases and the prevalence
of house-flies. The most clear-cut of these are the studies of the Army
Commission appointed to investigate the cause of epidemics of enteric
fever in the volunteer camps in the Southern United States during the
Spanish-American War. Though their findings as presented by Vaughan
(1909), have been quoted very many times, they are so germane to our
discussion that they will bear repetition:

"Flies swarmed over infected fecal matter in the pits and fed upon the
food prepared for the soldiers in the mess tents. In some instances
where lime had recently been sprinkled over the contents of the pits,
flies with their feet whitened with lime were seen walking over the
food." Under such conditions it is no wonder that "These pests had
inflicted greater loss upon American soldiers than the arms of Spain."

Similar conditions prevailed in South Africa during the Boer War. Seamon
believes that very much of the success of the Japanese in their fight
against Russia was due to the rigid precautions taken to prevent the
spread of disease by these insects and other means.

Veeder has pointed out that the characteristics of a typical fly-borne
epidemic of typhoid are that it occurs in little neighborhood epidemics,
extending by short leaps from house to house, without regard to water
supply or anything else in common. It tends to follow the direction of
prevailing winds (cf. the conclusions of Hindle and Merriman). It occurs
during warm weather. Of course, when the epidemic is once well under
way, other factors enter into its spread.

In general, flies may be said to be the chief agency in the spread of
typhoid in villages and camps. In cities with modern sewer systems they
are less important, though even under the best of such conditions, they
are important factors. Howard has emphasized that in such cities there
are still many uncared-for box privies and that, in addition, the
deposition of feces overnight in uncared-for waste lots and alleys is
common.

Not only unicellular organisms, such as bacteria and protozoa, but also
the eggs, embryos and larvæ of parasitic worms have been found to be
transported by house-flies. Ransom (1911) has found that _Habronema
muscæ_, a nematode worm often found in adult flies, is the immature
stage of a parasite occurring in the stomach of the horse. The eggs or
embryos passing out with the feces of the horse, are taken up by fly
larvæ and carried over to the imago stage.

Grassi (1883), Stiles (1889), Calandruccio (1906), and especially Nicoll
(1911), have been the chief investigators of the ability of house-flies
to carry the ova and embryos of human intestinal parasites. Graham-Smith
(1913) summarizes the work along this line as follows:

"It is evident from the investigations that have been quoted that
house-flies and other species are greatly attracted to the ova of
parasitic worms contained in feces and other materials, and make great
efforts to ingest them. Unless the ova are too large they often succeed,
and the eggs are deposited uninjured in their feces, in some cases up to
the third day at least. The eggs may also be carried on their legs or
bodies. Under suitable conditions, food and fluids may be contaminated
with the eggs of various parasitic worms by flies, and in one case
infection of the human subject has been observed. Feces containing
tape-worm segments may continue to be a source of infection for as long
as a fortnight. Up to the present, however, there is no evidence to show
what part flies play in the dissemination of parasitic worms under
natural conditions."

Enough has been said to show that the house-fly must be dealt with as a
direct menace to public health. Control measures are not merely matters
of convenience but are of vital importance.

Under present conditions the speedy elimination of the house-fly is
impossible and the first thing to be considered is methods of protecting
food and drink from contamination. The first of these methods is the
thorough screening of doors and windows to prevent the entrance of
flies. In the case of kitchen doors, the flies, attracted by odors, are
likely to swarm onto the screen and improve the first opportunity for
gaining an entrance. This difficulty can be largely avoided by
screening-in the back porch and placing the screen door at one end
rather than directly before the door.

The use of sticky fly paper to catch the pests that gain entrance to the
house is preferable to the various poisons often used. Of the latter,
formalin (40 per cent formaldehyde) in the proportion of two
tablespoonfuls to a pint of water is very efficient, if all other
liquids are removed or covered, so that the flies must depend on the
formalin for drink. The mixture is said to be made more attractive by
the addition of sugar or milk, though we have found the plain solution
wholly satisfactory, under proper conditions. It should be emphasized
that this formalin mixture is not perfectly harmless, as so often
stated. There are on record cases of severe and even fatal poisoning
from the accidental drinking of solutions.

When flies are very abundant in a room they can be most readily gotten
rid of by fumigation with sulphur, or by the use of pure pyrethrum
powder either burned or puffed into the air. Herrick (1913) recommends
the following method: "At night all the doors and windows of the kitchen
should be closed; fresh powder should be sprinkled over the stove, on
the window ledges, tables, and in the air. In the morning flies will be
found lying around dead or stupified. They may then be swept up and
burned." This method has proved very efficaceous in some of the large
dining halls in Ithaca.

The writers have had little success in fumigating with the vapors of
carbolic acid, or carbolic acid and gum camphor, although these methods
will aid in driving flies from a darkened room.

All of these methods are but makeshifts. As Howard has so well put it,
"the truest and simplest way of attacking the fly problem is to prevent
them from breeding, by the treatment or abolition of all places in which
they can breed. To permit them to breed undisturbed and in countless
numbers, and to devote all our energy to the problem of keeping them out
of our dwellings, or to destroy them after they have once entered in
spite of all obstacles, seems the wrong way to go about it."

We have already seen that _Musca domestica_ breeds in almost any
fermenting organic material. While it prefers horse manure, it breeds
also in human feces, cow dung and that of other animals, and in refuse
of many kinds. To efficiently combat the insect, these breeding places
must be removed or must be treated in some such way as to render them
unsuitable for the development of the larvæ. Under some conditions
individual work may prove effective, but to be truly efficient there
must be extensive and thorough coöperative efforts.

Manure, garbage, and the like should be stored in tight receptacles and
carted away at least once a week. The manure may be carted to the fields
and spread. Even in spread manure the larvæ may continue their
development. Howard points out that "it often happens that after a lawn
has been heavily manured in early summer the occupants of the house will
be pestered with flies for a time, but finding no available breeding
place these disappear sooner or later. Another generation will not breed
in the spread manure."

Hutchinson (1914) has emphasized that the larvæ of houseflies have
deeply engrained the habit of migrating in the prepupal stage and has
shown that this offers an important point of attack in attempts to
control the pest. He has suggested that maggot traps might be developed
into an efficient weapon in the warfare against the house-fly. Certain
it is that the habit greatly simplifies the problem of treating the
manure for the purpose of killing the larvæ.

There have been many attempts to find some cheap chemical which would
destroy fly larvæ in horse manure without injuring the bacteria or
reducing the fertilizing values of the manure. The literature abounds in
recommendations of kerosene, lime, chloride of lime, iron sulphate, and
other substances, but none of them has met the situation. The whole
question has been gone into thoroughly by Cook, Hutchinson and Scales
(1914), who tested practically all of the substances which have been
recommended. They find that by far the most effective, economical, and
practical of the substances is borax in the commercial form in which it
is available throughout the country.

"Borax increases the water-soluble nitrogen, ammonia and alkalinity of
manure and apparently does not permanently injure the bacterial flora.
The application of manure treated with borax at the rate of 0.62 pound
per eight bushels (10 cubic feet) to soil does not injure the plants
thus far tested, although its cumulative effect, if any, has not been
determined."

As their results clearly show that the substances so often recommended
are inferior to borax, we shall quote in detail their directions for
treating manure so as to kill fly eggs and maggots.

"Apply 0.62 pound borax or 0.75 pound calcined colemanite to every 10
cubic feet (8 bushels) of manure immediately on its removal from the
barn. Apply the borax particularly around the outer edges of the pile
with a flour sifter or any fine sieve, and sprinkle two or three gallons
of water over the borax-treated manure.

"The reason for applying the borax to the fresh manure immediately after
its removal from the stable is that the flies lay their eggs on the
fresh manure, and borax, when it comes in contact with the eggs,
prevents their hatching. As the maggots congregate at the outer edge of
the pile, most of the borax should be applied there. The treatment
should be repeated with each addition of fresh manure, but when the
manure is kept in closed boxes, less frequent applications will be
sufficient. When the calcined colemanite is available, it may be used at
the rate of 0.75 pound per 10 cubic feet of manure, and is a cheaper
means of killing the maggots. In addition to the application of borax to
horse manure to kill fly larvæ, it may be applied in the same proportion
to other manures, as well as to refuse and garbage. Borax may also be
applied to the floors and crevices in barns, stables, markets, etc., as
well as to street sweepings, and water should be added as in the
treatment of horse manure. After estimating the amount of material to be
treated and weighing the necessary amount of borax, a measure may be
used which will hold the proper amount, thus avoiding the subsequent
weighings.

"While it can be safely stated that no injurious action will follow the
application of manure treated with borax at the rate of 0.62 pound for
eight bushels, or even larger amounts in the case of some plants,
nevertheless the borax-treated manure has not been studied in connection
with the growth of all crops, nor has its cumulative effect been
determined. It is therefore recommended that not more than 15 tons per
acre of the borax-treated manure should be applied to the field. As
truckmen use considerably more than this amount, it is suggested that
all cars containing borax-treated manure be so marked, and that
public-health officials stipulate in their directions for this treatment
that not over 0.62 pound for eight bushels of manure be used, as it has
been shown that larger amounts of borax will injure most plants. It is
also recommended that all public-health officials and others, in
recommending the borax treatment for killing fly eggs and maggots in
manure, warn the public against the injurious effects of large amounts
of borax on the growth of plants."

"The amount of manure from a horse varies with the straw or other
bedding used, but 12 or 15 bushels per week represent the approximate
amount obtained. As borax costs from five to six cents per pound in
100-pound lots in Washington, it will make the cost of the borax
practically one cent per horse, per day. And if calcined colemanite is
purchased in large shipments the cost should be considerably less."

Hodge (1910) has approached the problem of fly extermination from
another viewpoint. He believes that it is practical to trap flies out of
doors during the preoviposition period, when they are sexually immature,
and to destroy such numbers of them that the comparatively few which
survive will not be able to lay eggs in sufficient numbers to make the
next generation a nuisance. To the end of capturing them in enormous
numbers he has devised traps to be fitted over garbage cans, into stable
windows, and connected with the kitchen window screens. Under some
conditions this method of attack has proved very satisfactory.

One of the most important measures for preventing the spread of disease
by flies is the abolition of the common box privy. In villages and rural
districts this is today almost the only type to be found. It is the
chief factor in the spread of typhoid and other intestinal diseases, as
well as intestinal parasites. Open and exposed to myriads of flies which
not only breed there but which feed upon the excrement, they furnish
ideal conditions for spreading contamination. Even where efforts are
made to cover the contents with dust, or ashes, or lime, flies may
continue to breed unchecked. Stiles and Gardner have shown that
house-flies buried in a screened stand-pipe forty-eight inches under
sterile sand came to the surface. Other flies of undetermined species
struggled up through seventy-two inches of sand.

So great is the menace of the ordinary box privy that a number of
inexpensive and simple sanitary privies have been designed for use where
there are not modern sewer systems. Stiles and Lumsden (1911) have given
minute directions for the construction of one of the best types, and
their bulletin should be obtained by those interested.

Another precaution which is of fundamental importance in preventing the
spread of typhoid, is that of disinfecting all discharges from patients
suffering with the disease. For this purpose, quick-lime is the cheapest
and is wholly satisfactory. In chamber vessels it should be used in a
quantity equal to that of the discharge to be treated. It should be
allowed to act for two hours. Air-slaked lime is of no value whatever.
Chloride of lime, carbolic acid, or formalin may be used, but are more
expensive. Other intestinal diseases demand similar precautions.


STOMOXYS CALCITRANS, THE STABLE-FLY--It is a popular belief that
house-flies bite more viciously just before a rain. As a matter of
fact, the true house-flies never bite, for their mouth-parts are not
fitted for piercing. The basis of the misconception is the fact that a
true biting fly, _Stomoxys calcitrans_ (fig. 110), closely resembling
the house-fly, is frequently found in houses and may be driven in in
greater numbers by muggy weather. From its usual habitat this fly is
known as the "stable-fly" or, sometimes as the "biting house-fly."

_Stomoxys calcitrans_ may be separated from the house-fly by the use of
the key on p. 145. It may be more fully characterized as follows:

The eyes of the male are separated by a distance equal to one-fourth of
the diameter of the head, in the female by one-third. The frontal stripe
is black, the cheeks and margins of the orbits silvery-white. The
antennæ are black, the arista feathered on the upper side only. The
proboscis is black, slender, fitted for piercing and projects forward in
front of the head. The thorax is grayish, marked by four conspicuous,
more or less complete black longitudinal stripes; the scutellum is
paler; the macrochætæ are black. The abdomen is gray, dorsally with
three brown spots on the second and third segments and a median spot on
the fourth. These spots are more pronounced in the female. The legs are
black, the pulvilli distinct. The wings are hyaline, the vein M_{1+2}
less sharply curved than in the house-fly, the apical cell being thus
more widely open (cf. fig. 110). Length 7 mm.

[Illustration: 110. Stomoxys calcitrans; adult, larva, puparium and
details, (×5). After Howard.]

This fly is widely distributed, being found the world over. It was
probably introduced into the United States, but has spread to all parts
of the country. Bishopp (1913) regards it as of much more importance as
a pest of domestic animals in the grain belt than elsewhere in the
United States. The life-history and habits of this species have assumed
a new significance since it has been suggested that it may transmit the
human diseases, infantile paralysis and pellagra. In this country, the
most detailed study of the fly is that of Bishopp (1913) whose data
regarding the life cycle are as follows:

The eggs like those of the house-fly, are about one mm. in length. Under
a magnifying glass they show a distinct furrow along one side. When
placed on any moist substance they hatch in from one to three days after
being deposited.

The larva or maggots (fig. 110) have the typical shape and actions of
most maggots of the Muscid group. They can be distinguished from those
of the house-fly as the stigma-plates are smaller, much further apart,
with the slits less sinuous. Development takes place fairly rapidly when
the proper food conditions are available and the growth is completed
within eleven to thirty or more days.

The pupa (fig. 110), like that of related flies, undergoes its
development within the contracted and hardened last larval skin, or
puparium. This is elongate oval, slightly thicker towards the head end,
and one-sixth to one-fourth of an inch in length. The pupal stage
requires six to twenty days, or in cool weather considerably longer.

The life-cycle of the stable-fly is therefore considerably longer than
that of _Musca domestica_. Bishopp found that complete development might
be undergone in nineteen days, but that the average period was somewhat
longer, ranging from twenty-one to twenty-five days, where conditions
are very favorable. The longest period which he observed was forty-three
days, though his finding of full grown larvæ and pupæ in straw during
the latter part of March, in Northern Texas, showed that development may
require about three months, as he considered that these stages almost
certainly developed from eggs deposited the previous December.

The favorite breeding place, where available, seems to be straw or
manure mixed with straw. It also breeds in great numbers in
horse-manure, in company with _Musca domestica_.

Newstead considers that in England the stable-fly hibernates in the
pupal stage. Bishopp finds that in the southern part of the United
States there is no true hibernation, as the adults have been found to
emerge at various times during the winter. He believes that in the
northern United States the winter is normally passed in the larval and
pupal stages, and that the adults which have been observed in heated
stables in the dead of winter were bred out in refuse within the warm
barns and were not hibernating adults.

Graham-Smith (1913) states that although the stable-fly frequents stable
manure, it is probably not an important agent in distributing the
organisms of intestinal diseases. Bishopp makes the important
observation that "it has never been found breeding in human excrement
and does not frequent malodorous places, which are so attractive to the
house-fly. Hence it is much less likely to carry typhoid and other germs
which may be found in such places."

Questions of the possible agency of _Stomoxys calcitrans_ in the
transmission of infantile paralysis and of pellagra, we shall consider
later.


OTHER ARTHROPODS WHICH MAY SERVE AS SIMPLE CARRIERS OF PATHOGENIC
ORGANISMS--It should be again emphasized that any insect which has
access to, and comes in contact with, pathogenic organisms and then
passes to the food, or drink, or the body of man, may serve as a simple
carrier of disease. In addition to the more obvious illustrations, an
interesting one is the previously cited case of the transfer of
_Dermatobia cyaniventris_ by a mosquito (fig. 81-84). Darling (1913) has
shown that in the tropics, the omnipresent ants may be important factors
in the spread of disease.




CHAPTER VI

ARTHROPODS AS DIRECT INOCULATORS OF DISEASE GERMS


We have seen that any insect which, like the house-fly, has access to
disease germs and then comes into contact with the food or drink of man,
may serve to disseminate disease. Moreover, it has been clearly
established that a contaminated insect, alighting upon wounded or
abraded surfaces, may infect them. These are instances of mere
accidental, mechanical transfer of pathogenic organisms.

Closely related are the instances of direct inoculation of disease germs
by insects and other arthropods. In this type, a blood-sucking species
not only takes up the germs but, passing to a healthy individual, it
inserts its contaminated mouth-parts and thus directly inoculates its
victim. In other words, the disease is transferred just as blood
poisoning may be induced by the prick of a contaminated needle, or as
the laboratory worker may inoculate an experimental animal.

Formerly, it was supposed that this method of the transfer of disease by
arthropods was a very common one and many instances are cited in the
earlier literature of the subject. It is, however, difficult to draw a
sharp line between such cases and those in which, on the one hand, the
arthropod serves as a mere passive carrier or, on the other hand, serves
as an essential host of the pathogenic organism. More critical study of
the subject has led to the belief that the importance of the rôle of
arthropods as direct inoculators has been much overestimated.

The principal reason for regarding this phase of the subject as
relatively unimportant, is derived from a study of the habits of the
blood-sucking species. It is found that, in general, they are
intermittent feeders, visiting their hosts at intervals and then
abstaining from feeding for a more or less extended period, while
digesting their meal. In the meantime, most species of bacteria or of
protozoan parasites with which they might have contaminated their
mouth-parts, would have perished, through inability to withstand drying.

In spite of this, it must be recognized that this method of transfer
does occur and must be reckoned with in any consideration of the
relations of insects to disease. We shall first cite some general
illustrations and shall then discuss the rôle of fleas in the spreading
of bubonic plague, an illustration which cannot be regarded as typical,
since it involves more than mere passive carriage.


SOME ILLUSTRATIONS OF DIRECT INOCULATION OF DISEASE GERMS BY ARTHROPODS

In discussing poisonous arthropods, we have already emphasized that
species which are of themselves innocuous to man, may occasionally
introduce bacteria by their bite or sting and thus cause more or less
severe secondary symptoms. That such cases should occur, is no more than
is to be expected. The mouth-parts or the sting of the insect are not
sterile and the chances of their carrying pyogenic organisms are always
present.

More strictly falling in the category of transmission of disease germs
by direct inoculation are the instances where the insect, or related
form, feeds upon a diseased animal and passes promptly to a healthy
individual which it infects. Of such a nature are the following:

Various species of biting flies are factors in the dissemination of
anthrax, an infectious and usually fatal disease of animals and,
occasionally, of man. That the bacteria with which the blood of diseased
animals teem shortly before death might be transmitted by such insects
has long been contended, but the evidence in support of the view has
been unsatisfactory. Recently, Mitzmain (1914) has reported a series of
experiments which show conclusively that the disease may be so conveyed
by a horse-fly, _Tabanus striatus_, and by the stable-fly, _Stomoxys
calcitrans_.

Mitzmain's experiments were tried with an artificially infected guinea
pig, which died of the disease upon the third day. The flies were
applied two and one-half hours, to a few minutes, before the death of
the animal. With both species the infection was successfully transferred
to healthy guinea pigs by the direct method, in which the flies were
interrupted while feeding on the sick animal. The evidence at hand does
not warrant the conclusion that insect transmission is the rule in the
case of this disease.

The nagana, or tsetse-fly disease of cattle is the most virulent disease
of domestic animals in certain parts of Africa. It is caused by a
protozoan blood parasite, _Trypanosoma brucei_, which is conveyed to
healthy animals by the bite of _Glossina morsitans_ and possibly other
species of tsetse-flies. The flies remain infective for forty-eight
hours after feeding on a diseased animal. The insect also serves as an
essential host of the parasite.

Surra, a similar trypanosomiasis affecting especially horses and mules,
occurs in southern Asia, Malaysia, and the Philippines where the
tsetse-flies are not to be found. It is thought to be spread by various
species of blood-sucking flies belonging to the genera _Stomoxys_,
_Hæmatobia_, and _Tabanus_. Mitzmain (1913) demonstrated that in the
Philippines it is conveyed mechanically by _Tabanus striatus_.

The sleeping sickness of man, in Africa, has also been supposed to be
directly inoculated by one, or several, species of tsetse-flies. It is
now known that the fly may convey the disease for a short time after
feeding, but that there is then a latent period of from fourteen to
twenty-one days, after which it again becomes infectious. This indicates
that in the meantime the parasite has been undergoing some phase of its
life-cycle and that the fly serves as an intermediate host. We shall
therefore consider it more fully under that grouping.

These are a few of the cases of direct inoculation which may be cited as
of the simpler type. We shall next consider the rôle of the flea in the
dissemination of the bubonic plague, an illustration complicated by the
fact that the bacillus multiples within the insect and may be indirectly
inoculated.


THE RÔLE OF FLEAS IN THE TRANSMISSION OF THE PLAGUE

The plague is a specific infectious disease caused by _Bacillus pestis_.
It occurs in several forms, of which the bubonic and the pneumonic are
the most common. According to Wyman, 80 per cent of the human cases are
of the bubonic type. It is a disease which, under the name of oriental
plague, the pest, or the black death, has ravaged almost from time
immemorial the countries of Africa, Asia, and Europe. The record of its
ravages are almost beyond belief. In 542 A. D. it caused in one day ten
thousand deaths in Constantinople. In the 14th century it was introduced
from the East and prevailed throughout Armenia, Asia Minor, Egypt and
Northern Africa and Europe. Hecker estimates that one-fourth of the
population of Europe, or twenty-five million persons, died in the
epidemic of that century. From then until the 17th century it was almost
constantly present in Europe, the great plague of London, in 1665
killing 68,596 out of a population of 460,000. Such an epidemic would
mean for New York City a proportionate loss of over 600,000 in a single
year. It is little wonder that in the face of such an appalling disaster
suspicion and credulity were rife and the wildest demoralization ensued.

During the 14th century the Jews were regarded as responsible for the
disease, through poisoning wells, and were subjected to the most
incredible persecution and torture. In Milan the visitation of 1630 was
credited to the so-called anointers,--men who were supposed to spread
the plague by anointing the walls with magic ointment--and the most
horrible tortures that human ingenuity could devise were imposed on
scores of victims, regardless of rank or of public service (fig. 112,
a). Manzoni's great historical novel, "The Betrothed" has well pictured
conditions in Italy during this period.

[Illustration: 111. A contemporaneous engraving of the pest hospital in
Vienna in 1679. After Peters.]

In modern times the plague is confined primarily to warm climates, a
condition which has been brought about largely through general
improvement in sanitary conditions.

At present, the hotbed of the disease is India, where there were
1,040,429 deaths in 1904 and where in a period of fifteen years, ending
with January 1912, there were over 15,000,000 deaths. The reported
deaths in that country for 1913 totaled 198,875.

During the winter of 1910-11 there occurred in Manchuria and North China
a virulent epidemic of the pneumonic plague which caused the death of
nearly 50,000 people. The question as to its origin and means of spread
will be especially referred to later.

[Illustration: 112 a. A medieval method of combating the plague. The
persecution of the anointers in Milan in 1630. From a copy of "Il
processi originale degli untori" in the library of Cornell University.]

Until recent years, the plague had not been known to occur in the New
World but there were outbreaks in Brazil and Hawaii in 1899, and in 1900
there occurred the first cases in San Francisco. In California there
were 125 cases in the period 1900-04; three cases in the next three
years and then from May 1907 to March 1908, during the height of the
outbreak, 170 cases. Since that time there have been only sporadic
cases, the last case reported being in May 1914. Still more recent were
the outbreaks in the Philippine Islands, Porto Rico, and Cuba.

On June 24, 1914, there was recognized a case of human plague in New
Orleans. The Federal Health Service immediately took charge, and
measures for the eradication of the disease were vigorously enforced. Up
to October 10, 1914 there had been reported 30 cases of the disease in
man, and 181 cases of plague in rats.

[Illustration: 112 b. The modern method of combating the plague. A day's
catch of rats in the fight against plague in San Francisco. Courtesy of
Review of Reviews.]

The present-day methods of combating bubonic plague are well illustrated
by the fight in San Francisco. Had it not been for the strenuous and
radical anti-plague campaign directed by the United States Marine
Hospital Service we might have had in our own country an illustration of
what the disease can accomplish. On what newly acquired knowledge was
this fight based?

The basis was laid in 1894, when the plague bacillus was first
discovered. All through the centuries, before and during the Christian
era, down to 1894, the subject was enveloped in darkness and there had
been a helpless, almost hopeless struggle in ignorance on the part of
physicians, sanitarians, and public health officials against the ravages
of this dread disease. Now its cause, method of propagation and means to
prevent its spread are matters of scientific certainty.

After the discovery of the causative organism, one of the first advances
was the establishment of the identity of human plague and that of
rodents. It had often been noted that epidemics of the human disease
were preceded by great epizootics among rats and mice. So well
established was this fact that with the Chinese, unusual mortality among
these rodents was regarded as foretelling a visitation of the human
disease. That there was more than an accidental connection between the
two was obvious when Yersin, the discoverer of _Bacillus pestis_,
announced that during an epidemic the rats found dead in the houses and
in the streets almost always contain the bacillus in great abundance in
their organs, and that many of them exhibit veritable buboes.

Once it was established that the diseases were identical, the attention
of the investigators was directed to a study of the relations between
that of rats and of humans, and evidence accumulated to show that the
bubonic plague was primarily a disease of rodents and that in some
manner it was conveyed from them to man.

There yet remained unexplained the method of transfer from rat to man.
As long ago as the 16th century, Mercuralis suggested that house-flies
were guilty of disseminating the plague but modern investigation, while
blaming the fly for much in the way of spreading disease, show that it
is an insignificant factor in this case.

Search for blood-sucking insects which would feed on both rodents and
man, and which might therefore be implicated, indicated that the fleas
most nearly met the conditions. At first it was urged that rat fleas
would not feed upon man and that the fleas ordinarily attacking man
would not feed upon rats. More critical study of the habits of fleas
soon showed that these objections were not well-founded. Especially
important was the evidence that soon after the death of their host, rat
fleas deserted its body and might then become a pest in houses where
they had not been noticed before.

Attention was directed to the fact that while feeding, fleas are in the
habit of squirting blood from the anus and that in the case of those
which had fed upon rats and mice dying of the plague, virulent plague
bacilli were to be found in such blood. Liston (1905) even found, and
subsequent investigations confirmed, that the plague bacilli multiply in
the stomach of the insect and that thus the blood ejected was richer in
the organisms than was that of the diseased animal. It was found that a
film of this infected blood spread out under the body of the flea and
that thus the bacilli might be inoculated by the bite of the insect and
by scratching.

Very recently, Bacot and Martin (1914) have paid especial attention to
the question of the mechanism of the transmission of the plague bacilli
by fleas. They believe that plague infested fleas regurgitate blood
through the mouth, and that under conditions precluding the possibility
of infection by dejecta, the disease may be thus transmitted. The
evidence does not seem sufficient to establish that this is the chief
method of transmission.

Conclusive experimental proof that fleas transmit the disease is further
available from a number of sources. The most extensive series of
experiments is that of the English Plague Commission in India, which
reported in 1906 that:

On thirty occasions a healthy rat contracted plague in sequence of
living in the neighborhood of a plague infected rat under circumstances
which prevented the healthy rat coming in contact with either the body
or excreta of the diseased animal.

In twenty-one experiments out of thirty-eight, healthy rats living in
flea-proof cages contracted plague when exposed to rat fleas
(_Xenopsylla cheopis_), collected from rats dead or dying of septicæmic
plague.

Close contact of plague-infected with healthy animals, if fleas are
excluded, does not give rise to an epizootic among the latter. As the
huts were never cleaned out, close contact included contact with feces
and urine of infected animals, and contact with, and eating of food
contaminated with feces and urine of infected animals, as well as pus
from open plague ulcers. Close contact of young, even when suckled by
plague-infected mothers, did not give the disease to the former.

If fleas are present, then the epizootic, once started, spreads from
animal to animal, the rate of progress being in direct proportion to the
number of fleas.

Aerial infection was excluded. Thus guinea-pigs suspended in a cage two
feet above the ground did not contract the disease, while in the same
hut those animals allowed to run about and those placed two inches above
the floor became infected. It had previously been found that a rat flea
could not hop farther than about five inches.

Guinea pigs and monkeys were placed in plague houses in pairs, both
protected from soil contact infection and both equally exposed to aerial
infection, but one surrounded with a layer of tangle-foot paper and the
other surrounded with a layer of sand. The following observations were
made:

(_a_) Many fleas were caught in the tangle-foot, a certain proportion of
which were found on dissection to contain in their stomachs abundant
bacilli microscopically identical with plague bacilli. Out of
eighty-five human fleas dissected only one contained these bacilli,
while out of seventy-seven rat fleas twenty-three were found thus
infected.

(_b_) The animals surrounded with tangle-foot in no instance developed
plague, while several (24 per cent) of the non-protected animals died of
the disease.

Thus, the experimental evidence that fleas transmit the plague from rat
to rat, from rats to guinea pigs, and from rats to monkeys is
indisputable. There is lacking direct experimental proof of its transfer
from rodents to man but the whole chain of indirect evidence is so
complete that there can be no doubt that such a transfer does occur so
commonly that in the case of bubonic plague it must be regarded as the
normal method.

Rats are not the only animals naturally attacked by the plague but as
already suggested, it occurs in various other rodents. In California the
disease has spread from rats to ground squirrels (_Otospermophilus
beecheyi_), a condition readily arising from the frequency of
association of rats with the squirrels in the neighborhood of towns, and
from the fact that the two species of fleas found on them are also found
on rats. While the danger of the disease being conveyed from squirrels
to man is comparatively slight, the menace in the situation is that the
squirrels may become a more or less permanent reservoir of the disease
and infect rats, which may come into more frequent contact with man.

The tarbagan (_Arctomys bobac_), is a rodent found in North Manchuria,
which is much prized for its fur. It is claimed that this animal is
extremely susceptible to the plague and there is evidence to indicate
that it was the primary source of the great outbreak of pneumonic plague
which occurred in Manchuria and North China during the winter of
1910-11.

Of fleas, any species which attacks both rodents and man may be an agent
in the transmission of the plague. We have seen that in India the
species most commonly implicated is the rat flea, _Xenopsylla cheopis_,
(= _Loemopsylla_ or _Pulex cheopis_) (fig. 89). This species has also
been found commonly on rats in San Francisco. The cat flea,
_Ctenocephalus felis_, the dog flea, _Ctenocephalus canis_, the human
flea, _Pulex irritans_, the rat fleas, _Ceratophyllus fasciatus_ and
_Ctenopsyllus musculi_ have all been shown to meet the conditions.

But, however clear the evidence that fleas are the most important agent
in the transfer of plague, it is a mistake fraught with danger to assume
that they are the only factor in the spread of the disease. The
causative organism is a bacillus and is not dependent upon any insect
for the completion of its development.

Therefore, any blood-sucking insect which feeds upon a plague infected
man or animal and then passes to a healthy individual, conceivably might
transfer the bacilli. Verjbitski (1908) has shown experimentally that
bed-bugs may thus convey the disease. Hertzog found the bacilli in a
head-louse, _Pediculus humanus_, taken from a child which had died from
the plague, and McCoy found them in a louse taken from a plague-infected
squirrel. On account of their stationary habits, the latter insects
could be of little significance in spreading the disease.

Contaminated food may also be a source of danger. While this source,
formerly supposed to be the principal one, is now regarded as
unimportant, there is abundant experimental evidence to show that it
cannot be disregarded. It is believed that infection in this way can
occur only when there is some lesion in the alimentary canal.

Still more important is the proof that in pneumonic plague the patient
is directly infective and that the disease is spread from man to man
without any intermediary. Especially conclusive is the evidence obtained
by Drs. Strong and Teague during the Manchurian epidemic of 1910-11.
They found that during coughing, in pneumonic plague cases, even when
sputum visible to the naked eye is not expelled, plague bacilli in large
numbers may become widely disseminated into the surrounding air. By
exposing sterile plates before patients who coughed a single time, very
numerous colonies of the bacillus were obtained.

But the great advance which has been made rests on the discovery that
bubonic plague is in the vast majority of cases transmitted by the flea.
The pneumonic type forms a very small percentage of the human cases and
even with it, the evidence indicates that the original infection is
derived from a rodent through the intermediary of the insect.

So modern prophylactic measures are directed primarily against the rat
and fleas. Ships coming from infected ports are no longer disinfected
for the purpose of killing the plague germs, but are fumigated to
destroy the rats and the fleas which they might harbor. When anchored at
infected ports, ships must observe strenuous precautions to prevent the
ingress of rats. Cargo must be inspected just before being brought on
board, in order to insure its freedom from rats. Even lines and hawsers
must be protected by large metal discs or funnels, for rats readily run
along a rope to reach the ship. Once infested, the ship must be
thoroughly fumigated, not only to avoid carrying the disease to other
ports but to obviate an outbreak on board.

When an epidemic begins, rats must be destroyed by trapping and
poisoning. Various so-called biological poisons have not proved
practicable. Sources of food supply should be cut off by thorough
cleaning up, by use of rat-proof garbage cans and similar measures. Hand
in hand with these, must go the destruction of breeding places, and the
rat-proofing of dwellings, stables, markets, warehouses, docks and
sewers. All these measures are expensive, and a few years ago would have
been thought wholly impossible to put into practice but now they are
being enforced on a large scale in every fight against the disease.

Rats and other rodents are regularly caught in the danger zone and
examined for evidence of infection, for the sequence of the epizootic
and of the human disease is now understood. In London, rats are
regularly trapped and poisoned in the vicinity of the principal docks,
to guard against the introduction of infected animals in shipping.
During the past six years infected rats have been found yearly, thirteen
having been found in 1912. In Seattle, Washington, seven infected rats
were found along the water front in October, 1913, and infected ground
squirrels are still being found in connection with the anti-plague
measures in California.

The procedure during an outbreak of the human plague was well
illustrated by the fight in San Francisco. The city was districted, and
captured rats, after being dipped in some fluid to destroy the fleas,
were carefully tagged to indicate their source, and were sent to the
laboratory for examination. If an infected rat was found, the officers
in charge of the work in the district involved were immediately notified
by telephone, and the infected building was subjected to a thorough
fumigation. In addition, special attention was given to all the
territory in the four contiguous blocks.

By measures such as these, this dread scourge of the human race is being
brought under control. Incidentally, the enormous losses due to the
direct ravages of rats are being obviated and this alone would justify
the expenditure many times over of the money and labor involved in the
anti-rat measures.




CHAPTER VII

ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC ORGANISMS


We now have to consider the cases in which the arthropod acts as the
essential host of a pathogenic organism. In other words, cases in which
the organism, instead of being passively carried or merely accidentally
inoculated by the bite of its carrier, or vector, is taken up and
undergoes an essential part of its development within the arthropod.

[Illustration: 113. Dipylidium caninum. The double pored tapeworm of the
dog.]

In some cases, the sexual cycle of the parasite is undergone in the
arthropod, which then serves as the _definitive_ or _primary host_. In
other cases, it is the asexual stage of the parasite which is undergone,
and the arthropod then acts as the _intermediate host_. This distinction
is often overlooked and all the cases incorrectly referred to as those
in which the insect or other arthropod acts as intermediate host.

We have already emphasized that this is the most important way in which
insects may transmit disease, for without them the particular organisms
concerned could never complete their development. Exterminate the
arthropod host and the life cycle of the parasite is broken, the disease
is exterminated.

As the phenomenon of alternation of generations, as exhibited by many of
the parasitic protozoa, is a complicated one and usually new to the
student, we shall first take up some of the grosser cases illustrated by
certain parasitic worms. There is the additional reason that these were
the first cases known of arthropod transmission of pathogenic organisms.


INSECTS AS INTERMEDIATE HOSTS OF TAPEWORMS

A number of tapeworms are known to undergo their sexual stage in an
insect or other arthropod. Of these at least two are occasional
parasites of man.

_Dipylidium caninum_ (figs. 113 and 114), more generally known as
_Taenia cucumerina_ or _T. elliptica_, is the commonest intestinal
parasite of pet dogs and cats. It is occasionally found as a human
parasite, 70 per cent of the cases reported being in young children.

In 1869, Melnikoff found in a dog louse, _Trichodectes canis_, some
peculiar bodies which Leuckart identified as the larval form of this
tapeworm. The worm is, however, much more common in dogs and cats than
is the skin parasite, and hence it appears that the _Trichodectes_ could
not be the only intermediate host. In 1888, Grassi found that it could
also develop in the cat and dog fleas, _Ctenocephalus felis_ and _C.
canis_, and in the human flea, _Pulex irritans_.

[Illustration: 114. Dipylidium caninum. Rostrum evaginated and
invaginated. After Blanchard.]

[Illustration: 115. Dipylidium caninum. Immature cysticercoid. After
Grassi and Rovelli.]

The eggs, scattered among the hairs of the dog or cat, are ingested by
the insect host and in its body cavity they develop into pyriform
bodies, about 300µ in length, almost entirely destitute of a bladder,
but in the immature stage provided with a caudal appendage (fig. 115).
Within the pear-shaped body (fig. 116) are the invaginated head and
suckers of the future tapeworm. This larval form is known as a
cysticercoid, in contradistinction to the bladder-like cysticercus of
many other cestodes. It is often referred to in literature as
_Cryptocystis trichodectis_ Villot.

As many as fifty of the cysticercoids have been found in the body cavity
of a single flea. When the dog takes up an infested flea or louse, by
biting itself, or when the cat licks them up, the larvæ quickly develop
into tapeworms, reaching sexual maturity in about twenty days in the
intestine of their host. Puppies and kittens are quickly infested when
suckling a flea-infested mother, the developing worms having been found
in the intestines of puppies not more than five or six days old.

[Illustration: 116. Dipylidium caninum. Cysticercoid. After Villet.]

Infestation of human beings occurs only through accidental ingestion of
an infested flea. It is natural that such cases should occur largely in
children, where they may come about in some such way as illustrated in
the accompanying figures 117 and 118.

_Hymenolepis diminuta_, very commonly living in the intestine of mice
and rats, is also known to occur in man. Its cysticercoid develops in
the body cavity of a surprising range of meal-infesting insects. Grassi
and Rovelli (abstract in Ransom, 1904) found it in the larvæ and adult
of a moth, _Asopia farinalis_, in the earwig, _Anisolabis annulipes_,
the Tenebrionid beetles _Akis spinosa_ and _Scaurus striatus_. Grassi
considers that the lepidopter is the normal intermediate host. The
insect takes up the eggs scattered by rats and mice. It has been
experimentally demonstrated that man may develop the tapeworm by
swallowing infested insects. Natural infection probably occurs by
ingesting such insects with cereals, or imperfectly cooked foods.

[Illustration: 117. One way in which Dipylidium infection in children
may occur. After Blanchard.]

_Hymenolepis lanceolata_, a parasite of geese and ducks, has been
reported once for man. The supposed cysticercoid occurs in various small
crustaceans of the family Cyclopidæ.

[Illustration: 118. The probable method by which Dipylidium infection
usually occurs.]

Several other cestode parasites of domestic animals are believed to
develop their intermediate stage in certain arthropods. Among these may
be mentioned:

_Choanotænia infundibulformis_, of chickens, developing in the house-fly
(Grassi and Rovelli);

_Davainea cesticillus_, of chickens, in some lepidopter or coleopter
(Grassi and Rovelli);

_Hymenolepis anatina_, _H. gracilis_, _H. sinuosa_, _H. coronula_ and
_Fimbriaria fasciolaris_, all occurring in ducks, have been reported as
developing in small aquatic crustaceans. In these cases, cysticercoids
have been found which, on account of superficial characters, have been
regarded as belonging to the several species, but direct experimental
evidence is scant.


ARTHROPODS AS INTERMEDIATE HOSTS OF NEMATODE WORMS


FILARIASIS AND MOSQUITOES--A number of species of Nematode worms
belonging to the genus _Filaria_, infest man and other vertebrates and
in the larval condition are to be found in the blood. Such infestation
is known as _filariasis_. The sexually mature worms are to be found in
the blood, the lymphatics, the mesentery and subcutaneous connective
tissue. In the cases best studied it has been found that the larval
forms are taken up by mosquitoes and undergo a transformation before
they can attain maturity in man.

The larvæ circulating in the blood are conveniently designated as
microfilariæ. In this stage they are harmless and only one species,
_Filaria bancrofti_, appears to be of any great pathological
significance at any stage.

_Filaria bancrofti_ in its adult state, lives in the lymphatics of man.
Though often causing no injury it has been clearly established that they
and their eggs may cause various disorders due to stoppage of the
lymphatic trunks (fig. 119). Manson lists among other effects, abscess,
varicose groin glands, lymph scrotum, chyluria, and elephantiasis.

The geographical distribution of this parasite is usually given as
coextensive with that of elephantiasis, but it is by no means certain
that it is the only cause of this disease and so actual findings of the
parasites are necessary. Manson reports that it is "an indigenous
parasite in almost every country throughout the tropical and subtropical
world, as far north as Spain in Europe and Charlestown in the United
States, and as far south as Brisbane in Australia." In some sections,
fully 50 per cent of the natives are infested. Labredo (1910) found
17.82 per cent infestation in Havana.

[Illustration: 119. Elephantiasis in Man. From "New Sydenham Society's
Atlas."]

The larval forms of _Filaria bancrofti_ were first discovered in 1863,
by Demarquay, in a case of chylous dropsy. They were subsequently noted
under similar conditions, by several workers, and by Wücherer in the
urine of twenty-eight cases of tropical chyluria, but in 1872 Lewis
found that the blood of man was the normal habitat, and gave them the
name _Filaria sanguinis hominis_. The adult worm was found in 1876 by
Bancroft, and in 1877, Cobbold gave it the name _Filaria bancrofti_. It
has since been found repeatedly in various parts of the lymphatic
system, and its life-history has been the subject of detailed studies by
Manson (1884), Bancroft (1899), Low (1900), Grassi and Noé (1900), Noé
(1901) and Fülleborn (1910).

The larvæ as they exist in the circulating blood, exhibit a very active
wriggling movement, without material progression. They may exist in
enormous numbers, as many as five or six hundred swarming in a single
drop of blood. This is the more surprising when we consider that they
measure about 300µ × 8µ, that is, their width is equal to the diameter
of the red blood corpuscle of their host and their length over
thirty-seven times as great.

Their organs are very immature and the structure obscure. When they have
quieted down somewhat in a preparation it may be seen that at the head
end there is a six-lipped and very delicate prepuce, enclosing a short
"fang" which may be suddenly exserted and retracted. Completely
enclosing the larva is a delicate sheath, which is considerably longer
than the worm itself. To enter into further details of anatomy is beyond
the scope of this discussion and readers interested are referred to the
work of Manson and of Fülleborn.

One of the most surprising features of the habits of these larvæ is the
periodicity which they exhibit in their occurrence in the peripheral
blood. If a preparation be made during the day time there may be no
evidence whatever of filarial infestation, whereas a preparation from
the same patient taken late in the evening or during the night may be
literally swarming with the parasites. Manson quotes Mackenzie as having
brought out the further interesting fact that should a "filarial subject
be made to sleep during the day and remain awake at night, the
periodicity is reversed; that is to say, the parasites come into the
blood during the day and disappear from it during the night." There have
been numerous attempts to explain this peculiar phenomenon of
periodicity but in spite of objections which have been raised, the most
plausible remains that of Manson, who believes that it is an adaptation
correlated with the life-habits of the liberating agent of the parasite,
the mosquito.

The next stages in the development of _Filaria nocturna_ occur in
mosquitoes, a fact suggested almost simultaneously by Bancroft and
Manson in 1877, and first demonstrated by the latter very soon
thereafter. The experiments were first carried out with _Culex
quinquefasciatus_ (= _fatigans_) as a host, but it is now known that a
number of species of mosquitoes, both anopheline and culicine, may serve
equally well.

When the blood of an infested individual is sucked up and reaches the
stomach of such a mosquito, the larvæ, by very active movements, escape
from their sheaths and within a very few hours actively migrate to the
body cavity of their new host and settle down primarily in the thoracic
muscles. There in the course of sixteen to twenty days they undergo a
metamorphosis of which the more conspicuous features are the formation
of a mouth, an alimentary canal and a trilobed tail. At the same time
there is an enormous increase in size, the larvæ which measured .3 mm.
in the blood becoming 1.5 mm. in length. This developmental period may
be somewhat shortened in some cases and on the other hand may be
considerably extended. The controlling factor seems to be the one of
temperature.

The transformed larvæ then reenter the body cavity and finally the
majority of them reach the interior of the labium (fig. 120). A few
enter the legs and antennæ, and the abdomen, but these are wanderers
which, it is possible, may likewise ultimately reach the labium, where
they await the opportunity to enter their human host.

It was formerly supposed that when the infested mosquito punctured the
skin of man, the mature larvæ were injected into the circulation. The
manner in which this occurred was not obvious, for when the insect feeds
it inserts only the stylets, the labium itself remaining on the surface
of the skin. Fülleborn has cleared up the question by showing that at
this time the filariæ escape and, like the hookworm, actively bore into
the skin of their new host.

[Illustration: 120. Filaria in the muscles and labium of Culex. After
Blanchard.]

Once entered, they migrate to the lymphatics and there quickly become
sexually mature. The full grown females measure 85-90 mm. in length by
.24-.28 mm. in diameter, while the males are less than half this size,
being about 40 mm. by .1 mm. Fecundation occurs and the females will be
found filled with eggs in various stages of development, for they are
normally viviparous.

_Filaria philippinensis_ is reported by Ashburn and Craig (1907) as a
common blood filaria in the Philippine Islands. As they describe it, it
differs from _Filaria bancrofti_ primarily in that it does not exhibit
periodicity. Its development has been found to occur in _Culex
quinquefasciatus_, where it undergoes metamorphosis in about fourteen or
fifteen days. There is doubt as to the species being distinct from
_bancrofti_.

Several other species occur in man and are thought to be transferred by
various insects, among which have been mentioned Tabanidæ and
tsetse-flies, but there is no experimental proof in support of such
conjectures.

_Filaria immitis_ is a dangerous parasite of the dog, the adult worm
living in the heart and veins of this animal. It is one of the species
which has been clearly shown to undergo its development in the mosquito,
particularly in _Anopheles maculipennis_ and _Aedes calopus_ (=
Stegomyia). The larval form occurs in the peripheral blood, especially
at night. When taken up by mosquitoes they differ from _Filaria
bancrofti_ in that they undergo their development in the Malpighian
tubules rather than in the thoracic muscles. In about twelve days they
have completed their growth in the tubules, pierce the distal end, and
pass to the labium. This species occurs primarily in China and Japan,
but is also found in Europe and in the United States. It is an
especially favorable species for studying the transformations in the
mosquito.

[Illustration: 121. Dracunculus medinensis; female; mouth; embryo. After
Bastian and Leuckart.]

_Filariæ_ are also commonly found in birds, and in this country this is
the most available source of laboratory material. We have found them
locally (Ithaca, N. Y.) in the blood of over sixty per cent of all the
crows examined, at any season of the year, and have also found them in
English sparrows.

In the crows, they often occur in enormous numbers, as many as two
thousand having been found in a single drop of the blood of the most
heavily infested specimen examined. For study, a small drop of blood
should be mounted on a clean slide and the coverglass rung with vaseline
or oil to prevent evaporation. In this way they can be kept for hours.

Permanent preparations may be made by spreading out the blood in a film
on a perfectly clean slide and staining. This is easiest done by
touching the fresh drop of blood with the end of a second slide which is
then held at an angle of about 45° to the first slide and drawn over it
without pressure. Allow the smear to dry in the air and stain in the
usual way with hæmatoxylin.


OTHER NEMATODE PARASITES OF MAN AND ANIMALS DEVELOPING IN ARTHROPODS

_Dracunculus medinensis_ (fig. 121), the so-called guinea-worm, is a
nematode parasite of man which is widely distributed in tropical Africa,
Asia, certain parts of Brazil and is occasionally imported into North
America.

The female worm is excessively long and slender, measuring nearly three
feet in length and not more than one-fifteenth of an inch in diameter.
It is found in the subcutaneous connective tissue and when mature
usually migrates to some part of the leg. Here it pierces the skin and
there is formed a small superficial ulcer through which the larvæ reach
the exterior after bursting the body of the mother.

[Illustration: 122. Cyclops, the intermediate host of Dracunculus.]

Fedtschenko (1879) found that when these larvæ reach the water they
penetrate the carapace of the little crustacean, _Cyclops_ (fig. 122).
Here they molt several times and undergo a metamorphosis. Fedtschenko,
in Turkestan, found that these stages required about five weeks, while
Manson who confirmed these general results, found that eight or nine
weeks were required in the cooler climate of England.

Infection of the vertebrate host probably occurs through swallowing
infested cyclops in drinking water. Fedtschenko was unable to
demonstrate this experimentally and objection has been raised against
the theory, but Leiper (1907), and Strassen (1907) succeeded in
infesting monkeys by feeding them on cyclops containing the larvæ.

_Habronema muscæ_ is a worm which has long been known in its larval
stage, as a parasite of the house-fly. Carter found them in 33 per cent
of the house-flies examined in Bombay during July, 1860, and since that
time they have been shown to be very widely distributed. Italian workers
reported them in 12 per cent to 30 per cent of the flies examined.
Hewitt reported finding it rarely in England. In this country it was
first reported by Leidy who found it in about 20 per cent of the flies
examined at Philadelphia, Pa. Since then it has been reported by several
American workers. We have found it at Ithaca, N. Y., but have not made
sufficient examinations to justify stating percentage. Ransom (1913)
reports it in thirty-nine out of one hundred and thirty-seven flies, or
28 per cent.

[Illustration: 123. An Echinorhynchid, showing the spinose retractile
proboscis.]

[Illustration: 124. June beetle (Lachnosterna).]

[Illustration: Larva]

Until very recently the life-history of this parasite was unknown but
the thorough work of Ransom (1911, 1913) has shown clearly that the
adult stage occurs in the stomach of horses. The embryos, produced by
the parent worms in the stomach of the horse, pass out with the feces
and enter the bodies of fly larvæ which are developing in the manure. In
these they reach their final stage of larval development at about the
time the adult flies emerge from the pupal stage. In the adult fly they
are commonly found in the head, frequently in the proboscis, but they
occur also in the thorax and abdomen. Infested flies are accidentally
swallowed by horses and the parasite completes its development to
maturity in the stomach of its definitive host.

_Gigantorhynchus hirudinaceus_ (= _Echinorhynchus gigas_) is a common
parasite of the pig and has been reported as occurring in man. The adult
female is 20-35 cm. long and 4-9 mm. in diameter. It lacks an alimentary
canal and is provided with a strongly spined protractile rostrum, by
means of which it attaches to the intestinal mucosa of its host.

The eggs are scattered with the feces of the host and are taken up by
certain beetle larvæ. In Europe the usual intermediate hosts are the
larvæ of the cockchafer, _Melolontha vulgaris_, or of the flower beetle,
_Cetonia aurata_. Stiles has shown that in the United States the
intermediate host is the larva of the June bug, _Lachnosterna_ (fig.
124). It is probable that several of the native species serve in this
capacity.

A number of other nematode parasites of birds and mammals have been
reported as developing in arthropods but here, as in the case of the
cestodes, experimental proof is scant. The cases above cited are the
better established and will serve as illustrations.




CHAPTER VIII

ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA


MOSQUITOES AND MALARIA

Under the name of malaria is included a group of morbid symptoms
formerly supposed to be due to a miasm or bad air, but now known to be
caused by protozoan parasites of the genus _Plasmodium_, which attack
the red blood corpuscles. It occurs in paroxysms, each marked by a
chill, followed by high fever and sweating. The fever is either
intermittent or remittent.

There are three principal types of the disease, due to different species
of the parasite. They are:

1. The benign-tertian, caused by _Plasmodium vivax_, which undergoes its
schizogony or asexual cycle in the blood in forty-eight hours or even
less. This type of the disease,--characterized by fever every two days,
is the most wide-spread and common.

2. The quartan fever is due to the presence of _Plasmodium malariæ_,
which has an asexual cycle of seventy-two hours, and therefore the fever
recurs every three days. This type is more prevalent in temperate and
sub-tropical regions, but appears to be rare everywhere.

3. The sub-tertian "æstivo-autumnal," or "pernicious" fever is caused by
_Plasmodium falciparum_. Schizogony usually occurs in the internal
organs, particularly in the spleen, instead of in the peripheral
circulation, as is the case of the tertian and quartan forms. The fever
produced is of an irregular type and the period of schizogony has not
been definitely determined. It is claimed by some that the variations
are due to different species of malignant parasites.

It is one of the most wide-spread of human diseases, occurring in almost
all parts of the world, except in the polar regions and in waterless
deserts. It is most prevalent in marshy regions.

So commonplace is malaria that it causes little of the dread inspired by
most of the epidemic diseases, and yet, as Ross says, it is perhaps the
most important of human diseases. Figures regarding its ravages are
astounding. Celli estimated that in Italy it caused an average annual
mortality of fifteen thousand, representing about two million cases. In
India alone, according to Ross (1910) "it has been officially estimated
to cause a mean annual death-rate of five per thousand; that is, to kill
every year, on the average, one million one hundred and thirty
thousand." In the United States it is widespread and though being
restricted as the country develops, it still causes enormous losses.
During the year 1911, "in Alabama alone there were seventy thousand
cases and seven hundred and seventy deaths." The weakening effects of
the disease, the invasion of other diseases due to the attacks of
malaria, are among the very serious results, but they cannot be
estimated.

Not only is there direct effect on man, but the disease has been one of
the greatest factors in retarding the development of certain regions.
Everywhere pioneers have had to face it, and the most fertile regions
have, in many instances been those most fully dominated by it. Herrick
(1903) has presented an interesting study of its effects on the
development of the southern United States and has shown that some parts,
which are among the most fertile in the world, are rendered practically
uninhabitable by the ravages of malaria. Howard (1909) estimates that
the annual money loss from the disease in the United States is not less
than $100,000,000.

It was formerly supposed that the disease was due to a miasm, to a
noxious effluvia, or infectious matter rising in the air from swamps. In
other words its cause was, as the name indicated "mal aria," and the
deep seated fear of night air is based largely on the belief that this
miasm was given off at night. Its production was thought to be favored
by stirring of the soil, dredging operations and the like.

The idea of some intimate connection between malaria and mosquitoes is
not a new one. According to Manson, Lancisi noted that in some parts of
Italy the peasants for centuries have believed that malaria is produced
by the bite of mosquitoes. Celli states that one not rarely hears from
such peasants the statement that "In such a place, there is much fever,
because it is full of mosquitoes." Koch points out that in German East
Africa the natives call malaria and the mosquito by the same name,
_Mbù_. The opinion was not lacking support from medical men. Celli
quotes passages from the writings of the Italian physician, Lancisi,
which indicate that he favored the view in 1717.

Dr. Josiah Nott is almost universally credited with having supported the
theory, in 1848, but as we have already pointed out his work has been
misinterpreted. The statements of Beauperthuy, (1853) were more
explicit.

The clearest early presentation of the circumstantial evidence in favor
of the theory of mosquito transmission was that of A. F. A. King, an
American physician, in 1883. He presented a series of epidemiological
data and showed "how they may be explicable by the supposition that the
mosquito is the real source of the disease, rather than the inhalation
or cutaneous absorption of a marsh vapor." We may well give the space to
summarizing his argument here for it has been so remarkably
substantiated by subsequent work:

1. Malaria, like mosquitoes, affects by preference low and moist
localities, such as swamps, fens, jungles, marshes, etc.

2. Malaria is hardly ever developed at a lower temperature than 60°
Fahr., and such a temperature is necessary for the development of the
mosquito.

3. Mosquitoes, like malaria, may both accumulate in and be obstructed by
forests lying in the course of winds blowing from malarious localities.

4. By atmospheric currents malaria and mosquitoes are alike capable of
being transported for considerable distances.

5. Malaria may be developed in previously healthy places by turning up
the soil, as in making excavations for the foundation of houses, tracks
for railroads, and beds for canals, because these operations afford
breeding places for mosquitoes.

6. In proportion as countries, previously malarious, are cleared up and
thickly settled, periodical fevers disappear, because swamps and pools
are drained so that the mosquito cannot readily find a place suitable to
deposit her eggs.

7. Malaria is most dangerous when the sun is down and the danger of
exposure after sunset is greatly increased by the person exposed
sleeping in the night air. Both facts are readily explicable by the
mosquito malaria theory.

8. In malarial districts the use of fire, both indoors and to those who
sleep out, affords a comparative security against malaria, because of
the destruction of mosquitoes.

9. It is claimed that the air of cities in some way renders the poison
innocuous, for, though a malarial disease may be raging outside, it does
not penetrate far into the interior. We may easily conceive that
mosquitoes, while invading cities during their nocturnal pilgrimages
will be so far arrested by walls and houses, as well as attracted by
lights in the suburbs, that many of them will in this way be prevented
from penetrating "far into the interior."

10. Malarial diseases and likewise mosquitoes are most prevalent toward
the latter part of summer and in the autumn.

11. Various writers have maintained that malaria is arrested by canvas
curtains, gauze veils and mosquito nets and have recommended the rise of
mosquito curtains, "through which malaria can seldom or never pass." It
can hardly be conceived that these intercept marsh-air but they
certainly do protect from mosquitoes.

12. Malaria spares no age, but it affects infants much less frequently
than adults, because young infants are usually carefully housed and
protected from mosquito inoculation.

Correlated with the miasmatic theory was the belief that some animal or
vegetable organism which lived in marshes, produced malaria, and
frequent searches were made for it. Salisbury (1862) thought this
causative organism to be an alga, of the genus _Palmella_; others
attributed it to certain fungi or bacteria.

In 1880, the French physician, Laveran, working in Algeria, discovered
an amoeboid organism in the blood of malarial patients and definitely
established the parasitic nature of this disease. Pigmented granules had
been noted by Meckel as long ago as 1847, in the spleen and blood of a
patient who had died of malaria, and his observations had been
repeatedly verified, but the granules had been regarded as degeneration
products, and the fact that they occurred in the body of a foreign
organism had been overlooked.

Soon after the discovery of the parasites in the blood, Gerhardt (1884)
succeeded in transferring the disease to healthy individuals by
inoculation of malarious blood, and thus proved that it is a true
infection. This was verified by numerous experimenters and it was found
that inoculation with a very minute quantity of the diseased blood would
not only produce malaria but the particular type of disease.

Laveran traced out the life cycle of the malarial parasite as it occurs
in man. The details as we now know them and as they are illustrated by
the accompanying figure 125, are as follows:

The infecting organism or _sporozoite_, is introduced into the
circulation, penetrates a red blood corpuscle, and forms the amoeboid
_schizont_. This lives at the expense of the corpuscle and as it
develops there are deposited in its body scattered black or reddish
black particles. These are generally called melanin granules, but are
much better referred to as hæmozoin, as they are not related to
melanin. The hæmozoin is the most conspicuous part of the parasite, a
feature of advantage in diagnosing from unstained preparations.

[Illustration: 125. Life cycle of the malaria parasite. Adapted from
Leuckart's chart, by Miss Anna Stryke.]

As the schizont matures, its nucleus breaks up into a number of daughter
nuclei, each with a rounded mass of protoplasm about it, and finally the
corpuscles are broken down and these rounded bodies are liberated in the
plasma as _merozoites_. These merozoites infect new corpuscles and thus
the asexual cycle is continued. The malarial paroxysm is coincident with
sporulation.

As early as Laveran's time it was known that under conditions not yet
determined there are to be found in the blood of malarious patients
another phase of the parasite, differing in form according to the type
of the disease. In the pernicious type these appear as large,
crescent-shaped organisms which have commonly been called "crescents."
We now know that these are sexual forms.

When the parasite became known there immediately arose speculations as
to the way in which it was transferred from man to man. It was thought
by some that in nature it occurred as a free-living amoeba, and that
it gained access to man through being taken up with impure water.
However, numerous attempts to infect healthy persons by having them
drink or inhale marsh water, or by injecting it into their circulation
resulted in failure, and influenced by Leuckart's and Melnikoff's work
on _Dipylidium_, that of Fedtschenko on _Dracunculus_, and more
especially by that of Manson on _Filaria_, search was made for some
insect which might transfer the parasite.

Laveran had early suggested that the rôle of carrier might be played by
the mosquito, but Manson first clearly formulated the hypothesis, and it
was largely due to his suggestions that Ross in India, undertook to
solve the problem. With no knowledge of the form or of the appearance in
this stage, or of the species of mosquito concerned, Ross spent almost
two and a half years of the most arduous work in the search and finally
in August, 1897, seventeen years after the discovery of the parasite in
man, he obtained his first definite clue. In dissecting a
"dappled-winged mosquito," "every cell was searched and to my intense
disappointment nothing whatever was found, until I came to the insect's
stomach. Here, however, just as I was about to abandon the examination,
I saw a very delicate circular cell, apparently lying amongst the
ordinary cells of the organ and scarcely distinguishable from them. On
looking further, another and another similar object presented itself. I
now focused the lens carefully on one of these, and found that it
contained a few minute granules of some black substance, exactly like
the pigment of the parasite of malaria. I counted altogether twelve of
these cells in the insect."

Further search showed that "the contents of the mature pigment cells did
not consist of clear fluid but of a multitude of delicate, thread-like
bodies which on the rupture of the parent cell, were poured into the
body cavity of the insect. They were evidently spores."

With these facts established, confirmation and extension of Ross's
results quickly followed, from many different sources. We cannot trace
this work in detail but will only point out that much of the credit is
due to the Italian workers, Grassi, Bignami, and Bastianelli, and to
Koch and Daniels.

It had already been found that when fresh blood was mounted and properly
protected against evaporation, a peculiar change occurred in these
crescents after about half an hour's time. From certain of them there
were pushed out long whip-like processes which moved with a very active,
lashing movement. The parasite at this stage is known as the
"flagellated body." Others, differing somewhat in details of structure,
become rounded but do not give off "flagella."

The American worker, MacCallum (1897), in studying bird malaria as found
in crows, first recognized the true nature of these bodies. He regarded
them as sexual forms and believed that the so-called flagella played the
part of spermatozoa. Thus, the "flagellated body" is in reality a
_microgametoblast_, producing _microgametes_, or the male sexual
element, while the others constitute the _macrogametes_, or female
elements.

It was found that when blood containing these sexual forms was sucked up
by an Anopheline mosquito and taken into its stomach, a microgamete
penetrated and fertilized a macrogamete in a way analogous to what takes
place in the fertilization of the egg in higher forms. The resultant,
mobile organism is known as the _migratory ookinete_. In this stage the
parasite bores through the epithelial lining of the "stomach"
(mid-intestine) of the mosquito and becomes encysted under the muscle
layers. Here the _oocyst_, as it is now known, matures and breaks up
into the body cavity and finally its products come to lie in the
salivary glands of the mosquito. Ten to twelve days are required for
these changes, after which the mosquito is infective, capable of
introducing the parasite with its saliva, when feeding upon a healthy
person.

Thus the malarial parasite is known to have a double cycle, an
alternation of generations, of which the asexual stage is undergone in
man, the sexual in certain species of mosquitoes. The mosquito is
therefore the definitive host rather than the _intermediate_, as usually
stated.

The complicated cycle may be made clearer by the diagram of Miss Stryke
(1912) which, by means of a double-headed mosquito (fig. 126) endeavors
to show how infection takes place through the biting of the human
victim, (at A), in whom asexual multiplication then takes place, and how
the sexual stages, taken up at B in the diagram, are passed in the body
of the mosquito.

[Illustration: 126. Life cycle of the malarial parasite. After Miss Anna
Stryke.]

The experimental proof that mosquitoes of the Anopheline group are
necessary agents in the transmission of malaria was afforded in 1900
when two English physicians, Drs. Sambon and Low lived for the three
most malarial months in the midst of the Roman Campagna, a region
famous for centuries as a hot-bed of malaria. The two experimenters
moved about freely throughout the day, exposed themselves to rains and
all kinds of weather, drank marsh water, slept exposed to the marsh air,
and, in short, did everything which was supposed to cause malaria,
except that they protected themselves thoroughly from mosquito bites,
retiring at sunset to a mosquito-proof hut. Though they took no quinine
and all of their neighbors suffered from malaria, they were absolutely
free from the disease.

To complete the proof, mosquitoes which had fed in Rome on malarious
patients were sent to England and allowed to bite two volunteers, one of
them Dr. Manson's own son, who had not been otherwise exposed to the
disease. Both of these gentlemen contracted typical cases of malaria and
the parasites were to be found in abundance in their blood.

[Illustration: 127. Eggs of Anopheles. After Howard.]

Since that time there have been many practical demonstrations of the
fact that malaria is transmitted exclusively by the bite of mosquitoes
and that the destruction of the mosquitoes means the elimination of the
disease.

We have said that the malarial parasite is able to undergo its
development only in certain species of mosquitoes belonging to the
Anopheline group. It is by no means certain that all of this group even,
are capable of acting as the definitive host of the parasites, and much
careful experiment work is still needed along this line. In the United
States, several species have been found to be implicated, _Anopheles
quadrimaculatus_ and _Anopheles crucians_ being the most common. The
characteristics of these species and the distinctions between them and
other mosquitoes will be discussed in Chapter XII.

In antimalarial work it is desirable to distinguish the anopheline
mosquitoes from the culicine species in all stages. The following
tabulation presents the more striking distinctions between the groups as
represented in the United States.

_Anopheles_                             _Culex, Aedes, etc_.

_Eggs_: Laid singly in small            Deposited in clumps in the
numbers upon the surface of the         form of a raft (Culex group) or
water. Eggs lie upon their sides        deposited singly in the water or
and float by means of lateral           on the ground in places which
expansions (fig. 127).                  may later be submerged.

_Larva_: When at rest floats in         When at rest (with few exceptions)
a horizontal position beneath the       floats suspended in an
surface film. No respiratory            oblique or vertical position, or
tube but instead a flattened            more rarely nearly horizontal,
area on the eighth abdominal            with the respiratory tube in
segment into which the two              contact with the surface film
spiracles open (fig. 128).              (fig. 128).

_Adults_: Palpi in both sexes           Palpi short in the female, in
nearly or quite as long as the          the male usually elongate.
proboscis. Proboscis projecting         Proboscis projects forward at an
forward nearly on line with the         angle with the axis of the body.
axis of the body. When at rest          When at rest on a vertical wall
on a vertical wall the body is          the body is usually held parallel
usually held at an angle with the       or the tip of the abdomen inclined
vertical (fig. 128). Wings frequently   towards the wall (fig. 128).
spotted (fig. 130).                     Wings usually not spotted.

[Illustration: 128. (_a_) Normal position of the larvæ of Culex and
Anopheles in the water. Culex, left; Anopheles, middle; Culex pupa,
right hand figure.]

These malarial-bearing species are essentially domesticated mosquitoes.
They develop in any accumulation of water which stands for a week or
more. Ponds, puddles, rain barrels, horse troughs, cess-pools, cans,
even the foot-prints of animals in marshy ground may afford them
breeding places.

[Illustration: 128. (_b_) Normal position of Culex and Anopheles on the
wall.]

It is clear from what has been said regarding the life cycle of the
malarial parasite that the mosquito is harmless if not itself diseased.
Hence malarial-bearing species may abound in the neighborhood where
there is no malaria, the disease being absent simply because the
mosquitoes are uninfected. Such a locality is potentially malarious and
needs only the introduction of a malarial patient who is exposed to the
mosquitoes. It is found that such patients may harbor the parasites in
their blood long after they are apparently well and thus may serve as a
menace, just as do the so-called typhoid carriers. In some malarious
regions as high as 80-90 per cent of the natives are such
malaria-carriers and must be reckoned with in antimalaria measures.

Based upon our present day knowledge of the life cycle of the malarial
parasite the fight against the disease becomes primarily a problem in
economic entomology,--it is a question of insect control, in its
broadest interpretation.

[Illustration: 129. Larva of Anopheles. After Howard.]

The lines of defence and offence against the disease as outlined by
Boyce (1909) are:

  1. Measures to avoid the reservoir (man):

    Segregation.

    Screening of patients.

  2. Measures to avoid Anopheles:

    Choice of suitable locality, when possible.

    Screening of houses and porches.

    Sleeping under mosquito nets.

  3. Measures to exterminate the Anopheles:

    Use of natural enemies.

    Use of culicides, oiling ponds, etc.

    Drainage and scavenging to destroy breeding places.

    Enforcement of penalties for harboring larvæ or keeping stagnant
      water.

    Educational methods.

  4. Systematic treatment with quinine to exterminate the parasites.


MOSQUITOES AND YELLOW FEVER

Yellow fever was until recently one of the most dreaded of epidemic
diseases. It is an acute, specific and infectious disease,
non-contagious in character but occurring in epidemics, or endemics,
within a peculiarly limited geographical area. It is highly fatal, but
those who recover are generally immune from subsequent attacks.

It is generally regarded as an American disease, having been found by
Cortez, in Mexico, and being confined principally to the American
continents and islands. It also occurs in Africa and attempts have been
made to show that it was originally an African disease but there is not
sufficient evidence to establish this view.

There have been many noted outbreaks in the United States. Boston
suffered from it in 1691 and again in 1693; New York in 1668 and as late
as 1856; Baltimore in 1819. In 1793 occurred the great epidemic in
Philadelphia, with a death rate of one in ten of the population. In the
past century it was present almost every year in some locality of our
Southern States, New Orleans being the greatest sufferer. In the latter
city there were 7848 deaths from the disease in 1853, 4854 in 1858, and
4046 in 1878. The last notable outbreak was in 1905. Reed and Carroll
(1901) estimated that during the period from 1793 to 1900 there had not
been less than 500,000 cases in the United States.

[Illustration: 130. Anopheles quadrimaculatus, male and female,
(×3œ). After Howard.]

As in the case of the plague, the most stringent methods of control
proved ineffective and helplessness, almost hopelessness marked the
great epidemics. A vivid picture of conditions is that given by Mathew
Cary, 1793 (quoted by Kelly, 1906) in "A Short Account of the Malignant
Fever Lately Prevalent in Philadelphia."

[Illustration: 131. Anopheles punctipennis. Female, (×4). After Howard.]

"The consternation of the people of Philadelphia at this period was
carried beyond all bounds. Dismay and affright were visible in the
countenance of almost every person. Of those who remained, many shut
themselves in their houses and were afraid to walk the streets. * * *
The corpses of the most respectable citizens, even those who did not die
of the epidemic, were carried to the grave on the shafts of a chair
(chaise), the horse driven by a negro, unattended by friends or
relative, and without any sort of ceremony. People hastily shifted their
course at the sight of a hearse coming toward them. Many never walked on
the footpath, but went into the middle of the streets to avoid being
infected by passing by houses wherein people had died. Acquaintances and
friends avoided each other in the streets and only signified their
regard by a cold nod. The old custom of shaking hands fell into such
disuse that many shrunk back with affright at even the offer of the
hand. A person with a crape, or any appearance of mourning was shunned
like a viper. And many valued themselves highly on the skill and address
with which they got to the windward of every person they met. Indeed, it
is not probable that London, at the last stage of the plague, exhibited
stronger marks of terror than were to be seen in Philadelphia from the
24th or 25th of August until pretty late in September."

[Illustration: 132. Anopheles crucians. Female (×4). After Howard.]

Such was the condition in Philadelphia in 1793 and, as far as methods of
control of the disease were concerned, there was practically no advance
during the last century. The dominant theory was that yellow fever was
spread by _fomites_, that is, exposed bedding, clothing, baggage, and
the like. As late as 1898 a bulletin of the United States Marine
Hospital Service stated:

"While yellow fever is a communicable disease, it is not contagious in
the ordinary acceptance of the term, but is spread by the infection of
places and articles of bedding, clothing, and furniture."

Based upon this theory, houses, baggage, freight, even mail, were
disinfected, and the most rigid quarantine regulations were enforced.
The hardships to which people of the stricken regions were subjected and
the financial losses are incalculable. And withal, the only efficient
check upon the disease seemed to be the heavy frosts. It was found that
for some reason, the epidemic abated with cold weather,--a measure
beyond human control.

[Illustration: 133. Culex sollicitans. Female (×4). After Howard.]

It is not strange that among the multitude of theories advanced to
explain the cause and method of dissemination of the disease there
should be suggestions that yellow fever was transmitted by the mosquito.
We have seen that Beauperthuy (1855) clearly urged this theory.

More detailed, and of the greatest influence in the final solution of
the problem were the arguments of Dr. Cárlos Finlay, of Havana. In 1881,
in a paper presented before the "Real Academia de Ciencias Médicas,
Físicas y Naturales de la Habana," he said:

"I feel convinced that any theory which attributes the origin and the
propagation of yellow fever to atmospheric influences, to miasmatic or
meteorological conditions, to filth, or to the neglect of general
hygienic precautions, must be considered as utterly indefensible."

He postulated the existence of a material transportable substance
causing yellow fever,--"something tangible which requires to be conveyed
from the sick to the healthy before the disease can be propagated" and
after discussing the peculiarities of the spread of the disease and the
influence of meteorological conditions, he decides that the carriers of
the disease must be sought among insects. He continues:

"On the other hand, the fact of yellow fever being characterized both
clinically and (according to recent findings) histologically, by lesions
of the blood vessels and by alterations of the physical and chemical
conditions of the blood, suggested that the insect which should convey
the infectious particles from the patient to the healthy should be
looked for among those which drive their sting into blood vessels in
order to suck human blood. Finally, by reason of other considerations
which need not be stated here, I came to think that the mosquito might
be the transmitter of yellow fever."

"Assimilating the disease to small-pox and to vaccination, it occurred
to me that in order to inoculate yellow fever it would be necessary to
pick out the inoculable material from within the blood vessels of a
yellow fever patient and to carry it likewise into the interior of a
blood vessel of a person who was to be inoculated. All of which
conditions the mosquito satisfies most admirably through its bite."

In the course of his study of the problem, Finlay made detailed studies
of the life history and habits of the common mosquitoes at Havana, and
arrived at the conclusion that the carrier of the yellow fever was the
_Culex mosquito_ or _Aëdes calopus_, as it is now known. With this
species he undertook direct experimental tests, and believed that he
succeeded in transmitting the disease by the bite of infected mosquitoes
in three cases. Unfortunately, possibility of other exposure was not
absolutely excluded, and the experiments attracted little attention.

Throughout the next twenty years Finlay continued his work on yellow
fever, modifying his original theory somewhat as time went on. Among his
later suggestions was that in the light of Smith's work on Texas fever,
his theory must be "somewhat modified so as to include the important
circumstance that the faculty of transmitting the yellow fever germ need
not be limited to the parent insect, directly contaminated by stinging a
yellow fever patient (or perhaps by contact with or feeding from his
discharges), but may be likewise inherited by the next generation of
mosquitoes issued from the contaminated parent." He believed that the
bite of a single mosquito produced a light attack of the disease and was
thus effective in immunizing the patient. Throughout the period, many
apparently successful attempts to transmit the disease by mosquitoes
were made. In the light of present day knowledge we must regard these as
defective not only because possibility of other infection was not
absolutely excluded but because no account was taken of the incubation
period within the body of the mosquito.

In 1900, while the American army was stationed in Cuba there occurred an
epidemic of yellow fever and an army medical board was appointed for
"the purpose of pursuing scientific investigations with reference to the
acute infectious diseases prevalent on the island." This was headed by
Walter Reed and associated with him were James Carroll, Jesse W. Lazear
and Aristides Agramonte, the latter a Cuban immune. For a detailed
summary of this work the lay reader cannot do better than read Dr.
Kelly's fascinating biography "Walter Reed and Yellow Fever."

Arriving at the army barracks near Havana the Commission first took up
the study of _Bacillus icteroides_, the organism which Sanarelli, an
Italian physician, had declared the causative agent in yellow fever.
They were unable to isolate this bacillus either from the blood during
life or from the blood and organs of cadavers and therefore turned their
attention to Finlay's theory of the propagation of yellow fever by means
of the mosquito. In this work they had the unselfish and enthusiastic
support of Dr. Finlay himself, who not only consulted with them and
placed his publications at their disposal, but furnished eggs from which
their experimental mosquitoes were obtained. Inoculations of eleven
non-immunes through the bite of infected mosquitoes were made, and of
these, two gave positive results. The first of the two was Dr. Carroll
who allowed himself to be bitten by a mosquito which had been caused to
feed upon four cases of yellow fever, two of them severe and two mild.
The first patient had been bitten twelve days before.

Three days after being bitten, Dr. Carroll came down with a typical case
of yellow fever. So severe was the attack that for three days his life
hung in the balance. During his convalescence an incident occurred which
showed how the theory of mosquito transmission of the disease was
generally regarded. We quote from Dr. Kelly: "One of his nurses who came
from Tennessee had had considerable experience with yellow fever, having
indeed, lost her husband and several children from it. One day early in
his illness Dr. Carroll mentioned to her that he had contracted the
disease through the bite of a mosquito, and noticed that she looked
surprised. Some time later, when well enough to look over the daily
records of his condition, he found this entry: 'Says he got his illness
through the bite of a mosquito,--delirious'."

The second case was that of an American who was bitten by four
mosquitoes, two of which had bitten severe (fatal) cases of yellow fever
twelve days previously, one of which had bitten a severe case (second
day) sixteen days before and one which had bitten a severe case eight
days before. Five days later, the subject developed a well pronounced
but mild case of the disease.

In the meantime, another member of the Commission, Dr. Lazear, was
accidentally bitten by a mosquito while collecting blood from yellow
fever patients. Five days later he contracted a typical case which
resulted fatally.

So clear was the evidence from these preliminary experiments that the
commission felt warranted in announcing, October 27, 1900, that, "The
mosquito serves as the intermediate host for the parasite of yellow
fever, and it is highly probable that the disease is only propagated
through the bite of this insect."

In order to extend the experimental evidence under conditions which
could leave no possibility of infection from other sources, a special
experimental sanitary station, named in honor of the deceased member of
the Commission, was established in an open field near the town of
Quemados, Cuba. Here there were constructed two small buildings known
respectively as the "infected clothing building" and the "infected
mosquito building."

The infected clothing building, 14 × 20 feet in size, was purposely so
constructed as to exclude anything like efficient ventilation, but was
thoroughly screened to prevent the entrance of mosquitoes. Into this
building were brought sheets, pillow-slips, blankets, etc., contaminated
by contact with cases of yellow fever and their discharges,--many of
them purposely soiled with a liberal quantity of black vomit, urine, and
fecal matter from patients sick with yellow fever. Nothing could better
serve as the fomites which were supposed to convey the dread disease.

Three non-immunes unpacked these articles, giving each a thorough
handling and shaking in order to disseminate through the air of the room
the specific agent of the disease. They were then used in making up the
beds which the volunteers occupied each night for a period of twenty
days. The experiment was repeated three times, volunteers even sleeping
in the soiled garments of yellow fever victims but in not a single case
was there the slightest symptom of disease. The theory of the spread of
yellow fever by fomites was completely demolished.

The infected mosquito building, equal in size to its companion, was the
antithesis as far as other features were concerned. It was so
constructed as to give the best possible ventilation, and bedding which
was brought into it was thoroughly sterilized. Like the infected
clothing building it was carefully screened, but in this case it was in
order to keep mosquitoes in it as well as to prevent entrance of others.
Through the middle of the room ran a mosquito-proof screen.

On December 5, 1900, a non-immune volunteer who had been in the
quarantine camp for fifteen days and had had no other possible exposure,
allowed himself to be bitten by five mosquitoes which had fed on yellow
fever patients fifteen or more days previously. The results were fully
confirmatory of the earlier experiments of the Commission--at the end of
three days, nine and a half hours, the subject came down with a well
marked case of yellow fever.

In all, ten cases of experimental yellow fever, caused by the bite of
infected mosquitoes were developed in Camp Lazear. Throughout the period
of the disease, other non-immunes slept in the little building,
separated from the patient only by the mosquito-proof screen, but in no
circumstances did they suffer any ill effects.

It was found that a yellow fever patient was capable of infecting
mosquitoes only during the first three or four days after coming down
with the disease. Moreover, after the mosquito has bitten such a
patient, a period of at least twelve days must elapse before the insect
is capable of transmitting the disease.

Once the organism has undergone its twelve day development, the mosquito
may remain infective for weeks. In experiments of the Commission, two of
the mosquitoes transmitted the disease to a volunteer fifty-seven days
after their contamination. No other volunteers presenting themselves,
one of these mosquitoes died the sixty-ninth and one the seventy-first
day after their original contamination, without it being determined
whether they were still capable of transmitting the disease.

So carefully carried out was this work and so conclusive were the
results that Dr. Reed was justified in writing:

"Six months ago, when we landed on this island, absolutely nothing was
known concerning the propagation and spread of yellow fever--it was all
an unfathomable mystery--but today the curtain has been drawn--its mode
of propagation is established and we know that a case minus mosquitoes
is no more dangerous than one of chills and fever."

The conclusions of the Commission were fully substantiated by numerous
workers, notably Dr. Guiteras of the Havana Board of Health, who had
taken a lively interest in the work and whose results were made known in
1901, and by the Brazilian and French Commission at Sao Paulo, Brazil,
in 1903.

Throughout the work of the Army Commission and down to the present time
many fruitless efforts have been made to discover the specific organism
of yellow fever. It was clearly established that the claims of Sanarelli
for _Bacillus icteroides_ were without foundation. It was found, too,
that whatever the infective agent might be it was capable of passing
through a Berkefeld filter and thus belongs to the puzzling group of
"filterable viruses." It was further found that the virus was destroyed
by heating up to 55° C for ten minutes. It is generally believed that
the organism is a Protozoan.

The question of the hereditary transmission of the yellow fever organism
within the mosquito was left unsettled by the Army Commission, though,
as we have seen, it was raised by Finlay. Marchoux and Simond, of the
French Commission devoted much attention to this phase of the problem
and basing their conclusions on one apparently positive case, they
decided that the disease could be transmitted through the egg of an
infected _Aëdes calopus_ to the second generation and thence to man. The
conclusion, which is of very great importance in the control of yellow
fever, has not been verified by other workers.

Once clearly established that yellow fever was transmitted solely by
mosquitoes, the question of the characteristics, habits, and
geographical distribution of the insect carrier became of vital
importance.

_Aëdes calopus_, more commonly known as _Stegomyia fasciata_ or
_Stegomyia calopus_ (fig. 134) is a moderate sized, rather strikingly
marked mosquito. The general color is dark-brown or reddish-brown, but
the thorax has a conspicuous broad, silvery-white curved line on each
side, with two parallel median silvery lines. Between the latter there
is a slender, broken line. The whole gives a lyre-shaped pattern to the
thorax. The abdomen is dark with silvery-white basal bands and silvery
white spots on each side of the abdominal segments. Legs black with
rings of pure white at the base of the segments.

Size of the female 3.3 to 5 mm.; male 3 to 4.5 mm.

[Illustration: 134. The yellow fever mosquito (Aëdes calopus). (×7).
After Howard.]

It is preeminently a domesticated species, being found almost
exclusively about the habitation of man. "Its long association with man
is shown by many of its habits. It approaches stealthily from behind. It
retreats upon the slightest alarm. The ankles and, when one is sitting
at a table or desk, the underside of the hands and wrists are favorable
points of attack. It attacks silently, whereas other mosquitoes have a
piping or humming note. The warning sound has doubtless been suppressed
in the evolutionary process of its adaptation to man. It is extremely
wary. It hides whenever it can, concealing itself in garments, working
into the pockets, and under the lapels of coats, and crawling up under
the clothes to bite the legs. In houses, it will hide in dark corners,
under picture moldings and behind the heads of old-fashioned bedsteads.
It will enter closets and hide in the folds of garments."--Howard.

It was claimed by the French Commission, and subsequently often stated
in discussions of the relation of the mosquito to yellow fever that the
mature _Aëdes calopus_ will bite only at night. If this were true it
would be of the greatest importance in measures to avoid the disease.
Unfortunately, the claim was illy founded and numerous workers have
clearly established that the exact converse is more nearly true, this
mosquito being pre-eminently a day species, feeding most actively in
early morning, about sunrise, and late in the afternoon. On cloudy days
it attacks at any time during the day. Thus there is peril in the
doctrine that infected regions may be visited with perfect safety during
the daytime and that measures to avoid the mosquito attack need be taken
only at night.

[Illustration: 135_a_. Aëdes calopus. Pupa. After Howard.]

Dr. Finlay maintained that the adult, even when starved, would not bite
when the temperature was below 23° C, but subsequent studies have shown
that this statement needs modification. The French Commission, working
at Rio de Janeiro, found that _Aëdes calopus_ would bite regularly at
temperatures between 22° and 25° and that the optimum temperature was
between 27° and 30° C, but their experiments led them to believe that it
would bite in nature at a temperature as low as 17° C.

The yellow fever mosquito breeds in cisterns, water barrels, pitchers
and in the various water receptacles about the house. In our own
Southern States it very commonly breeds in the above-ground cisterns
which are in general use. Often the larvæ (fig. 135b) are found in
flower vases, or even in the little cups of water which are placed under
the legs of tables to prevent their being overrun by ants. They have
been repeatedly found breeding in the holy water font in churches. In
short, they breed in any collection of water in close proximity to the
dwellings or gathering places of man.

The life cycle under favorable conditions is completed in from twelve to
fifteen days. These figures are of course very dependent upon the
temperature. The Army Commission in Cuba found that the cycle might be
completed in as brief a period as nine and a half days. Under less
favorable conditions it may be greatly lengthened.

The adults are long lived. We have seen that during the experimental
work in Cuba specimens were kept in captivity for sixty-nine and
seventy-one days, respectively, and that they were proved to retain
their infectivity for at least fifty-seven days. Dr. Guiteras
subsequently kept an infected adult for one hundred and fifty-four days.

Low temperatures have a very great effect not only on development, but
on the activity and even life of the adults. Long before the method of
transmission of yellow fever was discovered it was well known that the
epidemics were brought to a close by heavy frosts, and it is now known
that this is due to the killing of the mosquitoes which alone could
spread the disease.

[Illustration: 135_b_. Aëdes calopus; larva. (×7). After Howard.]

_Aëdes calopus_ has a very wide distribution since, as Howard says,
being a domestic mosquito, having a fairly long life in the adult stage,
and having the custom of hiding itself in the most ingenious ways, it is
particularly subject to carriage for long distances on board vessels, in
railway trains, even packed in baggage. In general, its permanent
distribution is from 40 degrees north latitude to 40 degrees south
latitude (Brumpt), in a belt extending around the world. In the United
States it breeds in most of our Southern States.

Thus, as in the case of malaria, there are many places where the insect
carrier is abundant but where yellow fever does not occur. Such, for
instance, are Hawaii, Australia and Asia. An outbreak may occur at any
time that a patient suffering from the disease is allowed to enter and
become a source of infection for the mosquitoes. In this connection
various writers have called attention to the menace from the Panama
Canal. When it is completed, it will allow of direct passage from
regions where yellow fever is endemic and this will greatly increase the
possibility of its introduction into these places where it is now
unknown. The result, with a wholly non-immune population, would be
appalling.

On the other hand, there are places wholly outside of the normal range
of _Aëdes calopus_ where the disease has raged. Such are New York,
Boston, and even Philadelphia, which have suffered notable epidemics.
These outbreaks have been due to the introduction of infected mosquitoes
during the heat of summer, when they have not only conveyed the disease
but have found conditions favorable for their multiplication. Or,
uninfected mosquitoes have been thus accidentally brought in and
developed in large numbers, needing then only the accidental
introduction of cases of the disease to start an epidemic.

Methods of control of various diseases have been revolutionized by the
discovery that they were insect-borne, but in no other case has the
change been as radical or the results as spectacular as in the case of
yellow fever. The "shot-gun quarantine," the sufferings and horrors, the
hopelessness of fighting absolutely blindly have given way to an
efficient, clear-cut method of control, based upon the knowledge that
the disease is carried from man to man solely by the mosquito, _Aëdes
calopus_. The lines of defense and offense are essentially as follows:

In the first place, when a case of yellow fever occurs, stringent
precautions must be adopted to prevent the infection of mosquitoes and
the escape of any already infected. This means that the patient must be
removed to a mosquito-proof room, or ward beyond reach of the insects,
and that the infected room must be thoroughly fumigated at once, to kill
the mosquitoes hiding within it. All cracks and openings should be
closed with strips of paper and fumigation with burning sulphur or
pyrethrum carefully carried out.

It should be remembered that if the first case noted is that of a
resident rather than imported, it means that the mosquito carriers
became infected more than two weeks before the case was diagnosed, for
as we have seen, the germ must undergo a twelve-day period of
development within its insect host. Therefore a careful search must be
made for mild cases which, though unrecognized, may serve as foci for
the spread of the disease.

In face of a threatened epidemic one of the most essential measures is
to educate the citizens and to gain their complete coöperation in the
fight along modern lines. This may be done through the schools, the
pulpit, places of amusement, newspapers and even bulletin boards.

Emphasis should be placed on the necessity of both non-immunes and
immunes using mosquito curtains, and in all possible ways avoiding
exposure to the mosquitoes.

Then the backbone of the fight must be the anti-mosquito measures. In
general, these involve screening and fumigating against adults, and
control of water supply, oiling, and drainage against the larvæ. The
region involved must be districted and a thorough survey undertaken to
locate breeding places, which must, if possible, be eradicated. If they
are necessary for water supplies, such as casks, or cisterns, they
should be carefully screened to prevent access of egg-laying adults.

The practical results of anti-mosquito measures in the fight against
yellow fever are well illustrated by the classic examples of the work in
Havana, immediately following the discoveries of the Army Commission and
by the stamping out of the New Orleans epidemic in 1905.

The opportunities for an immediate practical application of the theories
of the Army Commission in Havana were ideal. The city had always been a
hotbed of yellow fever and was the principal source from which the
disease was introduced year after year into our Southern States. It was
under martial law and with a military governor who was himself a
physician and thoroughly in sympathy with the views of the Commission,
the rigid enforcement of the necessary regulations was possible. The
story of the first campaign has been often told, but nowhere more
clearly than in Dr. Reed's own account, published in the _Journal of
Hygiene_ for 1902.

Closer home was the demonstration of the efficacy of these measures in
controlling the yellow fever outbreak in New Orleans in 1905. During the
spring and early summer of the year the disease had, unperceived, gained
a firm foothold in that city and when, in early July the local Board of
Health took cognizance of its existence, it was estimated that there had
been in the neighborhood of one hundred cases.

Conditions were not as favorable as they had been under martial law in
Havana for carrying on a rigid fight along anti-mosquito lines. The
densely populated city was unprepared, the public had to be educated,
and an efficient organization built up. The local authorities actively
began a general fight against the mosquito but in spite of their best
efforts the disease continued to spread. It was recognized that more
rigid organization was needed and on August 12th the United States
Public Health and Marine Hospital Service was put in absolute charge of
the fight. Up to this time there had been one hundred and forty-two
deaths from a total of nine hundred and thirteen cases and all of the
conditions seemed to threaten an outbreak to exceed the memorable one of
1878 when, as we have seen there were four thousand and forty-six
deaths.

With the hearty coöperation of the citizens,--physicians and laymen
alike,--the fight was waged and long before frost or any near approach
thereto the disease was stamped out,--a thing unheard of in previous
epidemics. The total loss of life was four hundred and sixty--about 11
per cent as great as that from the comparable epidemic of 1878. If the
disease had been promptly recognized and combated with the energy which
marked the fight later in the summer, the outbreak would have made
little headway and the great proportion of these lives would have been
saved.




CHAPTER IX

ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA (Continued)


INSECTS AND TRYPANOSOMIASES

By trypanosomiasis is meant a condition of animal parasitism, common to
man and the lower animals, in which trypanosomes, peculiar flagellate
protozoa, infest the blood. Depending upon the species, they may be
harmless, producing no appreciable ill-effect, or pathogenic, giving
rise to conditions of disease. A number of these are known to be
transferred by insects.

In order that we may consider more fully the developmental stage of
these parasites within their insect host, it is necessary that we
describe briefly the structure of the blood-inhabiting stage.

[Illustration: 136. Trypanosoma brucei. After Bruce.]

The trypanosomes are elongated, usually pointed, flagellated protozoa
(fig. 136) in which the single flagellum, bent under the body, forms the
outer limit of a delicate undulating membrane. It arises near one end of
the organism from a minute centrosome-like body which is known as the
blepheroplast, and at the opposite end extends for a greater or less
distance as a free flagellum. Enclosing, or close beside the
blepheroplast is the small kinetonucleus. The principal nucleus, round
or oval in form, is situated near the center of the body. Asexual
reproductions occurs in this stage, by longitudinal fission, the nucleus
and the blepheroplast dividing independently of one another. From the
blepheroplast of one of the daughter cells a new flagellum is formed.

Among the pathogenic species are to be found the causative organisms of
some of the most serious diseases of domestic animals and even of man.
It is probable that these pathogenic species secrete a specific poison.
The majority of them are tropical in distribution.

Though we are concerned especially with the species which infest man, we
shall first consider two of the trypanosomes of lower animals, known
long before any of those of man had been found.


FLEAS AND LICE AS CARRIERS OF TRYPANOSOMA LEWISI.--_Trypanosoma lewisi_,
the first mammalian trypanosome known, is to be found in the blood of
wild rats. Like its host, it appears to be cosmopolitan in distribution,
having been reported from several localities in the United States,
Brazil, Argentine, England, Germany, France, Italy, Russia, Asia and
Africa.

This species is usually regarded as non-pathogenic, but in experimental
work, especially with white rats, heavy infestations often result
fatally, and naturally infested specimens sometimes show evidence of
injury. Rats which have been infested exhibit at least temporary
immunity against new infection.

_Trypanosoma lewisi_ is transmitted from rat to rat by fleas and by
lice. Rabinowitsch and Kempner (1899) first found that healthy rats
which were kept with infested rats, showed trypanosomes in their blood
after about two weeks. They found the trypanosomes in the alimentary
canal of fleas which had fed on the diseased rats. On teasing such fleas
in physiological salt solution and inoculating them into fresh rats they
were able to produce the infection. Finally, they showed that the fleas
which had fed upon infested rats were able to carry the parasites to
healthy rats. Corresponding experiments with lice were not successful.
Prowazek (1905) found in the rat louse (_Hæmatopinus spinulosus_)
organisms which he regarded as developmental stages of the _Trypanosoma
lewisi_. He believed that the sexual cycle was undergone in this insect.

Nuttall (1908) readily transmitted the trypanosomes through the agency
of fleas, (_Ceratophyllus fasciatus_ and _Ctenopthalmus agyrtes_). He
believes that these insects are probably the chief transmitters of the
parasite. He was also able to transmit it from diseased to healthy rats
through the agency of the rat louse. He was unable to trace any
developmental stages in the louse and inclined to the opinion that
Prowazek was deceived by the presence of extraneous flagellates such as
are known to exist in a number of blood-sucking arthropods.

Nuttall concludes that since three distinct kinds of blood-sucking
insects are capable of transmitting _Trypanosoma lewisi_ it appears
doubtful that this flagellate is a parasite of the invertebrate "host"
in the sense claimed by Prowazek and other investigators.


TSETSE-FLIES AND NAGANA--One of the greatest factors in retarding the
development of certain regions of Africa has been the presence of a
small fly, little larger than the common house-fly. This is the
tsetse-fly, _Glossina morsitans_ (fig. 165) renowned on account of the
supposed virulence of its bite for cattle, horses and other domestic
mammals.

The technical characteristics of the tsetse-flies, or Glossinas, and
their several species, will be found in a later chapter. We need
emphasize only that they are blood-sucking Muscidæ and that, unlike the
mosquitoes, the sexes resemble each other closely in structure of the
mouth-parts, and in feeding habits.

In 1894, Colonel David Bruce discovered that the fly was not in itself
poisonous but that the deadly effect of its bite was due to the fact
that it transmitted a highly pathogenic blood parasite, _Trypanosoma
brucei_. This trypanosome Bruce had discovered in the blood of South
African cattle suffering from a highly fatal disease known as "nagana".
On inoculating the blood of infected cattle into horses and dogs he
produced the disease and found the blood teeming with the causative
organism. In the course of his work he established beyond question that
the "nagana" and the tsetse-fly disease were identical.

Tsetse-flies of the species _Glossina morsitans_, which fed upon
diseased animals, were found capable of giving rise to the disease in
healthy animals up to forty-eight hours after feeding. Wild tsetse-flies
taken from an infected region to a region where they did not normally
occur were able to transmit the disease to healthy animals. It was found
that many of the wild animals in the tsetse-fly regions harbored
_Trypanosoma brucei_ in their blood, though they showed no evidence of
disease. As in the case of natives of malarial districts, these animals
acted as reservoirs of the parasite. Non-immune animals subjected to the
attacks of the insect carrier, quickly succumbed to the disease.

A question of prime importance is as to whether the insect serves as an
essential host of the pathogenic protozoan or whether it is a mere
mechanical carrier. Bruce inclined to the latter view. He was unable to
find living trypanosomes in the intestines or excrements of the fly or
to produce the disease on the many occasions when he injected the
excrement into healthy animals. Moreover, he had found that the
experimental flies were infective only during the first forty-eight
hours and that if wild flies were taken from the infected region, "kept
without food for three days and then fed on a healthy dog, they never
gave rise to the disease."

Koch had early described what he regarded as sexual forms from the
intestine of the fly but it remained for Kleine (1909) to experimentally
demonstrate that a part of the life cycle of the parasite was undergone
in the fly. Working with _Glossina palpalis_, he found that for a period
of ten days or longer after feeding on an animal suffering from nagana
it was non-infective, but that then it became infective and was able to
transmit the disease for weeks thereafter. He discovered and described
developmental stages of the parasite within the intestine of the insect.
In other words, the tsetse-fly (in nature, _Glossina morsitans_), serves
as an essential host, within which an important part of the life cycle
of the parasite is undergone. These conclusions were quickly verified by
Bruce and numerous other workers and are no longer open to question.
Klein and Taute are even inclined to think that mechanical transmission
plays practically no rôle in nature, unless the fly is interrupted while
feeding and passes immediately to a new animal.


TSETSE-FLIES AND SLEEPING SICKNESS OF MAN--About the beginning of the
present century a hitherto little known disease of man began to attract
great attention on account of its ravages in Uganda and the region of
Victoria Nyanza in South Africa. It was slow, insiduous and absolutely
fatal, characterized in its later stages by dullness, apathy, and
finally absolute lethargy all day long, symptoms which gave it the name
of "sleeping sickness."

It was soon found that the disease was not a new one but that it had
been known for over a hundred years on the west coast of Africa. Its
introduction into Central and East Africa and its rapid spread have been
attributed primarily to the development of the country, the formation of
new trade routes and the free mingling of native tribes formerly
isolated. It is estimated that in the first ten years of the present
century there were approximately two hundred thousand deaths from the
disease in the Uganda protectorate. In the British province Bugosa, on
the Victoria Nyanza there were thirty thousand deaths in the period from
1902-1905.

While the disease is peculiarly African there are a number of instances
of its accidental introduction into temperate regions. Slaves suffering
from it were occasionally brought to America in the early part of the
last century and cases have sometimes been imported into England. In
none of the cases did the disease gain a foothold or spread at all to
other individuals.

In 1902 Dutton described a trypanosome, _T. gambiense_, which he and
Forde had found the year before in the blood of a patient suffering from
a peculiar type of fever in Gambia. In 1902-1903 Castellani found the
same parasite in the cerebro-spinal fluid of sleeping-sickness patients
and definitely reported it as the causative organism of the disease. His
work soon found abundant confirmation, and it was discovered that the
sleeping sickness was but the ultimate phase of the fever discovered by
Dutton and Forde.

When Castellani made known his discovery of the trypanosome of sleeping
sickness, Brumpt, in France, and Sambon, in England, independently
advanced the theory that the disease was transmitted by the tsetse-fly,
_Glossina palpalis_. This theory was based upon the geographical
distribution and epidemiology of the disease. Since then it has been
abundantly verified by experimental evidence.

Fortunately for the elucidation of problems relating to the methods of
transfer of sleeping sickness, _Trypanosoma gambiense_ is pathogenic for
many species of animals. In monkeys it produces symptoms very similar to
those caused in man. Bruce early showed that _Glossina palpalis_ "fed on
healthy monkeys eight, twelve, twenty-four and forty-eight hours after
having fed on a native suffering from trypanosomiasis, invariably
transmitted the disease. After three days the flies failed to transmit
it." In his summary in Osler's Modern Medicine, he continues "But this
is not the only proof that these flies can carry the infective agent. On
the lake shore there was a large native population among whom we had
found about one-third to be harboring trypanosomes in their blood. The
tsetse-flies caught on this lake shore, brought to the laboratory in
cages, and placed straightway on healthy monkeys, gave them the disease
in every instance, and furnished a startling proof of the danger of
loitering along the lake shore among those infected flies."

As in the case of nagana, Bruce and most of the earlier investigators
supposed the transmission of the sleeping sickness trypanosome by
_Glossina palpalis_ to be purely mechanical. The work of Kleine (1909)
clearly showed that for _Trypanosoma gambiense_ as well as for
_Trypanosoma brucei_ the fly served as an essential host. Indeed, Kleine
and many subsequent investigators are inclined to think that there is
practically no mechanical transmission of trypanosomes from animal to
animal by _Glossina_ in nature, and that the many successful experiments
of the earlier investigators were due to the fact that they used wild
flies which already harbored the transformed parasite rather than
directly inoculated it from the blood of the diseased experimental
animals. While the criticism is applicable to some of the work, this
extreme view is not fully justified by the evidence at hand.

Kleine states (1912) that _Glossina palpalis_ can no longer be regarded
as the sole transmitter of sleeping sickness. Taute (1911) had shown
that under experimental conditions _Glossina morsitans_ was capable of
transferring the disease and Kleine calls attention to the fact that in
German East Africa, in the district of the Rovuma River, at least a
dozen cases of the disease have occurred recently, though only _Glossina
morsitans_ exists in the district. It appears, however, that these cases
are due to a different parasite, _Trypanosoma rhodesiense_. This
species, found especially in north-east Rhodesia and in Nyassaland, is
transferred by _Glossina morsitans_.

Other workers maintain that the disease may be transmitted by various
blood-sucking flies, or even bugs and lice which attack man. Fülleborn
and Mayer (1907) have shown by conclusive experiments that _Aedes
(Stegomyia) calopus_ may transmit it from one animal to another if the
two bites immediately succeed each other.

It is not possible that insects other than the tsetse-flies (and only
certain species of these), play an important rôle in the transmission of
the disease, else it would be much more wide-spread. Sambon (1908)
pointed out that the hypothesis that is spread by _Aedes calopus_ is
opposed by the fact that the disease never spread in the Antilles,
though frequently imported there by West African slaves. The same
observation would apply also to conditions in our own Southern States in
the early part of the past century.

Since _Glossina palpalis_ acts as an essential host of the parasite and
the chief, if not the only, transmitter, the fight against sleeping
sickness, like that against malaria and yellow fever, becomes primarily
a problem in economic entomology. The minutest detail of the
life-history, biology, and habits of the fly, and of its parasites and
other natural enemies becomes of importance in attempts to eradicate the
disease. Here we can consider only the general features of the subject.

_Glossina palpalis_ lives in limited areas, where the forest and
undergrowth is dense, along the lake shore or river banks. According to
Hodges, the natural range from shore is under thirty yards, though the
distance to which the flies may follow man greatly exceed this.

It is a day feeder, a fact which may be taken advantage of in avoiding
exposure to its attacks. The young are brought forth alive and
full-grown, one every nine or ten days. Without feeding, they enter the
ground and under favorable conditions, complete their development in a
month or more.

[Illustration: 137. Sleeping sickness concentration camp in German East
Africa. Report of German Commission.]

Methods of control of the disease must look to the prevention of
infection of the flies, and to their avoidance and destruction. Along
the first line, much was hoped from temporary segregation of the sick in
regions where the fly was not found. On the assumption that the flies
acted as carriers only during the first two or three days, it was
supposed that even the "fly belts" would become safe within a few days
after the sick were removed. The problem was found to be a much more
difficult one when it was learned that after a given brief period the
fly again became infective and remained so for an indeterminate period.
Nevertheless, isolation of the sick is one of the most important
measures in preventing the spread of the disease into new districts.
Much, too, is being accomplished by moving native villages from the fly
belts. (c.f. fig. 137.)

All measures to avoid the flies should be adopted. This means locating
and avoiding the fly belts as far as possible, careful screening of
houses, and protection of the body against bites.

Clearing the jungle along the water courses for some yards beyond the
natural range of the fly has proved a very important measure. Castellani
recommends that the area be one hundred yards and around a village three
hundred yards at least.

Detailed studies of the parasites and the natural enemies of the
tsetse-fly are being undertaken and may ultimately yield valuable
results.


SOUTH AMERICAN TRYPANOSOMIASIS--The tsetse-flies are distinctively
African in distribution and until recently there were no trypanosomes
known to infest man in America. In 1909 Dr. Chagas, of Rio de Janeiro
described a new species, _Trypanosoma cruzi_, pathogenic to man.

_Trypanosoma cruzi_ is the causative organism of a disease common in
some regions of Brazil, where it is known as "opilacao." It is
especially to be met with in children and is characterized by extreme
anemia, wasting, and stunted development associated with fever, and
enlargement of the thyroid glands. The disease is transmitted by the
bites of several species of assassin-bugs, or Reduviidæ, notably by
_Conorhinus megistus_. The evolution of the parasite within the bug has
been studied especially by Chagas and by Brumpt. From the latter's text
we take the following summary.

The adult trypanosomes, ingested by a _Conorhinus megistus_, of any
stage, first change into Crithidia-like forms and then those which
remain in the stomach become ovoid and non-motile. Brumpt found these
forms in immense numbers, in a _Conorhinus_ which had been infested
fourteen months before. The forms which pass into the intestine quickly
assume the _Crithidia_ form and continue to develop rapidly under this
form. Some weeks later they evolve into the trypanosome forms,
pathogenic for man. They then pass out with the excrement of the bug and
infect the vertebrate host as soon as they come in contact with any
mucous layer (buccal, ocular or rectal). More rarely they enter through
the epidermis.

Brumpt showed that the development could take place in three species;
bed-bugs (_Cimex lectularius_, _C. hemipterus_) and in the tick
_Ornithodoros moubata_. The evolution proceeds in the first two species
of bed-bugs as rapidly as in Conorhinus, or even more rapidly, but they
remain infective for a much shorter time and hence Brumpt considers that
they play a much less important rôle in the spread of the disease.

_Conorhinus megistus_, like related forms in our Southern States, very
commonly frequents houses and attacks man with avidity. Chagas states
that the bites are painless and do not leave any traces. They are
usually inflicted on the lips, or the cheeks and thus the buccal mucosa
of a sleeper may be soiled by the dejections of the insect and the bite
serving as a port of entry of the virus, remain unnoticed.

The possibility of some of our North American Reduviidæ playing a
similar rôle in the transmission of disease should not be overlooked.


LEISHMANIOSES AND INSECTS--Closely related to the trypanosomes is a
group of intracellular parasites which have recently been grouped by
Ross under the genus _Leishmania_. Five species are known to affect man.
Three of these produce local skin infestations, but two of them,
_Leishmania donovani_ and _L. infantum_, produce serious and often fatal
systemic diseases.

The first of these, that produced by _L. donovani_, is an exceedingly
virulent disease common in certain regions of India and China. It is
commonly known as "Kala-azar," or "dum-dum" fever, and more technically
as tropical leishmaniasis. Patton (1907) believes that the parasite is
transmitted by the bed-bug _Cimex hemipterus_, and has described a
developmental cycle similar to that which can be found in artificial
cultures. On the other hand, Donovan was unable to confirm Patton's work
and believes that the true intermediate host is a Reduviid bug,
_Conorhinus rubrofasciatus_.

_Leishmania infantum_ is the cause of the so-called infantile splenic
leishmaniasis, occurring in northern Africa, Spain, Portugal, Italy, and
possibly other parts of Europe. The parasite occurs habitually in the
dog and is only accidentally transferred to children. Alvares and da
Silva, in Portugal (according to Brumpt, 1913) have found that the
excrement of a flea from a diseased dog contains flagellates, and they
suggest that the infection may be transmitted by the accidental
inoculation of this excrement by means of the proboscis of the flea, as
has been thought to occur in the case of the plague. To this Brumpt
objects that they and other workers who thought to trace the development
of _Leishmania infantum_ were apparently misled by the presence of a
harmless _Herpetomonas_ which infests dog fleas in all countries, even
where the leishmaniasis is unknown.

Basile (1910 and 1911) however, carried on numerous experiments
indicating that the disease was transferred from children to dogs and
from dog to dog by the dog flea, and was able to find in the tissues of
the insects forms perfectly identical with those found in children and
in dogs suffering from leishmaniasis. He also found that _Pulex
irritans_ was capable of acting as the carrier.

Of the cutaneous type of leishmaniasis, the best known is the so-called
"Oriental sore," an ulcerative disease of the skin which is epidemic in
many tropical and subtropical regions. The causative organism is
_Leishmania tropica_, which occurs in the diseased tissues as bodies
very similar to those found in the spleen in cases of Kala-azar. The
disease is readily inoculable and there is no doubt that it may be
transferred from the open sores to abraded surfaces of a healthy
individual by house-flies. It is also believed by a number of
investigators that it may be transferred and directly inoculated by
various blood-sucking insects.


TICKS AND DISEASES OF MAN AND ANIMALS

We have seen that the way to the discoveries of the relations of
arthropods to disease was pointed out by the work of Leuckart and
Melnikoff on the life cycle of _Dipylidium_, and of Fedtschenko and
Manson on that of _Filaria_. They dealt with grosser forms, belonging to
well-recognized parasitic groups.

This was long before the rôle of any insect as a carrier of pathogenic
micro-organisms had been established, and before the Protozoa were
generally regarded as of importance in the causation of disease. The
next important step was taken in 1889 when Smith and Kilbourne
conclusively showed that the so-called Texas fever of cattle, in the
United States, is due to an intracorpuscular blood parasite transmitted
exclusively by a tick. This discovery, antedating by eight years the
work on the relation of the mosquito to malaria, had a very great
influence on subsequent studies along these lines.

While much of the recent work has dealt with the true insects, or
hexapods, it is now known that several of the most serious diseases of
animals, and at least two important diseases of man are tick borne.
These belong to the types known collectively as _babesioses_ (or
"_piroplasmoses_"), and _spirochætoses_.

The term _babesiosis_ is applied to a disease of man or animals which is
caused by minute protozoan parasites of the genus _Babesia_, living in
the red blood corpuscles. These parasites have usually been given the
generic name _Piroplasma_ and hence the type of disease which they cause
is often referred to as "_piroplasmosis_." The best known illustration
is the disease known in this country as Texas fever of cattle.


CATTLE TICKS AND TEXAS FEVER--The cattle disease, which in the United
States is known as Texas fever, is a widely distributed, exceedingly
acute disease. In Australia it is known as _redwater fever_ and in
Europe as hæmoglobinuria, due to the fact that the urine of the diseased
animals is discolored by the breaking down of the red blood corpuscles
infested by the parasite.

In their historical discussion, Smith and Kilbourne, point out that as
far back as 1796 it was noted that Southern cattle, in a state of
apparent health, might spread a fatal disease among Northern herds. As
observations accumulated, it was learned that this infection was carried
only during the warm season of the year and in the depth of winter
Southern cattle were harmless. Moreover, Southern cattle after remaining
for a short time in the North lost their power to transmit the disease,
and the same was true of cattle which had been driven for a considerable
distance.

Very significant was the fact that the infection was not communicated
directly from the Southern to Northern cattle but that the ground over
which the former passed was infected by them, and that the infection was
transmitted thence to susceptible cattle _after a period of not less
than thirty days had elapsed_.

Of course a disease as striking as this, and which caused such enormous
losses of cattle in the region invaded was fruitful in theories
concerning its causation. The most widespread was the belief that
pastures were infected by the saliva, urine, or manure of Southern
cattle. There were not wanting keen observers who suggested that the
disease was caused by ticks, but little weight was given to their view.

Various workers had described bacteria which they had isolated from the
organs of the diseased animals, but their findings could not be
verified. In 1889, Smith and Kilbourne discovered a minute, pear-shaped
organism (fig. 138) in the red blood corpuscles of a cow which had
succumbed to Texas fever. On account of their shape they were given the
generic name _Pyrososma_ and because they were usually found two in a
corpuscle, the specific name, _bigeminum_. It is now generally accepted
that the parasite is the same which Babes had observed the year before
in Roumanian cattle suffering from hæmoglobinuria, and should be known
as _Babesia bovis_ (Babes).

[Illustration: 138. Babesia bovis in blood corpuscles. After Calli.]

[Illustration: 139. The cattle tick (Boophilus annulatus). (_a_) Female;
(_b_) male. After Comstock.]

By a series of perfectly conclusive experiments carried on near
Washington, D.C., Smith and Kilbourne showed that this organism was
carried from Southern cattle to non-immune animals by the so-called
Southern cattle tick, _Boophilus annulatus_ (= _Margaropus annulatus_)
(fig. 139).

Of fourteen head of native cattle placed in a field with tick-infested
Northern cattle all but two contracted the disease. This experiment was
repeated with similar results. Four head of native cattle kept in a plot
with three North Carolina cattle which had been carefully freed from
ticks remained healthy. A second experiment the same year gave similar
results.

Still more conclusive was the experiment showing that fields which had
not been entered by Southern cattle but which had been infected by
mature ticks taken from such animals would produce Texas fever in native
cattle. On September 13, 1889, several thousand ticks collected from
cattle in North Carolina three and four days before, were scattered in a
small field near Washington. Three out of four native animals placed in
this field contracted the disease. The fourth animal was not examined as
to its blood but it showed no external symptoms of the disease.

[Illustration: 140. Hyalomma ægypticum. After Nuttall and Warburton.]

In these earlier experiments it was believed that the cattle tick acted
as a carrier of the disease between the Southern cattle and the _soil_
of the Northern pastures. "It was believed that the tick obtained the
parasite from the blood of its host and in its dissolution on the
pasture a certain resistant spore form was set free which produced the
disease when taken in with the food." The feeding of one animal for some
time with grass from the most abundantly infected field, without any
appearance of the disease, made this hypothesis untenable.

In the experimental work in 1890 the astonishing fact was brought out
that the disease was conveyed neither by infected ticks disintegrating
nor by their directly transferring the parasite, but that it was
conveyed by the young hatched from eggs of infected ticks. In other
words, the disease was hereditarily transferred to ticks of the second
generation and they alone were capable of conveying it.

Thus was explained the fact that Texas fever did not appear immediately
along the route of Southern cattle being driven to Northern markets but
that after a certain definite period it manifested itself. It was
conveyed by the progeny of ticks which had dropped from the Southern
cattle and deposited their eggs on the ground.

These results have been fully confirmed by workers in different parts of
the world,--notably by Koch, in Africa, and by Pound, in Australia.

The disease is apparently transmitted by _Boophilus annulatus_ alone, in
the United States, but it, or an almost identical disease, is conveyed
by _Ixodes hexagonus_ in Norway, _Ixodes ricinus_ in Finland and France
and by the three species, _Boophilus decoloratus_, _Hyalomma ægypticum_
(fig. 140 and 141), and _Hæmaphysalis punctata_ in Africa.

[Illustration: 141. Hyalomma ægypticum. Capitulum of female; (_a_)
dorsal, (_b_) ventral aspect.]

In spite of the detailed study which it has received, the life cycle of
_Babesia bovis_ has not been satisfactorily worked out. The asexual
reproduction in the blood of the vertebrate host has been described but
the cycle in the tick is practically unknown.

More successful attempts have been made to work out the life cycle of a
related species, _Babesia canis_, which causes malignant jaundice in
dogs in Africa and parts of Southern Europe. In this instance, also, the
disease is transmitted by heredity to the ticks of the second
generation. Yet the larval, or "seed ticks," from an infected female are
not capable of conveying the disease, but only the nymphs and adults.
Still more complicated is the condition in the case of _Babesia ovis_ of
sheep, which Motas has shown can be conveyed solely by the adult,
sexually mature ticks of the second generation.

In _Babesia canis_, Christopher (1907) observed developmental stages in
the tick. He found in the stomach of adult ticks, large motile
club-shaped bodies which he considered as oökinetes. These bodies pass
to the ovaries of the tick and enter the eggs where they become globular
in form and probably represent an oocyst. This breaks up into a number
of sporoblasts which enter the tissues of the developing tick and give
rise to numerous sporozoites, which collect in the salivary glands and
thence are transferred to the vertebrate host. A number of other species
of _Babesia_ are known to infest vertebrates and in all the cases where
the method has been worked out it has been found that the conveyal was
by ticks. We shall not consider the cases more fully here, as we are
concerned especially with the method of transfer of human diseases.


TICKS AND ROCKY MOUNTAIN SPOTTED FEVER OF MAN--Ever since 1873 there has
been known in Montana and Idaho a peculiar febrile disease of man, which
has gained the name of "Rocky Mountain spotted fever." Its onset is
marked by chills and fever which rapidly become acute. In about four to
seven days there appears a characteristic eruption on the wrists, ankles
or back, which quickly covers the body.

McClintic (1912) states that the disease has now been reported from
practically all of the Rocky Mountain States, including Arizona,
California, Colorado, Idaho, Montana, Nevada, Oregon, Utah, Washington,
and Wyoming. "Although the disease is far more prevalent in Montana and
Idaho than in any of the other States, its spread has assumed such
proportions in the last decade as to call for the gravest consideration
on the part of both the state and national health authorities. In fact,
the disease has so spread from state to state that it has undoubtedly
become a very serious interstate problem demanding the institution of
measures for its control and suppression."

A peculiar feature of the Rocky Mountain spotted fever is a marked
variation in its severity in different localities. In Montana, and
especially in the famous Bitter Root Valley, from 33 per cent to 75 per
cent of the cases result fatally. On the other hand, the fatality does
not exceed four per cent in Idaho.

In 1902, Wilson and Chowning reported the causative organism of spotted
fever to be a blood parasite akin to the _Babesia_ of Texas fever, and
made the suggestion that the disease was tick-borne. The careful studies
of Stiles (1905) failed to confirm the supposed discovery of the
organism, and the disease is now generally classed as due to an
invisible virus. On the other hand, the accumulated evidence has fully
substantiated the hypothesis that it is tick-borne.

According to Ricketts (1907) the experimental evidence in support of
this hypothesis was first afforded by Dr. L. P. McCalla and Dr. H. A.
Brereton, in 1905. These investigators transmitted the disease from man
to man in two experiments. "The tick was obtained 'from the chest of a
man very ill with spotted fever' and 'applied to the arm of a man who
had been in the hospital for two months and a half, and had lost both
feet from gangrene due to freezing.' On the eighth day the patient
became very ill and passed through a mild course of spotted fever,
leaving a characteristic eruption. The experiment was repeated by
placing the tick on a woman's leg and she likewise was infected with
spotted fever."

The most detailed studies were those of the late Dr. H. T. Ricketts, and
it was he who clearly established the tick hypothesis. In the summer of
1906 he found that guinea pigs and monkeys are very susceptible to
spotted fever and can readily be infected by inoculation of blood from
patients suffering from the disease. This opened the way to experimental
work on tick transmission. A female tick was fed upon an infected guinea
pig for two days, removed and isolated for two days and then placed upon
a healthy guinea pig. After an incubation period of three and a half
days the experimental animal contracted a well-marked case of the
disease.

A similar result was obtained at the same time by King, and later in the
season Ricketts proved that the male tick was also capable of
transmitting the disease. He found that there was a very intimate
relation of the virus to the tick and that the transmission must be
regarded as biological throughout. Ticks remained infective as long as
they lived and would feed for a period of several months. If they
acquired the disease in the larval or nymphal stage they retained it
during molting and were infective in the subsequent stages. In a few
cases the larvæ from an infected female were infective.

The evidence indicated that the tick suffers from a relatively harmless,
generalized infection and the virus proliferates in its body. The
disease probably is transferred through the salivary secretion of the
tick since inoculation experiments show that the salivary glands of the
infected adult contain the virus.

It is probable that in nature the reservoir of the virus of spotted
fever is some one or more of the native small animals. Infected ticks
have been found in nature, and as various wild animals are susceptible
to the disease, it is obvious that it may exist among them unnoticed.
Wilson and Chowning suggested that the ground squirrel plays the
principal rôle.

Unfortunately, much confusion exists regarding the correct name of the
tick which normally conveys the disease. In the medical literature it is
usually referred to as _Dermacentor occidentalis_, but students of the
group now agree that it is specifically distinct. Banks has designated
it as _Dermacentor venustus_ and this name is used in the publications
of the Bureau of Entomology. On the other hand, Stiles maintains that
the common tick of the Bitter Root Valley, and the form which has been
collected by the authors who have worked on Rocky Mountain spotted fever
in that region, is separable from _D. venustus_, and he has described it
under the name of _Dermacentor andersoni_.

Mayer (1911) has shown experimentally that spotted fever may be
transmitted by several different species of ticks, notably _Dermacentor
marginatus_, _Dermacentor variabilis_ and _Amblyomma americanum_. This
being the case, the question of the exact systematic status of the
species experimented upon in the Bitter Root Valley becomes less
important, for since _Dermacentor occidentalis_, _Dermacentor venustus_
and _Dermacentor andersoni_ all readily attack man, it is probable that
either species would readily disseminate the disease if it should spread
into their range.

Hunter and Bishop (1911) have emphasized the fact that in the eastern
and southern United States there occur several species which attack man,
and any one of which might transmit the disease from animal to animal
and from animal to man. The following species, they state, would
probably be of principal importance in the Southern and Eastern States:
the lone star tick (_Amblyomma americanum_); the American dog tick
(_Dermacentor variabilis_); and the gulf-coast tick (_Amblyomma
maculatum_). In the extreme southern portions of Texas, _Amblyomma
cajennense_, is a common pest of man.

Since the evidence all indicates that Rocky Mountain spotted fever is
transmitted solely by the tick, and that some of the wild animals serve
as reservoirs of the virus, it is obvious that personal prophylaxis
consists in avoiding the ticks as fully as possible, and in quickly
removing those which do attack. General measures along the line of tick
eradication must be carried out if the disease is to be controlled. That
such measures are feasible has been shown by the work which has been
done in controlling the tick-borne Texas fever of cattle, and by such
work as has already been done against the spotted fever tick, which
occurs on both wild and domestic animals. Detailed consideration of
these measures is to be found in the publications of the Public Health
and Marine Hospital Service, and the Bureau of Entomology. Hunter and
Bishopp give the following summarized recommendations for control or
eradication measures in the Bitter Root Valley.

(1) A campaign of education, whereby all the residents of the valley
will be made thoroughly familiar with the feasibility of the plan of
eradication, and with what it will mean in the development of the
valley.

(2) The obtaining of legislation to make it possible to dip or oil all
live stock in the Bitter Root Valley.

(3) The obtaining of an accurate census of the horses, cattle, sheep,
mules, and dogs in the valley.

(4) The construction of ten or more dipping vats.

(5) The providing of materials to be used in the dipping mixture.

(6) The organization of a corps of workers to carry on the operations.

(7) The systematic dipping of the horses, cattle, sheep, and dogs of the
valley on a definite weekly schedule from approximately March 10 to June
9.

(8) The treatment by hand of the animals in localities remote from vats,
on the same schedule.

They estimate that after three seasons' operations a very small annual
expenditure would provide against reinfestation of the valley by the
incoming of cattle from other places.

Supplementary measures consist in the killing of wild mammals which may
harbor the tick; systematic burning of the brush and debris on the
mountain side; and in clearing, since the tick is seldom found on land
under cultivation.




CHAPTER X

ARTHROPODS AS ESSENTIAL HOSTS OF PATHOGENIC PROTOZOA [_Continued_]


ARTHROPODS AND SPIROCHÆTOSES OF MAN AND ANIMALS

The term spirochætoses is applied to diseases of man or animals which
are due to protistan parasites belonging to the group of slender, spiral
organisms known as spirochætes.

There has been much discussion concerning the relationship Of the
spirochætes. Formerly, they were regarded as bacteria closely related to
the forms grouped in the genus _Spirillum_. The results of the detailed
study which the spirochætes have received in recent years, have led most
of the workers to consider them as belonging to the protozoa. The merits
of the discussion we are not concerned with here, but rather with the
fact that a number of diseases caused by spirochætes are
arthropod-borne. The better known of these we shall discuss.


AFRICAN RELAPSING FEVER OF MAN--It has long been known to the natives of
Africa and to travelers in that country, that the bite of a certain
tick, _Ornithodoros moubata_, may be followed by severe or even fatal
fever of the relapsing type. Until recent years, it was supposed that
the effect was due to some special virulence of the tick, just as nagana
of cattle was attributed to the direct effect of the bite of the
tsetse-fly. The disease is commonly known as "tick-fever" or by the
various native names of the tick.

In 1904, Ross and Milne, in Uganda, and Dutton and Todd on the Congo,
discovered that the cause of the disease is a spirochæte which is
transmitted by the tick. This organism has been designated by Novy and
Knapp as _Spirochæta duttoni_.

_Ornithodoros moubata_ (fig. 142), the carrier of African relapsing
fever, or "tick-fever," is widely distributed in tropical Africa, and
occurs in great numbers in the huts of natives, in the dust, cracks and
crevices of the dirt floors, or the walls. It feeds voraciously on man
as well as upon birds and mammals. Like others of the _Argasidæ_, it
resembles the bed-bug in its habit of feeding primarily at night. Dutton
and Todd observed that the larval stage is undergone in the egg and that
the first free stage is that of the octopod nymph.

[Illustration: 142. Ornithodoros moubata. (_a_) Anterior part of venter;
(_b_) second stage nymph; (_c_) capitulum; (_d_) dorsal and (_e_)
ventral aspect of female; (_f_) ventral aspect of nymph; (_g_) capitulum
of nymph. After Nuttall and Warburton.]

The evidence that the fever is transmitted by this tick is conclusive.
Koch found that from five per cent to fifteen per cent, and in some
places, fifty per cent of the ticks captured, harbored the spirochæte.
The disease is readily transmitted to monkeys, rats, mice and other
animals and the earlier experiments along these lines have been
confirmed by many workers.

Not only are the ticks which have fed on infected individuals capable of
conveying the disease to healthy animals but they transmit the causative
organism to their progeny. Thus Möllers (1907), working in Berlin,
repeatedly infected monkeys through the bites of nymphs which had been
bred in the laboratory from infected ticks. Still more astonishing was
his discovery that ticks of the third generation were infective. In
other words, if the progeny of infected ticks were fed throughout life
on healthy animals, and on maturity deposited eggs, the nymphs which
hatched from these eggs would still be capable of carrying the
infection.

The developmental cycle of the spirochæte within the tick has not been
fully worked out, though the general conclusions of Leishman (1910) have
been supported by the recent works of Balfour (1911 and 1912), and
Hindle (1912), on the life cycle of spirochætes affecting fowls.

_Spirochæta duttoni_ ingested by _Ornithodoros moubata_ apparently
disappear within a few days, but Leishman believed that in reality they
break up into minute granules which are to be found in the alimentary
canal, the salivary glands and the Malpighian tubes of the tick. These
granules, or "coccoid bodies," as Hindle calls them, are supposed to be
the form in which the spirochætes infect the new host. We shall see
later that Marchoux and Couvy (1913) dissent wholly from this
interpretation.

According to Leishman, and Hindle, the coccoid bodies are not injected
into the vertebrate host with the saliva of the tick, as are the
sporozoites of malaria with that of the mosquito. Instead, they pass out
with the excrement and secondarily gain access to the wound inflicted by
the tick.

Nuttall (1912) calls attention to the fact that the geographical
distribution of _Ornithodoros moubata_ is far wider than our present
records show for the distribution of the relapsing fever in man and that
there is every reason to fear the extension of the disease. Huts where
the ticks occur should be avoided and it should be remembered that in
infected localities there is special danger in sleeping on the ground.


EUROPEAN RELAPSING FEVER--There is widely distributed in Europe a type
of relapsing fever which is caused by _Spirochæta recurrentis_. It has
long been supposed that this disease is spread by the bed-bug and there
is some experimental evidence to show that it may be conveyed by these
insects.

In 1897, Tictin found that he could infect monkeys by inoculating the
contents of bed-bugs which had fed upon a patient within forty-eight
hours. Nuttall, in 1907, in one experiment succeeded in transmitting
_Spirochæta recurrentis_ from mouse to mouse by bites of bed-bugs. The
bugs, thirty-five in number, were transferred at short intervals from
one mouse to another, not being allowed to take a full meal on the
first, or infected mouse.

On the other hand, there is much clinical evidence to show that the
European relapsing fever like various other types of the disease is
transmitted from man to man by head and body lice (_Pediculus humanus_
and _Pediculus corporis_).

Interesting supplementary evidence is that of Bayon's observations
(1912), in Moscow. "Having visited the big municipal night hospitals at
Moscow I soon noticed that they were kept with such scrupulous
cleanliness, disinfected so lavishly, the beds of iron, the floor
cemented, that it was not possible for bed-bugs to thrive to any extent
on the premises. The people sleeping there were allowed, however, to
sleep in their own clothes. The introduction of these model homes had
not had any effect on the incidence of relapsing fever, for the places
were still hot-beds of the fever during winter. On the other hand,
though I changed my rooms several times, I found bugs in every
successive lodging, and I was told in Moscow, this can hardly be
avoided. Yet no foreigner, or Russian of the better class, ever catches
relapsing fever. To this may be added the fact that when I asked for
clothes-lice and promised to pay a kopec for two, the attendants from
the night hostel brought me next morning a small ounce bottle crammed
with _Pediculus capitis_ (= _P. humanus_), and _Pediculus vestimentorum_
(= _P. corporis_) collected off the sleepers. If relapsing fever were
transmitted by bed-bugs, it would be much more disseminated than it is
at present in Moscow."

Direct experimental evidence of the agency of lice in transmitting
relapsing fever is especially clear in the case of a type of the disease
prevalent in parts of North Africa. We shall consider this evidence
later.


OTHER TYPES OF RELAPSING FEVER OF MAN--In addition to the three types of
human relapsing fever already referred to, several others have been
distinguished and have been attributed to distinct species of
spirochætes. The various spirochætoses of man are:

African, caused by _S. duttoni_; European, caused by _S. recurrentis_;
North African, caused by _S. berbera_; East African, caused by _S.
rossi_; East Indian, caused by _S. carteri_; North American, caused by
_S. novyi_; South American, caused by _S. duttoni_ (?).

Nuttall (1912) in his valuable résumé of the subject, has emphasized
that "in view of the morphological similarity of the supposedly
different species of spirochætes and their individual variations in
virulence, we may well doubt if any of the 'species' are valid. As I
pointed out four years ago, the various specific names given to the
spirochætes causing relapsing fever in man may be used merely for
convenience _to distinguish strains or races_ of different origin. They
cannot be regarded as valid names, in the sense of scientific
nomenclature, for virulence and immunity reactions are not adequate
tests of specificity."


NORTH AFRICAN RELAPSING FEVER OF MAN--The type of human relapsing fever
to be met with in Algeria, Tunis, and Tripoli, is due to a _Spirochæta_
to which does not differ morphologically from _Spirochæta duttoni_, but
which has been separated on biological grounds as _Spirochæta berberi_.

Experimenting with this type of disease in Algeria, Sergent and Foly
(1910), twice succeeded in transmitting it from man to monkeys by
inoculation of crushed body lice and in two cases obtained infection of
human subjects who had received infected lice under their clothing and
who slept under coverings harboring many of the lice which had fed upon
a patient. Their results were negative with _Argas persicus_, _Cimex
lectularius_, _Musca domestica_, _Hæmatopinus spinulosus_ and
_Ceratophyllus fasciatus_. They found body lice associated with every
case of relapsing fever which they found in Algeria.

Nicolle, Blaizot, and Conseil (1912) showed that the louse did not
transmit the parasite by its bite. Two or three hours after it has fed
on a patient, the spirochætes begin to break up and finally they
disappear, so that after a day, repeated examinations fail to reveal
them. They persist, nevertheless, in some unknown form, for if the
observations are continued they reappear in eight to twelve days. These
new forms are virulent, for a monkey was infected by inoculating a
single crushed louse which had fed on infected blood fifteen days
before.

Natural infection is indirect. Those attacked by the insect scratch, and
in this act they excoriate the skin, crush the lice and contaminate
their fingers. The least abrasion of the skin serves for the entrance of
the spirochætes. Even the contact of the soiled fingers on the various
mucosa, such as the conjunctive of the eye, is sufficient.

As in the case of _Spirochæta duttoni_, the organism is transmitted
hereditarily in the arthropod vector. The progeny of lice which have fed
on infected blood may themselves be infective.


SPIROCHÆTOSIS OF FOWLS--One of the best known of the spirochætes
transmitted by arthropods is _Spirochæta gallinarum_, the cause of a
very fatal disease of domestic fowls in widely separated regions of the
world. According to Nuttall, it occurs in Southeastern Europe, Asia,
Africa, South America and Australia.

In 1903, Marchoux and Salimbeni, working in Brazil, made the first
detailed study of the disease, and showed that the causative organism is
transmitted from fowl to fowl by the tick _Argas persicus_. They found
that the ticks remained infective for at least five months. Specimens
which had fed upon diseased birds in Brazil were sent to Nuttall and he
promptly confirmed the experiments. Since that date many investigators,
notably Balfour and Hindle, have contributed to the elucidating of the
life-cycle of the parasite. Since it has been worked out more fully than
has that of any of the human spirochætes, we present Hindle's diagram
(fig. 143) and quote the brief summary from his preliminary paper
(1911_b_).

"Commencing with the ordinary parasite in the blood of the fowl, the
spirochæte grows until it reaches a certain length (16-19µ) and then
divides by transverse division. This process is repeated, and is
probably the only method of multiplication of the parasite within the
blood. When the spirochætes disappear from the circulation, some of them
break up into the coccoid bodies which, however, do not usually develop
in the fowl. When the spirochætes are ingested by _Argas persicus_, some
of them pass through the gut wall into the coelomic fluid. From this
medium they bore their way into the cells of the various organs of the
tick and there break up into a number of coccoid bodies. These
intracellular forms multiply by ordinary fission in the cells of the
Malpighian tubules and gonads. Some of the coccoid bodies are formed in
the lumen of the gut and Malpighian tubules. The result is that some of
the coccoid bodies may be present in the Malpighian secretion and
excrement of an infected tick and when mixed with the coxal fluid may
gain entry into another fowl by the open wound caused by the tick's
bite. They then elongate and redevelop into ordinary spirochætes in the
blood of the fowl, and the cycle may be repeated."

[Illustration: 143. Spirochæta gallinarum. After Hindle.]

Hindle's account is clear cut and circumstantial, and is quite in line
with the work of Balfour, and of Leishman. Radically different is the
interpretation of Marchoux and Couvy (1913). These investigators
maintain that the granules localized in the Malpighian tubules in the
larvæ and, in the adult, also in the ovules and the genital ducts of the
male and female, are not derived from spirochætes but that they exist
normally in many acariens. They interpret the supposed disassociation
of the spirochæte into granules as simply the first phase, not of a
process of multiplication, but of a degeneration ending in the death of
the parasite. The fragmented chromatin has lost its affinity for stains,
remaining always paler than that of the normal spirochætes. On the other
hand, the granules of Leishman stain energetically with all the basic
stains.

Further, according to Marchoux and Couvy, infection takes place without
the emission of the coxal fluid and indeed, soiling of the host by the
coxal fluid diluting the excrement is exceptional. All of the organs of
the Argasid are invaded by the parasites, but they pass from the
coelom into the acini of the salivary glands and collect in its
efferent canal. The saliva serves as the vehicle of infection.

Thus, the question of the life cycle of _Spirochæta gallinarum_, and of
spirochætes in general, is an open one.

It should be noted that _Argas persicus_, the carrier of _Spirochæta
gallinarum_, is a common pest of poultry in the southwestern United
States. Though the disease has not been reported from this country,
conditions are such that if accidentally introduced, it might do great
damage.


OTHER SPIROCHÆTE DISEASES OF ANIMALS--About a score of other blood
inhabiting spirochætes have been reported as occurring in mammals, but
little is known concerning their life-histories. One of the most
important is _Spirochæta theileri_ which produces a spirochætosis of
cattle in the Transvaal. Theiler has determined that it is transmitted
by an Ixodid tick, _Margaropus decoloratus_.


TYPHUS FEVER AND PEDICULIDÆ

Typhus is an acute, and continued fever, formerly epidemically prevalent
in camps, hospitals, jails, and similar places where persons were
crowded together under insanitary conditions. It is accompanied by a
characteristic rash, which gives the disease the common name of
"spotted" or "lenticular" fever. The causative organism is unknown.

Typhus fever has not generally been supposed to occur in the United
States, but there have been a few outbreaks and sporadic cases
recognized. According to Anderson and Goldberger (1912_a_), it has been
a subject of speculation among health authorities why, in spite of the
arrival of occasional cases in this country and of many persons from
endemic foci of the disease, typhus fever apparently does not gain a
foothold in the United States. These same workers showed that the
so-called Brill's disease, studied especially in New York City, is
identical with the typhus fever of Mexico and of Europe.

The conditions under which the disease occurs and under which it spreads
most rapidly are such as to suggest that it is carried by some parasitic
insect. On epidemiological grounds the insects most open to suspicion
are the lice, bed-bugs and fleas.

In 1909, Nicolle, Comte and Conseil, succeeded in transmitting typhus
fever from infected to healthy monkeys by means of the body louse
(_Pediculus corporis_). Independently of this work, Anderson and
Goldberger had undertaken work along this line in Mexico, and in 1910
reported two attempts to transmit the disease to monkeys by means of
body lice. The first experiment resulted negatively, but the second
resulted in a slight rise in temperature, and in view of later results
it seems that this was due to infection with typhus.

Shortly after, Ricketts and Wilder (1910) succeeded in transmitting the
disease to the monkey by the bite of body lice in two experiments, the
lice in one instance deriving their infection from a man and in another
from the monkey. Another monkey was infected by typhus through the
introduction of the feces and abdominal contents of infested lice into
small incisions. Experiments with fleas and bed-bugs resulted
negatively.

Subsequently, Goldberger and Anderson (1912_b_) indicated that the head
louse (_Pediculus humanus_) as well, may become infected with typhus. In
an attempt to transmit typhus fever (Mexican virus) from man to monkey
by subcutaneous injection of a saline suspension of crushed head lice,
the monkeys developed a typical febrile reaction with subsequent
resistance to an inoculation of virulent typhus (Mexican) blood. In one
of the three experiments to transmit the disease from man to monkey by
means of the bite of the head louse, the animal bitten by the presumably
infected head lice proved resistant to two successive immunity tests
with virulent typhus blood.

In 1910, Ricketts and Wilder reported an experiment undertaken with a
view to determining whether the young of infected lice were themselves
infected. Young lice were reared to maturity on the bodies of typhus
patients, so that if the eggs were susceptible to infection at any stage
of their development, they would have every opportunity of being
infected within the ovary. The eggs of these infected lice were
obtained, they were incubated, and the young lice of the second
generation were placed on a normal rhesus monkey. The experimenters were
unable to keep the monkey under very close observation during the
following three or four weeks, but from the fact that he proved
resistant to a subsequent immunity test they concluded that he probably
owed this immunity to infection by these lice of the second generation.

Anderson and Goldberger (1912_b_) object that due consideration was not
given to the possibility of a variable susceptibility of the monkey to
typhus. Their similar experiment was "frankly negative."

Prophylaxis against typhus fever is, therefore, primarily a question of
vermin extermination. A brief article by Dr. Goldberger (1914) so
clearly shows the practical application of his work and that of the
other investigators of the subject, that we abstract from it the
following account:

"In general terms it may be stated that association with a case of
typhus fever in the absence of the transmitting insect is no more
dangerous than is association with a case of yellow fever in the absence
of the yellow fever mosquito. Danger threatens only when the insect
appears on the scene."

"We may say, therefore, that to prevent infection of the individual it
is necessary for him only to avoid being bitten by the louse. In theory
this may readily be done, for we know that the body louse infests and
attaches itself almost entirely to the body linen, and that boiling
kills this insect and its eggs. Individual prophylaxis is based
essentially, therefore, on the avoidance of contact with individuals
likely to harbor lice. Practically, however, this is not always as easy
as it may seem, especially under the conditions of such intimate
association as is imposed by urban life. Particularly is this the case
in places such as some of the large Mexican cities, where a large
proportion of the population harbors this vermin. Under such
circumstances it is well to avoid crowds or crowded places, such as
public markets, crowded streets, or public assemblies at which the
'peon' gathers."

"Community prophylaxis efficiently and intelligently carried out is,
from a certain point of view, probably easier and more effective in
protecting the individual than is the individual's own effort to guard
himself. Typhus emphasizes, perhaps better than any other disease, the
fact that fundamentally, sanitation and health are economic problems. In
proportion as the economic condition of the masses has improved--that
is, in proportion as they could afford to keep clean--the notorious
filth disease has decreased or disappeared. In localities where it still
prevails, its further reduction or complete eradication waits on a
further improvement in, or extension of, the improved economic status of
those afflicted. Economic evolution is very slow process, and, while
doing what we can to hasten it, we must take such precautions as
existing conditions permit, looking to a reduction in or complete
eradication of the disease."

"When possible, public bath houses and public wash houses, where the
poor may bathe and do their washings at a minimum or without cost,
should be provided. Similar provision should be made in military and
construction camps. Troops in the field should be given the opportunity
as frequently as possible to wash and _scald_ or _boil_ their body
linen."

"Lodging houses, cheap boarding houses, night shelters, hospitals, jails
and prisons, are important factors in the spread and frequently
constitute foci of the disease. They should receive rigid sanitary
supervision, including the enforcement of measures to free all inmates
of such institutions of lice on admission."

"So far as individual foci of the disease are concerned these should be
dealt with by segregating and keeping under observation all exposed
individuals for 14 days--the period of incubation--from the last
exposure, by disinfecting (boiling or steaming) the suspected bedding,
body linen, and clothes, for the destruction of any possible vermin that
they may harbor, and by fumigating (with sulphur) the quarters that they
may have occupied."

"It will be noted that nothing has been said as to the disposition of
the patient. So far as the patient is concerned, he should be removed to
'clean' surroundings, making sure that he does not take with him any
vermin. This may be done by bathing, treating the hair with an
insecticide (coal oil, tincture of larkspur), and a complete change of
body linen. Aside from this, the patient may be treated or cared for in
a general hospital ward or in a private house, provided the sanitary
officer is satisfied that the new surroundings to which the patient has
been removed are 'clean,' that is, free from vermin. Indeed, it is
reasonably safe to permit a 'clean' patient to remain in his own home if
this is 'clean,' for, as has already been emphasized, there can be no
spread in the absence of lice. This is a common experience in native
families of the better class and of Europeans in Mexico City."

"Similarly the sulphur fumigation above prescribed may be dispensed with
as unnecessary in this class of cases."




CHAPTER XI

SOME POSSIBLE, BUT IMPERFECTLY ESTABLISHED CASES OF ARTHROPOD
TRANSMISSION OF DISEASE


INFANTILE PARALYSIS OR ACUTE ANTERIOR POLIOMYELITIS

The disease usually known in this country as infantile paralysis or,
more technically, as acute anterior poliomyelitis, is one which has
aroused much attention in recent years.

The causative organism of infantile paralysis is unknown, but it has
been demonstrated that it belongs to the group of filterable viruses. It
gives rise to a general infection, producing characteristic lesions in
the central nervous system. The result of the injury to the motor nerves
is a more or less complete paralysis of the corresponding muscle. This
usually manifests itself in the legs and arms. The fatal cases are
usually the result of paralysis of the muscles of respiration. Of the
non-fatal cases about 60 per cent remain permanently crippled in varying
degrees.

Though long known, it was not until about 1890 that it was emphasized
that the disease occurs in epidemic form. At this time Medin reported
his observations on an epidemic of forty-three cases which occurred in
and around Stockholm in 1887. Since then, according to Frost (1911),
epidemics have been observed with increasing frequency in various parts
of the world. The largest recorded epidemics have been those in Vermont,
1894, 126 cases; Norway and Sweden, 1905, about 1,500 cases; New York
City, 1907, about 2,500 cases. Since 1907 many epidemics have been
reported in the United States, and especially in the Northern States
east of the Dakotas. In 1912 there were over 300 cases of the disease in
Buffalo, N. Y., with a mortality of somewhat over 11 per cent.

In view of the sudden prominence and the alarming spread of infantile
paralysis, there have been many attempts to determine the cause, and the
manner in which the disease spreads and develops in epidemic form. In
the course of these studies, the question of possible transmission by
insects was naturally suggested.

C. W. Howard and Clark (1912) presented the results of studies in this
phase of the subject. They dealt especially with the house-fly, bedbug,
head, and body lice, and mosquitoes. It was found that the house-fly
(_Musca domestica_) can carry the virus of poliomyelitis in an active
state for several days upon the surface of the body and for several
hours within the gastro-intestinal tract. Mosquitoes and lice were found
not to take up or maintain the virus. On the other hand, the bedbug
(_Cimex lectularius_) was found to take the virus from the infected
monkeys and to maintain it in a living state within the body for a
period of seven days. This was demonstrated by grinding up in salt
solution, insects which had fed on poliomyelitic animals and injecting
the filtrate into a healthy monkey. The experimenters doubted that the
bedbug is a carrier of the virus in nature.

Earlier in the same year, Brues and Sheppard published the results of an
intensive epidemiological study of the outbreak of 1911, in
Massachusetts. Special attention had been paid to the possibility of
insect transfer and the following conclusion was reached:

"Field work during the past summer together with a consideration of the
epidemiology of the disease so far as known, points strongly toward
biting flies as possible carriers of the virus. It seems probable that
the common stable-fly (_Stomoxys calcitrans_ L.) may be responsible to a
certain extent for the spread of acute epidemic poliomyelitis, possibly
aided by other biting flies, such as _Tabanus lineola_. No facts which
disprove such a hypothesis have as yet been adduced, and experiments
based upon it are now in progress."

As stated by Brues (1913), especial suspicion fell upon the stable-fly
because:

1. The blood-sucking habits of the adult fly suit it for the transfer of
virus present in the blood.

2. The seasonal abundance of the fly is very closely correlated with the
incidence of the disease, rising rapidly during the summer and reaching
a maximum in July and August, then slowly declining in September and
October.

3. The geographical distribution of the fly is, so far as can be
ascertained, wider, or at least co-extensive with that of poliomyelitis.

4. _Stomoxys_ is distinctly more abundant under rural conditions, than
in cities and thickly populated areas.

5. While the disease spreads over districts quickly and in a rather
erratic way, it often appears to follow along lines of travel, and it is
known that _Stomoxys_ flies will often follow horses for long distances
along highways.

6. In a surprisingly large number of cases, it appeared probable that
the children affected had been in the habit of frequenting places where
_Stomoxys_ is particularly abundant, i.e., about stables, barnyards,
etc.

The experiments referred to were carried on during the summer of 1912
and in September Dr. Rosenau announced that the disease was transferred
by the bite of the stable-fly.

A monkey infected by inoculation was exposed to the bites of upwards of
a thousand of the _Stomoxys_ flies daily, by stretching it at full
length and rolling it in a piece of chicken wire, and then placing it on
the floor of the cage in which the flies were confined. The flies fed
freely from the first, as well as later, after paralysis had set in.
Alternating with the inoculated monkey, healthy monkeys were similarly
introduced into the cage at intervals. New monkeys were inoculated to
keep a supply of such infected animals and additional healthy ones were
exposed to the flies, which fed willingly and in considerable numbers on
each occasion. "Thus the flies were given every opportunity to obtain
infection from the monkeys, since the animals were bitten during
practically every stage of the disease from the time of the inoculation
of the virus till their death following the appearance of paralysis. By
the same arrangement the healthy monkeys were likely to be bitten by
flies that had previously fed during the various stages of the disease
on the infected monkeys. The flies had meanwhile enjoyed the opportunity
of incubating the virus for periods varying from the day or two which
usually elapses between consecutive feedings, to the two or three-week
period for which at least some (although a very small percentage) of the
flies lived in the cage."

"In all, twelve apparently healthy monkeys of a small Japan species were
exposed to the flies in the manner described for the infected monkeys.
Some were placed in the cage only once or twice and others a number of
times after varying intervals. These exposures usually lasted for about
half an hour, but were sometimes more protracted. No results were
apparent until two or three weeks after the experiment was well under
way, and then in rather rapid succession six of the animals developed
symptoms of poliomyelitis. In three, the disease appeared in a virulent
form, resulting in death, while the other three experienced transient
tremblings, diarrhoea, partial paralysis and recovery."--Brues, 1913.

Very soon after the announcement of the results of experiments by
Rosenau and Brues, they were apparently conclusively confirmed by
Anderson and Frost (1912), who repeated the experiments, at Washington.
They announced that through the bites of the _Stomoxys_ flies that had
previously fed on infected monkeys, they had succeeded in experimentally
infecting three healthy monkeys.

The results of these experiments gained much publicity and in spite of
the conservative manner in which they had been announced, it was widely
proclaimed that infantile paralysis was conveyed in nature by the
stable-fly and by it alone.

Serious doubt was cast on this theory by the results of further
experiments by Anderson and Frost, reported in May of 1913. Contrary to
the expectations justified by their first experience, the results of all
the later, and more extended, experiments were wholly negative. Not once
were these investigators again able to transmit the infection of
poliomyelitis through _Stomoxys_. They concluded that it was extremely
doubtful that the insect was an important factor in the natural
transmission of the disease, not only because of their series of
negative results, "but also because recent experiments have afforded
additional evidence of the direct transmissibility or contagiousness of
poliomyelitis, and because epidemiological studies appear to us to
indicate that the disease is more likely transmitted largely through
passive human virus carriers."

Soon after this, Kling and Levaditi (1913) published their detailed
studies on acute anterior poliomyelitis. They considered that the
experiments of Flexner and Clark (and Howard and Clark), who fed
house-flies on emulsion of infected spinal cord, were under conditions
so different from what could occur in nature that one could not draw
precise conclusions from them regarding the epidemiology of the disease.
They cited the experiments of Josefson (1912), as being under more
reasonable conditions. He sought to determine whether the inoculation of
monkeys with flies caught in the wards of the Hospital for Contagious
Diseases at Stockholm, where they had been in contact with cases of
poliomyelitis, would produce the disease. The results were completely
negative.

Kling and Lavaditi made four attempts of this kind. The flies were
collected in places where poliomyelitics had dwelt, three, four and
twenty-four after the beginning of the disease in the family and one,
three, and fifteen days after the patient had left the house. These
insects were for the greater part living and had certainly been in
contact with the infected person. In addition, flies were used which had
been caught in the wards of the Hospital for Contagious Diseases at
Söderkoping, when numbers of poliomyelitics were confined there.
Finally, to make the conditions as favorable as possible, the emulsions
prepared from these flies were injected without previous filtering,
since filtration often causes a weakening of the virus. In spite of
these precautions, all their results were negative, none of the
inoculated animals having contracted poliomyelitis. They also
experimented with bedbugs which had fed upon infected patients at
various stages of the disease, but the results in these cases also were
wholly negative.

Kling and Levaditi considered at length the possibility of transmission
of the disease by _Stomoxys_. As a result of their epidemiological
studies, they found that infantile paralysis continued to spread in
epidemic form in the dead of winter, when these flies were very rare and
torpid, or were even completely absent. Numerous cases developed in the
northern part of Sweden late in October and November, long after snow
had fallen. On account of the rarity of the Stomoxys flies during the
period of their investigations they were unable to conduct satisfactory
experiments. In one instance, during a severe epidemic, they found a
number of the flies in a stable near a house inhabited by an infected
family, though none was found in the house itself. These flies were used
in preparing an emulsion which, after filtering, was injected into the
peritoneal cavity of a monkey. The result was wholly negative.

As for the earlier experiments, Kling and Levaditi believe if the flies
were responsible for the transmission of the disease in the cases
reported by Rosenau and Brues, and the first experiments of Anderson and
Frost, it was because the virus of infantile paralysis is eliminated
with the nasal secretions of paralyzed monkeys and the flies, becoming
contaminated, had merely acted as accidental carriers.

Still further evidence against the hypothesis of the transmission of
acute anterior poliomyelitis by _Stomoxys calcitrans_ was brought
forward by Sawyer and Herms (1913). Special precautions were used to
prevent the transference of saliva or other possibly infectious material
from the surface of one monkey to that of another, and to avoid the
possibility of complicating the experiments by introducing other
pathogenic organisms from wild flies, only laboratory-bred flies were
used. In a series of seven carefully performed experiments, in which the
conditions were varied, Sawyer and Herms were unable to transmit
poliomyelitis from monkey to monkey through the agency of _Stomoxys_, or
to obtain any indication that the fly is the usual agent for spreading
the disease in nature.

The evidence at hand to date indicates that acute anterior
poliomyelitis, or infantile paralysis, is transmitted by contact with
infected persons. Under certain conditions insects may be agents in
spreading the disease, but their rôle is a subordinate one.


Pellagra

PELLAGRA is an endemic and epidemic disease characterized by a peculiar
eruption or erythema of the skin (figs 144 and 145), digestive
disturbances and nervous trouble. Insanity is a common result, rather
than a precursor of the disease. The manifestations of pellagra are
periodic and its duration indeterminate.

[Illustration: 144. Pellagrous eruption on the face. After Watson.]

The disease is one the very name of which was almost unknown in the
United States until within the past decade. It has usually been regarded
as tropical, though it occurs commonly in Italy and in various parts of
Europe. Now it is known that it not only occurs quite generally in the
United States but that it is spreading. Lavinder (1911) says that "There
are certainly many thousand cases of the disease in this country, and
the present situation must be looked upon with grave concern."

It is not within the scope of this book to undertake a general
discussion of pellagra. The subject is of such importance to every
medical man that we cannot do better than refer to Lavinder's valuable
précis. We can only touch briefly upon the entomological phases of the
problems presented.

The most commonly accepted theories regarding the etiology of the
disease have attributed it to the use of Indian corn as an article of
diet. This supposed relationship was explained either on the basis of,
(a) insufficiency of nutriment and inappropriateness of corn as a prime
article of food; (b) toxicity of corn or, (c) parasitism of certain
organisms--fungi or bacteria--ingested with either sound or deteriorated
corn.

In 1905, Sambon proposed the theory of the protozoal origin of pellagra
and in 1910 he marshalled an imposing array of objections to the theory
that there existed any relationship between corn and the disease. He
presented clear evidence that pellagra existed in Europe before the
introduction of Indian corn from America, as an article of diet, and
that its spread was not _pari passu_ with that of the use of corn. Cases
were found in which the patients had apparently never used corn, though
that is obviously difficult to establish. He showed that preventive
measures based on the theory had been a failure. Finally, he believed
that the recurrence of symptoms of the disease for successive springs,
in patients who abstained absolutely from the use of corn, militated
against the theory.

[Illustration: 145. Pellagrous eruption on the hand. After Watson.]

On the other hand, Sambon believed that the periodicity of the symptoms,
peculiarities of distribution and seasonal incidence, and analogies of
the symptoms to those of other parasitic diseases indicated that
pellagra was of protozoal origin, and that it was insect-borne.

The insect carriers, he believed to be one or more species of Simuliidæ,
or black-flies. In support of this he stated that _Simulium_ appears to
effect the same topographical conditions as pellagra, that in its imago
stage it seems to present the same seasonal incidence, that it has a
wide geographical distribution which seems to cover that of pellagra,
and that species of the genus are known to cause severe epizootics.
Concluding from his studies in Italy, that pellagra was limited almost
wholly to agricultural laborers, he pointed out that the Simulium flies
are found only in rural districts, and as a rule do not enter towns,
villages, or houses.

[Illustration: 146. A favorite breeding place of Simulium. Ithaca, N.
Y.]

When Sambon's detailed report was published in 1910, his theory was
seized upon everywhere by workers who were anxious to test it and who,
in most cases, were favorably disposed towards it because of the
wonderful progress which had been made in the understanding of other
insect-borne diseases. In this country, the entomological aspects of the
subject have been dealt with especially by Forbes (1912), and by King
and Jennings, under the direction of W. D. Hunter, of the Bureau of
Entomology, and in coöperation with the Thompson-McFadden Pellagra
Commission of the Department of Tropical Medicine of the New York
Post-Graduate Medical School. An important series of experiments with
monkeys has been undertaken by S. J. Hunter, of Kansas, but
unfortunately we have as yet no satisfactory evidence that these animals
are susceptible to the disease--a fact which renders the whole problem
difficult.

The accumulated evidence is increasingly opposed to Sambon's hypothesis
of the transmission of pellagra by _Simulium_. This has been so clearly
manifested in the work of the Thompson-McFadden Commission that we quote
here from the report by Jennings (1914):

"Our studies in 1912 convinced us that there was little evidence to
support the incrimination of any species of _Simulium_ in South Carolina
in the transmission of pellagra. Reviewing the group as a whole, we find
that its species are essentially "wild" and lack those habits of
intimate association with man which would be expected in the vector of
such a disease as pellagra. Although these flies are excessively
abundant in some parts of their range and are moderately so in
Spartanburg County, man is merely an incidental host, and no disposition
whatever to seek him out or to invade his domicile seems to be
manifested. Critically considered, it is nearer the fact that usually
man is attacked only when he invades their habitat."

"As our knowledge of pellagra accumulates, it is more and more evident
that its origin is in some way closely associated with the domicile. The
possibility that an insect whose association with man and his immediate
environment is, at the best, casual and desultory, can be active in the
causation of the disease becomes increasingly remote."

"Our knowledge of the biting habits of _Simulium_ is not complete, but
it is evident, as regards American species at least, that these are
sometimes not constant for the same species in different localities.
Certain species will bite man freely when opportunity offers, while
others have never been known to attack him. To assume that the proximity
of a _Simulium_-breeding stream necessarily implies that persons in its
vicinity must be attacked and bitten is highly fallacious. In
Spartanburg County attacks by _Simulium_ seems to be confined to the
immediate vicinity of the breeding-places. Our records and observations,
exceedingly few in number, refer almost exclusively to such locations.
Statements regarding such attacks, secured with much care and
discrimination from a large number of persons, including many
pellagrins, indicate conclusively that these insects are seldom a pest
of man in this county. A certain number of the persons questioned were
familiar with the gnats in other localities, but the majority were
seemingly ignorant of the existence of such flies with biting habits.
This is especially striking, in view of the fact that the average
distance of streams from the homes of the pellagra cases studied was
about 200 yards, many being at a distance of less than 200 yards, and
that 78 per cent of these streams were found to be infested by larval
_Simulium_. Such ignorance in a large number of persons cannot be
overlooked and indicates strongly that our belief in the negligible
character of local attacks by _Simulium_ is well founded."

"In localities infested by 'sand-flies,' mosquitoes, etc., these pests
are always well known and the ignorance described above is very
significant."

"Such positive reports as we received nearly always referred to bites
received in the open, along streams, etc., and observations made of
their attack were of those on field laborers in similar situations.
Males engaged in agricultural pursuits are almost exempt from pellagra
in Spartanburg County. During the season of 1913, in some two or three
instances, observations were made of the biting of _Simulium_ and some
additional and entirely creditable reports were received. These
observations and reports were under conditions identical with those
referred to in the reports of 1912 and confirm the conclusions based on
the observations of that year. I would repeat with emphasis that it is
inconceivable that a fly of the appearance and habits of the prevalent
species of _Simulium_ could be present in such a region, especially
about the haunts of man and attack him with sufficient frequency and
regularity to satisfactorily account for so active and prevalent a
disease as pellagra without being a well-known and recognized pest."

"In connection with the conditions in the Piedmont region of South
Carolina, it may be well to cite the results of a study of those in the
arid region of western Texas."

"In May, 1913, in company with Capt. J. F. Siler of the
Thompson-McFadden Pellagra Commission, I visited the region of which
Midland in Midland County is the center. This region is very dry and
totally devoid of running water for a long distance in every direction.
The only natural source of water-supply, a few water holes and ponds,
were visited and found to be of such a nature that the survival of
_Simulium_, far less its propagation in them, is absolutely impossible.
The nearest stream affording possibilities as a source of _Simulium_ is
60 miles away, while the average distance of such possibility is not
less than 100 miles."

"Artificial sources of water-supply were also investigated carefully and
were found to offer no opportunity for the breeding of _Simulium_."

"At Midland the histories of five cases of pellagra were obtained, which
gave clear evidence that this place or its immediate vicinity was the
point of origin. Persons of long residence in the country were
questioned as to the occurrence of such flies as _Simulium_ and returned
negative answers. These included a retired cattle owner, who is a man of
education and a keen observer, an expert veterinarian stationed in the
country who has the cattle of the country under constant observation,
and a practical cattle man, manager of a ranch and of wide experience.
The latter had had experience with 'Buffalo gnats' in other localities
(in the East) and is well acquainted with them. His close personal
supervision of the cattle under his charge, makes it practically certain
that he would have discovered these gnats had they been present in the
country."

"At the time the study was made, _Simulium_ was breeding and active in
the adult state in the vicinity of Dallas, Texas, in the eastern part of
the state. We have here a region in which cases of pellagra have
originated, yet in which _Simulium_ does not and cannot breed."

Other possible insect vectors of pellagra have been studied in great
detail and the available evidence indicates that if _any_ insect plays a
rôle in the spread of the disease, _Stomoxys calcitrans_ most nearly
fills the conditions. This conclusion was announced by Jennings and King
in 1912, and has been supported by their subsequent work.

Yet, after all the studies of the past decade, the old belief that
pellagra is essentially of dietary origin is gaining ground. Goldberger,
Waring and Willets (1914) of the United States Public Health Service
summarize their conclusions in the statement, (1) that it is dependent
on some yet undetermined fault in a diet in which the animal or
leguminous protein component is disproportionately large and (2) that no
pellagra develops in those who _consume_ a mixed, well-balanced, and
varied diet, such, for example, as that furnished by the Government to
the enlisted men of the Army, Navy, and Marine Corps.


Leprosy

LEPROSY is a specific, infectious disease due to _Bacillus lepræ_, and
characterized by the formation of tubercular nodules, ulcerations, and
disturbances of sensation. In spite of the long time that the disease
has been known and the dread with which it is regarded, little is known
concerning the method of transfer of the causative organism or the means
by which it gains access to the human body.

It is known that the bacilli are to be found in the tubercles, the scurf
of the skin, nasal secretions, the sputum and, in fact in practically
all the discharges of the leper. Under such conditions it is quite
conceivable that they may be transferred in some instances from diseased
to healthy individuals through the agency of insects and other
arthropods. Many attempts have been made to demonstrate this method of
spread of the disease, but with little success.

Of the suggested insect carriers none seem to meet the conditions better
than mosquitoes, and there are many suggestions in literature that these
insects play an important rôle in the transmission of leprosy. The
literature has been reviewed and important experimental evidence
presented by Currie (1910). He found that mosquitoes feeding, under
natural conditions, upon cases of nodular leprosy so rarely, if ever,
imbibe the lepra bacillus that they cannot be regarded as one of the
ordinary means of transference of this bacillus from lepers to the skin
of healthy persons. He believes that the reason that mosquitoes that
have fed on lepers do not contain the lepra bacillus is that when these
insects feed they insert their proboscis directly into a blood vessel
and thus obtain bacilli-free blood, unmixed with lymph.

The same worker undertook to determine whether flies are able to
transmit leprosy. He experimented with five species found in
Honolulu,--_Musca domestica_, _Sarcophaga pallinervis_, _Sarcophaga
barbata_, _Volucella obesa_ and an undetermined species of _Lucilia_.
The experiments with _Musca domestica_ were the most detailed. From
these experiments he concluded, first, that all of the above-named
flies, when given an opportunity to feed upon leprous fluids, will
contain the bacilli in their intestinal tracts and feces for several
days after such feeding. Second, that considering the habits of these
flies, and especially those of _Musca domestica_, it is certain that,
given an exposed leprous ulcer, these insects will frequently convey
immense numbers of lepra bacilli, directly or indirectly, to the skins,
nasal mucosa, and digestive tracts of healthy persons. Additional
evidence along this line has recently been brought forward by Honeij and
Parker (1914), who incriminate both _Musca domestica_ and _Stomoxys
calcitrans_. Whether or not such insect-borne bacilli are capable of
infecting persons whose skin and mucosa are thus contaminated, Currie
was unwilling to maintain, but he concludes that until we have more
accurate knowledge on this point, we are justified in regarding these
insects with grave suspicion of being one of the means of disseminating
leprous infection.

Various students of the subject have suggested that bed-bugs may be the
carriers of leprosy and have determined the presence of acid-fast
bacilli in the intestines of bed-bugs which had fed on leprous patients.
Opposed to this, the careful experiments of Thompson (1913) and of
Skelton and Parkham (1913) have been wholly negative.

Borrel has recently suggested that _Demodex_, may play a rôle in
spreading the infection in families. Many other insects and acariens
have been suggested as possible vectors, but the experimental data are
few and in no wise conclusive. The most that can be said is that it is
quite possible that under favorable conditions the infection might be
spread by any of the several blood-sucking forms or by house-flies.


Verruga peruviana

VERRUGA PERUVIANA is defined by Castellani and Chalmers as "a chronic,
endemic, specific, general disorder of unknown origin, not contagious,
but apparently inoculable, and characterized by an irregular fever
associated with rheumatoid pains, anemia, followed by granulomatous
swellings in the skin, mucous membranes, and organs of the body." It has
been generally believed by medical men interested that the comparatively
benign eruptive verruga is identical with the so-called Oroya, or
Carrion's fever, a malignant type. This view is not supported by the
work of Strong, Tyzzer and Brues, (1913).

The disease is confined to South America and to definitely limited areas
of those countries in which it does occur. It is especially prevalent in
some parts of Peru.

The causative organism and the method of transfer of verruga are
unknown. Castellani and Chalmers pointed out in 1910 that the study of
the distribution of the disease in Peru would impress one with the
similarity to the distribution of the Rocky Mountain fever and would
lead to the conclusion that the ætiological cause must in some way be
associated with some blood-sucking animal, perhaps an arachnid, and that
this is supported by the fact that the persons most prone to the
infection are those who work in the fields.

More recently, Townsend (1913), in a series of papers, has maintained
that verruga and Carrion's disease are identical, and that they are
transmitted to man by the bites of the Psychodid fly, _Phlebotomus
verrucarum_. He succeeded in producing the eruptive type of the disease
in experimental animals by injecting a physiological salt trituration of
wild Phlebotomus flies. A cebus monkey was exposed from October so to
November 6, by chaining him to a tree in the verruga zone, next to a
stone wall from which the flies emerged in large numbers every night.
Miliar eruption began to appear on the orbits November 13 and by
November 21, there were a number of typical eruptions, with exudation on
various parts of the body exactly like miliar eruptive sores commonly
seen on legs of human cases.

An assistant in the verruga work, George E. Nicholson, contracted the
eruptive type of the disease, apparently as a result of being bitten by
the Phlebotomus flies. He had slept in a verruga zone, under a tight
net. During the night he evidently put his hands in contact with the
net, for in the morning there were fifty-five unmistakable Phlebotomus
bites on the backs of his hands and wrists.

Townsend believes that in nature, lizards constitute the reservoir of
the disease and that it is from them that the Phlebotomus flies receive
the infection.


Cancer

There are not wanting suggestions that this dread disease is carried, or
even caused, by arthropods. Borrel (1909) stated that he had found mites
of the genus _Demodex_ in carcinoma of the face and of the mammæ. He
believed that they acted as carriers of the virus.

Saul (1910) and Dahl (1910) go much further, since they attribute the
production of the malignant growth to the presence of mites which Saul
had found in cancers. These Dahl described as belonging to a new
species, which he designated _Tarsonemus hominis_. These findings have
since been confirmed by several workers. Nevertheless, the presence of
the mite is so rare that it cannot be regarded as an important factor in
the causation of the disease. The theory that cancer is caused by an
external parasite is given little credence by investigators in this
field.


IN CONCLUSION, it should be noted that the medical and entomological
literature of the past few years abounds in suggestions, and in
unsupported direct statements that various other diseases are
insect-borne. Knab (1912) has well said "Since the discovery that
certain blood-sucking insects are the secondary hosts of pathogenic
parasites, nearly every insect that sucks blood, whether habitually or
occasionally, has been suspected or considered a possible transmitter of
disease. No thought seems to have been given to the conditions and the
characteristics of the individual species of blood-sucking insects,
which make disease transmission possible."

He points out that "in order to be a potential transmitter of human
blood-parasites, an insect must be closely associated with man and
normally have opportunity to suck his blood repeatedly. It is not
sufficient that occasional specimens bite man, as, for example, is the
case with forest mosquitoes. Although a person may be bitten by a large
number of such mosquitoes, the chances that any of these mosquitoes
survive to develop the parasites in question, (assuming such development
to be possible), and then find opportunity to bite and infect another
person, are altogether too remote. Applying this criterion, not only the
majority of mosquitoes but many other blood-sucking insects, such as
Tabanidæ and Simuliidæ, may be confidently eliminated. Moreover, these
insects are mostly in evidence only during a brief season, so that we
have an additional difficulty of a very long interval during which there
could be no propagation of the disease in question." He makes an
exception of tick-borne diseases, where the parasites are directly
transmitted from the tick host to its offspring and where, for this
reason, the insect remains a potential transmitter for a very long
period. He also cites the trypanosome diseases as possible exceptions,
since the causative organisms apparently thrive in a number of different
vertebrate hosts and may be transmitted from cattle, or wild animals, to
man.

Knab's article should serve a valuable end in checking irresponsible
theorizing on the subject of insect transmission of disease.
Nevertheless, the principles which he laid down cannot be applied to the
cases of accidental carriage of bacterial diseases, or to those of
direct inoculation of pyogenic organisms, or of blood parasites such as
the bacillus of anthrax, or of bubonic plague. Accumulated evidence has
justified the conclusion that certain trypanosomes pathogenic to man are
harbored by wild mammals, and so form an exception. Townsend believes
that lizards constitute the natural reservoir of verruga; and it seems
probable that field mice harbor the organism of tsutsugamushi disease.
Such instances are likely to accumulate as our knowledge of the relation
of arthropods to disease broadens.




CHAPTER XII

HOMINOXIOUS ARTHROPODS


The following synoptic tables are presented in the hope that they may be
of service in giving the reader a perspective of the relationships of
the Arthropoda in general and enabling him to identify the more
important species which have been found noxious to man. Though
applicable chiefly to the arthropods found in the United States, exotic
genera and species which are concerned in the transmission of disease
are also included. For this reason the keys to the genera of the Muscids
of the world are given. As will be seen, the tables embrace a number of
groups of species which are not injurious. This was found necessary in
order that the student might not be lead to an erroneous determination
which would result were he to attempt to identify a species which
heretofore had not been considered noxious, by means of a key containing
only the noxious forms. The names printed in BOLD FACED TYPE indicate
the hominoxious arthropods which have been most commonly mentioned in
literature.


CRUSTACEA

Arthropods having two pairs of antennæ which are sometimes modified for
grasping, and usually with more than five pairs of legs. With but few
exceptions they are aquatic creatures. Representatives are: Crabs,
lobsters, shrimps, crayfish, water-fleas, and woodlice. To this class
belongs the CYCLOPS (fig. 122) a genus of minute aquatic crustaceans of
which at least one species harbors _Dracunculus medinensis_, the Guinea
worm (fig. 121).


MYRIAPODA

Elongate, usually vermiform, wingless, terrestrial creatures having one
pair of antennæ, legs attached to each of the many intermediate body
segments. This group is divided into two sections, now usually given
class rank: the DIPLOPODA or millipedes (fig. 13), commonly known as
thousand legs, characterized by having two pairs of legs attached to
each intermediate body segment, and the CHILOPODA or centipedes (fig.
14) having only one pair of legs to each body segment.


ARACHNIDA

In this class the antennæ are apparently wanting, wings are never
present, and the adults are usually provided with four pairs of legs.
Scorpions, harvest-men, spiders, mites, etc.


HEXAPODA (Insects)

True insects have a single pair of antennæ, which is rarely vestigial,
and usually one or two pairs of wings in the adult stage. Familiar
examples are cockroaches, crickets, grasshoppers, bugs, dragon-flies,
butterflies, moths, mosquitoes, flies, beetles, ants, bees and wasps.


ORDERS OF THE ARACHNIDA

a. Abdomen distinctly segmented. A group of orders including scorpions,
    (fig. 11), whip-scorpions (fig. 10), pseudo-scorpions, solpugids
    (fig. 12) harvest-men (daddy-long-legs or harvestmen), etc.
    ARTHROGASTRA

aa. Abdomen unsegmented, though sometimes with numerous annulations
    SPHÆROGASTRA

  b. A constriction between cephalothorax and abdomen (fig. 7). True
      Spiders ARANEIDA

  bb. No deep constriction between these parts.

    c. Legs usually well developed, body more or less depressed (fig.
        49). Mites ACARINA

    cc. Legs stumpy or absent, body more or less elongate or vermiform,
        or if shorter, the species is aquatic or semi-aquatic in habit.

      d. Four pairs of short legs; species inhabiting moss or water.
          Water-bears. TARDIGRADA

      dd. Two pairs of clasping organs near the mouth, instead of legs,
          in the adult; worm-like creatures parasitic within the nasal
          passages, lungs, etc. of mammals and reptiles (fig. 148).
          Tongue worms. LINGUATULINA

[Illustration: 148. Linguatula. (_a_) larva; (enlarged). (_b_) adult;
(natural size).]


ACARINA[E]

a. Abdomen annulate, elongate; very minute forms, often with but four
    legs (fig. 62). DEMODICOIDEA

  b. With but four legs of five segments each. Living on plants, often
      forming galls. ERIOPHYIDÆ

  bb. With eight legs, of three segments each. Living in the skin of
      mammals. DEMODICIDÆ

    To this family belongs the genus DEMODEX found in the sebaceous
        glands and hair follicles of various mammals, including man. _D.
        phylloides_ Csokor has been found in Canada on swine, causing
        white tubercles on the skin. _D. bovis_ Stiles has been reported
        from the United States on cattle, upon the skin of which they
        form swellings. D. FOLLICULORUM Simon is the species found on
        man. See page 78.

aa. Abdomen not annulate nor prolonged behind; eight legs in the adult
    stage.

  b. With a distinct spiracle upon a stigmal plate on each side of the
      body (usually ventral) above the third or fourth coxæ or a little
      behind (fig. 50); palpi free; skin often coriaceous or leathery;
      tarsi often with a sucker.

    c. Hypostome large (fig. 50), furnished below with many recurved
        teeth; venter with furrows, skin leathery; large forms, usually
        parasitic. IXODOIDEA

      d. Without scutum but covered by a more or less uniform leathery
          integument; festoons absent; coxæ unarmed, tarsi without
          ventral spurs; pulvilli absent or vestigial in the adults;
          palpi cylindrical; sexual dimorphism slight. ARGASIDÆ

        e. Body flattened, oval or rounded, with a distinct flattened
            margin differing in structure from the general integument;
            this margin gives the body a sharp edge which is not
            entirely obliterated even when the tick is full fed.
            Capitulum (in adults and nymphs) entirely invisible
            dorsally, distant in the adult by about its own length from
            the anterior border. Eyes absent. ARGUS Latr.

          f. Body oblong; margin with quadrangular cells; anterior tibiæ
              and metatarsi each about three times as long as broad. On
              poultry, southwest United States. A. PERSICUS MINIATUS

            _A. brevipes_ Banks, a species with proportionately shorter
                legs has been recorded from Arizona.

          ff. With another combination of characters. About six other
              species of _Argas_ from various parts of the world,
              parasitic on birds and mammals.

        ee. Body flattened when unfed, but usually becoming very convex
            on distention; anterior end more or less pointed and
            hoodlike; margin thick and not clearly defined, similar in
            structure to the rest of the integument and generally
            disappearing on distention; capitulum subterminal, its
            anterior portions often visible dorsally in the adult; eyes
            present in some species.

          f. Integument pitted, without rounded tubercles; body provided
              with many short stiff bristles; eyes absent. On horses,
              cattle and man (fig. 48). OTIOBIUS Banks.

            O. MEGNINI, a widely distributed species, is the type of
                this genus.

          ff. Integument with rounded tubercles or granules; body
              without stiff bristles. ORNITHODOROS Koch.

            g. Two pairs of eyes; tarsi IV with a prominent subterminal
                spur above; leg I strongly roughened. On cattle and man.
                O. CORIACEUS

            gg. No eyes; no such spur on the hind tarsi.

              h. Tarsi I without humps above. _O. talaje._

              hh. Tarsi I with humps above.

                i. Tarsi IV without distinct humps above. On hogs,
                    cattle and man. O. TURICATA

                ii. Tarsi IV with humps nearly equidistant (fig. 142).
                    Africa. O. MOUBATA

[Illustration: 149. Hæmaphysalis wellingtoni. Note short palpi. After
Nuttall and Warburton.]

      dd. With scutum or shield (fig. 50); festoons usually present;
          coxæ usually armed with spurs, tarsi generally with one or two
          ventral spurs; pulvilli present in the adults; sexual
          dimorphism pronounced. IXODIDÆ

        e. With anal grooves surrounding anus in front; inornate;
            without eyes; no posterior marginal festoons; venter of the
            male with non-salient plates. Numerous species, 14 from the
            United States, among them I. RICINUS (fig. 49 and 50),
            SCAPULARIS, COOKEI, _hexagonus_, _bicornis_. IXODES Latr.
            (including Ceratixodes).

        ee. With anal groove contouring anus behind, or groove faint or
            obsolete.

          f. With short palpi (fig. 149).

            g. Without eyes, inornate, with posterior marginal festoons;
                male without ventral plates. Numerous species. _H.
                chordeilis_ and _leporis-palustris_ from the United
                States. _Hæmaphysalis_ Koch.

[Illustration: 150. Stigmal plate of Dermacentor andersoni; (_a_) of
male, (_b_) of female. After Stiles. (_c_) Dermacentor variabilis, male;
(_d_) Glyciphagus obesus; (_e_) Otodectes cynotis; (_f_) Tyroglyphus
lintneri; (_g_) Tarsonemus pallidus; (_h_) anal plate and mandible of
Liponyssus; (_c_) to (_h_) after Banks.]

            gg. With eyes.

              h. Anal groove distinct; posterior marginal festoons
                  present.

                i. Base of the capitulum (fig. 150c) rectangular
                    dorsally; usually ornate. DERMACENTOR Koch.

                  j. Adults with four longitudinal rows of large
                      denticles on each half of hypostome; stigmal plate
                      nearly circular, without dorso-lateral
                      prolongation, goblets very large, attaining 43µ to
                      115µ in diameter; not over 40 per plate, each
                      plate surrounded by an elevated row of regularly
                      arranged supporting cells; white rust wanting;
                      base of capitulum distinctly broader than long,
                      its postero-lateral angles prolonged slightly, if
                      at all; coxæ T with short spurs; trochanter I with
                      small dorso-terminal blade. Texas, Arizona, etc.
                      _D. nitens_

[Illustration: 151. Rhipicephalus bursa, male. After Nuttall and
Warburton.]

                  jj. Adults with three longitudinal rows of large
                      denticles on each half of hypostome; goblet cells
                      always more than 40 per plate; whitish rust
                      usually present.

                    k. Dorso-lateral prolongation of stigmal plate small
                        or absent; plates of the adults distinctly
                        longer than broad; goblet cells large, usually
                        30µ to 85µ in diameter, appearing as very coarse
                        punctations on untreated specimens, but on
                        specimens treated with caustic potash they
                        appear very distinct in outline; base of
                        capitulum distinctly (usually about twice)
                        broader than long, the postero-lateral angles
                        distinctly produced caudad; spurs of coxæ I
                        long, lateral spur slightly longer than median;
                        trochanter I with dorso-terminal spur. _D.
                        albipictus_, (= _variegatus_), _salmoni_,
                        _nigrolineatus_.

                    kk. Dorso-lateral prolongation of stigmal plate
                        distinct.

                      l. Body of plate distinctly longer than broad;
                          goblet cells of medium size, usually 17.5µ to
                          35µ or 40µ in diameter, appearing as medium
                          sized punctuations on untreated specimens, but
                          on the specimens treated with caustic potash
                          they appear very distinct in outline, which is
                          not circular; base of capitulum usually less
                          than twice as broad as long, the
                          postero-lateral angles always distinctly
                          prolonged caudad.

                        m. Trochanter I with distinct dorso-subterminal
                            retrograde sharp, digitate spur;
                            postero-lateral angles of capitulum
                            pronouncedly prolonged caudal, 112µ to 160µ
                            long; goblet cells attain 13µ to 40µ in
                            diameter; type locality California. D.
                            OCCIDENTALIS

                        mm. Trochanter I with dorso-terminal blade;
                            postero-lateral angles of capitulum with
                            rather short prolongations.

                          n. Stigmal plate small, goblet cells not
                              exceeding 45 in the male or 100 in the
                              female; scutum with little rust, coxa I
                              with short spurs, the inner distinctly
                              shorter than the outer. _D.
                              parumapertus-marginatus_

                          nn. Stigmal plate larger; goblet cells over 70
                              in the male and over 100 in the female;
                              coxa I with longer spurs, inner slightly
                              shorter than the outer; scutum with
                              considerable rust. D. VENUSTUS[F]

                      ll. Goblet cells small, rarely exceeding 17.6µ,
                          occasionally reaching 19µ in diameter; on
                          untreated specimens they appear as very fine
                          granulations, and on specimens treated with
                          caustic potash they may be difficult to see,
                          but their large number can be determined from
                          the prominent stems of the goblets; surface of
                          outline of the goblets distinctly circular;
                          base of the capitulum usually less than twice
                          as broad as long, the postero-lateral angle
                          distinctly prolonged caudad; spurs of coxæ I
                          long. _D. reticulatus_ and _electus_ (=
                          _variabilis_?)

                ii. Base of the capitulum (fig. 151) usually hexagonal
                    (except in the male of _puchellus_); and usually
                    inornate.

                  j. No ventral plate or shield in either sex (fig.
                      153). R. BICORNIS from the United States.
                      RHIPICENTOR Nuttall

                  jj. Males with a pair of adanal shields, and usually a
                      pair of accessory adanal shields. Numerous
                      species, among them _R. sanguineus_ (fig. 154) and
                      _texanus_, the latter from the United States.
                      _Rhipicephalus_ Koch

              hh. Anal grooves faint or obsolete; no marginal festoons.

                i. Short palpi; highly chitinized; unfed adults of large
                    size; coxæ conical; male with a median plate
                    prolonged in two long spines projecting caudad;
                    segments of leg pair IV greatly swollen (fig. 155,
                    156). _M. winthemi_ _Margaropus_ Karsch

[Illustration: 152. Monieziella (Histiogaster) emtomophaga-spermatica,
ventral aspect, male and female. After Trouessart.]

                ii. Very short palpi, ridged dorsally and laterally;
                    slightly chitinized; unfed adults of smaller size;
                    coxæ I bifid; male with adanal and accessory adanal
                    shields (fig. 139). B. ANNULATUS. BOOPHILUS Curtis

          ff. Palpi longer than broad (fig. 157).

            g. Male with pair of adanal shields, and two posterior
                abdominal protrusions capped by chitinized points;
                festoons present or absent. Several species, among them
                H. ÆGYPTICUM (fig. 140) from the old world. HYALOMMA
                Koch

            gg. Male without adanal shields but small ventral plaques
                are occasionally present close to the festoons. Many
                species, a few from the United States (fig. 157).
                AMBLYOMMA Koch

              h. Coxa I with but one spine; metatarsi (except I) with
                  two thickened spurs at tips. _A. maculatum_

              hh. Coxa I with two spines; metatarsi without stout spurs
                  at tips, only slender hairs.

                i. Projections of coxa I blunt and short. Large species
                    on the gopher tortoise in Florida. _A. tuberculatum_

                ii. Projections of coxa I longer, and at least one of
                    them sharp pointed; second segment of palpus twice
                    as long as the third; coxa IV of the male with a
                    long spine.

                  j. Porose areas nearly circular; shield of both sexes
                      pale yellowish, with some silvery streaks and
                      marks, and some reddish spots; shield of female as
                      broad as long. A. CAJENNENSE (= MIXTUM).

                  jj. Porose areas elongate, shield brown, in the female
                      with an apical silvery mark, in the male with two
                      small and two or four other silvery spots; shield
                      of the female longer than broad (fig 158 e). A.
                      AMERICANUM.

[Illustration: 153. Rhipicentor bicornis, ventral aspect, male. After
Nuttall and Warburton.]

    cc. Hypostome small, without teeth, venter without furrows; body
        often with coriaceous shields, posterior margin of the body
        never crenulate (i.e. without festoons); no eyes. GAMASOIDEA.

      d. Parasitic on vertebrates; mandibles fitted for piercing; body
          sometimes constricted. DERMANYSSIDÆ.

        e. Anal plate present. DERMANYSSINÆ.

          f. Body short; legs stout, hind pair reaching much beyond the
              tip of the body. On bats. _Pteroptus_ Dufour.

          ff. Body long; hind legs not reaching beyond the tip of the
              body.

            g. Peritreme on the dorsum, very short; body distinctly
                  constricted. _Ptilonyssus_ Berl.

            gg. Peritreme on the venter, longer; body not distinctly
                  constricted.

                h. Mandibles in both sexes chelate. Parasitic on bats,
                    mice and birds (fig. 150, h). LIPONYSSUS Kol.

                  The species L. (= LEIOGNATHUS) SYLVIARUM frequents the
                      nests of warblers. An instance is on record of
                      these mites attacking man, causing a pruritis.

                hh. Mandibles in the male chelate (fig. 158 j), in the
                    female long, styliform. Parasitic on birds.
                    DERMANYSSUS Dug. Two species of importance may be
                    noted, _D. hirundinus_ and D. GALLINÆ. The latter
                    (fig. 51) is a serious pest of poultry, sometimes
                    attacking man, causing itching and soreness.

        ee. Anal plate absent. In lungs and air passages of some
            mammals. HALARACHNINÆ.

      dd. Free or attached to insects, rarely on vertebrates.

        e. First pair of legs inserted within the same body opening as
            the oral tube; genital apertures surrounded by the sternum.
            On insects. UROPODIDÆ.

[Illustration: 154. Rhicephalus sanguineus, male. After Nuttall and
Warburton.]

        ee. First pair of legs inserted at one side of the mouth
            opening; male genital aperture usually on the anterior
            margin of the sternal plate. GAMASIDÆ.

          This family contains a number of genera, some of which are
              found upon mammals, though the majority affect only other
              arthropods. One species, LÆLAPS STABULARIS, frequents the
              bedding in stables, and in one instance at least, has
              occasioned irritation and itching, in man.

  bb. No distinct spiracle in the stigmal plate on each side of the
      body.

    c. Body usually coriaceous, with few hairs, with a specialized seta
        arising from a pore near each posterior corner of the
        cephalothorax; no eyes; mouth parts and palpi very small;
        ventral openings of the abdomen large; tarsi without sucker. Not
        parasitic. ORIBATOIDEA.

    cc. Body softer; without such specialized seta.

      d. Aquatic species. HYDRACHNOIDEA.

      dd. Not aquatic.

        e. Palpi small, three segmented, adhering for some distance to
            the lip; ventral suckers at genital opening or near anal
            opening usually present; no eyes; tarsi often end in
            suckers; beneath the skin on the venter are seen rod-like
            epimera that support the legs; body often entire. Adults
            frequently parasitic. SARCOPTOIDEA.

          f. With tracheæ; no ventral suckers; legs ending in claws;
              body divided into cephalothorax and abdomen; the female
              with a clavate hair between legs I and II. Usually not
              parasitic on birds and mammals. TARSONEMIDÆ

            g. Hind legs of female ending in claw and sucker as in the
                other pairs. PEDICULOIDINÆ

              To this sub-family belongs the genus PEDICULOIDES

              P. ventricosus is described on page 69.

[Illustration: 155. Margaropus winthemi, male. After Nuttall and
Warburton.]

[Illustration: 156. Margaropus winthemi, capitulum and scutum.
After Nuttall and Warburton.]

            gg. Hind legs of the female end in long hairs. TARSONEMINÆ

              TARSONEMUS INTECTUS Karpelles, normally found upon grain,
                  is said to attack man in Hungary and Russia. Other
                  species of the genus affect various plants (c.f. fig.
                  150, g).

          ff. Without tracheæ; no such clavate hair.

            g. Genital suckers usually present; integument usually
                without fine parallel lines.

              h. Legs short, without clavate hair on tarsi I and II. On
                  insects. CANESTRINIDÆ.

              hh. Legs longer, with a clavate hair on tarsi I and II.
                  Not normally parasitic except on bees. TYROGLYPHIDÆ

                i. Dorsal integument more or less granulate; claws very
                    weak, almost invisible; some hairs of the body
                    plainly feathered; ventral apertures large.
                    GLYCIPHAGUS Her.

                  This genus occurs in the United States. In Europe the
                      mites have been found feeding on all sorts of
                      substances. They are known as sugar mites and
                      cause the disease known as grocer's itch. G.
                      DOMESTICUS and G. PRUNORUM are old world species
                      (fig. 150, d).

                ii. Dorsal integument not granulate; claws distinct; no
                    prominent feathered hairs; ventral aperture small.

                  j. Mandibles not chelate; elongate, and toothed below;
                      body without long hairs; palpi enlarged at tip and
                      provided with two divergent bristles. Species feed
                      on decaying substances. _Histiostoma_ Kram.

                  jj. Mandibles chelate; palpi not enlarged at the tip,
                      nor with two bristles.

                    k. No clavate hair on the base of tarsi I and II; no
                        suture between cephalothorax and abdomen. Live
                        on bees or in their nests. _Trichotarsus_ Can.

                    kk. A clavate or thickened hair at the base of tarsi
                        I and II.

                      l. The bristle on the penultimate segment of the
                          legs arises from near the middle; no suture
                          between the cephalothorax and abdomen. The
                          species, some of which occur in the United
                          States, feed on dried fruit, etc.
                          _Carpoglyphus_ Robin.

                      ll. The bristle on the penultimate segment of the
                          legs arise from near the tip; a suture between
                          cephalothorax and abdomen.

                        m. Cephalothorax with four distinct and long
                            bristles in a transverse row; tarsi I and II
                            about twice as long as the preceding segment
                            (fig. 150 f). TYROGLYPHUS Latr.

                          n. Some bristles on tarsi I and II near
                              middle, distinctly spine-like; the sense
                              hair about its length from the base of the
                              segment. Several species in the United
                              States belong to this group.

                          nn. No spine-like bristles near the middle of
                              the tarsi; sense hair not its length from
                              the base of the segment.

                            o. Of the terminal abdominal bristles, only
                                two are about as long as the abdomen;
                                leg I of the male greatly thickened and
                                with a spine at apex of the femur below.
                                T. FARINÆ.

                            oo. Of the terminal abdominal bristles at
                                least six or more are very long, nearly
                                as long as the body.

                              p. Bristles of the body distinctly plumose
                                  or pectinate; tarsi very long. T.
                                  LONGIOR.

                              pp. Bristles of the body not pectinate.

                                q. In mills, stored foods, grains, etc.
                                    Third and fourth joints of hind legs
                                    scarcely twice as long as broad;
                                    abdominal bristles not unusually
                                    long; legs I and II of the male not
                                    unusually stout. T. AMERICANUS.

                                qq. With other characters and habits.
                                    _T. lintneri_ (fig. 150 f) the
                                    mushroom mite, and several other
                                    species.

                        mm. Cephalothorax with but two long distinct
                            bristles (besides the frontal pair), but
                            sometimes a very minute intermediate pair;
                            tarsi I and II unusually short and not twice
                            as long as the preceding segment.

                          n. Tarsi with some stout spines. RHIZOGLYPHUS
                              Clap.

                            The species of this genus are vegetable
                                feeders. Several occur in the United
                                States. R. PARASITICUS and R.
                                SPINITARSUS have been recorded from the
                                old world, attacking human beings who
                                handle affected plants.

                          nn. Tarsi with only fine hairs. MONIEZIELLA
                              Berl.

                            The species of this genus, as far as known,
                                are predaceous or feed on recently
                                killed animal matter. Several species
                                occur in the United States. M. (=
                                HISTIOGASTER) ENTOMOPHAGA (fig. 152)
                                from the old world has been recorded as
                                injurious to man.

            gg. Genital suckers absent; integument with fine parallel
                lines. Parasitic on birds and mammals.

              h. Possessing a specially developed apparatus for clinging
                  to hairs of mammals. LISTROPHORIDÆ.

              hh. Without such apparatus.

                i. Living on the plumage of birds. ANALGESIDÆ.

                ii. In the living tissues of birds and mammals.

                  j. Vulva longitudinal. In the skin and cellular
                      tissues of birds. CYTOLEICHIDÆ.

                    This family contains two species, both occurring in
                        the United States on the common fowl.
                        _Laminosioptes cysticola_ occurs on the skin and
                        also bores into the subcutaneous tissue where it
                        gives rise to a calcareous cyst. _Cytoleichus
                        nudus_ is most commonly found in the air
                        passages and air cells.

                  jj. Vulva transverse. In the skin of mammals and
                      birds. SARCOPTIDÆ

                    k. Anal opening on the dorsum.

                      l. Third pair of legs in the male without apical
                          suckers. On cats and rabbits. NOTOEDRES
                          Rail.

                        The itch mite of the cat, N. CATI (fig. 61) has
                            been recorded on man.

                      ll. Third leg in the male with suckers. On bats
                          _Prosopodectes_ Can.

                    kk. Anal opening below.

                      l. Pedicel of the suckers jointed; mandibles
                          styliform and serrate near the tip. PSOROPTES
                          Gerv. P. COMMUNIS OVIS is the cause of sheep
                          scab.

                      ll. Pedicel of the suckers not jointed; mandibles
                          chelate.

                        m. No suckers on the legs of the females;
                            parasitic on birds, including chickens. _C.
                            mutans_ is itch mite of chickens.
                            _Cnemidocoptes_ Fürst.

                        mm. Suckers at least on legs I and II; parasitic
                            on mammals.

                          n. Legs very short; in the male the hind pairs
                              equal in size; body usually short.
                              SARCOPTES Latr.

                            S. SCABIEI is the itch mite of man (fig.
                                56).

[Illustration: 157. Amblyomma, female. After Nuttall and Warburton.]

                          nn. Legs more slender; in the male the third
                              pair is much larger than the fourth; body
                              more elongate.

                            o. Female with suckers on the fourth pair of
                                legs. Species do not burrow in the skin,
                                but produce a scab similar to sheep
                                scab. They occur in the ox, horse, sheep
                                and goat. CHORIOPTES Gerv. C. SYMBIOTES
                                BOVIS of the ox has been recorded a few
                                times on man.

                            oo. Female without suckers to the fourth
                                legs.

                              p. Hind part of the male abdomen with two
                                  lobes. On a few wild animals.
                                  _Caparinia_ Can.

                              pp. Hind part of the male abdomen without
                                  lobes. Live in ears of dogs and cats.
                                  _Otodectes_ Canestr.

                                _O. cynotis_ Hering (fig. 150 e) has
                                    been taken in the United States.

        ee. Palpi usually of four or five segments, free; rarely with
            ventral suckers near genital or anal openings; eyes often
            present; tarsi never end in suckers; body usually divided
            into cephalothorax and abdomen; rod-like epimera rarely
            visible; adults rarely parasitic.

          f. Last segment of the palpi never forms a thumb to the
              preceding segment; palpi simple, or rarely formed to hold
              prey; body with but few hairs. EUPODOIDEA.

            g. Palpi often geniculate, or else fitted for grasping prey;
                mandibles large and snout like; cephalothorax with four
                long bristles above, two in front, two behind; last
                segment of leg I longer than the preceding segment,
                often twice as long. BDELLIDÆ.

            gg. Palpi never geniculate (fig. 158a), nor fitted for
                grasping prey: beak small; cephalothorax with bristles
                in different arrangement; last segment of leg I shorter
                or but little longer than the preceding joint; eyes when
                present near posterior border. EUPODIDÆ

              Moniez has described a species from Belgium (TYDEUS
                  MOLESTUS) which attacks man. It is rose colored;
                  eyeless; its legs are scarcely as long as its body,
                  the hind femur is not thickened; the mandibles are
                  small and the anal opening is on the venter. The
                  female attains a length of about 0.3 mm.

          ff. Last segment of the palpus forms a thumb to the preceding,
              which ends in a claw (with few exceptions); body often
              with many hairs (fig. 158 k). TROMBIDOIDEA.

            g. Legs I and II with processes bearing spines; skin with
                several shields; coxæ contiguous. CÆCULIDÆ.

            gg. Legs I and II without such processes; few if any
                shields.

              h. Palpi much thickened on the base, moving laterally,
                  last joint often with two pectinate bristles; no eyes;
                  legs I ending in several long hairs; adult sometimes
                  parasitic. CHEYLETIDÆ

                CHEYLETUS ERUDITUS, which frequents old books, has once
                    been found in pus discharged from the ear of man.

              hh. Palpi less thickened, moving vertically; eyes usually
                  present; leg I not ending in long hairs.

                i. Coxæ contiguous, radiate; legs slender, bristly; body
                    with few hairs; no dorsal groove; tarsi not swollen.
                    ERYTHRÆIDÆ.

                ii. Coxæ more or less in two groups; legs less bristly.

[Illustration: 158. (_a_) Tydeus, beak and leg from below; (_b_)
Cheyletus pyriformis, beak and palpus; (_c_) beak and claw of
Pediculoides; (_d_) leg of Sarcoptes; (_e_) scutum of female of
Amblyomma americana; (_f_) leg I and tip of mandible of Histiostoma
americana; (_g_) Histiogaster malus, mandible and venter; (_h_)
Aleurobius farinæ, palpus and leg I of male; (_i_) Otodectes cynotis, tip of
abdomen of male, (_j_) beak and anal plate of Dermanyssus gallinæ female; (_k_)
palpus of Allothrombium. (_a_) to (_j_) after Banks.]

                  j. Body with fewer, longer hairs; often spinning
                      threads; no dorsal groove; tarsi never swollen;
                      mandibles styliform (for piercing). TETRANYCHIDÆ

                    The genus TETRANYCHUS may be distinguished from the
                        other genera occurring in the United States by
                        the following characters: No scale-like
                        projections on the front of the cephalothorax;
                        legs I as long or longer than the body; palp
                        ends in a distinct thumb; the body is about 1.5
                        times as long as broad. T. MOLESTISSIMUS Weyenb.
                        from South America, and T. TELARIUS from Europe
                        and America ordinarily infesting plants, are
                        said also to molest man.

                  jj. Body with many fine hairs or short spines; not
                      spinning threads; often with dorsal groove; tarsi
                      often swollen.

                    k. Mandibles styliform for piercing. RHYCHOLOPHIDÆ.

                    kk. Mandibles chelate, for biting. TROMBIDIDÆ

                      The genus TROMBIDIUM has recently been subdivided
                          by Berlese into a number of smaller ones, of
                          which some five or six occur in the United
                          States. The mature mite is not parasitic but
                          the larvæ which are very numerous in certain
                          localities will cause intense itching,
                          soreness, and even more serious complications.
                          They burrow beneath the skin and produce
                          inflamed spots. They have received the
                          popular name of "RED BUG." The names LEPTUS
                          AMERICANUS and L. IRRITANS have been applied
                          to them, although they are now known to be
                          immature stages. (Fig. 44.)


HEXAPODA (Insecta)

The Thysanura (springtails and bristletails), the Neuropteroids
(may-flies, stone-flies, dragon-flies, caddis-flies, etc.), Mallophaga
(bird lice), Physopoda (thrips), Orthoptera (grasshoppers, crickets,
roaches), are of no special interest from our viewpoint. The remaining
orders are briefly characterized below.


SIPHUNCULATA (page 275)

Mouth parts suctorial; beak fleshy, not jointed; insect wingless;
parasitic upon mammals. Metamorphosis incomplete. Lice.


HEMIPTERA (page 275)

Mouth parts suctorial; beak or the sheath of the beak jointed; in the
mature state usually with four wings. In external appearance the
immature insect resembles the adult except that the immature form (i.e.
nymph) never has wings, the successive instars during the process of
growth, therefore, are quite similar; and the metamorphosis is thus
incomplete. To this order belong the true bugs, the plant lice, leaf
hoppers, frog hoppers, cicadas, etc.


LEPIDOPTERA

The adult insect has the body covered with scales and (with the rare
exception of the females of a few species) with four wings also covered
with scales. Proboscis, when present, coiled, not segmented, adapted for
sucking. Metamorphosis complete, i.e. the young which hatches from the
egg is quite unlike the adult, and after undergoing several molts
transforms into a quiescent pupa which is frequently enclosed in a
cocoon from which the adult later emerges. The larvæ are known as
caterpillars. Butterflies and moths.


DIPTERA (page 285)

The adult insect is provided with two, usually transparent, wings, the
second pair of wings of other insects being replaced by a pair of
halteres or balancers. In a few rare species the wings, or halteres, or
both, are wanting. The mouth parts, which are not segmented, are adapted
for sucking. The tarsi are five-segmented. Metamorphosis complete. The
larvæ, which are never provided with jointed legs, are variously known
as maggots, or grubs, or wrigglers. Flies, midges, mosquitoes.


SIPHONAPTERA (page 316)

Mouth parts adapted for sucking; body naked or with bristles and spines;
prothorax well developed; body compressed; tarsi with five segments;
wings absent. Metamorphosis complete. The larva is a wormlike creature.
Fleas.


COLEOPTERA

Adult with four wings (rarely wanting), the first pair horny or
leathery, veinless, forming wing covers which meet in a line along the
middle of the back. Mouth parts of both immature stages and adults
adapted for biting and chewing. Metamorphosis complete. The larvæ of
many species are known as grubs. Beetles.


HYMENOPTERA

Adult insect with four, usually transparent, wings, wanting in some
species. Mouth parts adapted for biting and sucking; palpi small; tarsi
four or five-segmented. Metamorphosis complete. Parasitic four-winged
flies, ants, bees, and wasps.


SIPHUNCULATA AND HEMIPTERA

a. Legs with claws fitted for clinging to hairs; wings wanting;
    spiracles of the abdomen on the dorsal surface. (= ANOPLURA =
    PARASITICA) SIPHUNCULATA.

  b. Legs not modified into clinging hooks; tibia and tarsus very long
      and slender; tibia without thumb-like process; antennæ
      five-segmented HÆMATOMYZIDÆ Endr.

    _Hæmatomyzus elephantis_ on the elephant.

  bb. Legs modified into clinging hooks; tibia and tarsus usually short
      and stout; tibia with a thumb-like process; head not anteriorly
      prolonged, tube-like.

    c. Body depressed; a pair of stigmata on the mesothorax, and
        abdominal segments three to eight; antennæ three to
        five-segmented.

      d. Eyes large, projecting, distinctly pigmented; pharynx short and
          broad; fulturæ (inner skeleton of head) very strong and broad,
          with broad arms; proboscis short, scarcely attaining the
          thorax. PEDICULIDÆ

        e. Antennæ three-segmented. A few species occurring upon old
            world monkeys. _Pedicinis_ Gerv.

        ee. Antennæ five-segmented.

          f. All legs stout; thumb-like process of the tibia very long
              and slender, beset with strong spines, fore legs stouter
              than the others; abdomen elongate, segments without
              lateral processes; the divided telson with a conical
              process posteriorly upon the ventral side. PEDICULUS L.

            g. Upon man.

              h. Each abdominal segment dorsally with from one to three
                  more or less regular transverse rows of small setæ;
                  antenna about as long as the width of the head. Head
                  louse (fig. 65). P. HUMANUS.

              hh. "No transverse rows of abdominal setæ; antenna longer
                  than the width of the head; species larger." Piaget.
                  Body louse of man. P. CORPORIS.

            gg. Upon apes and other mammals. _P. pusitatus_ (?).

          ff. Fore legs delicate, with very long and slender claws;
              other legs very stout with short and stout claws;
              thumb-like process of the tibia short and stout; abdomen
              very short and broad; segment one to five closely crowded,
              thus the stigmata of segments three to five apparently
              lying in one segment; segments five to eight with lateral
              processes; telson without lateral conical appendages (fig.
              69). Crab louse of man. PHTHIRUS PUBIS.

      dd. Eyes indistinct or wanting; pharynx long and slender, fulturæ
          very slender and closely applied to the pharynx; proboscis
          very long. Several genera found upon various mammals.
          HÆMATOPINIDÆ.

    cc. Body swollen; meso- and metathorax, and abdominal segments two
        to eight each with a pair of stigmata; eyes wanting; antennæ
        four or five-segmented; body covered with stout spines. Three
        genera found upon marine mammals. ECHINOPHTHIRIIDÆ

aa. Legs fitted for walking or jumping; spiracles of abdomen usually
    ventral; beak segmented.

  b. Apex of head usually directed anteriorly; beak arising from its
      apex; sides of the face remote from the front coxæ; first pair of
      wings when present thickened at base, with thinner margins.
      HETEROPTERA

[Illustration: 159. Taxonomic details of Hemiptera-Heteroptera. (_a_)
Dorsal aspect; (_b_) seta from bedbug; (_c_) wing of Heteropteron; (_d_)
leg; (_e_) wing of Sinea.]

    c. Front tarsi of one segment, spade-form (palæformes); beak short,
        at most two-segmented; intermediate legs long, slender;
        posterior pair adapted for swimming. CORIXIDÆ

    cc. Front tarsi rarely one-segmented, never spade-form; beak free,
        at least three-segmented.

      d. Pulvilli wanting.

        e. Hemelytra usually with a distinct clavus (fig. 159), clavus
            always ends behind the apex of the scutellum, forming the
            commissure. (Species having the wings much reduced or
            wanting should be sought for in both sections.)

          f. Antennæ very short; meso- and metasternum composite; eyes
              always present.

            g. Ocelli present; beak four-segmented. OCHTERIDÆ and
                NERTHRIDÆ.

            gg. Ocelli wanting; antennæ more or less hidden in a groove.

              h. Anterior coxæ inserted at or near anterior margin of
                  the prosternum; front legs raptorial; beak
                  three-segmented BELOSTOMIDÆ (with swimming legs),
                  NEPIDÆ, NAUCORIDÆ.

                i. Metasternum without a median longitudinal keel;
                    antennæ always four-segmented.

                  j. Beak short, robust, conical; the hairy fleck on the
                      corium elongate, large, lying in the middle
                      between the inner angle of the membrane and the
                      outer vein parallel to the membrane margin;
                      membrane margin S-shaped.

                    k. The thick fore femur with a relatively deep
                        longitudinal furrow to receive the tibia.
                        Several American species (fig. 19f.). BELOSTOMA
                        (= Lethocerus Mayer)

                    kk. The less thickened fore femur without such a
                        furrow. B. GRISEUS. BENACUS Stäl.

                  jj. Beak slender, cylindrical; the hairy spot on the
                      corium rounded lying next to the inner angle of
                      the membrane.

                    k. Membrane large, furrow of the embolium broadened.
                        _Z. aurantiacum_, _fluminea_, etc. _Zaitha_

                    kk. Membrane very short; furrow of embolium not
                        broadened. Western genus. _Pedinocoris_

              ii. Metasternum with a long median longitudinal keel.
                  Southwestern forms. _Abedus ovatus_ and _Deniostoma
                  dilatato_

            hh. Anterior coxæ inserted at the posterior margin of the
                prosternum; legs natatorial. Back swimmers (fig. 19 b.).
                NOTONECTIDÆ

              i. Apices of the hemelytra entire; the three pairs of legs
                  similar in shape; beak three-segmented; abdomen not
                  keeled or hairy. _Plea_ Leach

              ii. Apices of hemelytra notched; legs dissimilar; beak
                  four-segmented; abdomen keeled and hairy.

                j. Hemelytra usually much longer than the abdomen;
                    fourth segment of the antenna longer than the third
                    segment; hind tarsi with claws. _Bueno_ Kirk.

                jj. Hemelytra but little longer than the abdomen; fourth
                    segment of the antenna shorter than the third
                    segment; hind tarsi without claws (fig. 19b).
                    NOTONECTA L.

          ff. Antennæ longer than the head; or if shorter, then the eyes
              and ocelli absent.

            g. Eyes, ocelli, and scutellum wanting; beak
                three-segmented; head short; hemelytra always short;
                membrane wanting. Insects parasitic on bats. POLYCTENIDÆ

            gg. Eyes present.

              h. First two antennal segments very short, last two long,
                  pilose, third thickened at the base; ocelli present,
                  veins of the hemelytra forming cells. DIPSOCORIDÆ (=
                  CERATOCOMBIDÆ) including SCHIZOPTERIDÆ.

              hh. Third segment of the antenna not thickened at the
                  base, second as long or longer than the third, rarely
                  shorter.

                i. Posterior coxæ hinged (cardinate), if rarely
                    rotating, the cuneus is severed, the membrane is one
                    or two-celled, and the meso- and metasternum are
                    composite.

                  j. Ocelli absent, clypeus dilated toward the apex;
                      hemelytra always short, membrane wanting. Species
                      parasitic. Bed bugs, etc. CIMICIDÆ

                    k. Beak short, reaching to about the anterior coxæ;
                        scutellum acuminate at the apex; lateral margin
                        of the elytra but little reflexed, apical margin
                        more or less rounded; intermediate and posterior
                        coxæ very remote.

                      l. Body covered with short hairs, only the sides
                          of the pronotum and the hemelytra fringed with
                          longer hairs; antennæ with the third and
                          fourth segments very much more slender than
                          the first and second; pronotum with the
                          anterior margin very _deeply sinuate_. CIMEX
                          L.

                        m. Sides of the pronotum widely dilated, broader
                            than the breadth of one eye, and densely
                            fringed with backward curved hairs; apical
                            margin of the hemelytra nearly straight,
                            rounded toward the interior or exterior
                            angles.

                          n. Body covered with very short hairs; second
                              segment of the antenna shorter than the
                              third; sides of the pronotum feebly
                              reflexed, fringed with shorter hairs than
                              the breadth of one eye; hemelytra with the
                              commissural (inner) margin rounded and
                              shorter than the scutellum, apical margin
                              rounded towards the interior angle. The
                              common bed bug (fig. 19h). C. LECTULARIUS
                              Linn

                          nn. Body covered with longer hairs; second and
                              third segments of the antenna of equal
                              length; side of the pronotum narrowly, but
                              distinctly, reflexed, fringed with longer
                              hairs than the breadth of one eye;
                              hemelytra with the commissural margin
                              straight and longer than the scutellum,
                              apical margin rounded towards the exterior
                              angle. Species found on bats in various
                              parts of the United States. _C.
                              pillosellus_ Hov.

                        mm. Sides of the pronotum neither dilated, nor
                            reflexed, fringed with less dense and nearly
                            straight hairs; hemelytra with the apical
                            margin distinctly rounded. Parasitic on man,
                            birds and bats. Occurs in the old world,
                            Brazil and the West Indies. C. HEMIPTERUS
                            Fabr. (= rotundatus)

                      ll. Body clothed with rather longer silky hairs;
                          third and fourth segments of the antenna
                          somewhat more slender than the first and
                          second; anterior margin of the pronotum _very
                          slightly sinuate_ or nearly straight in the
                          middle, produced at the lateral angles. This
                          is the species which in American collections
                          is known as _C. hirundinis_, the latter being
                          an old world form. It is found in swallows
                          nests. O. VICARIUS. OECIACUS Stäl

                    kk. Beak long, reaching to the posterior coxæ;
                        scutellum rounded at the apex; lateral margins
                        of the elytra strongly reflexed, apical margin
                        slightly sinuate toward the middle; intermediate
                        and posterior coxæ sub-contiguous. This species
                        infests poultry in southwest United States and
                        in Mexico. H. INODORUS. HÆMATOSIPHON Champ.

[Illustration: 160. Pselliopsis (Milyas) cinctus (×2). After C. V.
Riley.]

                  jj. Ocelli present, if rarely absent in the female,
                      then the tarsus has two segments; or if with three
                      tarsal segments, the wing membrane with one or two
                      cells.

                    k. Beak four-segmented, or with two-segmented tarsi.
                        ISOMETOPIDÆ, MICROPHYSIDÆ, and some CAPSIDÆ.

                    kk. Beak three-segmented.

                      l. Hemelytra with embolium; head horizontal, more
                          or less conical; membrane with one to four
                          veins, rarely wanting. ANTHOCORIDÆ

                        Several species of this family affecting man
                            have been noted, ANTHOCORIS KINGI and
                            CONGOLENSE, from Africa and LYCTOCORIS
                            CAMPESTRIS from various parts of the world.
                            LYCTOCORIS FITCHII Reuter (fig. 19 j), later
                            considered by Reuter as a variety of L.
                            CAMPESTRIS, occurs in the United States.

                      ll. Hemelytra without embolium. Superfamily
                          ACANTHIOIDEA (= SALDÆ Fieber and LEPTOPODÆ
                          Fieber)

                ii. Posterior coxæ rotating.

                  j. Claws preapical; aquatic forms. GERRIDÆ and VELIADÆ

                  jj. Claws apical.

                    k. Prosternum without stridulatory sulcus (notch for
                        beak).

                      l. Tarsus with three segments; membrane with two
                          or three longitudinal cells from which veins
                          radiate; rarely with free longitudinal veins
                          (Arachnocoris) or veins nearly obsolete
                          (Arbela); clavus and corium coriaceous; ocelli
                          rarely absent. NABIDÆ

                        REDUVIOLUS (= CORISCUS) SUBCOLEOPTRATUS (fig. 19
                            g), a species belonging to this family,
                            occurring in the United States, has been
                            accused of biting man. This insect is flat,
                            of a jet black color, bordered with yellow
                            on the sides of the abdomen, and with
                            yellowish legs. It is predaceous, feeding on
                            other insects.

                      ll. With other combinations of characters.
                          HYDROMETRIDÆ, HENICOCEPHALIDÆ, NÆOGEIDÆ,
                          MESOVELIADÆ, JOPPEICIDÆ

                    kk. Prosternum with stridulatory sulcus (notch for
                        beak); with three segments, short, strong.

                      l. Antennæ filiform or sometimes more slender
                          apically, geniculate; wing membrane with two
                          or three large basal cells; scutellum small or
                          moderate REDUVIIDÆ

                        For a key to the genera and species see next
                            page.

                      ll. Last antennal segment clavate or fusiform; win
                          membrane with the veins often forked and
                          anastomosing; scutellum large; tarsi each with
                          two segments; fore legs strong. (= PHYMATIDÆ)
                          MACROCEPHALIDÆ

        ee. Clavus noticeably narrowed towards the apex, never extending
            beyond the scutellum, the two not meeting to form a
            commissure; head horizontal, much prolonged between the
            antennæ, on each side with an antennal tubercle, sometimes
            acute; ocelli absent; meso- and metasternum simple; tarsi
            each with two segments; body flattened (fig. 19c). ARADIDÆ,
            including DYSODIIDÆ.

      dd. Pulvilli present (absent in one Australian family
          THAUMATOCORIDÆ in which case there is a membranous appendage
          at the tip of the tibia). CAPSIDÆ (= MIRIDÆ),[G] _Eotrechus_
          (in family GERRIDÆ), NÆOGAIDÆ, TINGITIDÆ, PIESMIDÆ,
          MYODOCHIDÆ, CORIZIDÆ, COREIDÆ, ALYDIDÆ, PENTATOMIDÆ,
          SCUTELLERIDÆ, etc.

  bb. Apex of head directed ventrally, beak arising from the hinder part
      of the lower side of the head; sides of face contiguous to the
      front coxæ; first pair of wings, when present, of uniform
      thickness. Cicadas, scale insects, plant lice (Aphids),
      spittle-insects, leaf hoppers, etc. HOMOPTERA


REDUVIIDÆ OF THE UNITED STATES

(Adapted from a key given by Fracker).

a. Ocelli none; wings and hemelytra always present in the adults; no
    discoidal areole in the corium near the apex of the clavus.
    _Orthometrops decorata_, _Oncerotrachelus acuminatus_, etc.,
    Pennsylvania and south. _Sarcinæ_

aa. Ocelli present in the winged individuals; anterior coxæ not as long
    as the femora.

  b. Hemelytra without a quadrangular or discoidal areole in the corium
      near the apex of the clavus.

    c. Ocelli not farther cephalad than the caudal margins of the eyes;
        segment two of the antenna single.

      d. Thorax usually constricted caudad of the middle; anterior coxæ
          externally flat or concave. PIRATINÆ

        e. Middle tibiæ without spongy fossa, head long, no lateral
            tubercle on neck. _S. stria_, Carolina, Ill., Cal.
            _Sirthenia_ Spinola

        ee. Middle tibiæ with spongy fossa; fore tibiæ convex above;
            neck with a small tubercle on each side.

          f. Apical portion of anterior tibiæ angularly dilated beneath,
              the spongy fossa being preceded by a small prominence.
              MELANOLESTES Stäl

            g. Black, with piceous legs and antennæ. N. E. States (fig.
                19a) M. PICIPES

            gg. Sides, and sometimes the whole dorsal surface of the
                abdomen red. Ill., and southward. M. ABDOMINALIS

          ff. Tibiæ not dilated as in "f"; spongy fossa elongate;
              metapleural sulci close to the margin. R. BIGUTTATUS (fig.
              22). South RASAHUS A. and S.

      dd. Thorax constricted in the middle or cephalad of the middle;
          anterior tarsi each three-segmented.

        e. Apex of the scutellum narrow, without spines or with a single
            spine REDUVIINÆ

          f. Antennæ inserted in the lateral or dorso-lateral margins of
              the head; antenniferous tubercles slightly projecting from
              the sides of the head; head produced strongly cephalad;
              ocelli at least as far apart as the eyes.

            g. Antennæ inserted very near the apex of the head; segments
                one and three of the beak short, segment two nearly four
                times as long as segment one. R. PROLIXUS. W. I.
                RHODNIUS Stäl

            gg. Antennæ inserted remote from the vertex of the head.

              h. Body slightly hairy; pronotum distinctly constricted;
                  angles distinct; anterior lobe four-tuberculate, with
                  the middle tubercles large and conical. _M.
                  phyllosoma_, large species from the southwest.
                  _Meccus_ Stäl

              hh. Body smooth, margin of the pronotum sinuous, scarcely
                  constricted; anterior lobe lined with little
                  tubercles. CONORHINUS Lap.

                i. Surface of the pronotum and prosternum more or less
                    granular.

                  j. Eyes small, head black; body very narrow, a fifth
                      as wide as long; beak reaches the middle of the
                      prosternum. California. C. PROTRACTUS

                  jj. Eyes large, head fuscous; body at least a fourth
                      as wide as long. Southern species. _C.
                      rubrofasciatus_

                ii. Pronotum and prosternum destitute of granules.

                  j. Border of abdomen entirely black except for a
                      narrow yellowish spot at the apex of one segment.
                      Texas. _C. gerstaeckeri_

                  jj. Border of abdomen otherwise marked.

                    k. Beak slender, joints one and two slightly pilose,
                        two more than twice as long as one; tubercles at
                        the apical angles of the pronotum slightly
                        acute, conical. Md. to Ill. and south. The
                        masked bed bug hunter (fig. 71). C. SANGUISUGUS

                    kk. Beak entirely pilose, joint two a third longer
                        than joint one; joint one much longer than
                        three; tubercles at the apical angles of
                        pronotum slightly elevated, obtuse. Ga., Ill.,
                        Tex., Cal. _C. variegatus_

          ff. Antenna inserted on top of the head between margins, close
              to the eyes; antenniferous tubercles not projecting from
              the side of the head.

            g. Anterior lobe of the pronotum with a bispinous or
                bituberculate disc; femora unarmed. _S. arizonica_, _S.
                bicolor_. Southwestern species. _Spiniger_ Burm.

            gg. Disc of pronotum unarmed; apex of scutellum produced
                into a spine; ocelli close to the eyes; eyes large and
                close together. REDUVIUS Lamarck

              h. Color piceous. Widely distributed in the United States.
                  (Fig. 20). R. PERSONATUS

              hh. More or less testaceous in color. Southwestern states.
                  R. SENILIS

        ee. Apex of scutellum broad, with two or three spines.
            ECTRICHODIINÆ

          f. First segment of the antenna about as long as the head. _E.
              cruciata_ Pa. and south; _E. cinctiventris_, Tex. and Mex.
              _Ectrichodia_ L. et S.

          ff. First segment of the antennæ short. _P. æneo-nitens_.
              South. _Pothea_ A. et S.

    cc. Ocelli cephalad of the hind margins of the eyes; first segment
        of the antennæ stout, second segment divided into many smaller
        segments. South and west. _Homalocoris maculicollis_, and
        _Hammatocerus purcis_. HAMMATOCERINÆ

  bb. Hemelytra with a quadrangular or discoidal areole in the corium
      near the apex of the clavus (fig. 159e).

    c. Anal areole of the membrane not extending as far proximad as the
        costal areole; basal segment of the antenna thickened, porrect;
        the other segments slender, folding back beneath the head and
        the first segment STENOPODINÆ

      d. Head armed with a ramous or furcate spine below each side,
          caudad of the eyes.

        e. First segment of the antenna thickened, apex produced in a
            spine beyond the insertion of the second segment. Species
            from Va., Ill. and south. _Pnirontis_ Stäl.

        ee. First segment of the antenna not produced beyond the
            insertion of the second segment. _Pygolampis_, N. E. states
            and south; _Gnathobleda_, S. W. and Mex.

      dd. Head unarmed below or armed with a simple spine; rarely with a
          subfurcate spine at the side of the base. Carolina, Missouri
          and south. _Stenopoda_, _Schumannia_, _Diaditus_, _Narvesus_,
          _Oncocephalus_

    cc. Anal areole of membrane extending farther proximad than the
        costal areole.

      d. Ocelli farther apart than the eyes. _A. crassipes_, widely
          distributed in the United States; other species occur in the
          southwest. _Apiomerus_ Hahn.

      dd. Ocelli not so far apart as the eyes. ZELINÆ

        e. Sides of mesosternum without a tubercle or fold in front.

          f. Fore femur as long as or longer than the hind femur; first
              segment of the beak much shorter than the second. _Z.
              audax_, in the north eastern states; other species south
              and west. _Zelus_ Fabr.

          ff. Fore femur shorter than the hind femur, rarely of equal
              length, in this case the first segment of the beak as long
              or longer than the second.

            g. First segment of the beak shorter than the second; fore
                femur a little shorter than the hind femur; the first
                segment of the beak distinctly longer than the head
                before the eyes. _P. cinctus_ a widely distributed
                species (fig. 160). _P. punctipes_, _P. spinicollis_,
                Cal., Mex. (= _Milyas_) _Pselliopus_ Berg.

            gg. First segment of the beak as long or longer than the
                second.

              h. Pronotum armed with spines on the disc.

                i. Juga distinctly prominent at the apex and often acute
                    or subacute; fore femur distinctly thickened;
                    hemelytra usually not reaching the apex of the
                    abdomen. _Fitchia aptera_, N. Y., south and west;
                    _F. spinosula_, South; _Rocconata annulicornis_,
                    Texas, etc.

                ii. Juga when prominent, obtuse at apex; eyes full width
                    of the head; fore femur not thickened; pronotum with
                    four spines on posterior lobe. _R. taurus_, Pa.,
                    south and west. _Repipta_ Stäl.

              hh. Pronotum unarmed on the disc.

                i. Spines on each apical angle of the penultimate
                    abdominal segment. _A. cinereus_, Pa., and south.
                    _Atrachelus_ A. et S.

                ii. Apical angle of the penultimate abdominal segment
                    unarmed. _Fitchia_ (in part); _Castolus ferox_,
                    Arizona.

        ee. Sides of the mesosternum with a tubercle or fold in front at
            the hind angles of the prosternum; first segment of the beak
            longer than the part of the head cephalad of the eyes.

          f. Fore femur thickened, densely granulated; hind femur
              unarmed.

[Illustration: 161. Taxonomic details of Diptera. (_a_) Ventral aspect
of abdomen of Cynomyia; (_b_) antenna of Tabanus; (_c_) ventral aspect
of abdomen of Chortophila; (_d_) ventral aspect of abdomen of Stomoxys;
(_e_) claw of Aedes (Culex) sylvestris, male; (_f_) claw of Hippoboscid;
(_g_) foot of dipterous insect showing empodium developed pulvilliform;
(_h_) hind tarsal segment of Simulium vittatum, female; (_i_) foot of
dipterous insect showing bristle-like empodium.]

            g. Fore tibiæ each with three long spines on the ventral
                side. _S. diadema_ (fig. 159e), a widely distributed
                species; and several southwestern species. _Sinea_ A. et
                S.

            gg. Fore tibiæ unarmed. _A. multispinosa_, widely
                distributed; _A. tabida_, Cal. _Acholla_ Stäl.

          ff. Fore femur unarmed, rarely a little thickened, a little
              granulated.

            g. Pronotum produced caudad over the scutellum, with a high
                mesal tuberculate ridge (fig. 19e). A. CRISTATUS. N. Y.
                to Cal. and south. ARILUS Hahn.

            gg. Caudal lobe of the pronotum six sided, neither elevated
                nor produced caudad. _H. americanus_, Southwest; also
                several W. I. and Mexican genera. HARPACTOR Lap.


DIPTERA (Mosquitoes, Midges, Flies)

a. Integument leathery, abdominal segments indistinct; wings often
    wanting; parasitic forms. PUPIPARA

  b. Head folding back on the dorsum of the thorax; wingless flies
      parasitic on bats. Genus _Nycteribia_. NYCTERIBIIDÆ

  bb. Head not folding back upon the dorsum of the thorax; flies either
      winged or wingless; parasitic on birds and on bats and other
      mammals.

    c. Antennæ reduced, wings when present, with distinct parallel veins
        and outer crossveins; claws simple; palpi leaf-like, projecting
        in front of the head. Flies chiefly found on bats. Several
        genera occur in North America. STREBLIDÆ

[Illustration: 162. Hippobosca equina, ×4. After Osborn.]

    cc. Antennæ more elongate, segments more or less distinctly
        separated; head sunk into an emargination of the thorax; wings
        when present with the veins crowded toward the anterior margin;
        palpi not leaf-like. HIPPOBOSCIDÆ

      d. Wings absent or reduced and not adapted for flight.

        e. Wings and halteres (balancers) absent. _M. ovinus_, the sheep
            tick. _Melophagus_ Latr.

        ee. Wing reduced (or cast off), halteres present.

          f. Claw bidentate; ocelli present. On deer after the wings are
              cast off. _L. depressa_. _Lipoptena_ Nitsch

          ff. Claw tridentate (fig. 161 f). On _Macropis_. _B.
              femorata._ _Brachypteromyia_ Will.

      dd. Wings present and adapted for flight.

        e. Claws bidentate.

          f. Ocelli present; head flat; wings frequently cast off. On
              birds before casting of the wing. _Lipoptena_ Nitsch.

          ff. Ocelli absent; head round; wings present. The horse tick
              H. EQUINA may attack man (fig. 162). HIPPOBOSCA L.

        ee. Claws tridentate (fig. 161 f.).

          f. Anal cell closed at apical margin by the anal crossvein.

            g. Ocelli absent. _Stilbometopa_ Coq.

            gg. Ocelli present.

              h. R_{4+5} does not form an angle at the crossvein. On
                  birds. There is a record of one species of this genus
                  attacking man. ORNITHOMYIA Latr.

              hh. R_{4+5} makes an angle at the crossvein. _O.
                  confluens_. _Ornithoica_ Rdi.

          ff. Anal cell not closed by an anal crossvein. _Lynchia_,
              _Pseudolfersia_, and _Olfersia_ are chiefly bird
              parasites. The first mentioned genus is said to be the
              intermediate host of _Hæmoproteus columbæ_.

aa. Abdominal segments chitinous; not parasitic in the adult stage.

  b. Antennæ with six or more segments and empodium not developed
      pulvilliform; palpi often with four segments.

    c. Ocelli present. BLEPHAROCERIDÆ, RHYPHIDÆ, BIBIONIDÆ,
        MYCETOPHILIDÆ, besides some isolated genera of other families.

    cc. Ocelli absent.

      d. Dorsum of the thorax with a V-shaped suture; wings usually with
          numerous veins; legs often very long and slender. Crane flies.
          TIPULIDÆ

      dd. Dorsum of the thorax without a V-shaped suture.

        e. Not more than four longitudinal veins ending in the wing
            margin; wing usually hairy: antennæ slender; coxæ not long;
            tibiæ: without spurs, legs long and slender. Small, delicate
            flies often called Gall gnats. CECIDOMYIIDÆ.

        ee. More than four longitudinal veins ending in the wing margin.

          f. The costal vein is not produced beyond the tip of the wing;
              radius with not more than three branches.

            g. Antennæ short, composed of ten or eleven closely united
                segments; legs stout; body stout; abdomen oval; anterior
                veins stout, posterior ones weak (fig. 163 b); eyes of
                the male contiguous over the antennæ. Black flies,
                buffalo flies, turkey gnats. Many North American
                species, several of them notorious for their blood
                sucking propensities. SIMULIIDÆ

              h. Second joint of the hind tarsus with basal scale-like
                  process and dorsal excision (fig. 161 h); radial
                  sector not forked; no small cell at the base of the
                  wing. _S. forbesi_, _jenningsi_, _johannseni_,
                  _meridionale_, _piscicidium_, VENUSTUM, VITTATUM, etc.
                  Widely distributed species (= EUSIMULIUM) SIMULIUM
                  Latr.

              hh. No basal scale-like process on the second joint of the
                  hind tarsus; radial sector usually forked (fig. 163
                  b).

                i. Face broad, small basal cell of the wing present. _P.
                    fulvum_, HIRTIPES, _mutatum_, PECUARUM, _pleurale_.
                    PROSIMULIUM Roub.

                ii. Face linear; small basal cell of the wing absent.
                    One species, _P. furcatum_, from California.
                    _Parasimulium_ Malloch

            gg. Flies of a different structure.

              h. Antennæ composed of apparently two segments and a
                  terminal arista formed of a number of closely united
                  segments. Rare flies with aquatic larvæ.
                  ORPHNEPHILIDÆ

              hh. Antennæ of six to fifteen segments, those of the male
                  usually plumose; legs frequently slender and wings
                  narrow CHIRONOMIDÆ

                i. Media forked (except in the European genus
                    _Brachypogon_); thorax without longitudinal fissure
                    and not produced over the head (except in four
                    exotic genera); antennæ usually fourteen-jointed in
                    both sexes; fore tibia with a simple comb of setulæ,
                    hind tibia with two unequal combs, middle tibia
                    without comb. CERATOPOGONINÆ

                  j. Thorax produced cap-like over the head, wing narrow
                      and very long. _Jenkinsia_, _Macroptilum_ and
                      _Calyptopogon_, eastern hemisphere;
                      _Paryphoconus_, Brazil.

                  jj. Thorax not produced over the head.

                    k. Eyes pubescent, empodium well developed, or if
                        short then R_{2+3} distinct and crossvein-like
                        or the branches of R coalescent; r-m crossvein
                        present; fore femora not thickened; wing either
                        with appressed hairs or with microscopic erect
                        setulæ _Dasyhelea_ Kieff.

                    kk. Eyes bare, or otherwise differing from the
                        foregoing.

                      l. Empodium well developed, nearly as long as the
                          claws and with long hairs at the base; femora
                          and fifth tarsal segments unarmed, i.e.
                          without spines or stout setæ; fourth tarsal
                          segment cylindrical.

                        m. Wing with erect and microscopic setulæ.
                            Widely distributed. (= Atrichopogon)
                            _Ceratopogon_ Meig.

                        mm. Wing with long and depressed hairs. Widely
                            distributed. _Forcipomyia_

                          n. Hind metatarsus shorter or not longer than
                              the following (i.e. the second tarsal)
                              segment. Subgenus _Prohelea_ Kieff

                          nn. Hind metatarsus longer than the following
                              segment. Subgenus _Forcipomyia_ Meig.

                      ll. Empodium short, scarcely reaching the middle
                          of the claws, or vestigial.

                        m. R-m crossvein wanting.

                          n. Palpi four segmented; inferior fork of the
                              media obliterated at the base. Australia.
                              _Leptoconops_ Skuse

                          nn. Palpi three-segmented.

                            o. Legs spinulose, tarsal claws of the
                                female with a basal tooth or strong
                                bristle, those of the male unequal, the
                                anterior with a long sinuous tooth, the
                                posterior with a short arcuate tooth.
                                Italy. MYCTEROTYPUS Noé

                            oo. Legs unarmed; no crossvein between the
                                branches of the radius (fig. 163e). New
                                Mexico. TERSESTHES Townsend

                        mm. R-m crossvein present.

                          n. Fore femora very much swollen, armed with
                              spines below, fore tibia arcuate and
                              applied closely to the inferior margin of
                              the femur.

                            o. R_{2+3} present, therefore cell R_1 and
                                R_2 both present; wing usually fasciate.
                                United States _Heteromyia_ Say.

                            oo. R_{2+3} not distinct from R_{4+5}, hence
                                cell R_3 obliterated. South America
                                _Pachyleptus_ Arrib. (Walker)

                          nn. Fore femur not distinctly swollen.

                            o. R_{2+3} present therefore cells R_1 and
                                R_3 both present, or if not, then the
                                branches of the radius more or less
                                coalescent, obliterating the cells.

                              p. At least the tip of the wing with erect
                                  setulæ; tip of R_{4+5} scarcely
                                  attaining the middle of the wing,
                                  empodium rather indistinct, not
                                  reaching the middle of the claws, the
                                  claws not toothed, equal, with long
                                  basal bristle; legs without stout
                                  setæ. Widely distributed. CULICOIDES
                                  Latr.

                                HÆMATOMYIDIUM and OECACTA are probable
                                    synonyms of this.

                              pp. Wings bare, if rarely with hair, then
                                  the radius reaches beyond two-thirds
                                  the length of the wing, or the femur
                                  or fifth tarsal segment with stout
                                  black spines.

                                q. Media unbranched. Europe.
                                    _Brachypogon_ Kieff

                                qq. Media branched.

                                  r. Hind femur much swollen and spined.
                                      America and Europe. _Serromyia_
                                      Meg.

                                  rr. Hind femur not distinctly swollen.

                                    s. Cell R_1 not longer than high;
                                        fork of the media distad of the
                                        crossvein; wing with microscopic
                                        setulæ _Stilobezzia_ Kieff

                                    ss. Cell R_1 elongate.

                                      t. Femora unarmed. Widely
                                          distributed. (= Sphaeromias
                                          Kieff. 1913 not Curtis?).
                                          JOHANNSENIELLA Will.

                                      tt. Femora, at least in part, with
                                          strong black spines. Widely
                                          distributed. _Palpomyia_
                                          Megerle

                            oo. R_{2+3} coalescent with R_{4+5} hence
                                cell R_3 is obliterated.

                              p. In the female the lower branch of the
                                  media with an elbow near its base
                                  projecting proximad, the petiole of
                                  the media coalescent with the basal
                                  section of the radius, wing long and
                                  narrow, radial sector ending near the
                                  tip of the wing; venation of the male
                                  as in _Bezzia_; front concave. United
                                  States. _Stenoxenus_ Coq.

                              pp. Venation otherwise, front not concave.

                                q. Subcosta and R_1 more or less
                                    coalescent with the costa; wing
                                    pointed at the apex, much longer
                                    than the body; antennæ fourteen
                                    segmented, not plumose. India.
                                    _Haasiella_ Kieff.

                                qq. Subcosta and radius distinct from
                                    the costa.

                                  r. Abdomen petiolate. _Dibezzia_
                                      Kieff.

                                  rr. Abdomen not petiolate.

                                    s. Head semi-globose; hind tarsi
                                        unusually elongate in the
                                        female; antennæ of the male not
                                        plumose. Europe. _Macropeza_
                                        Meigen.

                                    ss. Head not globose, more or less
                                        flattened in front; antennæ of
                                        the male plumose. Widely
                                        distributed. _Bezzia_ Kieff.

                                      t. Fore femora, at least, armed
                                          with stout spines below.
                                          Subgenus _Bezzia_ Kieff.

                                      tt. Femora unarmed. Subgenus
                                          _Probezzia_ Kieff.

                ii. Media of the wing simple, and otherwise not as in
                    "i". To this group belong numerous Chironomid
                    genera, none of which are known to be noxious to
                    man.

          ff. The costal vein apparently is continued around the hind
              margin of the wing; radius with at least four branches.

            g. Wing ovate pointed, with numerous veins; crossveins, if
                evident, before the basal third of the wing; veins very
                hairy; very small moth-like flies. PSYCHODIDÆ

              h. With elongate biting proboscis; the petiole of the
                  anterior forked cell of the wing (R_2) arises at or
                  beyond the middle of the wing (fig. 163d). PHLEBOTOMUS
                  Rdi.

[Illustration: 163. Wings of Diptera. (_a_) Anopheles; (_b_)
Prosimulium; (_c_) Johannseniella; (_d_) Phlebotomus (After Doerr and
Russ); (_e_) Tersesthes (after Townsend); (_f_) Tabanus; (_g_)
Symphoromyia; (_h_) Aphiochæta; (_i_) Eristalis; (_j_) Gastrophilus;
(_k_) Fannia; (_l_) Musca.]

              hh. With shorter proboscis; the petiole of the anterior
                  forked cell arises near the base of the wing.
                  _Psychoda_, _Pericoma_, etc.

            gg. The r-m crossvein placed at or beyond the center of the
                wing; wings not folded roof-like over the abdomen.

              h. Proboscis short, not adapted for piercing; wings bare
                  (DIXIDÆ); or wings scaled (CULICIDÆ, Subf.
                  CORETHRINÆ).

              hh. Proboscis elongate, adapted for piercing; wings
                  scaled, fringed on the hind margin; antennæ of the
                  male bushy plumose. Mosquitoes. CULICIDÆ (exclusive of
                  CORETHRINÆ)

                i. Metanotum without setæ.

                  j. Proboscis strongly decurved; body with broad,
                      appressed, metalescent scales; cell R_2 less than
                      half as long as its petiole; claws of female
                      simple, some of the claws of the male toothed.
                      Several large southern species believed to feed
                      only on nectar of flowers. _Megarhinus_ R. D.

                  jj. Proboscis straight or nearly so, or otherwise
                      different.

                    k. Scutellum evenly rounded, not lobed; claws simple
                        in both sexes. ANOPHELES Meig.

                      l. Abdomen with clusters of broad outstanding
                          scales along the sides; outstanding scales on
                          the veins of the wing rather narrow,
                          lanceolate; upper side of the thorax and
                          scutellum bearing many appressed lanceolate
                          scales. Florida and southward (CELLIA).

                        m. Hind feet from the middle of the second
                            segment largely or wholly snow white.

                          n. With a black band at the base of the last
                              segment of each hind foot. A.
                              ALBIMANUS*[H] and TARSIMACULATA*

                          nn. Without such a band A. ARGYRITARSIS*

                        mm. Hind feet black, mottled with whitish and
                            with bands of the same color at the sutures
                            of the segments. W. I. A. MACULIPES

                      ll. Abdomen without such a cluster of scales;
                          outstanding scales of the wing veins rather
                          narrow, lanceolate; tarsi wholly black.

                        m. Deep black, thorax obscurely lined with
                            violaceous, especially posteriorly; head,
                            abdomen and legs black; no markings on the
                            pleura; abdomen without trace of lighter
                            bindings; wing scales outstanding, uniform,
                            not forming spots, though little thicker at
                            the usual points indicating the spottings.
                            Florida. A. ATROPUS

                        mm. Otherwise marked when the wings are
                            unspotted.

                          n. Wings unspotted.

                            o. Petiole of the first forked cell (R_2)
                                more than a third the length of the
                                cell. Mississippi valley. A. WALKERI

                            oo. Petiole of the first forked cell a third
                                the length of the cell. Md. A. BARBERI

                          nn. Wings spotted.

                            o. Front margin of the wings with a patch of
                                whitish and yellow scales at a point
                                about two-thirds or three-fourths of the
                                way from base to apex of wing.

                              p. Veins of the wing with many broad
                                  obovate outstanding scales; thorax
                                  with a black dot near the middle of
                                  each side. W. I. A. GRABHAMI*

                              pp. The outstanding scales of the wings
                                  rather narrow, lanceolate.

                                q. Scales of the last vein of the wings
                                    white, those at each end black;
                                    R_{4+5} black scaled, the extreme
                                    apex white scaled. Widely
                                    distributed north and south (fig.
                                    131). A. PUNCTIPENNIS

                                  A dark variety from Pennsylvania has
                                      been named A. PERPLEXENS.

                                qq. Scales of the last vein of the wing
                                    white, those at its apex black;
                                    R_{4+5} white scaled and with two
                                    patches of black scales. South and
                                    the tropics. A. FRANCISCANUS and
                                    PSEUDOPUNCTIPENNIS*

                            oo. Front margin of the wings wholly black
                                scaled.

                              p. Last (anal) vein of the wings white
                                  scaled with three patches of black
                                  scales (fig. 132). New Jersey to
                                  Texas. A. CRUCIANS*

                              pp. Last vein of the wings wholly black
                                  scaled.

                                q. Widely distributed north and south
                                    (fig. 130), (= MACULIPENNIS). A.
                                    QUADRIMACULATUS*

                                qq. Distributed from Rocky Mountains
                                    westward. A. OCCIDENTALIS

                    kk. Scutellum distinctly trilobed.

                      l. Cell R_2 less than half as long as its petiole;
                          thorax with metallic blue scales; median lobe
                          of the scutellum not tuberculate; few small
                          species which are not common. URANOTÆNIA
                          Arrib.

                      ll. Cell R_2 nearly or quite as long as its
                          petiole, or otherwise distinct.

                        m. Femora with erect outstanding scales; occiput
                            broad and exposed. Large species. P.
                            CILIATA. P. HOWARDI PSOROPHORA R. D.

                        mm. Femora without erect scales.

                          n. Clypeus bearing several scales or hairs,
                              scutellum with broad scales only; back of
                              head with broad scales; scales along the
                              sides of the mesonotum narrow; some or the
                              claws toothed; thorax marked with a pair
                              of silvery scaled curved stripes; legs
                              black with white bands at the bases of
                              some of the segments (fig. 134). Yellow
                              Fever mosquito. AEDES (= STEGOMYIA)
                              CALOPUS.

                          nn. With another combination of characters.
                              Numerous species of mosquitoes belonging
                              to several closely related genera, widely
                              distributed over the country. (_Culex_,
                              _Aedes_, _Ochlerotatus_, etc.). CULEX in
                              the wide sense.

                ii. Metanotum with setæ. _Wyeomyia_ (found in the United
                    States); and related tropic genera.

  bb. Antennæ composed of three segments with a differentiated style or
      bristle; third segment sometimes complex or annulate, in which
      case the empodium is usually developed like the pulvilli, i.e.,
      pad-like (fig. 161 g).

    c. Empodium developed pad-like (pulvilliform) i.e., three nearly
        equal membranous appendages on the underside of the claw (fig.
        161g).

      d. Squamæ, head, and eyes large; occiput flattened or concave;
          third segment of the antennæ with four to eight annuli or
          segments, proboscis adapted for piercing; body with fine
          hairs, never with bristles; middle tibia with two spurs; wing
          venation as figured (fig. 163f); marginal vein encompasses the
          entire wing. Horse flies, greenheads, deer flies, gad flies
          TABANIDÆ[I]

        e. Hind tibia with spurs at tip; ocelli usually present
            (PANGONINÆ)

          f. Third joint of the antennæ with seven or eight segments;
              proboscis usually prolonged.

            g. Each section the third antennal segment branched. Central
                American species, _P. festæ_. _Pityocera_ G. T.

            gg. Sections of the third antennal segment not branched.

              h. Upper corner of the eyes in the female terminating in
                  an acute angle; wings of both sexes dark anteriorly.
                  _G. chrysocoma_, a species from the eastern states.
                  _Goniops_ Ald.

              hh. Upper corner of the eye in the female not so
                  terminating; wings nearly uniform in color, or
                  hyaline.

                i. Proboscis scarcely extending beyond the palpi; front
                    of the female wide; much wider below than above. S.
                    W. States. _Apatolestes_ Will.

                ii. Proboscis extending beyond the palpi.

                  j. Wing with cell M_3 closed. Tropic America. (=
                      _Diclisa_) _Scione_ Wlk.

                  jj. Cell M_3 open; ocelli present or absent. Two or
                      three eastern species; many south and west
                      PANGONIA Rdi.

          ff. Third segment of the antenna with five divisions; ocelli
              present.

            g. First and second segments of the antenna short, the
                second only half as long as the first, three western
                species. SILVIUS Rdi.

            gg. First and second segments of the antenna long, the
                second distinctly over half as long as the first. Deer
                flies. Many species, widely distributed. CHRYSOPS Meig.

        ee. Hind tibia without spurs; ocelli absent.

          f. Third segment of antenna with four divisions, no tooth or
              angulation; wings marked with rings and circles of darker
              coloring; front of the female very wide. Widely
              distributed. _H. americana_, _H. punctulata_. HÆMATOPOTA
              Meig.

          ff. Third segment of the antenna with five divisions (fig.
              161b).

            g. Third segment of the antenna not furnished with a tooth
                or distinct angular projection.

              h. Body covered with metallic scales; front of female of
                  normal width; front and middle tibiæ greatly dilated.
                  _L. lepidota_. _Lepidoselaga_ Macq.

              hh. Body without metallic scales; antennæ not very long,
                  the third segment not cylindrical, not situated on a
                  projecting tubercle; front of the female narrow.
                  South. _D. ferrugatus._ (= _Diabasis_) _Diachlorus_ O.
                  S.

            gg. Third segment of the antenna furnished with a tooth or a
                distinct angular projection.

              h. Hind tibiæ ciliate with long hairs. S. W. and tropics.
                  _Snowiella_ and _Stibasoma_.

              hh. Hind tibiæ not ciliate.

                i. Species of slender build, usually with a banded
                    thorax and abdomen; third segment of the antenna
                    slender, the basal prominence long; wings mostly
                    with brownish markings. Tropic America.
                    _Dichelacera_ Macq.

                ii. Species of a stouter build; third segment of the
                    antenna stout, its basal process short (fig. 161b).
                    Many species, widely distributed TABANUS L.

      dd. With another group of characters.

        e. Squamæ small, antennæ variable, thinly pilose or nearly bare
            species, without distinct bristles; wing veins not crowded
            anteriorly, R_4 and R_5 both present, basal cells large;
            middle tibiæ at least with spurs. LEPTIDÆ

          f. Flagellum of the antenna more or less elongated, composed
              of numerous more or less distinct divisions. XYLOPHAGINÆ
              and ARTHROCERATINÆ.

          ff. Antennæ short, third segment simple, with arista or style;
              face small, proboscis short LEPTINÆ

            g. Front tibiæ each with one or two spurs, or if absent,
                then no discal cell. _Triptotricha_, _Pheneus_,
                _Dialysis_, _Hilarimorpha_.

            gg. Front tibiæ without terminal spurs, discal cell present.

              h. Hind tibiæ each with a single spur.

                i. Anal cell open (fig. 163g); third antennal segment
                    kidney-shaped with dorsal or subdorsal arista; first
                    antennal segment elongate and thickened. About a
                    dozen species have been described from the United
                    States, of which at least one (S. PACHYCERAS) is
                    known to be a vicious blood sucker. SYMPHOROMYIA
                    Frauenf.

                ii. Anal cell closed; third antennal segment not
                    kidney-shaped. _Chrysopila_, _Ptiolina_, _Spania_.

              hh. Hind tibiæ each with two spurs.

                i. Third segment kidney-shaped, the arista subdorsal;
                    anal cell closed. _Atherix_ Meig.

                ii. Third segment of the antenna short and with terminal
                    arista; anal cell open _Leptis_ Fabr. Two European
                    species of this genus have been accused of blood
                    sucking habits, but the record seems to have been
                    based upon error in observation.

        ee. With another combination of characters. STRATIOMYIIDÆ,
            CYRTIDÆ, etc.

    cc. Empodium bristlelike or absent.

      d. Antennæ apparently two segmented, with three-segmented arista,
          wings (rarely wanting) with several stout veins anteriorly,
          the weaker ones running obliquely across the wing (fig. 163h);
          small, quick running, bristly, humpbacked flies. Several
          genera; APHIOCHÆTA, PHORA, TRINEURA, etc. PHORIDÆ

      dd. Flies with other characters.

        e. No frontal lunule above the base of the antennæ; both R_4 and
            R_5 often present; third segment of the antenna often with a
            terminal bristle. ASILIDÆ, MYDAIDÆ, APIOCERIDÆ, THEREVIDÆ,
            SCENOPINIDÆ, BOMBYLIIDÆ, EMPIDIDÆ, DOLICHOPODIDÆ,
            LONCHOPTERIDÆ.

        ee. A frontal lunule above the base of the antennæ; third
            segment of the antenna always simple, i.e., not ringed,
            usually with a dorsal arista; R_4 and R_5 coalesced into a
            simple vein.

          f. A spurious vein or fold between the radius and the media,
              rarely absent; the cell R_{4+5} closed at the apex by vein
              M_1; few or no bristles on the body, none on the head;
              flies frequently with yellow markings. ERISTALIS (fig.
              163i), HELOPHILUS, and many other genera. SYRPHIDÆ

          ff. No spurious vein present.

            g. Body without bristles; proboscis elongate and slender,
                often folding; front of both male and female broad.
                CONOPIDÆ

            gg. Bristles almost always present on head, thorax, abdomen
                and legs.

              h. Arista terminal; hind metatarsus enlarged, sometimes
                  ornamented, hind tarsus more or less flattened beneath
                  PLATYPEZIDÆ

              hh. Flies having a different combination of characters.

                i. Head large, eyes occupying nearly the entire head;
                    cell R_{4+5} narrowed in the margin; small flies.
                    PIPUNCULIDÆ

                ii. Head and eyes not unusually large.

                  j. Squamæ (tegulæ, or calyptræ, or alulæ) not large,
                      often quite small, the lower one lacking, or at
                      most barely projecting from below the upper one
                      (antisquama); front of both male and female broad,
                      the eyes therefore widely separated; posthumeral
                      and intraalar macrochæta not simultaneously
                      present; thorax usually without a complete
                      transverse suture; postalar callus usually absent;
                      the connectiva adjoining the ventral sclerites
                      always visible; hypopleural macrochætæ absent;
                      last section of R_{4+5} and M_{1+2} with but few
                      exceptions nearly parallel; subcostal vein often
                      wanting or vestigial or closely approximated to
                      R_1; the latter often short, basal cells small,
                      the posterior ones often indistinct or wanting;
                      vibrissæ present or absent. ACALYPTRATE MUSCOIDEA

                    k. Subcosta present, distinctly separated from R_1
                        at the tip; R_1 usually ends distad of the
                        middle of the wing; the small basal cells of the
                        wing distinct.

                      l. A bristle (vibrissa) on each side of the face
                          near the margin of the mouth. CORDYLURIDÆ,
                          SEPSIDÆ, PHYCODROMIDÆ, HETERONEURIDÆ,
                          HELOMYZIDÆ.

                      ll. No vibrissæ present.

                        m. Head nearly spherical, cheeks broad and
                            retreating; proboscis short; the cell R_5
                            closed or narrowed in the margin; legs very
                            long; tarsi shorter than the tibiæ. CALOBATA
                            and other genera. MICROPEZIDÆ

                        mm. Flies with another combination of
                            characters. RHOPALOMERIDÆ, TRYPETIDÆ,
                            ORTALIDÆ, SCIOMYZIDÆ.

                    kk. Subcosta absent or vestigial, or if present,
                        then apparently ending in the costa at the point
                        where R_1 joins it; R_1 usually ends in the
                        costa at or before the middle of the wing.

                      l. Arista long plumose, or pectinate above; oral
                          vibrissæ present; anal cell complete; costa
                          broken at the apex of R_1. DROSOPHILA,
                          PHORTICA, and other genera. DROSOPHILIDÆ

                      ll. With another combination of characters.

                        m. The cell M and first M_2 not separated by a
                            crossvein; anal cell absent; front bare or
                            only bristly above; usually light colored
                            flies. HIPPELATES, OSCINUS, and other
                            genera. (See also m m m.) OSCINIDÆ

                        mm. Cell M and cell first M_2 often separated by
                            a crossvein; anal cell present, complete,
                            though frequently small; scutellum without
                            spines or protuberances; oral vibrissæ
                            present; arista bare or short plumose; front
                            bristly at vertex only; small dark flies.
                            PIOPHILA (fig. 99), SEPSIS and other genera.
                            SEPSIDÆ

                        mmm. The GEOMYZIDÆ, AGROMYZIDÆ, PSILIDÆ,
                            TRYPETIDÆ, RHOPALOMERIDÆ, BORBORIDÆ and
                            DIOPSIDÆ differ in various particulars from
                            either the OSCINIDÆ and the SEPSIDÆ noted
                            above.

                  jj. Squamæ well developed, usually large, the lower
                      one frequently projecting from below the upper
                      one; both posthumeral and intraalar macrochætæ
                      present; thorax with a complete transverse suture;
                      postalar callus present and separated by a
                      distinct suture from the dorsum of the thorax;
                      front of the female broad, of the male frequently
                      narrow, the eyes then nearly or quite contiguous;
                      the connectiva adjoining the ventral sclerites
                      either visible or not; hypopleural macrochætæ
                      present or absent; subcosta always distinct in its
                      whole course, R_1 never short. CALYPTRATE
                      MUSCOIDEA[J]

                    k. Oral opening small, mouth parts usually much
                        reduced or vestigial. This family is undoubtedly
                        of polyphyletic origin but for convenience it is
                        here considered as a single family. OESTRIDÆ.

                      l. The costal vein ends at the tip of R_{4+5},
                          M_{1+2} straight, not reaching the wing
                          margin, hence cell R_5 wide open (fig. 163j);
                          squamæ small; arista bare; ovipositor of the
                          female elongate. Larvæ in the alimentary canal
                          of horses, etc. GASTROPHILUS

                        m. Posterior crossvein (m-cu) wanting; wings
                            smoky or with clouds. Europe. G. PECORUM

                        mm. Posterior crossvein (m-cu) present, at least
                            in part.

                          n. Wing hyaline with smoky median cross band,
                              and two or three spots; posterior
                              trochanters with hook in the male and a
                              prominence in the female. World wide
                              distribution. G. EQUI.

                          nn. Wings without spots.

                            o. Posterior crossvein (m-cu) distad of the
                                anterior crossvein (r-m); legs,
                                particularly the femora, blackish brown.
                                Europe and North America. G.
                                HÆMORRHOIDALIS

                            oo. Posterior crossvein opposite or proximad
                                of the anterior crossvein. Europe and
                                North America. G. NASALIS

                      ll. The costal vein ends at the tip of M_{1+2},
                          M_{1+2} with a bend, the cell R_5 hence much
                          narrowed in the margin, or closed.

                        m. Proboscis geniculate, inserted in a deep
                            slit; female without extricate ovipositor;
                            arista either bare or plumose; squamæ large;
                            facial grooves approximated below.

                          n. Arista bare, short. Larvæ in rodents.
                              Tropic America. _B. princeps_. _Bogeria_
                              Austen

                          nn. Arista pectinate above.

                            o. Tarsi broadened and flattened, hairy,
                                anal lobe of the wing large. Larvæ in
                                rodents. A number of American species.
                                _Cuterebra_.

                            oo. Tarsi slender, not hairy; anal lobe of
                                the wing moderate. Larvæ in man and
                                other mammals. Tropic America. D.
                                CYANIVENTRIS. DERMATOBIA Br.

                        mm. Mouth parts very small, vestigial; arista
                            bare.

                          n. Facial grooves approximated below, leaving
                              a narrow median depression or groove.

                            o. Cell R_5 closed and petiolate, body
                                nearly bare. Larvæ in the nasal cavities
                                of the smaller Ungulates. The sheep bot
                                fly. O. OVIS. Widely distributed OESTRUS
                                L.

                            oo. Cell R_5 narrowly open, body hairy.
                                Larvæ parasitic on deer. Europe and
                                America. _Cephenomyia_ Latr.

                          nn. Facial grooves far apart, enclosing
                              between them a broad shield-shaped
                              surface; squamæ large; female with
                              elongate ovipositor. Larvæ hypodermatic on
                              Ungulates HYPODERMA Clark

                            o. Palpi wanting; tibiæ thickened in the
                                middle.

                              p. Hair at apex of the abdomen yellow;
                                  legs including femora yellowish brown.
                                  H. DIANA

                              pp. Hair at the apex of the abdomen
                                  reddish yellow. Europe and America.

                                q. Tibiæ and tarsi yellow; femora black.
                                    H. LINEATA

                                qq. Legs black with black hair; tips of
                                    hind tibia and tarsi yellowish
                                    brown. H. BOVIS

                            oo. Palpi small, globular; tibiæ
                                cylindrical, straight. On reindeer. _O.
                                tarandi_ _Oedemagena_ Latr.

                    kk. Oral opening of the usual size; mouth parts not
                        vestigial.

                      l. Hypopleurals wanting; if three sternopleurals
                          are present the arrangement is 1:2;
                          conjunctiva (fig. 161c) of the venter usually
                          present; if the terminal section of M_{1+2} is
                          bent it has neither fold nor appendage
                          (ANTHOMYIIDÆ of Girschner).

                        m. Sternopleurals wanting; M_{1+2} straight
                            toward the apex, costa ends at or slightly
                            beyond the tip of R_{4+5}; mouth parts
                            vestigial. GASTROPHILINÆ. See OESTRIDÆ

                        mm. Sternopleurals present, if rarely absent
                            then differing in other characters.

                          n. Caudal margin of the fifth ventral
                              abdominal sclerite of the male deeply
                              notched on the median line usually to
                              beyond the middle; abdomen often
                              cylindrical or linear; abdomen often with
                              four to eight spots; eyes of the male
                              usually widely separated; sternopleurals
                              three, arranged in an equilateral
                              triangle; subapical seta of the hind tibia
                              placed very low; M_{1+2} straight; anal
                              vein abbreviated; wings not rilled.
                              _Cænosia_, _Caricea_, _Dexiopsis_,
                              _Hoplogaster_, _Schoenomyia_, etc.
                              (COENOSINÆ)[K]. ANTHOMYIIDÆ in part

                          nn. Caudal margin of the fifth ventral
                              abdominal sclerite of the male incurved,
                              rarely deeply cleft, rarely entire, in a
                              few genera deeply two or three notched;
                              M_{1+2} straight or curved; abdomen
                              usually short or elongate oval;
                              sternopleurals, if three are present,
                              arranged in the order 1:2 in a right
                              triangle. (MUSCINÆ-ANTHOMYIINÆ of
                              Girschner)

                            o. M_{1+2} straight, hence cell R_5 not
                                narrowed in the margin. ANTHOMYIIDÆ in
                                part

                              p. Underside of the scutellum more or less
                                  sparsely covered with fine hairs; anal
                                  vein nearly always reaches the hind
                                  margin of the wing; extensor surface
                                  of the hind tibiæ with a number of
                                  stout setæ; squamæ often small and
                                  equal. ANTHOMYIA, _Chortophila_,
                                  _Eustalomyia_, _Hammomyia_,
                                  _Hylemyia_, _Prosalpia_, _Pegomyia_,
                                  etc. HYLEMYINÆ-PEGOMYINÆ

                              pp. Underside of the scutellum bare; anal
                                  vein does not reach the wing margin.

                                q. First anal vein short, second anal
                                    suddenly flexed upwards; hind tibiæ
                                    each with one or two strong setæ on
                                    the extensor surface. FANNIA (=
                                    HOMALOMYIA), _Coelomyia_,
                                    _Choristoma_, _Euryomma_, _Azelia_,
                                    etc. FANNINÆ-AZELINÆ

                                qq. Anal veins parallel or divergent.

                                  r. Setæ on the exterior surface of the
                                      hind tibiæ wanting (except in
                                      _Limnaricia_ and _Coenosites_),
                                      lower squama not broadened to the
                                      margin of the scutellum.
                                      _Leucomelina_, _Limnophora_,
                                      _Limnospila_, _Lispa_, _Mydæa_,
                                      _Spilogaster_, etc.
                                      MYDÆINÆ-LIMNOPHORINÆ

                                  rr. One (rarely more) seta on the
                                      extensor surface of the hind
                                      tibia; squamæ usually large and
                                      unequal. HYDROTAEA, _Aricia_,
                                      _Drymeia_, _Ophyra_, _Phaonia_ (=
                                      _Hyetodesia_), _Pogonomyia_,
                                      _Trichophthicus_, etc. ARICINÆ

                            oo. M_{1+2} curved or bent, hence the cell
                                R_5 more or less narrowed in the margin.
                                (MUSCINÆ). MUSCIDÆ in part. See page 303
                                for generic synopsis.

                      ll. Hypopleurals present; when three
                          sternopleurals are present the arrangement is
                          2:1 or 1:1:1. (TACHINIDÆ of Girschner)

                        m. Conjunctiva of the ventral sclerites of the
                            abdomen present, frequently well developed,
                            surrounding the sclerites.

                          n. Mouth parts vestigial. OESTRIDÆ. See page
                              297 for generic synopsis.

                          nn. Mouth parts well developed.

                            o. M_{1+2} straight, hence cell R_5 wide
                                open in the margin; costa ending at the
                                tip of R_5; three sternopleurals
                                present; antennal arista plumose.
                                _Syllegoptera_. Europe.
                                (SYLLEGOPTERINÆ). DEXIIDÆ in part

                            oo. M_{1+2} bent, hence cell R_5 narrowed in
                                the margin; sternopleurals rarely
                                wanting, usually 1:1 or 0:1; facial
                                plate strongly produced below vibrissal
                                angle like the bridge of the nose;
                                antennal arista bare. Parasitic on
                                Hemiptera and Coleoptera. _Allophora_,
                                _Cistogaster_, _Clytia_, _Phasia_, etc.
                                (PHASIINÆ) TACHINIDÆ in part.

                        mm. Conjunctiva of the ventral sclerites
                            invisible (fig. 161a).

                          n. Second ventral sclerite of the abdomen
                              lying with its edges either upon or in
                              contact with the ventral edges of the
                              corresponding dorsal sclerite.

                            o. Outermost posthumeral almost always lower
                                (more ventrad) in position than the
                                presutural macrochæta; fifth ventral
                                abdominal sclerite of the male cleft
                                beyond the middle, often strongly
                                developed; body color very frequently
                                metallic green or blue, or yellow;
                                arista plumose. (CALLIPHORINÆ) MUSCIDÆ
                                in part.

                              See page 303 for generic synopsis.

                            oo. Outermost posthumeral macrochæta on
                                level or higher (more dorsad) than the
                                presutural macrochæta; arista bare,
                                pubescent, or plumose only on the basal
                                two-thirds; body coloring usually
                                grayish (fig. 106). SARCOPHAGIDÆ

                              p. Fifth ventral sclerite of the male
                                  either wanting or with the caudal
                                  margin straight; presutural intraalar
                                  rarely present. (SARCOPHAGINÆ)

                                q. Fifth ventral abdominal sclerite of
                                    the male much reduced, the remaining
                                    segments with straight posterior
                                    margin, overlapping scale-like; in
                                    the female only segment one and two
                                    scale-like, the others wholly or in
                                    part covered; sternopleurals usually
                                    three or more. SARCOPHAGA and
                                    related genera.

                                qq. Fifth ventral sclerite of the male
                                    plainly visible; sternopleurals
                                    usually two. SARCOPHILA,
                                    WOHLFAHRTIA, _Brachycoma_,
                                    _Hilarella_, _Miltogramma_,
                                    _Metopia_, _Macronychia_, _Nyctia_,
                                    _Paramacronychia_, _Pachyphthalmus_,
                                    etc.

                              pp. Fifth ventral abdominal sclerite of
                                  the male cleft to beyond the middle;
                                  ventral sclerites usually visible,
                                  shield-like. _Rhinophora_, _Phyto_,
                                  _Melanophora_ RHINOPHORINÆ

[Illustration: 164. Glossina palpalis. (×4.) After Austen.]

                          nn. Second ventral abdominal sclerite as well
                              as the others more or less covered,
                              sometimes wholly, by the edges of the
                              dorsal sclerite.

                            o. The presutural intraalar wanting; ventral
                                sclerites two to five nearly or quite
                                covered by the edges of the
                                corresponding dorsal sclerites; base of
                                the antennæ usually at or below the
                                middle of the eye; arista usually
                                plumose; legs usually elongate;
                                abdominal segments with marginal and
                                often discal macrochætæ. DEXIIDÆ

                            oo. Presutural intraalar present, if absent,
                                then the ventral sclerites broadly
                                exposed or the fifth ventral sclerite
                                vestigial; base of the antennæ usually
                                above the middle of the eye; arista
                                bare; at least two posthumerals and
                                three posterior intraalars present.
                                Parasitic on caterpillars, etc.
                                TACHINIDÆ


SYNOPSIS OF THE PRINCIPAL GENERA OF THE MUSCIDÆ OF THE WORLD

a. Proboscis long, directed forward, adapted for piercing, or oral
    margin much produced, snout-like.

  b. Oral margin produced snout-like; vibrissa placed high above the
      oral margin; antennal arista either pectinate or more or less
      plumose.

    c. Antennal arista short or long-plumose; neither sex with distinct
        orbital bristles.

      d. No facial carina between the antennæ. RHYNCHOMYIINÆ

        e. Arista short-plumose. _R. speciosa._ Europe. _Rhynchomyia_ R.
            D.

        ee. Arista long-plumose. _I. phasina_. Europe and Egypt.
            _Idiopsis_. B. B.

      dd. With flattened carina, the bases of the antennæ separated; no
          abdominal macrochætæ. COSMININÆ _C. fuscipennis_. South
          Africa. _Cosmina_

    cc. Antennal arista pectinate; bases of the antennæ separated by a
        flattened carina. RHINIINÆ R. D.

      d. Cell R_5 open, or closed at the margin.

        e. Third segment of the antenna twice as long as the second;
            claws of both sexes short; cell R_5 open. _I. lunata._
            Eastern Hemisphere. _Idia_ Meigen

        ee. Third segment of the antenna three times as long as the
            second; cell R_5 open or closed; claws of the male long and
            slender, of the female shorter than the last tarsal joint.
            _I. mandarina_, China. _Idiella_ B. B.

      dd. Cell R_5 petiolate. _Rhinia_; and _Beccarimyia_ Rdi.

  bb. Proboscis long, directed forward, adapted for piercing. STOMOXINÆ

    c. Arista flat, pectinate above with plumose rays; sternopleurals
        1:2; bases of the veins R_1 and R_{4+5} without setæ; base of
        the media bowed down; apical cell opens before the apex of the
        wing. African species. GLOSSINA Wied.

      d. Species measuring over twelve mm. in length. _G. longipennis_
          and FUSCA.

      dd. Species less than twelve mm. in length.

        e. All segments of the hind tarsi black.

          f. The fourth and fifth segments of the fore tarsi black;
              antennæ black (fig. 164). G. PALPALIS R. D.

          ff. Otherwise marked. _G. bocagei_, _tachinoides_,
              _pallicera._

        ee. First three segments of the hind tarsi are yellow, the
            fourth and fifth segments are black.

          f. Fourth and fifth segments of the first and second pair of
              tarsi are black.

            g. The yellow bands of the abdominal segments occupy a third
                of the segment (fig. 165). G. MORSITANS Westw.

            gg. The yellow band on each segment of the abdomen occupies
                a sixth of the segment. G. LONGIPALPIS Wied.

          ff. Tarsi of the first and second pairs of legs wholly yellow.
              _G. pallidipes_ Austen

    cc. Rays of the arista not plumose; only one or two sternopleurals;
        base of the media not strongly bowed down; apical cell opens at
        or very near the apex of the wing.

      d. Vein R_{4+5} without setæ at the base; palpi about as long as
          the proboscis.

        e. Arista pectinate (i.e. rays on one side only), the rays often
            undulate; two yellow sternopleurals often difficult to
            detect; vein M_{1+2} only slightly bent, the apical cell
            hence wide open. The horn fly, H. IRRITANS (= _Lyperosia
            serrata_) and related species. Widely distributed (figs.
            167, 168). HÆMATOBIA R. D. not B. B.

[Illustration: 165. Glossina morsitans. (×4.) After Austen.]

        ee. Arista also with rays below; vein M_{1+2} more strongly
            bent, the apical cell hence less widely open.

          f. Palpi strongly spatulate at the tips, lower rays of the
              arista about six in number, B. SANGUINOLENTUS. South Asia.
              BDELLOLARYNX Austen

          ff. Palpi feebly spatulate; apical cell of the wing narrowly
              open slightly before the tip; sternopleurals black,
              anterior bristle sometimes absent. H. ATRIPALPIS. Europe.
              HÆMATOBOSCA Bezzi

      dd. Vein R_{4+5} with setæ at the base.[L]

        e. Veins R_1 and R_{4+5} with setæ at the base; two equally
            prominent sternopleural macrochætæ; arista with rays both
            above and below; palpi as long as the proboscis; apical cell
            of the wing wide open. L. TIBIALIS. (_Hæmatobia_ B. B. not
            R. D.). LYPEROSIOPS Town.

        ee. Only vein R_{4+5} with basal setæ; anterior sternopleural
            macrochæta wanting; arista pectinate.

          f. Palpi as long as the proboscis, the latter stout, with
              fleshy terminal labellæ; apical cell narrowly open;
              sternopleural macrochætæ black. S. MACULOSA from Africa
              and related species from Asia. STYGEROMYIA Austen

          ff. Palpi much shorter than the proboscis, the latter pointed
              at the apex, without fleshy labellæ; apical cell of the
              wing wide open. S. CALCITRANS, the stable fly and related
              species. Widely distributed in both hemispheres (fig.
              110). STOMOXYS Geof.

aa. Proboscis neither slender nor elongate, the labellæ fleshy and not
    adapted for piercing.

  b. Hypopleuræ without a vertical row of macrochætæ. MUSCINÆ

    c. Arista bare; distal portion of M_{1+2} broadly curved at the end;
        hypopleuræ with a sparse cluster of fine hairs. _S.
        braziliana_, Southern States and southward. _Synthesiomyia_ B.
        B.

    cc. Arista pectinate or plumose.

      d. Arista pectinate. _H. vittigera_, with the posterior half of
          the abdomen metallic blue. Mexico. _Hemichlora_ V. d. W.

      dd. Arista plumose.

        e. Middle tibia with one or more prominent setæ on the inner
            (flexor) surface beyond the middle, or inner surface very
            hairy.

          f. R_1 ends distad of the m-cu crossvein; M_{1+2} with a broad
              curve near its apical end. (= _Neomesembrina_ Schnabl. =
              _Metamesembrina_ Town). _M. meridiana._ Europe.
              _Mesembrina_ Meigen

          ff. R_1 ends proximad of the m-cu crossvein.

            g. Eyes pilose, sometimes sparsely in the female.

              h. Female with two or three stout orbital setæ; the hind
                  metatarsus of the male thickened below at the base and
                  penicillate. _D. pratorum._ Europe. _Dasyphora_ R.
                  D.[M]

              hh. Neither sex with orbital setæ.

                i. Abdomen without macrochætæ; arista plumose. _C.
                    asiatica._ Eastern Hemisphere. _Cryptolucilia_ B. B.

                ii. Abdomen with strong macrochætæ; arista very
                    short-plumose, nearly bare. _B. tachinina._ Brazil.
                    _Reinwardtia_ B. B.

            gg. Eyes bare.

              h. Body densely pilose; thoracic macrochætæ wanting;
                  middle tibiæ much elongate and bent; last section of
                  M_{1+2} with a gentle curve. H. (_Mesembrina_)
                  _mystacea, et al._, Europe and _H. solitaria_, N.
                  America. _Hypodermodes_ Town.

              hh. Body not densely pilose.

                i. Dorsocentrals six; last section of M_{1+2} with a
                    gentle curve.

                  j. Inner dorsocentrals ("acrostichals") wanting;
                      sternopleurals arranged 1:3. _P. cyanicolor_,
                      _cadaverina_, etc. Europe and America _Pyrellia_
                      R. D.

                  jj. Inner dorsocentrals ("acrostichals") present;
                      sternopleurals arranged 1:2. E. _latreillii._
                      North America. _Eumesembrina_ Town.

                ii. Dorsocentrals five; inner dorsocentrals present;
                    last section of M_{1+2} with a rounded angle;
                    sternopleurals arranged 1:2. _P. cornicina_ Europe
                    and America. (_Pseudopyrellia_ Girsch.) _Orthellia_
                    R. D.

        ee. Middle tibia without a prominent bristle on the inner
            surface beyond the middle.

[Illustration: 166. Pycnosoma marginale. (×4.) After Graham-Smith.]

          f. Squamula thoracalis broadened mesad and caudad as far as
              the scutellum.

            g. Sternopleural macrochætæ arranged in an equilateral
                triangle; front of both sexes broad; genæ bare;
                dorsocentrals six, small; wing not rilled. (To
                COENOSINÆ). _Atherigona_ Rdi.

            gg. Sternopleural macrochætæ when three are present,
                arranged in a right triangle.

              h. Last section of M_{1+2} with a more or less rounded
                  angle (fig. 163l).

                i. Eyes of the male pilose or pubescent, of the female
                    nearly bare; m-cu crossvein usually at or proximad
                    of the mid-distance between the r-m crossvein and
                    the bend of M_{1+2}. P. (= _Placomyia_ R. D.)
                    _vitripennis_. _Plaxemyia_ R. D.

                ii. Eyes bare; the m-cu crossvein always nearer to the
                    bend of M_{1+2} than to the r-m crossvein.

                  j. Apex of the proboscis when extended reveals a
                      circlet of stout chitinous teeth. P. INSIGNIS
                      Austen, of India, bites both man and animals. (=
                      _Pristirhynchomyia_.) PHILÆMATOMYIA Austen

                  jj. Apex of the proboscis without black teeth.

                    k. Eyes of male separated by a distance equal to a
                        fourth the width of the head. House or typhoid
                        fly. M. DOMESTICA L. Widely distributed. MUSCA
                        L.

                    kk. Eyes of the male contiguous. E. CORVINA. Europe.
                        EUMUSCA Town

              hh. Last section of M_{1+2} with a gentle curve (fig.
                  102).

                i. Eyes pilose.

                  j. Claws in the male somewhat elongated; no orbitals
                      in either sex; antennæ separated at the base by a
                      flat carina; abdomen marked with red or yellow.
                      _G. maculata._ Europe and America. _Graphomyia_ R.
                      D.

                  jj. Claws short and equal in the two sexes; two or
                      three stout orbital macrochætæ in the female; R_1
                      scarcely produced beyond the r-m crossvein; eyes
                      contiguous in the male. _P. obsoleta._ Brazil.
                      _Phasiophana_ Br.

                ii. Eyes bare; fronto-orbital macrochætæ in a double
                    row, antennæ contiguous at the base.

                  j. One or more pairs of well developed anterior inner
                      dorsocentral (acrostichal) macrochætæ; seta on
                      extensor surface of hind tibia. M. ASSIMILIS,
                      STABULANS, etc. Europe and America. MUSCINA R. D.

                  jj. Anterior inner dorsocentrals and the setæ; on the
                      extensor surface of the hind tibia wanting. _M.
                      micans_, etc. Europe and North America. _Morellia_
                      R. D.

          ff. Squamula thoracalis not broadened mesad and caudad, not
              reaching the margin of the scutellum; macrochætæ on
              extensor surface of the hind tibia wanting.

            g. Eyes pubescent. _M. meditabunda._ Europe and America.
                _Myiospila_ Rdi.

            gg. Eyes bare; R_1 ends before the middle of the wing. A
                number of species from the tropics of both hemispheres.
                _Clinopera_ V. d. W.

  bb. Hypopleuræ with a vertical row of macrochætæ.

    c. Eyes pubescent.

      d. R_1 ends about opposite the r-m crossvein; basal section of
          R_{4+5} bristly nearly to the crossvein; _S. enigmatica_.
          Africa. _Somalia_ Hough

      dd. R_1 ends distad of the r-m crossvein.

        e. Eastern hemisphere. Australasia. _N. ochracea_,
             _dasypthalma._ _Neocalliphora_ Br.

        ee. Western Hemisphere. _T. muscinum._ Mexico. _Tyreomma_ V. d.
            W.

    cc. Eyes bare.

      d. The vibrissal angle situated at a noticeable distance above the
          level of the margin of the mouth.

        e. Sternopleural macrochætæ arranged in the order 1:1.

          f. Genæ with microchætæ.

            g. Body grayish, with depressed yellow woolly hair among the
                macrochætæ; wings folded longitudinally over the body
                when at rest. Cluster flies. _P. rudis_ and related
                species, widely distributed. _Pollenia_ R. D.[N]

            gg. Body metallic blue or green. Eastern Hemisphere.

              h. Vibrissal angle placed very high above the oral margin;
                  a carina between the antennæ; outer posthumeral
                  wanting; anterior intraalar present. _T. viridaurea_.
                  Java. _Thelychæta_ Br.

[Illustration: 167. Horn fly. (_a_) egg; (_b_) larva; (_c_) puparium;
(_d_) adult. (×4). Bureau of Entomology]

              hh. Vibrissal angle moderately high above the oral margin;
                  carina small or wanting; no post humeral macrochæta;
                  lower squamæ hairy above. (= _Paracompsomyia_ Hough)
                  (fig. 166). _Pycnosoma_ Br.

          ff. Genæ bare. _S. terminata_. Eastern Hemisphere
              _Strongyloneura_ Bigot

        ee. Sternopleurals arranged 2:1.

          f. Body metallic green or blue, with gray stripes; genæ hairy
              to the lower margin; post humerals often wanting; lower
              squamæ bare above. (= _Compsomyia_ Rdi.). CHRYSOMYIA R. D.

            g. With one or two orbitals; height of bucca less than half
                the height of the eye. South and east U. S. (fig. 107).
                C. MARCELLARIA

            gg. No orbitals; height of bucca about a third less than
                height of eye. West U. S. _C. wheeleri_ Hough

          ff. Body black or sordidly metallic greenish gray, usually
              yellow pollinose or variegate; genæ at most hairy above.
              _N. stygia_. Eastern Hemisphere. _Neopollenia_ Br.

      dd. Vibrissal angle situated nearly on a level of the oral margin.

        e. Species wholly blackish, bluish, or greenish metallic in
            color.

          f. First section of R_{4+5} with at most three or four small
              bristles at the immediate base.

            g. The bend of M_{1+2} a gentle curve; costal spine present;
                cell R_5 closed, ending before the apex of the wing. _S.
                cuprina._ Java. _Synamphoneura_ Bigot

            gg. Bend of M_{1+2} angular; or the insect differs in other
                characters; dorsal surface of the squamula thoracalis
                hairy (except in _Melinda_); arista plumose only on the
                basal two-thirds (except usually in _Calliphora_ and
                _Eucalliphora_).

[Illustration: 168. Head of horn-fly (Lyperosia irritans); (_a_) female;
(_b_) male; (_c_) lateral aspect of female. Bureau of Entomology]

              h. Arista plumose only on the basal two-thirds.

                i. Base of the antennæ ventrad of the middle of the eye;
                    eyes of the male nearly contiguous; genæ hairy;
                    second abdominal segment with median marginal
                    macrochætæ; two, rarely three, postsutural intraalar
                    macrochætæ.

                  j. Squamula thoracalis dorsally with long black hairs;
                      male hypopygium two-segmented, large, projecting;
                      claws and pulvilli of the male elongate; three
                      strong sternopleural macrochætæ; genæ at least
                      half the width of the eye; buccæ (cheeks) half the
                      height of the eyes; oviviparous. _O. sepulcralis._
                      Europe. _Onesia_ R. D.

                  jj. Dorsal surface of the squamula thoracalis bare;
                      male hypopygium small, scarcely projecting below;
                      claws and pulvilli not elongate; two stout
                      sternopleural macrochætæ, sometimes with a
                      delicate one below the anterior; genæ nearly
                      linear in the male; buccæ about a third of the eye
                      height; oviparous. _M. cærulea_. Europe.
                      _Melinda_. R. D.

[Illustration: 169. Lateral and dorsal aspects of the thorax, and
frontal aspect of the head of a muscoidean fly, with designations of the
parts commonly used in taxonomic work.]

                ii. Base of the antennæ dorsad of the middle of the eye;
                    eyes of both sexes distinctly separated; dorsal
                    surface of the squamula thoracalis with black hairs;
                    two postsutural intraalar macrochætæ.

                  j. Hypopygium of the male large, with a pair of
                      slightly curved forceps whose ends are concealed
                      in a longitudinal slit in the fifth ventral
                      sclerite; third posterior inner dorso-central
                      (acrostichal) macrochætæ absent; anterior
                      intraalar rarely present; abdomen usually not
                      pollinose; the second segment without median
                      marginal macrochætæ; face yellow. _C. mortuorum_,
                      _cadaverina_, and related species. Both
                      hemispheres. _Cynomyia_ R. D.[O]

[Illustration: 170. Sepsis violacea; puparium and adult. (See page 297.)
After Howard.]

                  jj. Three pairs of posterior inner dorsocentrals
                      (acrostichals) present; second abdominal segment
                      with a row of marginal macrochætæ; genæ hairy, at
                      least above.

                    k. Hypopygium of the male with a projecting style.
                        _S. stylifera_. Europe. _Steringomyia_ Pok.


                    kk. Hypopygium of the male without style. _A.
                        stelviana_ B. B. _Acrophaga_ B. B.

              hh. Arista usually plumose nearly to the tip; posterior
                  dorsocentrals and inner dorsocentrals (acrostichals)
                  well developed; dorsal surface of the squamula
                  thoracalis hairy; abdomen metallic and usually
                  pollinose; genæ hairy.

                i. With one pair of ocellar macrochætæ. C. VOMITORIA,
                    ERYTHROCEPHALA, VIRIDESCENS, and related species.
                    Both hemispheres. CALLIPHORA R. D.

                ii. With two strong pairs of ocellar macrochætæ. _E.
                    latifrons._ Pacific slope of the U. S.
                    _Eucalliphora_ Town.

          ff. First section of R_{4+5} bristly near or quite half way to
              the small crossvein; dorsal surface of the squamula
              thoracalis is bare; the hypopygium of the male is
              inconspicuous.

            g. Genæ bare; posterior inner and outer dorsocentrals
                distinct and well developed. _L. cæsar_, _sericata_,
                _sylvarum_, and related species. Widely distributed in
                both hemispheres (fig. 103). LUCILIA R. D.

            gg. Genæ with microchætæ, at least down to the level of the
                base of the arista.

              h. Mesonotum flattened behind the transverse suture.

                i. Posterior dorsocentrals inconstant and unequally
                    developed; one pair of posterior inner
                    dorsocentrals. _P. terrænovæ._ North America.
                    _Protophormia_ Town.

                ii. Posterior dorsocentrals well developed, the inner
                    dorsocentrals (acrostichals) unequally developed.
                    _P. azurea_, _chrysorrhoea_, etc. Europe and America.
                    _Protocalliphora_ Hough

              hh. Mesonotum not flattened behind the transverse suture;
                  posterior inner and outer dorsocentrals inconstant and
                  unequally developed. _P. regina._ Europe and America.
                  _Phormia_ R. D.

        ee. Species more or less rufous or yellow in color.

          f. Anterior dorsocentrals wanting; first section of the
              R_{4+5} at most only bristly at the base, bend near apex
              of M_{1+2} rectangular, R_1 ends over the crossvein;
              fronto-orbital macrochæta absent; eyes of the male
              contiguous. _C. semiviridis._ Mexico. _Chloroprocta_
              V. d. W

          ff. With another combination of characters.

            g. Body robust, of large size, abdomen elongate, not round;
                genæ with several ranges of microchætæ; vibrissal ridges
                strongly convergent; abdomen with well developed
                macrochætæ; costal spine usually absent; eyes of the
                male widely separated.

[Illustration: 171. Stigmata of the larvæ of Muscoidea. Third instar.
(_a_) Cynomyia cadaverina; (_b_) Phormia regina; (_c_) Chrysomyia
macellaria; (_d_) Musca domestica; (_e_) Sarcophaga sp.; (_f_) Oestris
ovis; (_g_) Gastrophilus equi; (_h_) Sarcophaga sp.; (_i_) Pegomyia
vicina; (_j_) Protocalliphora azurea; (_k_) Hypoderma lineata; (_l_)
Muscina stabulans. Magnification for f, g, and k, ×25; all others, ×
50.]

              h. Peristome broad, pteropleural macrochætæ distinct; one
                  or two sternopleurals; in the female a single orbital
                  macrochæta; last abdominal segment without discal
                  macrochætæ; hypopygial processes of the male with a
                  long stylet; second abdominal segment of the female
                  sometimes much elongate. A. LUTEOLA (fig. 86).
                  Africa. The sub-genus _Choeromyia_ Roub. is included
                  here. AUCHMEROMYIA B. B.

              hh. Peristome narrow; no pteropleurals, two
                  sternopleurals; two orbitals in the female; second
                  segment not elongate; the fourth with two well
                  developed discal macrochætæ. B. DEPRESSA. Africa.
                  BENGALIA R. D

            gg. With another combination of characters.

              h. Costal spine present; body in part black; antennæ
                  noticeably shorter than the epistome, inserted above
                  the middle of the eye and separated from each other by
                  a carina; abdominal segments with marginal macrochætæ;
                  sternopleurals 2:1 or 1:1. _Paratricyclea_ Villen.

              hh. Costal spine not distinct, or if present, insect
                  otherwise different.

                i. Genæ with several ranges of microchætæ; vibrissal
                    ridges strongly converging; peristome broad; arista
                    moderately plumose; sternopleurals usually 1:1;
                    color entirely testaceous. C. ANTHROPOPHAGA (fig.
                    87) and GRUNBERGI. Africa. CORDYLOBIA Grünb.

                ii. Genæ bare or with but one range of setæ; vibrissal
                    ridges less converging; peristome narrow; arista
                    long plumose.

                  j. Genæ with a single row of microchætæ.

                    k. Sternopleurals 2:1; color entirely testaceous.
                        _Ochromyia_ Macq.[P]

                    kk. Sternopleurals 1:1. _P. varia_ Hough. Africa.
                        _Parochromyia_ Hough

                  jj. Genæ bare.

                    k. Basal section of R_{4+5} bristly only at the
                        immediate base, distally M_{1+2} with a broad
                        curve; distal portion of the abdomen metallic;
                        sternopleurals usually 1:1, rarely 2:1. _M.
                        æneiventris_ Wd. Tropic America.
                        _Mesembrinella._ G. T.

                    kk. R_{4+5} bristly at least nearly half way to the
                        small crossvein; sternopleurals 1:1.

                      l. Macrochætæ of the abdomen marginal; neither sex
                          with orbitals; no carina between the base of
                          the antennæ; three pairs of presutural inner
                          dorsocentrals. Eastern hemisphere. _T.
                          ferruginea._ _Tricyclea V. d. W_. (=
                          _Zonochroa_ B. B. according to Villeneuve
                          1914).

                      ll. Abdomen without macrochætæ; wing usually with
                          a marginal streak and gray markings. Brazil.
                          Hemilucilia B. B.

[Illustration: 172. Left hand stigmata of the larvæ of muscoidea. Third
instar. (_a_) Lucilia cæsar; (_b_) Calliphora vomitoria; (_c_) Stomoxys
calcitrans; (_d_) Orthellia cornicina; (_e_) Pyrellia cadavarina;
(_f_) Hæmatobia irritans; (_g_) Mesembrina mystacea; (_h_) Mesembrina
meridiana; (_i_) Myospila meditabunda; (_j_) Mydæa urbana; (_k_)
Polietes albolineata; (_l_) Polietes lardaria; (_m_) Morellia hortorum;
(_n_) Hydrotæa dentipes; (_o_) Hebecnema umbratica; (_p_) H. vespertina;
(_q_) Limnophora septemnotata; (_r_) Muscina stabulans. (_a_ and _b_)
after MacGregor; (_d_) after Banks; all others after Portchinsky.
Magnification varies. The relative distance to the median line is
indicated in each figure.]


SIPHONAPTERA. Fleas

Adapted from a table published by Oudemans.

a. Elongated fleas, with jointed (articulated) head, with combs
    (ctenidia) on head and thorax; with long, oval, free-jointed
    flagellum of the antenna (fig. 92d). Suborder FRACTICIPATA

  b. With ctenidia in front of the antennæ and on the genæ (cheeks);
      maxillæ with acute apices; labial palpi five-segmented,
      symmetrical; eyes poorly developed or wanting. On rodents.
      HYSTRICHOPSYLLIDÆ

    c. Abdominal segments without ctenidia.

      d. Post-tibial spines in pairs and not in a very close set row;
          head with ctenidia. _Ctenophthalmus_ Kol.

      dd. Post-tibial spines mostly single and in a close set row.
          _Ctenopsyllus_ and _Leptopsyllus_. The last genus has recently
          been erected for _L. musculi_, a widely distributed species
          occurring on rats and mice.

    cc. Abdominal segments with one or more ctenidia; post-tibial
        spines in numerous, short, close-set transverse rows on
        posterior border with about four spines in each row. _H.
        americana._ _Hystrichopsylla_ Taschenb.

  bb. With only two pairs of subfrontal ctenidia; labial palpi
      five-segmented, symmetrical; eyes vestigial or wanting. On bats.
      (= ISCHNOPSYLLIDÆ). NYCTERIDIPSYLLIDÆ

    With more or less blunt maxilla; all tibiæ with notch; a single
        antepygidial bristle; metepimeron without ctenidium. _N.
        crosbyi_ from Missouri was found on bats. Rothschild suggests
        that this is probably the same as _N. insignis_. (=
        _Ischnopsyllus_ = _Ceratopsyllus_), _Nycteridiphilus_

aa. Head not jointed, i.e. the segments coalescent, traces of the
    segmentation still being visible in the presence of the vertex
    tubercle, the falx (sickle-shaped process), and a suture. Suborder
    INTEGRICIPITA

  b. Flagellum of the antennæ long and oval.

    c. Usually elongate fleas, with a free-segmented flagellum of the
        antenna; thorax not shorter than the head, longer than the first
        tergite.

      d. Genæ of the head and the pronotum with ctenidia. NEOPSYLLIDÆ

        e. Labial palpi four or five-segmented; symmetrical; hind coxæ
            with patch of spines inside; row of six spatulate spines on
            each side in front of the antennæ. _C. ornate_ found on a
            California mole. _Corypsylla_

        ee. Labial palpi two-segmented, transparent, membranous. On
            hares. _Spilopsyllus_ Baker

      dd. No ctenidium on the head.

        e. Pronotum with ctenidium. DOLICHOPSYLLIDÆ

          f. Labial palpi five-segmented, symmetrical.

            g. Antepygidial bristles one to three; eyes present.

              h. Inner side of hind coxæ distally with a comb of minute
                  teeth; falx present. On rodents and carnivores.
                  _Odontopsyllus_ Baker

              hh. Inner side of hind coxæ without comb or teeth. Many
                  North American species on rodents. CERATOPHYLLUS
                  Curtis

            gg. Antepygidial bristles five on each side; eyes absent;
                suture white. _D. stylosus_ on rodents. _Dolichopsyllus_
                Baker

          ff. Labial palpi four or five-segmented; asymmetrical
              (membranous behind), apex acute. _Hoplopsyllus anomalus_
              found on Spermophiles in Colorado. HOPLOPSYLLIDÆ

        ee. Pronotum without ctenidium. _Anomiopsyllus californicus_ and
            _nudatus_ on rodents. ANOMIOPSYLLIDÆ

    cc. Very short fleas; flagellum of the antenna with pseudo-segments
        coalescent; thorax much shorter than the head and than the first
        tergite. HECTOPSYLLIDÆ

      Flagellum of the antenna with six coalescent pseudo-segments;
          maxilla blunt. The chigger on man (fig. 93). D. PENETRANS. (=
          RHYNCHOPRION = SARCOPSYLLA) DERMATOPHILUS Guérin

  bb. Flagellum short, round, free portion of the first segment shaped
      like a mandolin.

    c. Thorax not shorter than the head, longer than the first tergite;
        flagellum either with free segments or in part with the segments
        coalescent.

      d. Head and pronotum with ctenidium; labial palpi asymmetrical.
          ARCHÆOPSYLLIDÆ

        With four subfrontal, four genal, and one angular ctenidia.
            Widely distributed. CTENOCEPHALUS Kol.

        e. Head rounded in front (fig. 92a). Dog flea. C. CANIS

        ee. Head long and flat (fig. 92b). Cat flea. C. FELIS

      dd. Neither head nor pronotum with ctenidium. Labial palpi
          asymmetrical, membranous behind. PULICIDÆ

        e. Mesosternite narrow, without internal rod-like thickening
            from the insertion of the coxæ upwards. Human flea, etc.
            PULEX L.

        ee. Mesosternite broad with a rod-like internal thickening from
            the insertion of the coxæ upwards (fig. 89). X.
            (LOEMOPSYLLA) CHEOPIS, plague or rat flea. XENOPSYLLA

    cc. Thorax much shorter than the head and than the first tergite.
        ECHIDNOPHAGIDÆ. E. GALLINACEA, the hen flea also attacks man
        (fig. 96). (= ARGOPSYLLA = XESTOPSYLLA) ECHIDNOPHAGA Olliff.


FOOTNOTES:

[E] Adapted from Banks, Nuttall, Warburton, Stiles, _et al._

[F] Dr. C. W. Stiles considers the species which is responsible for
spotted fever distinct from the _venustus_ of Banks, separating it as
follows:

Goblet cells about 75 in the male or 105 in the female. Texas. _D.
venustus._

Goblet cells 157 in the male, or 120 in the female; stigmal plate shaped
as shown in the figure (figs. 150 a, b). Montana, etc. D. ANDERSONI.

[G] Professor C. R. Crosby who has been working upon certain capsids
states that he and his assistant have been bitten by LYGUS PRATENSIS,
the tarnished plant bug, by CHLAMYDATUS ASSOCIATUS and by ORTHOTYLUS
FLAVOSPARSUS, though without serious results.

[H] Species marked with an * are known to transmit malaria. Species
found only in tropical North America and not known to carry malaria have
been omitted from this table, but all found in the United States are
included.

[I] This table to the North American genera of the Tabanidæ is adapted
from one given by Miss Ricardo.

[J] The classification of the Muscoidea as set forth by Schiner and
other earlier writers has long been followed, although it is not
satisfactory, being admittedly more or less artificial. Within the last
two or three decades several schemes have been advanced, that of Brauer
and Bergenstamm and of Girschner, with the modifications of Schnabl and
Dziedzicki having obtained most favor in Europe. Townsend, in 1908,
proposed a system which differs from Girschner's in some respects, but
unfortunately it has not yet been published in sufficient detail to
permit us to adopt it. From considerations of expediency we use here the
arrangement given in Aldrich's Catalogue of North American Diptera,
though we have drawn very freely upon Girschner's most excellent paper
for taxonomic characters to separate the various groups.

It may sometimes be found that a species does not agree in all the
characters with the synopsis; in this case it must be placed in the
group with which it has the most characters in common.

[K] There are several genera of flies of the family _Cordyluridæ_; (i.e.
_Acalyptratæ_) which might be placed with the _Anthomyiidæ_ (i.e.
_Calyptratæ_), owing to the relatively large size of their squamæ. As
there is no single character which will satisfactorily separate all
doubtful genera of these two groups we must arbitrarily fix the limits.
In general those forms on the border line having a costal spine, or
lower squama larger than the upper, or the lower surface of the
scutellum more or less pubescent, or the eyes of the male nearly or
quite contiguous, or the eyes hairy, or the frontal setæ decussate in
the female; or any combination of these characters may at once be placed
with the _Anthomyiidæ_. Those forms which lack these characteristics and
have at least six abdominal segments (the first and second segments
usually being more or less coalescent) are placed with the Acalyptrates.
There are other acalyptrates with squamæ of moderate size which have
either no vibrissæ, or have the subcosta either wholly lacking or
coalescent in large part with R_1 or have spotted wings; they, therefore
will not be confused with the calyptrates.

[L] _Pachymyia_ Macq. is closely related to _Stomoxys_. It differs in
having the arista rayed both above and below. _P. vexans_, Brazil.

[M] The genus _Eudasyphora_ Town. has recently been erected to contain
_D. lasiophthalma_.

[N] _Nitellia_, usually included in this genus has the apical cell
petiolate. _Apollenia_ Bezzi, has recently been separated from
_Pollenia_ to contain the species _P. nudiuscula_. Both genera belong to
the Eastern hemisphere.

[O] The following three genera are not sufficiently well defined to
place in this synopsis. In color and structural characters they are
closely related to _Cynomyia_ from which they may be distinguished as
follows. _Catapicephala_ Macq., represented by the species _C.
splendens_ from Java, has the setæ on the facial ridges rising to the
base of the antennæ and has median marginal macrochætæ on the abdominal
segments two to four: _Blepharicnema_ Macq., represented by _B.
splendens_ from Venezuela has bare genæ, oral setæ not ascending; tibiæ
villose; claws short in both sexes; _Sarconesia_ Bigot with the species
_S. chlorogaster_ from Chile, setose genæ; legs slender, not villose;
claws of the male elongate.

[P] _Plinthomyia_ Rdi. and _Hemigymnochæta_ Corti are related to
_Ochromyia_, though too briefly described to place in the key.




APPENDIX

HYDROCYANIC ACID GAS AGAINST HOUSEHOLD INSECTS


The following directions for fumigating with hydrocyanic acid
gas are taken from Professor Herrick's circular published by the
Cornell Reading Course:

Hydrocyanic acid gas has been used successfully against household
insects and will probably be used more and more in the future.
It is particularly effective against bed-bugs, and cockroaches, but
because _it is such a deadly poison it must be used very carefully_.

The gas is generated from the salt potassium cyanid, by treating
it with sulfuric acid diluted with water. Potassium cyanid is a
most poisonous substance and the gas emanating from it is also
deadly to most, if not all, forms of animal life. The greatest care
must always be exercised in fumigating houses or rooms in buildings
that are occupied. Before fumigation a house should be vacated.
It is not necessary to move furniture or belongings except brass or
nickel objects, which may be somewhat tarnished, and butter, milk,
and other larder supplies that are likely to absorb gas. If the nickel
and brass fixtures or objects are carefully covered with blankets
they will usually be sufficiently protected.

There may be danger in fumigating one house in a solid row of
houses if there is a crack in the walls through which the gas may find
its way. It also follows that the fumigation of one room in a house
may endanger the occupants of an adjoining room if the walls between
the two rooms are not perfectly tight. It is necessary to keep
all these points in mind and to do the work deliberately and thoughtfully.
The writer has fumigated a large college dormitory of 253
rooms, once a year for several years, without the slightest accident
of any kind. In order to fumigate this building about 340 pounds
of cyanid and the same amount of sulfuric acid were used each time.
In addition to this, the writer has fumigated single rooms and smaller
houses with the gas. In one instance the generating jars were too
small; the liquid boiled over and injured the floors and the rugs.
Such an accident should be avoided by the use of large jars and by
placing old rugs or a quantity of newspapers beneath the jars.


THE PROPORTIONS OF INGREDIENTS

Experiments and experience have shown that the potassium
cyanid should be ninety-eight per cent pure in order to give satisfactory
results. The purchaser should insist on the cyanid being of
at least that purity, and it should be procurable at not more than
forty cents per pound. The crude form of sulfuric acid may be used.
It is a thickish, brown liquid and should not cost more than four or
five cents a pound. If a room is made tight, one ounce of cyanid for
every one hundred cubic feet of space has been shown to be sufficient.
It is combined with the acid and water in the following proportions:

  Potassium cyanid                       1 ounce
  Commercial sulfuric acid               1 fluid ounce
  Water                                  3 fluid ounces


A SINGLE ROOM AS AN EXAMPLE

Suppose a room to be 12 by 15 by 8 feet. It will contain 12 × 15 × 8, or
1440 cubic feet. For convenience the writer always works on the basis of
complete hundreds; in this case he would work on the basis of 1500 cubic
feet, and thus be sure to have enough. The foregoing room, then, would
require 15 ounces of cyanid, 15 ounces of sulfuric acid, and 45 ounces
of water. The room should be made as tight as possible by stopping all
the larger openings, such as fireplaces and chimney flues, with old rags
or blankets. Cracks about windows or in other places should be sealed
with narrow strips of newspaper well soaked in water. Strips of
newspaper two or three inches wide that have been thoroughly soaked in
water may be applied quickly and effectively over the cracks around the
window sash and elsewhere. Such strips will stick closely for several
hours and may be easily removed at the conclusion of the work.

While the room is being made tight, the ingredients should be measured
according to the formula already given. The water should be measured and
_poured first_ into a stone jar for holding at least two gallons. The
jar should be placed in the middle of the room, with an old rug or
several newspapers under it in order to protect the floor.

The required amount of sulfuric acid should then be poured rather slowly
into the water. _This process must never be reversed; that is, the acid
must never be poured into the jar first._ The cyanid should be weighed
and put into a paper bag beside the jar. All hats, coats, or other
articles that will be needed before the work is over should be removed
from the room. When everything is ready the operator should drop the bag
of cyanid gently into the jar, holding his breath, and should walk
quickly out of the room. The steam-like gas does not rise immediately
under these conditions, and ample time is given for the operator to walk
out and shut the door. If preferred, however, the paper bag may be
suspended by a string passing through a screw eye in the ceiling and
then through the keyhole of the door. In this case the bag may be
lowered from the outside after the operator has left the room and closed
the door.

The writer has most often started the fumigation toward evening and left
it going all night, opening the doors in the morning. The work can be
done, however, at any time during the day and should extend over a
period of five or six hours at least. It is said that better results
will be obtained in a temperature of 70° F., or above, than at a lower
degree.

At the close of the operation the windows and doors may be opened from
the outside. In the course of two or three hours the gas should be
dissipated enough to allow a person to enter the room without danger.
The odor of the gas is like that of peach kernels and is easily
recognized. The room should not be occupied until the odor has
disappeared.


FUMIGATING A LARGE HOUSE

The fumigation of a large house is merely a repetition, in each room and
hall, of the operations already described for a single room. All the
rooms should be made tight, and the proper quantities of water and
sulfuric acid should be measured and poured into jars placed in each
room with the cyanid in bags besides the jars. When all is ready, the
operator should _go to the top floor and work downward_ because the gas
is lighter than air and tends to rise.


PRECAUTIONS

The cyanid should be broken up into small pieces not larger than small
eggs. This can best be done on a cement or brick pavement. It would be
advantageous to wear gloves in order to protect the hands, although the
writer has broken many pounds of cyanid without any protection on the
hands. Wash the hands thoroughly at frequent intervals in order to
remove the cyanid.

The operations of the work must be carried out according to directions.

The work should be done by a calm, thoughtful and careful person--best
by one who has had some experience.

Conspicuous notices of what has been done should be placed on the doors,
and the doors should be locked so that no one can stray into the rooms.

The gas is lighter than air, therefore one should always begin in the
rooms at the top of the house and work down.

After fumigation is over the contents of the jar should be emptied into
the sewer or some other safe place. The jars should be washed thoroughly
before they are used again.

_It must be remembered that cyanid is a deadly poison_; but it is very
efficient against household insects, if carefully used, and is not
particularly dangerous when properly handled.


LESIONS PRODUCED BY THE BITE OF THE BLACK-FLY

While this text was in press there came to hand an important paper
presenting a phase of the subject of black fly injury so different from
others heretofore given that we deem it expedient to reproduce here the
author's summary. The paper was published in _The Journal of Cutaneous
Diseases_, for November and December, 1914, under the title of "A
Clinical, Pathological and Experimental Study of the Lesions Produced by
the Bite of the Black Fly (_Simulium venustum_)," by Dr. John Hinchman
Stokes, of the University of Michigan.


RESUME AND DISCUSSION OF EXPERIMENTAL FINDINGS

The principal positive result of the work has been the experimental
reproduction of the lesion produced by the black-fly in characteristic
histological detail by the use of preserved flies. The experimental
lesions not only reproduced the pathological pictures, but followed a
clinical course, which in local symptomatology especially, tallied
closely with that of the bite. This the writer interprets as
satisfactory evidence that the lesion is not produced by any living
infective agent. The experiments performed do not identify the nature of
the toxic agent. Tentatively they seem to bring out, however, the
following characteristics.

1. The product of alcoholic extraction of flies do not contain the toxic
agent.

2. The toxic agent is not inactivated by alcohol.

3. The toxic agent is not destroyed by drying fixed flies.

4. The toxic agent is not affected by glycerin, but is, if anything,
more active in pastes made from the ground fly and glycerin, than in the
ground flies as such.

5. The toxic agent is rendered inactive or destroyed by hydrochloric
acid in a concentration of 0.25%.

6. The toxic agent is most abundant in the region of the anatomical
structures connected with the biting and salivary apparatus (head and
thorax).

7. The toxic agent is not affected by a 0.5% solution of sodium
bicarbonate.

8. The toxic agent is not affected by exposure to dry heat at 100° C.
for two hours.

9. The toxic agent is destroyed or rendered inactive in alkaline
solution by a typical hydrolytic ferment, pancreatin.

10. Incomplete experimental evidence suggests that the activity of the
toxic agent may be heightened by a possible lytic action of the blood
serum of a sensitive individual, and that the sensitive serum itself may
contain the toxic agent in solution.

These results, as far as they go (omitting No. 10), accord with Langer's
except on the point of alcoholic solubility and the effect of acids. The
actual nature of the toxic agent in the black-fly is left a matter of
speculation.

The following working theories have suggested themselves to the writer.
First, the toxin may be, as Langer believes in the case of the bee, an
alkaloidal base, toxic as such, and neutralized after injection by
antibodies produced for the occasion by the body. In such a case the
view that a partial local fixation of the toxin occurs, which prevents
its immediate diffusion, is acceptable. Through chemotactic action,
special cells capable of breaking up the toxin into harmless elements
are attracted to the scene. Their function may be, on the other hand, to
neutralize directly, not by lysis. This would explain the rôle of the
eosinophiles in the black-fly lesion. If their activities be essential
to the destruction or neutralization of the toxin, one would expect them
to be most numerous where there was least reaction. This would be at the
site of a bite in an immune individual. A point of special interest for
further investigation, would be the study of such a lesion.

Second, it is conceivable that the injected saliva of the fly does not
contain an agent toxic as such. It is possible, that like many foreign
proteins, it only becomes toxic when broken down. The completeness and
rapidity of the breaking down depends on the number of eosinophiles
present. In such a case immunity should again be marked by intense
eosinophilia.

[Illustration: 173. Fifth day mature lesion. Lower power drawing showing
papillary oedema and infiltrate in the region of the puncture. After Dr.
J .H. Stokes]

Third, lytic agents in the blood serum may play the chief rôle in the
liberation of the toxic agent from its non-toxic combination. An immune
individual would then be one whose immunity was not the positive one of
antibody formation, but the negative immunity of failure to metabolize.
An immune lesion in such a case might be conceived as presenting no
eosinophilia, since no toxin is liberated. If the liberation of the
toxin is dependent upon lytic agents present in the serum rather than in
any cellular elements, a rational explanation would be available for the
apparent results (subject to confirmation) of the experiment with
sensitive and immune sera. In this experiment it will be recalled that
the sensitive serum seemed to bring out the toxicity of the ground
flies, and the serum itself seemed even to contain some of the dissolved
or liberated toxin. The slowness with which a lesion develops in the
case of the black-fly bite supports the view of the initial lack of
toxicity of the injected material. The entire absence of early
subjective symptoms, such as pain, burning, etc., is further evidence
for this view. It would appear as if no reaction occurred until lysis of
an originally non-toxic substance had begun. Regarding the toxin itself
as the chemotactic agent which attracts eosinophiles, its liberation in
the lytic process and diffusion through the blood stream attracts the
cells in question to the point at which it is being liberated. Arriving
upon the scene, these cells assist in its neutralization.

The last view presented is the one to which the author inclines as the
one which most adequately explains the phenomena.

A fourth view is that the initial injection of a foreign protein by the
fly (i.e., with the first bite) sensitizes the body to that protein. Its
subsequent injection at any point in the skin gives rise to a local
expression of systematic sensitization. Such local sensitization
reactions have been described by Arthus and Breton, by Hamburger and
Pollack and by Cowie. The description of such a lesion given by the
first named authors, in the rabbit, however, does not suggest,
histopathologically at least, a strong resemblance to that of the
black-fly. Such an explanation of many insect urticariæ deserves further
investigation, however, and may align them under cutaneous expressions
of anaphylaxis to a foreign protein injected by the insect. Depending on
the chemical nature of the protein injected, a specific chemotactic
reaction like eosinophilia may or may not occur. Viewed in this light
the development of immunity to insect bites assumes a place in the
larger problem of anaphylaxis.

[Illustration: 174. Experimental lesion produced from alcohol-fixed
flies, dried and ground into a paste with glycerin. After Dr. J. H.
Stokes]


SUMMARY

In order to bring the results of the foregoing studies together, the
author appends the following résumé of the clinical data presented in
the first paper.

The black-fly, _Simulium venustum_, inflicts a painless bite, with
ecchymosis and hæmorrhage at the site of puncture. A papulo-vesicular
lesion upon an urticarial base slowly develops, the full course of the
lesion occupying several days to several weeks. Marked differences in
individual reaction occur, but the typical course involves four stages.
These are, in chronological order, the papular stage, the vesicular or
pseudovesicular, the mature vesico-papular or weeping papular stage and
the stage of involution terminating in a scar. The papule develops in
from 3 to 24 hours. The early pseudovesicle develops in 24 to 48 hours.
The mature vesico-papular lesion develops by the third to fifth day and
may last from a few days to three weeks. Involution is marked by
cessation of oozing, subsidence of the papule and scar-like changes at
the site of the lesion. The symptoms accompanying this cycle consist of
severe localized or diffused pruritus, with some heat and burning in the
earlier stages if the oedema is marked. The pruritus appears with the
pseudovesicular stage and exhibits extraordinary persistence and a
marked tendency to periodic spontaneous exacerbation. The flies tend to
group their bites and confluence of the developing lesions in such cases
may result in extensive oedema with the formation of oozing and
crusted plaques. A special tendency on the part of the flies to attack
the skin about the cheeks, eyes and the neck along the hair line and
behind the ears, is noted. In these sites inflammation and oedema may
be extreme.

A distinctive satellite adenopathy of the cervical glands develops in
the majority of susceptible persons within 48 hours after being bitten
in the typical sites. This adenopathy is marked, discrete and painful,
the glands often exquisitely tender on pressure. It subsides without
suppuration.

Immunity may be developed to all except the earliest manifestations, by
repeated exposures. Such an immunity in natives of an infested locality
is usually highly developed. There are also apparently seasonal
variations in the virulence of the fly and variations in the reaction of
the same individual to different bites.

Constitutional effects were not observed but have been reported.




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HONEIJ, J. A. and PARKER, R. R. 1914. Leprosy: flies in relation to the
   transmission of the disease. Journ. Med. Research, Boston, xxx, p.
   127-130.

HOOKER, W. A. 1908 a. Life history, habits, and methods of study of the
   Ixodoidea. Jour. Econ. Ent. i, p. 34-51.

---- 1908 b. A review of the present knowledge of the rôle of ticks in
   the transmission of disease. ibid., i, p. 65-76.

HOPE, F. W. 1837. On insects and their larvæ occasionally found in the
   human body. Trans. Ent. Soc., London, ii, p. 256-271.

HOUGH, G. DE N. 1899 a. Synopsis of the Calliphorinæ of the United
   States. Zoological Bulletin, ii, p. 283-290.

---- 1899 b. Some Muscinæ of North America, Biological Bulletin i, p.
   19-33.

---- 1899 c. Some North American Genera of Calliphorinæ. Entom. News,
   x, p. 62-66.

HOVARTH, G. 1912. Revision of the American Cimicidæ. Ann. Mus. Nat.
   Hungarici, x, p. 257-262.

HOWARD, C. W. 1908. A list of the ticks of South Africa, with
   descriptions and keys to all the forms known. Ann. Transvaal Mus. 1,
   p. 73-170.

HOWARD, C. W. and CLARK, P. F. 1912. Experiments on insect transmission
   of the virus of poliomyelitis. Journ. Exper. Med. xvi, p. 805-859.

HOWARD, L. O. 1899. Spider bites and kissing bugs. Pop. Sci. Mo. lv, p.
   31-42.

---- 1900. A contribution to the study of the insect fauna of human
   excrement. Proc. Wash. Acad. Sci. ii, p. 541-604.

---- 1901. Mosquitoes, how they live, how they carry disease, how they
   are classified, how they may be destroyed. 8vo. New York, Doubleday,
   Page & Co. (xv + 241 p.)

---- 1909. Economic loss to the people of the United States, through
   insects that carry disease. U. S. Dept. Agric. Bur. of Ent. Bul. 78,
   p. 1-40.

HOWARD, L. O., DYAR, H. G. and KNAB, F. 1913-. The mosquitoes of North
   and Central America and the West Indies. Vol. I. A general
   consideration of mosquitoes, their habits, and their relations to the
   human species. 4^o. Carnegie Institution of Washington (vii + 520
   p.).

HOWARD, L. O. and MARLATT, C. L. 1902. The principal household insects
   of the United States. U. S. Dept. Agric., Bur. Ent. Bul. 4.

HUEBNER, W. 1907. Ueber das Pfeilgift der Kalahari. Arch. exper. Path.
   und Pharm., lvii, p. 358-366.

HUNTER, S. J. 1913. Pellagra and the sand-fly. Jour. econ. Ent. vi, p.
   96-99.

HUNTER, W. D. 1913. American interest in medical entomology. Jour. econ.
   Ent. vi, p. 27-39.

HUNTER, W. D. and BISHOPP, F. C. 1910. Some of the more important ticks
   of the United States. U. S. Dept. Agric. Yearbook 1910, p. 219-230,
   pls. xv-xvi.

---- 1911. The Rocky Mountain spotted fever tick. With special reference
   to the problem of its control in the Bitter Root Valley in Montana.
   U. S. Dept. Agric., Bur. Ent. Bul. 105, p. 1-47.

HUTCHISON, R. H. 1914. The migratory habit of housefly larvæ as
   indicating a favorable remedial measure. An account of progress. U.
   S. Dept. Agric., Bul. 14, p. 1-11.

JENNINGS, A. H. 1914. Summary of two years' study of insects in relation
   to pellagra. Journ. of Parasitology, i, p. 10-21.

JENNINGS, A. H. and KING, W. V. 1913. One of the possible factors in the
   causation of pellagra. Journ. Amer. Med. Assoc., lx, p. 271-274.

JEPSON, F. P. 1909. Notes on colouring flies for purposes of
   identification. Rep't to the Local Gov't Board on Publ. Health, n. s.
   16, p. 4-9.

JOHANNSEN, O. A. 1903. Aquatic Nematocerous Diptera. N. Y. State Mus.
   Bul., 68, p. 328-448, pls. 32-50.

---- 1905. Aquatic Nematocerous Diptera II. (Chironomidæ). ibid. 86, p.
   76-330, pls. 16-37.

---- 1908. North America Chironomidæ. ibid., 124, p. 264-285.

---- 1911. The typhoid fly and its allies. Maine Agric. Exp. Sta. Bul.,
   401, p. 1-7.

---- 1911. Simulium and pellagra. Insect Notes for 1910. Maine Agr.
   Exper. Station. Bul. 187, p. 4.

KELLOGG, V. L. 1915. Spider poison. Jour. of Parasitology, i, p. 107+

KELLY, H. A. 1907. Walter Reed and yellow fever. 8vo. New York, McClure,
   Phillips & Co. (xix + 310 p.).

KEPHART, CORNELIA F. 1914. The poison glands of the larva of the
   browntail moth (Euproctis chrysorrhoea Linn.). Journ. Parasit., i,
   p.

KIEFFER, J. J. 1906. Chironomidæ. Genera Insectorum. Fasc. 42, p. 1-78.

---- 1913. Nouv. étude sur les Chironomides de l'Indien Museum de
   Calcutta. Records of the Indian Mus., ix, p. 119-197.

KING, A. F. A. 1883. Insects and disease--mosquitoes and malaria. Pop.
   Sci. Mo. xxiii, p. 644-658.

KIRKLAND, A. H. 1907. Second annual report of the Superintendent for
   suppressing the gypsy and browntail moths. 8vo. Boston. 170 p.

KLEINE, E. 1909. Postive Infektionsversuche mit _Trypanosoma brucei_
   durch _Glossina palpalis._ Deutsche med. Wochenschr., xxxv, p.
   469-470.

   Weitere wissenschaftliche Beobachtungen über die Entwicklung von
      Trypanosomen in Glossinen. ibid. p. 924-925.

   Weitere Untersuchungen über die Ætiologie der Schlafkrankheit. ibid.,
      p. 1257-1260.

   Weitere Beobachtungen über Tsetsefliegen und Trypanosomen. ibid., p.
      1956-1958.

KLING, C. and LEVADITI, C. 1913. Études sur la poliomyélite aiguë
   épidémique. Ann. Inst. Pasteur, xxvii, p. 718-749, 739-855.

KNAB, F. 1912. Unconsidered factors in disease-transmission by
   blood-sucking insects. Journ. Econ. Ent., v, p. 196-200.

---- 1913 a. The species of Anopheles that transmit human malaria. Amer.
   Journ. Trop. Dis. and Preventive Med., i, p. 24-43.

---- 1913 b. Anopheles and malaria. ibid., i, p. 217.

---- 1913 c. The life history of _Dermatobia hominis_. ibid., i, p.
   464-468.

KNAB, F. See Howard, Dyar, and Knab.

KOBERT, R. 1893. Lehrbuch der Intoxikationen. 4^o. Stuttgart, Enke. (xxii
   + 816 p.). 2d ed. in 2 vols., 1906.

---- 1901. Beiträge zur Kenntniss der Giftspinnen. 8^o. Stuttgart, Enke.
   (viii + 191 p.).

KOLBE, H. J. 1894. Der Pfeilgiftkäfer der Kalahari-Wüste, _Diamphidia
   simplex_. Stett. Ent. Zeitg., iv, p. 79-86.

KRAUSE, M. 1907. Untersuchungen über Pfeilgifte aus unseren
   africanischen Kolonien. Verhand. deutsche Kolonien kong. 1905. p.
   264-288.

LALLIER, P. 1897. Étude sur la myase du tube digestif chez l'homme.
   Thesis, Paris, 8^o. 120 p.

LANGER, J. 1897. Ueber das Gift unserer Honigbiene. Archiv. exper. Path.
   und Pharm., xxxviii, p. 381-396.

LAVINDER, C. H. 1911. Pellagra: a précis. U. S. Publ. Health Service
   Bul. 48, 37 p.

LEIDY, J. 1847. History and anatomy of the hemipterous genus
   _Belostoma_. Journ. Acad. Philad. (2), i, p. 57-67.

LEIPER, R. T. 1907. The etiology and prophylaxis of dracontiasis.
   British Med. Journ. 1907, p. 129-132.

LEISHMAN, W. B. 1910 a. Observations on the mechanism of infection in
   tick fever and on the hereditary transmission of _Spirochæta duttoni_
   in the tick. Trans. Soc. Trop. Med. Hyg., iii, p. 77-95. Abstr. in
   Bul. Inst. Pasteur, viii, p. 312-313.

---- 1910 b. On the hereditary transmission and mechanism of infection
   in tick fever and on the hereditary transmission of _Spirochæta
   duttoni_ in the tick. Lancet., clxxvii, p. 11.

LINNELL, R. McC. 1914. Notes on a case of death following the sting of a
   scorpion. Lancet, 1914, p. 1608-1609.

LIVINGSTONE, D. 1857. Missionary travels and researches in South Africa.

LUCAS, H. 1843. (note) _Latrodectus malmignatus_ Bul. Soc. Ent., France,
   1843, p. viii.

LUDLOW, C. S. 1914. Disease bearing mosquitoes of North and Central
   America, the West Indies and the Philippine Islands. War Dept.,
   Office of Surgeon General. Bul. No. 4, 1-96.

LUGGER, 1896. Insects injurious in 1896. Agr. Exp. Sta. Bul. 48. p. 33
   to 270.

MacCALLUM, W. C. 1898. On the hæmatozoan infection of birds. Journ. Exp.
   Med. iii, p. 117.

MacGREGOR, M. E. 1914. The posterior stigmata of dipterous larvæ as a
   diagnostic character. Parasitology, vii, p. 176-188.

MacLOSKIE, G. 1888. The poison apparatus of the mosquito. Amer.
   Naturalist, xxii, p. 884-888.

MALLOCH, J. P. 1913. American black-flies or Buffalo gnats. U. S. Dept.
   Agric. Bur. Ent. Tech. Bul. 26, p. 1-72.

---- 1914. Notes on North American Diptera. Bul. Illinois State Lab.
   Nat. Hist., x, p. 213-243.

MANSON, P. 1911. Tropical diseases: a manual of the diseases of warm
   climates. 8^o. London, Cassell & Co. (xx + 876 p.). 4 ed. (1907).
   Reprinted.

MARCHOUX, E. and COUVY, L. 1913. Argas et spirochætes (1 mémoire). Les
   granules de Leishman. Ann. Inst. Pasteur, xxvii, p. 450-480. 2
   mémoire. Le virus chez l'acarien. ibid. p. 620-643.

MARCHOUX, E. and SELIMBENI, A. 1903. La spirillose des poules. Ann.
   Inst. Pasteur, xvii, p. 569-580.

MARCHOUX, E. and SIMOND, P. L. 1905. Études sur la fièvre jaune. Ann.
   Inst. Pasteur, xx, pp. 16-40, 104-148, 161-205.

MARLATT, C. L. 1902. (See Howard, L. O. and Marlatt, C. L.)

---- 1907. The bed-bug (_Cimex lectularius_ L.) U. S. Dept. Agric., Bur.
   Ent., Circ. No. 47, revised ed., 8 pp.

MARTIN, G. LEBOEUF, and ROUBAUD. 1909. Rapport de la mission d'études de
   la maladie du sommeil au Congo français. 4^o. Paris, Masson & Cie.
   (vi + 722 p., 8 pls. and map.).

MAVER, MARIA B. 1911. Transmission of spotted fever by other than
   Montana and Idaho ticks. Journ. Infec. Dis., viii, p. 322-326.

McCLINTIC, T. B. 1912. Investigations of and tick eradications in Rocky
   Mountain spotted fever. Publ. Health Repts., Washington, xxvii, p.
   732-760.

MECKEL, H. 1847. Uber schwarzes Pigment in der Milz und im Blute einer
   Geisteskranken. Allgem. Zeitschr. f. Psychiatrie, iv, p. 198-226.

MEGNI, P. 1906. Les insectes buveurs de sang. 12mo. Paris, Rudeval. (150
   p.).

MELNIKOFF, N. 1869. Ueber die Jugendzustände der _Tænia cucumerina_.
   Arch. f. Naturg., xxxv, p. 62-70.

MENSE, C. 1913. Handbuch der Tropenkrankheiten. 1 Band. 4^o. Leipzig,
   Barth (xv + 295 p.) Entomological parts by A. Eysell, and by Doerr
   and Russ.

MINCHIN, E. A. 1912. An introduction to the study of the Protozoa, with
   special reference to the parasitic forms. 8^o. London. Arnold (xi +
   517 p.).

MITCHELL, EVELYN G. 1907. Mosquito life. 8vo. New York, Putmans. (xxii +
   281 p.).

MITZMAIN, M. B. 1910. General observations on the bionomics of the
   rodent and human flies. U. S. Publ. Health Service. Bul., 38, p.
   1-34.

---- 1912. The rôle of _Stomoxys calcitrans_ in the transmission of
   _Trypanosoma evansi_. Philippine Journ. Sci., vii, p. 475-519, 5 pls.

---- 1913 a. The biology of _Tabanus striatus_ Fabricius, the horsefly
   of the Philippines. ibid., vii, B. p. 197-221.

---- 1913 b. The mechanical transmission of surra. ibid., viii, sec. B.,
   p. 223-229.

---- 1914 a. Experimental insect transmission of anthrax. U. S. Public
   Health Repts. xxix, p. 75-77.

---- 1914 b. I. Collected studies on the insect transmission of
   _Trypanosoma evansi_. II. Summary of experiments in the transmission
   of anthrax by biting flies. U. S. Pub. Health Service, Hyg. Lab.
   Bul., 94, p. 1-48.

MIYAKE, H. and SCRIBA, J. 1893. Vorläufige Mitteilung über einen neuen
   Parasit des Menschen. Berl. klin. Wochenschr., xxx, p. 374.

MOLLERS, B. 1907. Experimentelle Studien über die Uebertragung des
   Rückfallfiebers durch Zecken. Zeitschr. für Hyg. u.
   Infektionskrankheiten, lviii, p. 277-286.

MOTE, D. C. 1914. The cheese-skipper (_Piophila casei_). Ohio Naturalist
   xiv, p. 309-310.

NEIVA, A. 1910. Beiträge zur Biologie der _Conorhinus megistus_ Burm.
   Memorias de Institute Oswaldo Cruz., ii, p. 206-212.

NEVEU-LEMAIRE, M. 1907. Un nouveau cas de parasitisme accidental d'un
   myriapode dans le tube digestif de l'homme, C. R. Soc. der Biol.,
   lxiii p. 305-308.

---- 1908. Précis de parasitologie humaine. 8vo. Paris, Rudeval. (v +
   712 p.).

NEWSTEAD, R. 1911. The papataci flies (Phlebotomus) of the Maltese
   Islands. Bul. of Ent. Research, ii, p. 47-78, pls. 1-3.

NICOLL, W. 1911. On the part played by flies in the disposal of the eggs
   of parasitic worms. Repts. to the Local Gov't. Board on Publ. Health
   and Med. Subjects, n. s. No. 53, p. 13-30.

NICOLLE, C. 1910, Recherches expérimentales sur la typhus exanthématique
   entreprises à l'Institut Pasteur de Tunis pendant l'année 1909. Ann.
   Inst. Pasteur, xxiv, p. 243-275.

---- 1911. Recherches expérimentales sur la typhus exanthématique
   entreprises à l'Institut Pasteur de Tunis pendant l'année 1910.
   ibid., xxv, p. 1-55, 97-154.

NICOLLE, C., BLAIZOT, A., and CONSEIL, E. 1912 a. Étiologie de la fièvre
   récurrente. Son mode de transmission par le pou. C. R. Acad. Sci.,
   cliv, p. 1636-1638.

---- 1912 b. Conditions de transmission de la fièvre récurrente par le
   pou. ibid., clv., p. 481-484.

NICOLLE, C. and CATOUILLARD, G. 1905. Sur le venin d'un scorpion commun
   de Tunisie (_Heterometrus maurus_). C. R. Soc. Biol. lviii: p.
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NOE, G. 1901. Sul ciclo evolutivo della _Filaria bancrofti_ e delta
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   viii, p. 275-353.

NORMAN, W. W. 1896. The effect of the poison of centipedes. Trans. Texas
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NUTTALL, G. H. F. 1899. On the rôle of insects, arachnids, and myriapods
   as carriers in the spread of bacterial and parasitic diseases of man
   and animals. Johns Hopkins Hosp. Repts., viii, 154 p., 3 pls.

---- 1908 a. On the behavior of Spirochætæ in _Acanthia lectularia_.
   Parasitology, i, p. 143-151.

---- 1908 b. The transmission of _Trypanosoma lewisi_ by fleas and lice.
   ibid., i, p. 296-301.

---- 1908 c. The Ixodoidea or ticks, spirochætosis in man and animals,
   piroplasmosis. Journ. Roy. Inst. Publ. Health, xvi, p. 385-403,
   449-464, 513-526.

---- 1914. Tick paralysis in man and animals. Parasitology, vii, p.
   95-104.

NUTTALL, G. H. F. and JEPSON, F. P. 1909. The part played by _Musca
   domestica_ and allied (non-biting) flies in the spread of infective
   diseases. A summary of our present knowledge. Rept. to the Local
   Gov't Board on Publ. Health and Med. Subjects, n. s. 16, p. 13-41.

NUTTALL, G. H. F. and SHIPLEY, E. A. 1901-03. Studies in relation to
   malaria. The structure and biology of Anopheles. Journ. Hyg., vols.
   i, ii, and iii.

ORTH, J. 1910. Ueber die Beziehungungen der Haarsackmilbe zu
   Krebsbildungen in der Mamma. Berliner klin. Wochenschr., xlvii, p.
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OSBORN, HERBERT. 1896. Insects affecting domestic animals. U. S. Dept.
   Agric., Bur. of Ent. Bul., 5, n. s., 302 p.

---- 1902. Poisonous insects. Article in Reference Handbook. Med. Sci.,
   v, p. 158-169.

OSLER, W. 1887. An address on the Hæmatozoa of malaria. British Med.
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OSTEN SACKEN, C. R. 1875-78, Prodrome of a Monograph of North American
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OUDEMANS, A. C. 1910. Neue Ansichten über die Morphologie des
   Flohkopfes, sowie über die Ontogenie, Phylogenie und Systematik der
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PATTON, W. S. 1907. Preliminary report on the development of the
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   Dept., Gov't of India, 28, p. 1-19.

PATTON, W. S. and CRAGG, F. W. 1913. A textbook of medical entomology.
   4^o. London, Christian Literature Society for India. (xxxiv + 764 p.)

PAWLOWSKY, E. 1906. Ueber den Steck- und Saug-apparat der Pediculiden.
   Zeitschr. wiss. Insektenbiol., ii, p. 156-162, 198-204.

PAWLOWSKY, E. 1913. Scorpiotomische Mitteilungen. I. Ein Beitrag zur
   Morphologie des Giftdrüsen der Skorpione. Zeitschr. wiss. Zool., cv.,
   p. 157-177. Taf. x-xi.

PEPPER, W., SCHNAUSS, F. W., and SMITH, A. J. 1908. Transient parasitism
   in men by a species of _Rhizoglyphus_. Univ. of Pa. Med. Bul. xxi, p.
   274-277.

PETROVSKAIA, MARIA. 1910. Sur les myases produites chez l'homme par les
   Oestrides (Gastrophilus et Rhinoestrus). Thèse, Fac. de médecine,
   Paris, 79 p.

PETTIT, A. and KROHN, A. 1905. Sur la structure des glandes salivaires
   du Notonecte (_Notonecta glauca_). Arch. anat. micr. Paris, vii, p.
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PHISALIX, MME. 1900. Un venin volatil. Sécrétion cutanée du _Iulus
   terrestris_. C. R. Soc. Biol. Paris, 1900, p. 1033-1036.

---- 1912. Effets physiologiques du venin de la Mygale de Haïti, le
   _Phormictopus cancerides_ Pocock. Effets physiologiques du venin de
   la Mygale de Corse (_Cteniza sauvaga_ Rossi); Bul. Mus. Paris, 1912:
   134-138.

PORTSCHINSKY, I. A. 1908. _Rhinoestrus purpureus_, a parasite of
   horses which deposits its larvæ in the eyes of man. Mss. transl. by
   Miss S. L. Weissman, in library of Ent. Dept., Cornell University.

---- 1910. Biology of _Stomoxys calcitrans_ and other coprophagous
   flies. Monograph in Russian. Mss. summarized transl. by Miss S. L.
   Weissman, in Library of Ent. Dept., C. U.

---- 1911. _Gastrophilus intestinalis_. Mss. transl. by Miss S. L.
   Weissman, in library of Ent. Dept., C. U.

---- 1913 a. The sheep gad-fly, _Oestrus ovis_, its life, habits,
   methods of combating it, and its relation to man. Russian. Mss.
   summarized trans. by Miss S. L. Weissman, in library of Ent. Dept.,
   C. U.

---- 1913 b. _Muscina stabulans_. A monograph in Russian. Mss., trans.
   by J. Millman, in library of Ent. Dept., Cornell Univ.

PROWAZEK, S. 1905. Studien über Säugetiertrypanosomen. Arb. aus dem
   kais. Gesundheitsamte xxii, p. 351-395.

PUSEY, W. A. 1911. The principles and practice of dermatology. 2 ed,
   8vo. Appleton & Co. (1079 p.)

RABINOWITSCH, L. and KEMPNER, W. 1899. Beitrag zur Kentniss der
   Blutparasiten, speciell der Ratten trypanosomen. Zeitschr. f. Hyg.
   xxx, p. 251-291.

RANSOM, B. H. 1904. An account of the tape worms of the genus
   _Hymenolepis_ parasitic in man. Bul. No. 18, Hyg. Lab., U. S. Pub.
   Health and Mar.-Hosp. Serv., Wash., p. 1-138.

---- 1911. The life history of a parasitic nematode, _Hebronema muscæ_.
   Science n. s. xxxiv, p. 690-692.

---- 1913. The life history of _Habronema muscæ_, (Carter), a parasite
   of the horse transmitted by the house-fly. U. S. Dept. Agric. Bur.
   Animal, Ind. Bul. 163, p. 1-36.

REAUMUR, R. A. F. DE. 1738. Mémoires pour servir a l'histoirie des
   insectes. Histoire des cousins, iv, p. 573-636.

REED, WALTER. 1900. The etiology of yellow fever. Philadelphia Med.
   Jour. Oct. 27, 1900, vi, p. 790-796.

REED, W. and CARROLL, J. 1901. The prevention of yellow fever. Med.
   Record, Oct. 26, 1901, p. 441-449.

REUTER, ENZIO. 1910. Acari und Geschwulstätiologie. Centralbl. Bakt.
   Jena. Abt. 1 lvi.; Originale 339-344.

REUTER, O. M. 1912. Bemerkungen über mein neues Heteropterensystem. Ofv.
   Finska Vetensk. Soc. Förh., liv. Afd. A. vi, p. 1-62.

RIBAGA, C. 1897. Sopra un organo particolare della Cimici dei letti
   (_Cimex lectularius_ L.). Rivista di Patologia Vegetale, v, p.
   343-352.

RICARDO, GERTRUDE. 1900. Notes on the Pangoninæ. Ann. and Mag. Nat.
   Hist. v, p. 97-121.

---- 1901. Further Notes on the Pangoninæ. ibid. viii, p. 286-315.

---- 1904. Notes on the smaller genera of the Tabanidæ. ibid. xiv, P.
   349-373.

RICKETTS, H. T. 1906-1910. Contributions to medical sciences by Howard
   Taylor Ricketts. 1870-1910. Univ. of Chicago Press. 1911.

---- 1909. A microorganism which apparently has a specific relationship
   to Rocky Mountain spotted fever. A preliminary report. Jour. Amer.
   Med. Assoc. iii, p. 373-380.

---- Spotted fever reports 1 and 2. In the 4th Bien. Rept. State Board
   of Health, Montana, 1909, p. 87-191.

RICKETTS, H. T. and WILDER, R. M. 1910. The transmission of the typhus
   fever of Mexico (tabardillo) by means of the louse, _Pediculus
   vestimenti_. Journ. Am. Med. Assoc. liv. p. 1304.

RILEY, C. V. and HOWARD, L. O. 1889. A contribution to the literature of
   fatal spider-bites. Insect life, Washington, i. p. 204-211.

RILEY, W. A. 1906. A case of pseudoparasitism by dipterous larvæ.
   Canadian Ent. xxxviii, p. 413.

---- 1910 a. Earlier references to the relation of flies to disease.
   Science n. s. xxxi, p. 263-4.

---- 1910 b. _Dipylidium caninum_ in an American child. Science n. s.
   xxxi, p. 349-350.

---- 1911. The relation of insects to disease. Cornell Countryman ix, P.
   51-55.

---- 1912 a. Notes on the relation of insects to disease. 8vo. Ithaca,
   N. Y. 51 p.

---- 1912 b. Notes on animal parasites and parasitism. 8vo. Ithaca, N.
   Y. 55 p.

---- 1913. Some sources of laboratory material for work on the relations
   of insects to disease. Ent. News. xxiv, p. 172-175.

---- 1914. Mr. Nott's theory of insect causation of disease. Jour. of
   Parasitology. i, p. 37-39.

ROSENAU, M. J. and BRUES, C. T. 1912. Some experimental observations on
   monkeys, concerning the transmission of poliomyelitis through the
   agency of _Stomoxys calcitrans_. Monthly Bul. Mass. State Board of
   Health. Vol. vii, p. 314-317.

ROSS, R. 1904. Researches on Malaria. The Nobel Medical Prize Lecture
   for 1902, Stockholm, Norstedt & Söner. 89 p. 9 pls. In "Les Prix
   Nobel en 1902."

---- 1910. The prevention of malaria. 4^o. New York. Dutton & Co. (xx +
   669 p.).

ROTHSCHILD, N. C. 1905 a. North American Ceratophyllus. Novitates
   Zoologicæ xii, p. 153-174.

---- 1905 b. Some further notes on _Pulex canis_ and _P. felis_. ibid.
   xii, p. 192-193.

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INDEX


Abscess, 178

Acanthia, 87

Acariasis, 58

Acarina, 23, 58, 131, 259

Acarus dysenteriæ, 132

Accidental parasites, 131, 132, 134

Aedes, 194, 293

Aedes calopus, 182, 201, 205, 206, 208

Aedes cantator, 101

Aedes sollicitans, 101

Aedes tæniorhynchus, 101

Aerobic bacteria, 152

Æstivo-autumnal, 186

African Relapsing Fever, 230

Akis spinosa, 177

Alternation of Generations, 175

Amblyomma, 264

Amblyomma americanum, 67

Amblyomma cajennense, 67

American dog tick, 228

Amoeboid organism, 189

Anisolabis annulipes, 177

Anterior poliomyelitis, 241

Anopheles, 194, 291

Anopheles crucians, 199

Anopheles maculipennis, 182

Anopheles punctipennis, 198

Anopheles quadrimaculatus, 197

Anopheline, 192

Anthocoris, 279

Anthomyiidæ, 300

Anthomyia, 138

Anthrax, 165

Antipruritic treatment, 72

Ants, 42

Aphiochæta, 295

Apis mellifica, 36

Arachnida, 258

Araneida, 6

Argas, 64

Argas persicus, 63, 235, 237

Argasidæ, 62

Argopsylla, 317

Argus, 259

Arilus, 284

Arthropods, poisonous, 6

Asopia farinalis, 177

Assassin-bugs, 31, 219

Auchmeromyia, 117

Automeris io, 47

Avicularoidea, 12


Babesia, 226

Babesia bovis, 223

Babesia ovis, 225

Babesiosis, 221-222

Bacilli, 170

Bacillus icteroides, 202, 205

Bacillus pestis, 166

Bacillus typhosus, 153

Back swimmers, 30

Bdellolarynx, 304

Beauperthuy, Louis Daniel, 2

Bed-bug, 86, 88, 90, 173, 219-220

Bed-bug, cone-nosed, 92

Blister beetles, 54

Belostoma, 28, 277

Belostoma americana, 31

Belostomatidæ, 30

Bengalia, 314

Bird-spiders, 10

Black death, 1, 166

Black flies, 33, 104, 247

Black heads, 80

Blaps mortisaga, 134

Blepharoceridæ, 286

Boophilus, 264

Boophilus annulatus, 67, 223-225

Bot-flies, 112

Blue bottle flies, 140

Brill's disease, 238

Brown-tailed moth, 48

Bruck, 34

Buthus quinquestriatus, 21


Cabbage butterfly, 56

Calliphora, 136, 140, 312

Calliphora erythrocephala, 141

Calobata, 296

Camponotinæ, 43

Cancer, 254

Cantharidin, 54

Cantharidin poison, 55

Canthariasis, 134

Capsidæ, 280

Carriers, simple, 4, 144

Carriers of disease, 144

Carrion's fever, 253

Caterpillar rash, 45

Cat flea, 172

Cattle ticks, 222

Causative organism, 170

Cellia, 291

Centipedes, 25, 257

Ceratophyllus, 120, 316

Ceratophyllus acutus, 123

Ceratophyllus fasciatus, 122, 172, 213

Ceratopogon, 108

Cheese-fly, 137

Cheyletus eruditus, 271

Chigger, 60, 70

Chigoes, 126

Chilopoda, 25, 257

Chiracanthium nutrix, 18

Chironomidæ, 107

Chorioptes, 270

Chrysomelid, 55

Chrysomyia, 136, 308

Chrysomyia macellaria, 117, 140

Chrysops, 294

Chylous dropsy, 179

Chyluria, 178

Cicadidæ, 55

Cimex L., 278

Cimex boueti, 92

Cimex columbarius, 92

Cimex hemipterus, 91, 220

Cimex hirundinis, 92

Cimex inodorus, 92

Cimex lectularius, 87, 219

Citheronia regalis, 44

Clinocoris, 87

Coleoptera, 134, 274

Comedons, 80

Complete metamorphosis, 80

Compressor muscle, 20

Compsomyia, 117

Cone-nosed bed-bug, 92

Conjunctivitis, nodular, 52

Conorhinus, 282

Conorhinus megistus, 93, 219-220

Conorhinus rubrofasciatus, 220

Conorhinus sanguisugus, 32, 92

Copra itch, 72

Cordylobia, 118

Coriscus, 280

Coriscus subcoleoptratus, 32

Creeping myasis, 112

Crustacea, 257

Cryptocystis, 176

Cryptotoxic, 54-55

Cteniza sauvagei, 13

Ctenocephalus, 120, 172, 213, 317

Culex, 194, 201, 293

Culex pipiens, 35, 98

Culex quinquefasciatus, 180

Culex sollicitans, 200

Culex territans, 101

Culicidæ, 33, 97

Culicin, 34

Culicoides, 109, 288

Cyclops, 183, 257

Cynomyia, 136, 311


Dance, St. Vitus, 8

Dancing mania, 8

Deer-flies, 110

Definitive host, 192

Demodecidæ, 78

Demodex, 259

Demodex folliculorum, 78

Dermacentor, 262

Dermacentor andersoni, 67, 228

Dermacentor occidentalis, 227

Dermacentor variabilis, 67

Dermacentor venustus, 24, 228

Dermanyssidæ, 68

Dermanyssus, 266

Dermanyssus gallinæ, 68

Dermatitis, 72, 77, 85

Dermatobia, 115, 298

Dermatobia cyaniventris, 163

Dermatophilus, 317

Dermatophilus penetrans, 60, 126

Diamphidia simplex, 55

Dimorphism, 65

Direct inoculators, 4

Diplopoda, 25, 257

Diptera, 33, 94, 274

Dipterous Larvæ, 135

Dipylidium, 175, 221

Dipylidium caninum, 4, 175-176

Dog flea, 172

Dracunculus, 257

Dracunculus medinensis, 182

Drosophila, 296

Dum-dum fever, 220

Dysentery, 154


Ear-flies, 110

Earwig, 177

Echidnophaga, 317

Echinorhynchus, 185

Elephantiasis, 178-179

Empoasca mali, 33

Empretia, 46

English Plague Commission, 171

Epeira diadema, 18

Epizootic, 170

Eristalis, 137, 295

Essential hosts, 4, 165

Eumusca, 307

European Relapsing Fever, 233

Euproctis chrysorrhoea, 48

Eusimulium, 286


Facultative parasites, 131

Fannia, 136, 138, 145, 300

Federal Health Service, 169

Fever, lenticular, 237
  African Relapsing, 230, 234
  Carrion's, 253
  dum-dum, 154
  European Relapsing, 233
  pappatici, 96
  red water, 220
  Rocky Mt. Spotted, 226
  three day, 96
  Typhus, 237

Filaria, 178, 221
  immitis, 182

Filariasis, 178

Flannel-moth larvæ, 44

Fleas, 119, 166, 213
  cat, 172
  dog, 172
  human, 172, 176
  rodent, 123, 172
  rat, 171

Flesope, 125

Formaldehyde, 91

Fomites, 199, 204

Fulgoridæ, 28

Fumigation, 320


Gamasid, 68

Gangrene, 129

Gastrophilus, 113, 297

Giant crab spiders, 13

Giant water bugs, 30

Gigantorhynchus, 185

Glossina, 117, 297, 303

Glossina morsitans, 214, 217
  palpalis, 215, 217, 218

Glyciphagus, 267

Grain moth, 69

Grocer's itch, 72

Guinea-worm, 182


Habronema muscæ, 156, 183

Hæmatobia, 166, 304
  irritans, 146

Hæmatobosca, 304

Hæmatomyidium, 288

Hæmatopinus spinulosus, 213

Hæmatopota, 294

Hæmatosiphon, 279

Hæmoglobinuria, 222

Hæmozoin, 189

Harpactor, 284

Harvest mites, 60
  effect of, 59

Head-louse, 173

Helminthiasis, 138

Helophilus, 295

Hemiptera, 27, 86, 273-275

Heteropodidæ, 13

Heuchis sanguinea, 55

Hexapod larvæ, 58

Hexapoda, 27, 80, 258

Hippelates, 297

Hippobosca, 285

Histiogaster, 269
  spermaticus, 132

Homalomyia, 136, 138, 300

Honey bee, 36
  poison of, 37

Hornets, 43

Horn-fly, 137, 304, 308

Horse-fly, 110, 165

House-fly, 137-139, 144, 183
  control of, 156, 160

Human flea, 124

Host, definitive, 175
  intermediate, 175
  primary, 175

Hyalomma, 264
  ægypticum, 224-225

Hydrocyanic Acid Gas, 318

Hydrotæa, 300

Hymenolepis diminuta, 176

Hymenoptera, 36, 275

Hypoderma, 113, 298
  diana, 113
  lineata, 113

Hypopharynx, 80


Immunity from stings, 39

Incomplete metamorphosis, 80

Infantile paralysis, 162, 241
  splenic, 220
  Direct inoculation, 164

Insects, 258
  blood-sucking, 170

Intermediate host, 192, 203

Intestinal infestation, 112, 133
  myasis, 137

Isosoma, 69

Itch, 73-74
  mite, 73
  Norwegian, 77

Ixodes, 260
  ricinus, 66, 225
  scapularis, 66

Ixodidæ, 64-65

Ixodoidea, 62


Janthinosoma lutzi, 116

Jigger, 60

Johannseniella, 110, 288

Journal of Tropical Medicine and Hygiene, 36

Julus terrestris, 25

June bug, 185


Kala-azar, 220

Karakurte, 14

Katipo, 14

King, A. F. A., 3

Kircher, Athanasius, 1, 8

Kissing-bug, 31


Labium, 29, 80

Labrum, 28, 80

Lachnosterna, 185

Lælaps, 266

Lagoa crispata, 45

Lamblia intestinalis, 154

Langer, Josef, 37

Larder beetles, 135

Latrodectus, 12, 14, 17
  mactans, 15

Leishmanioses, 220

Lenticular fever, 237

Lepidoptera, 274

Lepidopterous larvæ, 134

Leprosy, 252

Leptidæ, 112

Leptis, 295

Leptus, 60, 273

Lice, 80

Linguatulina, 258

Liponyssus, 265

Loemopsylla, 172, 317

Lone star tick, 228

Louse, body, 84
  crab, 85
  dog, 176
  head, 82
  pubic, 85

Lucilia, 136, 312

Lycosa tarantula, 10

Lycosidæ, 10

Lyctocoris, 279

Lygus pratensis, 33

Lymphangitis, 67

Lymph scrotum, 178

Lyperosia, 304

Lyperosiops, 305


Macloskie, 34

Maggots, rat-tail, 137

Magnes sive de Arte Magnetica, 8

Malaria, 186

Malmigniatte, 14

Mandibles, 28, 80

Mange, 73-75

Margaropus, 237, 264
  annulatus, 223

Masked bed-bug hunter, 32

Mastigoproctus giganteus, 19, 80

Maxillæ, 28

Meal infesting species, 135

Melanin granules, 189

Melanolestes, 280
  picipes, 32

Mena-vodi, 14

Mercurialis, 1

Merozoites, 190

Metamorphosis, 80

Miana bug, 63

Microgametoblast, 192

Midges, 107

Migratory ookinete, 192

Millipedes, 25, 257

Mites, 23, 58

Monieziella, 269

Mosquitoes, 33, 97, 178, 196, 250
  treatment for bites of, 34, 36, 102

Musca, 137, 307
  domestica, 139, 145, 146, 157, 162

Muscidæ, 117

Muscina, 137, 146, 307
  stabulans, 140

Mutualism, 57

Myasis, 112, 135
  intestinal, 135-140
  nasal, 141

Mycterotypus, 287

Myiospila, 146, 307

Myriapoda, 225, 132, 257


Nagana, 165, 214

Nasal infestation, 114, 133

Necrobia, 135

Nematode parasite, 182

Nepa, 28

Nephrophages sanguinarius, 132

Nettling insects, 43
  larvæ, poison of, 53

Neurasthenia, 89

Nits, 86

North African Relapsing Fever, 234

Norwegian itch, 77

No-see-ums, 109

Notoedres, 269
  cati, 78

Notonecta, 28, 277

Notonectidæ, 30

Nott, Dr. Josiah, 2

Nuttall, 34


Occipital headaches, 138

Oecacta, 288

Oeciacus, 279

Oesophageal diverticula, 35

Oestridæ, 112, 136

Oestris ovis, 113

Oestrus, 298
  oocyst, 192
  ookinete, 192

Opsicoetes personatus, 32

Opthalmia, 155
  nodosa, 52

Oriental sore, 221

Ornithodoros, 65, 260
  moubata, 220, 230

Orthotylus flavosparsus, 33

Ornithomyia, 286

Oroya, 253

Oscinus, 297

Otiobius, 259
  megnini, 65

Otodectes, 271


Pangonia, 294

Pappatici fever, 96

Parasimulium, 286

Parasite, 3, 57, 131, 134, 182
  accidental, 3, 131, 134
  facultative, 3, 57, 131
  nematode, 182
  stationary, 57
  temporary, 57
  true, 3

Parasitism, accidental, 134

Pathogenic bacteria, 152
  organisms, 144, 164

Pawlowsky, 81

Pediculoides, 267
  ventricosus, 69, 72

Pediculosis, 81

Pediculus, 275
  corporis, 84, 233, 238
  humanus, 82, 173

Pellagra, 162, 246

Pernicious fever, 186

Pest, 166

Phidippus audax, 19

Philæmatomyia, 306

Phisalix, 13, 43

Phlebotomus, 289
  papatasii, 94
  verrucarum, 254
  vexator, 95

Phora, 295

Phormia, 136

Phormictopus carcerides, 13

Phthirus pubis, 85, 275

Phortica, 296

Pieris brassicæ, 56

Piophila, 297

Piophila casei, 136, 137

Piroplasmosis, 222

Plague, 166
  bubonic, 166, 169, 170
  pneumonic, 167

Plasmodium, 186

Platymetopius acutus, 33

Plica palonica, 83

Pneumonic, 166
  plague, 167, 173

Poisoning by nettling larvæ, 53

Poison of spiders, 7

Pollenia, 308
  rudis, 146, 147

Primary gland, 28

Prionurus citrinus, 20

Prosimulium, 286

Protocalliphora, 136, 312

Protozoan blood parasite, 165

Pseudo-tubercular, 52

Psorophora, 293

Psoroptes, 270

Psychodidæ, 94

Pulex, 120, 124, 126, 172, 317
  cheopis, 172
  irritans, 124
  penetrans, 126
  serraticeps, 120

Pulvillus, 150

Punkies, 109

Pycnosoma, 308


Rasahus, 280
  thoracicus, 32

Rat fleas, 120, 124, 171

Rat louse, 213

Red bugs, 70-72

Reduviidæ, 31

Reduviolus, 280

Reduvius, 282
  personatus, 32

Redwater fever, 222

Relapsing fever, 230, 233

Rhinoestrus nasalis, 115

Rhipicentor, 264

Rhipicephalus, 264

Rhizoglyphus, 269

Rhodnius, 281

Rocky Mountain Spotted Fever, 226
  spotted fever tick, 67

Russian gad-fly, 115


St. Vitus's or St. John's dance, 8

Salivary syringe, 28

Sand-flies, 109, 250

Sanguinetti, 11

Sarcophaga, 136, 142, 143

Sarcophila, 302

Sarcopsylla, 317
  penetrans, 126

Sarcoptes, 270
  minor, 78
  scabiei, 73

Sarcoptidæ, 72

Scabies, 72, 73, 74, 75

Scaurus striatus, 177

Schaudinn, 34

Schizont, 189, 190

Scholeciasis, 134

Scolopendra morsitans, 26

Scorpions, 20
  poison of, 21

Screw worm fly, 140

Sepsidæ, 296

Sepsis, 136, 297

Shipley, 34

Sibine, 46

Silvius, 294

Simple carriers, 4, 144

Simuliidæ, 33, 104

Simulium, 247, 249, 286, 321
  pictipes, 104

Siphonaptera, 119, 274, 316

Siphunculata, 80, 275

Sitotroga cerealella, 69

Skippers, 137

Sleeping sickness, 166, 215

Snipe-flies, 112

Solpugida, 22

Spanish fly, 54

Spermatozoa, 192

Spinose ear-tick, 65

Spirochæta, 35
  berberi, 234
  duttoni, 234

Spirochætosis, 235

Sporozoite, 189

Spotted fever, 67, 226

Squirrel flea, 123

Stable-fly, 137, 160, 163, 165

Stegomyia, 182, 293
  calopus, 206
  fasciata, 206

Stomoxys, 137, 305
  calcitrans, 117, 146, 160, 161, 165, 242

Straw-worm, 69

Stygeromyia, 305

Sucking stomach, 35

Sulphur ointment, 77

Surra, 165

Symbiosis, 57

Symphoromyia, 112, 295


Tabanidæ, 110

Tabanus, 110, 166, 294
  striatus, 165

Taenia, 175

Tapeworm, 4, 176

Tarantella, 8

Tarantism, 8

Tarantula, 10

Tarsonemidæ, 69

Tarsonemus, 267

Tenebrionid beetles, 127

Tersesthes, 110, 288

Tetanus, 129

Tetranychus, 273

Texas fever, 220-223

Three-day fever, 96

Tick, 23, 226
  bites, Treatment of, 68
  fever, 230
  paralysis, 67

Treatment,
  Bee stings, 36, 41
  Bites of,
    Bed-bugs, 90, 93
    Blackflies, 107
    Buffalo flies, 107
    Bugs, 31, 33
    Centipedes, 26, 27
    Chiggers, 127
    Chigoes, 127
    Fleas, 127
    Harvest mites, 61
    Jiggers, 129
    Lice, 83, 85
    Mosquitoes, 34, 36, 102
    Phlebotomus flies, 97
    Sand flies, 96, 107, 109
    Scorpions, 22, 23
    Spiders, 19
    Ticks, 61, 68, 72
    Ticks, ear, 65
  Blister beetle poison, 55
  Brown-tail moth rash, 45
  Cantharidin poison, 55
  Caterpillar rash, 45
  Ear ticks, 65
  House fly control, 156, 160
  Itch, 77
  Itch, grocer's, 72
  Lice, 85
  Nasal myasis, 143
  Rocky Mt. spotted fever, 228, 229
  Rash, caterpillar, 45
  Scabies, 77
  Sleeping sickness control, 218
  Spotted fever, 228, 229
  Stings, bee, 36, 41
  Typhus fever, prophylaxis, 239

Trichodectes canis, 176

Trichoma, 82

Trineura, 295

Trochosa singoriensis, 11

Trombidium, 60, 273

True insects, 80

Trypanosoma, 35

Trypanosoma, brucei, 165

Trypanosoma cruzi, 219

Trypanosoma lewisi, 213

Trypanosomiases, 212

Trypanosomiasis, 165, 219

Tsetse flies, 117, 166, 214, 219

Tsetse flies disease, 165

Tuberculosis, 155

Tumbu-fly, 118

Tydeus, 271

Typhoid, 155

Typhoid fever, 154

Typhus, 237

Typhus fever, 237

Tyroglyphus, 72, 131, 268

Dr. Tyzzer, 49


Uranotænia, 292


Vancoho, 14

Varicose groin glands, 178

Verruga peruviana, 253

Vescicating insects, 54


Wanzenspritze, 29

Warble-flies, 112

Wasps, 43

Whip-scorpions, 19

Wohlfahrtia, 143, 302

Wolf-spiders, 10

Wyeomyia smithii, 101, 293


Xenopsylla, 172, 317

Xenopsylla cheopis, 171, 124

Xestopsylla, 317


Yaws, 2

Yellow fever, 196, 203, 205




TRANSCRIBER'S NOTES

The following discrepancies in the text are as in the original:

  The inconsistent hyphenation of the following:
    assassin-bugs/assassin bugs;
    bedbug/bed-bug (and bedbugs);
    beekeeper/bee-keeper (and beekeepers);
    blackflies/black-flies;
    blow-flies/blow flies;
    bluebottles/blue-bottles;
    bot-flies/bot flies;
    bristlelike/bristle-like;
    browntail/brown-tail;
    coextensive/co-extensive;
    deer-flies/deer flies;
    dorsocentral/dorso-central;
    ectoparasites/ecto-parasites;
    endoparasites/endo-parasites;
    flesh-fly/flesh fly (and flesh flies);
    hotbed/hot-bed;
    housefly/house-fly (and houseflies);
    horsefly/horse-fly (and horse flies);
    horse-manure/horse manure;
    midsummer/mid-summer;
    preeminently/pre-eminently;
    sandfly/sand-fly (and sandflies);
    screw-worm fly/screw worm fly;
    stable-fly/stable fly;
    subequal/sub-equal;
    subfamily/sub-family;
    subtropical/sub-tropical;
    tapeworm/tape-worm (and tapeworms);
    today/to-day;
    tsetse-flies/tsetse flies;
    widespread/wide-spread;
    wormlike/worm-like.

  Inconsistent use of diaeresis in Aëdes/Aedes

  Inconsistent spelling of the following:
    defence/defense;
    disc/disk;
    hemolysis/hæmolysis;
    hemolytic/hæmolytic;
    hexapod/hexopod;
    Levaditi/Lavaditi;
    metalescent/metallescent;
    Mitzmain/Mitzman;
    Neveau-Lemaire/Neveau-Lamaire;
    offence/offense;
    Phthirus/Phthirius
    Portschinsky/Portchinsky/Portchinski;
    travelled/traveled;
    ventra-/ventro-;
    Villot/Villet;
    Wohlfartia/Wohlfahrtia;

  Inconsistent use of ligatures in Taenia/Tænia

toxine, insiduous, efficaceous, cyanid are spelt as in the original

In the first paragraph of chapter XII, "the student might not be lead"
is as in the original. Lead perhaps should be led

In the bibliography, the entry for Vaughan without a text specified is
as in the original





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