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London: CHAPMAN & HALL, Limited 




Copyright, 1918, 1922 


Asa C. Chandler 

Stanbope ipress 









It is the belief of the writer that one of the most pressing needs 
of the present time is the education of the people as a whole in 
the subjects of vital importance with which this book deals, 
and an increased interest in this field of scientific work. Scien- 
tists are the leaders of the world, and should constantly endeavor 
to keep a little ahead of the lay population who follow them. 
It is, however, important that the leaders should not only 
blaze the trail, but should make it sufficiently easy to find so 
that the followers may not fall too far behind. In the intense 
fascination of exploring the trail, and the eager impulse to press 
on to newer and ever newer fields, the scientist is in danger of 
forgetting the handicaps of his followers, and of leaving them 
hopelessly in the rear. Popular ignorance of many important 
facts of parasitology and preventive medicine, even facts which 
have been common bases of operation for scientists for many 
years, is deplorable. To a large extent, however, the scientists 
themselves are to blame, for in their enthusiasm for discovery 
they have forgotten to make it possible for the laity to reap the 
benefits of their investigations. There is even a tendency to 
belittle the efforts of those workers who devote their energies 
toward assisting the general public to keep in touch with scientific 
progress. A book or paper which collects the work of others, 
models it into a connected whole, and makes readily available 
what before was widely scattered and accessible only to a skilled 
" library-prowler,'^ is stigmatized by the term '' mere com- 
pilation." It is the firm belief of the writer that this is not 
only unjust but unwise. No less mental and physical energy, 
if not perhaps even more, is necessary for efficient '* mere com- 
pilation " than for the addition of new facts to scientific knowl- 
edge, and the value to civilization, which must be the ultimate 
criterion by which all scientific work is judged, must be equally 
as great, if not greater. The value of connecting related facts 
is twofold: it helps to keep the world in general somewhere 
nearly abreast of the times, and it is a distinct aid to further 



progress. Having the courage of his convictions along these 
lines, the writer has spent much time which he might other- 
wise have spent on original research in the compilation and popu- 
larization of the subject matter of this book. 

It is the aim of this volume to present the important facts of 
parasitology, as related to human disease, in such a manner as 
to make it readable and useful not primarily to the parasi- 
tologist, but to the public health and immigration service officers ; 
to the physicians who are concerned with something more than 
their local practice; to teachers of hygiene, domestic science or 
other subjects in which health and preventive medicine are im- 
portant; to college and high school students; to the traveler; 
and to the farmer or merchant who is interested in the progress 
of science and civilization. It is the hope of the author that 
this book may not only be a means of making available for the 
laity facts which may and probably will be of direct importance 
to them at one time or another, but that it may also be instru- 
mental in arousing the interest of more students in this branch 
of science, to the ultimate end of enlisting a larger number in 
the ranks of its workers. 

No attempt has been made in the following pages to give 
detailed descriptions of parasites, or to go further into their 
classification than seemed necessary to give a correct conception 
of them. Likewise discussions of correct scientific names and 
synonymy have been entirely omitted, since, important and 
interesting as they may be to a parasitologist, they are of no 
interest to the lay reader. An attempt has been made to use 
scientific names which are most generally accepted as correct, 
except that in cases of disagreement between American and 
European usage, the American name has been used. In cases 
where some other name than that adopted in this book has been 
or is still in common use, it is given in parenthesis to afford a 
clue to the literature associated with it. 

The endeavor to avoid repetition in the discussion of certain 
parasites in one chapter, and of their transmitting agents in 
another, has often presented difficulties, since some facts might 
equally well be included in either place. As far as possible 
these facts have been given in the place where the author has 
felt that they would most often be sought, but mistakes have 
undoubtedly been made, and furthermore what one reader would 


search for under " malaria," for instance, another would seek 
under '' mosquitoes," and vice versa. For this reason frequent 
cross-references are given. 

As far as has seemed advisable, without too greatly encumber- 
ing the text with round-about phrases, scientific terms have been 
omitted or if used have been explained. It is difficult to keep 
constantly before one the unfamiliarity with even everyday 
scientific terms of many readers for whom this book is intended, 
but an earnest attempt to do so has been made. 

In the text the author has purposely refrained from citing 
references and from mentioning more than a few names of in- 
vestigators. It obviously would be imj>ossible to give refer- 
ences, or even to mention more than a small per cent of the thou- 
sands of contributors to the material here assembled without 
making the text cumbersome and unreadable, especially for the 
readers for whom the book is especially prepared. Only a few 
of the leading figures in the history of each group of parasites 
have been mentioned; other citations would have meant a 
more or less arbitrary selection of a few from among many, 
which must inevitably result in injustice. 

For similar reasons no bibliography is given. Instead, the 
author has prepared a list of '^ Sources of Information " which 
includes the names of all the leading periodicals in which im- 
portant articles on parasitology have appeared or are likely to 
appear, and a list of books which cover all or a portion of the field 
of parasitology in a comprehensive manner. In these books 
will be found bibliographies; most of the references cited in 
these bibliographies will be found in the magazines or papers 
listed in '' Sources of Information " and this list will aid any- 
one interested in pursuing the subject farther to keep in touch 
with the new work which is constantly appearing. The author 
has felt that more real value would attach to such a list than to 
a list perhaps 50 times as long and yet inevitably incomplete, 
containing exact references to particular articles. 

The illustrations, with two or three exceptions, have been 
drawn by the author either from specimens or from illustrations 
of other authors. Pen and ink drawings have been used con- 
sistently in place of photographs since it is believed that such 
drawings, if carefully done, are far more valuable for scientific 
purposes than are photographs. The trained eye is able by 


voluntary concentration on certain parts, and inattention to 
others, to see much more than can a camera, which has no such 
power of adjustment. A pen and ink drawing can, therefore, 
represent more accurately what can be seen by the eye than can 
a photograph. The author has received valuable advice re- 
garding the illustrations from Mr. A. J. Stover, scientific il- 
lustrator at the Oregon Agricultural College, and wishes to take 
this opportunity to express appreciation for it. 

Deep appreciation is felt for the invariable willingness with 
which authors, editors and publishers of scientific papers and 
books have given permission to copy illustrations. Special 
mention should be made, however, of the generosity of Sir 
Patrick Manson and of the American publishers of his " Tropical 
Diseases," Wm. Wood and Co.; of Dr. A. Alcock, author of 
*' Entomology for Medical Officers"; of Professor Wm. A. Riley 
and Dr. Johannsen, authors of '' A Manual of Medical Ento- 
mology," and of Dr. A. W. Sellards, who, in the absence of Dr. 
Strong, lent photographs taken in Peru by the Harvard School 
of Tropical Medicine. The illustrations taken from the journal 
Parasitology have been especially numerous, and mention should, 
therefore, be made of the unreserved permission to use them 
given by the editor. Professor G. H. F. Nuttall. Many illus- 
trations of worms have been taken from the work of two of the 
real pioneers in the study of helminthology. Professor Karl 
Leuckart of the University of Leipzig, under whom many of 
the present parasitologists were trained, and Professor Arthur 
Looss of the University of Cairo in Egypt. It is a high tribute 
to the work of Professor Leuckart that many illustrations 
published by him in the first comprehensive work on the animal 
parasites of man, in 1863, are still the best available ones and 
will be found reproduced in the majority of modern works on 
the subject. 

Particular appreciation is felt for the assistance received from 
three publications which contain reviews of current literature 
in particular phases of medical zoology, namely, the Tropical 
Diseases Bulletin, which reviews practically all current work 
on protozoan parasites and helminthology, the Review of Applied 
Entomology, Series B, containing abstracts of nearly all work 
on medical and veterinary entomology, and the Journal of the 
American Medical Association, which gives references to all 


articles in the leading medical journals of all countries, and 
reviews many of them. Any of these periodicals will be lent 
by the Association library, at the average cost of postage, to 
any member of the Association. These three publications, on 
account of their scope and thoroughness, are of inestimable 
value to anyone who attempts to keep pace with the progress 
of the medical sciences. There are, however, few if any of the 
journals or books listed under " Sources of Information " which 
have not been drawn upon either for illustrations or infor- 
mation or both. All of these, collectively, have made this book 
possible, and to them, and to the workers who contribute to 
them, are due, therefore, not only the thanks of the author but 
also the thanks of everyone who may profit in any way by this 

The writer is very deeply indebted to the authorities who have 
been kind enough to read the manuscript, and who have freely 
given the benefit of helpful suggestions and criticisms. Pro- 
fessor Gary N. Calkins, Professor of Protozoology at Columbia 
University, Dr. B. H. Ransom, Zoologist of the U. S. Bureau of 
Animal Industry, and Dr. L. 0. Howard, Chief of the U. S. 
Bureau of Entomology, have helped materially to round off 
the rough corners, and fill in the chinks, of the sections on Pro- 
tozoa, " worms," and arthropods, respectively. 

Hearty thanks is also due my wife, Belle Clarke Chandler, 
for the invaluable assistance she has given by her constant and 
efficient cooperation in the editorial part of the work. 


Chap. Pages 

I. Introduction 1-11 

II. Parasites in General 12-25 


III. Introduction to Protozoa 2&-37 

IV. Spirochetes 38-73d 

Relapsing Fever 42-48 

Syphilis 48-62 

Yaws 63-65 

Infectious Jaundice 65-69 

Yellow Fever 69-72 

Rat-bite Fever 73-73a 

Other Spirochaete Diseases 73a-73d 

V. Leishman Bodies and Leishmaniasis 74-92 

Kala-azar 77-82 

Infantile Kala-azar 82-84 

Oriental Sore 84-88 

Espundia 89-92 

VI. Trypanosomes and Sleeping Sickness 93-114 

Sleeping Sickness 98-108 

Chagas' Disease 108-114 

VII. Intestinal Flagellates and Ciliates 115-127 

Bi-flagellate Protozoa 117-118 

Multi-flagellate Protozoa 118-125 

CiUates 126-127 

VIII. Amebje 128-146B 

Intestinal Amoebae 132-142 

Mouth Amoebae 142-146B 

IX. Malaria 147-167 

X. Other Sporozoa, and Obscure or Invisible Parasites 168-194 

Coccidians 170-173 

Rhinosporidium 173-174 

Sarcosporidia 174-176 



Chaf. Pages 

Oroya Fever 176-181 

Dengue 182-184 

Phlebotomus Fever 184-185 

Rickettsia-like Organisms 185-191 

Chlamydozoa 191-194 


XI. Introduction to the "Worms" 196-206 

XII. The Flukes 207-230 

Blood Flukes 213-220 

Lung Flukes 220-224 

Liver Flukes 224-228 

Intestinal Flukes 228-230 

XIII. The Tapeworms 231-253 

Family Tseniidae 239-245 

Family Dibothriocephalidae 245-247 

Larval Tapeworms in Man 247-253 

XIV. Hookworms 254-269 

XV. Other Intestinal Roundworms 270-285 

XVI. Trichina Worms 286-297 

XVII. FiLARi^ and their Allies 298-314 

Filaria hancrofti 299-307 

Other Species of Filariae 307-314 

XVIII. Leeches 315-321 


XIX. Introduction to Arthropods 322-330 

XX. The Mites 331-351 

Harvest Mites 333-337 

Other Occasionally Parasitic Species 337-341 

Itch Mites 342-346 

Hair-foUicle Mites 346-348 

Tongue-Worms 348-351 

XXI. Ticks 352-369 

Ticks and Disease 359-363 

Other Troublesome Ticks 364-369 


Chap. Pages 

XXII. Bedbugs and their Allies 370-386 

Bedbugs 371-379 

Other Parasitic Bugs 379-383 

Remedies and Prevention 383 

Fumigation 383-386 

XXIII. Lice 387-403 

XXIV. Fleas .'. . 404-423 

XXV. Mosquitoes 424-462 

Mosquitoes and Malaria 438-443 

Mosquitoes and Yellow Fever 443-448 

Mosquitoes and Dengue 448-449 

Mosquitoes and Filaria 449-451 

Mosquitoes and Dermatohia 451-453 

Mosquito Bites and Remedies for Them 453-455 

Control and Extermination 455-462 

XXVI. Other Blood-sucking Flies 463-508 

Phlebotomus Flies 466-473 

True Midges (Chironomidae) 473-477 

Blackflies or Buffalo Gnats 478-484 

Gadflies (Tabanid^) 484-490 

Tsetse FHes 490-504 

Stable-FUes, Stomoxys, and Their AUies 504-508 

XXVII. Fly Maggots and Myiasis 509-528 

Blood-sucking Maggots 511-513 

Maggots under the Skin 513-519 

Myiasis of Wounds and of Natural Cavities of the Body 519-523 

Myiasis of the Intestine 523-528 

Sources of Information 529-533 



One of the most appalling realizations with which every student 
of nature is brought face to face is the universal and unceasing 
struggle for existence which goes on during the life of every 
living organism, from the time of its conception until death. 
We like to think of nature's beauties; to admire her outward 
appearance of peacefulness; to set her up as an example for 
human emulation. Yet under her seeming calm there is going 
on everywhere — in every pool, in every meadow, in every 
forest — murder, pillage, starvation and suffering. 

Man often considers himself exempt from this interminable 
struggle for existence. His superior intelligence has given him 
an insuperable advantage over the wild beasts which might 
otherwise prey upon him; his inventive genius defies the attacks 
of climate and the elements; his altruism, which is perhaps his 
greatest attribute, protects, to a great extent, the weak and 
poorly endowed individuals from the quick elimination which is 
the inevitable lot of the unfit in every other species of animal on 
the earth. Exempt as we are, to a certain extent, from these 
phases of the struggle for existence, we have not yet freed our- 
selves from two other phases of it, war and disease. We have 
some reason for hoping that after the present world-wide con- 
flagration of war has burned itself out and its ashes, the flesh and 
bones of its countless victims, have disintegrated and disappeared 
from view, we may be able to free ourselves from the probability 
of ever again taking part in or witnessing such a spectacle. 
That the helpless bondage in which we were once held by disease 
will never again be our lot, we can say with more assurance. 



One by one the diseases which formerly held the world in terror, 
or made parts of it practically uninhabitable, are falling before 
the onslaught of modern science. The vast majority of human 
and animal diseases are now known to be caused by organisms 
which live as parasites within the body. In all but a few cases 
these organisms are now definitely known, their habits under- 
stood, their means of transmission and multiplication worked 
out. What such knowledge means to the human race can hardly 
be overestimated. In the 14th century Europe was swept by an 
epidemic of plague which destroyed probably one-fourth of her 
entire population — something like 25,000,000 people. That 
a similar epidemic would have swept over the United States 
in the present century had it not been for modern scientific 
knowledge of the cause and means of transmission of plague, 
which made it possible to nip the epidemic in the bud in San 
Francisco and New Orleans, is reasonable to believe. In the 
latter part of the 19th century the French attempt to build a 
canal at Panama failed dismally after a stupendous loss of life 
from yellow fever and malaria. Shipload after shipload of 
laborers, engineers, nurses and doctors were sent to the great 
'' white-man's graveyard," the majority to succumb in a few 
weeks or months to these diseases, at that time uncontrollable. 
In the early part of the 20th century, by exterminating malaria 
and yellow fever on the Canal Zone, through the application of 
the knowledge which had been gained in the intervening years, 
the Americans made possible the building of the Panama Canal. 
In an incredibly short time this zone was transformed from a 
veritable pest hole to one of the healthiest places in the world, 
and incidentally the " conquest of the tropics,'' previously looked 
upon as a more or less hopeless task, was shown to be not only 
possible but profitable. To quote another example, through- 
out the history of the world typhus fever has hovered like a 
death dragon over nearly every army camp ever assembled, 
and has followed in the wake of war to add the last touch of 
horror and desperation to the inhabitants of the countries involved. 
In the present unprecedented war only those countries which have 
not kept abreast of the times in the application of scientific knowl- 
edge have suffered seriously from this terrible scourge. Were it 
not for the application of modern knowledge the horrors of the 
present war would have been even more awful than they are now. 


A decade or two ago a child's reader contained the following 
lines : 

" Baby Bye, 
Here's a fly; 

We will catch him, you and I. 
How he crawls 
Up the walls, 
Yet he never falls! 
I believe with six such legs 
You and I could walk on eggs. 
There he goes 
On his toes, 
Tickling Baby's nose." 

What a contrast to this attitude toward the housefly are our 
present-day fly-swatting campaigns, our crusades against possible 
breeding places of flies, and our education of the public by slogans, 
placards, lectures, magazine articles and books regarding the 
filthy habits and disease-carrying propensities of this selfsame 

But let us not think for a moment that the battle is won. Not 
only are there some diseases which still baffle our attempts to 
cure them or to control them, or even to understand their nature, 
but those which we already know how to control are by no 
means subdued. Plague continues to take a toll of life in India 
amounting to at least several hundreds of thousands a year; 
malaria even today destroys directly or indirectly millions of 
people every year and more or less completely incapacitates 
many millions more; syphilis is yet one of the principal causes 
of insanity, paralysis, still-births and barrenness in the civilized 
world, and is estimated to exist in 10 per cent of the population 
of the United States, i.e., in about 10,000,000 people; hook- 
worms still infect and render more or less imperfect over half a 
billion people in the world ; — and these are all diseases the causes 
of which are known, the means of transmission recognized, 
methods of prevention understood, and the cure of which, with 
the exception of plague, is entirely possible. 

It is evident that the crying need of the present time is not 
so much additions to our knowledge of the cause, control and 
prevention of diseases, much as this is to be hoped for, as it is 


the efficient application of what we already know. Popular 
ignorance of diseases, even such common ones as malaria and 
syphilis, is nothing short of appalling. This ignorance is by 
no means confined to the poorly educated masses; it is wide- 
spread among educated, college-bred people, and, piteous as it 
may seem, is characteristic of many professional men, among 
them even physicians bearing good reputation. There are a 
number of causes for this unfortunate condition. Many physi- 
cians of the old school have been so busy or so unprogressive 
that they have never attempted to add to or modify the knowl- 
edge they had when they first took up the medical profession 20 
or 30 years ago; people with erroneous or distorted views of 
things publish their ideas in newspapers or magazines as authori- 
tative statements, and thus unmeaningly mislead the enormous 
number of people who swallow such newspaper articles without 
even a flicker of hesitation; quack doctors, those hellish buz- 
zards who prey upon the innate gullibility of the greater part 
of the human race, willfully mislead and scatter at random the 
seeds of misinformation which have held back the progress of 
sanitation and health to a pitiful extent and have borne as their 
fruit sorrow, misery and suffering; and, finally, such is the 
conservativeness, or rather imperviousness, of our species that 
a new idea requires, often, not decades but centuries to penetrate 
thoroughly the popular mind. It is nearly 60 years since Darwin 
brought the theory of evolution into serious consideration and 
showed the folly of belief in special creation, yet it is no exag- 
geration to say that a very large majority of people at the present 
time do not believe in evolution. It is 250 years since the idea 
that living organisms do not spontaneously spring into exis- 
tence from non-living matter was first promulgated, and nearly 
60 years since the last vestige of possibility was torn from the 
theory of spontaneous generation, yet even today the prev- 
alence of such beliefs as that " horse-hair snakes " develop 
out of horse hairs in water is nothing short of astonishing. It 
is 120 years since Jenner proved the efficacy of vaccination 
against smallpox, yet there exist at the present time numerous 
anti-vaccination societies whose sole purpose is to denounce 
vaccination as an impractical and illogical proceeding. How 
can we expect popular belief in the mosquito transmission of 
malaria which was demonstrated only 20 years ago! 


The importance of the study of parasites in connection with 
human disease to every community in the world is becoming 
more and more obvious, even to those relatively free from para- 
sitic diseases. There are those who think that such diseases 
as kala-azar, sleeping sickness, Oriental fluke infections and 
many other local or " tropical " diseases are of no vital im- 
portance except to inhabitants of the countries directly influ- 
enced or to travelers through these countries. That the im- 
portance of such parasitic diseases is far greater than this is 
obvious from the fact that, with modern facilities for com- 
munication and with the extent of foreign immigration at the 
present time, there is no part of the world so remote that the 
things which affect it may not also affect any other part of 
the world if conditions are suitable. 

There is probably no common exotic infection which is not 
repeatedly brought into the United States through immigration 
ports, especially in ports where the most thorough medical in- 
spection of immigrants is not made. In the port of San Fran- 
cisco alone over 50 per cent of 6428 Orientals whose faeces were 
examined in the course of a little over two years were infected 
with hookworms, each one capable of starting a new center of 
infection in a previously free community. According to Dr. 
BiUings of the U. S. Immigration Service, during the " Hindu 
Invasion " of the Pacific Coast of the United States in 1911, 
about 90 per cent of all arriving Hindus were found to be in- 
fected with hookworms. It is unfortunate that even at the 
present time a considerable proportion of arriving Orientals 
cannot, under the immigration law, be subjected to medical 

The possibility or probability of other diseases becoming 
established in places not before troubled by them is a subject 
of vital importance to any community or nation. Some of them 
have already become established in places which were formerly 
free. The fact that acquaintance with these exotic diseases is 
lacking in the new territory, their nature not understood, means 
of curing them unfamiliar, and means of prevention of spread 
unknown, often results in much needless suffering and loss of 
life. Furthermore, many infections are much wider in distri- 
bution than has formerly been supposed. To cite one example, 
amebic dysentery, and liver abscess which is often the sequel to 


it, occurs over the greater part of the United States, yet not 
only are the people unfamiUar with the disease and its cause, 
but most physicians are unacquainted with it and do not know 
how to diagnose or treat it. 

The history of modern medicine, so far as infectious diseases 
are concerned, is nothing more nor less than the history of para- 
sitology in its broad sense, including bacterial and fungous para- 
sites as well as animal parasites. Previous to the beginnings of 
our knowledge of the existence of microscopic parasites, and of 
the effects produced by them, nearly all diseases were interpreted 
as visitations from angry deities, as the work of demons or as 
the effect of supernatural causes. Such ideas are still prevalent 
in those parts of the world where bacteriology and parasitology 
have not yet penetrated. 

With the exception of the superficial acquaintance which the 
ancients had with external parasites and a few parasitic worms, 
parasitology began about the middle of the 16th century when 
Fracastorio, an Italian, published his belief that disease was due 
to invisible organisms multiplying within the body. With the 
invention of the microscope by the Dutch lens-grinder, Leeu- 
wenhoek, actual observation of microscopic organisms became 
possible, and this famous pioneer in science observed, in 1675, 
'^ animalculae " in rain-water, putrid infusions, saliva, and 
diarrheal excretions, and made illustrations of them. Based 
on these scanty observations, the idea that all diseases were 
caused by these '' animalculse " became rampant during the 
succeeding century. In 1762 Plenciz, a physician of Vienna, 
apparently with the tongue of a prophet, expressed the idea 
that all infectious diseases were caused by living organisms, 
that there was a special " germ " for each disease, that the 
incubation period of diseases was due to the time necessary for 
the infecting organisms to multiply, and that the organisms 
might be conveyed through the air as well as by direct or indirect 
contact. In the 18th and 19th centuries there was much con- 
troversy as to the origin of '' germs " and the possibility of their 
spontaneous generation from putrefying matter. A belief in the 
origin of living organisms only from pre-existing organisms was 
first expressed by the Italian Redi, in 1668, but scientific proof 
of it came much later. Experiments by Spallanzani in 1769, 
Schulze in 1836, Schwann in 1839, Schroeder and von Dusch in 


1854, and finally Pasteur in 1860 removed one by one the last 
straws to which the sinking theory of spontaneous generation 
was still clinging. 

With the exception of tapeworms and some intestinal round- 
worms, one of the first worm parasites to be discovered in man 
was Trichinella, in its larval stage in the muscles, this discovery 
being made by Peacock in 1828. The hookworm was discovered 
by Dubini in Italy in 1838; the blood fluke and the dwarf tape- 
worm by Bilharz in Egypt in 1851; Filaria (larvae) by Demar- 
quay in 1863; the Chinese human liver fluke by MacConnell 
in India and MacGregor in Mauritius in 1874; the adult Filaria 
by Bancroft in 1876. The first parasitic protozoan to be dis- 
covered and recognized as such was the ciliate, Balantidium 
coll, a cause of dysentery, discovered by Malinsten in 1856. 
The spirochaete of relapsing fever was discovered by Obermeier 
in 1873; the dysentery ameba by Losch in 1875; the malaria 
parasite by Laveran in 1880; the sleeping sickness trypanosome 
by Forde and Button in 1901 ; the Leishman bodies of kala-azar 
by Leishman, and independently by Donovan, in 1903; the 
spirochaete of syphilis by Schaudinn in 1905. 

Knowledge of the complicated life histories characteristic of 
many parasites practically began with Zenker's demonstration 
of the life cycle of Trichinella in 1860 and Leuckart's experimental 
proof of the strange life cycle of the beef tapeworm in 1861. 
In 1874 Weinland discovered the snail in which the liver fluke 
develops, though the relation of flukes to molluscs had been 
previously suspected. In 1879 the epoch-making discovery of 
the role of the mosquito in the development of filarial worms was 
made by Manson and the science of Medical Entomology was 
born. This discovery has been so far reaching in its results and 
it has revolutionized preventive medicine to such an extent that 
it may justly be looked upon as marking the beginning of a new 
era in the history of preventive medicine, comparable with the 
discovery of the germ causation of disease. One of the first 
and certainly the greatest outcome of the discovery was the 
discovery by Ross in 1898 of the relation between mosquitoes and 
malaria. Other important discoveries concerning life histories 
and modes of infection quickly followed. The transmission of 
trypanosome diseases by tsetse flies was discovered by Bruce in 
1893; the relation of mosquitoes to yellow fever by the American 


Yellow Fever Commission in 1900, and to dengue by Graham 
in 1902; the relation of ticks to African relapsing fever by Button 
and Todd, and independently by Koch, in 1905; the relation 
of ticks to spotted fever by Ricketts in 1906; the relation of 
lice to typhus by Nicolle and his fellow workers in Algeria in 1909, 
and independently by Ricketts and Wilder and by Anderson and 
Goldberger in Mexico in the same year (published in 1910); 
the relation of cone-noses to a South American trypanosome 
disease by Chagas in 1909; the life history of blood flukes by 
Leiper in 1914 and 1915; and the r61e of crabs as second inter- 
mediate hosts of lung flukes by Nakagawa in 1916. 

The evolution of knowledge concerning the treatment of para- 
sitic diseases has proceeded along two distinct lines, one, de- 
struction of the parasites by drugs which are more or less 
specifically poisonous to them, the other by vaccination or immu- 
nization. One of the first specific drugs known was quinine for 
malaria. The use of cinchona bark from which quinine in its 
various forms is manufactured is said to have originated with the 
Indians of Ecuador, and to have been introduced into Europe 
by Spaniards in 1642. The sulphate of quinine, which is the 
form of the drug in commonest use now, was first used in 1840. 
In 1880 Bozzolo, an Italian, first introduced thymol as a remedy 
for intestinal worms, especially hookworm, and this has been 
considered a standard and almost specific cure for hookworm 
until within the last two years, when oil of Chenopodium has 
been substituted for it to a large extent. The next specific drug 
of great importance to be discovered was salvarsan for spiro- 
chsetes, discovered by Ehrlich in 1905. In the same year 
atoxyl, one of the most efficient remedies yet discovered for 
trypanosome diseases, was discovered by Thomas. Emetin was 
discovered to be a specific remedy for amebic dysentery by 
Rogers in 1913 as the result of Vedder's work with ipecac, from 
which emetin is manufactured. In 1914 tartar emetic, pre- 
viously used as an alternative for arsenic compounds (chiefly 
atoxyl) against trypanosomes, was discovered by Vianna to be 
a wonderfully efficient specific remedy for the severe South 
American leishmaniasis, and was subsequently found to be spe- 
cific for all Leishmania diseases. 

Treatment and prevention of disease by immunization has 
experienced a wonderful development in the past 35 or 40 years. 


Some of the phenomena of natural acquired immunity were of 
course familiar even to the ancients, and people have practiced 
for centuries exposing themselves to diseases at convenient times 
in order to acquire subsequent immunity. Jenner in 1797 
devised vaccination with cowpox to give immunity to smallpox. 
It was not until 1880 and 1881 that Pasteur discovered the 
possibility of producing immunity by inoculation of germs arti- 
ficially rendered harmless or relatively harmless, or by the inocu- 
lation of the strained excretions of the bacteria as they exist in 
pure cultures. 

From Pasteur's epoch-making discoveries has arisen in the 
last 25 years the science of immunology. Although up to the 
present time the successful use of vaccinations or inoculations 
for cure of, or protection from, disease germs has been applied 
chiefly to bacterial diseases, the same principles of immunity 
apply to diseases caused by animal parasites and we may con- 
fidently expect in the not distant future a great extension of this 
relatively new field of medicine to diseases caused by animal 
parasitesJ It has already been applied successfully to some 
spirochse^e diseases, and to some trypanosome diseases. The 
difficulty of growing many animal parasites in cultures has largely 
held back progress along this line, and it is only recently that 
much advancement has been made. Only a few years ago 
culturability and non-culturability were believed to be dis- 
tinguishing characteristics between bacteria and Protozoa. 
Although methods for growing pure cultures of bacteria arti- 
ficially were devised and used by Pasteur in 1858, and greatly 
improved by Robert Koch 15 or 20 years later, it was not until 
1903 that the artificial cultivation of trypanosomes was ac- 
complished by two American workers, Novy and MacNeal. 
In 1905 Rogers in India succeeded in cultivating the Leishman 
bodies of kala-azar, and thus established their relationship to 
certain flagellated parasites of invertebrate animals. Since then 
other investigators have succeeded in the cultivation of other 
parasitic protozoans, the latest important accomplishment along 
this line being the successful cultivation of spirochsetes by 
Noguchi in 1910-12, and of malarial parasites by Bass and Johns 
in 1913. As yet no pathogenic amebae have been successfully 
cultured, probably due to their dependence on the presence and 
action of certain kinds of bacteria. 


Even more important, if anything, than abiHty to grow para- 
sites on artificial cultures in order to experiment with them, is 
ability to transplant them into animals which can be experi- 
mented on. Only by wholesale animal experimentation, car- 
ried on patiently and persistently, for years sometimes, could 
many of the great medical victories of the past 25 years have 
been won. To quote from MacNeal, '' The importance of ex- 
perimentation upon animals in the development of our knowledge 
concerning disease-producing microorganisms can hardly be 
over-estimated. . . . Only in this way (by the use of animals 
in considerable numbers) has it been possible to discover the 
causal relation of bacteria to disease, and the way in which 
diseases are transmitted. . . . The inoculation of animals also 
provides accurately controlled material for studying the course 
and termination of the disease as well as the gross or microscopic 
lesions produced by it." One can hardly help feeling bitter 
against those well-meaning but misguided individuals who 
publicly denounce and endeavor to minimize the unselfish and 
tireless labors of scientists who have made possible the allevi- 
ation and prevention of so much human misery and suffering. 
To quote from Dr. W. W. Keen in speaking of the results of 
Dr. Flexner's experiments on monkeys and guinea-pigs with one 
of the most deadly human diseases, cerebrospinal meningitis: 
'' which was the more cruel. Dr. Flexner and his assistants who 
operated on 25 monkeys and 100 guinea-pigs with the pure and 
holy purpose of finding an antidote to a deadly disease and with 
the result of saving hundreds, and in the future thousands on 
thousands of human lives ; or the women who were ' fanned 
into fury ' in their opposition to all experiments on living animals 
at the Rockefeller Institute ' no matter how great the antici- 
pated benefit? ' 

"If these misguided women had had their way, they would have 
nailed up the doors of the Rockefeller Institute, would have pre- 
vented these experiments on one hundred and twenty-five animals, 
and by doing so would have ruthlessly condemned to death for 
all future time five hundred human beings in every one thousand 
attacked by cerebrospinal meningitis! 

''If your son or daughter falls ill with the disease, to whom 
will you turn for help — to Flexner or to the anti-vivisec- 


It is inconceivable that any anti-vivisectionist, if bitten by a 
rabid dog, would not hasten to be given a Pasteur treatment to 
prevent the horrible death from hydrophobia which would 
otherwise almost inevitably result, or if stricken with syphilis 
would not submit to treatment with salvarsan in order to pre- 
vent the probable ruin not only of his own life, but also of the 
lives of his life-mate and of his unborn children. There is little 
thought then of the blood of the monkeys, guinea-pigs, or other 
animals with which the God of Knowledge was paid to make 
such treatments possible! 

The discoveries mentioned in this brief resum^ of the history 
of parasitic diseases are but a few of the more conspicuous mile- 
stones on the path of progress of modern medicine as related to 
animal parasites. They may be likened to the posts of a fence, 
while the hundreds of other discoveries, less striking in them- 
selves, perhaps, but nevertheless necessary, correspond to the 
pickets. The posts are useless without the pickets as are the 
pickets without the posts. There is not one of the great out- 
standing discoveries in the field of parasitology and preventive 
medicine which could have been made without the aid of the 
less illustrious accomplishments of many other scientists. Our 
present ability to cope with and control disease is due not alone 
to the great work of such men as Manson, Laveran, Ross, Pasteur, 
Koch, Reed, Schaudinn and Ricketts, but also to the careful, 
pains-taking work of thousands of other investigators, who, often 
without any semblance of the honor and recognition which they 
deserve, and perhaps even under the stigma of public denuncia- 
tion, work for the joy of the working and feel amply repaid if they 
add a few pickets to the fence of scientific progress. 


Definition. — According to the Standard Dictionary, a parasite 
is a living organism, either animal or plant, that lives on or in 
some other organism from which it derives its nourishment for 
the whole or part of its existence. In the following pages only 
those parasites which belong to the animal kingdom are taken 
into consideration. The vegetable parasites, chiefly bacteria and 
fungi, are dealt with only incidentally. 

It is often difficult to draw a sharp line between parasites and 
predatory animals; a panther is unquestionably a predatory 
animal, and a tapeworm is unquestionably a parasite, but a 
mosquito or horsefly might well belong in either category. It is 
usual to look upon an organism as a parasite when it habitually 
preys upon other organisms which are superior to it in size and 
strength. In accordance with this view all animals which 
habitually prey upon man, other than a few which occasionally 
attack and overcome him by superior physical prowess, may be 
considered as parasites and are so treated here. 

The state of dependence of an inferior on a superior organism 
probably arose very soon after life began to differentiate in the 
world. It would be difficult, if not impossible, to explain step 
by step the details of the process of evolution by which some of 
the highly specialized parasites reached their present condition. 
In some cases parasitism has probably grown out of a harmless 
association of different kinds of organisms, one of the members 
of the association, by virtue, perhaps, of characteristics already 
possessed, developing the power of living at the expense of the 
other, and ultimately becoming more and more dependent upon it. 

Kinds of Parasites. — There are all kinds and degrees of para- 
sitism. There are facultative parasites which may be para^ 
sitic or free-living at will, and obligatory parasites which must 
live on or in some other organism during all or part of their lives, 
and which perish if prevented from doing so. There are inter- 



mittent parasites which visit and leave their hosts at intervals. 
Some, as mosquitoes, visit their hosts only long enough to get a 
meal, others, as certain lice, leave their hosts only for the purpose 
of moulting and laying eggs, and still others, as the cattle tick, 
Margaropus annulatus, never leave except to lay eggs. There 
are parasites which pass only part of their life cycles as para- 
sites; botflies, for instance, are parasitic only as larvae, hook- 
worms only as adults. Some organisms Uve parasitically in two 
or more different animals, often of widely different species, in 
the course of their life histories. Such, for instance, are the 
filarial worms and numerous protozoan parasites, which begin 
life in a vertebrate animal, continue it in an insect, and finish it 
in a vertebrate again; the tapeworms, which begin life in cer- 
tain vertebrates and finish it in other individuals of the same or 
different species; the flukes, which begin life as free-living em- 
bryos, continue it through two or more asexual generations in 
particular species of snails, become again free-living or else 
parasitize second intermediate hosts such as crabs or fishes, and 
finally gain admittance to their ultimate vertebrate hosts. 
There are permanent parasites which live their whole lives, from 
the time of hatching to death, in a single host, but in which the 
eggs, or the corresponding cysts in the case of Protozoa, must be 
transferred to a new host before a second generation can develop. 
Such are many intestinal protozoans and round worms. The 
final degree of parasitism is reached, perhaps, in those parasites 
which live not only their whole lives, but generation after gener- 
ation on a single host, becoming transferred from host to host 
only by direct contact. Such are the scab mites and many 
species of lice. There is every gradation among all the types of 
parasites mentioned above, and a complete classification of para- 
sites according to mode of life would contain almost as many types 
as there are kinds of parasites. 

It is sometimes convenient to classify parasites according to 
whether they are external or internal. External parasites, as 
the name implies, are those which live on the surface of the body 
of their hosts, sucking blood or feeding upon hair, feathers, skin 
or secretions of the skin. Internal parasites live inside the body, 
in the digestive tract or other cavities of the body, in the organs, 
in the blood, in the tissues, or even within the cells. No sharp 
line of demarcation can be drawn between external and internal 


parasites since inhabitants of the mouth and nasal cavities and 
such worms and mites as burrow just under the surface of the 
skin might be placed in either category. 

Effects of Parasitism on Parasites. — The effect of parasit- 
ism is felt by both parasite and host. There is a sort of mutual 
adaptation between the two which is developed in proportion 
to the time that the relationship of host and parasite has existed. 
It is obviously to the disadvantage of internal parasites to cause 
the death of their host, for in so doing they destroy themselves. 
It is likewise to the disadvantage of external parasites, not so 
much to cause the death of their host, as to produce such pain 
or irritation as to lead to their own destruction at the hands of 
the irritated host. It is interesting to note, for instance, that 
insects which depend to a large extent on man for food have 
less painful bites than do insects which only occasionally or ac- 
cidentally bite human beings. Together with a softening down 
of the effects of the parasite on the host, there is a concomitant 
increase in the tolerance of the host to the parasite. It is a well- 
established fact that a disease introduced into a place where it 
is not endemic, i.e., does not normally exist, is more destructive 
than in places where it is endemic. The variations in suscepti- 
bility to parasites are directly connected with the subject of 
immunity, which will be discussed later. An organism and the 
parasites which are particularly adapted to live with it may, in 
a way, be looked upon as a sort of compound organism. Those 
parasites which live part of their life in vertebrate animals and 
part in other parasites of these animals, as lice, ticks and biting 
flies, are absolutely dependent for their existence on the relation- 
ships of the vertebrates and their parasites, and form a sort of 
third party to the association. 

Aside from the toning down of their effects on the host, para- 
sites are often very highly modified in structure to meet the de- 
mands of their particular environment. As a group, parasites 
have little need for sense organs and seldom have them as highly 
developed as do related free-living animals. Fixed parasites do 
not need, and do not have, well-developed organs of locomotion, 
if, indeed, they possess any at all. Intestinal parasites do not need 
highly organized digestive tracts, and the tapeworms and spiny- 
headed worms have lost this portion of their anatomy completely. 
On the other hand, parasites must be specialized, often to a very 


high degree, to adhere to or to make theu* way about in their 
particular host, or the particular part of the host, in which they 
find suitable conditions for existence. Examples of speciali- 
zations of external parasites are the compressed bodies of fleas, 
permitting them to glide readily between the hairs of their hosts; 
the backward-projecting spines of fleas, which are of much assist- 
ance in forcing a path through dense hair by preventing any 
back-sUding; the clasping talons on the claws of lice; the barbed 
probosces of ticks; and the tactile hairs of mites. In these same 
parasites can be observed marked degenerations in the loss of 
eyes and other sense organs, absence of wings, and, in some 
cases, reduction of legs. Internal parasites are even more pe- 
culiar combinations of degeneration and specialization. They 
possess all sorts of hooks, barbs, suckers and boring apparatus, 
yet they have practically no sense organs or special organs of 
locomotion, a very simple nervous system, and sometimes, as 
said before, a complete absence of the digestive tube. 

Still more remarkable are the specializations of parasites, in 
their reproduction and life history, to insure, as far as possible, 
a safe transfer to new hosts for the succeeding generations. 
Every structure, every function, every instinct of many of these 
parasites is modified, to a certain extent, for the sole purpose of 
reproduction. A fluke does not eat to live, it eats only to re- 
produce. The complexity to which the development of the re- 
productive systems may go is almost incredible. In some adult 
tapeworms not only does every segment bear complete male 
and female reproductive systems, but it bears two sets of each. 
The number of eggs produced by many parasitic worms may run 
well into the hundreds of thousands. The complexity of the 
life history is no less remarkable. Not only are free-living stages 
interposed, and intermediate hosts made to serve as transmitting 
agents, but often asexual multiplications, sometimes to the ex- 
tent of several generations, are passed through during the course 
of these remarkable experiences. 

Effects of Parasites on Hosts. — The effects of parasites on 
their hosts are almost as numerous and as varied as are the kinds 
of parasites, and vary besides with the susceptibility of the in- 
dividual concerned, his physical condition, and complication with 
other infections. In general it may be said that a parasite damages 
its host in one or more of three ways: (1) by robbing it of food 


which has not yet been assimilated and utilized, (2) by mechani- 
cally injuring its tissues or organs, (3) by the formation of ex- 
cretions or " toxins," which act as poisons. 

The first method of damage is of least importance, though it 
is obvious that the amount of food abstracted by some parasites, 
e.g., large tapeworms which may reach a length of several yards 
and grow at the rate of several feet a month, must be considerable. 

Much more serious are the various kinds of mechanical injury 
to tissues or organs. This damage is done by the blood-sucking 
parasites, such as hookworms, flukes, leeches and blood-sucking 
arthropods and the tissue-devouring forms, such as dysenteric 
amebse, malaria parasites, lung flukes, and fly maggots, which 
may not only devour the cells of the body, but may also cause 
hemorrhages, give portals of entry for other infections, and per- 
forate the intestine. Here also belong the obstructing parasites, 
which by their presence block bloodvessels, as do subtertian 
malaria parasites or blood flukes; stop up lymph vessels, as do 
adult filarial worms; or partially or completely close up such 
ducts as the bile duct and pancreatic duct, as do liver flukes. 
There are also parasites which damage and inflame the tissues by 
boring through them, as does Trichinella, the guinea-worm, itch 
mites and fly maggots. 

The third type of injury, by excretion of toxic substances, is 
done to some extent by practically all parasites. In external 
parasites the damage is usually done by an excretion, usually 
of the salivary glands, which prevents the coagulation of blood, 
and tends to inflame the tissues with which it comes in contact. 
In the case of internal parasites the toxic substances are prob- 
ably in most cases the waste products of the parasites, voided 
into or absorbed by the blood or neighboring tissues. In many 
cases these toxins have specific actions on particular tissues or 
organs, so that parasites in one part of the body may do their 
chief damage to an entirely different part. Intestinal worms, 
for instance, may produce considerably greater derangements 
of the blood or of the nervous system than of the intestine; the 
trypanosome of Chagas' disease produces, by means of toxins, 
specific effects on the thyroid gland and gives rise to the symp- 
toms which result from interference with the gland, even though 
the parasites may not be located in the gland itself; the bite of 
certain ticks along the line of the spinal cord or on the middle 


line of the cranium produces a specific effect on the motor nerves, 
causing paralysis, presumably through the action of salivary 
secretions or of the excretion from the coxal glands; the amebse 
of pyorrhea, or the bacteria associated with them, which infect 
the teeth and gums give rise to such symptoms as rheumatic 
pains in the joints, anemia and a disturbance of digestion. In 
fact it may be said that a very large number of diseases or ab- 
normal conditions which were once attributed to purely physical 
causes, such as imperfections in the organization of the body, 
or which have been accepted merely as common derangements 
of the human machine for which no direct cause could be found, 
have been traced to the effect of particular parasites located, 
perhaps, in some unsuspected part of the body. We are daily 
widening the scope of this phase of pathology, and this is one of 
the main reasons for the present important position of parasi- 
tology among the medical sciences. 

Modes of Infection and Transmission. — The portals of entry 
and means of transmission of parasites is a question of the most 
vital importance from the standpoint of preventive medicine. 
In the past few decades wonderful strides in our knowledge along 
these lines have been made, but there is much yet to be found 

With a very few exceptions animal parasites do not exist in 
air and dust as do many vegetable parasites, although some 
spirochaetes, coughed from the lungs or throat, may infect other 
individuals by being breathed in, and the granules formed by 
some of these spirochetes may be blown about with dust and 
thus infect in the manner of many bacteria. 

Many parasites may be spread by direct or indirect contact 
with infected parts, e.g., the spirochaetes of syphilis and yaws, 
the mouth amebse, the parasites of Oriental sore, itch mites and, 
of course, free-moving external parasites. The parasites of the 
digestive system and of other internal organs gain entrance in 
one of two ways. They may bore directly through the skin as 
larvse, e.g., hookworm. More commonly they enter the mouth 
as cysts or eggs, e.g., dysentery amebse and Ascaris; as larvae, 
e.g., pin worm; or as adults, e.g., leeches. Access to the mouth 
is gained in many different ways, but chiefly with impure water, 
with unwashed vegetables fertilized with " night soil," or with 
food contaminated by dust, flies or unclean hands. The para- 


sites of the blood or lymphatic systems usually rely on biting 
arthropods (insects, ticks and mites) to transmit them from host 
to host, and it is in this capacity, i.e., as transmitters and inter- 
mediate hosts of blood parasites, that parasitic arthropods are 
of such vast importance (see p. 322). 

Geographic Distribution. — The geographic distribution and 
dispersal of parasites is another subject which has received 
much fruitful attention in recent years. Parasites, like other 
organisms, are dependent upon certain physical conditions of 
their environment in order to thrive. One of the most important 
limitations on the dispersal of a parasitic disease is the distri- 
bution of suitable hosts. Some parasites can live with ap- 
parently equal vigor in a large number of hosts, others are 
confined to a few or to one only. A double limitation is placed 
on parasites which require two hosts in order to complete their 
life history; they obviously cannot exist beyond the territory 
where both hosts exist together. The local as well as geographic 
distribution of the hosts is, of course, effective in limiting the dis- 
tribution of the parasites. In the case of human parasites, the 
alternate host is practically the only limiting factor. The geo- 
graphic distribution of human sleeping sickness is coincident 
with the distribution of certain species of tsetse flies; the distri- 
bution of yellow fever nowhere extends beyond the range of a 
certain species of mosquito; Rocky Mountain spotted fever is 
geographically limited by the distribution of a certain species of 
tick. The accidental or gradual extension of the range of one of 
these intermediate hosts is likely to be followed by an extension 
of the disease carried by it. It sometimes happens that a strain 
of a certain parasite establishes itself in a new host, thus often 
greatly extending the territory which it affects, and this is a 
possibility which must always be remembered and watched 
for. The trypanosome of Rhodesian sleeping sickness, for in- 
stance, is very possibly a race of Trypanosoma hrucei, which is 
common i^ domesticated and wild game animals in a large 
portion of Africa. Some slight alteration in the nature of the 
parasite has made it possible for it to affect human beings and 
thus give rise to a new disease. A somewhat different situation 
is presented in the case of Rocky Mountain spotted fever, the 
parasite of which has not yet been discovered. In nature ap- 
parently only one species of tick acts as an intermediate host, 


though experimentally other ticks may become infective. There 
is obviously a constant possibility of the establishment of the 
disease in other species of ticks and thus of greatly widening the 
area affected. 

Temperature is an important limiting factor for those parasites 
which can be directly influenced by it, as external parasites and 
those which are free-living during a part of their existence. 
In Mexico, for instance, human lice are entirely absent from the 
hot coastal plains, though abundant on the high central plateau. 
Hookworms, which are free-living in their young stages, are con- 
fined to a broad strip around the tropical and warm temperate 
portions of the world, and occur outside these limits only in 
short-lived epidemics during the warm part of the year. Such 
parasites as bots and screw-worms are equally exposed to the 
influence of climate, since they are free-Hving in the adult stage. 

Some parasites are limited by other environmental conditions. 
In the case of such intermittent external parasites as mosquitoes, 
biting flies and cone-noses it is obvious that not only tempera- 
ture and humidity, but also the presence of suitable breeding 
places and of suitable haunts during resting times must be neces- 
sary for their continued existence. Again, the local distribution 
of hookworms is determined, to a large degree, at least, by the 
nature of the soil. These worms abound where sandy soil occurs, 
but are rare or absent where there is only limey or clayey soil. 

Natural Immunity. — As has already been pointed out, when 
a parasite is introduced into a region where it was previously 
unknown, or, what amounts to the same thing, new hosts are 
introduced into its territory, its ravages are usually worse than 
in places where it has been endemic for a long time. The hosts 
and parasites of a given region come to a point of equilibrium. 
The host becomes largely immune to the effects of the parasite, 
and yet harbors it in sufficient numbers to form a reservoir for 
it, and thereby acts as a ''carrier." In some cases a total or 
partial immunity is built up in youth, when the power of resist- 
ance to parasitic invasion is usually high; in other cases it is the 
result of a long struggle extending through many generations. 
A good example of immunity acquired in youth is found in the 
case of yellow fever, and of partial immunity, gained through 
many generations of adaptation, in the case of hookworms in 
negroes. The terrible destruction wrought by sleeping sickness 


when introduced into virgin territory in Uganda is a good ex- 
ample of the results which may come from such an introduction: 
in districts where sleeping sickness has existed for a long time 
the death rate from it is often only two or three per thousand, 
whereas in one district in Uganda the population was reduced 
from 300,000 to 100,000 in about seven years. It is not im- 
probable that the extinction of many of the striking types of 
animals which dominated the earth in past geologic ages may have 
been brought about by the sudden appearance of or exposure to 
new and deadly parasites; only those forms of life which were 
able to resist the onslaught of the parasites remained to continue 
the course of evolution. 

This leads us to a consideration of the remarkable facts of 
immunity. The power of the blood .of vertebrate animals to 
react against invading organisms or poisons by producing sub- 
stances which will destroy them is one of the most wonderful 
adaptations in all the realm of nature. Though the details of 
the reaction are still unknown, the chemical substances concerned 
still undetermined, and many of the influencing factors not yet 
understood, yet the progress in our knowledge of the mechanism 
of acquired immunity has taken great strides since Pasteur 
first placed the development of immunity on a scientific basis 
not quite 40 years ago. There are several ways in which the 
body may react against parasites. One method is by the ac- 
tivity of the large free-moving white blood corpuscles, which 
actually capture and devour the parasites after the manner of 
predaceous protozoans. This, of course, can be done only in case 
of very small parasites, such as bacteria and Leishman bodies. 
Apparently the parasites first must be rendered digestible to the 
white blood corpuscles by the presence of an accessory substance 
in the blood, known as an opsonin. This substance may be 
thought of as acting like a sugar coating on a bitter pill, though its 
effect is more analogous to that of cooking on starch, i.e. increased 
digestibility. Opsonins are normally present in the blood but 
increase as a reaction to the presence of parasites. The degree 
of development of opsonins in the blood, and consequent power 
of the white blood cells to capture and digest parasites, is known 
as the opsonic index. 

Sometimes a number of cells work together to form a capsule 
around larger parasites, thus walling them in and limiting the 


sphere of their activity; this occurs in the case of Trichinella, 
filarial worms, larval tapeworms, fly maggots, etc. It occa- 
sionally happens that enzymes are developed which enable 
the surrounding cells slowly to digest the parasites thus im- 

More important than these physical methods by which the 
body is able to combat parasites are the biological or chemical 
methods. One of the most wonderful adaptations in the animal 
kingdom is the ability of tissues, chiefly the blood and lymph of 
vertebrate animals, to react against invading cells, whether they 
be bacteria. Protozoa, blood corpuscles of unrelated animals, or 
other foreign cells, by producing substances known as anti- 
bodies which dissolve these cells, or cause them to agglutinate, 
i.e., clump together and lose any motile power they may have. 
The living body is also able to destroy the poisonous action of the 
excretions or toxins of parasites by the development of protective 
substances known as anti-toxins which form some sort of a chemi- 
cal union with the toxins. Other poisonous products are ren- 
dered harmless by the formation of " precipitins " which have 
the special property of uniting with the toxic substances to pro- 
duce insoluble and consequently harmless precipitates. Pre- 
cipitins are found to react against any foreign protein, of para- 
sitic origin or otherwise, introduced into the body. There is 
some question as to whether immunity reactions against animal 
parasites are exactly comparable with those against bacteria, 
but the difference is probably a matter of degree and not of 
fundamental nature. The higher organization of Protozoa and 
of other animal parasites enables some of them to react against 
the destructive influence of the serum by encysting, or by form- 
ing spores, and thus they are able to continue their existence in 
spite of the development of immunity, though in very limited 
numbers and with limited activity. The result is immunity 
without sterilization; in other words, although the body becomes 
more or less completely immune as far as suffering from the 
effects of the parasite is concerned, yet the parasites, limited in 
number and activity, still exist within it, and such a host becomes 
an " immune carrier." With few exceptions protozoan diseases 
are contrasted with bacterial diseases in this respect. The 
gradual development of anti-toxins, precipitins, etc., probably 
accounts to a large extent for the relative immunity which is 


developed against the effects of intestinal worms as well as against 
blood and tissue parasites. 

Artificial Immunity. — In every case the reaction of the body 
against parasites invading it is due to the presence of some 
particular substance in the parasite which stimulates the body 
to react against it. This substance, whatever it may be, is 
called an antigen. The possibility of acquiring immunity with- 
out being subjected to the disease lies in the fact that the antigen 
is also present in parasites which have been weakened, by one of 
several methods, to such an extent as to be powerless to cause 
the usual symptoms. It may also be present in the dead para- 
sites or even in the strained excretions from parasites, as obtained 
from pure cultures. Vaccinations, in the broad sense, are inoc- 
ulations into the system of weakened or dead parasites or of 
their products. The body reacts against the harmless antigen 
thus injected and antibodies are built up just as if the disease had 
been actually passed through. Antibodies persist throughout 
life in the case of some parasites, for several years in others, and 
for only a short time in still others. When the efficacy of the 
naturally or artificially acquired immunity is gone, as determined 
by experimentation, a new vaccination must be submitted to in 
order to obtain protection. Thus yellow fever immunity, which, 
however, cannot be artificially produced, normally persists 
through life; smallpox immunity, as acquired by vaccination, 
for a number of years; and artificially acquired typhoid immunity 
for about three years. 

Still another method of inducing immunity is possible. By 
rendering some susceptible animal very highly immune to a 
particular parasite by repeated inoculations of virulent germs, 
its serum becomes so charged with antibodies and so powerful 
in its action against the particular parasite involved, that a very 
small quantity of such serum injected into another animal or 
man is sufficient to give a " passive " immunity — passive be- 
cause the second animal has taken no active part in the for- 
mation of antibodies. Such immune serum has been found of 
value in the prevention and cure of certain spirochsete dis- 
eases as well as a number of bacterial diseases. It has the 
advantage of causing no discomfort during the development of 
the immunity, but usually is of shorter duration than " active '^ 


The principles of artificial immunity, as remarked before, have 
only recently become understood, but the science of immunology 
is yearly becoming extended. As this paper is being written, 
experiments with preventive and curative inoculations against 
typhus fever and against infantile paralysis are being worked 
out and there is reason to hope that before another year dawns 
these two terrible diseases may be added to the already consid- 
erable list of diseases which can be prevented by artificially 
produced immunity. Smallpox, rabies, cholera and diphtheria 
are some of the more important diseases whose guns have been 
unloaded by this means. While, as remarked before, compara- 
tively little advance has been made in the application of the 
principles of immunity to animal parasites, yet there seems to be 
hope that in the coming years many diseases caused by Protozoa 
and worms may be conquered by further knowledge of immu- 

Anaphylaxis. — Mention should be made of the phenomenon 
of anaphylaxis, commonly defined as an exaggerated suscepti- 
bility to the poisonous effect of foreign substances in the blood, 
and to account for which many different explanations have been 
proposed. Based on extensive experimental work, Novy and 
De Kruif have recently (1917) offered a new and revolutionary 
explanation which is bound to be of far-reaching significance. 
According to these workers, normal circulating blood must be 
presumed to contain a substance, termed the " poison matrix," 
comparable in a general way with the substance in the blood 
known as fibrinogen. The latter substance, under certain condi- 
tions or in the presence of certain reagents, is transformed into 
fibrin, which forms a network of fibers in the meshes of which the 
blood corpuscles are caught, and by means of which the clotting of 
blood is effected. The same reaction which leads to the coagu- 
lation of blood also transforms the poison matrix into an actively 
poisonous substance or '' anaphylatoxin," which produces the 
symptoms commonly known as anaphylaxis. Furthermore, it 
is shown that the transformation of the poison matrix into 
anaphylatoxin is induced or accelerated by the addition of al- 
most any foreign substance to the blood, e.g., bacteria, trypano- 
somes, tissue cells, agar, peptone, starch, various salts, and even 
distilled water. In other words '' the circulating blood, through 
a variety of agents, may be changed from a beneficial and harm- 


less to an injurious and poisonous state. The foreign substance 
is merely the trigger which, so to speak, ignites or explodes the 
charge contained within the blood vessels." In the case of so- 
called " specific anaphylaxis," in which anaphylactic poison- 
ing results from the injection of particular kinds of organisms 
or toxins, as, for instance, the shock that results from typhoid 
vaccination of a person already immune to typhoid, the specific 
action is due to the production of ordinary anaphylatoxin by the 
interaction of an antibody, already developed, with the antigen 
which produced it. To cite another example, it has been shown 
that injection of the ground bodies of ox warbles into cattle 
which have been infested by even small nunibers of these mag- 
gots produces an anaphylactic shock. According to the theory 
of Novy and De Kruif this would be explained as follows: the 
presence of warbles in the cattle causes the production of anti- 
bodies in the blood. Injection of warbles places large quantities 
of the antigen in the blood. Interaction of antibody and antigen 
produces a substance which transforms the poison matrix al- 
ways present in the blood into anaphylatoxin, and the latter 
produces the symptoms of poisoning. The theory has recently 
been advanced that the severe effects of the bites of some blood- 
sucking arthropods, such as ticks, mites and blackflies, in which 
the first attacks are much milder than the later ones, may be 
in the nature of anaphylactic reactions. According to the 
theory of Novy and De Kruif, these effects would be produced 
by the formation of anaphylatoxin as the result of an interaction 
of an antigen in the arthropod's salivary secretions with an anti- 
body already formed in the bitten individual. 

Novy and De Kruif point out the possibility that substances 
inducing the formation of anaphylatoxin may be produced in a 
normal individual by some pecuHarity of diet, exposure, obscure 
infections, etc., and while the amount of poison thus produced 
may not be sufficient to cause an acute anaphylactic shock, it 
may be sufficient to cause a subacute or chronic form of poison- 
ing, leading to anemia, cachexia, etc. The significant state- 
ment is also made, and is apparently well supported, that a con- 
siderable part of the toxic effects of infectious diseases is in all 
probability due to the formation of anaphylatoxin. The so- 
called " endotoxins " supposed to be liberated in the blood by 
the disintegration of bacteria and other parasites possibly do 


not exist as specifically toxic substances. They may be sub- 
stances which induce the formation of anaphylatoxin. 

Should further investigation indicate that much of the toxic 
effects in various infectious diseases are really produced by a 
single substance, anaphylatoxin, the treatment of such diseases 
will be revolutionized. In addition to the giving of drugs to de- 
stroy the infecting organisms, an attempt must be made to find 
an agent to destroy anaphylatoxin in the blood and to pre- 
vent its further formation. Novy and De Kruif have shown 
that, in test tubes at least, alkali not only destroys but also pre- 
vents the further formation of this poison, and they suggest the 
use of alkalis in the treatment of conditions in which anaphylaxis 
may be playing a part. Already striking results have been 
obtained in severe cases in which anaphylactic poisoning was 
believed to exist, by the simple administration of sodium bi- 
carbonate or sodium acetate in doses of from three to five grams 
dissolved in about a half a glass of water, given at intervals of 
half an hour to an hour. The object of this is to raise the alka- 
linity of the blood to a maximum level and to keep it there during 
the time anaphylatoxin is being formed. If confirmed by further 
investigation, these facts must be looked upon as among the most 
important discoveries in the entire history of medicine, and how 
far reaching their effects may be cannot now be even guessed. 



Place of Protozoa in the Animal Kingdom. — It is usual for 
zoologists at the present time to divide the entire Animal King- 
dom into two great sub-kingdoms, the Protozoa and the Metazoa. 
These groups are very unequal as regards number of species. 
The Metazoa include all the animals with which the majority 
of people are familiar, from the simple sponges and jellyfishes, 
through the worms, molluscs, and the vast horde of insects and 
their allies, to the highly organized vertebrate animals, including 
man himself. The Protozoa, on the other hand, include only 
microscopic or almost microscopic animals, the very existence of 
which is absolutely unknown to the average lay person. Al- 
though some Protozoa are readily visible to the naked eye there 
are others, such as the yellow fever organism, which are too small 
to be seen even under the highest power of the microscope. There 
is no question but that in point of numbers of individuals the 
Protozoa exceed the other animals, millions to one; a pint jar 
of stagnant water may contain many billions of these minute 
animals. About 10,000 species of Protozoa have been described, 
but it is probable that there are thousands more which are not 
yet known to science. 

The distinction between the Protozoa and Metazoa is based 
on a characteristic which is of the most fundamental nature. 
The Protozoa are animals which perform all the essential func- 
tions of life within the compass of a single cell. The Metazoa, 
on the other hand, are many-celled animals, with specialized 
cells set apart to perform particular functions. A protozoan 
cell, even though sometimes living in a colony of individuals 
which are all bound together, can live its life and reproduce its 
kind quite independently of any other cells, having in itself the 
powers of digestion, respiration, excretion and secretion, sensi- 



bility, motility and reproduction. Most metazoan cells, on 
the other hand, are so specialized for particular functions that, 
if separated from the other cells with which they are associated 
in the body, they die almost immediately. 

The very fact of evolution makes it difficult to draw a sharp 
and fast line between two groups of organisms, even between 
such fundamentally different groups as the Protozoa and Meta- 
zoa. There are always border line exceptions which make the 
work of the systematic zoologist at once difficult and interesting. 
In the case in hand there are colonial Protozoa in which all of the 
cells are not exactly alike, but have at least the beginnings of 
specialization. Some protozoans, such as the intestinal flagel- 
late Giardia (or Lamblia), are composed, as adults, of essentially 
two cells instead of one. Such animals have been placed by 
some authors in a distinct order to which the name Diplozoa 
(double animals) has been appHed. On the other hand, in the 
lowest metazoans, the sponges, there is only very limited speciali- 
zation of the cells, while in the little-known animals which are 
designated as " Mesozoa " there is even less differentiation. 

The distinction between Protozoa and Bacteria, though in- 
volving the distinction between animals and plants, is much 
more difficult. As we descend the evolutionary scale of plants 
and animals the usual distinctions between them disappear and 
it becomes difficult if not impossible definitely to place certain 
species in either the plant or animal kingdom. The possession 
of a distinct nucleus of some kind and some type of sexual re- 
production are the characteristics which usually distinguish the 
Protozoa from the less highly organized Bacteria. Often, how- 
ever, it is difficult to discover sexual phenomena, or to interpret 
them with safety, and the presence or absence of a nucleus is 
sometimes equally difficult to determine. In such cases pe- 
cuharities in life cycle, chemical reactions, staining properties 
and the like are resorted to as distinguishing characteristics. 
Most biologists are now inclined to group all of the single-celled 
animals and plants, including Bacteria, into one great group 
known as the Protista, a suggestion first made by Ernest Haeckel. 
The existence of such groups of organisms as the Spirochaetes 
and the Piroplasmata, occupying intermediate positions between 
Protozoa and Bacteria, and of such groups as the chlorophyll- 
bearing flagellates, occupying an intermediate position between 




— ocs. 


protozoans and green algae, makes such a group as the Protista 

appear both natural and convenient. 

Structure. — A protozoan, in its simplest form, conforms to 

the usual definition of a cell — a bit of protoplasm containing 

a nucleus. S o m e- 
^^•>op.cU. times there are two 
or more similar nuclei 
and in the majority 
of ciliates there are 
two nuclei which dif- 
fer from each other 
(str. rKn ocs.) both in form and func- 
tion, a large " macro- 
nucleus " which is 
associated with the 
ordinary vegetative 
processes of the cell, 
and a small " micro- 
nucleus '* which ap- 
parently is concerned 
only with sexual re- 
production. In some 
protozoans nuclear 
material is extruded 
from the nucleus itself 
into the protoplasm 
outside where it floats 
about in the form of 

Fig. 1. A complex ciliate, Diplodinium ecatidatum, minUte partlCles or 

showing highly developed organelles; caec, caecum or granules known aS 
rectal canal; cut., cuticle; c.v., contractile vacuole; , ... ,11,, 

cy top., cytopyge or cell anus; cytost., cytostome or cell CnromiQia, tne latter 

mouth; d.m., dorsal membranelle; ect., ectoplasm; sometimes having the 
end., endoplasm; mac. n., macronucleus ; mic. n., mi- , . 

cronucleus; myon. (str. retr. oes.), myonemes, strands pOWCr, Unuer certam 

for retracting oesophagus; oes., oesophagus; or. cil., cirCUmstanceS of 

oral cilia; sk. lam., skeletal laminae. X 750. (After „ . , . 

Sharpe.) formmg new nuclei. 

In some Protozoa 
there is no nucleus as such, though the essential substance of 
the nucleus, chromatin, is always present, but in scattered par- 

The protoplasm of a protozoan is usually more or less clearly 


— end. 





divisible into an outer and inner zone, the ectoplasm and endo- 
plasm, respectively (Fig. 1). There is no fundamental difference 
between these two layers of protoplasm, merely a difference in 
density. The ectoplasm is the less fluid and comparatively clear, 
while the endoplasm is more fluid and somewhat granular. The 
clearness of the differentiation between ectoplasm and endo- 
plasm is sometimes useful in distinguishing species of protozoans, 
especially amebse. The ectoplasm differs from the endoplasm 

Fig. 2. Types of organs of locomotion in Protozoa; A, Amasha with pseudo- 
podia; B, a heliozoan with "axopodia"; C, Bodo with free flagella; D, Trypanosoma 
with flagellum attached to undulating membrane; E, Choanoflagellate with flagel- 
lum and "collar"; F, Pleuronema with cilia and undulating membrane formed of 
fused cilia; G, modes of insertion of cilia; H, Aspidisca with cirri. (Figs. F to H 
from Calkins.) 

in function as well as in appearance. The ectoplasm may be 
likened to the body wall and appendages of higher animals while 
the endoplasm may be compared with the viscera or inter- 
nal organs. The endoplasm digests food and has the power of 
secretion and excretion, while the ectoplasm produces the vari- 
ous organelles for locomotion, food getting, oxygen absorption 
and special senses. The term '' organelle " is used in place of 
" organ " for structures which are only parts of a single cell. 

Organelles. — The organelles contained in a protozoan's body 
may be many and varied. Those connected with movement or 
locomotion differ in different groups and form the chief charac- 
teristic on which the usual classification into Sarcodina, Flagellata, 



Ciliata and Sporozoa has been based. The simplest type of 
movement is by means of simple outfiowings of the body proto- 
plasm known as pseudopodia (Fig. 2A). This is the common 
type of movement in one of the four great classes of Protozoa, 
the Sarcodina. In the Flagellata the organelles for locomotion 
are long lashlike outgrowths known as flagella (Fig. 2C), from 
one to eight or more in number. These originate from a parti- 
cle of deep-staining material which is called the blepharoplast or 
" centrosome." In many parasitic flagellates there is another 
deep-staining body, of very variable size and form, known as the 

parabasal body (also 
called by some au- 
thors the kineto-nu- 
cleus or blepharo- 
plast). Various types 
of parabasal bodies 
are shown in Fig. 3. 
This body usually 
arises from the basal 
granule and often 
remains connected 
with it, apparently 
being associated with 
the function of loco- 
motion. From the 
fact that it seldom 
occurs except in 
parasitic forms it is possibly a special adaptation to the peculiar 
environment encountered by such animals. By some protozo- 
ologists the parabasal body has been looked upon as a second 
nucleus with the special function of control over the locomotor 
activities of the animal, and it has been thought to originate by 
direct division from the main nucleus, but there is no conclusive 
evidence for this view. As a result of the idea that the parabasal 
body is of nuclear nature some workers have separated those 
protozoans which possess a distinct " kineto-nucleus " from those 
which lack it, creating the order " Binucleata " for them. 

In the Ciliata the organs of locomotion are in the form of cilia 
(Fig. 2F), hairlike outgrowths which are shorter and more 
numerous than flagella and different from them in motion. 

Fig. 3. Types of parabasal bodies (p). A, Leish- 
mania; B, Herpetomonas; C, Trypanosoma: D, Prowa- 
zekia cruzi; E, Prowazekia lacertce; F, Polymas; G, 
Trichomonas augusta. 


Each cilium arises from a tiny deep-staining dot or basal granule 
(Fig. 2G), which, however, is probably not homologous with the 
blepharoplast of the flagellates. 

Various modifications of the organelles of locomotion occur, 
e.g., the undulating membrane of many flagellates (Fig. 2D), 
formed by a delicate membrane connecting a flagellum with the 
body; the '^ collar" of the choanoflagellates (Fig. 2E); the mem- 
branelles and cirri of cilia tes (Fig. 2F and H), formed by the 
fusion of rows or groups of cilia; and the axopodia (Fig. 2B) of 
some Sarcodina formed by the development of supporting rods 
in pseudopodia, thus making a permanent structure. Of quite 
a different nature, but none the less organelles of movement, are 
the myonemes (Fig. 1, myo.), found in many Protozoa, and cor- 
responding to the muscle fibers of Metazoa. They enable the 
animals to twist and bend their bodies. The myonemes are 
extremely delicate contractile fibers which run in various direc- 
tions in the ectoplasm of the animal; they occur most commonly 
in flagellates and ciliates. In some protozoans structures have 
been described which show every evidence of being highly or- 
ganized neuromotor apparatus, i.e., a definitely arranged and 
organized substance having a nervous control over the contrac- 
tile fibers or myonemes (Fig. 1, mot.). 

Organelles for food-taking occur chiefly in the flagellates and 
ciliates. Such protozoans may have a " cytostome " or cell 
mouth for the ingestion of food (Fig. 1), and a " cytopyge " or 
cell anus for the elimination of waste matter. They may also 
have a delicate membranous pharynx (Fig. 1, cjrtost.) for leading 
the food material into the endoplasm, and food vacuoles into 
which the food is accumulated and in which it is circulated in- 
side the body. In some protozoans, namely the Suctoria, a 
much modified group of ciliates, there are developed suck- 
ing tentacles or the absorption of food. In others there are 
tiny capsules in the ectoplasm containing minute threads 
which can be shot forth when stimulated, and used either to 
overpower prey or for protection from enemies. For the ex- 
cretion of waste products of the body there is often present one 
or more contractile vacuoles (Fig. 1, c.v.), little cavities in the 
protoplasm of the body which expand with water containing 
area and other waste matters conducted to them by tiny radiating 
canals, and which periodically contract, forcing their contents 


outside of the cell, sometimes through a definite excretory pore. 
Sense organs in the form of pigment spots sensitive to light, 
and outgrowths sensitive to chemical substances, giving, perhaps, 
a sensation comparable with taste, are present in some species, 
especially in free-living ones. Various organelles serving the 
function of a skeleton may be developed in the form of a tough 
cuticle, a chitinous, calcareous or siliceous shell, a chitinous sup- 
porting rod or '^ axostyle " (Fig. 30, axo), or even a complicated 
internal skeleton of calcareous material. While no protozoan 
possesses all of these organelles, many possess a considerable 
number of them and exhibit a degree of complexity and or- 
ganization almost incredible in a single-celled animal which is 
barely, if at all, visible to the naked eye. 

Physiology and Reproduction. — In their physiology and 
manner of life the Protozoa differ among themselves almost as 
much as do the Metazoa. Some ingest solid food through a 
cytostome or by wrapping themselves around it, others possess 
chlorophyll and are nourished in a typical plant manner, and 
still others absorb nutriment by osmosis from the fluids or 
tissues in which they live. Acid substances corresponding to 
the gastric juice and alkaline substances simulating the intesti- 
nal juices may be present in the protozoan body, often localized 
in definite regions, and acting upon the food as it circulates in 
the food vacuoles. The waste material either is voided through 
a cytopyge or is left behind by a simple flowing away of the 
protoplasm. Body excretions are collected by the contractile 
vacuoles and voided by them, or they are simply passed through 
the body wall by osmosis. 

The multiplication or reproduction of protozoans is of two 
quite distinct types, an asexual multiplication, more or less 
comparable with the multiplication of cells in a metazoan body, 
and sexual reproduction, comparable with a similar phenomenon 
in the higher animals. Several common asexual methods of 
multiplication occur amongst protozoans, namely, simple fission, 
or division into two more or less equal parts; budding, or separa- 
tion of one or more small parts from the parent cell; and multiple 
fission or sporulation, a breaking up into a number of individuals 
or spores. Multiplication by one of these asexual methods may go 
on with great rapidity for a long time, but sooner or later some 
process at least remotely resembling sexual reproduction usually 


occurs. While such a process has not been observed in many 
protozoans, it presumably occurs in all under certain conditions. 
The analogy between a protozoan life cycle and a metazoan 
life cycle has become understood only in recent years. As a 
result of the painstaking experiments of Calkins and other pro- 
tozoologists, it is now usual to compare the entire life cycle of a 
protozoan animal from one sexual reproduction to the next, 
including all the intervening asexual generations, resulting per- 
haps in millions of individuals, with the life cycle of a single 
metazoan. According to this view the asexual reproduction, 
as remarked above, is comparable with the multiplication of 
cells in a metazoan body, except that, instead of all the cells 
resulting from such multiplication remaining together and be- 
coming specialized for particular functions, they separate and 
live as independent individuals. Just as the cells of a meta- 
zoan body grow old after a variable length of time and lose their 
youthful vitality and reproductive power, so the protozoan 
cells, after a variable number of multiplications, gradually lose 
their vitality and reproductive power. In the metazoan certain 
cells have the power of renewing their waning vitality by union 
with a cell of the opposite sex (sexual reproduction), thus be- 
ginning the cycle again. In the protozoan the sexual phenomena 
which have been observed are believed to have the same signifi- 
cance, and there is evidence that at least in some Protozoa the 
sexual power may be confined to certain individuals which would 
then be comparable with the sex cells of the metazoans. Calkins' 
experiments led him to believe that in Paramcecium, a common 
ciliated protozoan on which he experimented particularly, old 
age and death were inevitable after a variable number of asexual 
generations without sexual reproduction. It has recently been 
shown, however, that when conditions of life are perfect, Para- 
mcecium may continue to multiply asexually for an indefinite 
time. Periodically, however, a complete reorganization of the 
cells occurs which apparently has an effect similar to that pro- 
duced by sexual reproduction, the animals having renewed vi- 
tality for many generations. This remarkable process, named 
'* endomixis," is strikingly analogous to parthenogenesis (de- 
velopment of unfertilized eggs) in higher animals. Another 
analogy is that under unfavorable or adverse conditions sexual 
reproduction replaces endomixis, just as in such animals as 


rotifers and small crustaceans it replaces parthenogenesis, 
though either endomixis or parthenogenesis apparently may con- 
tinue indefinitely with conditions favorable. 

Another phenomenon which is often, though not always, 
associated with sexual reproduction is encystment, i.e., the de- 
velopment of an impervious enclosing capsule in which the 
delicate protozoan cell is able to resist extremely adverse en- 
vironmental conditions, such as very high or low temperatures, 
drouth, presence of injurious substances, lack of oxygen, etc. 
The degree of protection afforded by encystment can be judged 
from the fact that encysted amebae exist in considerable numbers 
on the sun-baked sands of Egypt. Encystment may take place 
whenever environmental conditions become unfavorable, or as a 
normal stage of existence following sexual reproduction, thus 
being comparable with the impervious shelled eggs of many 
higher animals, or sometimes as a step preliminary to some form 
of asexual reproduction. Nearly or quite all parasitic protozoans 
which are not transmitted by an intermediate host adapt them- 
selves for passive transfer from one host to another by encystment. 

A full understanding of the significance and limitations of the 
sexual and asexual phases of the life histories of parasitic Proto- 
zoa is of great importance, since means of control and prevention 
often hinge on these points. In many species of protozoan para- 
sites a different host is required for the sexual portion of the 
life xiistory than that utilized for asexual reproduction, though 
this is not true, in general, of the intestinal parasites. Some 
species, although normally utilizing a second host for the 
sexual reproduction, are apparently able at times to pass from 
host to host without the intervention of an intermediate host of 
different species. This is true, for instance, of the sleeping 
sickness trypanosome, T. gambiense, which is normally trans- 
mitted by a tsetse fly, Glossina palpalis, as an intermediate host, 
but which is thought to be capable of direct transmission by 
sexual intercourse as well. It is interesting to note also that, 
according to observations made by Gonder on trypanosomes 
(quoted by Nuttall), characters such as immunity to certain 
drugs, acquired by protozoans and maintained through thousands 
'^f asexual generations in vertebrate hosts, may be blotted out at 
a stroke in the invertebrate host by the sexual process which 
presumably occurs there. The great significance of this is 


evident : one of the difl&culties connected with drug treatment of 
some protozoan diseases is the power of the protozoans to be- 
come immune to the drug when given in doses which are not 
destructive to the host; if such immunity is lost during trans- 
mission by an intermediate host there is no danger of an immune 
race of the parasite becoming permanently established. 

Classification. — It is little wonder that such a varied assem- 
blage of single-celled animals as constitutes the group Protozoa 
should be difficult to classify. It is obvious that these simple 
animals may be profoundly modified by their environment and 
such modifications can actually be seen in the course of the life 
history of many. The changes in form undergone by a trypano- 
some, for instance, under different environmental conditions and 
at different periods in the life history are represented in Fig. 18. 

It has been the custom among zoologists to divide the Protozoa 
into four classes, based principally upon the nature of the organs 
of locomotion. These classes in brief are as follows: Sarcodina, 
including forms with pseudopodia; Flagellata, including forms 
with flagella; Ciliata, including forms with cilia; and Sporozoa, 
a heterogeneous assemblage of parasitic protozoans which as 
adults have no organs of locomotion, and which reproduce by 
breaking up into spores. Though other classifications have 
been attempted, the above system is the one generally used. 
It is probable that it is not in all respects a natural classifica- 
tion, and that changes in it will be made with increasing 
knowledge of Protozoa. A few examples of the difficulties con- 
nected, with this classification may be pointed out. There are 
protozoans, as Craigia, which are typical Sarcodina during 
part of their life cycle and typical flagellates during another 
part, and some, such as certain soil amebae, which readily 
change from one phase to another under the influence of varying 
environmental conditions; there are others, as Mastigamceba, 
which exhibit at once typical pseudopodia and a whip-like organ 
which can only be regarded as a flagellum; there are species 
having organs in every way intermediate between flagella and 
cilia; the Sporozoa contain some species, such as the malaria 
parasites, Plasmodium, which during a part of their life have 
typical pseudopodia and suggest relationship with the Sarcodina, 
others which show striking affinities to the Flagellata, and still 
others which possess coiled projectile threads in polar capsules, 


resembling the nematocysts of jelly fishes. Some of the latter 
have recently been elevated to the rank of a separate class, 
Cnidosporidia, by the German parasitologist, Braun. Many 
other difficulties in connection with the classification of the 
Protozoa as outlined above could be cited, but since no more 
acceptable classification has yet been proposed this classification 
is followed here. 

The class Sarcodina consists in the main of free-living forms 
occurring in the ocean, fresh water and soil. Many of the marine 
forms are furnished with calcareous shells which are largely in- 
strumental in building up chalk deposits. The majority of the 
parasitic species belong to the genus EndamoBha. 

The class Flagellata contains some of the most primitive as 
well as some very highly specialized kinds of animals. Many of 
the free-living forms possess chlorophyll and are included by 
botanists in the Plant Kingdom. There could be little question 
about their vegetable nature were it not for the fact that there is 
every gradation between those which are typical plants in form 
and function and those which are equally typical animals in 
every respect. The parasitic species are all of distinctly animal 
nature, some ingesting and devouring solid food, others absorb- 
ing food by osmosis. With the flagellates were once included, 
also, the spirochaetes on account of a supposed relationship with 
the trypanosomes, but this theory has long since been exploded, 
and the spirochaetes are now usually looked upon as only dis- 
tantly related to the flagellates. 

The class Ciliata is least important of the four classes of Pro- 
tozoa from the parasitologist's point of view. There is only 
one species of ciliate, Balantidium coli, which is common and 
widespread enough and pathogenic enough in its effects to deserve 
serious consideration as a human parasite. A few other intestinal 
ciliates have been discovered in man but they are of little im- 

The class Sporozoa contains parasitic forms exclusively, but 
fortunately man is peculiarly exempt from the attacks of all but 
a few species. Among the few, however, are included the ma- 
larial parasites, which rank among the first of pathogenic organ- 
isms as regards significance to the human race as a whole. It is 
possible that the undiscovered parasites of such diseases as 
Rocky Mountain spotted fever, yellow fever and dengue, and 


the parasites of obscure nature associated with smallpox, rabies 
and other important diseases may prove to be members of this 

Importance. — Taken as a whole the Protozoa must be looked 
upon as a group of organisms of prime importance as human para- 
sites. Although Leeuwenhoek discovered the existence of Pro- 
tozoa nearly 250 years ago, the first parasitic species, Balantidium 
coli, was discovered by Malmsten in 1856, only 61 years ago. 
At the present time a large proportion of medical practice and 
disease prevention in tropical countries, and a considerable pro- 
portion in all countries, depends on our knowledge of the habits 
and life history of parasitic Protozoa, nearly all of which has been 
gained in the last 35 years, and much of it in the last 15 years. 
Almost daily new discoveries in connection with disease-causing 
Protozoa are being made; there are few branches of scientific 
research which offer a brighter or more promising field of endeavor 
for students at the present time than the investigation of patho- 
genic Protozoa. 


General Account. — On the vague unsettled borderline be- 
tween Bacteria and Protozoa there is a group of organisms which 
are waging a frightful war against human life and health. These 
organisms, commonly known as spirochsetes, when first discovered 
were supposed to be of bacterial nature. Later, for many ap- 
parently valid reasons, they were thought to belong to the Pro- 
tozoa, but one by one these reasons for looking on them as animals 
rather than bacteria are falling away and many biologists at the 
present time relegate them to their old place among the Bacteria. 
They still serve as a bone of contention, however, between bac- 
teriologists and protozoologists, and at present we can only look 
upon them as occupying an intermediate position between the 
Bacteria on one hand and the Protozoa on the other. 

Like Bacteria the spirochsetes lack any distinct nucleus; their 
multiplication is commonly by transverse division, although the 
more typically protozoan longitudinal division has also been 
claimed for them by some investigators; and no unquestionable 
conjugation or other sexual process has been observed. Like 
Protozoa, on the other hand, some of the spirochsetes have a 
membrane, the '^ crista," which reminds one somewhat of the 
undulating membranes of trypanosomes; they react to certain 
stains and chemicals in a protozoan manner; and they multiply 
in a specific intermediate host which serves as a means of trans- 
mission to a new host. Until recently it was believed that some 
spirochsetes passed through a distinct phase of development in 
such intermediate hosts as ticks or bedbugs, but some doubt has 
been cast on this, and it is now the commonly accepted belief 
that the organisms live and multiply in the body of a tick or 
insect just as bacteria do in artificial cultures, without going 
through any phase of their life history which does not at least 
occasionally occur in the vertebrate host. 

Spirochsetes are excessively slender threadlike animals, spirally 



twisted like corkscrews. They are very active in movement, 
and dart back and forth across the field of a microscope so 
swiftly that they can hardly be followed by the eye. The move- 
ment is apparently by wave motions passing through the body, 
often accompanied by a rotation of the body in corkscrew fashion. 
Swiftly moving spirochsetes show many small waves in their 
bodies, while the more slowly moving ones have larger and more 
graceful curls. They also have the power of bending their 
bodies to and fro, and of oscillating while attached to some object 
by one end. Spirochsetes ordinarily divide by a transverse 
division of a single thread into two; a spirochsete in the act of 
such division can be seen in Fig. 6. The result of growth in 
length and transverse division is that the spirochsetes of any 
given species are very variable in size. Often individuals can 
be found which have incompletely divided and which hang to- 
gether in long chains. Another interesting method of repro- 
duction in spirochaetes, the details of which have been worked out 
largely by Fantham and his students, is by " granule-shedding,'^ 
i.e., the production of tiny granules by a breaking up of the 
body substance inside the delicate enclosing membrane into a 
chain of round '' coccoid bodies," resembling coccus forms of 
bacteria (Fig. 4). These minute bodies are set 
free either by a disintegration of the enclosing 
membrane or by a rupture of the latter at 
one end. The elongation of the granules, the 
taking on of the sinuous form and the ultimate 
development of diminutive spirochsetes are said 
by several investigators to have been observed 
by them in living cultures of these organisms. 
It is probable that the granule-shedding occurs ^ ff •* 

at regular periods in the life of spirochsetes, ^ \ • 
and that it is comparable to the process of Fig.4. Spirochceta 
sporulat ion in malarial parasites. It appears to duttoni, showing 
be particularly associated with the existence in P^'ocess of granule 
the intermediate host if there is one, but it ^^'^^^^^^ ^^^ ^^ed- 

.,,,,.. ding. (After Fan- 

also occurs m the blood of the vertebrate host, tham.) 
sometimes apparently in preparation for the 
transfer to the intermediate host, sometimes as a protection 
against adverse conditions. It is quite likely that some spiro- 
chsetes may be able to resist atmospheric drying up while in 


the granule stage and may thus be transmitted in dust or on the 
bodies of flies. Spirochoeta bronchialis, causing a form of bron- 
chitis, is probably transmitted in this way. 

There is a wonderful variation in the size and form of spi- 
rochsetes and also in their mode of life. A few species are free- 
Hving and of very large size, in fact almost visible to the naked 
eye {^ mm. in length), and there are many large species which 
live as harmless commensals with various mollusks. The 
disease-causing species (some examples of which are shown in 


)i> )ii }t g 

Fig. 5. Types of parasitic spirochaetes. A, Sp. duttoni; B, Sp. novyi; C, Sp. 
pallida; D, Sp. refringens; E, Sp. balanitidis; F, Sp. vincenti; G, Sp. icterohemor- 
rhagicB. X about 1500. (After various authors.) 

Fig. 5) are very much smaller, often being so delicate and slender 
as to be hardly visible under the highest powers of the micro- 
scope. Not all the small spirochaetes of vertebrates are patho- 
genic however; two species occur almost invariably in the 
human mouth, living on the tartar of the teeth and about the 
roots of the teeth, and yet, normally at least, cause no ill effects. 
One of these inhabitants of our mouths, Sp. huccalis, is a relatively 
short blunt species, but the other, Sp. dentium, is excessively 
slender, and practically indistinguishable when living from the 
spirochsete of syphilis. Other harmless spirochaetes occur in 
various stagnating secretions or excretions of the body, about the 
tonsils, and in the intestinal mucus. 

Spirochaetes and Disease. — There is some question about 
how many distinct human diseases are caused by spirochaetes. 
The mere presence of spirochaetes in sores or diseased tissue is 
not sufficient reason for believing that they are the direct cause 
of the diseased condition, for, like many bacteria, they are often 
found in exposed sores which are known to be due to other 
causes. Spirochaetes are often found associated in sores or ulcers 
with certain kinds of bacteria, and both bacteria and spirochaetes 


have been thought by some workers to be different stages in the 
Hfe history of a single organism. 

Spirochsetes living in animal bodies have a strong tendency to 
localize in definite parts of the body or in special tissues. The 
spirochsetes which choose the mouth, the teeth or the digestive 
tract as a habitat have already been mentioned. Spirochoeta 
bronchialis confines itself to the respiratory tract, causing a cer- 
tain type of bronchitis. Sp. schaudinni localizes in skin tissue, 
causing ulcers, in certain tropical countries; Sp. iderohemorrhagice, 
although probably invading many parts of the body, especially 
affects the liver and kidneys; the spirochsetes of the various types 
of relapsing fever confine themselves to the blood; Sp. pertenuis, 
the cause of yaws, produces a local sore followed by a general in- 
vasion of the body, but it returns to the skin tissues and settles 
there; Sp. pallida, of syphilis, is able to produce lesions almost 
anywhere in the body, but in any given case usually attacks 
some special organ or tissue, such as the central nervous system, 
skin, bones, reproductive system, arteries, etc. Other spiro- 
chsetes have been found in connection with many different 
maladies, for instance, Sp. orientalis in '^ ulcerating granuloma 
of the pudenda," an ulceration which spreads over the skin 
and mucous membranes of the external genital organs; Sp. 
vincenti in Vincent's angina, a diphtheria-like affection of the 
tonsils and throat; Sp. bronchialis in certain types of bron- 
chitis; and Sp. balanitidis in balanitis, an erosion or ulceration 
of the glans of the penis. There seems to be more or less 
evidence that the spirochsetes found in connection with these 
diseases, often associated with bacteria of various kinds, may 
be at least partially responsible for them, but to prove this is a 
very difficult matter. 

In general the diseases caused by spirochsetes may be divided 
into three groups. The first of these is the type in which the 
organisms live in the blood and cause general symptoms, such as 
fever, spleen enlargement, and anemia, and have a tendency to 
cause relapses. Of such a nature is rat-bite fever and the vari- 
ous forms of relapsing fever. Second, there is the type in which 
there are general constitutional symptoms often preceded by a 
local lesion of some kind, followed later by a localization of the 
organisms in special organs or tissues. This type, characterized 
by continued or remittent attacks rather than by short relapses, 

42 spirochtETES 

includes such diseases as syphilis, yaws, and infectious jaundice. 
The third type is that in which occur only local ulcerating sores 
of skin or mucous membrane; of such a nature are the other 
diseases named above. 

Relapsing Fever 

In every continent in the world, with the possible exception of 
Australia, there occurs a form of relapsing fever caused by spiro- 
chsetes in the blood. In Africa it ranks next to malaria and 
sleeping sickness as a scourge of that disease-cursed country. 
In India it is hardly less severe, while in Eastern Europe and 
America it is a mild disease. The cUnical effects of these various 
strains of the disease vary, especially in the number and duration 
of the relapses. The mode of transmission also varies and the 
parasites are apparently distinguishable and are therefore given 
different scientific names. The African spirochsete, Spirochceta 

duttoni (Fig. 6), is the largest, 

being about 16 /x (y^^Vu of an 
inch) in length ; it has only two 
or three complete spiral turns 
and is quite generally admitted 
to constitute a distinct species. 
The other forms, Sp.recurrentis 
of Europe, Sp. novyi (Fig. 5B) 
of America, Sp. carteri of ori- 
ental countries, and perhaps 
still others in other regions, 
are often looked upon as mere 
strains or varieties of Sp. re- 
FiG. 6. Spirochceta duttoni in blood of cuvrentis, which was the One 

experimentally infected rat. Upper indi- gj.g^ described. These SO- 
vidual shows transverse fission. X 1000. ^^ i • j-cc 

called species differ among 

(After Novy and Knapp.) i i • n • • i 

themselves chietly in size, and 
in the closeness and regularity of the coils. Each type, however, 
is quite variable within itself, and one is likely to be misled as 
to size by the hanging together of several individual or partially 
divided spirochsetes in a chain. The varying symptoms of the 
different types of the disease and the fact that immunity to one 
does not give immunity to another are reasons for considering the 
relapsing fever spirochaetes as constituting several species. 


Although relapsing fever was known to physicians over a 
century ago, it was not until 1873 that Obermeier discovered 
the hitherto unseen agitator which causes it; he made his dis- 
covery during one of the epidemics which spread from Russia 
over Poland and Prussia. 

Many great epidemics have swept Russian, Austrian and 
Balkan cities. Early in the present European war Serbia was 
held in the grip of an epidemic of relapsing fever of unusual 
severity and of high fatality. In Bombay and other Indian 
cities the oriental type of the disease is nearly always present, 
and it sporadically appears in various parts of North Africa, 
China and Japan. In tropical Africa it occurs over a large 
part of the continent occupied by the tick which transmits it. 
It is also probably widely distributed throughout Mexico and 
Central and South America. In the United States it occurs 
chiefly as irregular epidemics among immigrants. Just recently 
a small epidemic occurred in Colorado. 

Transmission. — In Africa, where the disease is commonly 
known as " tick fever," it was thought for a long time to be the 
result of the poisonous nature of the bite of a common house- 
infesting tick, Ornithodorus mouhata (see p. 360, and Fig. 155). 
This tick, which inhabits the huts of natives throughout Central 
Africa, is the chief if not the only transmitter of the Central 
African relapsing fever spirochaete, Spirochceta duttoni. It can 
infect both man and monkeys by its bite. 

It has been shown that the spirochsetes can live for a long time 
in the ticks though they apparently disappear from the digestive 
tract after nine or ten days, many of them penetrating to the 
blood-filled body cavity while still in the spirochaete form. Leish- 
man found that the spirochaetes break up into a series of tiny 
granules which penetrate many of the organs of the tick, in- 
cluding the ovaries and eggs. When the ticks are exposed to a 
temperature of 95° F. for a few days the spirochaetes reappear. 
The ticks may remain infective a year and a half after feeding 
on an infected person though frequently fed on clean blood in 
the meantime, and a single tick may, therefore, infect a number 
of people. By means of the granules the spirochaetes may be 
passed on to a second, or even to a third, generation of ticks 
through the eggs. Young ticks reared in the laboratory from 
infected parents have been found capable of transmitting the 


disease. Indeed, the tiny unfed nymphs are very infective, and 
on account of their small size are particularly dangerous since 
they are not easily detected. The ticks do not usually transmit 
the parasites by means of the beak but deposit a bit of infected 
excrement beside the wound they make; from here the spiro- 
chsetes make their way into the blood, aided by the scratching 
which follows the tick bite. However, when the tick is kept 
for a few days at a temperature of 95° F. the salivary glands as 
well as nearly all other organs become infective, and the disease 
may then be transmitted in the usual insect manner, by injection 
with saliva. The relapsing fever of Abyssinia and Somaliland 
is transmitted by a closely allied tick, Ornithodorus savignyi. 
African tick fever is said to have been imported into Persia, 
where it is transmitted by 0. tholosani. The complete life cycle 
of Spirochoeta duttoni is shown diagrammatically in Fig. 7. 

The other types of relapsing fever spirochetes do not appear 
to have such definite and invariable transmitters. Nicolle and 
his fellow workers have shown that in Algeria the head and 
body lice are undoubtedly the means of spreading the disease. 
In experimental work they have shown that there is a rapid tem- 
porary disappearance of the spirochsetes from the body of the 
louse after they have been sucked with blood from an infected per- 
son; during this time they are presumably in the granular stage. 
After about eight days the spirochsetes reappear and are abundant 
in the body cavity of the louse for some 12 days before they 
finally disappear for good. The lice are infective while spiro- 
chetes are present in their usual form, and also just before they 
reappear at the end of eight days. It is by crushing the louse 
and allowing the juices from its body cavity to contaminate the 
wound that infection is obtained. 

In experimental work in Algeria a man experimented upon 
was bitten several thousand times by infected lice without con- 
tracting the disease, but one louse crushed, and the body fluids 
placed on the conjunctiva, caused the disease to develop. The 
same result would undoubtedly have occurred if the crushed 
louse had come in contact with a wound of the skin. 

In some cases the spirochetes are transmitted through the 
eggs to the next generation of lice, just as in the case of ticks and 
the African disease. The louse has been shown to be the trans- 
mitter of relapsing fever in India also. 



In Europe several different pests are probably implicated in 
the transmission of relapsing fever. In Persia and neighboring 
countries the miana tick, Argas persicus (see p. 364, and Fig. 159), 
is probably the chief offender, while in Russia, Serbia and the 

Fig. 7. Life cycle of Spirochceta gallinarum, applicable also to Sp. dutloni of 
relapsing fever. A, multiplication by transverse division in vertebrate blood; B, 
formation of coccoid bodies in vertebrate blood: C, infection of cells of tick and 
formation of coccoid bodies; D, multiplication of coccoid bodies in tick; E, de- 
velopment of spirochaete forms from coccoid bodies after reentering vertebrate 
blood. X 1500. (After Hindle.) 

Balkan States lice and probably also bedbugs are the trans- 
mitters (see p. 378). It is noteworthy that relapsing fever al- 
ways thrives best in those countries where body cleanliness is 
neglected, and where vermin are in consequence abundant. In 
fact, the prevalence of relapsing fever in any country, as of typhus, 


is in inverse proportion to the prevalence of the use of soap and 
water. Relapsing fever, in countries where it is transmitted by 
lice, always spreads most rapidly in cold weather when people 
are huddled together in stuffy, filthy houses, thus giving the lice 
ideal opportunities for doing their evil work. 

In Mexico and Central America it is believed that certain ticks, 
Ornithodorus talaje and 0. turicata, which in form and habits 
closely resemble the African relapsing fever tick, transmit the 
disease, but this has not been proved. 0. turicata is said to be 
the transmitter in Colombia, but the bedbug and other ticks are 
also suspected. 

Relapsing fever is not a contagious disease as was formerly 
supposed. A typical case in the Bellevue Hospital in New York 
failed to spread the infection to anyone else during the 89 days' 
stay of the patient, although no special precautions were taken 
to prevent it from spreading. 

The Disease. — In the human body the spirochsetes appear to 
live exclusively in the blood, where they become fairly common, 
though never abundant, at regular intervals. In the meantime 
they apparently disappear though they are undoubtedly present 
either in the granular form, or else in such limited numbers as 
to be practically impossible to find. The repeated increase and 
decrease of the spirochsetes in the blood goes hand in hand with a 
recurring fever broken by periods of apparently almost normal 
health. The time of incubation of the disease varies from two 
days to two weeks, but in most cases the initial attack comes on 
the third or fourth day. It usually begins with severe chilly 
sensations, headache and shooting pains in the limbs. The 
ensuing fever lasts intermittently for several days, being accom- 
panied by such symptoms as rapid pulse, enlarged spleen, con- 
stipation, nausea and mental disturbances. After several days 
the temperature suddenly drops below normal and remains so 
for a period of seven or eight days, during which time the patient 
recovers rapidly, feels perfectly well and thinks it unnecessary to 
remain at home or in the hospital any longer. Then comes the 
first relapse, repeating all the symptoms of the first attack, some- 
times in somewhat milder form. Following this there is a second 
period of apparently normal health, usually followed by a second 
relapse, this time much milder. The number of relapses varies: 
in the European and allied types the second relapse is mild, and 


is the last one felt; in the African type, on the other hand, there 
are usually four or five relapses, of shorter duration and more 
irregular in occurrence. In a Gibraltar case Manson observed 
eight distinct relapses, but this is very unusual. Hemorrhages 
under the skin and in various organs of the body often occur, 
and cases have occurred recently in Hungary in which the men- 
inges (tissues covering the brain and spinal cord) were severely 
affected, causing various nervous disorders. Spleen, liver and 
other organs are frequently affected. 

Even the African type of the disease does not ordinarily have 
a high mortality, though some epidemics are more serious than 
others. In an epidemic in Tonkin in 1912, 48 per cent of 703 
cases were fatal. In India the fatality is often high on account 
of the well-meant but pernicious habit of depriving fever-stricken 
people of food, thus often increasing the exhaustion caused by 
the disease. Abortion is a common result in pregnant women. 
A single attack gives permanent immunity to any one particular 
type of the disease but not to others. 

Treatment and Prevention. — Ehrlich's famous spirochete 
poison, " No. 606," or salvarsan, destroys the spirochsetes of 
relapsing fever more readily, if anything, than it does other 
species of spirochsetes, since the parasites live in the blood stream 
into which the drug is directly injected. A single injection 
nearly always causes the disappearance of the parasites from the 
blood and prompt recovery from all symptoms of the disease. 
Preventive and curative inoculations of the serum of highly im- 
mune animals has been found to be effective in rats and monkeys. 
The power of the immune serum can be so increased by repeatedly 
inoculating an animal that very small injections of it are sufficient 
not only to cut short the course of the disease in these animals 
but also to give an immunity of considerable duration. It is 
probable that the same serum would immunize human beings 
as well. 

Eradication of vermin from person and home and avoidance 
of places where infected parasites might be acquired are the 
most important protective measures in places where an epidemic 
is raging. Methods for the control of ticks are discussed on page 
369, of lice on page 400 and of bugs on page 383. Since the 
parasites are not ordinarily introduced directly into the blood 
by the beak of the transmitter, but are simply voided with the 


excrement in the vicinity of the wound, careful disinfection, with 
alcohol or carbolic acid, of the wound before the removal of the 
parasite is a good means of prevention if the suspected trans- 
mitter be caught in the act of biting. 


History. — There are few diseases which mean more to the 
human race as a whole than syphilis, due in part to its almost 
universal distribution, and in part to its insidious and deceiving 
course, thereby leading to untold misery and disaster. Rosenau 
says " civilization and syphilization have been close companions "; 
the one has followed in the wake of the other like the gueril- 
las behind an army. Unlike most diseases, syphilis is one of 
whose origin among civilized nations we have strong evidence. 
There are many reasons for believing that syphilis was acquired 
by the members of Columbus' crew when they discovered the 
island of Haiti, and that it was carried back to Spain by them on 
their return. These adventurers promptly joined the army of 
Charles VIII of France in its invasion of Italy in 1494. Soon 
after the army had triumphantly set up a court in Naples it 
became weakened through the ravages of a terrible venereal 
disease of unusual intensity, hitherto apparently unknown in 
Europe. The following year the army retreated almost in a 
rout and was broken up, the miscellaneous troops scattering all 
over Europe to their respective home countries, and carrying the 
new disease with them. In the next four years the disease had 
spread to practically every country in Europe, and was soon car- 
ried by the Portuguese to Africa and the Orient. The venereal 
nature of the disease was fully recognized, and its foreign origin 
was well known, each nation trying to shift the responsibility to 
another by name, many peoples calling it the '' French disease," 
others the " Spanish disease," etc., while the Spanish alone seemed 
aware of its real origin in America and called it '^ espanola " 
which then meant Haiti. The absence of any reference to a 
disease resembling syphilis in the historical records before the 
discovery of America; the absence of any bones showing evidence 
of syphilitic attack in the abundant pre-Columbian remains in 
Europe, and abundance of such bones in American remains, 
many of which must certainly be pre-Columbian; the positive 


evidence of Spanish physicians and historians at the time of the 
return of Columbus; and the severity of the great epidemic 
in the latter part of the 15th century, — it being almost in- 
variable for an infectious disease, when first introduced among a 
new people, to rage with unwonted severity; all these facts 
point strongly to the American origin of syphilis. 

Interesting as is the early history of the disease, the recent 
history is infinitely more so. By the beginning of the twentieth 
century medical men had come to the end of their rope in knowl- 
edge and treatment of the disease, and found themselves at a 
standstill. But in 1902 the disease was successfully transmitted 
to animals where it could be conveniently studied; in 1905 
Schaudinn discovered the spirochsete, Spirochceta {or Treponema) 
pallida (Fig. 5C), which is believed to cause the disease. In 
1906 Wassermann demonstrated the possibility of detecting 
latent syphilis by the reaction which bears his name; in 1910 
Ehrlich made the epoch-making discovery of his famous drug, 
'' No. 606," or salvarsan, a deadly poison for spirochsetes of all 
kinds, and a cure for syphilis in nearly all stages; in 1913 the 
direct relation of syphilis to insanity, paralysis and other diseased 
conditions of the central nervous system was demonstrated by 
the discovery of the organisms in the cerebrospinal fluid, and in 
the same year a method of destroying the parasites in the central 
nervous system was discovered. There is no other instance in 
the history of medical science where such wonderful strides 
have been made in such a short time in the knowledge and control 
of a disease. At the beginning of the twentieth century syphilis 
was one of the most horrible, hopeless and tragic diseases known 
to ravage the human body; it is now a disease which can be 
readily recognized even in latent stages; it can be cured in its 
early stages; and the terrible tragedies resulting from apparent 
but imperfect cure can be avoided. Its eradication, however, 
will not soon, if ever, be accomplished, since in this are involved 
some of the most intricate moral and social questions with which 
we have to deal. 

Prevalence. — The prevalence of syphilis is difficult to de- 
termine for at present the recording of syphilitic cases is prac- 
ticed to a very slight extent, and accurate data can be obtained 
only in military organizations and certain public and private 
institutions. Sir William Osier places syphilis as third or fourth 


of the killing diseases. The use of the Wassermann reaction for 
the detection of syphilis has greatly extended the possibility of 
arriving at an estimate of the prevalence of the disease, and has 
shown that it is far more common than was formerly believed. 
Yet even the Wassermann test fails in about 10 per cent of cases. 
It is now known that the disease may be present in latent but 
nevertheless infective form for many years after all active symp- 
toms have disappeared. The recently published report of the 
British Royal Commission on Venereal Diseases concluded that 
the number of people infected with syphilis cannot fall below 
ten per cent in large cities, and that at least one-half the regis- 
tered still-births are due to this disease. They found that in 
Britain this as well as other venereal diseases is most prevalent 
in the unskilled labor class, and least among miners and agri- 
cultural laborers. Fournier estimated that in Paris 15 per cent 
were infected. In China syphilis is, next to tuberculosis, the 
most common disease. In the United States conditions are 
no better than elsewhere; some cities, notably San Francisco, 
are much more heavily infected than others. Of 111 cases ad- 
mitted to the Children's Hospital in Boston 31 per cent were 
infected with syphilis. Of 102 children admitted to a Chicago 
hospital, none of them for syphilis, 30 were syphilitic. In the 
" red light " districts of cities, which undoubtedly serve as the 
centers of distribution for the disease, the per cent of syphilitic 
prostitutes is very high. Dr. Browning found every one of 
104 prostitutes in Glasgow infected, and a like condition among 
10,9 men, women and children classed as " vagrants". 

According to Capt. E. B. Vedder of the U. S. Army, the sta- 
tistics compiled from over 1000 new recruits in two widely sepa- 
rated camps (in New York and Ohio respectively) showed that 
over 19 per cent of all applicants for enlistment, approximately 
one in five, are probably syphilitic, although only a trifle over 2 
per cent showed any symptoms of the disease which would ex- 
clude them from the army as the result of a rigid physical exam- 
ination. From this Vedder concludes that there is a good reason 
for believing the percentage of syphilis among the young men in 
civil life, between the ages of 20 and 30, to be fully 20 per cent. 
" It means that when a man's daughter marries, the chances are 
just one to five that she will become the victim of ' damaged 
goods'." Vedder shows further that in the relatively select class 


of young men at West Point from two to five per cent are prob- 
ably syphilitic. In the U. S. Army, as a whole, Vedder beheves 
an estimate of 16 per cent of syphilis among the whites is con- 
servative, and his statistics show that the per cent increases 
steadily with the ages of the enlisted men, and as the years of 
service increase. Among enlisted negroes, who are notoriously 
more syphilitic in civil life than are whites, syphilis is two or 
three times as prevalent as among white enlisted men. " This 
study confirms observations that have already been published 
indicating that syphilis is so prevalent among negroes that it is 
possibly the greatest single factor in the production of disability 
and high mortahty rates among the race." The figures obtained 
from an examination of 531 Porto Rican enlisted men are most 
startling of all — over 50 per cent show evidence of being probably 

Transmission. — Syphilis is fundamentally a venereal disease, 
transmitted by sexual intercourse, and over 90 per cent of cases 
are undoubtedly of such origin. It is a common belief that this 
is the only way in which the disease can be acquired, and some- 
times an unjust stigma of shame and disgrace is attached to a 
perfectly innocent case of syphilis. As already remarked, in 
the vast majority of cases the parasites are directly acquired 
from their usual habitat in the underworld, but over 20,000 
cases of innocent syphilis have been reported, and five per cent 
of infections occurring in the army are of innocent origin. A 
horrible case is on record where seven young women at a church 
social in Philadelphia acquired syphilis from kissing a young 
man who had a syphilitic sore on his lip. A case recently oc- 
curred in one of our western cities which was ultimately traced to 
the eating of apples sold by an Italian who was in the habit of 
spitting on his fruits and rubbing them on his sleeve to shine them. 
Public drinking cups, public towels and soiled bed-linen serve 
admirably as temporary abodes for the spirochaetes of syphilis, 
but fortunately these curses of civilization are in most places 
abolished by law. Unsanitary barbers and dentists can easily 
spread infection, and dentists and physicians often themselves 
contract the disease from handling syphilitic patients, the 
spirochaetes readily entering the smallest cut or abrasion of the 
skin. Mid wives and wet nurses are likewise exposed to infection 
from diseased babies, as are the babies from diseased nurses. 



Indeed, when we think of the many ways in which syphilis 
spirochsetes may be transmitted from person to person it is sur- 
prising that the number of innocent cases is not much greater. 

The Spirochaetes. — The spirochsetes of syphiHs, Spirochceta 
pallida (Fig. 5C), vary in length from four to 14 fjL (^Au to js\jf of 
an inch) and are immeasurably slender. They are more closely 
curled than the spirochsetes of relapsing fever, having usually 
from six to 14 very regular, short, sharp curls, quite different from 
the long graceful curves of a relapsing fever parasite. The 
living organisms are very active and dart with great speed 
across a slide, threading their way between blood corpuscles or 
cells. The spiral turning of the body reminds one of the undulat- 
ing movements of a swimming snake. Another spirochsete, Sp. 
refringens (Fig. 5D), is often found associated with Sp. pallida. 

During the early stages 
of their sojourn in the body 
the spirochsetes can always 
be found in the primary and 
secondary lesions, and in the 
neighboring lymph glands. 
During the second phase 
of the disease and also 
toward the end of the 
first phase the spirochaetes 
occur in variable numbers 
in the blood, and very 
early make their way into 
the cerebrospinal fluid in 
the brain and spinal cord. 
After it was found that 
the spirochsetes actually 
invade the central nervous system, and cause diseases of it, it was 
supposed that this occurred only occasionally in late stages of 
the disease. During the last year or two it has been shown, 
however, that the great majority (80 per cent) of syphilitics show 
distinct pathological changes in the spinal fluid, due to spiro- 
chsetes in it, from the date of the primary sore, and are therefore 
possible candidates for syphilis of the nervous system. During 
the second phase the spirochsetes make a general invasion of 
the entire body, later showing some special predilection for 

Fig. 8. Spirochceta -pallida in liver tissue 
of a congenital syphilitic. 


certain tissues or organs. The gummy sores or " gummas " 
which often break out during the third stage of the disease have 
usually been considered non-infective, and spirochsetes could not 
be found in them. Recently, however, the parasites have been 
found in some of these lesions, also. In congenital syphilis 
the parasites often multiply in enormous numbers in the unborn 
child, penetrating practically every organ and tissue of the body. 
The liver especially is often found literally teeming with spiro- 
chsetes (Fig. 8). 

The Disease. — SyphiHs is a disease which has no equal in its 
deceptive nature. It is largely due to this fact that so many 
tragedies result from its ravages. Its effects on the individual 
are often horrible enough, leading to disease of almost any tissue 
or organ in the body, but it is only when judged in the light of 
the additional damage that is done to the innocent wife or 
husband, as the case may be, and to the next generation, that 
the true meaning of syphilis can be measured. Syphihs may 
remain latent and unsuspected for twenty years or more, and the 
carrier still be infective. Meanwhile, perhaps in ignorance of 
his condition, he may infect a hitherto sound person whom he 
has taken for a life companion, and cause her, or him, to be 
ravaged and slowly destroyed by this horrible disease. Worse 
than this his chances of having healthy children are small. It 
has been shown that about 45 per cent of those who later become 
victims of general paralysis from syphilis never can have any 
children, either on account of sterility or of repeated abortions. 
The author of the statement in the Bible that " the sins of the 
fathers shall be visited upon the heads of the children unto 
the third and fourth generations " may well have had in mind 
the hereditary effects of venereal diseases, but he might have 
stated further that often there is no third or fourth generation. 
The only pity of it is that this is not always the case, for those 
who are brought into the world are in the majority of cases 
hopelessly handicapped either mentally or physically. Feeble- 
mindedness is five times as common in syphilitic families as in 
normal ones. There is some reason for believing that the hideous 
mentally deficient children known as mongols are the result of 
syphilis in parents. And finally, as if all this were not enough, 
the carrier of latent syphilis may later develop general paralysis, 
or some other disease of the nervous system or other organs, which 


will render him an ineffectual social unit, and make him and his 
family a burden to the community. 

In the majority of cases the disease begins with a hard sore 
on the skin or mucous membrane known as the '' primary 
chancre." This usually appears at the point of infection in from 
ten days to three weeks after the infection occurs. In some cases 
such a chancre never develops. The chancre gradually heals 
up and the second stage begins, in which general constitutional 
symptoms appear, as fever, anemia and a general run-down 
condition during which the patient is very susceptible to other 
diseases, such as tuberculosis. Often there is an extensive 
breaking out on the body, production of scaly patches of skin, 
and inflammation of the mucous membranes of the mouth and 

From this point on the course of the disease depends on what 
particular tissues or organs the spirochsetes especially attack, 
for although the parasites, as said before, may produce disease 
almost anywhere in the body, in any given case there is usually a 
localization. It seems that certain strains of the parasites have 
special preference for certain tissues. The differences in this 
respect have been shown by Nichols to hold good through many 
transfers from animal to animal, and visible differences in the 
parasites can be observed. In about 40 per cent of cases syphilis 
settles in the nervous system, causing a great variety of evil 
effects, such as feeble-mindedness, tabes, or locomotor ataxia, 
general paralysis, epilepsy, insanity and moral defectiveness. 
Often it settles in the skin and mucous membranes, producing 
the gummy sores or " gummas " which were formerly supposed to 
be the usual tertiary stage of syphilis. It may select the bones, 
muscles, arteries, heart, reproductive system, or any other part 
of the body, in each case producing a different set of symptoms, 
but in every case weakening the vitality and leading ultimately 
to an early grave. 

An active attack on one tissue or organ of the body seems to 
have an inhibiting effect on other attacks. It is well known that 
an infected person presumably with an active attack of the 
spirochsetes on some organ in his body will not develop new 
lesions when re-infected. Possibly this explains why there is 
often a relapse of the nervous system after incomplete treatment 
of skin syphilis. The spirochsetes in the nervous system which 


are not reached by the drugs may flare up and produce a serious 
attack after the spirochaetes in other parts of the body have 
been killed and the skin lesions healed. On the other hand 
paralytics with an active attack on the central nervous system 
seldom show any other symptoms. Unborn babies seem not 
to be subject to such speciahzed attacks, but, as already pointed 
out, are often found with every organ and tissue in the body full 
of spirochaetes. There is a form of the disease occurring in 
adults known as " malignant syphilis " in which ulcerating sores 
appear early and gradually eat away large portions of the skin. 
It is marked by extreme anemia and great weakness, and usually 
causes an early death. 

Diagnosis. — The modern methods of diagnosing syphilitic 
infection have revolutionized our knowledge of the disease, and 
have done much toward placing its treatment and control on a 
scientific basis. In at least 50 per cent of syphilitic cases there 
are no symptoms which can be attributed positively to syphilis, 
but we now have several tests for the disease, two of which are 
of wide application, and, together with the characteristic lesions 
in certain stages of the disease, make it possible to detect syphi- 
lis in practically any phase. 

The simplest of these indicators for syphilis is the " luetin 
test." This consists of the injection into the skin of a sterile 
emulsion of the dead bodies of the spirochaetes from a culture. 
If the test is positive, i.e., if syphilis is present, the inoculation 
results in a solid or a pus-filled pimple, usually appearing in a 
few hours but sometimes not for several days. This test is ap- 
plicable to latent, tertiary and congenital syphilis and does not 
give positive results during the active primary and secondary 
stages of the disease. Its value lies in the fact that it is sometimes 
sensitive to latent infections which the Wassermann reaction, 
now to be described, does not demonstrate. 

The Wassermann reaction, although it fails to reveal syphilis 
in rare cases, is one of the most valuable and dependable means 
of diagnosis known in medicine. It is now almost universally 
used in well-equipped laboratories. The reaction is also positive 
to some other diseases, such as yaws (also a spirochaete disease), 
leprosy, malaria, scarlet fever and other diseases, but all of 
these can be diagnosed beyond doubt by other means and thus 
prevent a false diagnosis of syphilis. The reaction in brief is as 


follows: A little serum from the suspected person is mixed with 
an extract of liver or heart and some guinea pig serum and in- 
cubated a short time. A suspension of blood corpuscles and a 
hemolytic serum is then added and the mix- 
ture is incubated again. If the suspected serum 
is not syphilitic the blood corpuscles are dis- 
solved by this mixture and the serum becomes 
*%• B i ?o& ^^^' whereas if the serum is syphilitic no change 
in the blood corpuscles takes place, and they 
sink to the bottom. The more highly syphi- 
FiG. 9. WassTrmann ^^^^^ ^^^ individual the more complete is the 
Reaction. Neg., nega- sedimentation of the corpuscles. As stated 

tive; Pos., positive. i i? iv -r i i? • xi • 

before there are possible sources of error in this 
test, but if properly made with standard reagents, and with suffi- 
cient control tests, it can be confidently relied upon. 

Treatment. — There are many quack doctors who are still 
practicing the same inefficient methods of curing syphilis that were 
in vogue several centuries ago. Syphilitic sores are powdered 
and cauterized and cured, and the patient is given to believe 
that his disease is cured. Unfortunately, as we have seen, the 
course of the disease is of such a nature that the doctor's claim of 
having cured may be borne out for months or years before the 
insidious disease appears again, this time in a much more de- 
structive and perhaps incurable state. Superficial treatment of 
syphilis sores, accompanied perhaps by a few " tonic " pills, in 
no way destroys the virulence of the parasites or alters the future 
course of the disease. It merely makes the chance of correctly 
diagnosing the disease more difficult, and it frequently results in an 
unsuspecting victim carrying the disease untreated to a stage 
where it has wrought irreparable damage to himself, his life-mate 
and his children. 

Treatment of the disease formerly consisted in the adminis- 
tration of mercuric chloride. While this sometimes effected an 
apparently complete cure, over 80 per cent of syphilitics suffered 
relapses in spite of the most persistent treatment. In 1910 
Ehrlich, after years of experimentation, offered humanity his 
famous preparation, " No. 606," known as salvarsan, an arsenic 
compound which is deadly to spirochsetes. When this drug is 
injected into the veins of a syphilitic, it almost immediately 
kills all the spirochsetes except a few which have stowed away in 


inaccessible parts of the body, and these must be caught by con- 
tinued administration of the drug, or by special methods. The 
most successful method of treatment is an alternate use of 
mercury and salvarsan, this apparently being more effective 
than salvarsan alone. There is now on the market a modified 
form of salvarsan, known as neosalvarsan, which is milder in 
its effects on the body but usually considered less powerful in 
destroying the spirochetes. Several other more or less valuable 
substitutes for salvarsan are now prepared. On account of the 
war, salvarsan itself, a German product, is at present difficult to 

Salvarsan injected into the veins does not reach the spiro- 
chsetes in the central nervous system, and since it is too injurious 
to be injected directly into the spinal fluid, the usual treatment 
of syphilis is inapplicable to syphilitic infections of the nervous 
system. An injection of salvarsan into the lymph spaces under 
the fibrous coverings of the brain is sometimes used, but is not 
always successful. Swift and Ellis, of the Rockefeller Institute, 
discovered in 1913 that the blood serum of a syphilitic who had re- 
cently been given salvarsan was destructive to spirochsetes and 
could be injected into the spinal fluid without injurious results. 
Out of this grew the so-called Swift-Ellis treatment of syphilis 
of the nervous system by the use of '* auto-sal varsanized serum," 
i.e., the serum of the patient himself after having been given 
salvarsan an hour before. This serum is heated for half an hour 
to make the salvarsan in it more active, then diluted and injected 
into the spinal canal. While complete cures in late cases of 
paralysis and other nervous diseases could hardly be expected 
from this or any other method, the results which have been ob- 
tained are very encouraging. It has been suggested that in all 
cases of syphilis the Swift-Ellis treatment be made routine as a 
protective measure since, in the majority of cases, the spiro- 
chaetes invade the nervous system in the early stages of the 
disease and the consequences of their establishment there are so 
terrible as to warrant every possible preventive measure. 

The modern methods of diagnosing syphilitic infection have 
given a definite standard of cure, and the success or failure of 
treatment can be positively demonstrated. A uniform negative 
Wassermann reaction given several times during a year, and ab- 
sence of any symptoms, can be looked upon as an indication of 


cure, though some doctors consider a negative Wassermann reac- 
tion for two years necessary to indicate a certain cure on account 
of rare cases of relapse, even after a year of apparent absence of 
the spirochaetes. In contrast to the 85 per cent of relapses which 
occurred when mercury alone was used to treat syphilis, less than 
four per cent of relapses occur after treatment with both mercury 
and salvarsan. Certainly salvarsan may justifiably be con- 
sidered " one of the mightiest weapons in medicine." 

Prevention. — The control and ultimate eradication of syphilis 
is, in spite of our present methods of diagnosis and treatment, a 
dream of the distant future. In its prevention are involved so 
many social and moral problems upon which people will not 
agree that the task is beset with great difficulties. 

According to Dr. Snow of the American Social Hygiene Asso- 
ciation, the means of controlling and preventing syphilis fall 
into three groups: (1) care and treatment of existing cases with 
a view to preventing their spreading the infection, (2) protection 
of the uninfected by education and administrative measures, (3) 
the development of social defenses against the disease. 

As regards the first type of preventive measures, practically 
all medical men and public health workers are agreed. Adequate 
means for the diagnosis and treatment of syphilis should be pro- 
vided in all cases. At present not only are there no laboratories 
for diagnosis or free hospitals or clinics for treatment provided at 
public expense, but most of our private physicians and hospitals 
shun syphilitics, and refuse to care for them. Many physicians 
at the present time have little knowledge of venereal diseases. 
The suggestion of the British Royal Commission on Venereal 
Diseases urging that this subject be given a prominent place in 
all medical schools is certainly worthy of being put into practice 
immediately. In many of our large cities and in most of the 
small ones there is not a single hospital which will admit a patient 
for a venereal disease. Of 30 general hospitals in New York 
City, only ten receive patients with recognized syphilis in the 
infective stages. Theoretically a syphilitic in the infective stages 
should be as carefully watched and cared for as a leper or small- 
pox patient, yet the syphilitic, the victim of immorality usually, 
but sometimes only of the carelessness of some other culprit, 
is turned loose without treatment, but with full power to infect 
all with whom he comes in contact directly or indirectly. We 


seem to have made little advance since 1496, when the Parlia- 
ment of Paris decreed that all persons found infected with syphilis 
should leave the city within 24 hours. 

The British Royal Commission urged the provision of ample 
facilities for free diagnosis of these diseases and for free treat- 
ment when necessary. Such measures have already been at- 
tempted in a few instances in our own country and their ultimate 
success on a large scale is insured. The New York City Health 
Department in a single year examined 59,614 specimens of serum 
for the presence of syphilis and three-fourths of these were re- 
ceived from private physicians. A few public health institutions 
are doing splendid work in the operation of a department for the 
diagnosis of venereal diseases and the giving of personal advice. 
The Oregon State Board of Health is undertaking an extensive 
correspondence with persons in all parts of the state who write 
for information in response to venereal disease placards posted in 
appropriate places. The provision of ample facilities for the 
free treatment of syphilis in the way of hospital service when 
necessary, of proper medication, and of the extension of Social 
Service hospital work is something which we have only begun to 
touch upon, but which will undoubtedly come in time. The 
fact that no facilities have hitherto been provided for the care 
of syphilitics either at public expense, or in the private practice 
of physicians and hospitals, is a disgrace to our civilization and a 
menace to our health. The medical prevention of syphilitic in- 
fection after exposure to it is possible and succeeds in the great 
majority of instances if attended to within a few hours after ex- 
posure. The use of self-applied medical treatments has been 
fairly successful in military life, but as shown by Dr. Snow it is 
of doubtful value in civil life, since the intelligence required to 
apply medical preparations properly is lacking in those who need 
it most — immature boys, drink-befuddled men, defective girls, 
and the average prostitutes. These classes constitute the bulk 
of the citizens who become exposed to infection and since the 
personal supervision of a physician is necessary in most cases, 
it might best be required in all. Private physicians, dispensary 
officers and the health department staff are the persons qualified 
to employ medical treatment designed to prevent infection after 
exposure to it. Avoidance of exposure constitutes the best and 
only safe preventive measure before exposure. 


As to the second type of prevention, the protection of the unin- 
fected by education and administrative measures, great advances 
are being made. One of the most important measures, and one 
to which we are slowly coming, is the compulsory notification of 
the Public Health Department of all cases of venereal diseases so 
that whatever action seems best may be taken to safeguard the 
public health. There can be no question but that such a record- 
ing of venereal diseases would work for the best good of all con- 
cerned, both the patient and the public. Laws compelling the 
notification of health departments of venereal diseases now exist 
in eleven states and a number of cities in the United States, 
but only in rare instances are they enforced. Such a law in 
modified form has been passed and is being enforced in Western 

With the notification of venereal diseases, many other prac- 
tical measures could be inaugurated, such as the exclusion of 
infectious syphilitics from occupations connected with the 
preparation and serving of food; the careful instruction of 
syphilitics concerning various phases of their disease, and possible 
means of transmission, thus in many cases securing their active 
cooperation; and the effective prevention of the marriage of 
syphilitics. The last is one of the most important measures 
that could be adopted. Many states at present prohibit the mar- 
riage of persons with venereal diseases but without enforcement 
of notification these laws are worse than useless, since they may 
give a false sense of security. Knowing the awful consequences 
of inherited syphilis it is the duty of society to prevent the 
marriage of syphilitics even with the full knowledge and consent 
of both parties. The Royal Commission urged only the full 
information of the undiseased party in marriage, allowing the 
union to be made if then consented to. In this they seem not 
to have given due consideration to the rights of the next genera- 
tion. With compulsory notification of venereal diseases, and a 
law refusing a marriage license to any person who has or has had 
syphilis and cannot pass the accepted laboratory tests for the 
disease, the pitiful results of hereditary syphilis could be largely 
prevented. Even the remote possibility of the spectacle of a 
diseased wife and of stillborn, insane, or physically imperfect 
children should be enough to induce any man worthy of the 
name to take every precaution to avoid such a tragedy, but if 


he is unwilling to do this for himself and his posterity, social laws 
should do it for him. 

Sanitary laws are in effect in many places which help to pre- 
vent infection from such sources as public drinking cups, towels, 
bed-linen, and other articles, but such laws, excellent as far as they 
go, are inadequate, since no law can cover all the articles which 
may be rendered infective by contact with a syphilis sore. One 
common source of infection, though more for gonorrhea than for 
syphilis, is the improperly constructed toilets in public schools. 
These are usually built so high, and of such a type that school 
children, little girls especially, are exposed to infection every 
time they use them. Many cases of venereal diseases in school 
children, particularly in larger cities, have been traced to this 

No preventive measure which does not strike directly at the 
primary source of infection can be adequate in coping with any 
disease. Just as we fight malaria through the mosquito, sleep- 
ing sickness through tsetse flies and typhoid through contami- 
nated water and houseflies, so we must fight syphilis and other 
venereal diseases through prostitution. The abolishment of this 
vice would unquestionably mean the abolishment of venereal 
diseases. At present, at least in many places, this is certainly 
not possible. The abolition of " red Hght " districts is invariably 
followed by a parallel increase in clandestine prostitution, luring 
many who would abstain from unmasked brothels, to say nothing 
of the increase in seduction and rape of innocent girls. The 
most feasible plan at present, as successfully tried in many 
European cities, especially Germany, is the municipal supervision 
of restricted " red light " districts. By continuous medical 
attendance, and the enforcement of strict sanitary measures, the 
normal spread of disease from this source has been reduced to a 
great extent. It may be argued that municipal control of prosti- 
tution implies public sanction of it, and is therefore morally 
wrong. This perhaps is true but there can be no question about 
the futility of attempting, at the present state of our civilization, 
to abolish prostitution or even to lessen it materially by passing 
laws against it. In view of this it is merely a question of a greater 
or lesser evil, and there can be no moral crime in lessening the 
dangers from an evil which we are powerless to destroy. It may 
be said that the lessening of danger from disease in houses of 


prostitution will increase their popularity. The same argument 
might be used, and has been used by the ultramoralists, to show 
that it is morally wrong to attempt to cure venereal diseases, 
since this lessens the terror of them. Such arguments might have 
more force if syphilis were a disease which affects only the indi- 
vidual, and was not a source of danger and burden to the com- 
munity. Moreover it seems doubtful whether the person whose 
character is such a combination of moral weakness and cowardice 
that he shuns houses of prostitution only from dread of disease, 
will not spend his time in seducing innocent girls, or in other 
hardly less despicable crimes. It may further be pointed out 
that disease and immorality go hand in hand. A healthy body 
is conducive to a healthy mind, so by eliminating disease we 
would be doing at least as much toward giving a death stab to 
immorality as toward extending it. 

The medical supervision of prostitution, adopted as a tempo- 
rary measure, should be accompanied by efforts toward its 
ultimate reduction. The abolition of alcoholic drinks, the im- 
provement of conditions in slums, the furnishing of decent 
surroundings and wholesome sports and exercises, and the en- 
forcement of minimum wage laws for women are all measures 
which tend toward the reduction of prostitution, but foremost 
of all such measures should be education; in this lies our most 
powerful weapon against immorality and venereal disease. Hos- 
pitals, public schools, churches, libraries and the lecture plat- 
form all have the power of spreading the gospel of sex hygiene, 
each in its own way, each in a way especially suited to its listeners. 
Even the theatre can enter the field of education and it has done 
so. The play, and the motion picture patterned after it, entitled 
'' Damaged Goods," in the estimation of the author, has done a 
great deal of practical good. Yet many ministers, teachers and 
newspapers, often in total ignorance of the real nature of the 
play, and in absolute neglect of their own opportunities for 
educating, have severely criticized the play as " immoral." Such 
men and women, who should know better, are nothing short of 
a disgrace to the institutions they represent and are largely 
responsible for the present popular ignorance concerning one of 
the matters of most vital interest to humanity — sex hygiene. 



A common feature of nearly all tropical countries is the disease 
known as yaws or frambesia. In the Fiji Islands all healthy 
children are expected to pass through an attack of yaws and are 
sometimes inoculated with it by their parents. It is common in 
many parts of equatorial Africa, particularly on the West Coast. 
In the West Indies it is also a very common disease, especially in 
the islands which are largely inhabited by negroes. There is 
some evidence that yaws was imported to America from Africa 
with the slaves as were some others of the most troublesome Amer- 
ican diseases. In Brazil the disease is called " buba brasiliensis " 
and is often confused with Leishmanian diseases. 

The parasite which is the cause of this loathsome disease is a 
spirochete, Sp. pertenuis, which is hardly distinguishable from 
the spirochsete of syphilis, and was for a long time thought to be 
identical with it. Recent investigations, however, have shown 
that there are some slight differences in the two parasites, though 
not enough to be recognizable by anyone but an expert. Like 
the spirochsete of syphilis, Sp. pertenuis inhabits many different 
organs and tissues of the body, being found especially in the 
spleen and lymph glands and in the tumor-like " yaws." It is 
not yet conclusively proved that yaws and syphilis are not slightly 
different types of the same disease, though most workers believe 
in their distinctness, and for practical purposes, at least, it is best 
to consider them as distinct. One of the arguments in favor of 
the unity of the two diseases is that typical syphilis seldom occurs 
where yaws is prevalent, and vice versa, but this may be due to 
a reciprocal immunity, i.e., yaws giving immunity to syphilis, and 
syphilis to yaws. 

The Disease. — In from 12 to 20 days and occasionally longer 
after infection constitutional symptoms appear, such as fever, 
rheumatic pains, and general illness. These symptoms are some- 
times very severe, but usually they are slight and often hardly 
noticeable. After several days of such symptoms there appears a 
peculiar powdery scaling-off of the skin, sometimes almost invisible 
but at other times making white marks, especially conspicuous 
on the dark skin of negroes. After several days little pimples 
appear over the hair follicles in the patches of powdery skin. 
As these grow the raw flesh from beneath pushes the horny 


epidermis up, causing it to crack over the surface in such a way 
as to give the Httle tumor the appearance of a raspberry. Little 
yellow summits soon develop on the tumors, composed not of 
pus but of a cheesy material. Some of the pimples grow no 

further, but most of them become capped 
over with the yellow cheesy substance 
which catches and holds particles of dust, 
and thus become very dirty. These are 
the " yaws " from which the disease takes 
its name. During their formation they 
cause some itching, but are not painful. 
They reach the height of their develop- 
ment in 12 or 14 days and then usually 
begin to shrink, the dirty yellow cap, now 
dark colored, falling off and leaving a 
sound patch of pale skin. Sometimes, 
^''* }?k \T^^ ""^ ^^'^^' however, though in less than ten per cent 

(After Manson.) , . . , 

of cases, ulceration of the yaws takes 
place, but this is probably due to comphcating infections. The 
time that the disease lasts varies greatly according to the general 
health and constitution of the patient. In normal mild cases it 
may be all over in less than two months, while in weak or sickly 
individuals crop after crop of yaws may appear for months or 
years, recurring at irregular intervals. There is some evidence also 
that there may be a rare tertiary stage of yaws corresponding to 
a similar stage in syphilis, characterized by a diseased condition 
of the bones of the arms and legs, ulcers, etc., though this may 
often be due to mixed infections with syphilis or other diseases. 
The disease known as gangosa, prevalent in Guam and other East 
Indian Islands, is thought by some to be a consequence of yaws. 
Yaws is very seldom a fatal disease except in young children. 
Like syphilis it is very contagious, but the parasites are not 
transmitted from mother to baby before birth or by nursing. 

Treatment and Prevention. — Care of the general health of 
yaws patients and conditions leading to the free eruption of 
the yaws aid much in shortening and alleviating the course of 
the disease. Salvarsan is poisonous for the parasites of yaws 
as it is for other spirochsetes, and is an almost sure cure at any 
stage of the disease when injected either into the veins or muscles. 
In experimental animals the parasites disappear within 24 hours 


after the injection of salvarsan. Galyl and other arsenical sub- 
stitutes for salvarsan are also effective against the disease. 

The suppression of yaws in communities where it is common 
consists largely in affording isolated hospitals or houses for 
yaws patients and in preventing the patients by proper care and 
treatment from spreading the disease by contagion. Personal 
care on the part of the patient is often more than could be 
expected, considering that yaws is most common among half- 
civilized and ignorant tropical races. However, the lure of a 
comfortable and congenial ward where he could get good treat- 
ment would undoubtedly induce many a native to submit to the 
practice of being sanitary, however it might grate upon his nerves 
at first. His accounts of the good treatment received would 
help in luring others, and what few ideas of sanitation he might 
have retained would help in spreading the gospel of sanitation. 
In this way the prevalence of the disease, at least in local areas, 
could be greatly reduced, and public money used for such pur- 
poses could be considered well spent. 

Infectious Jaundice or Weil's Disease 

In parts of Europe and in Japan, and also reported from various 
parts of North America, there occurs a disease characterized 
especially by fever and jaundice {i.e., affection of the liver causing 
a marked sallow color due to bile pigments in the blood) , the cause 
of which has long been a puzzle to medical men. It has often 
been confused with yellow fever and with bilious typhoid, and it 
is not certain even now that the latter is not a very severe type of 
Weil's disease. Early in 1915 the connection of a new species 
of spirochaete, Leptospira icterohcemorrhagice, with the disease was 
discovered by two Japanese investigators, Inada and Ido. Later 
in the same year, and independent of the Japanese work, the same 
organism was discovered in Germany in ccJnnection with WeiPs 
Disease, the German investigators suggesting the name Sp. 
nodosa. One could almost wish that the German name had been 
given first! 

The Disease. — A week or more after infection the first symp- 
toms appear rather suddenly in the form of headache, high 
fever, and a feeling of leaden fatigue in the legs which soon 
changes to intense pains. The muscles become so tender that 



even a slight touch is unbearable. Usually the spirochsetes are 
abundant in the liver, suprarenals, blood and other organs and 
tissues during this initial 'Afebrile" stage of the disease, but they 
are destroyed in the liver and suprarenals by antibodies usually 
by the seventh day. During the second week of the disease, 
termed the ''icteric" stage, the fever subsides and marked jaundice, 
accompanied by swelling and pain in the liver, usually appears, 
though this symptom is sometimes evident as early as the third 
day. In some cases, in Europe at least, jaundice may not appear 
at all. The fever usually reappears in milder form about the 
end of the second week, but it is of short duration. Such symp- 
toms as vomiting, nose bleed, upsetting of the digestive system, 
swollen spleen, weak but rapid pulse, and meningitis are usually 
associated with the disease, and kidney trouble is nearly always 
present, and is 'sometimes more severe than the jaundice. A 

tendency for the mucous 
membranes and various 
organs to bleed is a common 
and dangerous symptom. 
During the icteric stage of 
the disease the spirochsetes 
disappear from the blood, 
and are gradually destroyed 
in other parts of the body; 
they persist longest in the 
kidneys, since the antibodies 
which destroy them else- 
where are apparently ineffec- 
tual against those situated 
in the kidney tubules. They 
continue to be excreted with 
the urine for six or seven 
weeks, though nearly all symptoms usually disappear much earlier. 
If death occurs, it nearly always comes between the eighth and 
sixteenth days of illness. The disease is said to be not as severe 
in Europe as in Japan, the mortality among infected soldiers in 
Flanders being less than six per cent. 

The spirochaetes are found in the blood, the cerebrospinal fluid, 
and in many of the tissues of the body, especially the liver and the 
kidneys. They vary in length from only four or five ii to 20 fj. 

Fig. 11. Liver of patient who died from 
Weil's disease on sixth day, showing Spiro- 
chceta icterohemorrhagice in tissue. X 200. 
(Sketched from figure by Inada et al.) 


i^jyuTj to Y3fVn of an inch) and are characterized by pointed and 
usually hooked ends (Fig. 5G). According to the workers in 
Japan the undulations are irregular and more like those of the 
relapsing fever spirochsetes than like those of the spirochsete of 
syphilis. Noguchi, however, states that the number of coils in 
a given length is greater than that in any spirochsete hitherto 
known, there being ten or twelve coils in five n (^Air of an inch). 
The figure (Fig. 5G) shows only the gross undulations of the 
organism and not the individual coils. From their descriptions 
it would seem that the Japanese workers have mistaken these 
gross undulations for the true coils. Noguchi believes this 
spirochsete to have characteristics sufficiently distinctive to war- 
rant its being placed in a new genus, Leptospira. The spiro- 
chaetes become most numerous from the 13th to the 15th day of 
illness, and begin to diminish and degenerate by the 24th or 
25th days, though they may continue to be excreted with the 
urine for six or seven weeks. 

It is probable that the spirochsetes gain access to the body 
either by way of the alimentary canal or directly through the 
skin. The disease can be experimentally transmitted to guinea- 
pigs by applying an emulsion of diseased liver to the shaved but 
uninjured skin, infection taking place in as short a time as five 
minutes. Infection is more certain if any abrasion of the skin 

It has been shown that both the urine and the faeces of infected 
people contain living spirochsetes and that these excretions are 
infective. Since infection can occur directly through the skin 
contact with contaminated ground is dangerous and probably 
accounts for the prevalence of the disease in certain mines in 
Japan. Rats have been shown by Japanese investigators to 
serve as a reservoir for infectious jaundice. The spirochsetes are 
very common in rats, especially in the kidneys, being con- 
stantly excreted with the urine. Examination of 86 rats in 
cities and coal mines in Japan where infective jaundice occurs 
showed that nearly 40 per cent carried virulent spirochsetes in their 
kidneys, in most cases demonstrable by microscopic examination 
of kidney tissue or urine as well as by experimental inoculations. 
In America the parasites have been demonstrated in wild rats 
caught in the vicinity of New York City and in Nashville, Tenn. 
The ease with which rats may contaminate food with their ex- 


cretions makes it appear probable that these animals are an im- 
portant means of spreading the disease, and this most readily 
explains the common occurrence of epidemics in families. Two 
cases have been reported as having resulted from the bites of 
rats. That rats serve to spread Weil's disease in Europe also 
appears evident from its common occurrence where rats are 
abundant. In Europe butchers are especially prone to it, and 
severe epidemics of it have broken out in the rat-infested war 

Treatment and Prevention. — The Japanese investigators find 
evidence that salvarsan is destructive to Sp. iderohemorrhagice, 
but their results are far from convincing and the German inves- 
tigators say that salvarsan does not destroy the parasites. More 
investigation and experimentation needs to be done before this 
question can be settled. 

Investigators of both countries have had greater success in 
treating the disease by injection of the serum of a convalescent or 
of an animal which has become immune. The Germans found 
the convalescent serum effectual, either as a preventive or for 
cure, when diluted 100 times. Japanese workers, on the other 
hand, put far more faith in active immunization. They inject 
spirochsetes which have been weakened by subjection to very 
dilute carbolic acid and left on ice for a week. Guinea-pigs can 
be immunized by such injections, or even by injections of dead 
parasites or the products of their disintegration. 

Prevention of this disease, as of plague, evidently resolves itself 
largely into rat destruction by poisoning, trapping and rat-proof- 
ing. Some reduction should be obtained by keeping food where 
rats cannot get access to it, and, of course, where it cannot be- 
come infected, directly or indirectly, by the excretions of human 
patients. However, since the parasites are able to penetrate 
directly through thin skin, especially if there are any abrasions, 
care should be taken to prevent contamination with urine of 
objects or surfaces which are likely to come in contact with the 
hands or other parts of the body of other people. As remarked 
before, epidemics in mines are largely due to insanitary habits 
and contamination of the ground. In mines or other places 
where sanitary conditions are difficult to enforce, wholesale im- 
munization would probably be effective, but good results can 
also be obtained by disinfecting the ground. According to 



Japanese authors, two epidemics in coal mines have already been 
prevented by the latter method, combined with removal of inun- 
dated water. 

Yellow Fever 

Distribution. — Yellow fever is a disease which is especially 
characteristic of the seaport towns of tropical America, although 
it is also endemic on the west coast of Africa, whence many think 
it was imported to America with the slaves. Its approximate 
distribution is shown in Fig. 12. In the past, before the days 
of the strict quarantine laws now enforced, serious epidemics of 
this dread disease appeared during the summer in numerous 
seaports of subtropical and temperate countries. At one time 

Fig. 12. Map showing geographic distribution of the yellow fever mosquito, 
Aedes calopus (black lines) , and former distribution of yellow fever (red stipple) . 

there was no city on the whole Atlantic and Gulf coasts of the 
United States which was exempt from yellow fever epidemics, and 
the disease exerted a serious influence on the economic conditions, 
especially of our Southern States. In New Orleans there have 
been epidemics which have cost thousands of lives, the last one 
occurring in 1905. In temperate cities the epidemics always 
ended with the coming of frost and destruction of the transmitting 
mosquitoes. Now the situation is quite different and there is 
no reason to believe that the world will ever again see such a sight 


as was formerly only too common — a frantic, terrorized city 
helpless in the grip of a deadly yellow fever epidemic. No epi- 
demic has occurred in the United States since 1905 and many 
of the tropical cities, such as Havana, Manaos and Rio de Janiero, 
which were formerly famous as endemic centers of the disease, 
and from which it was carried to seaports in all parts of the world, 
are now practically free from it. It is only in such notoriously 
unsanitary cities as Merida in Yucatan and Buenaventura in 
Colombia that yellow fever still rages, with little or no attempt 
on the part of the inhabitants to stamp it out. 

Nature of the Disease. — Our present knowledge of the nature 
of yellow fever and of its dissemination, which has made pos- 
sible the scientific checking of the disease and will undoubtedly 
result ultimately in its complete extermination, is largely the 
result of the noble and self-sacrificing work of the American 
Yellow Fever Commission appointed in 1900, consisting of Reed, 
Carroll, Lazear and Agramonte. Three of these illustrious men, 
Doctors Lazear, Reed and Carroll, lost their lives directly or 
indirectly as the result of their work, but their achievements are 
of inestimable value to the human race and their names will 
not soon be forgotten. The discovery by Noguchi of the organism 
causing the disease in 1918 has opened up new possibilities in the 
way of immunization. 

Yellow fever was shown by the American Commission to be 
not a contagious disease, but one which can be transmitted only 
by the yellow fever mosquito, Aedes calopus, or by injections of 
blood from an infected person. The organism causing the disease 
was discovered by Noguchi at Guayaquil in 1918, and was found 
to be a spirochsete-like organism closely related to, and very 
closely resembling, the spirochaete of infectious jaundice. It 
was named by Noguchi Leptospira icteroides. The organism can 
be found in the blood serum and also in the tissues of the liver, 
kidneys and other organs. It has been obtained in pure culture 
both from blood of patients and from inoculated animals. It is 
an extremely delicate filament varying in length from 4 to 9 m, and 
tapering gradually toward the extremities which end in immeas- 
urably thin sharp points. The filament is minutely wound at 
short and regular intervals, the length of each spiral measuring 
about one-fourth of a micron. The windings are so placed as to 


form a zigzag line by the alternate right angle change of direction 
of each consecutive spiral. The organism is smaller than that 
of infectious jaundice and is actively motile. 

Since the mosquitoes cannot transmit the disease by biting 
until 12 or 14 days after sucking infected blood the parasites 
evidently undergo a cycle of development in the mosquito. The 
appearance and habits of the yellow fever mosquito are described 
on page 443. 

The Disease. — Yellow fever has an incubation period of from 
three to six days. The first symptoms are severe headache and 
aches in the bones, followed by a sudden fever during which 
the face is flushed and swollen and the skin dry. This fever 
slowly subsides, and after three or four days there is a period 
of '' calm " during which the temperature is near normal but the 
pulse very slow. By the third day the skin usually becomes a 
characteristic yellow color, which, as the disease progresses, 
changes to a deep coffee brown. A striking but not invariable 
symptom, and one of ill omen, is the " black vomit," a gushing 
up through the oesophagus of a coffee-colored or even black fluid, 
consisting largely of fragments of red blood corpuscles and freed 
haemoglobin, and sometimes even pure blood. The period of 
" calm " may lead to recovery in a few days or there may be a 
second fever which lasts irregularly for a longer time than the first. 

Yellow fever is a very fatal disease. During the French oper- 
ations at Panama relay after relay of laborers were stricken 
with the yellow plague and were turned loose to die without mercy 
or help, to be replaced by a new set. Not only the laborers but 
the engineers, nurses and others were stricken down. One vessel 
is reported to have brought over 18 young French engineers, 
all but one of whom died of yellow fever within a month after 
their arrival. 

Fortunately yellow fever gives a permanent immunity after 
one attack has been successfully withstood. In children the 
disease is often very mild so that it is frequently not even recog- 
nized, yet the immunity it gives is permanent. Natural im- 
munity is unknown in any race, sex or age, though the negroes 
suffer less from the disease and have a much lower per cent of 
mortality than the whites. 

Treatment and Prevention. — Until the discovery of the or- 
ganism causing yellow fever by Noguchi and its isolation in pure 


culture, the treatment of yellow fever consisted only of careful 
nursing and in the maintenance of the best hygienic conditions: 
there are no drugs known which have any value as specifics 
against the disease. Recently, however, Noguchi and his fellow 
workers at the Rockefeller Institute have demonstrated the 
development of antibodies in animals and man inoculated with 
killed cultures of the leptospira, and from the results of vaccin- 
ation in guinea pigs, concluded that with the inoculation of a 
sufficient quantity of dead organisms they were rendered immune 
to subsequent infection. Distinctly encouraging results have been 
obtained from the vaccination of human beings. Of 8000 non- 
immune persons vaccinated in tropical America, excluding those 
exposed to the disease just before or immediately after vaccin- 
ation, no cases of yellow fever have developed, while among 
unvaccinated persons during the same period and in the same 
locality there have been about 700 cases of the disease. A thera- 
peutic serum has also been prepared for treatment of yellow fever. 
According to Noguchi persons treated with a sufficient quantity 
of the serum before the third day of illness have invariably re- 
covered. By the fourth day of illness the injuries to organs are 
so great as to be irreparable in severe cases. The usual 50 to 
60 per cent mortality from yellow fever was reduced to 9 per cent 
by the use of the serum, while still in an experimental state. 

The eradication of yellow fever consists largely in the applic- 
ation of sanitary measures to exterminate the yellow fever mos- 
quito Aedes calopus, but in the face of an epidemic this can now 
be supplemented by vaccination to cut off the supply of non- 
immunes from infected mosquitoes. According to Noguchi a 
threatening epidemic in Central America in 1920 is reported to 
have been checked by these methods within a month, i.e., before 
the development of the second set of cases. The value of im- 
munization as an emergency measure does not, however, mini- 
mize the importance of anti-mosquito campaigns, since the elimin- 
ation of both factors — non-immune human beings and infected 
mosquitoes — is necessary for the eradication of yellow fever. The 
habits of the mosquito, as described on p. 444, are such that it is not 
difficult to combat and successful campaigns against it, with a re- 
sultant obliteration of yellow fever, have been made in many places. 
Panama, Havana, Rio de Janiero, and recently Manaos and 


Yquitos, are conspicuous examples of tropical cities which have 
been cleared of the disease which once made them highly dangerous 
to visitors and a menace to the rest of the world. In connection 
with an incessant war on the transmitting mosquito in all stages 
of its life history, all known or suspected cases of yellow fever 
should be carefully screened so that mosquitoes can have no access 
to them. 

Rat-bite Fever 

In many parts of the world, especially in Japan, there occurs a 
disease which follows a rat bite, and is therefore known as " rat- 
bite fever." It has been reported from various localities in the 
United States. Some inflammation occurs at the place of the 
bite and the neighboring lymph glands swell up. After several 
weeks a high fever ensues, preceded by chills and headache. 
The apparently healed rat bites become inflamed and there is 
usually a red rash which spreads all over the body. In from three 
to seven days the fever subsides but it recurs, usually within 
a week, with similar symptoms, and the rash is more constantly 
present than in the first attack. In some cases there are still 
more relapses. 

The similarity of the disease to such spirochsete diseases as the 
relapsing fevers is obvious, and its spirochsete nature was long 
suspected by Japanese physicians, especially when they found 
salvarsan to be effective in its treatment. Within the past 
few years some Japanese physicians (Futaki, Takaki, Taniguchi 
and Osumi) discovered in seven out of eight patients numerous 
actively moving spirochsetes in the broken-out skin and in swollen 
l3anph glands. Animals were successfully inoculated with the 
disease by means of bits of skin tissue and blood containing spiro- 
chsetes. The organism, which has been named Spirochceta morsus 
muris, is described as being an actively moving animal, larger 
than Sp. pallida of syphilis, but smaller than the relapsing fever 
spirochsetes. It is rather short and thick with an attenuated 
portion or flagellum at each end. Long spirochsetes, at first 
thought to be specifically distinct from the short thick forms, 
also are found in human infections. According to Kaneko and 
Okuda these are probably degenerate forms resulting from the 
action of antibodies. 

The Japanese investigators have been unable to find the spiro- 

73a spirochetes 

chaete in the saliva of infected rats or of other rodents, but only 
in their blood. From this the conclusion has been drawn that 
the source of infection in a rat bite is blood from hemorrhages 
of the gums or tongue which contaminates the teeth. 

Both mercury and salvarsan are effective in the treatment of 
this disease as of most other spirochsete diseases. 

Attention should be called to the fact that rat bites may often 
give rise to diseases which may be of quite different nature from 
the " rat-bite fever " described above. It is well known that 
many different infective organisms live in the mouth and around 
the teeth of such animals as rats, and it is not surprising that 
infections of divers kinds may result from rat bites, and that 
these infections should have been confused with typical rat-bite 
fever. Several investigators have described a vegetable organ- 
ism, Streptothrix, as the cause of rat-bite fever. Recently Ruth 
Tunnicliff has shown that a form of pneumonia in rats is pro- 
duced by a Streptothrix very similar to, if not identical with, that 
described in some cases of rat-bite fever. It is very probable 
that these cases were really infections with the pneumonia-caus- 
ing organism, and quite distinct from the Japanese disease. 

Other Spirochsete Diseases 

Spirochsetes, often in association with bacteria of various kinds, 
have been found in a number of other human diseases, and are 
in all probability at least partially the cause of them. 

The common spirochsete, Sp. huccalis, which lives about the 
gums and roots of the teeth in almost all human mouths is 
thought by some investigators to be entirely harmless, living 
only on waste matter. By others it is thought to become 
pathogenic under some circumstances, and, in partnership with 
certain cigar-shaped bacteria, to be the cause of Vincent's angina, 
a diphtheria-like ulceration of the tonsils and throat; of noma, 
an ulceration of the mouth cavity and cheeks; of ulcerations of 
the nose, teeth and lungs; and of balanitis, an ulceration of the 
genital organs which may occur after unnatural sexual relations. 
In central America there is a common disease " mal de boca " 
(disease of the mouth) which is marked by swollen, spongy and 
tender gums over which a whitish pellicle forms. It is infectious 
and is probably caused by a delicate spirochsete found on the 


lesions. Some workers believe that some or all of these auctions 
are due to difterent species of spirochsetes and bacteria, but the 
fact that both organisms are found together in all these diseases, 
and that they show only such slight differences from the organ- 
isms in the mouth as would be expected under altered conditions, 
makes it seem quite possible that Spirochceta huccalis and its con- 
stant companion, a cigar-shaped bacterium, are the causes of 
all of them. The conditions which seem to favor the growth and 
disease-producing propensities of these organisms are heat, 
moisture, filth and absence of air. Wherever these conditions 
prevail, and these ordinarily harmless organisms can get a foot- 
hold, sores and ulceration are likely to result, accompanied by 
more or less fever and digestive disturbance due to absorption 
of poisonous substances from the decaying tissues. 

The treatment of these affections must vary with their location. 
For the sores on the tonsils or mouth cavity in Vincent's angina or 
noma either salvarsan or silver nitrate is effective. It should be 
daubed on the injured tissue with a piece of cotton. The silver 
nitrate is less dangerous than salvarsan and equally effective for 
these superficial ulcers. Treatment of the infected parts with 
a two per cent solution of silver nitrate for a few days results in 
a rapid healing. In case of balanitis, ordinary cleanliness and 
exposure to air is sufficient to cause a spontaneous healing in 
four or five days. Washing with hydrogen peroxide, which 
liberates oxygen in the presence of organic matter, is very de- 
structive to such organisms as these, which thrive best in the 
absence of air. 

In the Sudan region of Africa, and also in Colombia, South 
America, there is found a certain type of bronchitis, marked by 
fever and often by hemorrhages along the respiratory tubes, 
which is accompanied by the spirochse, . Sp. hronchialis. This 
parasite has very slender pointed ends, and averages eight to 
nine fj, (^^jViy of a,n inch) in length, but its most marked charac- 
teristic is its variability. These spirochsetes reproduce by the 
peculiar method of *' granule shedding," breaking up into tiny 
round bodies which later develop into new spirochsetes. It is 
probable that these little particles of living matter can resist 
drying up in air, especially in humid atmospheres, and may there- 
fore be transmitted with dust or with little droplets of moisture 
propelled by coughing. 


Tropical Ulcer. — Still another human disease that has been 
attributed to spirochsetes is tropical ulcer, also known by the 
more impressive name, " tropical sloughing phagedsena." This 
is a type of sore on the skin, most commonly of the leg, which 
originates either in some slight abrasion of 
the skin or in some preexisting wound or 
sore, especially in persons debilitated by 
some other disease or by alcohol. It begins 
in a tiny blister which soon bursts, and the 
sore thus exposed spreads very rapidly, con- 
stantly sloughing a yellowish, moist and 
exceedingly fetid matter. After a few days, 

Fig. 13. Tropical ulcer. , -i ,-, • ,'^^ ■,• ,, . 

(Drawn from photo by while the sore IS Still spreadmg, the center 
Haiberstadter in KoUe of the slough begins to liquefy and is grad- 
and Wassermann.) ^^^^^ sloughed off and heals. Usually the 

ulceration confines itsQlf to the skin but sometimes it goes deep 
into the muscles, nerves and bloodvessels, even injuring the 
bones and joints. Sometimes permanent deformity or even 
death results from these extensive excavations, death resulting 
especially from the opening of some large bloodvessel. 

Tropical ulcer occurs in nearly all hot damp tropical countries. 
Although not definitely proved, it is usually accepted that the 
spirochsetes, Spirochoeta schaudinni, which can almost always be 
found in the ulcers, together with cigar-shaped bacteria found in 
association with them, are the ringleaders in producing it. The 
treatment usually recommended is a thorough cauterization of 
the sore, followed by antiseptic washes and applications. Sal- 
varsan and other arsenic compounds have been found beneficial 
in many cases. Finocchiaro and Migliano in Brazil claim to 
have found a specific cure for this loathsome disease in an appli- 
cation of powdered permanganate of potash or in a compress of a 
one to ten solution of this substance. They achieved a complete 
cure in from ten to thirty days in every one of seven cases. 

Ulcerating Granuloma. — Of a somewhat similar nature to 
tropical ulcer, and of wide distribution in the tropics, is '' ulcerating 
granuloma of the pudenda," a sore which spreads, very slowly 
however, over the external genitals and along the moist folds 
of skin in neighboring regions. Both spirochsetes and bacteria 
have been found deeply situated in the tissues at the bases of 
these sores, but to what extent either or both are responsible for 


the condition is not known. The disease is pecuHar in being 
very refractory to treatment by any of the usual methods of 
cauterization or appUcation of drugs. Recently, however, it 
has been found to succumb to X-ray treatment, and this method 
is now extensively employed. A.ragao and Vianna in Brazil 
and Breinl and Priestley in Australia have obtained excellent 
results from intravenous injections of tartar emetic. 

Japanese Seven-Day Fever. — A number of Japanese workers 
have recently described this disease as resembling infectious 
jaundice but usually without the occurrence of jaundice. It has 
a fairly wide distribution in Japan among field workers. A 
spirochaete morphologically indistinguishable from Leptospira ic- 
ier ohcemorrhagice, but distinct in its immune reactions, has been 
found in blood and urine of human cases, and in inoculated 
animals. The organism was named Spirochceta hebdomadis, but 
if related to the organism of infectious jaundice should be called 
Leptospira hehdomadis. A spirochaete believed to be identical 
with this was found in the field mouse, Microtus montehelli, 
and the Japanese believe that this mouse acts as a reservoir for 
the disease as does the rat for infectious jaundice. 

Other Spirochaetes. — Spirochsetes have been found in con- 
nection with still other human afflictions, and it is possible that 
they may be the cause of them. In most cases, however, it is 
more probable that spirochsetes which are normally harmless and 
Hve only on dead matter find congenial surroundings in tissues 
diseased by some other cause, and that this accounts for their 
presence. Often, however, such ordinarily harmless spirochajtes 
may change their habits under suitable conditions and become 
pathogenic, thus aggravating the diseased condition. The patho- 
genic propensities of spirochsetes have been demonstrated in so 
many cases, however, that they may rightly be looked upon as 
one of the most destructive groups of human parasites. 



Leishman Bodies in General. — While investigating the cause 
of a deadly disease of tropical India known to the natives as 
kala-azar or dumdum fever, Leishman, in 1903, and at about the 
same time, Donovan, discovered in the spleen of victims numerous 
little round parasites. These looked to Leishman exactly like the 
non-flagellated stage of a trypanosome (see Chapter VI), and he 
naturally took them to be developmental stages of trypanosomes, 
and added another terrible disease to the credit of those murder- 
ous animals. Later, however, it was found that while these little 
round organisms resemble a certain stage in the life history of a 
trypanosome, yet they never reach this fully developed form. 
Nevertheless it was discovered that when transferred to the in- 
testine of certain insects, or when grown on artificial cultures, 
they undergo a wonderful transformation. They become elon- 
gate in form and develop a waving flagellum, assuming what is 
known as a *' Herpetomonas " form (see Fig. 14L), and they move 
about so actively that it is difficult to believe that they are really 
transformed from the un-animal-like round bodies found in 
diseased human bodies. Such flagellates, under the name " Lep- 
tomonas " or " Herpetomonas/^ had been known before, and were 
recognized as common parasites of insects, belonging to a primi- 
tive group of the class Flagellata. They were also known to 
present, during their development, this unflagellated round 
condition, but always in the bodies of insects. Here was a 
vicious form of the parasite which was not content with life in an 
insect, but must adapt itself to live in the bodies of warm-blooded 
animals. There is reason to believe that some of the flagellates 
which normally live exclusively in the intestines of blood-sucking 
insects have the power, if injected into warm-blooded animals, 
to adapt themselves to the conditions they find there, causing 
more or less local inflammation and sores. In Panama, for 
instance, sporadic cases of sores occur in which are found Leish- 



man bodies in small numbers, resulting from the bite of horse- 
flies (Tabanidae) of various species. There is every reason to 
believe that the parasites in these sores are normally parasitic 
in the insects only, but are able to adapt themselves to their new 
environment in human flesh and to multiply there for a time. 
They are permanently sidetracked, however, and have no further 
chance of completing their life history or of reaching new hosts, 
unless a suitable fly should, by some infinitesimally small chance, 
suck blood from the sore in which they were developing, and thus 
rescue them. 

Several investigators have recently shown that a number of 
typical insect flagellates, if injected into mice and rats or other 
mammals, or even birds, may become pathogenic and even 
cause the death of the animal. That the well-established Leish- 
mania diseases of man and other animals originated from insect 
flagellates can hardly be doubted, but it is possible that in some 
cases the parasites may have adapted themselves to their new 
type of host to such an extent as to have become quite independ- 
ent of the insects from which they originated. Fantham suggests 
that all forms of Leishmania and Herpetomonas may be mere 
physiological races of a single species which is variously adapted 
to live in a variety of different hosts, and perhaps able to adapt 
itself anew to unaccustomed hosts under certain conditions. 

Leishmania and Herpetomonas belong to a group of the class 
Flagellata known as the Hsemoflagellata. This group presents 
a series of forms from the simple Leishmania, which at times is 
a non-motile, unflagellated organism, through the increasingly 
highly developed Herpetomonas and Crithidia to the trypano- 
somes (see Fig. 18). Some reach only the Herpetomonas stage as 
adults, others only the Crithidia stage, while others pass through 
the entire series of developmental stages and reach the final 
trypanosome stage. All of them are probably primarily parasites 
of the guts of insects or other invertebrates, and only compara- 
tively few of them have adapted themselves to spending part 
of their existence in the blood or tissues of vertebrates. Ap- 
parently only the Leishmania and trypanosome forms are 
adapted for existence in vertebrates, since the other forms are 
not found in them, except in rare instances when Herpetomonas 
forms are found in the blood of Le^^s/imama-infected individuals. 
A number of species have become thoroughly adapted to life in 


vertebrates and are now normal parasites of them, and others, 
as already shown, if accidentally introduced may be able to 
multiply sufficiently to cause local or temporary sores, or even a 
fatal infection. 

All the species of hsemoflagellates which normally live in warm- 
blooded animals in the form of Leishman bodies are grouped 
together in the genus Leishmania. A number of human diseases 
are known to be caused by them. Kala-azar of southern Asia, 
already mentioned, is the most severe one. A similar disease, 
infantile kala-azar, occurs around the Mediterranean, especially 
in children. There are also a number of Leishmanian diseases 
which, instead of causing constitutional disturbances, cause sores 
or ulcers on the skin or mucous membrane. One type, oriental 
sore, also called by various local names, is widespread throughout 
many tropical countries, especially southern Asia and around the 
eastern end of the Mediterranean, and possibly in tropical South 
America. It causes temporary sores on the skin, chiefly of the 
exposed parts of the body; the sores may or may not ulcerate. 
In South America there occurs a much more vicious type of 
the disease in which the skin sores are followed by ulcers spreading 
over extensive areas of the mucous membranes of nose and mouth, 
often resulting fatally. A parasite, Aphthomonas infestans, be- 
lieved to be aUied to Leishmania, has recently been described by 
Stauffacher as the cause of foot-and-mouth disease. 

The clinical manifestations of these ulcers and sores on the skin 
or mucous membranes are extremely variable and indicate the 
possibility of there being a number of different species or at least 
varieties of Leishmania causing them. There are some parasi- 
tologists who believe that all the different kinds of Leishmani- 
asis — internal, cutaneous or mucosal — are caused by different 
strains of the same species, while others believe in the existence 
of several species. Usually four species are recognized, as fol- 
lows: Leishmania donovani, causing kala-azar; L. infantum, 
causing infantile leishmaniasis; L. tropica, causing cutaneous 
sores; and L. americana (hrasiliensis) , causing sores or ulcers of 
long duration on the skin and mucous membranes. However, 
until we are familiar with the adult forms of all the various types 
of Leishmania, and know more about their life histories, we can 
only guess at their classification. 



About 1870 there began a great epidemic of a strange and 
deadly disease in Assam, India, which spread up through the 
Brahmaputra Valley. It was believed to have been imported 
by the British from Rangpur, where a similar epidemic had been 
raging for some time before. Whole villages and settlements 
were depopulated and the country was terrorized by the '' black 
sickness." It is said that victims of the disease were driven out 
of the villages, sometimes being made unconscious with drink, 
taken into the jungle, and. burnt to death. Some villages com- 
pletely isolated themselves from the outside world, and still 
others were entirely deserted for new and uninfected districts. 
The natives were most severely affected, no doubt due both to 
their filthiness and unsanitary habits and to their weak con- 
dition as the result of almost universal malaria ^ .1 hookworm. 
Before the true nature of the disease was discovered it was usu- 
ally diagnosed as ''severe malaria"; one physician concluded 
that it was excessive hookworm infection, since he found hook- 
worms almost universally present in kala-azar sufferers. 

This Assam epidemic, which lasted for many years, is the only 
recent case of a great epidemic of kala-azar, although the disease 
now occurs endemically in many parts of India and Southern 
China, and is spreading in the Sudan region of North Africa. 
It has been pointed out that the endemic parts of China, chiefly 
along the north bank of the Yangtse River and its tributaries, 
correspond closely in latitude and climate to a considerable part, 
of southern United States, and since kala-azar is believed by some 
to be spread by bedbugs and perhaps other vermin, there is danger 
that once introduced it might become endemic in America. 
A single case has been found in Brazil, contracted in a region 
where another form of Leishmaniasis is prevalent. How this 
case should be explained is difficult to know. 

Transmission. — In spite of numerous experimental investiga- 
tions to discover the mode of transmission of the kala-azar para- 
site, Leishmania donovani, the question is still obscure. Captain 
Patton, of the British Medical Service in India, adduced some 
evidence that the common Indian bedbug, Cimex hemipterus 
{rotundatus) J is the normal intermediate host and transmitter 
of kala-azar. Using laboratory-bred bugs, Patton succeeded in 


getting abundant growths of the parasites in the intestines of 
the bugs after they had been fed on infected blood. When 
sucked up by the bugs, the Leishmania-laiden cells in the blood are 
digested and the parasites set at liberty in the stomach. Here 
after several days they begin to go through their remarkable 
transformations and active flagellated Herpetomonas forms de- 
velop similar to those which occur in artificial cultures (Fig. 14, 
F to 0). After several days of free active life the parasites 
round up again, lose their flagella, and are then presumably 
ready for inoculation into a new host. All these changes occur 
during a period of 12 days. Patton has not, however, shown 
that the bedbug is capable of transmitting the parasites to other 
victims by means of its bites, though it is possible that scratching 
of the bites and crushing of the bugs might cause infection. 
Developmental stages have also been traced in the mosquito. 
Anopheles punctipennis, but here again there is no proof of the 
insect's method or power of transmitting the parasites to new 
hosts. The facts connected with the spread of the disease in 
India seem to favor the theory of transmission by a household 
insect. Rarity of the parasites in the circulating blood has been 
claimed as an argument against the insect transmission theory, 
but Patton has shown that almost every smear of blood from an 
infected person contains white blood corpuscles with the Leish- 
man bodies in them. On the other hand the manner of spreading 
of the disease in Sudan is rather opposed to a theory of insect 
transmission, and it has been suggested that infection may take 
place through the medium of contaminated water or food, since 
experimental animals occasionally become infected when fed on 
infected material. The suggestion is also made that an intestinal 
wound of some kind may be necessary to allow the entrance of 
parasites into the blood and organs of the body. Bodies re- 
sembling Leishman bodies have been found in the faeces of in- 
fected persons, so that faeces may in some way have to do with 
the transmission of the parasites. The difficulty experienced in 
inoculating the disease into experimental animals makes the 
investigation of its transmission very difficult. The parasites 
develop readily in artificial cultures at relatively low tempera- 
tures, presenting the series of changes shown in Fig. 14. These 
forms are practically identical with those found by Patton in the 
intestine of the bedbug and undoubtedly represent part, at least, 



of a possible cycle in an insect host. That this phase of the 
life history of the parasite may normally be omitted is never- 
theless quite possible. 

Human Cycle. — After entering the human body, the para- 
sites probably utilize the blood and lymph streams to obtain 
transportation to all parts of the body, but do not live free in 

Fig. 14. Parasites of kala-azar, Leishmania donovani; A, isolated parasites 
from spleen; B, dividing forms from liver and bone marrow; C, spleen cell with 
parasites; Z), group of cells with parasites; E, parasite ingested by leucocyte; F-0, 
from cultures; F and G, early stages after ingestion; H, large dividing forms; /, 
development of flagellum; J, small flagellated form; K and L, flagellated Herpe- 
tomonas forms; M and A^, unequal division; 0, parasites resulting from unequsU 
division shown in M and A^". X about 1500. (After Leishman.) 


the body fluids. They enter the deUcate endothehal cells which 
Hne the blood and lymph vessels, and also the cells of the spleen, 
liver and lymph glands. Within the cell they have entered 
they grow and multiply rapidly (Fig. 14C and D). The indi- 
vidual parasites (Fig. 14A) are exceedingly small, about two ii 
(less than 7^7^ of an inch) to four /^ in diameter. They are 
round or oval in form with a large nucleus and a smaller para- 
basal body shaped like a little rod and set more or less at a tan- 
gent to the nucleus. 

In a short time, by dividing and re-dividing, the Leishman 
bodies completely fill the cell they inhabit, causing it to enlarge to 
many times its normal size (Fig. 14C). There may be as many 
as several hundred parasites in a single enlarged cell. The 
parasitized endothelial cells often seem to " run amuck," breaking 
loose from their normal position on the lining of bloodvessels 
and becoming free-living carnivorous cells like the white blood 
corpuscles. When these parasite-filled cells finally burst, the 
liberated parasites enter new cells, or are gobbled up by the 
white blood corpuscles (Fig. 14E). It is probable that the para- 
sites are ingested by bedbugs while inside free endothehal cells 
or white corpuscles in the blood. 

The Disease. — The incubation period of kala-azar after in- 
fection is not definitely known, but Manson cites one case where 
an Englishman was attacked by a fever, which terminated in 
kala-azar, within ten days after arriving in an endemic locality. 

A high fever usually marks the onset of the disease, and this 
persists more or less irregularly for several weeks. Meanwhile 
the spleen and liver enlarge enormously, increasing and decreas- 
ing with the fluctuations of the fever. After several weeks the 
fever drops and the patient becomes almost normal for some 
time, only to be attacked by the fever again, with an enlargement 
of spleen and liver. These remittent attacks gradually dwindle 
to the steady low fever, accompanied by sweating spells, rheu- 
matism-like aches, high pulse rate, anemia and a general wasting 
away, with the skin often a dark earthen color. Dysenteric 
symptoms, with discharges of blood and mucus, are common, 
especially in the late stages of the disease, and frequently after 
death the intestine is found to be extensively ulcerated, with 
numerous parasites in the walls of the ulcers. Parasites are 
usually found most abundantly in the spleen, liver capillaries, 


bone marrow and lymph glands. When the chronic condition 
is reached the patient presents an appearance not unlike that 
resulting from chronic malaria, and it is little wonder that the 
diseases were long confused. Usually complication by some 
other disease, especially dysentery, which gets a severe hold on 
account of the low vitality of the victim, causes death (accord- 
ing to Rogers in 96 per cent of cases), but in a relatively small 
per cent of cases there is recovery. A steady gain in weight, 
however slight, is said by Mackie to be a fairly accurate sign of 

Treatment. — Within the past few years (1914-1921) the 
remarkable destructive effect of antimony, especially in the form 
of tartar emetic, on Leishman bodies has been thoroughly es- 
tablished. Tartar emetic as a cure for Leishmanian diseases 
was first tried out in 1912 with astonishing success by Vianna, 
a Brazilian investigator, on the Leishmanian ulcers of the face 
and nasal mucosa. Similar treatment has been applied with 
equal success to oriental sores and to infantile kala-azar. Its 
application to the more severe Indian kala-azar has been attended 
with great success, and even advanced stages of the disease can 
sometimes be cured by its use. Rogers and Hume have used 
it extensively in India. Injections of metallic antimony have 
also been found of great benefit in treatment of this disease. 

The usual method of giving tartar emetic is by injections into 
the veins, as in trypanosome diseases. From one to ten cc. of a 
one per cent solution is given, the dose being gradually increased 
in accordance with the age and tolerance of the patient. The 
drug is a powerful one, and if given in over-doses may cause 
severe disturbances of the digestive tract and of the kidneys, but. 
if it is given in small quantities to begin with, and its effects 
carefully watched as the doses are increased, it can be used with- 
out danger and constitutes a treatment as specific in its effects 
as is quinine on malarial parasites, or salvarsan on spirochsetes. 

Prevention. — On account of the uncertainty which exists con- 
cerning the mode of transmission of kala-azar, victims of the 
disease and those who have closely associated with them should 
be quarantined and their houses thoroughly disinfected to kill 
any bedbugs or other vermin, as well as any Leishman bodies 
which might exist in any body excretions. The safest method 
in the case of the native huts which are hopelessly filthy and 


unsanitary is to burn them with all their junk. This method of 
stamping out the disease before it has had time to spread has 
been successfully used on some of the tea estates in Assam. 
For the successful prevention of the spread of the disease, an 
isolation of 300 to 400 yards has been found sufficient, a fact 
which exonerates most flying insects as transmitters. Houses in 
endemic regions should be kept scrupulously free from bedbugs, 
and any place where bugs might be acquired should be care- 
fully avoided. 

Since the parasites have been shown to exist in the faeces of 
infected persons, careful and thorough disposal of the faeces 
should be attended to. The possibility exists that non-blood- 
sucking flies which frequent human faeces may be instrumental 
in spreading infection. Until proved otherwise, precautions 
against this should be taken in endemic places. 

Infantile Kala-azar 

In many of the countries bordering the Mediterranean — Algeria, 
Tunis, Malta, Crete, Greece, southern Italy, Sicily, Spain and 
other regions — there occurs a disease which in many respects 
closely resembles true kala-azar, but differs from it very strikingly 
in other ways. While true kala-azar attacks young and old 
alike, the Mediterranean disease attacks infants and children 
almost if not quite exclusively. Children between one and two 
years old are most frequently subject to it, while children over 
six years old are practically exempt. While true kala-azar is 
not readily communicable to other animals than man, the Medi- 
terranean disease occurs naturally in the dogs of endemic regions 
and in some places where the disease is not known to occur in 
children. It can be experimentally transmitted not only to 
dogs but also to rats, mice and, with more difficulty, to monkeys. 
Cats cannot be successfully inoculated. It is believed by some 
that the disease in dogs is different from that in children, but the 
similarity in symptoms, and geographic distribution, as well as 
the fact that dogs can be infected by parasites from human 
beings, and other dogs from these dogs, all point to the identity 
of the diseases. 

Transmission. — A remarkable fact connected with artificial 
inoculation of the disease is the great quantity of infective ma- 


terial which is necessary to produce infection. Injection of 
infected material under the skin does not transmit the disease, 
although in nature this is probably the mode of transmission. 
Evidently, then, the natural means of transmission must be by 
more powerful or virulent parasites than can be obtained from 
already infected animals. The common opinion is that the dog 
flea, Ctenocephalus cams (see p. 416), is the usual transmitting 
agent, and that this insect serves as an intermediate host for the 
parasites. This opinion is based on the fact that parasites ap- 
parently identical with those in infected children have been 
found in the tissues and faeces of fleas. Brumpt, however, be- 
lieves that there has been confusion with an apparently harmless 
flagellate which is frequent in fleas even where infantile kala-azar 
does not occur. Patton suggests that the kala-azar of dogs may 
really be an infection quite distinct from the infantile disease and 
caused by infection with the common intestinal flagellate of fleas, 
Herpetomonas ctenocephali. The possibility that the human dis- 
ease may also be caused by this flagellate seems to have been 
overlooked; the fact that the fleas do not readily become in- 
fected from sucking an infected child does not necessarily argue 
against the origin of the human parasites from fleas. Recent 
work by da Silva and Spagnolio in attempting to infect fleas by 
allowing them to feed on a naturally infected child has been un- 
successful. They fed 25 fleas on an advanced case of the disease 
and secured no infection of the fleas in 484 feeds. These authors 
do not believe in the relation of fleas to infantile kala-azar, and 
point out that the disease is at its height in the spring before 
fleas have become very abundant. 

Infection of bedbugs with Leishmania infantum is not suc- 
cessful. If fleas do serve as the usual transmitting agents, it is 
probable that after development in the flea the Leishman bodies, 
as suggested above, become more resistant and are able to establish 
themselves in situations where they would otherwise be destroyed 
before they had a chance to multiply and adapt themselves. 

Since so many dogs around the Mediterranean are infected, 
although only a small number give any indication of it, they 
probably serve as a reservoir for the disease. Not infrequently 
children attacked by kala-azar have been known to have played 
with diseased dogs, and it is easy to see how the fleas which 
almost always infest dogs in these regions could infect children. 


The Disease. — The disease is much Hke true kala-azar in 
most of its chnical manifestations, though differing in details. 
It is characterized by fever, aches and anemia, and by excessive 
enlargement of the spleen, the liver also enlarging somewhat. 
Though in some places comparatively mild, in others it is ex- 
tremely fatal. Recovery is rarer the younger the patient; in 130 
cases reported from Palermo and Naples, 93 per cent of the chil- 
dren under two years old succumbed to it, while 87 per cent of 
the older children died. Similar high mortality has been re- 
ported in other parts of Italy. 

Usually after recovery from a single attack immunity is given, 
almost always lasting until the susceptible age is passed. 

Treatment and Prevention. — Wonderfully successful results 
have been obtained in the treatment of infantile kala-azar with 
tartar emetic as described on page 81. Of eight children treated 
with tartar emetic in Italy, all of whom were between five and 
27 months old, except one boy of six years, seven recovered com- 
pletely. In the last stages of the disease the vitality is so weak- 
ened that recovery is impossible even with the destruction of all 
the parasites. 

Prevention obviously lies in keeping infected dogs away from 
children. In endemic regions dogs should be kept scrupulously 
free from fleas, and all dogs showing the slightest symptoms of 
feverishness, enlarged spleen or emaciation should be killed, and 
their bodies burned to destroy fleas. Even if this were done it 
would not be sufficient to stamp out the disease completely, since 
so many dogs carry the infection in latent condition, serving as 
a reservoir for it without showing any appreciable symptoms. 
Basile showed the value of attacking the disease in dogs by de- 
stroying all obviously infected dogs in a certain township in 
Italy. In the year the dogs were destroyed there were seven 
new cases of the disease in children in a population of 2000, but 
in the following year not a single new case appeared, and in the 
year after only one. 

Oriental Sore 

One of the commonest sights in many tropical cities, particu- 
larly in the cities of the eastern Mediterranean region and south- 
western Asia, is the great number of children, usually under three 
years of age, who have on the exposed parts of their bodies un- 



sightly ulcerating sores, upon which swarms of flies are constantly- 
feeding. The exudations from such sores are teeming with Leish- 
man bodies, Leishmania tropica (Fig. 15A and B), which very 
closely resemble those of kala-azar. In some cities infection by 
these parasites is so com- 
mon and so inevitable 
that normal children are 
expected to have the dis- 
ease and visitors to the 
cities seldom escape a 
sore as a souvenir, even 
if present for only a short 
time. In Bagdad, Wenyon 
has shown that almost as 
soon as the children are 
relieved of the wrappings 
in which they are covered 
as babies, and allowed to 
run free and play in the 
streets, they are almost 
certain of infection. Since 
one attack gives immu- 
nity, oriental sores ap- Fig. 15. Parasites of oriental sore (Lm/imanMi 

pearing on an adult person [''''^''^^ ' /^' ^^ ^J"^ ^' parasites from sore, the 
. 1 1 . torpedo-shaped forms (A) being found outside 

m Bagdad brands him as the cells, the others (B and C) within the cells; 
a new arrival, and the D Herpetomonas form taken from bedbug 48 

hours after feeding on sore; E, the same, dividing 
same is undoubtedly true form. X 4000. (After Wenyon.) 

in many other tropical 

cities. The disease is prevalent from India through Persia, Syria 
and Arabia and along the south shore of the Mediterranean as 
far as Morocco. True oriental sore probably occurs commonly 
in many cities of tropical South America, though here it is ob- 
viously difficult to distinguish it from the skin sores of espundia. 
Transmission. — Though oriental sores may appear at any time 
of the year, they are particularly abundant in the autumn months 
in most cities of the Old World. Since the usual time of the 
appearance of the sore, as nearly as can be judged, is about two 
months after infection, though sometimes much less and often 
much longer than this, infection must usually occur during the 
hot mid-summer months. This fact suggests the probability of 


the parasites being transmitted by some biting insect which 
appears during this season. There can be no doubt that the 
myriads of flies which collect on the sores must mechanically 
carry the parasites in many cases from infected individuals and 
deposit them on wounds or cuts of others where they gain access 
to the body. It may be that one or more kinds of insects act as 
intermediate hosts; in fact, it has been claimed that in India the 
bedbug is an intermediate host for this as well as for the kala-azar 
parasite. In Teheran, where a large proportion of the dogs (in 
one case 15 out of 21 street dogs) show Leishmanian sores, the 
parasites have been found in the gut of a fly, Hippohosca canina, 
common on the dogs. Camels and horses are also subject to 
infection in some places. A number of French workers in North 
Africa have suggested that the sandfly, Phlehotomus minutus, 
which is very abundant there, is the transmitter of the disease 
and that the common Algerian gecko, Tarentola mauritanica, 
may play the role of a reservoir for the disease. The sandflies 
swarm about the lizards in large numbers, and also bite man 
readily. Leishman bodies have been found in the blood of a 
number of geckos near Tunis. On the western face of the Andes 
in Peru there occurs a similar disease known as uta, which has been 
shown by Townsend, of the U. S. Bureau of Entomology, to 
develop in the intestine of two little gnats, Forcipomyia utce and 
Fordpomyia townsendi, very closely allied to the American 
" punkies." Inoculation of the gut contents of these insects into 
guinea-pigs produces sores believed to be identical with uta, and 
Townsend believes the insects transmit the disease in nature by 
voiding the Leishman bodies from the anus while sucking blood, 
the puncture being contaminated in this way. Whether this dis- 
ease is a very mild form of espundia, described below, or is more 
closely allied to true oriental sore, is difficult to say. According 
to the description given by Dr. Strong and his colleagues of the 
Harvard expedition to Peru, uta is not so mild, and may attack 
the mucous membranes as does espundia. Possibly both diseases 
occur there. Dr. Strong has pointed out that the flagellated 
stage of the uta parasite differs from that of other Leishmania 
in possessing a basal granule in addition to the nucleus and para- 
basal body. 

The Disease. — Although oriental sore often has a long incu- 
bation period, and produces such profound constitutional changes 


as to build up an immunity which is usually effective for life, 
the general symptoms are so mild as to be usually unnoticed. 
Slight fevers and general malaise are frequent at all times in 
tropical countries, and it would be extremely difficult to connect 
such non-characteristic symptoms with a sore appearing perhaps 
months afterward. There is some evidence, however, that at 
least in some cases fevers do occur which are attributable to the 
parasites of oriental sore. 

The nature and course of the sores vary to some extent in 
different locaUties. The sore usually begins as a small dark pimple 
which causes very slight itching and little if any inflammation of 
the surrounding skin. The pimple grows slowly and develops in 
one of two ways, forming either an ulcerating or a non-ulcerating 
sore, more popularly known as female and male sores respectively. 
In the former type, under a flaky scab which soon falls away or is 
scratched off, there develops a shallow ulcer exuding a foul-smell- 
ing yellow fluid. Usually the sore covers an area about the size 
of a dollar, the older portion often healing while the ulcer is still 
extending in another direction. The surface of the ulcer is 
covered by red granulations which bleed readily. In most lo- 
calities these ulcers are not painful, but those occurring along 
the eastern slope of the Andes in Peru and Bolivia are said to be 
very painful. 

The non-ulcerating or male sores grow slowly and develop a 
covering of white flaky scales over a thin red skin, below which is 
a mass of red granulations where the parasites may be found in 
large numbers. The non-ulcerating sores sometimes break down 
and ulcerate, but usually grow to about the same size as do the 
" female " sores, and then gradually shrink, finally healing as 
do the others. 

The sores, of either kind, nearly always occur on exposed parts 
of the body, as the face, neck, arms or legs. Occasionally they 
occur on the lips or edges of the nose and spread to the mucous 
membranes, but this must not be confused with the mucous 
membrane ulcerations of American leishmaniasis. A single sore 
is the most common condition, but secondary sores sometimes 
develop in its vicinity, and sometimes a great many sores may 
occur on an individual. In the Peruvian uta several sores seem 
to be the rule, these occurring at the sites of the bites of gnats 
and possibly other insects. 


The sores usually last for a year, more or less, gradually healing 
over, but leaving permanent scars. The uta sores of the Peru- 
vian Andes, which have a much shorter incubation period, may 
run their course and heal in much less time, according to Town- 
send in as short a time as 15 days. Except in rare cases, after 
an oriental sore has once run its course and healed a person is 
permanently immune to any further attacks. 

Treatment and Prevention. — The use of tartar emetic as a 
cure for oriental sores is as productive of good results as it is in 
the case of other Leishmanian infections. With the usual one per 
cent or two per cent solutions of this drug injected into the veins 
the sores yield promptly and, if treated at an early stage, can be 
prevented from leaving scars. 

In badly infected places there might be some advantage in 
allowing the sore to run its course, inoculating it on an inexposed 
part of the body where it could cause no visible disfigurement, 
since in this way a permanent immunity to further infection 
could be prevented. It is better to keep the sores open than to 
allow a scab to form over them, since the scab shuts in the pus 
and results in more extensive ulceration and inflammation. Ap- 
plications of various kinds which will soothe the inflammation 
and keep the sores as dry and clean as possible are beneficial. 
The use of hypodermic injections of dead cultures of the parasite, 
as in anti-typhoid vaccinations, has been found to hasten the 
healing. The inoculation of the active disease germs on inex- 
posed parts of the body, especially in young children in whom 
the sores are never very extensive, is easily accomplished, and has 
been practiced in Bagdad and other cities where the disease is so 
prevalent as to make avoidance of it almost impossible. Such 
a procedure tends to lessen the number of exposed sores, to 
which flies or other insects might get access. Unless the disease 
should be found to be transmitted by insects which suck the 
parasites from the circulating blood, which seems very unhkely, 
the protection of the sores will greatly reduce the prevalence of 
this unpleasant feature of tropical cities. 

It is possible that an immunity may be established by the 
inoculation of dead parasites as in the case of typhoid fever, but 
this has not yet been demonstrated. 


Espundia or American Leishmaniasis 

In many parts of Brazil, Paraguay, Bolivia, Venezuela, French 
Guiana and other countries of tropical South America there 
occurs a horrible form of Leishmanian ulcers which attack both 
the skin and the mucous membranes of the nose and mouth 
cavity. These ulcers do not grow to a limited size and then heal, 
but slowly and constantly spread further and further, lasting 
for a period of five, ten, fifteen or more years. The disease goes 
by a great variety of local names of which espundia is the most 
common. The best name of all is probably '' American Leish- 
maniasis." The name *' buba braziUensis " has been given it by 
some writers, but erroneously, since this name properly belongs 
to another tropical disease, yaws. A few cases of Leishmania 
ulcers have been observed in dogs in South America. Monkeys 
can be experimentally inoculated. The organism causing these 
intractable ulcers has been named Leishmania americana (bra- 
ziUensis). It is a very minute animal, and is found usually in 
rather scanty numbers in the sores; it can be distinguished 
from the parasite of oriental sore, L. tropica, of which many 
authors believe it is a mere variety, rather by its pathogenic effects 
than by any pecuHarity of form. Flagellated forms of the para- 
site are occasionally found in the sores. 

Skin Sores. — The sores on the skin, which do not always 
ulcerate, usually begin as one or two itching spots that seem to 
be produced by the bites of insects. If the sores are of the non- 
ulcerating type there is produced a great deal of red granular 
tissue, raised slightly above the surrounding skin, and bleeding 
easily. The surface, which is rosy in color, is rough, resembling, 
according to one author, a cauliflower. An intolerably foul- 
smelling fluid is constantly emitted which sometimes dries over 
the sore to form a crust of varying thickness. The fluid given 
off is infectious and starts new sores if it comes in contact with 
any broken skin on the same or another individual. 

In the ulcerating type of the disease in the skin the same fetid 
fluid is emitted, but instead of the sore being elevated, it is ex- 
tensively excavated and has raised borders. Often an enclosing 
crust forms over it and it is improperly called a " dry sore." In 
this case the fluid is shut in between the crust and the sore and 
causes even more intensive destruction of the tissues. Some- 


times nearby lymph glands also become infected. Such general 
symptoms as evening fever, pains in the joints, headache, etc., 
sometimes accompany the ulceration, probably due to the ab- 
sorption of toxins. 

As remarked before, the exudations from the sores are extremely 
infectious for either the same individual or another one. Con- 
sequently it is not infrequent to find on a single individual a 
great many sores, up to 50 or more, in all stages of development, 
though more often there are only a few. In one case recorded 
from Brazil there were 35 active sores and 29 extinct ones, and 
these were arranged in a more or less symmetrical manner, sug- 
gesting the influence of the nervous system on their location. 
The sores become secondarily infected with bacteria and spiro- 
chsetes and are sometimes attacked by screw-worms and other 
fly maggots. The rarity of Leishman bodies in the late stages of 
the sores suggests that the secondary infections may then play 
an important role, though the prompt cure which follows treat- 
ment destructive to the protozoans shows that the latter still play 
a leading part. 

Mucous Membrane Ulceration. — A far more vicious mani- 
festation of the disease and one which follows the cutaneous sores 
is the ulceration of the mucous membranes of the nose and mouth 
(Fig. 16). It may be several months or over a year after the 
skin sores develop and often after they have healed that the 
mucous ulcerations appear. In rare cases ulcers have been 
known to occur in the vagina also. Ordinarily the infection 
commences as a tiny itching hardness or swelling of the mucous 
membrane, usually in the nose, the infected membrane becoming 
inflamed, and marked either with small granular sores or with 
bhster-like swellings. The lymph glands in the infected regions 
become swollen and turgid. A granular ulceration begins in a 
short time, invading all the mucous membranes of the nose and 
spreading, by means of infective fluid which flows down over the 
upper lip, into the mouth cavity, attacking the membranes of 
the hard and soft palate. Its advance is obstinate and slow, and 
gives rise to serious complications. The nostrils become too 
clogged to admit the passage of sufficient air and the patient 
has to keep his mouth constantly open to breathe. His repul- 
sive appearance and fetid breath help to make his life miserable. 
Affections of the organs of smell and hearing, and even sight, 



often supervene, and the voice is weakened or even temporarily 
lost. The digestive tract becomes upset from the constant escape 
down the throat of the exudations from the ulceration, mixed with 
saliva or food. A spreading of the nose due to the eating away 
of the septum is a characteristic feature. Although in late stages 
of the disease the entire surface of the palate and nasal cavities 
is attacked, and the septum between the nostrils destroyed, the 
bones are left intact, a feature which readily distinguishes a 
Leishmanian ulcer from a syphilitic one. Usually the victim of 
espundia, after long suffering, sometimes for 20 or 30 years, 
succumbs to the disease from pure exhaustion and from poison- 
ing by exuded liquids which are swallowed. 

Fig. 16. A case of espundia before and after treatment with tartar emetic. 
(After d'Utra e Silva.) 

Treatment and Prevention. — It was in connection with ulcers 
caused by Leishmania americana that the curative action of 
tartar emetic was first worked out by Vianna in the Institute 
Oswaldo Cruz at Rio de Janeiro. The treatment of espundia 
with this drug, injected into the veins, has been thoroughly tried 
out in the past two years with great success. Although the 
mucous membrane ulcers do not yield to the treatment as readily 
as do skin sores, yet they can be cured with persistent treatment, 
even in cases in which the nose and throat had been infected for 
several years. The tartar emetic is injected as a one to two per 
cent solutian, as for other Leishmanian diseases, five to ten cc. 


being injected daily for from five to 40 days. As remarked else- 
where, it must be administered very carefully and slowly since 
it is likely to produce much irritation. 

Practically nothing can be said about the prevention of the 
disease, since its method of transmission is unknown. The 
natives of South America believe that it results from the bite of 
some jungle insect, probably a horsefly (tabanid), but nothing 
definite is known about it. Blackflies, mosquitoes and ticks 
have been suggested as transmitters also. Since the disease is 
contracted in forests in the daytime, and the sores usually de- 
velop on exposed parts of the body, tabanids seem to be in- 
criminated by circumstantial evidence. However, it is possible 
that houseflies or other non-biting insects may carry the infection, 
the punctures of biting insects serving merely to open a door of 
entrance for the parasites. Natives of Paraguay believe that 
rattlesnakes harbor the parasites and that the latter are trans- 
mitted to man either by blackflies or ticks, both of which attack 
the snakes. Although only a popular belief, this is interesting in 
view of the incrimination of geckos as reservoirs of oriental sore 
parasites in Algeria. 

It would seem obvious that in case a skin sore of the espundia 
type develops, great care should be taken not to allow the mu- 
cous membranes to become infected by contact. Yet a case is 
cited by da Matta where an ignorant wood-cutter who had been 
tormented by espundia of the skin for five years and who persist- 
ently cleaned his nose with infected fingers, never developed the 
slightest affection of the mucous membranes. In other cases, 
simultaneous affection of the mucous membranes and skin is 


Importance of Trypanosome Diseases. — One of the blackest 
clouds overhanging the civiUzation of tropical Africa is the 
terrible scourge of sleeping sickness, a disease caused by protozoan 
parasites known as trypanosomes. The destiny of the equatorial 
parts of Africa depends largely on the issue of the struggle of 
medical science against this haunting malady. The ravages of 
the disease were well known to the old slave traders, and the 
presence of " lazy niggers " lying prostrate on wharves and 
decks with saliva drooling from their mouths, insensible to emo- 
tions or pain, was a famiUar sight. It did not take these astute 
merchants long to find that death was the inevitable outcome of 
the disease, and they very soon recognized swollen glands in the 
neck as an early symptom and refused to accept as slaves negroes 
with swollen glands (see Fig. 24). Nevertheless sleeping sick- 
ness must often have been introduced with its parasites into 
various parts of North and South America, as it frequently is even 
at the present time, and only the absence gf a suitable means of 
transmission has saved the Western Hemisphere from being 
swept by it. 

Up to about thirty years ago sleeping sickness was confined to 
a hmited part of tropical West Africa, but with the opening up of 
Central Africa by whites and the consequent movements of 
disease-carrying inhabitants to new portions of the continent, 
the afflicted country was greatly extended. The great explorer 
Stanley, in his expedition to reach Emin Pasha, was almost un- 
questionably responsible for the introduction of the scourge into 
Uganda and the lake regions of Central Africa in 1888, where it 
had hitherto been unknown. In one district of Central Africa 
the population was reduced from 300,000 to 100,000 in the course 
of seven years, from 1901 to 1908, and there are records of whole 
villages and islands being depopulated. 

In 1909 there occurred a case of sleeping sickness contracted in 




Rhodesia in southeastern Africa occasioned by a distinct and ap- 
parently newly originated type of trypanosome, as indicated 
by its sudden appearance and startlingly rapid spread. This 
type of sleeping sickness is more deadly than the older type and 
there is reason to fear that unless efficient methods of control- 
ling it and stamping it out are discovered it will spread over a 
large part of tropical Africa. The disease has 'already spread 
over a great part of Rhodesia, Nyasaland and Portugese East 
Africa, and has been reported from German East Africa. There 
is apparently a rather high natural immunity to the disease, which 
alone is responsible for the small number of the victims. 

In the same year, 1909, a fever 
caused by a trypanosome was dis- 
covered by Chagas in tropical 
Brazil, and has since been found 
to be widely distributed there, and 
to be the cause of much of the 
non-malarial " fever " for which 
the jungles of tropical South 
America are famous. 

The Parasites. — The trypano- 
somes, next only to the malarial 
parasites, may be considered man's 
most deadly enemies among the 
Protozoa. Like the Leishman 
bodies described in the preceding 
chapter, they are members of a 
primitive group of the class Flagel- 
lata, but of somewhat higher or- 
ganization, and probably higher in 
the scale of evolution. Trypano- 
somes are very active, wriggling 
little creatures somewhat suggest- 
ing diminutive " artistic dolphins " (Fig. 17). They are about 25 /j, 
(about YXHTTT of an inch) or even less in length, spindle-shaped, and 
somewhat flattened from side to side like an eel. Along the " back" 
runs a flagellum connected with the body by an undulating mem- 
brane, Hke a long fin or crest. This terminates at what is really 
the anterior end in a free tail-like flagellum. It is by means of 
the wave motions of the membrane and the lashing of the flagel- 

FiG. 17. Trypanosoma gamhiense, 
slender form. p. b., parabasal body; 
b. gr., basal granule; und. m., undu- 
lating membrane; n., nucleus; fl., fla- 
gellum. X4000. 



lum that the animal moves through the blood or other fluids of 
the body, either forward or backwards, so rapidly that it is difficult 
to observe under the high power of a microscope as it wends its 
way between the blood corpuscles on a shde. The body of the 
animal contains, in addition to the large round nucleus near the 
fniddle, another deeply-staining structure, the parabasal body 
(see p. 31) at the posterior end near where the flagellum origi- 
nates. The body also contains other granules of various sizes. 

There are a great many kinds of trypanosomes inhabiting many 
different animals. Those living in cold-blooded animals have 
no apparent effect on their hosts but the species infesting mammals 
almost always cause disease. In man their effect is particularly 
deadly and the African species usually cause death if allowed to 
run to the sleeping sickness stage. Unlike many kinds of para- 
sites most trypanosomes can live in a great many different hosts. 
The common sleeping sickness trypanosome, for instance, can 
live not only in man but also in monkeys, dogs, rodents, domestic 
animals and a large number of the wild game animals of Africa. 

Most kinds of trypanosomes, like the malarial parasites, live 
only part of their life histories in the blood or other fluids of 
their vertebrate hosts, undergo- 
ing another phase of it in the 
digestive tracts of insects or other 
invertebrates. In their interme- 
diate hosts they undergo remark- 
able transformations; the whole 
series of forms through which 
trypanosomes may pass in their 
development, and which may 
represent a phylogenetic as well 
as an ontogenetic series, is shown 
in Fig. 18. The first or Leish- 

. - r • 1. X J J. J.T- Fig. 18. Diagram of developmental 

mama form, which stands at the types of trypanosomes; A, trypanosome 

foot of the series, is a rounded form; B, Cnthidial form; C, Herpeto- 

, , .,, , ,1 monas form ; D, Leishmania form. (After 

body With a large central nu- wenyon.) 
cleus and small rod-shaped para- 
basal body usually set at a tangent to the nucleus (Fig. 18D). 
Next in development comes the Herpetomonas form which differs 
in having a long slender body and in having a flagellum produced 
from the parabasal body (Fig. 18C). Next comes the Crithidia 


form, differing from the preceding in that the parabasal body 
has moved back to near the middle of the body, and the flagellum 
is connected with the body for half its length by an undulating 
membrane (Fig. 18B). This type is a very common develop- 
mental phase in nearly all trypanosomes, but it is also the adult 
condition of many insect parasites. Finally there occurs the 
fully-developed trypanosome form (Fig. 18A), apparently es- 
pecially adapted in form and structure for life in vertebrate 

bodies. The method of develop- 
ment of this form from a crithidial 
type can easily be seen from Fig. 18. 
Only the first or Leishmania form 
and the last or trypanosome form 
normally occur in vertebrate bodies, 
though all of the four types are 
found in the digestive tracts of in- 
vertebrates. The fact that some 
flagellates never develop further 
than the Herpetomonas form, and 
others never further than the Crith- 
idia form, makes a study of this 
group of Flagellates very confusing, 
since when a Herpetomonas or crith- 
idial type is found in an insect gut 
it is very difficult if not impossible 
Fig. 19. Trypanosoma rhodesi- ^o Say whether it is an adult animal 
ense, from blood of monkey inocu- which never Undergoes any further 

lated from case of human sleeping j i ^ • i j i 

sickness. Note posterior position of development or IS only a develop- 
nucieus in short blunt forms, espe- mental phase of a trypanosome of 

cially in lower figure. X 2000. i. u i. • i 

(After Kinghorn and Yorke.) ^ vertebrate animal. 

It is often very difficult to dis- 
tinguish different species of trypanosomes; of over 70 known 
species only a few can be distinguished on morphological grounds. 
Average size, position of nucleus and parabasal body, length of 
snout, and presence or absence of a free flagellum are sometimes 
useful in identifjdng them. More reliable, however, are their so- 
called " biological characteristics," such as pathologic effects on 
different animals, susceptibility of different hosts, the effect of 
serum immune to certain species, and the " cross-immunity re- 
actions." The last is the most certain method. Thus, if an 



animal has recovered from an attack by one strain of trypano- 
some it is rendered immune and will not succumb to second 
attacks of the same strain, though it is still susceptible to others. 
As remarked before there are at least three species of trypano- 
somes which are known to cause disease in man, two in Africa 
and one in South America. The African species, causing sleep- 
ing sickness, are the most deadly but the South American species 
is frequently fatal, especially to children, and often renders a life 
worse than useless. The Gambian trypanosome, Trypanosoma 

Fig. 20. Trypanosoma gambiense in rat blood, showing long, intermediate and 
short forms all in one microscopic field. X about 1200. Drawn from microphoto- 
graph by Minchin. 

gambiense, is the cause of the commoner and more widespread 
form of sleeping sickness, while the Rhodesian species, T. rho- 
desiense, is the cause of the recently established East African 
form of the disease. The most salient distinguishing character- 
istic between these two species of trypanosomes is the posterior 
situation of the nucleus of the Rhodesian parasite in a certain 
per cent of individuals when they are developed in rats and some 
other animals (Fig. 19). This is a feature never observed in the 
Gambian trypanosome. Both species vary a great deal in form, 


and three distinct types may be observed at once in the blood of 
an infected animal, a long slender form with a long free flagellum, 
a short stumpy form with a short flagellum and a form interme- 
diate between these (Fig. 20). Some investigators regard the 
trypanosome causing the mild sleeping sickness of Nigeria as a 
distinct species, named T. nigeriense. 

Sleeping Sickness 

Transmission. — Sleeping sickness of either type, and also 
many trypanosome diseases of lower animals, is transmitted 
primarily by certain species of tsetse flies which act as inter- 
mediate hosts for the trypanosomes. The Gambian parasite, as 
first shown by Sir David Bruce, is normally transmitted by the 
tsetse fly, Glossina palpalis, and its distribution is now almost 
coincident with the range of this species. It occurs on the 
west coast of Africa from the Senegal River to the State of 
Mossamedes in Portuguese West Africa, including nearly all 
the tributaries of the Niger and Congo Rivers. Eastward it 
extends to the valley of the Upper Nile and Lake Victoria Nyanza 
in Uganda and along the east shore of Lake Tanganyika. 

The Rhodesian trypanosome depends on the more widespread 
and less easily controlled Glossina morsitans. This species of 
tsetse fly occurs all the way from northeastern Transvaal to 
northern Nigeria in West Africa and to southern Sudan in the 
basin of the Nile in East Africa. So far, the disease caused by 
the Rhodesian parasite is limited to a small portion of East 
Central Africa but it is spreading both north and south. 

Experimentally other species of tsetses are able to transmit 
the Gambian disease, but it is doubtful whether any except 
G. palpalis are important transmitting insects in nature. As in- 
timated above it is only the absence of tsetse flies in other parts 
of the world that we have to thank for the fact that sleeping 
sickness when introduced is not propagated. Experiments show 
that it is also possible for the Gambian trypanosome to be trans- 
mitted mechanically by the stable-flies, Stomoxys, though this 
probably seldom happens in nature. Macfie has shown that in 
Nigeria the human trypanosomes undergo developmental stages 
in a stable-fly, S. nigra, but circumstances did not allow him to 
determine whether the salivary glands become infective as in 


tsetse flies. There is evidence that sleeping sickness, Uke surra, 
a trypanosome disease of horses, may also be transmitted sexu- 
ally or through abrasions of the skin, but this is certainly not 
the usual method of transmission. 

The tsetses are blood-sucking flies resembhng stable-flies, 
which inhabit the brushy borders of lakes, streams or swamps, 
— the so-called "fly-belts." The distinguishing characteristics 
of the tsetse flies and of the various disease-carrying species are 
discussed in the chapter on biting flies, p. 490. 

For a long time it was thought that the tsetse flies could trans- 
mit trypanosomes only in a simple mechanical way, the para- 
sites adhering to the proboscis, and being subsequently injected 
into the blood of another person. It is now known that the 
trypanosomes of sleeping sickness can be transferred in this 
manner only for a few minutes after an infective feed, but that the 
fly again becomes infective after a period of three or four weeks. 
Meanwhile the parasites have undergone a series of changes in 
the gut of the insect and finally become stored in the salivary 
glands from which they are poured with the saUvary juices into 
the blood of a new victim. 

Life Cycle in Fly. — According to observations on Trypanosoma 
gamhiense in Glossina palpalis by Miss Robertson the critical 
time for the trypanosomes after they are sucked up by the fly 
is when the fly feeds the next time, since in many cases they are 
swept out of the body with the new influx of blood, or digested. 
Having stood their ground until they have become established in 
the new influx of blood they multiply so rapidly that permanent 
infection of the fly is almost certain. The difficulty experienced 
by the parasites in estabUshing themselves in the gut of their 
insect hosts largely accounts for the relatively low percentage 
(usually less than five per cent) of infections which result from^feed- 
ing of tsetse flies on infected blood. When conditions are favor- 
able for development in the fly the parasites multiply first in 
the middle intestine, producing long-snouted forms such as shown 
in Fig. 2 IB. After the tenth to fifteenth day long slender forms 
(Fig. 21C) are developed, and these move forward in the digestive 
tract. These slender trypanosomes have long snouts and differ 
most strikingly from the earUer forms in the appearance of the 
nucleus (Fig. 21C). After several days more the trypanosomes 
make their way to the fly's salivary glands, to the walls of which 



they attach themselves "by their flagella (Fig. 2 ID) and, rapidly 
multiplying, undergo a crithidial stage. As multiplication con- 
tinues free-swimming trypanosome forms are again produced 

To cerebrospinal fluid cau&in^ sleeping 
dlckness and deaih. 

Transmission by 
bite of tsetse fJLy. 



in human blood causing 
Trypanosome j^^^r. 

Transmission by bfe 
Man, Antelope, etc. [ of tsetse fly. 

Forms in 5a[Wary glands 
ready for re. infection. 
\20"'-50*'' day) 

Tsetse riy 

Crltbidial /ortns in 
salivacy jglands 
(2. or v3 days later) 

Forms in midgut,{V5/ 
offer infective meal). 

newly arrh/ed form in 
^afivary aland. 

Fig. 21. 

Lona slender forms In proventricutas. 
("about I0*'«tol5**'days) 

Life History of Trypanosoma gambiense. X 1500. (Constructed 
from figures by Miss Robertson.) 

which very closely resemble the parasites in vertebrate blood 
(Fig. 21 E) and which are now capable of infecting a vertebrate 
host. The whole cycle in the fly usually occupies from 20 to 30 
days. According to Kinghorn and Yorke the time required for 



Glossina morsitans to become infective varies from 11 to 25 days, 
but under unfavorable conditions the parasites may remain in 
the fly in an incomplete stage of development for at least two 
months. A temperature between 75° F. and 85° F. is necessary 
for the full development of the parasite n the fly, ending in 
invasion of the salivary glands. For two days after the trypa- 
nosomes have been swallowed by the fly they remain infective if 
injected into a vertebrate, but after this time they must pass 
through the crithidial stage before they are again infective. 

The reader will note that 
no sexual reproduction, 
such as is so conspicuous in 
the mosquito cycle of the 
malarial parasites, has been 
described in this fly cycle 
of the trypanosome, though 
the general features of the 
cycle are so parallel. It 
can hardly be doubted that 
sexual reproduction of some 
kind, or at least something 
which takes the place of it, 
does occur in the tsetse fly, 
but it has ' not yet been 

recognized by scientific ob- Fig. 22. Method of division in trypano- 

somes. A, elongated form ready for division; 
B, form with divided parabasal body and par- 
Life Cycle in Man. — The tially split undulating membrane; C, form with 
nnrfl^ifp*^ whpn iniPpfpH ^""^^^^ parabasal body, double undulating 
parasites, wnen mjeciea membrane, and double nucleus; D, almost 
into man or other SUSCepti- completely divided forms, adhering by poste- 

ble animals by a tsetse fly, 

live and multiply in the blood, swimming free in the serum with- 
out entering the corpuscles (Fig. 21 A). They obtain nourishment 
by simply absorbing food material through the delicate cuticle which 
covers them. The method of division is the usual protozoan type of 
simple fission. When about to divide the trypanosome elongates 
(Fig. 22A) and the parabasal body at the posterior end divides 
first (Fig. 22B). Then the flagellum and undulating membrane 
begin to split from the posterior end forward, the central nucleus 
divides (Fig. 22C), and the animal splits into two parts which hang 
together longest by the ''snouts" or posterior ends (Fig. 22D). 


The fast-multiplying parasites do not remain in the blood of 
their victim but penetrate many of the tissues and organs of 
the body, especially the liver, spleen, lungs and lymph vessels 
and glands. The last mentioned are probably one of the main 
strongholds of the parasite in the body and the swelling of 
lymph glands, especially in the neck, has already been men- 
tioned as one of the characteristic symptoms of sleeping sickness. 
The parasites are not present in constant numbers in the blood, 
but periodically appear in large numbers and then apparently 
disappear at fairly regular intervals. Often the trypanosomes 
are so few in the blood that their presence can be proved only by 
causing disease through the injection of some of the blood into a 
susceptible animal or by causing the parasites to multiply, as 

they will quite readily do, in a 
suitable artificial culture me- 
dium. In Nigeria the parasites 
are hardly ever seen in the blood 
of infected persons, but they can 
be found by puncturing a lymph 
gland. According to recent 
investigations by Fantham the 
trypanosomes, probably as a re- 
action against antibodies which 
tend to destroy them*, shrink into 
Fig. 23. Agglutination of trypano- rounded sporehke bodies with- 

somes, T. lewxsi, in blood of immunized i • i 

rat. (After Laveran and Mesnil.) OUt locomotory Organs but With 

a protective shell. In this 
condition they remain until conditions again become favorable 
for them when they once more elongate, develop a flagellum and 
undulating membrane, multiply and reappear in the circulating 
blood. After several months or years the parasites penetrate 
the cavity of the brain and spinal cord and Hve in the cerebro- 
spinal fluid which fills it; this invasion of the central nervous 
system is the direct cause of the dread sleeping sickness stage of 
the disease. 

While under normal and favorable conditions the trypanosomes 
merely live and multiply in the way described above, they are 
capable of reacting in a very peculiar manner when exposed to 
unfavorable conditions, such as the presence of drugs, low tem- 
perature or administration of serum from an immune animal. 


Under such circumstances they have a tendency to mass together 
in large numbers, up to a hundred or more, hke sheep in a storm, 
all with their flagellated ends projecting from a common center 
(Fig. 23). Such '^ primary agglomerations " may adhere to form 
'' secondary agglomerations " comprising altogether many hun- 
dreds of parasites. When the unfavorable conditions disappear, 
the trypanosomes disentangle themselves without any apparent 
ill effects, although a few of them remaining agglutinated may 
die and disintegrate. Another peculiar habit described by some 
investigators is the extrusion from their bodies of very minute 
granules, really tiny buds from the nucleus, which ultimately 
develop into new trypanosomes. This is said to occur just be- 
fore the temporary disappearance of the trypanosomes from the 

The Disease. — The course of the disease caused by trypano- 
some infection is insidious and irregular in the extreme. The 
Gambian and Rhodesian diseases are essentially alike in their 
symptoms and in the course they run, except that the latter is 
usually more rapid in development and more virulent in effect, 
as a rule causing death within three or four months after in- 
fection. The variety of the 
Gambian disease found in 
Nigeria is comparatively mild 
and of long duration. 

The bite of an infected tsetse 
fly is usually followed by itching 
and irritation near the wound. 
After a few days fever is felt 
and a peculiar tenderness of the 
muscles develops, so that strik- 
ing against an object causes 
undue pain. Usually the fever 
comes and goes at irregular in- 
tervals of days or weeks or even Fig. 24. Negro infected with trypano- 
months, an infected person f^es, showing enlarged cervical glands. 
. . ^ (After KoUe and A\ assemiann.) 

sometimes carrymg the para- 
sites in his blood, as shown by its infectivity when injected into 
susceptible animals, for months at a time without any appreciable 
fever, and in insufficient numbers to be seen readily by microscopic 
examination. When the attacks of typical trypanosome fever do 


come they generally are worse in the evening, unlike malarial fevers. 
After a variable time the victim becomes weak and anemic, probably 
due to toxins secreted by the parasites, his pulse becomes rapid, 
and various lymph glands, especially those of the neck, tend to 
swell up and become tender. Often an irritating rash breaks out 
on the skin during the early stages of the disease. Loss of am- 
bition and vitahty usually figure prominently, and childbirth 
is seriously interfered with. It is possible that after weeks or 
months or years of irregular fever and debihty the disease may 
spontaneously disappear, and never become more than trypano- 
some fever. Usually, however, the parasites ultimately succeed in 
penetrating to the cerebrospinal fluid in the cavity of the brain 
and spinal cord, and " sleeping sickness " results. In some cases 
the onset of this horrible disease has been known to be delayed 
for seven years after the beginning of the disease, but usually it 
comes in the course of a few months. 

Sleeping sickness is ushered in by an increase in the general 
physical and mental depression, the symptoms being not unhke 
those of hookworm disease but more pronounced. The victim 
wants to sleep constantly and lies in a stupor; his mind works 
very slowly, and even the slightest physical .exertion is obnoxious. 
Eventually the sleepiness gets such a hold on him that he is 
likely to lose consciousness at any time and even neglects to swal- 
low his food. After weeks of this increasing drowsiness, his 
body becomes emaciated, a trembling of the hands and other 
parts of the body develops, with occasional muscular convulsions 
and sometimes maniacal attacks. He finally passes into a state 
of total loss of consciousness ending in death, or death may end 
the unhappy condition earlier during an unusually intense con- 
vulsion or fever, or through the agency of some complicating 
disease. If untreated, death is the inevitable outcome. A 
large per cent of infections occur among people of middle age. 
Old people are significantly few in number in sleeping sickness 
districts. The presence of these few may be due to a natural 
or acquired immunity. In Nigeria the disease predominates in 
young people, possibly because they are water-carriers and are 
therefore more exposed to the bites of tsetse flies. 

Treatment. — Various drugs have been tried in the treatment 
of trypanosomiasis, especially arsenic and antimony compounds. 
Until recently the most effective drugs in use have been arsenic 


in the form of atoxyl or salvarsan, injected intramuscularly, or 
antimony in the form of tartar emetic, injected intravenously. 
Atoxyl is injected in weak solution, the doses being repeated 
every few days for a period of many months, even long after the 
symptoms of the disease have disappeared. A serious objection 
to atoxyl is the slight tolerance which many people have for it, 
and its serious effects on the optic nerve and digestive apparatus. 
Tartar emetic is also injected in weak solutions, care being taken 
not to allow it to escape into the muscles or connective tissues, 
to which it is very irritating. Usually a high fever follows the 
administration of either drug, probably due to toxic substances 
liberated from dead trypanosomes. Recently the Rockefeller 
Institute has produced a new arsenic compound, tryparsamide, 
which promises to be more valuable than any other drug yet tried. 
It is very soluble in water, can be given either intramuscularly 
or intravenously, produces practically no untoward effects, ef- 
fects very rapid destruction of the parasites in the blood, brings 
about very marked improvement in the condition of the spinal 
fluid in advanced cases, and results in remarkable general ben- 
eficial effects. 

The chief difficulty in the use of any of these drugs is that the 
trypanosomes tend to build up a tolerance for them, in much 
the same way that a man may build up a tolerance for opium 
or other drugs. This tolerance is hereditary and] gives rise to 
" arsenic-fast " or " antimony-fast " strains of trypanosomes. 
In such cases the parasites cannot be destroyed. It is an inter- 
esting fact that in at least one species of trypanosome, T. lewisi 
of rats and mice, and probably others as well, when strains im- 
mune to atoxyl are passed through their intermediate host, a 
louse, where they presumably undergo sexual reproduction or 
some process which takes its place, the tolerance is entirely lost. 
Thus the sexual process at a stroke ehminates acquired charac- 
ters which have been maintained through thousands of asexual 
generations in passages from mouse to mouse or from rat to rat. 
This fact, if invariably true, is of considerable importance in 
the outlook for the treatment of sleeping sickness, since it would 
prevent what would otherwise inevitably happen, the evolution 
of a permanent strain of trypanosomes immune to both arsenic 
and antimony. The fact that parasites resistant to arsenic may 
not be resistant to antimony, and vice versa, makes it advisable 


in treating trypanosome fever to give both drugs either to- 
gether or alternately. 

When the disease has reached the sleeping sickness stage 
and the parasites have penetrated the cerebrospinal fluid, a 
cure has so far never been accomplished. The arsenic and anti- 
mony compounds which are so destructive to trypanosomes 
will not permeate the nervous tissue and diffuse into the cerebro- 
spinal fluid, and they are too poisonous to be injected into the 
spinal canal. The success that has been attained in the use of 
salvarsanized serum (see p. 57) against spirochsetes in the cere- 
brospinal canal gives hope that a similar mode of treatment may 
be used in the case of sleeping sickness. All that can be done 
for sleeping sickness now is to alleviate the suffering and postpone 
the inevitable end. 

Although the use of immune serum from animals which have 
recovered has been very successful in curing and immunizing 
various lower animals against certain trypanosome diseases, this 
has not yet been accomplished for man. 

The Rhodesian trypanosome consistently resists both arsenic 
and antimony treatment, and no successful drug has been found 
for combating this parasite. 

Prevention. — Since the tsetse flies, Glossina palpalis and G. 
morsitans, are by all odds the most important means of trans- 
mitting the Gambian and Rhodesian trypanosomes respec- 
tively, the prevention of the diseases resolves itself into the prob- 
lem of avoiding or exterminating these insects. Methods for 
controlhng and destroying tsetse flies are discussed in the chap- 
ter on Biting Flies, p. 501. 

In places where tsetse fly extermination has not or cannot be 
accomplished the best safeguard is the avoidance of the '' fly- 
belts." In the case of G. palpalis these belts consist of narrow 
strips along the brushy edges of water, but with G. morsitans 
they are not so closely limited, the flies being sometimes found 
at considerable distances from water. Villages or camps should 
always be removed from fly-belts, and travel through the belts, 
when absolutely necessary, should be done on dark nights when 
the flies seldom bite. Occupations carried on in fly-infested 
areas should be discouraged or prohibited. In Uganda fishing 
along the fly-infested streams and lake shores is one of the chief 
occupations indulged in by the natives, who go naked and are 


constantly bitten. The deadly epidemic of sleeping sickness in 
Uganda was fostered by the fishing industry. It has been sug- 
gested that by importing dried sea fish to trade for agricultural 
products the natives might be induced to change their occu- 
pation. In Congo the rubber industry is the one which is the 
most deprecated. Personal protection against tsetse flies is dis- 
cussed on page 501. 

Another method of protection is suggested by the researches 
of Van den Branden who has found that a single injection into 
the veins of salvarsan or neosalvarsan or some of their compounds 
will sterilize the blood against trypanosomes for a period of several 
months — in the case of salvarsan copper for 19 to 24 months. 

Infected individuals should not only be kept away scrupulously 
from places where flies can possibly get access to them, but should 
also be prevented from traveling to new places. Some strains 
of trypanosomes seem to be much more virulent than others, 
and the introduction of a virulent strain to a region where a 
mild strain previously existed has occasionally caused a con- 
siderable increase in the disease. The strict quarantine of in- 
fected persons, while unquestionably worth while, is not a meas- 
ure sufficient to stamp out the disease, since many of the wild 
animals of Africa serve as reservoirs for the disease, harboring 
the parasites in their blood but not succumbing to them. Tsetse 
flies on the shores and islands of Lake Victoria, after the entire 
population had been stringently kept away for three years so 
that the flies could not have fed on human blood during this time, 
were found to be still infective. The situtunga antelope and 
other wild game undoubtedly served as a reservoir. It has been 
suggested that a war of extermination be made on the rich and 
interesting wild game of the countries infected with the Rho- 
desian trypanosome in the hope of checking the rapid spread of 
the disease (see p. 503). It has recently been shown by Taute, 
however, that a large proportion of the wild game of Nyasa- 
land is infected with a trypanosome indistinguishable from 
Trypanosoma rhodesiense in all its general characters but non- 
pathogenic to man. Taute evidently had the courage of his 
convictions since he tried several times to infect himself with 
this trypanosome without success. It is possible, however, that 
a high natural immunity to the parasite may exist in many people, 
and thus explain Tautens negative results. 


Probably the deadly Trypanosoma rhodesiense is merely a strain 
of this wild game trypanosome which has undergone some 
physiologic change or mutation, making it possible for it to live 
in the human body. Bruce and some others consider it identical, 
in every respect except its ability to live in human bodies, with 
the well-known and widespread T. brucei which causes nagana in 
wild and domesticated animals. 

A concrete example of sleeping sickness extermination is to be 
found in the fight against it on the Island of Principe by the 
Portuguese Sleeping Sickness Commission. Sleeping sickness 
had been a scourge on the island for years when the Commission 
began its work in 1911. Its efforts were directed against the 
tsetse fly, but this was accompanied by an active campaign 
against pigs, dogs and other trypanosome carriers, and the 
thorough care and treatment of human victims. The methods 
used are discussed in Chapter XXVI. The Commission cleared the 
island of sleeping sickness in a four years' campaign, but the tsetse 
flies are not yet totally exterminated, and the present condition 
on the island can only be maintained by constant work in the 
future, though at comparatively slight cost. 

Chagas* Disease 

A very different but hardly less destructive disease is caused 
by a trypanosome, Trypanosoma (or Schizotrypanum) cruzi, in 

certain parts of South America. 
Chagas, of the Oswaldo Cruz 
Institute, first investigated the 
disease in the state of Minas 
Geraes in Brazil. He found that 
nearly all children in the endemic 
regions were stricken with the 
disease, usually before they were 

Fig. 25. Trypanosoma cruzi in blood i ^ rr^i i ^•l 

of experimentally infected monkey. O^e year old. The mortality WaS 

A, so-called male form; B, so-called found to be very high, and those 

female form. (After Chagas.) , -1^1 • • . • i 

who survived the initial acute 
attack usually passed over into a chronic diseased condition, very 
often being left to live a worse than useless life as paralytics, 
idiots or imbeciles. The disease has since been found in other 
parts of Brazil and in neighboring countries. Large bloodthirsty 



bugs of the genus Triatoma serve as intermediate hosts; bugs of 
a number of species infected with trypanosomes morphologically 
indistinguishable from-T. cruzi have been found all the way from 
Central America to Argentina, but the disease in man has been 
recognized only in 
a small part of 
this extensive area, 
though it is sus- 
pected of existing 
in northern Argen- 
tina and may oc- 
cur in many more 
places than is now 

Human Cycle. — 
The trypanosome 
causing this disease 
very closely resem- 
bles the sleeping 
sickness trypano- 
somes in form but 
it is quite different 
in its life history. 
In the human body, 
Chagas recognized 
two distinct types 
which he believed 
to be male and fe- 
male forms, but 
subsequent work 
indicates that these n 

merely young and capillary; unpar. c, unparasitized cells. X 1000. (After 

adult forms of the 
parasite. Unlike other trypanosomes this species as found in 
the blood never exhibits stages in division, and this fact led 
Chagas to search for some other form of multiplication. He 
found in the lungs of infected animals what he thought to be 
a process of division of the trypanosomes into eight parts, but 
this later was found to be a stage in the life history of an entirely 

Fig. 26. Trypanosoma cruzi. A, cyst containing Leish- 
mania forms in muscle fiber of guinea-pig, cross section; 
nucleus of muscle fiber. B, older cyst, containing 
. trypanosome forms, in neuroglia cell in gray matter of 

types are cerebrum; n., nucleus of parasitized cell; bl. cap., blood 
capillary : 


different parasite. The real method of multipHcation was first 
discovered by Vianna in the bodies of man and animals who had 
died of the disease. Vianna found in various tissues, especially in 
the walls of the heart, the striped muscles, the central nervous 
system and various glands, greatly swollen cells which served as 
cysts, enclosing a mass of rapidly dividing trypanosomes, varying 
in number from just a few to many hundreds. In younger cysts 
the parasites are round in form and exactly resemble Leishman 
bodies (Fig. 26 A), while in older cysts the flagellum can be seen 
on many individuals and the trypanosome form becomes evident 
(Fig. 26B). When the enclosing cell has swollen to the bursting 
point, the swarming mass of trypanosomes is liberated. Each 
parasite, unless destroyed, then penetrates a new cell somewhere 
in the body, usually near where it originated, and begins the 
process of reproduction again. Only in the early acute stage of 
the disease can the parasites live in the blood, since the blood 
serum rapidly reacts by the formation of antibodies, and be- 
comes deadly to trypanosomes. Chagas believed that the para- 
sites could hve within the corpuscles as well as in the serum, but 

later work does not confirm this. 
On account of the development of 
antibodies in the blood serum, the 
parasites are very seldom found in 
the blood of chronic cases of the 
disease, though their cysts may be 
abundant in various tissues and 
glands in the body. 

Fig. 27. Trypanosoma cruzi in Life Cycle in BugS, and TronS- 

biood of ape said to be inside cor- mission. — The intermediate host 

puscles. (After Chagas.) 

of Trypanosoma cruzi is a large 
black and red bug, Triatoma megista, known to the natives as 
*'barbeiro." It is related to the cone-nose, Triatoma sanguisuga, 
of our southern states. The barbeiro is a fierce blood-sucking 
insect which infests the dirty thatched or mud houses of the 
natives, coming out at night and skillfully secreting itself in the 
daytime (see p. 379, and Fig. 168). 

It was found that the bugs in the houses where Chagas' disease 
had been observed were invariably infected with trypanosomes 
in their gut, and from this fact and from the habits of the bug 
Chagas rightly deduced and later proved that the bug was the 



transmitting agent of the trypanosome. A few hours after a 
bug has fed on infected blood the trypanosomes begin to change 
form in the midgut, becoming round and Leishmania-like in form, 
losing the flagellum and undulating membrane (Fig. 28A, B and 
C.) Then comes a period of very rapid increase in number, the 
parasites gradually pushing backward toward the hindgut by 
sheer multiplication. After about two days Crithidia forms 
begin to develop and become numerous in the hindgut, being 

Fig. 28. Development of Trypanosoma cruzi in digestive tract of bug (Tria- 
toma megista). A, freshly ingested form; B, rounding up and loss of flagellum, 6 
to 10 hrs. after ingestion; C, Leishmania-\\^e form in midgut, 10 to 20 hrs. after 
ingestion; D, redevelopment of flagellum and undulating membrane, 21 hrs. after 
ingestion; E and F, crithidial forms in hindgut, 25 hrs. after ingestion; G, trypa- 
nosome form from salivary gland. 8 days or more after ingestion. (After Chagas.) 

voided with the excrement from time- to time (Fig. 28D, E and F). 
It has been suggested that these crithidial forms do not play any 
part in the transmission of the disease to man but that they rep- 
resent a return to a primitive condition suited to existence in the 
bugs, and that they may be transmitted from bug to bug in this 
form, since the bugs are known to prey to some extent upon each 
other and a^so upon their excrement. Torres, however, considers 
transmission of the flagellates from bug to bug as very doubtful. 
Chagas believes that there is a second cycle of development in 


the bugs which he interprets as sexual reproduction. After about 
ten days there occasionally occurs in the midgut of the bugs 
round organisms with thick capsules, and in a few cases Chagas 
has observed, after about six days, what seemed to be a division 
of this body into eight individuals each presumably giving rise 
to a trypanosome of a new generation. Whether or not the 
infective trypanosomes arise in this way they appear in the mid- 
gut from the eighth day onward. The occurrence of the infective 
parasite in the salivary glands (Fig. 28G) is very irregular. The 
fact that parasites have occasionally been found in the body 
cavity of bugs suggests that the trypanosomes may make their 
way through it to reach the salivary glands. As already re- 
marked the trypanosomes in the bugs have never been found 
infective before the eighth day, but once the infective forms have 
developed they persist in the bugs for over a year. 

The barbeiro is not the only insect capable of acting as an 
intermediate host for Trypanosoma cruzi. Several other South 
and Central American species of Triatoma have been found to 
be naturally infected with this trypanosome or with one mor- 
phologically indistinguishable from it, and experimentally the 
trypanosomes develop in the cosmopolitan species, T. ruhro- 
fasdata and other cone-noses and in bedbugs. Nor is man the 
only vertebrate host. Experimentally apes, dogs and guinea- 
pigs are subject to infection, and in nature the common Bra- 
zilian armadillo, Dasypus novemcindus, and various rodents have 
been found infected, their infection undoubtedly being carried 
by the common bug, Triatoma geniculata, which infests their 
burrows. The fact that infected bugs occur in some places 
where Chagas' disease is not known to occur suggests that, as is 
the case with Trypanosoma rhodesiense and the trypanosomes 
undistinguishable from it except by their harmlessness to man, 
not all strains of the parasite cause human disease. It is inter- 
esting to note that a very similar trypanosome has recently been 
discovered by Kofoid and McCulloch in Triatoma protracta of 
southwestern United States. This bug is common in nests of 
wood-rats and frequently attacks man also. This discovery 
suggests one of two things: either the trypanosome described 
as T. triatomce, and which is admitted by the discoverers to differ 
from T. cruzi only in sUght characteristics of questionable im- 
portance, is really identical with or a mere variety of T. cruzi, 


or else others of the trypanosomes observed in species of Triatoma 
from Argentina to Central America may not be identical with 
the trypanosome which is the cause of Chagas' disease. 

The Disease. — In endemic regions Chagas' disease is so 
prevalent that children are usually attacked within a few months 
after birth, and at this tender age are often unable to withstand 
its effects. If death does not result the disease passes over into 
one or other of its various chronic forms. As a result it is very 
rare to find acute cases in anyone but young children or new 
arrivals. The latter, however, usually come from other infected 
regions and show marks of the chronic disease, and so are not 
susceptible to a new acute infection. 

The acute infection is marked by a constant high fever, lasting 
from ten to thirty days, often without remission, and by a charac- 
teristic swollen face, noticeable from a considerable distance. 
The skin has a pecuUar feeling of '' crepitation " due to the 
mucous infiltration of the tissue under the skin. The lymph 
glands especially in the neck and arm pits swell up, the liver and 
spleen become enlarged, and the thyroid gland becomes swollen 
as in goitre. In fact, most of the symptoms are connected with 
interference with the thyroid gland which, while becoming 
massive in size, becomes reduced in function, thereby causing a 
number of nervous and constitutional symptoms. This inter- 
ference is due, apparently, not so much to invasion by the para- 
sites as to a specific effect of the toxins produced by them and 
carried by the blood. These are the constant features of the 
disease; the other symptoms vary according to the localization 
of the parasites. Frequently they multiply in the heart muscles, 
and the functions of the heart may be seriously interfered with. 
Very often, and with the most dire results, the parasites invade 
the brain and spinal cord. When this happens the mortality is 
high, and it is only a pity that it is not higher, since it would 
be better if death always eliminated these unfortunate trypano- 
some victims who are spared only for an unproductive, piteously 
mutilated life, doomed to grow up with the intellect of an infant, 
or as paralytics, idiots or imbeciles. 

The chronic forms of the disease follow the acute form by the 
development of a substance in the blood which is deadly to the 
trypanosomes, so that the latter are restricted to the protecting 
tissue cells in which they multiply. The commonest chronic 


form is that in which the predominating symptoms result from 
an enlarged but insufficient thyroid gland — goitre, cretinism, con- 
vulsions, swollen skin and various functional disturbances, includ- 
ing imperfect heart and intellectual defects. Another chronic form 
is that in which the heart is especially affected. The fact that 
the parasites have a special predilection for the heart muscles 
makes this form of the disease very common. The results of locali- 
zation of the parasites in the nervous system have already been 
mentioned. The intensity of the motor disturbances, varying 
from paralysis or spasmodic convulsions of a single muscle to 
complete paralysis or convulsions of the whole body, has no rela- 
tion to the degree of intellectual affection, which may vary from 
a simple cretinoid condition to complete idiocy or infantilism. 

It is doubtful whether the disease is ever recovered from entirely 
if left to run its course. Sometimes the symptoms become 
gradually less intense, in other cases they become worse and new 
ones develop, or recurrences of acute symptoms may develop, 
due either to reinfection or to a loss of the trypanocidal power of 
the blood. 

Treatment and Prevention. — The treatment of Chagas' dis- 
sease is still in the experimental stage but there is some evidence 
that tartar emetic may prove to be of great value in deaUng with 
it, at least in early stages. In fact it was the success obtained by 
Vianna in combating the disease with tartar emetic that first 
suggested to him its use against Leishmanian diseases. 

Prevention of the disease consists largely in avoiding and ex- 
terminating the barbeiros. It is practically impossible to keep 
the bugs out of mud or thatched houses. For this reason the re- 
building of houses with other material is being urged everywhere 
in Brazil and with good results. The town of Bello Herizonte, 
for example, which was formerly termed " a nest of cretins " is 
now nearly free from Chagas' disease, due to the remodeling of 
the houses. People traveling through infected districts can 
readily protect themselves by sleeping under mosquito nets and 
by avoiding the native houses. There is said to be no danger 
of being bitten by the bugs in daytime or in the presence of arti- 
ficial light, since they come forth only in the dark. 

The extermination in the vicinity of villages of armadillos and of 
the various rodents which harbor the trypanosomes would be a 
valuable aid in the reduction of the disease. 


The human intestine furnishes a habitat for a considerable 
number of animals belonging to all four classes of Protozoa, 
though it is not so subject to such infections as are the digestive 
tracts of many lower animals, especially the ruminants. By 
far the most important intestinal protozoan of man is an ameba, 
Endamoeba histolytica, discussed in connection with other para- 
sitic amebse in a subsequent chapter. Probably next to the 
amebse from a pathogenic point of view should stand the ciliate, 
Balantidium coli, which is, however, not common in most parts 
of the world. The various flagellates of the intestine, from the 
simple bi-flagellate forms, such as Bodo, Cercomonas and Emhado- 
monas, some of which are probably only accidentally parasitic, to 
the highly organized multi-flagellate forms, such as Trichomonas 
and Giardia, which are very common human parasites, differ 
greatly as regards their pathogenic importance, and opinions 
do not agree concerning the importance of particular ones. 

General Characteristics of Intestinal Protozoa. — In some 
respects nearly all the Protozoa which make their home in the 
digestive tracts of animals resemble one another. Nearly all of 
them secrete for themselves resistant transparent cysts which 
protect them from drying up or from the presence of an unfa- 
vorable medium. In the encysted state intestinal protozoans are 
able to exist under the unfavorable conditions found outside the 
body of the host, and are capable of remaining in this state in a 
sort of torpid condition for long periods of time until they gain 
access to a new host. The cysts of intestinal protozoans are 
analogous to the resistant eggs of intestinal worms, and like 
worm eggs their presence in the faeces of infected persons serves as 
a convenient means of diagnosis. The unencysted protozoans 
which may be carried out of the intestine die quickly and 
probably could not produce a new infection even if swaUowed 
immediately, since in some species at least they are unable to 



withstand the action of the acid juices of the stomach. None of 
tlie human intestinal Protozoa require a second host to transmit 
them as do the blood-dwelhng parasites. While outside the 
body they remain dormant in their cysts for weeks or months 
until they can gain access to a host again through food or water. 
There is still much doubt as to the extent to which intestinal 
protozoans are confined to particular hosts. Some workers 
believe that each animal has its own species peculiar to it, and 
that these species are not capable of infecting different hosts. 
Evidence is accumulating, however, to show that in some cases 
at least this is not so, and that many intestinal protozoans of 
man are able to live in such animals as rats, mice and hogs. 
Most intestinal protozoans are of very wide geographic distri- 
bution, their abundance in any given place being largely deter- 
mined by the warmth of the climate and the sanitary, or rather 
unsanitary, conditions. 

As remarked before there has been much discussion concerning 
the effect produced by various species of flagellates in the in- 
testine. Naturally these parasites are seldom discovered except 
when there is some intestinal ailment, since in normal health 
faeces are seldom submitted for examination. Where routine 
examinations have been made regardless of physical condition, 
it has been found that a large per cent of people in unsanitary 
places are infected. Stiles, in a town in one of our southern 
states, found that from 50 to 100 per cent of the children were 
infected, and it would probably be easily within the bounds of 
truth to say that 75 per cent of all people in warm countries liv- 
ing in places where unsanitary conditions prevail are subject 
to infection with one or several species of intestinal Protozoa. 
As Stiles has pointed out, such infection usually means that the 
infected person has swallowed human excrement, since it would be 
impossible for any natural agency to separate the microscopic 
protozoan cysts from the faeces in which they are found. This 
fact, impressed upon the mothers of infected children, especially 
when accompanied by the remark that one could not tell whether 
the infection had come from the excrement of a white or a negro, 
was found by Stiles to be one of the most powerful means of 
improving sanitary conditions in the South. 

Facts which support the view that intestinal flagellates are of 
more importance pathogenically than has commonly been sup- 



posed have been furnished recently by the findings in returned 
British soldiers, in whom uncomphcated infections with flagel- 
lates have been found in many dysenteric cases, and also by the 
investigations of Lynch, Barlow, Escomel and others in various 
parts of the world. Still further evidence is furnished by the 
fact that parasites very closely allied to species found in man 
have recently been shown to be unquestionably of pathogenic 
importance, at least under certain conditions, in lower animals. 

Obviously, however, in view of the large number of infected 
persons, the intestinal protozoans must often have little or no 
pathogenic effect. There is, nevertheless, much individual dif- 
ference in susceptibility, and different strains of the same para- 
site seem to vary in the effects they produce. Moreover it is 
highly probable that a great many slight and perhaps almost 
unnoticed symptoms, resulting in a certain amount of interference 
with the digestive tract and in a general lowering of the health, 
may find their ultimate cause in intestinal parasites, either pro- 
tozoans or worms or both. The health of people living in warm 
and tropical countries, even aside from the effects of malaria and 
other warm-climate diseases, is proverbially less perfect than that 
of people in the usually more sanitary northern countries. It is 
quite probable that intestinal Protozoa may play a part in this 
lowering of the tone of health. 

In the paragraphs below a brief account of the more important 
intestinal flagellates and ciliates is given, with what is known of 
their pathogenic effects, in the following order: (1) the bi-flagel- 
late forms, Bodo, Cercomonas and Embadomo7ias, (2) the multi- 
flagellate forms, Trichomonas, Enteromonas, Chilomastix and 
Giardia; and (3) the ciliate, Balantidium. 

Bi-flagellate Protozoa 

Most primitive of the intestinal flagellates are the bi-flagel- 
lated forms, several genera of which have been found in the human 
intestine. The relation of these animals to the still more primi- 
tive mono-flagellated trypanosomes and their allies is shown 
by the parasites of the genus Trypanoplasma. The animals of 
this genus resemble trypanosomes in the general form of the body 
and in the possession of a parabasal body and an undulating 
membrane, but have an additional free flagellum. In Cercomonas 


(Fig. 29C), according to Wenyon, the trailing flagellum is at- 
tached to the side of the body as far as the posterior end, usually 
being continued as a free flagellum. According to others Cer- 
comonas has only a single flagellum, the free one at the anterior 
end. Bodo (Fig. 29B) has two free flagella, one waving anteriorly, 

Fig. 29. Bi-flagellated parasites A, Prowazekella, separation from Bodo 
proposed on account of absence of parabasal body. B, Bodo, note parabasal body 
(par. b.). C, Cercomonas; note trailing flagellum attached to side of body. This 
is not recognized as a flagellum by some workers. X 2000. (After Wenyon.) 

the other trailing behind; some species not showing a parabasal 
body have been placed in a genus Prowazekella (Fig. 29A) of 
doubtful validity. Most of these flagellates are coprozoic, i.e., 
saprophytic faecal protozoa, rather than true parasites, the cysts 
being accidentally ingested with water or food. 

A slipper-shaped flagellate, Emhadomonas (Waskia) intestinalis, 
first described by Wenyon and O'Connor in Egypt, and since 
recorded by Kofoid, Kornhauser and Plate in American troops 
returning from overseas, and by Hogue from a person who had 
never been out of the United States, is probably a true human 
intestinal parasite. It is only from 4 to 8 /^ in length, has a rather 
large cytostome, an anterior nucleus, and two flagella, one of 
which is short and thick and lies in the cytostome. The cysts 
are very small and pear-shaped. A larger species, Emhado- 
monas sinensis has been found by Faust in China. 

Multi-fiagellate Intestinal Protozoa 

Trichomonas hominis, — Of the several flagellates which 
have been found in the human digestive tract and faeces. Tricho- 
monas is the commonest. It makes its home in the upper 



c>t.— -V 


part of the large intestine and coecum, often multiplying in 
prodigious numbers. Trichomonas also lives in the vagina and 
in the urinary tract, being quite often found in vaginal discharges, 
especially in cases of leucorrhea. It has been commonly believed 
that the vaginal parasite, which is larger than that of the intestine, 
is a distinct species, and it has been given the name T. vaginalis^ 
but there is reason for believing that it is identical with the in- 
testinal parasite. Other intestinal parasites are sometimes 
found in the urinary tract. This or a closely allied species is also 
occasionally found in the mouth, 
about the tartar of the teeth. Ac- 
cording to Goodey the mouth form 
differs from the intestinal form to 
a sufficient extent to warrant its 
being given a distinct name, at least 
provisionally, and he proposes the 
name Trichomonas ( Tetratrichomo- 
nas) buccalis. 

Trichomonas hominis (Fig. 30) 
is a pear-shaped flagellate averaging 
about eight to 15 ^u (^tjVit to j-^ of 
an inch) in length, the size being in- 
versely proportional to the rapidity 
of multiplication. Typically it has 
three vigorously moving anterior 
flagella arising from the blunt an- 
terior end, and a fourth wavy one 
which turns backward and is at- 
tached to the side of the body by 
an undulating membrane. Some 
investigators however, record four free flagella and others five. 
On this basis new species and genera have been created but, as 
pointed out by Faust, it is more probable that all of them may be 
included under a single species, with races among which the 
number of flagella may vary, but within any one of which it tends 
to remain constant, usually either three or four. Goodey de- 
scribes the mouth form of the parasite as having four flagella. 
Along the line of attachment of the undulating membrane to the 
body is a structure which takes a deep stain, called the chro- 
matic basal rod or " costa." It is beheved by some workers to 


Fig. 30. Trichomonas hominis; 
n., nucleus; cyt., cytostome; axo., 
axostyle; par. b., parabasal body 
(?) ; und. m., undulating membrane. 
X 2400. (After Wenyon.) 


be a modified parabasal body; in some forms it is broken up into 
a row of chromatinic granules. At the point of insertion of the 
flagella, and serving as the center of the neuromotor apparatus is 
a basal granule or blepharoplast. Arising near the anterior end 
and running through the body is a sort of supporting rod called the 
" axostyle," which, according to Kofoid and Swezy, is also used 
as an organ of locomotion. At the anterior end at one side of 
the point where the flagella originate is a slight depression or 
" cytostome " which serves as a mouth. The small round nu- 
cleus lies in the body just behind the origin of the flagella. 

Trichomonas swims by active lashing movements of the free 
flagella and by wave motions of the undulating membrane. 
The body revolves as the animal wends its way through the 
semi-hquid substances in which it lives. Multiplication is by 
longitudinal division of the body, the flagella and undulating 
membranes and internal structures all being duplicated before 
the animal splits into two. A process of multiple fission resulting 
in the formation of eight individuals has also been described. 

Encystment, such as occurs in other intestinal protozoans, 
has definitely been observed only recently in Trichomonas. 
Some of the flagellates, after escaping from the body with the 
fseces, soon degenerate, gradually losing all their appendages 
except the undulating membrane. With- 
out their flagella, and with their ameboid 
movements, these animals closely resemble 
amebse but can usually be identified by the 
undulating movement which persists at one 
side of the body. Others, without losing 
inJe^ruiiisi A^^rtZcyZ ^^^^^ appendages, become round and mo- 
ment stage; B, encysted tionless as if in a cyst, but with no cyst 
Lynch.) ^ • ( ter ^^jj around them. When warmed up 
they stretch themselves out and resume 
an active life. It is probable that these forms are preparing for 
encystment, since they correspond with pre-encystment forms 
(Fig. 31 A) recently described by Lynch. Lynch, who found con- 
siderable numbers of cysts in a heavily infected case in South 
Carolina, describes the cysts (Fig. 31B) as thin-shelled, pear- 
shaped bodies, about three-fourths the size of the active flagellates. 
The oval body of the animal with its appendages can be seen 
clearly through the cyst wall in properly prepared microscopic 


slides. It is the opinion of many protozoologists, however, that 
these so-called cysts are really degenerate forms, and that cyst 
formation has not yet been satisfactorily demonstrated. Lynch 
and others have succeeded in cultivating Trichomonas and in 
infecting rabbits with it, but specimens cannot be kept alive in 
water or f seces for more than a few days under the most favorable 

Trichomonas is generally regarded as a harmless parasite, but 
there seems to be strong evidence that it often causes diarrhea, 
sometimes very severe and of long duration. Epidemics of 
diarrhea and mild dysenteric symptoms in man apparently caused 
by Trichomonas have been reported from Peru, Brazil, China, 
South Carolina and Indiana, and it is probable that the parasite 
is at least mildly pathogenic wherever it occurs, tending to ag- 
gravate other intestinal ailments if not causing them directly. 
Haughwout suggests the following possible ways in which this 
parasite may damage its host: (1) production of growth-inhibiting 
substances; (2) production of substances directly toxic; (3) 
liberation of injurious metabolic products; (4) mechanical ir- 
ritation of mucous membranes; (5) interference with absorption 
by adherence to intestinal walls; (6) invasion and destruction of 
tissues. On the other hand Wenyon and O'Connor regard the 
presence of Trichomonas in cases of diarrhea as usually accidental, 
and fixed upon as the cause because the most conspicuous or- 
ganism present. A case has recently been reported of an Oriental 
who was suffering from a foul-smelling decay of the jaw, accom- 
panied by pains in the joints, in which numerous Trichomonas 
were found in the jaw lesion. After treatment with emetin there 
was rapid improvement, which suggests that Endamoeha may 
also have been present. 

No specific drug for use against Trichomonas has yet been 
found. Methylene blue in weak solutions is absorbed by the 
parasites and causes them to become round and quiet. Castellani 
recommends taking methylene blue both by mouth and by means 
of an enema, i.e.^ irrigation of the large intestine. With this 
treatment the flagellates are said to decrease rapidly and to disap- 
pear usually within a few days. Escomel, who has found Tri- 
chomonas an important factor in diarrhea in Peru, advises an 
enema consisting of one grain of iodine in a liter of water, taken 
in the evening on three successful days. Unless the parasites 



have established themselves in the membranes high up in the 
intestine they are said to disappear after this treatment. As 
with other intestinal Protozoa infection occurs through polluted 
food or water. 

Enteromonas hominis. — This minute spherical or nearly- 
spherical organism, 5 to 6 /z in diameter, was first described by 
Fonseca in Brazil. It possesses two equal anterior flagella, and 
a larger trailing flagellum ; the nucleus is situated anteriorly as in 
Chilomastix. It is probable that Tricercomonas and Diplocerco- 
monas, described as distinct human parasites, are really identical 
with Enteromonas. 

Chilomastix {or Macrostoma) mesnili, — A parasite which 
closely resembles Trichomonas in many respects is Chilomastix 

Fig. 32. Chilomastix (or Macrostoma) mesnili; A, adult parasite (n., nucleus; 
cyt., cytostome, 4th fl., fourth flagellum) ; B, end view of adult parasite, showing 
eytostome with flagellum in it; C, degenerating form, resembling an ameba; D, 
cyst, showing nucleus and cytostome. X 2000. (After Wenyon.) 

mesnili (Fig. 32). It is smaller than the former, averaging about 
eight or ten n (^t^Vtt of an inch) in length. It has three slender 
anterior flagella like Trichomonas but has no conspicuous undulat- 
ing membrane. It has a large and conspicuous slit or cytostome 
along one side which corresponds to the very small mouth cavity 
of Trichomonas. Within the cytostome is a fourth inconspicu- 
ous flagellum which seems to be attached to a small undulating 
membrane. The posterior end of the body is drawn out into a 
long point. As in Trichomonas the nucleus hes just behind the 
origin of the flagella. The rest of the body contains numerous 
vacuoles filled with bacteria, the latter apparently serving as the 
staple article of diet. 


The ordinary multiplication of Chilomastix is no doubt similar 
to that of Trichomonas. When ready to leave the body oval 
cysts are formed from 7 to 8 m (^/t)-?^ of an inch) in length, 
within which the animal with its nucleus and large cytostome can 
be seen (Fig. 32D). Wenyon has found Chilomastix cysts with 
four nuclei and thinks that some multiplication may occur 
within the cysts as it does in Endamoeba. The methods of trans- 
mission and means of prevention differ in no way from those 
of Trichomonas. 

Giardia (or Lamhlia) intestinalis, — Next to Trichomonas, 
Giardia is the most common flagellate in the human digestive 
tract. Unlike most of the other intestinal protozoans it estab- 
lishes itself in the upper part of the small intestine. It is one 
of the oddest-shaped little animals known. Wenyon aptly 
describes it as follows: *' In shape it resembles a pear split into 
two parts along the longitudinal axis. There is a flat surface 
on which there is a sucking disk with raised edge, and a convex 
surface. The tapering extremity or tail can be turned over the 
convex back, and it terminates in two flagella. There are three 
other pairs of flagella, the arrangements of which are best seen 
by referring to the plate." (Fig. 33.) 

Giardia is remarkable in being perfectly bilaterally symmetrical, 
every organelle, including the nucleus, being accurately repro- 
duced on each side of the middle line. Between the two small 
nuclei are a pair of rodlike structures (Fig. 33, par. b.) thought by 
some workers to be parabasal bodies, from which the flagella 
arise. As seen in face view the parasite has a comical owl-Hke 
appearance. This fantastic little animal, 12 to 18 /x (^(jVt? to t^js 
of an inch) in length fastens itself to the convex surface of an 
epithelial cell by means of its sucking disk, resting with its 
flagella streaming like the barbels of a catfish (Fig. 33F). Some- 
times long rows of them can be found resting on the surface of the 
epithelial cells of digestive glands. Miss Porter, who has studied 
Giardia infections in British soldiers from Gallipoli, estimated 
recently that in one case the number of cysts, each having been 
an active flagellate in the intestine, exceeded 14,000,000,000 in 
a single stool. The number of cysts in an average stool in a 
case of moderate infection she estimated at 324,000,000. 

Evidently this flagellate multiplies very rapidly, but its method 
of multiplication is not fully understood. Division of unen- 



cysted forms has very rarely been observed, and some writers 
have even gone so far as to say that it does not occur. It is well 
known that division into two individuals takes place after en- 
cystment, and Wenyon has recently expressed the opinion that 
if the division is completed before the cyst is expelled from the 
body of the host, the cyst may burst and liberate the two animals, 

Fig. 33. Giardia (or Lamblia) intestinalis; A, side view (s. sucker-like depres- 
sion); B, ventral view (par. b., parabasal bodies, n., nucleus); C, young cyst with 
four nuclei; Z>, mature cyst containing two parasites; E, end view of young cyst; 
F, parasite resting on epithelial cell. Figs. A-E, X 2Q00, after Wenyon; Fig. F, 
X 1000, after Grassi and Schewiakoff. 

the cysts thus serving as a means of multiplication. Kofoid 
and Christiansen have recently succeeded in finding numerous 
individuals of an allied parasite of the mouse, Giardia muris, 
in process of division into two and also into four and eight indi- 
viduals, both in the free and in the encysted state. That a simi- 
lar process really occurs in the human parasite can hardly be 
doubted, both from its similarity to the mouse parasite and from 
the enormous numbers which may occur in an infected person 
at one time. 

The free active parasites become motionless and die soon after 
leaving the body of the host with the faeces, but encysted forms 
(Fig. 33C, D and E) may retain their vitality for a very long time. 


The cysts usually form around single animals which then proceed 
to divide into two or more individuals. The commonest condi- 
tion is that of two parasites lying with their anterior ends at 
opposite ends of the cyst (Fig. 33D). 

According to Wenyon, Giardia is a very persistent flagellate, 
often keeping an individual infected for years. It is sometimes 
noticeably pathogenic, causing intermittent diarrhea in which 
blood and mucus is passed, swarming with parasites. Between 
such attacks the infected person passes apparently normal stools, 
with only the cysts of Giardia in them. An active increase of 
parasites accompanied by attacks of diarrhea is likely to occur 
after exposure to weather, irregular diet, or other weakening 
conditions. Many cases of dysentery and diarrhea in British 
soldiers invalided home from Gallipoli were found to be due to 
Giardia infection. The acute symptoms last from one to six 
months, after which the symptoms practically disappear for a 
variable length of time. Strangely enough there is always 
spontaneous improvement upon a change to a cooler cHmate. 

Giardia infections are extremely difficult to get rid of, and 
some infections seem to survive every attempt at treatment. 
They do not respond to emetin, though they are sometimes 
destroyed by beta-naphthol. The latter drug in combination 
with bismuth saUcylate has been found successful in some cases. 
Escomel in Peru uses a method of dieting followed by calomel 
and castor oil and claims to rid his patients of the parasite by the 
third day. The difficulty experienced in expelling these para- 
sites is probably due to their habit of lodging themselves in the 
digestive glands outside the main passage of the intestine, where 
it is difficult for drugs of any kind to reach them. 

Like other intestinal protozoans, Giardia is transmitted in the 
encysted state with polluted food and water. Stiles has shown 
that flies play an important role, carrying the cysts on their feet 
from open privies and depositing them on human food. By cap- 
turing flies known to have fed on Giardia-iniected material and 
shaking them up in distilled water, Stiles was able to recover 
Giardia cysts from them. 

Deschiens has recently adduced strong evidence by experimental 
infections that the Giardia of rats and mice is really only a variety 
of the human species, in which case the faeces of the rodents 
would afford a means of dispersal. Cats also may serve as a 
reservoir and means of dissemination for the infection. 




Balantidium coli. — Although several species of ciliates have 
been recorded as human parasites, there is only one species, 
Balantidium coli (Fig. 34A), normally parasitic in hogs, which is 
common enough to be of any importance. This large ciliate 
stands next to Endamoeba histolytica among the Protozoa as a 

Fig. 34. Balantidium coli; A, free ciliate from intestine; n., nucleus; c. v., 
contractile vacuoles; f. v., food vacuole; cyt., cytostome. B, cyst, as passed in 
faeces, containing two parasites. X about 500. (After Wenyon.) 

cause of human dysentery. It is a large animal for a protozoan, 
averaging from 50 to 100 /* (^^^ to ^^^jj of an inch) in length, and 
thus being visible to the naked eye. Its body is oval and en- 
tirely covered with ciha, and at the anterior end there is a gash- 
like slit leading to the mouth or " cytostome " (Fig. 34, cyt.). 
The large bean-shaped nucleus (Fig. 34, n.) lies near the middle of 
the body and near each end is a pulsating cavity or contractile 
vacuole (Fig. 34, c.v.) which excretes waste matter. These 
parasites multiply by transverse division, often so rapidly that 
the animals do not have time to grow to full size and so become 
very small. When ready to leave the body they form an oval 
cyst about themselves. Sometimes two occupy a single cyst 
(Fig. 34B), and later fuse together. Since the ciUated bodies of 
the protozoans can be seen, under a microscope, inside the large 
transparent cysts, their identification is not difficult. The cysts 
can exist outside the body for a long time, awaiting an opportunity 
for reinfection. 


Balantidium swims about in the contents of the large intestine 
devouring particles of faecal material. As long as the animal 
confines its activities to this, no ill effects result, but it also has 
the power, like Endamoeba histolytica, of invading the tissues 
and causing ulceration, perhaps after an injury from some other 
cause has given an opening for invasion. Although many in- 
fected persons do not show any dysenteric symptoms, these are 
likely to appear at any time. When they do appear, they are 
of a very serious nature, and cause a high mortality. On post 
mortem examination the large intestine is often found in a hor- 
rible condition, ulcerated from end to end, with shreds of muti- 
lated or dead tissue hanging from the walls. 

Unfortunately there is no specific treatment for balantidial 
dysentery as there is for the amebic disease. In some cases 
emetin and alcresta ipecac (see p. 135) have caused a disap- 
pearance of the parasites, but these are not reliable remedies. 
Salvarsan and methylene blue have also been recorded as suc- 
cessful in some cases. Organic compounds of silver seem to 
have some value in destroying Balantidium, and there are other 
drugs and herbs of much local fame which are undoubtedly 
sometimes effective. Rest and care of the general health are 
always required. 

Prevention of balantidial dysentery consists not only in the 
sanitary disposal of human faeces, as in the case of other human 
intestinal protozoans, but also in the proper care of hogs, since 
Balantidium is a common parasite of these animals, and is 
probably norrrially a hog parasite. A large proportion of hogs 
are infected in almost all warm and temperate countries, and it is 
nearly always in hog-raising countries, and in places where there 
is too close association between hogs and man, that balantidial 
dysentery occurs. Around Manila, where the disease is fairly 
common, the majority of the hogs are infected and pass encysted 
parasites in their faeces almost constantly. In Colombia the 
disease is found only in those altitudes where hogs are raised 
and among those who raise them. 


Those of us who have had an opportunity, in studying micro- 
scopic life in water, to observe the restless movements of the 
tiny bits of naked protoplasm which we call amebae, having 
watched them slowly creep along the surface of a slide, extending 
a portion of the body as a finger-like projection or '' pseudo- 
podium " and then allowing the rest of the body to flow up to 
the new position; having seen them creep up on tiny protozoans 
or other single-celled organisms and devour them by merely 
wrapping themselves around them, thus engulfing them in an 
improvised stomach; and having seen them propagate their 
kind by simply constricting in the middle and dividing in two; 
— those of us who have observed these acts on the part of such 
tiny and simple animals have come to be fascinated by them and 
to like them, and find it hard to realize that certain species are 
'nstrumental in causing some important human diseases. Amebae 
are found almost everywhere in water, soil and carrion. They 
have even been found recently to exist in large numbers in the 
sunbaked sands of the Egyptian deserts, lying dormant in their 
cysts which protect them from evaporation, ready to emerge 
and resume an active life when they become moistened. In 
view of the wide adaptability of these animals it is not surprising 
to discover some living as parasites, finding congenial surround- 
ings in the bodies of higher animals. 

Classification. — Amebae are protozoans belonging to the sub- 
class Sarcodina, a group characterized by a body without a 
cuticle, though sometimes protected by a shell or cyst wall, and 
by their peculiar method of locomotion. In the adult form they 
have neither flagella nor cilia, but simply outgrowths of proto- 
plasm, called pseudopodia. In the amebae and their close rela- 
tives the pseudopodia can be projected anywhere on the surface 
of the body, now here, now there, though the number, form and 
activity of the pseudopodia are quite different in different species. 



The life history also varies in the different species, many free- 
living forms possessing a flagellated stage. On the basis of struc- 
ture, life history, and habits the old genus Amoeba has been broken 
into a number of genera distinguishable from each other prin- 
cipally by the structure of the nucleus and the nature of the cysts. 
The life history is simple in all of them, so far as it is known. The 
cases of spore formation, multiple fission, conjugation or sexual 
processes described by various investigators have not been sub- 
stantiated by subsequent work. All of the parasitic amebae are 
characterized by the absence of contractile vacuoles. One species, 
Endamoeba histolytica, habitually feeds on blood corpuscles and 
living tissues, and another, Councilmania lafleuri, does so to some 
extent. The other species apparently feed principally on bacteria 
and other organic material with which they are associated in their 
normal habitat. 

The principal amebae occurring in human beings may be ten- 
tatively grouped in the five genera Endamoeba, Councilmania, 
Endolimax, lodamoeba, and Dientamoeba, but the classification 
of the parasitic amebae cannot yet be considered as satisfactorily 
settled. The characteristics of these genera are briefly as follows : 

Endamoeba; nucleus vesicular with chromatin arranged in a 
peripheral layer of beadlike granules of fairly uniform size, and a 
small compact karyosome; a capsule-like structure can usually 
be seen surrounding the karyosome. Cysts, if produced, with 
normally 4 or 8 nuclei of similar structure to those of the free 
forms, and including also glycogen masses and refractile '' chro- 
matoid " bodies, though these masses and bodies commonly 
disappear before or soon after the cysts become mature. (See 
Figs. 36 and 37.) 

Councilmania; nucleus with chromatin distributed in a peri- 
pheral zone on nuclear membrane and in an irregular karyosome. 
Cysts normally with 8 nuclei which have relatively large and very 
variable karyosomes, and very little peripheral chromatin. Buds 
containing single nuclei escape from a pore in the cyst wall until 
the cyst is emptied of all its nuclei. (See Fig. 41.) 

Endolimax; nucleus vesicular without a distinct peripheral 
layer of chromatin. A fairly large compact mass of chromatin 
(karyosome) in the interior, usually more or less eccentric and 
connected by threads or processes with one or more smaller masses. 
Mature cysts oval, with four nuclei in the single known species, 
similar in structure to those of the free forms. The cysts contain, 



^ n. 

Fig. 36. Endamoeba histolytica. X 1650. A, stained vegetative ameba; 
B, cyst with four nuclei; n., nucleus, showing peripheral chromatin granules and 
central karyosome; r. b. c, ingested red blood corpuscles; chr. b., chromatoid 
body. (After Dobell.) 

Fig. 37. Endamoeba coli. X 1650. A, stained vegetative ameba; B, cyst, 
with eight nuclei; n., nucleus, showing coarse peripheral chromatin granules, 
chromatin granules in "clear zone" between periphery and karyosome, and 
eccentric karyosome; chr. b., remnant of chromatoid body. Note large number 
of food vacuoles in vegetative ameba. (After Dobell.) 

Fig. 38. Endolimax nana. X 1650. A, two stained vegetative forms, show- 
ing nuclei with large irregular karyosome, and numerous food vacuoles. B, cyst 
with four nuclei. (After Dobell.) 




Fia. 39. lodamoeba butschlii. X 1650. A, stained vegetative ameba, showing 
numerous food vacuoles and nucleus (n.), the latter with large central karyosome 
and a single layer of granules between karyosome and nuclear membrane. B, 
cyst, showing nucleus (n.) with peripheral karyosome, and glycogen mass (gl. m.) 
or "iodophilic body," from which these cysts received the name "Iodine or I. 
cysts." (After Dobell.) 

Fio. 40. Dientamoeba fragilis. X 1650. A, stained vegetative ameba, show- 
ing two nuclei with granular karyosomes, and tood vacuoles; B, living ameba, 
showing leaf -like pseudopodia. (A, after Dobell; B, after Jepps and Dobeli.) 

Fig. 41. Councilmania lafteuri. X 1650. A, stained vegetative ameba with 
a pseudopodium in early phase of protrusion and one nearly retracted and filled 
with endoplasm; nucleus showing peripheral chromatin and large irregular, ec- 
centric karyosome; endoplasm filled with food vacuoles. B, cyst showing 8 
nuclei, thick wall, and chromaphile ridge (dark) nearly encircling body, and chro- 
matoid bodies in form of scattered threads. C, cyst showing bud escaping with 
one nucleus; large chromatoid body in center of cyst. (After Kofoid and Swezy.) 

132 AMEB^ 

in addition to the nuclei, a number of small refractile granules 
of a substance known as volutin. The young cysts also contain 
masses of glycogen. (See Fig. 38.) 

lodamoeba. — Nucleus vesicular with moderate-sized central 
karyosome and well developed membrane without a distinct 
peripheral zone of chromatin, but with a single layer of rather 
large granules between the karyosome and the outer membrane; 
cysts very characteristic, formerly known as Iodine cysts or I. 
cysts, of very irregular shape, containing, besides a single nucleus, 
a number of brightly refractile granules and a relatively large 
clearly defined solid mass of glycogen which stains very deeply 
in iodine. The nucleus is peculiar in that the karyosome comes 
to lie peripherally in contact with the nuclear membrane. (See 
Fig. 39.) 

Dientamoehci. — Mature individuals with two similar nuclei; 
these are vesicular with a large central karyosome consisting of 
a number of granules; nuclear membrane very delicate without 
distinct peripheral chromatin; cysts not found. (See Fig. 40.) 

Intestinal Amebae 

The intestinal amebae of man, according to Dobell, consist 
of Endamoeha histolytica, E. coli, Endolimax nana, lodamoeha 
hutschlii :.nd Dientamoeha fragilis, and to these must be added 
Councilmania lafleuri recently described by Kofoid and Swezy. 
A number of other species have been described by various writers, 
but these have probably been either deteriorated examples of the 
known species, body cells mistaken for amebae, or a confusion of 
two other organisms. The discovery by Craig of an intestinal 
ameba having a flagellated stage, and now known as Craigia hom- 
iniSj and the discovery of an allied species, Craigia migrans, by 
Barlow, have not been corroborated by other workers, and, as 
Dobell has pointed out, these organisms are probably in reality a 
mixture of known amebae and flagellates. A number of species of 
free-living amebae are occasionally found in faeces of human beings, 
apparently being able to pass through the digestive tract uninjured, 
but unable to thrive there. These amebae are usually placed in the 
genus Vahlkampfia, in which there is not a flagellated stage in the 
development. Another species of Sarcodina occasionally found 
in human faeces is Chlamydophrys stercorea. This is a common 


organism in the faeces of various animals and in sewage, but there 
is no reason to beheve that it should be considered a human para- 

Endamoeha histolytica. Endamoeba histolytica, (Figs. 35 and 
36) the dysentery ameba, is a large and active species, 18 ^ to 40 /z 
iiiJi^ to -^'Qj^ of an inch) in diameter, the majority being be- 
tween 20 ft and 30 /x in diameter. They are rather transparent 
in appearance, with blunt pseudopodia, and when perfectly fresh 
from the intestine creep along in a sluglike manner. After they 
have been outside the body for a short time they remain in one 
place and throw out large clear pseudopodia composed of ecto- 
plasm sharply separated from the endoplasm (Fig. 35). The 
nucleus is very indistinct and usually eccentric in position. The 
most characteristic feature of the living ameba, however, is the 
presence ot ingested blood corpuscles and tissue cells. Ordin- 
arily there are from one to ten of these, but according to Dobell 
there may be forty. The amebae after being fixed and stained 
can be distinguished from the closely allied E. coli by the nu- 
cleus. This has a peripheral layer of small uniform granules of 
chromatin, no chromatin in the clear zone between this layer 
and the karyosome, and a small centrally placed karyosome sur- 
rounded by an indefinite clear halo. (Fig. 36A.) E. coli has 
a thicker layer of peripheral chromatin, a number of chromatin 
granules in the clear zone, and a larger karyosome, eccentric in 
position, with a more distinct " halo " (Fig. 37A). 

There are two stages in the life history of this ameba, the vege- 
tative and the cystic. As long as conditions in the intestine are 
favorable for their growth and development, the amebae continue 
in their active vegetative condition, multiplying by simple divi- 
sion of the body into two. When conditions have become unfavor- 
able for them, however, as in later stages of the disease, they 
decrease in size, become rounded, and begin to develop a cyst 
wall. This is known as the precystic stage. From this stage 
they pass rapidly into the cystic stage by the completion of the 
cyst wall and the division of the nucleus into four daughter nu- 
clei, thus forming the well-known " tetragena " cysts, long sup- 
posed to belong to a distinct species (Fig. 36B). The size of the 
cysts varies from 5 jn to 20 m (zih-^ ^o tAtt o^ ^^ inch) in 
diameter and there are a number of races or varieties of the ameba 
which differ from each other in the average size of the cysts. 

134 AMEB^ 

The nuclei have exactly the same structure as in the free amebse 
but are smaller. The majority of freshly passed cysts contain 
blocks or masses of a highly refractile substance, called chroma- 
toid bodies by Dobell (Fig. 36B, Chr. b.). These gradually dis- 
appear in the course of a few days. The normal cysts of the 
dysentery ameba are distinguishable from those of E. coli by 
the number of nuclei, and also by the central position of the 
karyosomes. The cysts pass out with the fseces of the infected 
individual, and live outside the body for a number of weeks if 
kept cool and moist. They are destroyed by desiccation and 
degenerate rapidly at high temperatures. 

As cysts the amebae are dispersed by " night soil " when used 
as fertilizer, by seepage into water, by flies and other insects, 
or by other means. If by any of these means they reach human 
food or water and thus secure entrance to the digestive tract, 
the cyst wall is dissolved by the pancreatic juice and four little 
amebae, each containing one of the daughter nuclei which were 
formed when the cyst first developed, are set free in the intestine 
and begin to grow and multiply. The active vegetative amebae 
from an acute case of dysentery are destroyed in the stomach if 
swallowed, and only the parasites in the encysted stage, with an 
enclosing capsule to protect them from being digested, can reach 
the intestine and cause disease. 

The dysentery amebae inhabit the tissues of the walls of the 
large intestine, where they cause more or less extensive ulcer- 
ation. From this point they are carried by the lymph or blood 
stream to various other parts of the body, where they form 
local abscesses. Such abscesses are commonest in the liver but 
occasionally occur in other organs, such as the lungs, brain and 
spleen. The amebae probably live entirely on the living tissues 
and blood corpuscles, the tissues being destroyed by means of a 
powerful cell-destroying substance produced by them. 

Until recently the dysentery ameba was thought to be almost 
exclusively a parasite of tropical and subtropical countries, but 
in recent years it has been shown to be widespread throughout 
temperate climates as well, having been found endemic in nearly 
all parts of the United States and in the British Isles and Central 
Europe. The amount of endemic infection in temperate parts 
of both Europe and America has been greatly increased since the 
European war. Kofoid Kornhauser and Plate found 10.8 per 


cent infection among returned American overseas troops m con- 
trast to 3 per cent in home service troops. In India, on the other 
hand, MacAdam estimates that one-third of the inmates of 
hospital wards are infected with E. histolytica. 

Amebic Dysentery and Liver Abscesses. — One of the most 
serious menaces in the tropics is dysentery; people who have 
always lived in temperate countries have no conception of the se- 
verity of this ailment. In many tropical countries dysentery ranks 
next only to malaria as a cause of death, and very often it finishes 
the work of such diseases as malaria, kala azar and other fevers. 
There are many different types of dysentery, especially in the 
tropics, each showing somewhat different symptoms and having 
to be treated in different ways. Some cases of dysentery are due 
merely to improper diet, some to disturbances of the digestive 
tract due to other diseases, and the majority to intestinal para- 
sites of some kind, either bacteria, protozoans, or worms. In 
a restricted sense " dysentery " is used for intestinal diseases 
caused by bacteria or protozoans. The diseases caused by pro- 
tozoans other than amebse are discussed in the chapter preceding 
this. " Bacillary dysentery " is a bacterial disease and need not 
be discussed here except in comparison with other types of dysen- 
tery. It occurs in temperate as well as in tropical countries and 
is very common in epidemic form in armies, prisons and asylums. 
Amebic dysentery, on the other hand, is uncommon outside of 
warm climates, but is of frequent occurrence in local areas in almost 
all tropical and subtropical countries, where frequently a large 
majority of dysentery cases are caused by amebse. The propor- 
tion of cases of amebic dysentery to infections with the amebae 
seems to be higher, and the disease more severe, in warm than in 
temperate climates. Many of the cases of " trench diarrhea " 
which occurred in France were a mild form of amebic dysentery. 

The role played by amebae in dysentery was in doubt for a 
long time. The presence of amebae in perfectly healthy individ- 
uals and the fact that amebae grown in artificial cultures would 
never give rise to dysentery experimentally confused the problem. 
There are several reasons for this confusion. In the first place 
there are common species of intestinal amebae, especially Enda- 
moeha coli and Endolimax nana which do not attack the tissues 
or cause dysenteric symptoms, but which are easily confused 
with E. histolytica. In the second place, non-parasitic amebae 

136 AMEB.E 

normally found in water or soil, may pass through the intestine 
uninjured, and these are the ones which have commonly been ob- 
tained in cultures from faeces. In the third place infection with 
Endamoeha histolytica does not by any means cause dysentery 
in all cases; in fact, it may be said that in a normal infection 
there is sufficient resistance on the part of the host so that no 
appreciable harm results from the attacks of the parasites. The 
injury done to the tissues is repaired rapidly, and while a certain 
amount of ulceration probably exists in practically all cases, 
it may not be sufficient to cause dysentery. Individuals 
who thus harbor amebae without being greatly inconvenienced 
by them are the so-called " carriers " of the disease. It is prob- 
able that only a small percent of infections, possibly only 10 per 
cent, actually give rise to dysenteric symptoms. The carriers 
constitute the principal means of dispersal of the parasites, since, 
to protect themselves against the reactions of the host, the amebse 
are constantly encysting, and the cysts are constantly being lib- 
erated with the faeces. In acute cases only free amebse, which 
cannot infect other individuals, are passed; convalescents, how- 
ever, usually become carriers for variable lengths of time, and 
may frequently suffer relapses. 

The Disease. — Experiments made by Walker and Sellards 
in feeding ameba-infected material to animals and human vol- 
unteers showed that dysenteric symptoms, if they appeared, oc- 
curred in from 20 to 94 days, averaging about two months. The 
most marked symptom is an acute diarrhea in which the stools 
consist largely of blood and mucus. In a typical case from Ala- 
bama a patient passed as many as fifteen or twenty stools in an 
hour. This condition had been going on for years, recurring 
about three or four times a year, lasting a month at a time. In 
the intervals between these attacks the symptoms were mild and 
the patient passed only two or three stools a day. Sometimes 
the attacks are more regularly chronic, or may recur at long in- 
tervals. Often the dysentery is accompanied by evening fever 
and anemia from loss of blood in the bowels. 

Instead of producing ulcers on the mucous surface of the large 
intestine such as occur in bacillary dysentery, the amebae com- 
monly work deeper into the muscular linings of the intestines. 
Local swellings first appear, followed by an ulceration of the 
mucous membrane. This produces a portal for the entrance of 


the amebae to the tissue underlying the mucous membrane, and 
here they make extensive excavations. The lesions are most 
common in the upper half of the large intestine but can be found 
from the lower part of the small intestine to the rectum. The 
exposed ulcerations vary from the size of a pinhead to that of a 
silver dollar, their ragged edges tending to roll into the crater- 
like areas. Often the tunnel-like excavations under the mucous 
membrane connect with one another. 

Liver abscess is a common result of infection with Endamceba 
histolytica. Often these abscesses are of large size, filled with a 
slimy and somewhat bloody chocolate-colored pus. Over a quart 
of such pus has been removed from an amebic liver abscess. 
The parasites are found at the edges of the abscess, eroding more 
tissue and enlarging the pus cavity. How they reach the liver 
to do their damage is not certainly known, but it seems probable 
that they bore into blood vessels in the walls of the diseased large 
intestine and are carried by the portal vein to the liver, where 
they find a fertile feeding ground. 

Infections with E. histolytica are very persistent, and, with- 
out treatment, may persist throughout the lifetime of the host. 
In many cases dysenteric symptoms never develop, while in other 
cases there may be intermittent attacks or an attack after the 
infection has persisted harmlessly for months or years. 

Treatment and Prevention. — One of the greatest discoveries 
in the field of medical treatment since the production of salvar- 
san by Ehrlich is the discovery of emetin as a specific against 
amebic dysentery. Emetin is an alkaloid prepared from ipecac, 
the extract of the roots of a Brazilian herb. It was long known 
that ipecac sometimes had a very marked effect on dysentery, 
but since amebic dysentery has only recently been differentiated 
from other forms very variable results were obtained from its use. 
Ipecac has a decided disadvantage in that it causes violent vom- 
iting, but its alkaloid, emetin, in the form of emetin hydrochloride, 
while possessing all the beneficial properties of ipecac, can be used 
in the form of injections into the veins, and therefore does not 
cause vomiting. Experiments with cultural species of amebae 
showed that emetin (emetin hydrochloride) is destructive to 
amebae when diluted 500,000 times, and the intestinal amebae 
on a microscope slide become round and motionless and appar- 
ently dead when subjected to this very dilute solution. It is now 

138 AMEByE 

thought however, that emetin acts rather by its effect on the tissues 
of the host than by its direct poisonous action on the amebae. 
Emetin is given in hypodermic injections. Almost without 
exception the effect of the drug on the disease is certain and rapid. 
Severe cases which have been running on for years can be cured 
in four or five days by this simple treatment. One of the chief 
disadvantages is that the treatment is often discontinued too 
soon. The dysenteric symptoms disappear as if by magic and 
the patient is often not willing to be subjected to continued drug 
injections until every trace of the amebae has disappeared. 
Emetin is powerless against encysted amebae and an apparently 
cured patient may continue to harbor and scatter these dangerous 
microscopic particles of living matter for some time, thus en- 
dangering other members of the community. Possibly self- 
infection from the cysts lodged in the tissues of the intestine is 
the cause of the frequent recurrence of infection after inadequate 
treatment, but it is more probable that some of the free parasites 
escape the action of the drug and continue to multiply and de- 
velop new cysts. Under continued treatment the cysts gradually 
disappear from the intestine, but their exodus is hastened by purges. 

Bismuth subnitrate has been used with good success in con- 
junction with emetin, the bismuth acting as a sedative on the 
intestine and aiding in healing of the lesions, and also as an amebi- 
cide. A daily enema of saline solution also seems to aid the 
efficiency of emetin. 

Another preparation of emetin, alcresta ipecac, is effective 
against dysentery amebae, though not so certain in its action 
as the hydrochloride. It has an advantage in that it can be 
taken in the form of tablets when a physician is not available 
and the apparatus for hypodermic injection is not at hand. 
Some doctors in southern United States have advocated the 
use of extract of a common southern plant, Chaparro amargosa, 
to destroy intestinal amebae. This extract is very cheap and en- 
tirely devoid of danger in ordinary doses, but its use in place 
of emetin has not yet been sufficiently justified. 

Walker and Emrich have recently (1917) reported the success- 
ful use of oil of chenopodium for treatment of mild cases of amebic 
dysentery, and especially of "carriers.'' It is pointed out that 
emetin in its various forms is often inefficient in treatment of 
carriers on account of its powerlessness against encysted amebae 


and its inability to eliminate them. These investigators em- 
phasize the importance, before giving the oil, of a preliminary- 
purgation with Epsom salts (magnesium sulphate) sufficient to 
produce fluid bowel movements, the purpose being both to re- 
move excess faecal matter from the intestine and to bring the 
amebse out of their protective cysts and subject them in the 
unencysted condition to the action of the chenopodium. The 
treatment found most effective by Walker and Emrich is as fol- 
lows: (1) magnesium sulphate, from one-half to one ounce, 
at 6 A. M. ; (2) oil of chenopodium, 16 minims in gelatine capsules 
(to obviate disagreeable odor and taste), at 8 a.m., 10 a.m. and 
12 M., and (3) castor oil, one ounce, containing 50 minims chloro- 
form, at 2 p. M. This or any other treatment should be followed 
by examination of the faeces at intervals for some weeks after 
treatment, to make certain of the cure. 

The keynote to the prevention of dysentery whether it be 
caused by amebae or other protozoans or bacteria is sanitation. 
The efficacy of sanitary measures was well illustrated by the fact 
that during the first month of the occupancy of Vera Cruz by 
the Americans in 1914 there were four times as many cases of 
dysentery as during the second month when sanitary measures 
had been taken and were enforced. The fact that only the en- 
cysted parasites as found in the fresh or dried faeces of infected 
individuals can cause disease suggests a simple remedy in the 
proper disposal of infected faeces. In tropical countries, however, 
such a preventive measure is not so simple as it sounds. In 
many districts where amebic dysentery is endemic the first ru- 
diments of sanitation are unknown and every possible method of 
transmission of amebic dysentery is given full opportunity. 
Polluted drinking water, uncleanHness, transmission by flies, 
and the almost universal use of " night-soil " (human faeces) 
for fertilizer, all help the cause of dysentery and account for its 

The segregation and cure of dysentery patients, and the care- 
ful disposal of their faeces, is not enough to eradicate the disease 
entirely since there are many immune carriers of the disease who, 
though apparently well, harbor the encysted amebae in their 
faeces and thereby constitute a source of danger to the community. 
Thorough sanitation throughout the community is the only pre- 
ventive measure which is adequate. 

140 AMEB^ 

Still anotner possible factor in the distribution of dysentery 
amebse is the rat. Dr. Lynch of Charleston, S. C, states that in 
that city rats suffer from amebic dysentery as well as man. 
The fact that rats became infected by eating infected human 
fseces, the frequent occurrence of the disease in rats in houses 
where human amebic dysentery has occurred, and the ready 
transmission of the disease from rat to rat indicate that the rat 
infection is identical with that in man, and is not due to the ameba 
peculiar to rats, E. muris, and that rats may play an important 
role in the spread of the human infection. It may be that rat 
destruction will prove to be an important preventive measure 
against amebic dysentery. Chatton has recently transmitted the 
disease to guinea pigs also. 

Other Intestinal Amebae. — As stated above there are a number 
of other species of amebse which occur as human parasites, but as 
compared with E. histolytica most of them are of little importance. 
They are not tissue parasites, except possibly Councilmania 
lafleuri, but feed principally if not exclusively on bacteria or dead 
organic matter with which they are associated in the intestine. 
Their principal importance lies in the possibility of their confusion 
with the dysentery amebse. 

One of the commonest species is Endamceha coli. In stained 
preparations this species can be distinguished from E. histolytica, 
which it resembles in size and habitat, by the characteristics 
given on p. 133, (cf. also Figs. 36 and 37). E. coli is usually 
more sluggish in movement than E. histolytica. It never con- 
tains blood corpuscles, but the body is often filled with nu- 
merous food vacuoles containing bacteria or' other material 
ingested from the intestinal contents (Fig. 37A). The cysts 
of E. coli (Fig. 37B) are, on the average, larger than those of 
E. histolytica, but as with the latter species there are races dis- 
tinguishable by the size of the cysts. The average sizes in differ- 
ent races vary from 15 /x to about 22 n. The mature cysts nor- 
mally contain eight nuclei in contrast to the four usually found in 
E. histolytica. Even in the four-celled stage the cyst can readily 
be distinguished from those of E. histolytica by the eccentric 
position of the karyosomes of the nuclei. According to Dobell 
" E. coli has been found living as a harmless commensal in the 
colon of man wherever and whenever it has been sought : no race, 


nor any country, has yet been discovered in which infections with 
this species are not common." 

There is no effective treatment for E. coli infections. Since 
the parasites do not hve in the tissues they are, Uke the intestinal 
flagellates, unaffected by emetin. 

Councilmania lafleuri (Fig. 41), formerly confused with En- 
damceba coli, has recently been described by Kofoid and Swezy. 
The free amebae are very active, and creep about with re- 
markable rapidity. They commonly produce only a single pseu- 
dopodium at a time, and this is composed entirely of clear 
ectoplasm. The pseudopodia are peculiar in that they are shot 
out almost instantaneously for the greater part of their length. 
The endoplasm is usually loaded with food vacuoles containing 
bacteria, faecal particles, and also frequently red blood corpuscles, 
the latter fact indicating that this parasite, like Endamceha 
histolytica, is in part a tissue parasite. The most striking and 
distinctive characteristic is the method of escape of amebulae 
from the cysts by a repeated process of budding, a single nucleus 
at a time slipping out through a pore in the cyst wall, surrounded 
by a part of the cytoplasm (Fig. 41C). It is probably the only 
parasitic ameba in which the cysts act as a means of multiplica- 
tion without transfer to a new host. 

Another common intestinal ameba of man is Endolimax nana, 
(Fig. 38), the principal characteristics of which are given under 
the genus Endolimax on p. 129. It is a small ameba measuring 
from 6 Ai to 12 /z (^uVir to -^^-^ of an inch) in diameter. It creeps 
sluggishly like E. coli, and, like that species, often contains numer- 
ous food vacuoles filled with bacteria. The four-nucleated cysts 
(Fig. 38B) might be confused with those of E. histolytica, but are 
distinguishable by their small size (usually 8 to 10 /z by 7 to 8 /x), 
their oval shape, and the peculiar structure of the nuclei, described 
on p. 129. This is a very common human parasite, having been 
found in as high as 33 per cent of some series of examinations 
made by competent workers. Although frequently found in 
dysenteric patients associated with Endamoeha histolytica, there 
is no evidence that this species is at all pathogenic. Like E. coli, 
this ameba cannot be eliminated by emetin or any other drugs 
although it temporarily disappears during emetin treatment. 
Its exact habitat in the intestine is not known, but it is certainly 
not a tissue parasite. 

142 AMEB^ 

lodamoebe butschlii (Fig. 39) is a small ameba (usually 9 m to 
13 fx in length) the characteristics of which have been sufficiently 
described on p. 132. The cysts of this species (Fig. 39B) were 
until recently thought to be of vegetable nature and were known 
as Iodine or I. cysts. The cysts are not smaller than the free 
amebse; they are of very irregular shape, as if formed under 
pressure. This ameba, also, has a wide geographic distribution 
and, while not so common as the intestinal amebae hitherto dis- 
cussed, the available data indicate its occurrence in from 3 per 
cent to 5 per cent of all human beings in temperate or tropical 

Another very small human ameba, Dientamoeha fragilis (Fig. 
40), has recently been described by Jepps and Dobell. This 
species averages only about 8 or 9 m (^^^ of an inch) in diameter, 
thus resembling Endolimax nana. The free amebae are active, 
showing well marked ectoplasm and endoplasm. The pseudo- 
podia are of ectoplasm, and are flat and leaf like (Fig. 40B). The 
peculiar features of the organism are described on p. 129. The 
most characteristic feature of this ameba is the division of the 
nucleus shortly after cell division has occurred, so that mature 
individuals have two similar nuclei. No cysts have yet been 
found, yet it is highly improbable that the infection is transmit- 
ted by the free amebae, since the latter are very short-lived outside 
the body. The habits of the organisms are probably similar to 
those of the harmless amebae already described. Only ten cases 
of infection have so far been discovered, but the evidence afforded 
by these cases indicates a wide geographic distribution. 

Mouth Amebae 

The occurrence of amebae in the human mouth has been known 
for many years, but particular interest has attached to them 
only recently, since a number of investigators have brought forth 
evidence to show that the common mouth ameba, Endamoeba 
gingivalis, is pathogenic, and an important factor in pyorrhea. 

Pyorrhea, or Rigg's Disease, in some stage afflicts the ma- 
jority of all adult people, and over 50 per cent of all permanent 
teeth which are lost are lost as the result of pyorrhea. The 
apparent relation between this disease and the presence in the 
mouth of the above-mentioned ameba, E. gingivalis (or buccalis), 
was first demonstrated in 1914 by Smith and Barrett. Since 


then there has been much controversy as to the role played by 
the amebse in connection with the disease, and most authorities 
are now inclined to look upon the amebae as having little or no 
important part in the pathogenic process, but this question cannot 
be considered as settled. The prevalence of amebae in the mouth, 
even in young children, is well shown by a recent investigation 
by Anna Williams of the mouths of over 1600 school children in 
New York City. Of the children between five and seven years 
of age 35 per cent were found infected, while of those between five 
and fifteen years 60 per cent were infected. 

The mouth ameba, E. gingivalis, can be found by placing a 
bit of the pus from a tooth pocket, or the scrapings from the 
teeth, on a microscope slide. Here the parasites will be found 
intermingled with pus cells and bacteria. They are from one to 
three times the diameter of the pus cells, usually from 12 /* to 20 m 
(ttjV^ to T^Vir of an inch) in diameter, and have a granular ap- 
pearance; the nucleus is relatively very small. Often when 
stained they show dark bodies inside of them which are probably 
the nuclei of other organisms or of semi-digested pus cells. When 
living the amebae prowl about sluggishly, pushing out a blunt 
pseudopodium now on one side of the body, now on the other, then 
drawing up the body, and pushing out more pseudopodia, thus 
slowly working their way about between the pus cells and frag- 
ments of tissue. The outer layer of the body, or ectoplasm, 
which serves as a sort of protecting envelope, like the rind on a 
melon, is clear and transparent but is not readily distinguishable 
except when the animal is moving. The pseudopodia are always 
formed first out of this clear ectoplasm, the more granular, gray- 
ish inner substance or endoplasm pouring out into it later. The 
reproduction of these little animals is by a simple division of the 
body into two when they have grown large enough to feel cumber- 
some as single individuals. Although cysts have been described 
by some workers, there is insufficient evidence for their existence, 
and it is more probable that infection is spread by simple direct 
or indirect transfer of the free amebae from mouth to mouth. 

Some investigators have suggested the possible identity of 
E. gingivalis and E. histolytica, but, as pointed out by Craig, 
the sluggish movements, small nucleus, inability to produce 
dysentery when swallowed and other characteristics all indicate 
that without doubt the mouth ameba is quite distinct from the 
intestinal amebae. 




Endamoeba gingivalis and Disease. — As intimated above, 
although the presence of amebse in the mouth has been known 
for many years, these parasites attracted Httle interest until 
1914 when several investigators called attention to ah apparent 
relationship between the amebse and the presence of pus pockets 
between the teeth and gums, a disease known to dentists and 
physicians as " pyorrhea alveolaris." The amebse do not thrive 
on exposed surfaces in the mouth, but find a congenial environ- 
ment in any little secluded pockets between the teeth and gums, 
in crevices between close-fitting teeth, or where a bit of food forms 
a protected spot for them. Stowed away 
in such places, and invariably accompanied 
by bacteria and often spirochsetes, they 
multiply rapidly. That they feed largely 
on other organisms cannot be doubted, but 
that they prey also on the living tissue 
cells is very probable. Eventually the 
delicate peridental membrane surrounding 
the roots of the teeth (Fig. 42), correspond- 
ing in a general way to the periosteum of 
bones, is eaten away and becomes ulcerated. 
The eating away of the living membranes 
of the teeth and gums is accompanied by 
a constant formation of pus, and a marked 
proneness for the gums to bleed, often with- 
out provocation. The swallowing and ab- 
sorption of the pus and of the poisonous 
waste products generated by the parasitic 
organisms are probably the cause of the 
more or less noticeable constitutional symptoms which accom- 
pany the disease. These may consist of feverishness, dis- 
ordered digestion, nervous troubles, rheumatic pains in the 
joints, anemia, or various combinations of these ailments. We 
have long known that unhealthy mouths were the cause of gen- 
eral bad health, but we never until recently had any definite clue 
to the reason why. 

As the ulceration of the membrane continues, the tooth is 
gradually loosened from the gum. Just as meadow mice girdle 
fruit trees, so these amebae, or the bacteria or spirochsetes which 
accompany them, eat away the living *' bark " of the teeth and 


Fig. 42. Sketch of 
tooth showing peridental 
membrane, which is the 
tissue attacked by Enda- 
moeba gingivalis and the 
seat of pyorrhea, peri- 
dent., peridental mem- 
brane; periost., perios- 
teum; cr., crown; r., 
root; p. pulp. (After 
Bass and Johns.) 


gums, eventually causing the teeth to fall out. As already stated, 
over 50 per cent of all permanent teeth which are lost fall out as 
the result of pyorrhea. 

Whether the formation of the pus pockets is initiated by the 
amebse or by other organisms is not known, but certain it is that 
Endamceha gingivalis is with few exceptions found in the lesions, 
and at the very bottom of them, often burrowing into the in- 
flamed tissues to a depth of several times its own diameter, de- 
vouring cells and transporting bacteria. The belief in the role 
of the amebse is based on these facts and on the fact that often, 
though not always, the disease is greatly improved by treatment 
with emetin, which has a specific action on amebic dysentery. 
Some investigators, notably Craig, consider it, to quote from Craig, 
" more than doubtful that Endamceha gingivalis is the cause of 
pyorrhea alveolaris, this conclusion being based upon the follow- 
ing facts: the occurrence of the parasite in a large per cent of 
healthy mouths and in the material that can be scraped from 
healthy teeth and gums; the occurrence and persistence of the 
parasite in patients treated with emetin, even when marked 
improvement in the clinical symptoms have occurred; the ab- 
sence of the parasite in some typical cases of pyorrhea; the lack 
of improvement with emetin shown in numerous instances of the 
disease, although the endamebae may disappear; and the fact 
that emetin acts upon other organisms as well as upon endamebae 
and the possibility that the improvement that often follows its 
administration may be due to such action or to a favorable action 
on the tissue cells." That these facts argue against the causa- 
tion of pyorrhea by amebae alone is unquestionable. These 
facts, however, are not only not opposed to the possibiUty of 
amebae being partly or indirectly responsible for the disease, 
but may be interpreted as being in support of such a view. It is 
entirely in accord with the known facts about the disease to 
suppose that the pus pockets may be initiated or enlarged by the 
action of amebae, the damage being then continued by bacteria 
which have been given a portal of entry. This would account for 
the occasional absence of amebae in typical cases of pyorrhea and 
for the occasional cases of the disease which are not improved by 
emetin. It is further quite conceivable that the amebae may live 
for a long time in crevices in the mouth without doing any 
damage, and yet be capable of causing or aggravating pus pockets 

146 AMEB^ 

under suitable conditions. Perhaps some slight injury to the 
membranes or the combined action of the amebae and certain 
bacteria is necessary to start the process. Parallel cases of 
parasites which may hve for a long time as harmless messmates 
and then, under favorable conditions, become pathogenic are 
well known; one of the best examples is the intestinal ciliate, 
Balantidium coli. This would account for the presence of 
Endamceha gingivalis in healthy mouths. It is significant that in 
her investigation of school children in New York, Anna Williams 
found only 30 per cent of apparently healthy mouths, and 94 
per cent of mouths with spongy and bleeding gums, infected. 
As to the statement that amebse still exist in pus pockets after 
treatment with emetin, even when there is marked improvement 
in clinical symptoms, there is no doubt but that the number of 
amebse is greatly reduced, and those on the frontier where the 
most damage is done are undoubtedly killed, since they are most 
exposed to emetin in the blood. The ineffectiveness of emetin 
against amebse which are not directly in the tissues has been 
demonstrated in the case of the intestinal amebae which are not 
tissue parasites (see p. 139). Again, were the improvement 
following treatment with emetine due to favorable action on the 
tissue cells, such improvement would invariably follow. That 
emetin affects other organisms besides amebae is true, but it is 
more active against these protozoans than against any other or- 
ganisms, as far as is known. The complete cure of pyorrhea 
which emetin sometimes effects, the usual improvement shown 
after its use, and the occasional failure of it, all point to the in- 
strumentality of amebae in causing or aggravating the disease, 
but indicate that they may be aided and abetted, or entirely re- 
placed, by bacteria or other organisms. 

There is some evidence that chronic tonsilitis also is often 
caused by E. gingivalis, since this parasite is found in the ma- 
jority of diseased tonsils, irritating the tissues and opening the 
road for bacteria. 

An indirect relation of this same mouth ameba to certain types 
of goitre also has been shown to be very probable. Evans, 
Middleton and Smith found that diseased tonsils and nasal 
passages and enlarged thyroid glands (goitre) are frequent com- 
panions in the goitre belt of Wisconsin. They believe that the 
amebse injure the tissues sufficiently to give ample opportunity 


for bacteria to enter and multiply in enormous numbers, and that 
certain of these bacteria produce poisonous substances which 
exert a stimulative effect on the thyroid glands, thus causing 
goitre. The effect of the presence of amebse, indirect as it is, 
can be fully demonstrated by destroying them with emetin. In 
18 out of 23 cases of goitre treated with emetin the size of the 
thyroid mass was obviously reduced. 

Prevention and Treatment. — Ordinary cleanliness of the 
mouth by frequent brushing of the teeth, rinsing of the mouth, 
and care of imperfect teeth is the most important factor in keep- 
ing the gums healthy and free from an injurious degree of amebic 
infection. In the investigation of school children in New York 
already mentioned the number of ameba-infected mouths was 
reduced one-half by ordinary cleanliness and care. Such 
methods, however, are of little value if the amebae have estab- 
lished themselves in a pus pocket, since in such situations they 
cannot be reached by the usual methods of mouth cleansing. In 
the New York investigation it was found that mouths could almost 
always be freed of amebae by using a mouth wash with a weak 
solution of emetin, the latter being a valuable preventive measure. 
In older people, however, where the amebae have often already 
succeeded in stowing themselves away in little crevices and 
pockets where mouth washes cannot reach them, some other 
method must be employed. The ideal method is to open up and 
thoroughly clean out any pus pockets which can be found. 
This should be followed by a hypodermic injection of emetin, 
repeated on a few successive days to destroy the amebae if possible. 
The effect of the emetin on Endamoeba gingivalis is not as marked 
as was formerly thought, and Dobell goes so far as to say " it thus 
seems probable that emetin has no specific action upon E. gingi- 
valis, and that the original claims were based upon insufficient 
evidence." Usually with the administration of emetin the sore- 
ness ceases, the pus formation stops, the gums stop bleeding and 
the general health rapidly improves. Of course it takes time for 
the injured tissue to heal and the part destroyed is never replaced. 
There is also constant danger of reinfection and the already eroded 
pocket forms an excellent place for fresh amebae to take up a 
claim and begin their work. Furthermore there are cases of 
pyorrhea which do not respond to treatment with emetin, prob- 
ably because the work is continued by bacteria. Emetin, diluted 

146b ameb^ 

200 to 400 times in alcohol and applied with a tooth brush, 
is usually sufficient to kill recently implanted amebic infections. 
A thorough mouth rinse with a drop or two of emetin in half a 
glass of water is an excellent protective measure but even with 
the use of these means of prevention some apparently cured cases 
of pyorrhea get reinfections within a few months. 

As intimated before, the prevention of infection with End- 
amoeba gingivalis is largely a matter of ordinary mouth hygiene. 
Infection can be avoided to a large extent by care in eating and 
drinking. One should never eat or drink with the same articles 
that have been used by other people. The practice of promis- 
cuous kissing is, of course, a ready means of transmission for 
these parasites as for many others. 

Occasional infection with Endamceha gingivalis is, however, 
almost inevitable. If the mouth is kept scrupulously clean and 
in as near perfect condition as possible the amebse may find no 
congenial place to settle down, but in the vast majority of mouths 
there is an abundance of fertile ground for them. 


Importance. — Of all human diseases there is none which is of 
more importance in the world today than malaria, and this in 
spite of the fact that we have a very full knowledge of its cause, 
the manner of its spread, its cure, and means of prevention. It 
has been estimated to be the direct or indirect cause of over one- 
half the entire mortality of the human race. Sir Ronald Ross 
says that in India alone it is officially estimated that malaria kills 
over one million persons a year, a greater number of deaths than 
was caused by the great European war in the first two years of 
its existence. When there is added to this the thousands from 
the rest of Asia, Africa, Southern Europe, South and Central 
America, and the southern part of our own country who are 
annually sacrificed on the altar of the malarial parasite; the 
millions of others who are broken in health, incapacitated for 
work and made easy victims of other diseases; the valleys, 
countries, and even continents which have been barred from full 
civilization and development by this more than by any other 
cause; then only can we get a glimpse of the real meaning of 
malaria to man. Ross argues convincingly that the downfall 
of the great Greek empire and the present poverty-stricken 
bhghted condition of many parts of Greece is probably due 
primarily to the invasion of that country, not by burning and 
devastating armies of men, but by the malaria parasite, an in- 
finitely more terrible though unseen foe which destroyed the new- 
born infants, undermined the health of the children or killed 
them outright, rendered the richest agricultural lands uninhabi- 
table, and, in a word, sapped the vitafity of the people until the 
boasted power and glory of Greece is but a mocking memory. 

Though historians and economists have failed to recognize it, 
the r61e of malaria and other endemic diseases must have played 
an enormous part in the history of the world and in the progress 
of nations. Malaria and its powerful accomplice, the hook- 



worm, are largely responsible for the present deplorable condition 
of some parts of our own South. Dr. Howard estimated in 1907 
that there were nearly 12,000 deaths a year in the United States 
from malaria. This, however, is probably almost inconsiderable 
when the amount of damaged health and weakened resistance to 
other diseases is taken into consideration. Dr. Von Ezdorf , of the 
U. S. Public Health Service, in a recent attempt to estimate the 
prevalence of malaria in the United States, obtained data, based 
on morbidity reports, which indicate that at least four per cent of 
the population of eight southeastern states — 1,000,000 people 
— is affected by the disease annually, and found by 13,526 blood 
examinations that over 13 per cent harbored malarial parasites 
in their blood, the percentage being much higher in negroes 
than in whites. Dr. Howard thinks that an estimate of 3,000,000 
cases of malaria a year in the United States would not be too 
high. Millions of acres of fertile land in this country are rendered 
useless or only imperfectly cultivable. Taking everything into 
consideration. Dr. Howard makes the astounding but well- 
founded statement that the annual financial loss to the United 
States from malarial diseases is not less than $100,000,000. 
This is the condition in the United States, a large portion of which 
is relatively free from malaria, and in no part of which is the dis- 
ease so prevalent or so destructive as in the tropical portions 
of Asia, Africa and South and Central America. In a broad way 
one-third of the population of highly malarial countries suffer from 
the disease annually. According to Ross the number of deaths 
from malaria in India must reach 1,300,000 every year. Obvi- 
ously the importance of this disease to mankind is not Hkely to 
be overestimated. 

History. — " Malaria " means bad air, and was therefore ap- 
plied to a number of fevers which were commonly associated 
with the bad air of swampy regions. The idea that malaria is 
caused by bad air, unwholesome odors, damp night winds, or 
impure drinking water is even yet adhered to not only by some 
of the populace but even by a few unenlightened medical men. 
Ross says that it takes ten years for the world to grasp a new 
idea, but his estimate is far too low; it is now (1917) 37 years 
since the organism causing malaria was discovered and 19 years 
since its transmission by mosquitoes was experimentally proved. 
It was in 1880 that Laveran, a French army surgeon in Algeria, 


discovered a parasitic " germ " which he proved to be the true 
cause of malarial fevers. Dr. King, of Washington, in 1883 
suggested the probabihty of malaria parasites being spread by- 
mosquitoes, adducing much circumstantial evidence in support 
of his views. It was not until 1898, however, that Sir Ronald 
Ross, an Englishman in the Indian Medical Service, experiment- 
ally proved that the malaria parasite is absolutely dependent 
upon certain species of mosquitoes for its transmission from man 
to man. Only six years ago (1911) the parasites of malaria were 
first successfully cultured outside the human body by Bass and 
Johns at New Orleans, a feat which will eventually lead to new 
and valuable discoveries. Other workers deserve no less credit, 
perhaps, for suggestive ideas, or for additional facts concerning 
the life and control of the malarial parasites. The ultimate 
results of their discoveries have only begun to be felt, but al- 
ready such enterprises as the building of the Panama Canal have 
been rendered possible. The Canal could never have been built 
under the old regime of medical ignorance. Statues of the 
pioneers in the work of unraveling the truths about malaria 
and yellow fever might well have occupied conspicuous places 
at the Panama Pacific International Exposition at San Francisco. 

Malarial Parasites. — Malarial fevers, of which there are 
several different kinds, we now know to be caused by protozoan 
parasites which live at the expense of the red blood corpuscles, 
and are injected into the human body and transmitted from 
person to person only by the bite of certain species of mosquitoes. 

The malarial parasites belong to the protozoan class Sporozoa, 
or spore animals, so called from their habit of reproducing by 
breaking up into a number of small parts or spores, instead of 
simply dividing into two as do most of the Protozoa. All of the 
Class Sporozoa are parasitic and have no organs of locomotion 
when full grown. Although there are many different kinds 
which live as parasites in other animals, very few normally attack 
man and only the malarial parasites, belonging to the genus 
Plasmodium, are of primary importance. There is still consider- 
able disagreement as regards the classification of the human 
malarial parasites. Nearly all workers on the subject agree 
that there are at least three well-defined species of Plasmodium 
causing human malaria, and there is some evidence that distinct 
subspecies or varieties of some of these occur. The commonest 


and most widely distributed species is Plasmodium vivax, which 
causes tertian malaria. Of somewhat more limited geographic 
range, being confined to tropical and subtropical countries, but 
of infinitely more importance on account of the deadly nature of 
its attacks, is Plasmodium falciparum, the cause of the sestivo- 
autumnal type of malaria, also called malignant tertian or subter- 
tian fever. During the hot part of the year in the tropics 96 per 
cent of malarial cases are of the sestivo-autumnal type. The third 
species, Plasmodium malarice, causing quartan malaria, is relatively 
uncommon, though more frequent in temperate than in tropical 
countries. These three species of malarial parasites differ from 
each other in a number of important details of structure and 
life history and in the diseases which they produce. 

Life History of Plasmodium falciparum,; Human Cycle. — 
The life history of malarial parasites may well be exemplified 
by that of the malignant aestivo-autumnal parasite, Plasmodium 
falciparum, as diagrammatically shown on Fig. 43. When first 
injected into the human blood by a mosquito the animal is 
exceedingly minute (Fig. 43 A). It immediately enters or at- 
taches itself to a red blood corpuscle, where it grows until it 
occupies one-half or two-thirds of the corpuscle, meanwhile un- 
^dergoing a number of different forms. It first goes through a 
''signet ring" stage (Fig. 43B), the ringlike appearance being 
due to the presence of a transparent area occupying the middle 
of the parasite, while the tiny round nucleus occupies a position 
at one side of the parasite, simulating the setting in a ring. As 
the parasite grows larger it becomes irregular in shape (Fig. 43C) 
and quite active, constantly changing its form, thrusting out 
little clublike processes or pseudopodia, now here and now 
there. Although it has been taken for granted that malarial 
parasites penetrate the blood corpuscles and live inside of them 
recent investigations by Mary R. Lawson (Mrs. Johnson) indi- 
cate that this may not be the case at all, but that the parasites 
may attach themselves to the surface of the corpuscles, squeezing 
up little mounds of the substance of the corpuscles and encircling 
these mounds with their bodies, just as a bit of skin might be 
squeezed up between the fingers. Sometimes several parasites 
attach themselves on top of each other around a single mound. 
A number of facts give support to Mrs. Johnson's theory: it 
affords a logical explanation for the ring forms of the parasite; it 



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explains the occasional distinct projection of the parasites at 

the periphery or edge of the corpuscles (Fig. 44) ; and it accounts 

for the ease with which the parasites may be distorted in making 

blood smears. Another argument in favor of 

Othis theory as opposed to the intracorpuscular 
1 theory is that the haemoglobin in the corpuscles 
' is believed to be in a more or less solid state, 
A and would therefore make it difficult for the 
parasites, if situated inside, to indulge in such 

O active movements as they do. The majority 
of protozoologists, however, have not accepted 
B Mrs. Johnson's conclusions. 
As the parasite develops there is a distinct 
Fig. 44. Blood tendency for the affected corpuscles to clump 

corpuscles showing '^ . . ^ ^ 

malaria parasites together, thus clogging the tiny capillaries which 
at periphery. B ^^^ large enough to allow the passage of only a 

shows two para- . ^ T r- o ^ 

sites resting one smgle corpuscle at a time. In this way the 
??i°Tt-*^r °*^^^' capillaries of such organs as brain, spleen, bone 

(Sketches from mi- ^ ° ? i- ; 

crophotographs by marrow and others may be obstructed to a 
Mary Lawson ^^^^^ degree. Three-fourths of the life cycle of 

[Mrs. Johnsonj.) ° . . , -^ 

the parasites is usually passed in the plugged 
capillaries so that only during one-fourth of their cycle can they 
be found readily in the circulating blood. 

After about forty hours the nucleus of the parasite divides into 
a variable number of fragments, usually from ten or 15 to as 
many as 32, i.e., under favorable conditions it may split five 
times, into two, four, eight, 16, and 32 parts. The rest of the 
body divides itself into portions, one surrounding each fragment 
of the nucleus, thus forming a little heap of '' spores " (Fig. 43E) 
ready to burst apart and leave the corpuscle on which the 
parent parasite had been feeding. In the center of the heap 
can be found a little mass of coal-black pigment granules, the 
waste products resulting from the digestion of the oxygen- 
carrying red substance of the blood, haemoglobin. When the 
parent parasite bursts the young parasites formed by this rapid 
process of multiplication are set free (Fig. 43F) in the blood where 
each enters a new corpuscle and repeats the process of growth 
and reproduction. The pigment and other waste products 
which are left behind when the parasite multiplies are released 
into the blood stream where they are carried to all parts of the 


body and deposited in the spleen or other organs or under the 
skin, causing the sallow color so characteristic of malarial patients. 
It is at the time of the bursting of the corpuscles and release of 
the waste matters which act as poisons that the characteristic 
chills and fever of malaria are felt. Since the cycle from one 
generation to the next is usually about 48 hours in the sestivo- 
autumnal parasite the attacks of ague are felt at these intervals. 
In this malignant type of malaria the bursting of all the para- 
sitized corpuscles and release of poisonous waste matter does not 
occur so nearly simultaneously as it does in the other species, 
the result being that the paroxysms of chill and fever are drawn 
out over many hours. 

A " quotidian " type of malignant malarial fever in which 
agues occur every 24 hours is occasionally met with, the parasites 
of which are thought by some authors to constitute one, or even 
two, distinct species. The majority of cases of malaria with 
daily-recurring fevers are due to double or triple infections, the 
different broods maturing on different days. 

This rapid process of multiplication in the human blood re- 
sults in a short time in an enormous number of parasites, some- 
times many billions. The actual quantity of parasites in a 
human body in a case of severe sestivo-autumnal malaria has 
been estimated at 600 cc, or over one pint. It may or may not 
mean more to the reader to know that such a quantity of ma- 
larial parasites would number 3,000,000,000,000. A better con- 
ception of the real meaning of such a number may perhaps be 
gained when it is realized that to count off this number at the 
rate of 100 per minute day and night without cessation would 
require 30 times the period of time that has elapsed since the 
birth of Christ. Eventually, however, either the parasite kills 
its host, which very commonly happens with this particular 
species, or the host, by the development of a temporary immunity 
in his body, kills or, as it more often happens, suppresses the 
parasite. Such a course of events unaltered, would lead to a 
very early and complete extermination of the parasite. There is 
a second chapter in the life history of Plasmodium which saves 
it from such an early death. 

After the parasites have been developing in the blood for about 
two weeks or more there are developed special sexual forms or 
gametocytes, male and female, in the form of sausage-shaped 


crescents (Fig. 43K and L). Just as in the case of other kinds 
of animals and plants, nature has adapted these animals to cope 
with their environment. As long as the blood of their host forms 
a suitable environment they continue to multiply in the normal 
manner, but when conditions due to the formation of antibodies 
become unfavorable they produce these sexual crescents in large 
numbers and patiently await rescue at the hands, or rather the 
beak, of a mosquito. The crescents may persist in the blood for 
several weeks, gradually disappearing after all other symptoms 
of infection have vanished. Only slight differences can be seen 
between the male and female gametocytes, the female being more 
granular in appearance, and with the pigment particles arranged 
in a more regular triangular manner (Fig. 43K and L). 

Mosquito Cycle. — When sucked into the digestive tract of the 
mosquito these gametocytes begin a complex developmental 
cycle, providing conditions of temperature are favorable. The 
most favorable temperatures are between 75° and 85° F. The 
digestive fluids dissolve the remnant of the blood corpuscles, but 
the crescents resist digestion (Fig. 43M and N) and become more 
obviously sexually differentiated. The male gametocyte de- 
velops into a " flagellated body " (Fig. 43P), a little sphere from 
which several long slender filaments project. These are very 
active, constantly lashing to and fro, and ultimately break loose 
and wriggle about in the stomach of the mosquito like little 
spermatozoa, which, in effect, they are. The female gameto- 
cyte develops into an inactive sphere or gamete (Fig. 430) and 
one of the filaments from the flagellated male enters to fertilize 
it (Fig. 43Q). How perfectly the process simulates the act of 
fertilization of an egg by a spermatozoan in the higher animals! 

The result of the union of the filament from the flagellated 
body with the inactive female gamete is a body which corre- 
sponds in every way to a fertilized egg of a higher animal. This 
new individual, the beginning of a new generation, grows, elon- 
gates, and becomes quite hke a little worm (Fig. 43 R). It now 
wriggles and worms itself about in the stomach of the mosquito 
and penetrates the wall, lodging itself between the inner and 
outer finings of the stomach (Fig. 43S). Here more rapid growth 
takes place and a heavy capsule develops, protruding on the outer 
surface of the mosquito's stomach fike a wart (Fig. 45). Mean- 
while the contents of the capsule undergo important changes, 


dividing into daughter cells (Fig. 43T) from each of which slender 

spindle-shaped bodies project like the " stickers " on a chestnut 

burr (Fig. 43 U). Ultimately the cells lose their identity and 

the entire capsule or cyst becomes crammed 

full to the bursting point with myriads of 

these spindle-shaped bodies which have now 

developed into spores (Fig. 43V). Such a 

capsule may contain over 10,000 spores, and 

there may be as many as 500 capsules on a 

single mosquito's stomach (Fig. 46). About fig. 45~*Cross sec- 

12 days or more, according to temperature, tion of stomach of 

after the infected blood was swallowed by the fr^Sr^^l^Zl'^i 

mosquito, the capsule becomes mature and subtertian malaria. 

bursts, releasing the spores into the body cavity Qr^ssU* ^^ ^ *^^ 

of the mosquito. From here the little parasites 

make their way to the three-lobed salivary gland (Fig. 46, sal. gl.) 

lying in the fore part of the thorax and connecting with the 

sucking beak. They assemble in the cells lining the salivary 

Fig. 46. View of digestive tract of Anopheles, showing spore-filled capsules of 
malaria parasites on wall of stomach, pal., palpi; prob., proboscis; ant., antennae; 
ph., pharynx; oes., oesophagus; sal. gl., salivary glands; f. res., ventral food 
reservoir; d. f. res., dorsal food reservoirs; prov., proventriculus ; St., stomach; 
malp. tub., malpighian tubules; int., intestine. X 10. 

glands (Fig. 43 W) and remain there perhaps for weeks, until the 
mosquito bites. When this happens the parasites flow with the 
poisonous saliva into the puncture made by the mosquito and, 
should the prey of the mosquito be a human being, the whole 


process of asexual multiplication in the human blood corpuscles 
begins over again. Since it takes ten or 12 days for the sexual 
cycle to be completed in the case of sestivo-autumnal malaria, 
an infected mosquito is not dangerous for at least this length of 
time after biting a malarial patient. However, once the new 
generation of spores has been developed, the mosquito remains 
dangerous for several weeks and may infect many persons, as not 
all the parasites are poured out of the saUvary glands at one 

It is commonly believed that malaria parasites not only do not 
develop but cannot live in the mosquito at winter temperatures, 
and conflicting results have been obtained from experimentation. 
King in America and Wenyon in Macedonia have succeeded in 
exposing infected mosquitoes to low temperatures without destroy- 
ing the parasites, whereas Mayne (Mitzmain) found that in 
Anopheles infected prior to hibernation, healthy normal sporo- 
zoites did not last through the winter in the salivary glands. Rou- 
baud obtained similar results in France. It is still doubtful 
whether the malaria parasites normally pass the winter in the 
mosquito hosts in places where the mean temperature falls much 
below 60° F. for any considerable time. 

Other Species. — The other species of malarial parasites dif- 
fer only in minor details of their structure and development. 
The tertian parasite, Plasmodium vivax, during the early stages 
of its development in the blood corpuscles is extremely active. 
Its unceasing restless changing of shape is fascinating to watch 
under the microscope and one feels that it was very appro- 
priately named " vivax." Unlike the malignant parasites of 
sestivo-autumnal malaria, the tertian parasites do not tend to 
clump together, and so do not become plugged in the capillaries 
but remain constantly in the circulation. To this fact, as will 
be shown later, is due the " benign " nature of this and also of 
the quartan parasite. The tertian parasites have the peculiarity 
of growing very large and of causing the corpuscles which they 
parasitize to enlarge and become unhealthy in appearance. 
The number of spores which result from the sporulation every 
48 hours ranges from ten to 25. According to Ross the normal 
number of splits of the nucleus is four, which would result in 
16 spores. One of the most striking points of difference from 
the " malignant " parasites is the fact that the gametocytes 



are not in the form of crescents, but instead resemble mature 
parasites ready to sporulate. A comparison of Fig. 47 A, A' and 
A" with B, B' and B" and C, C and C" brings out the prin- 
cipal differences among the three species of parasites as regards 
size at maturity (A, B, C), number of spores (A', B', C) and form 
of gametocytes (A", B", C"). 

Fig. 47. Comparison of three species of malaria parasites X 2000 (figures 
selected largely from Manson). A, A' and A", Plasmodium vivax; B, B' and B'\ 
Plasmodium malarioe; C, C and C", Plasmodium falciparum. 

A, B and C, mature parasites in red corpuscles. 

A\ B' and C, segmented parasites ready to leave corpuscles. 

A", B" and C , mature gametocytes. 

The quartan parasite more closely resembles the tertian para- 
site in flexibility of body and form of gametocytes (Fig. 47B''), but 
it differs in that it does not cause the corpuscle to enlarge (Fig. 
47B) and is never active in movements. It produces only from 
five to ten spores, the nucleus normally undergoing three splits. 
The spores form a very regular rosette or '* daisy-head," ar- 
ranging themselves petal-like around the dark mass of pigment 
in the center (Fig. 47B'). Unlike either of the other parasites 
this one causes ague by its sporulation once in 72 hours instead 
of in 48 hours. A comparison of certain phases of this parasite 
with the same phases of the others will be found in Fig. 47. 

Propagation. — As remarked above infection with malaria is 
now known to take place exclusively through the bites of certain 
species of mosquitoes, all belonging to the genus Anopheles (in- 
cluding its subgenera). While over a hundred species of Anoph- 


eles have been described, less than one-third have been proved 
to be carriers of malaria. Some species will carry certain types 
of malaria and not others (see p. 439). A knowledge of the 
malaria-transmitting ability of various species of mosquitoes 
and their habits is of the utmost importance in any attempt to 
exterminate malaria by exterminating mosquitoes. The knowl- 
edge that A. malefactor of Panama, breeding in cavities of stumps 
and trees, was not a malaria carrier saved several hundred thou- 
sand dollars in the anti-malarial campaigns in the Canal Zone. 
The distinguishing characteristics of Anopheles and a brief 
account of a few of the more important malaria-carrying species 
will be found on pp. 439-441. 

Reports of malarial outbreaks have occurred which were said 
to be due to some other cause than mosquito transmission, but 
when completely investigated there has always been found to be 
a '' leak " somewhere. Sometimes the presence of mosquitoes 
was unsuspected, sometimes other fevers have been mistaken 
for malaria, and sometimes the malarial parasites have been 
harbored for weeks or months in " latent " form. This is a 
phase of malaria which is little understood, but it is a well-known 
fact that long after symptoms of the disease have disappeared, 
and the parasites can no longer be found in the blood, a fresh 
outbreak may occur, coincident with some loss of vitality, or 
some physiological shock on the part of the host from some 
other cause. Often a mere change of climate and environment is 
sufficient to precipitate " latent " malaria. It is highly probable 
that the ordinary blood parasites are carried in the meantime 
in such small numbers as to be practically impossible to find. 
Ross has pointed out that if 1000 parasites in the body were 
able to withstand the unfavorable conditions and existed there 
during the " latent " stages, a man working 12 hours a day 
searching blood smears would have a chance of finding one 
only once in five years. Some authors have advanced the theory 
that the gametocytes, suddenly stimulated by some unknown 
cause, develop by parthenogenesis, i.e., without the ordinary sexual 
mosquito cycle, and thus cause the relapse. This idea has been 
widely accepted but there seems to be little ground for it and some 
positive evidence against it. The parasites naturally thrive 
best when their host is weakened by some other influence which 
then acts as an accomplice for them. Such influences are ex- 


posure to sudden changes in climate, fatigue, dissipation and 
other sickness. Even educated people often come to believe 
that malaria is directly caused by these conditions. 

Suffice it to say that many experiments, carried out with the 
utmost care and accuracy, and checked by numerous repetitions, 
have proved beyond doubt that the mosquito is the necessary 
transmitter and intermediate host of malarial parasites. A few 
investigators think it possible that other animals besides man 
may serve as hosts for the malarial parasites, so that malaria 
may occur even in uninhabited regions. Although many para- 
sites are able to live in a number of different kinds of animals, 
this does not seem to be true with the malarial parasites, and 
all attempts to infect even monkeys have so far failed. Until 
some definite proof of the role of some other animal as a host 
for human malarial parasites has been brought forward we may 
look upon this as very improbable. Possibly the alleged presence 
of malaria in uninhabited regions may be explained by the 
malarial parasites in the mosquito passing into the eggs of the 
mosquito, and thus being carried on generation after generation. 
Though the germs of some diseases are known to do this in their 
insect hosts, experiments with hereditary transmission of ma- 
larial parasites in mosquitoes have so far been unsuccessful. 

The Disease. — Malaria as a disease is extremely variable. 
A " typical " case of malaria, in the tropics at least, is a rather 
unusual thing. As we have seen, there are at least three different 
kinds of malarial parasites, each of which produces a somewhat 
different disease. While ordinarily all the parasites of a brood 
mature at regular intervals, a person in a malarial district may 
be infected with two or more broods maturing at different times, 
and the case may be farther complicated by a " mixed '' infec- 
tion, that is, by more than one species of malaria at a time. 
Varying degrees of immunity, the effects of insufficient quinine 
or other drugs, the presence of complicating diseases and the 
virulence of the particular strain of parasites all have a hand in 
modeling the effects produced by " malaria." It is little wonder 
that in some places practically every ailment or feeling of " ma- 
laise " is attributed to malaria. In the tropics such a diagnosis 
would be correct in a great many cases. However, the habit 
of attributing any indisposition which cannot be accounted for 
otherwise to malaria has been transplanted into non-malarial 


places, and it is not uncommon to hear of a person having a 
'' touch of malaria " when in reahty he has only indigestion, a 
cold or a light case of la Grippe. It is largely due to this fact 
that malaria is looked upon in non-malarial districts as of such 
small consequence. 

The early stages of all types of malaria are similar except that 
the quartan type produces the intermittent fevers on every third, 
instead of every second, day. During the incubation period of 
the disease there is a feeling of ennui with headache and perhaps 
slight fever. After about a week, when the parasites have mul- 
tiplied to 150,000,000 or more, the regular intermittent fevers 
set in. Each attack begins with a shivering chill, sometimes 
accompanied by convulsions, so severe that the teeth chatter 
and goose-flesh stands out all over the body. Yet the tempera- 
ture will be found to be several degrees above normal, and still 
going up. In the wake of the chill comes a burning and weak- 
ening fever, with violent headache and vomiting and a tempera- 
ture from six to eight degrees above normal. The fever stage in 
turn is followed by a period of sweating, so profuse that the 
clothes or bedding may become wringing wet. The sweating 
gradually subsides, the temperature drops rapidly, often below 
normal, and the patient, after from six to ten hours in the case 
of benign infections and about 20 hours in malignant infections, 
rests fairly easy until the next attack. The fact that the attacks 
most commonly occur between midnight and noon, instead of in 
the evening, is often useful in distinguishing malaria from other 
intermittent fevers. 

In the case of '' benign " (tertian and quartan) infections 
after these agues have recurred for about ten days or two weeks, 
the symptoms gradually subside and the patient experiences a 
rally. From this point either he may recover completely (even if 
untreated) or he may suffer a relapse with all the old symptoms of 
regular agues. Then comes another rally and a second relapse, 
this continuing for months or years, aided, perhaps, by constant 
reinfections. During all this time general symptoms of emaci- 
ation, sallowness, anemia and enlarged spleen constantly in- 
crease at a diminishing rate with each elapse, and decrease at 
a similarly diminishing rate with each rally, so that eventually a 
fairly constant state of spleen-enlargement, emaciation, anemia, 
sallowness and general run-down condition is arrived at — the 


well-known condition of chronic malaria, or malarial cachexia, 
common especially in children. The spleen enlargement is the 
most readily recognizable symptom of chronic malaria and there- 
fore the '* spleen rate," i.e., the percentage of enlarged spleens 
in a community, gives a fairly accurate measure of the prevalence 
of malaria to which some degree of immunity has been developed. 
Usually, unless the weakened condition has given some other 
disease a chance to put an end to it all, a general improvement 
ultimately begins. This is especially true in children, so that 
by the time they reach adult life they are in fairly good health 
and immune to malaria. 

In the case of sestivo-autumnal or malignant malaria the 
course of the disease is often not so light, and early death is not 
a rare occurrence. The fact that the bodies of the malignant 
parasites clump together and plug the capillaries, thus preventing 
the proper flow of blood in the vital organs, is probably the chief 
cause of their malignant nature. One of the most certain symp- 
toms of a malignant attack of malaria is a total loss of conscious- 
ness or coma, due to a plugging of the capillaries in the brain. 
Indeed, 50 per cent of the deaths from malaria are said to be 
caused by a plugging of the brain capillaries. The type of brain 
disease which may be caused is very variable but some mental 
disturbance almost always occurs, and may take place at almost 
any time during the course of the disease, though it never occurs 
during the first fever fit, probably because the parasites are not 
yet numerous enough to do any great damage. 

In connection with malarial fevers there must be mentioned 
a much dreaded and little understood condition known as '^ black- 
water fever." This is a disease in which something destroys 
the red blood corpuscles in large numbers, causing the coloring 
matter of the blood, haemoglobin, to be liberated, eventually to 
be voided with the urine, giving the latter a very dark color. 
At the same time there is a more or less irregular fever, biHous 
vomiting and severe aches. In a gi'eat many cases it results in 
death. This disease has usually been considered as an outcome 
of severe malaria, since it always occurs in malarial countries 
and usually follows or accompanies an attack of malaria. It 
is not uncommon in southeastern United States, some parts of 
tropical Africa, southern Europe and many parts of tropical 
Asia and the East Indies. In many other malarial districts it 


is entirely absent. It is suggested by Manson that the fever is 
caused by a distinct organism, and that malaria is merely a 
predisposing cause. 

Immunity and Epidemics. — Absolute immunity to malaria 
is rarely if ever acquired but, as already remarked, oft-repeated 
infections especially in childhood tend to build up a high de- 
gree of tolerance to the effects of the parasites and a diminution 
in the number of parasites in the body. The protection afforded 
by a single infection is very slight, and is retained for only a 
short time in the absence of reinfections. Even the cumula- 
tive effect of numerous infections disappears rapidly in the 
course of a few years. Some authors divide malaria into two 
types. There is a *' tropical " form, occurring in places where 
reinfections can occur practically throughout the year on 
account of the continued warm temperature. The other, a 
" subtropical " form, is found in regions where cold weather 
causes an annual seasonal interruption of infection by a cessation 
of breeding on the part of Anopheles, and by a discontinuance of 
growth on the part of the parasites in the mosquitoes. In tropi- 
cal malaria a fairly constant degree of immunity is maintained, 
and epidemics are rare if they occur at all. In Java and other 
tropical places, according to Robert Koch, nearly every native 
child, under four years of age, has his blood teeming with ma- 
laria parasites from which he suffers little inconvenience. These 
parasites gradually become scarcer in older children and are 
often practically absent in adults who, however, have been shown 
to be passive " carriers " of small numbers of the parasites and 
therefore a source of danger to the community. The " carriers,'* 
though relatively immune to the more acute symptoms of the 
disease, are left in the run-down condition of malarial cachexia. 
As pointed out by Gill, there is a striking analogy between the 
confirmed opium-eater and the malarial cachectic. Both have 
purchased their immunity at a heavy price. In the former the 
emaciated frame, sallow complexion and other signs of debility 
proclaim the victim of a drug habit; in the latter the enlarged 
spleen, the lack of physical and mental energy, and the shrunken 
body bear witness to the havoc wrought by long-standing ma- 
laria. In the case of neither does death often take place as the 
direct effect of their respective poisons, but both readily fall 
victims to intercurrent affections. In subtropical malaria, on 


the other hand, the average tolerance of the community to the 
disease suffers an annual relapse, and may constantly decrease 
for a number of years. When the immunity of the community 
as a whole becomes quite low, and there is a sudden increase in 
the probability of infection by a great increase in number of 
mosquitoes, accompanied possibly by an influx of infected people, 
an epidemic of the disease may occur of such extraordinary se- 
verity as to involve almost the entire population, and to cause a 
mortality of several hundreds per thousand. Such devastating 
epidemics, probably of the subtertian type of malaria, have been 
termed ''fulminant malaria" and are believed to occur quite 
extensively in malarial countries lying just outside the region of 
" tropical " malaria. Fulminant malaria in especially severe 
form occurs periodically in parts of India and in Italy. 

It was formerly thought that considerable racial immunity 
protected the negro races, but it has been shown that in many 
cases, at least, the immunity has been acquired by constant 
exposure to the disease, and that it disappears upon removal from 
infected regions. The whites in southern United States are said 
to suffer markedly more from malaria than do the negroes though 
the latter are more frequently parasitized, but this may be due, 
in part at least, to the more permanent residence of the latter 
in the malarial districts. As said before, individual resistance 
to the effects of the disease is variable. Occasionally there is 
found a fortunate individual who is naturally absolutely immune, 
but this is a very rare occurrence. 

Treatment. — It is one of the greatest blessings in the world 
that we have for malaria a definite and specific cure as near to 
being a " sure cure " as has been discovered for any disease. 
Quinine has been found absolutely destructive to malarial para- 
sites. While a dose of quinine given during a fever attack will 
not act quickly enought to cut it short, it will, if given immediately 
after an attack, prevent the next one, or at least alleviate it. 
Meanwhile the organisms disappear from the circulation. It is 
usually supposed that they are directly killed by the quinine, 
which acts as a virulent poison for them, though this is doubted 
by some workers. The methods of administering quinine must, 
of course, vary with the age and condition of the patient, and the 
state of the disease. Sometimes very speedy action is needed, 
and it is not safe to wait for quinine to be slowly absorbed from 


the stomach. Many a patient has died from malaria with 
enough quinine in his stomach to have saved his hfe had it been 
properly given. In such cases injections into the muscles, or 
still better, directly into the veins, is necessary. In malignant 
malaria quinine does not reach the parasites plugged in the 
capillaries and therefore can destroy them only as they sporulate 
and get back into the circulation. Since the parasites of this 
type often sporulate at irregular intervals a constant supply of 
quinine at a killing concentration must be kept in the blood. 
However, overdosing with quinine is not an uncommon fault 
with physicians. Quinine poisoning in some respects resembles 
malarial symptoms and the physician, thinking the latter are 
not abating, gives still more quinine until the patient succumbs 
to it. Not a few malarial deaths are really due to excessive 
quinine. Malarial specialists, such as Professor Bass of New 
Orleans, say that it is never necessary to give more than ten or 
possibly fifteen grains of quinine at a time, if given as the case 
requires it. Twenty grains of quinine sulphate a day taken by 
mouth in several doses for a period of two weeks is said by Bass to 
disinfect anyone. Quinine must be avoided during or immedi- 
ately following an attack of blackwater fever, since the symptoms 
of this malady are intensified by its use. 

In case of severe malarial cachexia, the only safe course is for 
the patient to leave the malaria-infected country in which he 
has been living, and stay away for an extended period of time. 
He should take regularly small doses of quinine to kill any lurk- 
ing parasites which may remain in his body, and do everything 
possible to build up his general health and to regain his lost 

Prevention. — The prevention of malaria is a problem that 
should be solved not by individuals but by civic effort. Ross 
says: '' It (malaria) is essentially a political disease — one which 
affects the welfare of whole countries; and the prevention of it 
should therefore be an important branch of public administration. 
For the state as for the individual health is the first postulate 
of prosperity. And prosperity should be the first object of 
scientific government." 

Since the malarial parasites have two hosts, man and mosquito, 
the possibility of exterminating them in either host presents itself. 
Stephensport, in New Guinea, was practically cleared of malaria 


in a few months by destroying the parasites in man by whole- 
sale " quininization." In most places, however, the difficulties 
connected with this method of extermination are even greater 
than those associated with its alternative, the destruction of 
malarial mosquitoes. The relation of partially or entirely im- 
mune ^' carriers " to the spread of malaria is of extreme impor- 
tance and is usually greatly underestimated. The number of 
such apparently healthy carriers in malarial districts is astonish- 
ingly large. Eradication of malaria by attacking it in man would 
entail the persistent and thorough quinine treatment of all these 
carriers as well as of patients. 

Undoubtedly in practically every case, if accompanied by as 
extensive a use of quinine as is possible, eradication of malarial 
mosquitoes is the most effective and most permanent preventive 
measure. A discussion of methods of reducing and controlling 
such mosquitoes will be found on pages 455^62. 

Complete extermination of malarial mosquitoes is not necessary 
to reduce or even to eradicate malaria entirely. Ross has shown 
by mathematical computation that a relatively high number of 
malarial mosquitoes per person is necessary in a community to 
propagate malaria successfully. A small deviation above or 
below a certain number of malarial mosquitoes, probably between 
40 and 60 per person during a month, a deviation too small to 
be detected readily, will mean the difference between an ulti- 
mate extermination of the disease and its permanent estabUsh- 
ment. Ross also shows that the relation between the amount 
of malaria in a given region and the number of malarial mosqui- 
toes is so definite that it can be mathematically computed. 
These facts are of importance in the fight against malaria since 
they demonstrate to us that we do not have to exterminate 
totally even the malaria-carrying species of Anopheles in order 
to exterminate malaria, and our task becomes much less difficult. 
By this partial extermination some of the most malarial districts 
in the world have been practically freed. Up to 1900 over 16,000 
deaths a year from malaria occurred in Italy; now they may be 
counted in hundreds. One of the first demonstrations of what 
could be accomplished by mosquito extermination was made by 
Major Ross in 1902 at Ismailia on the Suez Canal where from 
1100 to 2500 cases of malaria occurred annually in a population 
of less than 10,000. Four years later not a single new case 


occurred there. The same thing on a much larger scale was 
accomplished in the Canal Zone at Panama by Surgeon-General 
Gorgas and his staff. On this relatively large malaria-infested 
area the death rate for the total population of about 100,000 was 
reduced 64 per cent in four years. The deaths from malaria 
were reduced about 85 per cent in less than four years, and yellow 
fever was totally eradicated. Similar feats have been accom- 
plished at Havana, Staten Island, and other places. One of the 
most recent examples of what can be done was furnished by the 
American occupation of Vera Cruz in 1914. The American troops 
were severely attacked by malaria of all three types, and an anti- 
mosquito campaign was immediately inaugurated. It cost the 
Sanitary Department $5000 a month to oil the pools, drain the 
low parts of the city and its environs, and dispose of the standing 
water in street gutters, refuse heaps, etc., but in a few months 
Vera Cruz, one of the most deadly malarial districts in the world, 
was practically freed from Anopheles, and danger of malaria 
reduced to almost nothing. 

Obviously the wholesale reduction or extermination of malarial 
mosquitoes can be accomplished only by communities or by 
government aid. San Antonio has freed itself of mosquitoes 
and mosquito-borne diseases by enlisting the services of the 
school children. In our southern states, where there are 
65,000,000 acres of swamp land, and where the chief malarial 
mosquitoes are swamp breeders, malaria can never be destroyed 
until state and federal governments are willing to invest money 
as readily to take water off the land in these parts of the country 
as they now invest it to put water on the land in the arid western 

Much can be done toward reduction of malaria in selecting 
dry brushless sites for houses and in constructing them in mos- 
quito-proof fashion. The houses one sees in the American 
Government settlements on the Canal Zone, built well up off 
the ground and with open sleeping porches, wide verandas and 
airy windows, all carefully screened, are ideal for tropical dis- 
tricts where malaria and other insect-borne diseases are common. 
They present a happy combination of airiness, sanitation, and 
complete protection from insect pests. 

In well-known malarial districts it is a good personal safeguard 
to use screens as much as possible and to take regular doses of 


quinine at all times as a preventive measure. In the pine swamps 
and along the coasts of Florida malaria is practically absent on 
account of the effectiveness of screening necessitated by the 
abundance of non-malarial mosquitoes. Three to five grains of 
quinine daily, or ten to fifteen grains once a week, is an almost 
certain malaria preventive. Quinine, however, is apt to cause 
abortion in pregnant women, though less so than is a severe 
attack of malaria. Some people are naturally very susceptible 
to quinine and cannot take it; such people should carefully 
avoid malarial districts. Tea, coffee and other mild stimulants 
are also said to be beneficial, but the safest course is always the 
same — quinine. 



Although the class Sporozoa includes a very large number of 
species, all of which are parasitic, and many of them the cause of 
fatal diseases in vertebrate as well as invertebrate animals, yet 
very few other than the malaria parasites, already discussed, 
are normally parasitic in man, and none of these can be looked 
upon as of prime importance in the causation of human disease. 
Of greatest importance, perhaps, are the Coccidiida or coccidians, 
which in lower animals are frequently the cause of fatal diseases 
and have been known to be fatal to man, though in some cases 
causing very little inconvenience. Another sporozoan parasite 
which is of importance where it occurs is Rhinosporidium, which 
produces tumors in the nose. A group of muscle-dwelling 
Sporozoa, the Sarcosporidia, occur accidentally or sporadically 
in man. 

There is another group of Sporozoa, the Piroplasmata, related 
to the malaria parasites, which are the cause of some of the most 
fatal diseases of domestic animals, including Texas fever and East 
Coast fever of cattle, biliary fever of horses, etc. These diseases 
are invariably, as far as known, transmitted by ticks. There is 
one human parasite, Bartonella hacilliformis, the cause of Oroya 
fever of Peru, which is thought to belong to this group of organ- 
isms. Possibly the Rickettsia-like organisms of typhus, trench 
fever, Rocky Mountain spotted fever, and the related Japanese 
disease, kedani, are related to the Piroplasmata. 

There are a number of other diseases, some of them of great 
importance, of which the " germ " either has never been seen or is 
of obscure nature. It is not always possible to guess at the 
nature of such undiscovered parasites but in some cases we can 
get a fairly accurate conception of them from a study of the course 
of the diseases they cause, the conditions under which they thrive 
and their means of dissemination. One by one the villains be- 



hind the screens are brought to hght, experimented with, and 
brought under control but there are still some which have defied 
the most ardent researches of modern science and have never yet 
been discovered. The fact that many of them are able to pass 
through filters of certain kinds, as shown by the infectiveness of 
fluids containing them after having been passed through the 
filters, demonstrates that at least in some stages of their de- 
velopment they are actually too small to be visible under the 
highest power of the microscope. 

However, in the case of some of these unseen parasites we have 
suflicient knowledge of their habits and life histories to wage a 
fairly intelligent war against them, at least as regards prevention. 
The parasite of yellow fever, for instance, was not discovered 
until 1918. Yet we knew much about its probable nature, we 
knew its full life history in a general way, and to a large extent 
we knew how to combat it, far better, in fact, than we know how 
to combat some of the well-known parasites. There are two 
other diseases, dengue and phlebotomus fever, which are prob- 
ably caused by parasites related to that of yellow fever, but they 
have not yet been discovered. 

The organisms of typhus fever, trench fever, spotted fever 
and kedani have only recently been discovered. They are all 
minute bodies showing various morphological types, which occur 
in both vertebrate and arthropod hosts. They are here grouped 
together as " Rickettsia-like organisms." Their affinities, whether 
with bacteria or protozoa, are at present entirely problematical, 
but for the present they may best be considered, like the spiro- 
chsetes, to represent a more or less intermediate group. 

Several other diseases, some of them of prime importance, of 
which the parasites are of obscure nature, are believed by some 
workers to be caused by Protozoa: such are hydrophobia or 
rabies, trachoma, smallpox, verruga peruviana (not Oroya fever), 
foot-and-mouth disease, measles, scarlet fever and a few others. 
The parasites or parasite-like bodies which are associated 
with these diseases are in some cases minute, in other cases, 
e.g., hydrophobia, of relatively large size. In most of these 
diseases the " germ " or virus is capable of passing through 
ordinary bacterial filters, as shown by the infectiveness of filtered 
material. It is also evident from this that the viruses live out- 


side the cells or blood corpuscles, at least during part of their 
life history. On the other hand, in these diseases there have 
been discovered bodies of various kinds within the cells, inter- 
preted by some workers as true parasites, by others as reaction 
products of the cells. These bodies have received zoological 
names, e.g., the Negri bodies of hydrophobia were named Neuro- 
ryctes hydrophohiw, the cell inclusions in smallpox Cytorydes 
variolce, and so on. It is now a commoner belief that these bodies 
consist of material extruded from the nucleus of the cell into its 
cytoplasm where it surrounds one or many of the minute or- 
ganisms during the intracellular portion of their life history. 

For these problematical organisms, minute in size, of uncertam 
life history, and apparently enshrouded in a mantle of extruded 
nuclear material during their intracellular life, the name Chlamy- 
dozoa (meaning mantle animals) has been given. Whether these 
bodies have been correctly interpreted as described above and 
whether they should be considered Protozoa is open to question. 
Their animal nature has not been sufficiently demonstrated to 
warrant more than brief mention of them and the diseases they 
cause in a treatise on animal parasites. 

In the following paragraphs the sporozoan parasites and ob- 
scure or invisible parasites which have been briefly mentioned 
above will be discussed in a little more detail in the following 
order: (1) coccidians, (2) Rhinosporidium, (3) Sarcosporidia, 
(4) Oroya fever, (5j dengue and phlebotomus fever, (Uj Rickettsia- 
like organisms, (7) Chlamydozoa. 


There are a number of serious diseases of animals which are 
caused by parasites of the class Sporozoa known as coccidians. 
These are very small animals, without distinct organs of lo- 
comotion, which have both an asexual and a sexual phase in 
their life history (Fig. 48). The asexual phase is not unlike 
what takes place in the asexual phase of malaria parasites, ex- 
cept that the parasites live inside of cells lining the intestine 
instead of in the blood. Like the malaria parasites, a coccidian, 
within the epithehal cell in which it is living (Fig. 48A-C), di- 
vides into two, four, eight, sixteen, or perhaps twenty or more 
daughter cells, arranged somewhat like the segments of an 
orange (Fig. 48D). The young coccidians, escaping from the 



host cell which has been preyed upon and destroyed, invade fresh 
cells, multiply again, and thus eventually destroy large portions 
of the lining of the digestive tract. The daughter coccidians 
are not adapted for withstanding conditions outside the intestine 

Fig. 48. Life history of Eimeria avium. A, infection of epithelial cells of in- 
testine by sporozoites ingested with food or water; B, growth inside cell; C and D, 
sporulation and formation of young spores; E and G, formation of female gamete; 
F and H, formation of male gametes; /, fertilization; J, fully developed oocyst as 
passed out with faeces; K, L and M, formation of four sporocysts; N, complete 
development of sporocysts, each containing two sporozoites; O, same, ingested by 
susceptible animal; P, sporocyst liberated from oocyst in alimentary canal; Q, 
liberated sporozoite ready to infect epithelial cell, as shown in A. 

of the host, and therefore the parasite would be exterminated 
with the death of its host were it not protected in some manner 
against this calamity. The sexual phase of its life history serves 


this important purpose. At intervals the coccidians, instead 
of multiplying in the usual manner, differentiate into sexual forms, 
corresponding to eggs and sperms (Fig. 48G and H). One of the 
spermlike individuals penetrates an egglike individual and fuses 
with it (Fig. 481), in precisely the same manner as a spermatozoon 
fertilizes an egg in higher animals. The fertihzed individual 
develops a thick resistant cyst wall and is then known as an 
'^ oocyst" (Fig. 48J)l The parasite is now ready to hazard the 
dangers of an exit into the outside world, and is passed out with 
the faeces. Eventually, sometimes within a few days, the con- 
tents of the oocyst divide into several parts, each known as a 
'' sporocyst " (Fig. 48K, L and M). Each sporocyst in turn 
develops within itself a number of " sporozoites " (Fig. 48N), 
each capable of infecting a separate cell 
in a new host. The oocysts with their 
contained sporocysts and sporozoites can 
exist in soil or dust for a long time, 
awaiting an opportunity to enter a new 
Fig. 49. Oocyst of iso- victim with food or water. 
spora from British soldier Infection with coccidians has not often 

returned from Gallipoli. i v i • i_ j. -i • 

Note presence of only two ^een observed m man but it IS pos- 
sporocysts, each with four sibly more prevalent than is commonly 

sporozoites. X 1000. (After ii i j. a r r ' t • r 

Wenyon.) thought. A fcw cases 01 coccidian infec- 

tion of the human liver have been recorded 
and it has been generally assumed that the parasite was identical 
with Eimeria stiedce of rabbits, but Dobell has pointed out that 
there is no sound reason for this belief. Recently Wenyon has 
reported the not uncommon occurrence of oocysts of two species 
of coccidians in the faeces of British soldiers returning from Gal- 
lipoli. The cysts of the commoner species, Isospora hominis, 
contain a single mass of protoplasm, when first passed, but in three 
or four days they become fully developed and contain two sporo- 
cysts, each with four sporozoites (Fig. 49). The cysts measure 
12 M to 14 At by 7 M to 9 M (about -j^Vo by ^oVo of ^^ inch). The 
cysts of the other species, Eimeria wenyoni, are fully developed 
when passed, and possess four sporocysts with two sporozoites 
each (Fig. 50) They measure 20 /x in diameter. Only four 
cases of infection are known. A single case each of infection with 
two other species have been recorded: E. oxy spora, with large 
spherical cysts (36 fx in diameter) and straight sharp-pointed 
spores, recorded by Dobell; and E. snijderi, with still larger 




cysts but smaller spores, by Snijder in Sumatra. Little is known 
of the symptoms produced by these parasites, but since they live 
inside epithelial cells of the intestine or liver they must be in- 
jurious. Wenyon has recently reported 
dysenteric symptoms in a case in which 

no intestinal parasites except Isospora / //MIW \ oocyst 

were present. Coccidians are un- 
doubtedly spread by means of water 
or food polluted by mud and dirt, by un- 
sanitary habits, and by flies. 

Rhinosporidiuniy a Parasite of the 
In natives of India there is occasion- ^^^-.^^ Oocyst of ^tmerio 

. containing four sporocysts, each 

ally observed a peculiar mfection of the with two sporozoites. 
nose in which a red tumor, flecked with 

whitish spots, and likened by some authors to a raspberry, grows 
out from the partition or septum of the nose, remaining attached 
by a narrow stalk. The tumors are not very painful, but they 
tend to block the nasal passages. It has been suggested that 
this disease, kjiown as nasal polypus, may have the same in- 
fluence on the intellect of children that o her impediments of 
the nose and throat are known to have. 

When the tumor is cut the white spots visible on the surface 
are seen to be scattered throughout the tissue and to be of very 
variable size. Microscopic examination shows them to be the 
cysts of a protozoan parasite in various stages of development. 
The parasite has been named Rhinospo idium kinealyi, and is 
classified as a member of the group of Sporozoa known as Haplo- 

The cysts in the tumor are filled with great numbers of spherical 
or oval bodies, the pansporoblasts, each of these in turn contain- 
ing from one to a dozen closely-packed spores (see small portion 
of a cyst in Fig. 51). The manner of development of the cysts 
and of the tumor can readily be discovered from the various 
stages of development of different cysts and parts of cysts which 
can be observed in a single tumor. The youngest cysts are small 
granular masses of protoplasm, more or less irregular in shape. 
As one of these minute animals grows there are developed within 
it small bodies with definite shape which are destined to become 
the pansporoblasts already mentioned. However, the proto- 


plasm at the periphery of the animal continues to grow, constantly 
becoming differentiated into new pansporoblasts. The young 
pansporoblasts (Fig. 51, yg. pansp.), at first simple masses of 
protoplasm, soon form within themselves one, two, four, and 
ultimately as many as 12 spores, tightly clumped together so 

as to resemble little mul- 

(»ysf, — ^ ^g^;= ~ ^^^^^^^ ^^ ^^^^ berries (Fig. 51, mat. 

_ pansp.). From the mode 

c,g. pansp. ^^^^^^^ of development of the 

cysts it is clear that the 
older pansporoblasts are 
the ones near the center 
of the cyst, the younger 
ones those toward the 

rrictt pansp. ^^i^^^^lf periphery. When the 

" ' " cysts have reached a 

^p ""ii^^l^^^ii^S^ certain size the growth 

of the periphery ceases, 
all the pansporoblasts ma- 

FiG. 51. Portion of fully developed cyst of , j xi, x x 

Rhinosporidium; c. w., cyst wall; yg. pansp., ture and the Cyst ruptureS, 

young pansporoblasts; mat. pansp., fully de- liberating the SporeS into 

veloped pansporoblasts containing spores, sp. ,i j. ,• 

X about 100. (After Fantham and Porter.) ^he SUrrOUndmg tlSSUe, 

each to develop into a 
new cyst. How the parasites are transmitted to new hosts is 
not known. 

A similar disease was found some years ago in South America 
and a parasite, then named Coccidium seeberi, has been described 
from the tumors. It is possible that this may be the same 
organism as that of Indian nasal polypus, but according to Fan- 
tham, who was one of the original describers of Rhinosporidium, 
there are a number of differences between them. 

Sarcosporidia, Parasites of the Muscles 

Brief mention should be made of a group of Sporozoa known 
as the Sarcosporidia which develop relatively enormous cysts 
in the muscles of vertebrate animals, especially in mammals. 
These parasites are usually found in the striped muscles but they 
also occur in other muscles. Infected muscles (Fig. 52B and D) 
appear to have white streaks or patches in them, sometimes 



several inches in length. Microscopic examination shows that 
these patches are cysts containing thousands of tiny spores, 
segregated into chambers (Fig. 52A) which correspond to the 
pansporoblasts of Rhinosporidium. The spores (Fig. 52C), es- 
caping from the cyst, ultimately develop into new cysts in much 


Fig. 52. Sarcosporidia. A, Sarcocystis blanchardi of ox, longitudinal section of 
infected muscle fiber (m. f.) showing spores (sp.) in chambers of compartments 
(comp.); n., nucleus of muscle fiber, X 265. (After von Eecke from Wasilewsky.) 
B, cross section of sarcocyst from human larynx, probably S. tenella, X 200. D, 
same, longitudinal section. (After Baraban and St. Remy.) C, spore of S. tenella 
of sheep. (After Laveran and Mesnil.) 

the same way as is the case with the nose parasite. Although 
the muscle parasites have been known to parasitologists for 
many years there are portions of the life history which are not 
yet known. Darling and others have suggested that these pe- 
culiar protozoans may be " side-tracked varieties of parasites of 
invertebrate animals." We have no definite knowledge of the 
normal means of transmission although a number of possible 
methods are known. It has been found that infections can be 
spread by cannibalism, and that the faeces of infected mice can 
infect other mice; it has also been stated that spores occur in 
the circulating blood, which would mean that blood-sucking ar- 
thropods may be instrumental in the transfer. Fleshflies may 
also play a part in dispersing the spores. • 

Erdmann has shown that when spores of Sarcosporidia de- 
velop in the intestine a very powerful toxin, called sarcocystin, 
is discharged and destroys the neighboring epithelial cells of the 
intestine and thus breaks a way for the young parasite into the 


lymphatics and ultimately into the muscles. Crawley has re- 
cently described in Sarcocystis muris of mice what he interprets 
as sexual differentiation of the spores and fertilization within 
18 hours after the spores have been ingested by mice. Crawley 
beheves the Sarcosporidia to be closely aUied to the Coccidia, and 
suggests that there may be an unrecognized stage of development 
in a carnivorous animal. It is quite evident from the various 
hypotheses and speculations mentioned above that there is much 
yet to be learned about these enigmatic parasites. 

Only a few scattered cases of Sarcosporidia in man have been 
recorded, and these may be looked upon as purely accidental. 
The parts affected have been the muscles of the heart and larynx. 
Many speculations as to how these infections occurred have been 
made, but nothing definite is known about it. It is probable 
that the human infections are due to Sarcocystis muris, a species 
which produces a very fatal disease in mice, and infections may 
have been due to contamination of food or water with the ex- 
crement of infected mice. The use of meat of Indian buffaloes 
infected with another species, Sarcocystis tenella huhali, seems to 
have no injurious effect on man, but ingested spores cause ir- 
regular fever. 

Oroya Fever 

The Disease. — Since at least the time of the Incas, Peru has 
suffered from a strange disease which has swept over the country 
from time to time in the form of frightful epidemics, some of 
which have cost thousands of lives. One of the severest recent 
outbreaks occurred among the workmen building the Peruvian 
Central Railway between Lima and Oroya and it is estimated 
that at least 7000 individuals died in it. In 1906 at least one- 
tenth of 2000 workmen employed building tunnels and bridges 
on the Central Railway died of the fever, and one bridge in par- 
ticular, which was the scene of a great many deaths from the dis- 
ease, has come to be known as the Oroya Fever Bridge (Fig. 53). 

The disease is at present endemic in the deep cleft canyons or 
quehradas (Fig. 53) characteristic of the west face of the Andes, at 
an elevation of between 2500 and 8000 ft., but it is probable that it 
has a wider distribution than is now supposed. It shows a marked 
seasonal prevalence, most of the cases occurring from January to 
April, especially toward the close of the warm, rainy season. 



Fig. 53* Above, a typical " quebrada " or canyon on the west slopB of the Andes 
Where Oroya fever abounds. Below, the famous "Oroya Fever Bridge " on Peruvian 
Central Railway where hundreds of lives were lost from Oroya fever. (Photos 
kindly lent by Harvard School of Tropical Medicine, previously published by 
Strong et aX>.) 


Oroya fever has been constantly confused with other diseases; 
and it was not until the South American expedition of the 
Harvard School of Tropical Medicine, under the leadership of 
Dr. R. P. Strong, made an investigation of the disease that 
soine order was brought out of the confusion. Malaria, para- 
typhoid, and particularly verruga peruviana are the diseases 
which have been most frequently confused with Oroya fever. 
Mixed infection of these diseases and others such as yaws and 
tuberculosis with true Oroya fever has still further complicated 
matters. From the time of the Incas verruga peruviana and 
Oroya fever have been associated and regarded as different phases 
of the same disease, and this view is still held by some investi- 
gators. The fact that the characteristic nodules of verruga were 
usually associated with a very mild form of fever and sometimes 
with none at all, while oroya fever was of very severe type caus- 
ing very high fatality, raised some question as to the distinctness 
of the diseases. To settle this point a Peruvian medical stu- 
dent, Daniel Carrion, vaccinated himself with blood from a 
verruga nodule. Five or six weeks later he died of a severe 
fever, and the question of the identity of the disease was ap- 
parently settled, and the fever was called '^ Carrion's Fever '' 
in his honor. The notes regarding Carrion's illness have been 
lost and it is now believed that he may have died of some other 
disease or that the patient from whom he inoculated himself 
may have been suffering from some other disease in addition to 

As a result of their own studies, Dr. Strong and his colleagues 
believe that the diseases are quite distinct. They have shown 
that Oroya fever is caused by a very minute parasite Kving in 
the red blood corpuscles and multiplying in the endothelial cells, 
and that it cannot be inoculated into animals ; verruga peruviana, 
on the other hand, is caused by a virus which is ultra-microscopic, 
probably related to the smallpox virus, and can be successfully 
inoculated into laboratory animals. It is easy to understand 
how the two diseases were confused, since to a large extent their 
ranges overlap and a visitor to endemic regions would be likely 
to contract both. Verruga, being less quickly contracted and 
having a longer incubation period, would tend to appear later 
than Oroya fever, and would therefore be looked upon as a later 
stage of the same disease. The native belief that a general erup- 



tion was favorable to recovery, a belief undoubtedly based upon 
the benign nature of verruga, leads to the adoption of all sorts of 
methods to invoke a breaking out of the skin, such as applications 
of turpentine, rubbing with irritant leaves, etc., and undoubtedly 
a great many cases of eruptions following Oioya fever are really 
only the eruptions caused by the artificial irritation of the skin. 

Oroya fever, after an incubation period of about 20 days, begins 
with a general feeling of malaise and aches in the joints, followed 
by chills and fever, which last irregularly for many weeks. The 
fever is accompanied by a rapid pernicious anemia, the red blood 
corpuscles being reduced in some cases to one-fifth, or even less, 
of their normal number. This causes severe prostration and 
in a large per cent of cases death results within three or four 
weeks. The skin assumes a yellowish waxy color, and there are 
often slight hemorrhages of the mucous membranes and various 
internal organs, as demonstrated by post mortem examinations. 
The liver and spleen become moderately enlarged, and the lymph 
glands are swollen. 

The Parasite. — The true parasite of Oroya fever was first 
discovered by Barton, of Lima, Peru, in 1905 and confirmed by 
him in 1909, at which time he 
suspected that it might be a 
protozoan. The parasites were 
more thoroughly studied by 
the Harvard expedition in 1913 
and 1914 and named Barton- 
ella hadlliformis. Dr. Strong 
and his colleagues describe 

them as minute rods or, more Fig. 54. Bartonella badUiformis, liv- 

1 rl rl K rl' ^^^" ^' -^ ^^^ ^' successive drawings of 

rarely, rOUndea DOClieS occur- ^ single red corpuscle showing movements 

ring inside the red blood cor- of parasite within it ; Z),£^ and F, corpuscle 

1 <"t?' 'A r\ KK\ containing two rod-shaped and four round 

pUSCleS (l^lgS. 04 ana OO;. parasites, showing migrations of the rod- 

These parasites, the rod form shaped individuals. x 2000. (After 
of which are only 1.5 to 2.5 /a ^^^^ ^ 

(less than ^ ^ ^^ ^ ^ of an inch) in length and the round bodies 0.5 to 
1 fjL in diameter, are definitely motile, moving about freely inside 
the corpuscles. In severe infections there may be found from 
one to ten parasites in a single corpuscle. 

A multiplicative stage of the parasite occurs in large swollen 
endothelial cells in the lymph glands and spleen. In these swollen 



Fig. 55. Bartonella hacillifonnis in stained blood 
from Oroya fever patient. Some cells show chains of 
parasites. Bodies v ith large dark nuclei are leuco- 
cytes (leuc). X about 1000. (After Strong et al.) 

Fig. 56. Development of Bartonella bacilliformis 
in endothelial cells. A, endothelial cell, with large 
nucleus (n.) at left, containing five rounded bodies in 
early stage of development; B, endothelial cell show- 
ing rounded bodies developing large numbers of small 
rod-shaped parasites; C, red corpuscles lying near 
with parasites identical with those escaping from such 

cells are mitiut^ 
rounded bodies, some- 
times a few, some- 
times great masses of 
them (Fig. 56B)- 
Some of these rounded 
bodies contain only 
one, two or four deep 
staining granules 
(Fig. 56A), while 
others contain large 
numbers of them. 
It appears that these 
granule - filled bodies 
break up into a large 
number of parts each 
containing one gran- 
ule; these become 
elongated, and finally 
appear as distinct rods 
containing the gran- 
ule at one end. In 
this condition they 
are identical with the 
parasites which occur 
in the red blood cor- 
puscles (Fig. 56C) and 
indicate the manner 
in which the corpus- 
cular parasites arise. 
Dr. Strong and his 
colleagues believe 
Bartonella bacilli-' 
for mis to be a pro- 
tozoan probably re- 

;e escaping irom sucn i , i j. +v> ♦> f 

a cell as shown in B. X 2000. (After Strong et al.) ^^^^^ ^^ ^^^ grOUp 01 

parasites known as 
the Piroplasmata, including the Texas fever parasite of cattle and 
a number of other disease-causing parasites of wild and domestic 
animals. Its exact classification cannot yet be determined, and 


it is simply looked upon as possibly belonging to a group of micro- 
organisms intermediate, as perhaps are the spirochaetes, between 
Bacteria and Protozoa, but with a decided leaning toward the 
latter. Possibly they are related to Rickettsia. (See p. 185.) 

Transmission. — The method of transmission of Oroya fever 
is still in doubt, but it seems practically certain that some ar- 
thropod acts as a transmitting agent. All the other parasites 
of the group to which Bartonella belongs are transmitted by ticks, 
but there is apparently no tick having habits compatible with the 
occurrence of the disease. The Harvard expedition attempted 
to obtain the development of Bartonella in a mosquito, Pha- 
langomyia dehilis, which is common in the infected zones, but 
without success. That the transmitting agent is a nocturnal 
blood-sucker of very limited distribution but abundant within 
its range is strongly indicated by the limitations of the disease 
and by the fact that in many cases a single night in the infected 
zone is suificient for contracting it, whereas there is apparently 
no danger a short distance from the infected zone, or within it 
in the daytime. According to Townsend, who spent two years 
investigating verruga (which he considers identical with Oroya 
fever) the only arthropod which fulfills all the conditions is a 
sandfly, Phlebotomus verrucarum, which is a very abundant 
nocturnal blood-sucker apparently limited in its distribution to 
the verruga zones. Townsend attempted experiments with the 
transmission of the disease through the agency of this insect but 
his results have not been generally accepted. Whether or not 
Phlebotomus is instrumental in transmitting Oroya fever is a 
matter which will have to be proved by further research but the 
circumstantial evidence against the insect is strong. 

As pointed out by Townsend, the portions of Peru which are 
haunted by Oroya fever and verruga have one of the most perfect 
and healthful climates in the world and they would be ideal for 
sanatoriums and resorts were it not for these diseases. It is to 
be hoped that the diseases may soon be more thoroughly worked 
out and gotten under control. However, if Phlebotomus is in- 
strumental in the transmission of either, the hope of eradicating 
them in the near future is slight, judging by the difficulties which 
have been experienced in Mediterranean countries in controlling 
these minute rock-breeding insects. 


Dengue and Phlebotomus Fever 

These two diseases are wide-spread in tropical and subtropical 
countries, and are frequently confused. They have commonly 
been associated with yellow fever, none of the parasites causing 
them having been discovered until Noguchi discovered a* Lep- 
tospira as the causative organism of yellow fever in 1918. It is 
possible that the other two diseases will also be shown to be 
caused by species of Leptospira. Dengue is a much milder disease 
than yellow fever and is seldom fatal, though its after-effects 
linger for many months. Phlebotomus or three-days' fever is a 
still milder disease and, as its name implies, of short duration. 
Like dengue it has lingering after-effects but they are not so severe 
or so persistent as in the former disease. 

Both diseases are caused by blood parasites, so far undiscovered, 
which are transmitted by dipterous insects in which they ap- 
parently undergo part of their life cycle. The diseases each begin 
with a sudden high fever and headache, and pass through es- 
sentially similar stages, intense rheumatism-like aches being very 
characteristic of all. Each disease confers immunity, often of 
long duration in dengue and often transitory in phlebotomus 
fever. It seems not improbable that the parasites of these dis- 
eases and of yellow fever are closely allied- 

Dengue, seven-days' fever, or breakbone fever, is a disease of 
tropical and subtropical countries. It is very common in the 
West Indies and great epidemics have swept through Panama, 
the eastern Mediterranean and southern Asian countries, the 
Philippine Islands and various South Sea Islands. An epidemic 
has recently been reported from Argentina and Uruguay, the dis- 
ease supposedly having been introduced from Spain, Dengue also 
occurs in southern United States where it is probably often over- 
looked, being diagnosed as something else. In some places, e.g., 
southeastern Europe and India, there is some confusion between 
dengue and phlebotomus fever. Both diseases vary somewhat 
and mild types of the former and severe types of the latter may 
easily be, and frequently are, confused. Dengue occurs in the 
form of sudden and rapidly spreading epidemics which sweep 


over limited areas, affecting a large per cent of the popu- 

Nearly every fluid and organ of the body has been examined 
in an effort to find the organism causing dengue, but although 
many supposed parasites have been found, the true cause of the 
disease is still unknown. In at least one stage of its life history 
the parasite, like that of yellow fever, is ultra-microscopic. The 
disease has been proven by experimentation to be transmitted 
commonly by the tropical house mosquito, Culex quinquefasciatus, 
and its distribution geographically coincides very closely with 
that of this mosquito. However, Aedes calopus has also been in- 
criminated, and in Formosa another closely related species, 
Desvoidea obturhans. 

Unlike yellow fever, dengue has a very short incubation period 
in the mosquito — in one experiment it was only 48 hours. This 
fact, together with the short incubation period in the human 
body (from two to five days), explains the rapidity with which 
dengue epidemics spread. 

The disease begins with startling suddenness. Within a few 
hours a normal healthy individual acquires a prostrating fever, 
a severe headache and terrible aches in the bones and joints 
which make it necessary to lie still. His face and sometimes 
his whole body becomes flushed and purple with congested blood- 
vessels, and the patient is to say the least very miserable. In 
a day or two the fever moderates, and usually is terminated by 
a sudden crisis of nose-bleed and diarrhea, relieving the con- 
gestion which has been felt in all parts of the body. Then follows 
an interval of apparently normal condition during which the 
patient feels perfectly well. After a few days there is a return of 
more or less severe fever and aches accompanied by a measles- 
like rash. The latter fades in from three to five days and is fol- 
lowed by a powdery scaling off of the skin. If lucky, the patient 
now quickly recovers but more often he has lingering and recur- 
ring aches in various joints, especially the knees and ankles, and 
he may be thus afflicted for several weeks before final recuper- 
ation, whence the name " breakbone fever." The disease is 
dangerous to life only if complicated in some way. 

An attack of dengue usually confers immunity on an individ- 
ual but this sometimes lasts only a year and is sometimes not 
established at all, since more than one attack during a single 
epidemic have been known to occur. 


There is no specific remedy known that will cure dengue. 
Care of the general health, including measures to lessen the fever, 
headache and bone aches, help in making life worth living during 
the eight or ten days of suffering. 

Once an epidemic has broken out, it is almost as useless to 
attempt to stop it as to stop a tidal wave, as far as the mass of 
people is concerned. Houses screened against mosquitoes, if 
available, are havens of refuge, but the tropical villages or cities 
in which there are enough screened houses to care for even a 
small per cent of the population are hopelessly lacking, and the 
rapidity of the spread of the disease makes the isolation of early 
cases in mosquito-proof wards almost futile. Anti-mosquito 
campaigns, conducted not merely during an epidemic but at all 
times, are the only methods now known of preventing epidemics 
of dengue or of lessening their local prevalence. 

Phlebotomus Fever 

Of the same general nature as yellow fever and dengue, and 
concluding this series of gradually milder diseases, is phlebot- 
omus or three-days' fever. This disease occurs especially on 
the shores of the Mediterranean and in India, and possibly also 
in other parts of the world. In endemic countries it occurs in 
the form of annual epidemics. It is estimated that in the earth- 
quake regions of Italy where the disease is especially prevalent, 
50,000 persons are attacked annually, incurring a financial loss 
of over $7,000,000 by the prolonged incapacitation for work which 
follows the disease. In central India, every non-immune person 
is said to be attacked by the end of June each year. 

Phlebotomus fever begins suddenly, like dengue, with a high 
fever, severe headache and aches in the bones and joints. The 
nervous symptoms are marked, and the pulse and respiration are 
accelerated. Usually the fever subsides on the third day, though 
in India it often lasts four or five days. The aches and general 
depression continue for ten or twelve days or even longer after 
the disappearance of the fever. 

The disease, the parasite of which has never been discovered, 
is transmitted by the gnat or sandfly, Phlebotomus papatasii 
(see p. 470, and Fig. 212), which is extremely abundant in the 
regions where phlebotomus fever is endemic. The appearance 
and habits of this insect are described on p. 471. The prevalence 


of phlebotomus fever in the earthquake districts is due to the 
abundance of ideal breeding places for the gnats furnished by 
the ruined walls. It is possible that other species of Phlebotomus 
may also transmit the disease. 

The gnats become infective about a week after feeding on an 
infected person. The incubation period of the disease in man is 
about four or five days. Natural immunity is extremely rare, 
but in most cases an immunity of variable duration results from 
an attack of the disease. 

No specific cure has yet been discovered. Prevention lies 
in avoiding the bites of Phlebotomus papatasii and in reducing 
their numbers as far as possible by methods described on p. 473. 
In case of prolonged residence in an endemic region, there is 
little hope of escaping infection, and willful exposure to it at a 
time when the disease will be least inconvenient is usually ad- 
visable, in view of the usually persistent immunity which results. 

Rickettsia-Like Organisms 
Within the past few years there have been described as the 
probable cause of a number of human diseases, organisms of very 
minute size, frequently less than half a micron in diameter, which 
may show a number of morphological types. Round or diplococcal 
forms are of most frequent occurrence, but there also occur minute 
rod-shaped bodies and occasionally threadlike forms. The re- 
lationships of these organisms is very obscure. They are looked 
upon by some investigators as bacteria, and by others as protozoa, 
while still others consider them merely by-products of the infection. 
In their staining reactions they resemble spirochaetes rather than 
bacteria, and the possibility of their representing modified granule 
stages of spirochaetes has been suggested. They are non-motile, 
and very difficult to cultivate. They occur in a number of kinds 
of arthropods, usually multiplying on or in the epithelial cells of 
the alimentary canal, but some species, at least, occur in other 
organs also, including the reproductive glands, and are hereditarily 
transmitted. The resemblance to spirochaetes is further borne 
out by the way in which reproduction takes place by granule- 
shedding from elongated threadlike forms, and by their hereditary 
transmission among arthropods. Species of Rickettsia or closely 
allied forms have been found in human lice (Pediculus), Mal- 
lophaga, fleas, bugs {Cimex), sheep ticks (Melophagus), and true 


ticks (Dermacentor) , and undoubtedly will be found in other ar- 
thropods. Their occurrence in non-bloodsucking insects, aside 
from the fact that no vertebrate disease is known to be associated 
with many of these infections in parasitic insects, is evidence for 
the fact that these organisms, like the intestinal flagellates of 
insects (see p. 75), are primarily parasites of arthropods, a com- 
paratively few species of which have become adapted to live in 
the blood of vertebrate animals, where they may cause disease. 

The human diseases with which Rickettsia-like bodies have been 
definitely associated are typhus, trench fever, and Rocky Mountain 
spotted fever. In the Japanese disease, kedani or tsutsugamushi, 
which shows some affinities with spotted fever, parasites have been 
described which may be referable to this group. 

Typhus Fever. — This deadly disease, which so frequently 
breaks out when human beings are crowded together where per- 
sonal care and cleanliness are either neglected or impossible, 
has for ages been associated with wars and prison camps. In 
some parts of Europe and North America typhus persists in an 
endemic or mild epidemic state, ready to burst into flame when 
opportunity comes, giving rise to terrible epidemics. The dis- 
ease is endemic on the Mexican plateau, where it is known as 

Typhus has a sudden onset, and is characterized by high fever, 
headache, aches in the bones and muscles, bronchial troubles, 
congestion of peripheral blood-vessels and a red rash later giving 
rise to dark blotches. In an endemic state the mortality is very 
low, but when an epidemic breaks out there may be 50 to 79 per 
cent mortality. 

Typhus has been conclusively shown to be transmitted prin- 
cipally, and perhaps solely, by body lice. Details of the role of 
the lice, and an account of some recent epidemics, will be found 
on pp. 397 to 399. 

Attention was first directed to minute granules associated with 
typhus fever by Ricketts in 1909, but these bodies were first 
described in detail from typhus-infected lice by Rocha-Lima in 
1916 and named Rickettsia prowazeki. The organism occurs in 
abundance in the gut of infected lice as single granules, diploid 
bodies, or in clumps evidently resulting from continued multi- 
plication without separation of the individuals; occasionally 
bacillus-like or thread forms occur. Multiplication seems to 


take place inside the epithelial cells of the insect. This organism 
has been found in the blood and tissues of typhus patients also. 

A great deal of dispute concerning the relationship of Rickett- 
sia prowazeki to typhus has arisen from the fact that Rickettsia 
also occurs in lice which could not have been infected from typhus 
patients. It is now generally believed that there is a distinct 
species or variety of Rickettsia, named R. pediculi, which is an 
inhabitant of the gut of the body louse, but which is non-patho- 
genic to man, in fact probably limited to the insect host. 

Trench Fever. — This disease, which was unknown before the 
great war, but which was one of the most important diseases 
afflicting troops participating in it, was shown in 1918 by a com- 
mission of the Medical Research Committee of the American 
Red Cross and also by a British committee to be normally trans- 
mitted by body lice (see p. 399), although the possibility of trans- 
mission by body excretions also exists. A form of the disease 
occurring in Central Europe was known as Volhynian fever. 

After an incubation period which is probably usually between 
14 and 30 days, there is a sudden onset of fever accompanied by 
headache, dizziness, muscular pains and other symptoms. The 
fever may last continuously for several weeks, or it may be more 
or less definitely relapsing. In most cases the spleen is enlarged, 
and there is a rash on the back, chest and abdomen. Usually 
the patient recovers in from five to six weeks, but the illness may 
be greatly prolonged. 

In 1916 Toepfer first described a species of Rickettsia, R. quin- 
tana, as occurring in lice fed on trench fever patients. This or- 
ganism closely resembles that of typhus fever but is more con- 
stantly rounded or diploid in form, and most writers agree that it 
does not occur inside the epithelial cells of the gut of the louse. 
This parasite may be merely a pathogenic variety of R. pediculi, 
mentioned in the preceding section, which has acquired the ability 
to thrive in human blood. In infected lice the organisms are 
found attached to the surface of the cells of the midgut. They 
gradually fill the lumen, and are eventually voided with the faeces. 

According to Hindle, who is inclined to regard the organisms 
as bacteria rather than protozoa, no distinct portion of the life 
cycle occurs in the louse, this insect merely acting as a culture 
tube as does the flea for the bacilli of plague. The negative period 
of four or five days after a louse becomes infected until it is ca- 



pable of transmitting the disease, Hindle thinks is probably due to 
insufficient numbers of Rickettsia in the Hce. In the human host 
the parasites, as shown by transmission experiments, occur in 
the blood plasma and also in various body excretions. They are 
ordinarily not filterable, but in some stages of their development 
will pass through bacterial filters. 

Rocky Mountain Spotted Fever. — For many years certain 
limited districts in the Rocky Mountain region of northwestern 

United States (Fig. 57), partic- 
ularly Idaho and Montana, 
have been known to be affected 
by this very serious disease. 
Its yearly occurrence in well- 
defined areas has given rise to 
panic and hysterical fear of en- 
tering the '' haunted " places. 
Houses were deserted, land de- 
preciated in value, and some of 
the richest valleys in the North- 
west left unpopulated. In 1906 
it was shown by Ricketts that 
the disease was invariably pre- 
ceded by the bite of a common 

Fig. 57. Map showing distribution of local WOOd-tick, Dermaceutor 
Rocky Mountain spotted fever. Com- , . ^^^ i t-c 

piled from U. S. Public Health Reports. veuustus (see p. 361, and Fig. 

156), which was experimentally 
shown to be the intermediate host of the parasite. Wolbach in 
1919 demonstrated the regular appearance of minute organisms, 
which he named Dermacentroxenus rickettsi, in the cells of blood- 
vessels of infected mammals, and also in nearly all the tissues of 
infected ticks. The organism shows several morphological 
types, but most frequently appears as paired lanceolate bodies, 
the length of a pair being about l/z. It is transmitted by ticks 
to their young with the eggs. It requires from two to ten hours 
feeding for a tick to become infective, but after an incubation 
period of a few days it may remain infective for many months. 
Although D. venustus appears to be the only transmitter in nature, 
experimentally other ticks have been shown to act as suitable 

In man the incubation period is usually from four to seven 


days. The disease begins with a general feehng of illness fol- 
lowed by chills and aches. A constant fever gradually increases 
until the tenth or twelfth day, when death is Ukely to occur. 
In mild cases the fever gradually subsides during the five or six 
days following. Usually on the third day a rose-colored rash 
breaks out on the head and upper part of the body, followed a 
day or two later by a characteristic spotting of the arms and 
legs, and later of much of the body, caused by the bursting of 
blood capillaries in the skin. The spots often become brownish 
or grayish in color, giving the spotted appearance from which 
the disease takes its name. In Montana, especially in the Bitter 
Root Valley, the disease has a high fatality, 75 per cent or more 
of the cases ending in death. The fatality is also high in eastern 
Oregon, but in other endemic regions is very much lower. The 
disease appears only in spring and early summer when ticks are 
abundant. So far no specific remedy has been discovered. 

There is evidence that spotted fever may be harbored by some 
of the wild mammals on which the wood tick normally occurs, 
but this has not yet been proved. The transmitting tick, D. 
venitstus, is a species which requires two years to reach maturity. 
In its immature stages it infests many of the local rodents, nearly 
all of which are susceptible to the disease, and capable of trans- 
mitting it to uninfected ticks. As adults the ticks live on many 
of the larger wild animals and on domestic animals, especially 
cattle and horses. Whether some of these animals may be 
carriers of spotted fever has not been determined. 

Prevention of spotted fever consists primarily in fighting ticks 
by various methods (see p. 368), and in destroying rodents, both 
to reduce the number of host animals for the young ticks, and to 
prevent the possibility of their acting as carriers of the disease. 

There is grave danger that spotted fever may be introduced 
into other parts of the country where suitable ticks for trans- 
mitting it can be found. The exportation by railroad of wild 
deer, elk, goats or other tick-infested animals to zoological parks 
or government preserves is a dangerous proceeding unless great 
care is taken to destroy all ticks and to exclude any individuals 
which might be harboring the disease germ. The occasional 
occurrence of the disease in various parts of the United States 
should be carefully watched for, and every precaution taken to 
prevent local ticks from getting access to the infection. 


Kedani or Japanese Flood Fever. — In certain parts of Japan 
there occurs a disease usually called kedani, or tsutsugamushi, 
which is reminiscent of American spotted fever. It begins after 
an incubation of five or six days or longer with a fever and break- 
ing out of the skin, the fever reaching its height between the 
third and seventh days. It lasts from one to three weeks and 
is accompanied by a swelling of the lymph glands, especially in 
the vicinity of the point of infection. This is usually the armpit, 
neck or groin region, where a small ulcerous wound can be found 
resulting from the bite of a mite. 

The disease is transmitted by the bite of a very small reddish 
mite, probably an immature mite of the genus Tromhidium, 
or harvest bug. These mites live in great numbers on a very 
abundant local field-mouse, Microtus montehelli. The mice are 
not only the hosts of the mites but are also subject to the disease 
and undoubtedly are an important factor in its distribution and 
control. Kedani is apparently most common in laborers working 
in hemp fields in July and August, on the plains which are an- 
nually flooded by the overflow of certain rivers. 

In Sumatra a similar disease, which is either identical or closely 
related to kedani, occurs commonly among Chinese and Japanese 
laborers in the tobacco fields. The disease as it occurs in Su- 
matra, where it is called pseudo-typhus, 
differs in some slight respects from the 
typical Japanese disease and has a very 
much lower fatality. In its incubation 
period, eruption, and general course it re- 
sembles spotted fever more closely than 
does the Japanese disease, and Schueffner, 
who has worked most with it, thinks it 
, -^P- „ ^?- " Granular j^ |^g transmitted by ticks as well as 

bodies m mononuclear *^ • i i i 

leucocyte, supposed to be mites. The disease has also been reported 
parasites of Kedani ^^^^ ^^iQ Philippines, and about 150 cases 

{Theilena tsutsugamushi). ^^ . tv/t i oi 

(After Hayashi.) have been reported m the Malay States. 

It is not improbable that it will be found 
to be widely distributed in southeastern Asia, having been in- 
correctly diagnosed as other diseases. 

A number of organisms thought to be the cause of Kedani have 
been described. Hayashi has recently found granular bodies of 
several morphological types in both the plasma and cells of the 



blood of infected individuals, and in the primary sore. These 
he believed to be piroplasma-like organisms, and named them 
Theileria tsutsugamushi. From the description and figures of 
these organisms, however, it seems more probable that they are 
related to Rickettsia or Dermacentroxenus. The blood of infected 
individuals injected subcutaneously causes the disease. The 
organisms do not pass through bacterial filters. 

Prevention in the endemic regions obviously consists in avoid- 
ing mites by skin applications or other means. The extinction 
of the field-mice and with them most of the mites would un- 
doubtedly lessen the danger of the disease. 


The protozoan affinities claimed for the parasites or parasite- 
like bodies included in the so-called Chlamydozoa is, as said 
before, doubtful, and new investigations do not, in most cases, 
tend to substantiate the claim of these structures to considera- 
tion as animal parasites. A brief account of the parasites or cell 
inclusions in some of the principal diseases attributed to this group 
is all that can be given here. 

Smallpox and Vaccine. — The youngest forms of the parasite 
are minute granules or " elementary bodies " measuring about 
0-5 M (50:000 oi an inch) in diameter. As growth takes place 
the granules increase in number and become surrounded by 
material which is usually interpreted as a reaction product of 
the cell, forming the " Guarnieri bodies " (Fig. 59 A). These 
eventually rupture, liberating the granules to infect new cells. 
The smallpox parasites differ from those of cowpox in that they 
attack the nuclei as well as the cytoplasm of the cells. 

Scarlet Fever. — In the skin cells of scarlet-fever patients are 
found characteristic inclusions which have been referred to the 
Chlamydozoa and named Cyclasterion scarlatince (Fig. 59B). 
These bodies in one stage of their development are of irregular 
shape with numerous enclosed granules, while in another stage 
the granules become radiately arranged around a larger central 

Hydrophobia or Rabies. — There usually occur in certain brain 
cells of animals suffering from hydrophobia specific bodies which 
are popularly known as " Negri bodies " in honor of their discov- 
erer, and which have been given the scientific name Neurorydes 




Cornea cells showing developmental stages of Guarnieri bodies, Cytoryctes vac- 
cinice. (After Tyzzer.) 



Epithelial cells of skin showing various stages in development of Mallory bodies, 
Cyclasterion scarlatinoe. Radiate form shown in middle figure. (After Mallory.) 



Epithelial cell of conjunctiva showing Prowazek bodies. (After Halberstaedter.) 


Nerve cells of Ammon's horn of cerebrum showing Negri bodies, Neuroryctes 
hydrophobioB. (After Maresch.) 

Fig. 59. — Various types of Chlamydozoa. Note that in each case the parasite- 
like bodies are enclosed in a ground substance supposed to be extruded by the 


hydrophohice (Fig. 59D). At first thought to be simple parasites, 
these bodies are now generally regarded, as are other Chlamydozoa, 
as reaction products of the host cell surrounding one or many mi- 
nute granules which are the true parasites. The minute size of 
the granules and the difficulty of identifying them when they are 
separated from their " mantles " probably accounts for the 
negative findings in infective parts of the nervous system in 
which Negri bodies are not found, and also in the saliva, which is 
highly infective. The weight of evidence seems to favor the 
protozoan affinities of the microorganism of hydrophobia, but 
the nature of the parasite is still shrouded in uncertainty. 

Trachoma. — The belief in the protozoan nature of the parasite 
of trachoma, a disease of the eyes causing inflammation of the con- 
junctiva, rests on similar ground. In the affected portions of the 
eye are found numerous tiny granules known as ^' Prowazek's 
bodies " (Fig. 59C), sometimes within the cells and even within the 
nuclei and # at other times free in the serum, which have been 
thought to be the cause of the disease. The fact that these bodies 
are sometimes found in other affections has thrown some doubt 
on their relation to trachoma. Recent investigations by Anna 
Williams of 4000 school children in New York with eye infec- 
tions or inflammations, none of which were typical cases of '* tra- 
choma," showed " trachoma inclusions " to be common, and gave 
evidence that these inclusions were in reality " nests " of growing 
bacteria, of various kinds, in the epithelial cells of the conjunc- 
tiva. Miss Williams' investigations throw doubt on the existence 
of a specific disease to which the name trachoma can be applied. 

Other Diseases Caused by Obscure Parasites 

The diseases mentioned above are those which are most com- 
monly thought .to be caused by organisms of this problematic 
group, Chlamydozoa. There are a number of others, however, 
which may belong here, but on which much further investigation 
is necessary. Among. these are foot-and-mouth disease, in which 
Stauffacher has recently found an organism, Aphthomonas infes- 
tans, which, however, is probably more closely related to Leish- 
mania (see p. 76); verruga peruviana, which in some respects 
resembles smallpox; the ubiquitous measles; and a number of 
diseases which are of rare or of more or less limited distribution. 
That all of these diseases, or even all of those separately discussed 


above, are caused by protozoan parasites is very doubtful, and 
only further investigation can determine the true status of their 
causative microorganisms. The recent development of knowledge 
concerning such groups of pathogenic organisms as the Spiro- 
chaetes and Rickettsia-like organisms, on the border line of visibil- 
ity, leads to speculation as to whether some of these other diseases 
may not be found to be caused by parasites of similar nature. 



Classification. — The name worm is an indefinite though sug- 
gestive term which is popularly applied to any elongated creeping 
thing which is not obviously something else. There is hardly 
a branch or phylum of the Animal Kingdom which does not 
contain members to which the term " worm " has been applied, 
not excepting the great group Chordata, to which the back- 
boned animals, including man himself, belong. In fact some 
animals, such as many insects, are " worms " during one phase 
of their life history, and something quite different during another. 

In a more restricted sense the name " worm " is applied to three 
great groups of animals, with a few outlying forms, which super- 
ficially all resemble one another in being unquestionably " worm- 
like," though in life and structure they are widely different. 
To these animals, together with a few other heterogeneous forms, 
the collective name " Vermes," meaning worms, was applied by 
the early workers on zoological classification. Upon more de- 
tailed study it became obvious that different types of the '' Ver- 
mes " differed from one another to such an extent that they 
would have to be divided into several great branches or phyla of 
the Animal Kingdom. At the present time the majority of these 
animals are classified in three phyla, as follows: the Platyhel- 
minthes or flatworms, the Nemathelminthes or roundworms 
and the Annelida or segmented worms. There are a number of 
" worms " which will not readily fit into any of these groups but 
are incertoe sedis, showing affinity to one group in some respects 
and to another in others. Some species are so profoundly modi- 
fied by their peculiar modes of life that it is practically impossible 
even to guess at their true relationships. All three of the phyla 
of '* worms " contain parasitic species, though none of them con- 
tain parasites exclusively. 

Flatworms. — The group of lowest organization is the Platyhel- 
minthes. The worms included in this phylum are flattened 




from the dorsal to the ventral side, whence the common name 
" flat worms." Unlike nearly all other many-celled animals 
they have no body cavity, the organs being embedded in a sort 
of spongy " packing " tissue. The digestive tract has only a 
single opening which serves both for mouth and vent (Fig. 60A), 
and in the tapeworms the entire alimentary canal is absent. 
The nervous system is very simple. Performing the function 
of kidneys is a system of tubes, the terminal branches of which 
are closed by '' flame cells," so called from the flamelike flickering 
of a brush of cilia which keeps up a flow of fluid toward the 

Fig. 60. Types of digestive tracts in worms; A, fluke, — note branching and 
absence of anus; B, roundworm, — note simple form, with only pharynx differen- 
tiated, and presence of anus; C, leech, — note extensive pouches or ccEca which 
serve as reservoirs for surplus food. 

larger branches of the system and ultimately to the excretory 
pore, thus conducting the waste products out of the body. The 
absence of any kind of blood system or other apparatus for trans- 
porting food or waste products in the body necessitates a branched 
condition of the digestive and excretory systems. The most 
highly developed system of organs and one which occupies a 
large portion of the body is that concerned with reproduction. 
Usually there is a complete male and female system in each 
worm and in some tapeworms there is a double system of each 

The flatworms are usually divided into three classes, the Tur- 
bellaria, the Trematoda and the Cestoda. The Turbellaria are 
for the most part free-living animals and include the " pla- 
narians " which can be found creeping on the under side of stones 
in ponds. The Trematoda include the flukes, all of which are 
parasitic, some externally on aquatic animals, others internally 


on aquatic or land animals. They are flattened animals, usually 
oval or leaf-shaped, furnished with suckers for adhering to their 
hosts. The flukes which live as external parasites of aquatic 
animals have a comparatively simple life history, while those 
which are internal parasites of land animals have a complex 
life history, in the course of which they pass through two or three 
different hosts. The third class, Cestoda, is comprised by the 
tapeworms. As adults they are all parasites of the digestive tracts 
of various animals and are profoundly modified for this kind 
of an existence. Their peculiar method of multiplication by bud- 
ding results in the formation of a chain of segments, sometimes 
of great length, which collectively constitute a tapeworm; each 
segment, however, is practically complete in itself and capable of 
separate existence if it had some method of retaining its position 
in the host's intestine. Some tapeworms have a life history 
comparable in its complexity with that of the flukes but as a 
rule it is much simpler. With the flatworms are usually asso- 
ciated the Nemertinea, marine worms some of which are more 
or less parasitic. None of them is of any interest in connection 
with human parasitology. 

Roundworms. — Of somewhat higher organization than the 
flatworms is the phylum Nemathelminthes or roundworms. 
These worms are cylindrical instead of flattened, they possess a 
body cavity, and they have an opening at each end of the digestive 
tract (Fig. GOB). The excretory system usually consists of simple 
tubes running the length of the body. The presence of a fluid- 
filled body cavity through which food and other substances can 
diffuse obviates the necessity for having branched organs. The 
sexes are separate, and the reproductive systems are much 
simpler than in the flatworms. 

Usually there is only a single class recognized as belonging to 
this phylum, namely, the Nematoda or nematodes. Some of 
the nematodes are not parasitic but many of them parasitize 
either plants or animals. There are many important human 
parasites among the Nematoda, for instance, the hookworms, 
pin worms, Ascaris and other intestinal worms, Trichinella, Filaria 
and the guinea-worm. In some of these the life history is fairly 
simple while in others it is more complex and involves two dif- 
ferent hosts. 

Some zoologists associate with this phylum two other classes 


of worms, the Acanthocephala and the Nematomorpha. The 
former class, as indicated by the name, include the spiny-headed 
worms. These are cylindrical worms of peculiar anatomy, 
notable for the complete absence of a digestive tract as in the 
tapeworms. The head is furnished with a proboscis which is 
armed with rows of thornlike booklets. The adults live in the 
digestive tracts of their hosts, burying the thorny proboscis 
deep into the mucous membranes. They have a complex Hfe 
history, the larval stage being passed in insects of various kinds. 
Several species are occasionally but rarely found in man. 

The class Nematomorpha is comprised by the " horse-hair 
snakes," so called from the popular belief that they develop from 
horse hairs which fall into water. They are exceedingly long 
slender worms, usually parasitic in insects. Occasionally they 
are accidentally swallowed by man with drinking water and are 
usually vomited, much to the surprise and horror of the tempo- 
rarily infected person. 

Annelids. — The most highly organized phylum of worms is 
Annelida, including the segmented worms or annelids. In three 
important respects these worms are the first animals in the scale 
of evolution to develop the type of structure characteristic of 
the vertebrate animals, consisting, namely, in a division of the 
body into segments, in the presence of a blood system, and in 
the presence of " nephridia " or primitive excretory organs of 
the same fundamental type as are the kidneys of higher animals. 
In addition the digestive system is highly developed and there is 
a well-developed nervous system distinctly concentrated in the 
head. In some annelids the sexes are separate, while in others 
both reproductive systems occur in the same individual. 

At least three classes of Annelida are usually recognized, namely 
the Archi-annelida, including a few primitive marine forms; 
the Chsetopoda, including the worms which are furnished with 
bristles or setse, such as the earthworms and marine sand worms; 
and the Hirudinea or leeches, in which there are two suckers but 
no setse. There are a number of other groups of worms which 
many zoologists include with the annelids, but as their systematic 
position is doubtful and as they include no parasitic forms they 
need not be mentioned here. The only class of annelids which 
includes parasites of man are the Hirudinea or leeches. These 
animals superficially resemble flatworms but they can readily 


be recognized externally by the segmentation of the body; 
the internal anatomy is totally different. Both sexes are repre- 
sented in each individual. 

The number of different species of worms in these three phyla 
which have been found in man is well up in the hundreds. In 
the following pages each group of these worms which contains 
important human parasites will be dealt with, but only those 
species which are important, or which are particularly inter- 
esting from some other point of view, will be individually 

Parasitic Habitats. — As to the parts of the body which may 
be attacked by worms of one kind or another, there is hardly 
any organ or tissue which is exempt. There are flukes which 
habitually infest the intestine, liver, lungs and bloodvessels, 
and one species occasionally wanders to the muscles, spleen, 
brain and many other organs. The adult tapeworms are all 
resident in the small intestine, but larval tapeworms are found 
in various locations in the body. The majority of the parasitic 
nematodes of man are found in the intestinal canal but there 
are exceptions to this. The adult TrichinelloB, for instance, 
inhabit the intestine, but the larvae are found in the muscles; 
the adult Filarice usually live in the lymph vessels, whereas the 
larvae swarm in the blood; the guinea- worm and some other 
nematodes creep under the skin in the connective tissue; the 
lungworm of the hog, Metastrongylus apri, which occasionally 
occurs in man, infests the lungs and bronchial tubes; and Dioc- 
tophyme renale (or Eustrongylus gigas) is an occasional human 
parasite which occurs in the kidneys and rarely in the body cavity. 
The leeches, on the other hand, are parasitic on the surface of 
the body or in the cavities of the nose and mouth. 

Life History and Modes of Infection. — The life history and 
mode of infection of worms varies with the habitat in the body. 
Every parasitic worm must have some method of gaining access 
to the body of its host, and must have some means for the escape 
of its offspring, either eggs or larvae, from the host's body in 
order to continue the existence of its race. Many species utilize 
intermediate hosts as a means of transfer from one host to an- 
other; others have a direct life history, i.e., they either develop 
inside the escaped egg and depend on such agencies as food and 
water to be transferred to a new host, e.g., pinworm, or they 


develop into free-living larvae which are swallowed by or burrow 
into a new host when opportunity offers, e.g., the hookworms. 

Most of the intestinal parasites apparently enter their host 
by way of the mouth, and the eggs escape with the faeces. Many 
species enter as larvae in the tissues of an intermediate host which 
is eaten by the final host. Of such a nature are most of the 
tapeworms and flukes and some nematodes, e.g., Trichinella. 
Some nematodes of the intestine, as the pinworm and whip- 
worm, enter contaminated food or water as fully developed 
embryos in the eggs. Still other species, as the hookworms and 
Strongyloides, usually reach their destination in an indirect way 
by burrowing through the skin. All the intestinal worms except 
Trichinella produce eggs or larvae which escape from the body 
with the faeces. In Trichinella the larvae encyst in the muscles 
and in order for them to be released the host must be eaten by 
another animal. Many of the worm parasites of other organs 
of the body also enter by way of the mouth and digestive tract, 
though they have various means of exit for the eggs or larvae. 
The liver flukes enter and escape from the body as do ordinary 
intestinal parasites; the lung flukes enter by the mouth, but the 
eggs are expelled with sputum; the blood flukes enter by bur- 
rowing through the skin, and the eggs escape either with faeces or 
urine; the FilarioB, like blood-dwelling protozoans, enter and 
leave the body by the aid of blood-sucking insects; the guinea- 
worm enters by the mouth, and the larvae leave through the skin. 
The larval tapeworms which infest man enter either by the 
mouth or by accidental invasion of the stomach from an adult 
in the intestine. Like Trichinella they are usually permanently 
sidetracked in man, since they can escape only by being eaten 
with the tissues in which they are imbedded. 

Effects of Parasitism. — The effects produced by parasitic 
worms depend in part on the organs or tissues occupied, in part 
on the habits of the worms and in part on the poisonous qualities 
of their secretions or excretions, to which the susceptibility of 
different individuals is very variable. The effects of some kinds 
of worms is a much disputed point. Some investigators tend to 
minimize the damage done by worm parasites, especially intestinal 
ones, while others undoubtedly overestimate it. Improved facili- 
ties for discovering infection have demonstrated the presence of 
intestinal parasites in so many unsuspected cases that we are 


likely to incriminate them in nearly every morbid condition for 
which we cannot, with equal readiness, discover another cause. 
It cannot be doubted, however, that many of the morbid con- 
ditions really are, in part at least, produced by intestinal worms. 
Much of the difference of opinion regarding the effects of these 
parasites is no doubt due to the variable susceptibility of dif- 
ferent individuals. 

The amount of nutriment which is absorbed by worms such 
as Ascaris and the pin worm, which live on semi-digested food in 
the lumen of the intestine, is probably in most cases relatively 
slight: Leuckart states that Tcenia saginata, for instance, gives 
off about 11 proglottids a day, which would amount to one and 
two-thirds pounds in a year. This would not, of course, repre- 
sent more than a fraction of the food materials used. Such a 
loss would, however, be inappreciable in adults, though it would 
be felt in growing children unless compensated for by increased 
appetite. Many intestinal parasites, as the hookworms, devour 
cells of the mucous membrane and suck blood, sometimes causing 
extensive bleeding. 

The most serious injury from intestinal worms is undoubtedly 
the toxic effects of their secretions and excretions. We know 
that the diseases caused by most Bacteria and Protozoa are 
the result, not of the actual damage done by the parasites in 
devouring tissues, but of the poisonous waste products and se- 
cretions given off by these organisms. Until recently little was 
known about the toxic effects of worms, but that toxins were pro- 
duced by them was evident from symptoms disproportionate to 
the mechanical injury the parasites could do, and from effects 
which could in no way be the direct result of mechanical injury. 
In 1901 a French worker, Vaullegeard, actually obtained from 
certain tapeworms and from Ascaris toxic substances which 
acted upon the nervous system and upon the muscles. Recent 
investigations by Flury have shown that Ascaris, a nematode, 
contains certain substances which are very irritating to mucous 
membranes, other substances which have blood-destroying and 
tissue-destroying properties, and still others which have an in- 
toxicating effect on the nervous system, causing hallucinations, 
dehrium and other disturbances. These toxins, derived from 
the body and excretions of Ascaris, when introduced into a ver- 
tebrate animal, cause the same symptoms which often accom- 


pany Ascaris infection, but which have usually been attributed 
to other causes. With such an array of formidable chemical 
compounds in the body substance of intestinal worms, it is not 
necessary to search for mechanical factors to explain intestinal 
disturbances, abdominal pains, nervous and mental symptoms, 
and the various other apparently unrelated conditions which 
accompany infection with such worms. When, as in the case 
of hookworms, such effects are combined with blood-sucking and 
bleeding from wounds, facilitated by secretions which prevent 
coagulation of blood, it is not difficult to understand how such 
profound anemia and loss of vitality are produced by compara- 
tively few small worms. The presence in blood of toxins ab- 
sorbed from worms in the intestine is further indicated by changes 
in the blood itself. The anemia of hookworm disease, due both 
to reduction of blood corpuscles and to diminution in percentage 
of haemoglobin, is so well known that anemia is sometimes used 
as a synonym for hookworm disease. Similar though usually 
less marked anemia occurs in cases of infection with other worms, 
e.g., the fish tapeworm, Dihothriocephalus latus, the blood flukes, 
etc. Another symptom of the presence of worms in the body is 
a change in number and kinds of leucocytes or white blood 
corpuscles. An almost universal symptom, though one which is 
occasionally absent even in the infections in which it is most 
characteristic, is an increase in the number of so-called " eosin- 
ophiles," white blood corpuscles containing granules which 
stain red with eosin. These cells are supposed to be for the pur- 
pose of destroying toxins in the blood just as some of the leuco- 
cytes are apparently for the purpose of capturing and destroying 
bacteria or other foreign cells. The mere presence of an in- 
creased number of them is, therefore, sufficient reason for as- 
suming the presence of toxins for them to destroy. The normal 
number of eosinophiles varies from one per cent to four per cent of 
the total number of leucocytes, whereas in infections with such 
parasites as trichina, blood flukes, echinococcus cysts, etc., 
the number nearly always rises to five per cent or higher, and in 
some cases reaches over 75 per cent. 

Another factor which is undoubtedly of prime importance is 
the portal of entry which intestinal worms give to Bacteria and 
Protozoa. We have awakened to the importance of a " whole 
skin " and the danger which accompanies the piercing of it by the 


unclean probosces of biting flies, bugs or other insects. We have 
not yet fully awakened to the importance of an uninjured mu- 
cous membrane. As has been pointed out by Shipley, the in- 
testinal worms play a part within our bodies similar to that 
played by blood-sucking arthropods on our skins, except that they 
are more dangerous since, after all, only a relatively small per 
cent of biting insects have their probosces soiled by organisms 
pathogenic to man, whereas the intestinal worms are constantly 
accompanied by bacteria, such as Bacillus coli, which are capable 
of becoming pathogenic if they gain access to the deeper tissues 
as they are able to do through the injuries made by hookworms, 
whipworms, tapeworms, etc. Weinberg, for instance, found that 
whereas he was unable to infect unparasitized apes with typhoid 
bacilli, apes infested with tapeworms or whipworms readily con- 
tracted typhoid fever, the bacteria presumably gaining entrance 
through wounds in the mucous membrane made by the worms. 
The relation of intestinal worms to appendicitis is more than 
hypothetical, and it is probable that far more cases of appendi- 
citis are the outcome of injury done by worms than is usually 
supposed. Although it has been objected that very few of the 
thousands of appendices removed yearly are reported to contain 
parasites, it must be pointed out that parasites are very seldom 
sought, could easily be overlooked, and might not be recognized 
as such if found. It is furthermore possible that parasites which 
initiated the inflammation and ulceration might no longer be 
present in the appendix upon its removal, since they are able to 
move about freely in the digestive tract. Shipley remarks that 
appendicitis is a commoner disease now than it was when ver- 
mifuges were more frequently given. 

Diagnosis. — The diagnosis of infection with various species of 
worms depends principally on the identification of their eggs or 
larvse as found in the fseces or other excretions by microscopic ex- 
amination. Nearly every species of parasite has recognizably dis- 
tinct characterics of the eggs, the chief variations being in size, 
shape, color, thickness of shell, stage in development, appearance 
of the embryo if present, and presence or absence of an operculum 
or lid. Some of the commoner worm eggs are shown in a com- 
parative way in Fig. 61. 




Fig. 61. 

Eggs of parasitic worms, drawn to scale, 

X 200. (After various 

A, Schistosoma hoematobium, voided with 0, 


B, Schistosoma mansoni, voided with faeces. P, 

C, Schistosoma japonicum, voided with fseces. 

D, Paragonimus ringeri, voided with sputum. Q, 

E, Fasciola hepatica, voided with fseces. R, 

F, Clonorchis sinensis, voided with faeces. S, 

G, Opisthorchis felineus, voided with faeces. 

H, Opisthorchis noverca, voided with fseces. T, 
I, Fasciolopsis buski, voided with fseces. 

J, Gastrodiscoides hominis, voided with faeces. U, 

K, Heterophyes heterophyes, voided with fseces. V, 

L, Yokagawa yokagawa, voided with faeces. W, 

M, Taenia saginata, voided with faeces, usually X, 

in proglottids. Y, 
N, Tcenia solium, voided with faeces, usually 

in proglottids. Z, 

Hymenolepis nana, voided with faeces, 

usually in proglottids. 
Hymenolepis diminuta, voided with faeces, 

usually in proglottids. 
Dibothriocephalus latus, voided with faeces. 
Diplogonoporus grandis, voided with faeces. 
Davainea madagascariensis, voided with 

faeces, usually in proglottids. 
Dipylidium caninum, voided with fseces, 

usually in proglottids. 
Ascaris lumbricoides, voided with faeces. 
Trichuris trichiura, voided with faeces. 
Ancylostoma duodenale, voided with faeces. 
Necalor am,ericanus, voided with faeces. 
Trichostrongylus orientalis, voided with 

Oxyuris vermicularis, voided with faeces. 


In cases of heavy infection it is usually possible to find the eggs 
in the faeces or other excretions by simple microscopic exam- 
ination of a smear made directly from the faecal sample. Many 
light infections, however, escape detection by this method, and 
various means of concentrating the eggs so that they can be more 
readily found have been devised. One method of concentration 
is to mix with water, strain, and centrifuge, thus eliminating 
coarse material and throwing the relatively heavy eggs to the 
bottom of a tube. The principal objection to both methods is 
the small size of the sample which is examined. 

Several methods for the quick and efficient examination of 
large samples of faeces have recently been devised. One method, 
known as the glycerine-salt method, developed by Barber, con- 
sists in thoroughly mixing a fairly large faecal sample with a mix- 
ture of equal parts of glycerine and saturated magnesiun sul- 
phate solution. The eggs present float to the surface and can 
be poured off on large slides for examination. By centrifuging 
negative specimens and again floating the eggs in a glycerine-salt 
solution a still higher percentage of positives can be found. In 
a test trial in Siam 35.5 per cent of 45 faecal samples were found to 
be hookworm-infected by examination of two slides by the plain 
smear method, whereas 84.4 per cent were positive by the exam- 
ination of a single slide by the glycerine-salt method, and 86.6 
per cent by examination of two slides. 

A still more accurate method is the brine flotation-loop method 
of Kofoid and Barber. A large faecal sample is thoroughly mixed 
with concentrated brine in a paraffin paper container of two or 
three ounces capacity. The coarse float is forced below the 
surface by means of a disk of No. 9 steel wool, and the container 
is allowed to stand an hour for the eggs to float to the surface. 
The surface film is then wiped off with wire loops one-half inch 
in diameter, the material transferred to a large slide, and exami- 
nation made. The number of positives escaping detection by this 
method is practically negligible. Another very simple and effect- 
ive method is to mix the faecal sample thoroughly with a con- 
centrated salt solution in a container so filled that there is a slight 
meniscus. After standing a few minutes the eggs rise and adhere 
to a glass slide touched to the surface of the meniscus. This 
method is very effective especially for hookworm eggs, but is 
said not to be useful for operculated eggs or for larvae. 



General Account. — The flukes are animals of a very low order 
of development in some respects and of very high specialization 
in others. In shape they are flat and often leaflike, with the 
mouth at the bottom of a sucker at the anterior end and with a 
second little sucker, for adhesion, on the ventral side of the body. 
They are all parasitic when adult and attach themselves to their 
hosts, either externally or internally, by means of their suckers, 
sometimes aided also by hooks. The development of the ner- 
vous system is of a very low grade, and the only tendency towards 
a brain is the presence of a small ganglion at the forward end of 
the body which gives off a few longitudinal nerves. Sense organs 
are almost lacking — • there is usually no sense of sight and none 
of sound; in fact no sensations whatever except a meager sense 
of touch falls to the lot of these lowly animals. There is no blood 
or blood system, the result being that the digestive tract and 
excretory system are branched, often to a surprising extent, in 
order to carry food to all parts of the body and to carry waste 
products out from all parts. In these respects the flukes are 
very primitive animals, but in other respects they equal or surpass 
any other animals in their complexity. We would have to look 
long to find more intricate and highly specialized reproductive 
systems than they possess, and their life histories are so mar- 
velously complex as to tax our credulity. We are accustomed 
to think of a butterfly as having a wonderful life history in that 
it passes through two phases of life, the first as a caterpillar, the 
second as a mature butterfly, the two being separated by a third 
inactive phase of existence. But by comparison with the flukes 
this life history appears simple. Many flukes, especially those 
which live as internal parasites in the land animals, pass through 
four and sometimes even five distinct phases of existence, during 
some of which they are free-living, and during others may para- 
sitize successively two or even three different hosts. 



In all flukes except those of the family Schistosomidse both 
male and female reproductive systems occur in the same individ- 
ual, and occupy a large portion of the body of the animal. We 
are familiar with animals which appear to live almost wholly 
to eat; the flukes are animals 

which seem to live merely for re- j^^^ " ^' 

production. They are reproduc- ^IWhiS ' 

tive machines, all the other or- f:f^4^i^^:\Q ryat.&izi. 

gans of their bodies being devel- WMcmMt^ ^n*- 

oped only to a sufficient extent |»//^^^\t% ^-s- 

to ensure the proper develop- |- m3^ ^M^'rl •3-'* 

ment and maturity of the eggs. I^jK^ ^H^ ctI" " ^^ 
The eggs proper and the shell f|Br^^^j5Bgi"~ "*" 
materials are produced by sepa- WB^^^^Mm'" °^' 
rate glands, and sometimes the ^K^^^rS^— se^t.V. 
canal for conducting the sperms ^^^M^^^'^""^' 

from another individual into the ^^j:^^~ ex^.c. 

body to fertilize the egg is distinct 

» ii i 1 • 1 1 J. ii Fig. 62. Heterophyes heterophyes, a 

from that which conducts the ^e^y small intestinal fluke of man; A, 

eggs out of the body. The male adult; B ( X 350), spines from genital 

, • J. f 4- ^^'^s; g- r., genital ring; g. p., genital 

system consists of two or more pores; other abbrev. as in Fig. 74. X 33. 

glands or testes for the produc- Egg shown above, x 500. (After 
tion of the sperms, two sperm 

ducts which meet and enlarge into a "cirrus pouch" for storing 
the sperms until ready to be used, and a rectractile copulatory 
organ. All these complex sexual organs in a single animal which 
may be no larger than the head of a pin (Fig. 62)! 

Almost as soon as the fluke reaches its final host and assumes 
its mature form, development of the reproductive systems be- 
gins. Although both sexes are usually in the same individual, 
mutual cross-fertilization generally takes place, the sperms of 
two individuals simultaneously fertilizing each other. The num- 
ber of eggs maturing in a single fluke is enormous, and while it 
undoubtedly varies in different species and in different individuals, 
the eggs are probably always to be reckoned in the thousands, 
and sometimes in the hundreds of thousands. 

Life History. — The life histories of all the flukes which are 
internal parasites have much in common, and all of them undergo 
a series of marvelous transformations from egg to adult. 

The fluke which is most thoroughly known in every respect 


is the almost cosmopolitan liver fluke, Fasdola (or Distomum) 
hepatica, of sheep, goats and other ruminants. This species 
occasionally establishes itself in man also, but it can be looked 
upon only as an accidental parasite as far as man is concerned. 
Its life history (shown diagrammatically in Fig. 63) will be 
described in some detail since it is more thoroughly known than 
is that of most of the flukes, and because it is typical of the group. 

The adult of the liver fluke (Fig. 63A) Hves normally in the 
bile passages and liver tissue of its host. About three weeks 
after the flukes have reached their destination in or near the 
liver, reproduction commences. Eggs (Fig. 63B) begin to pass 
out through the uterus of the fluke, and are carried by the bile 
of the host to the intestine and thence out of the body by the 
faeces, a single fluke producing as many as 50,000 eggs. Since 
there may be over 200 flukes in a single host, the number of 
eggs voided may amount to many millions. These eggs, if they 
chance to fall into water of moderate temperature, hatch out 
little ciliated embryos known as miracidia (Fig. 63D), which 
resemble ciliated protozoans. They are about 100 /* {^^jj of an 
inch) in length. Each of the embryos swims about for a day or 
two, by means of its cilia, in an effort to find a suitable interme- 
diate host, in this case certain species of snails of the genus 
Limncea (Fig. 63E), and if successful it bores into the snail by 
means of a little pimple-like projection at the anterior end of 
the body. It is obvious that only a small per cent of the embryos 
are likely to survive the double risk of not reaching water, and 
if safely in water of not reaching a suitable snail to bore into. 
However, once safely within the tissues of the snail, the embryo 
begins the second phase of its existence, during which it reproduces 
to make up for the enormous mortaHty encountered in the trans- 
fer from sheep to snail. 

In the course of some days the ciliated embryo transforms into 
a saclike body or ''sporocyst" (Fig. 63F), the inner /' germina- 
tive " cells of which act as parthenogenetic eggs {i.e., eggs which 
do not need fertilization), each developing into a larva of a new 
type, known as a redia (Fig. 63G). The latter, when nearly 
mature, burst the wall of the mother sporocyst and migrate into 
other tissues of the snail. The redise are very simple organisms 
with a sucker and an unbranched blind pouch for a digestive 
tract. Like the sporocyst they contain germinative cells within 




Fig. 63. Life history of liver fluke, Fasciola hepatica; A, adult in liver of sheep; 
B, freshly passed egg; C, egg with developed embryo, ready to hatch in water; D, 
ciliated embryo in water, about to enter pulmonary chamber of snail (E) ; F, 
sporocyst containing redise; G, redia containing daughter redise; H, redia of 2nd 
generation containing cercarise; /, cercaria; /, same, having emerged from snail 
into water; K, cercarise encysted on blade of grass; L, cercaria liberated from cyst 
after ingestion by sheep; M, young fluke developing in liver of sheep. 



their bodies and these develop into a second generation of redise 
(Fig. 63H) ultimately escaping from a little " hatching pore " 
in the body wall of the parent. In this way even a third genera- 
tion of redise may be developed, but usually the second generation 
of redise produce from their germinative cells a new type of larva, 
the cercaria (Fig. 631), quite different from either the embryo 
or the redia. The cercarise are furnished with a sucker and a 
forked digestive tract, and have an actively moving tail. They 
worm their way out of the body of the snail in which they were 
developed and swim about in the water by means of lashing 
movements of their tails (Fig. 63 J). Eventually they attach 
themselves to a submerged blade of grass or aquatic plant, lose 
their tails, secrete a cyst about themselves (Fig. 63K), and wait to 
be eaten or drunk by a sheep or a goat. When so swallowed the 
cyst is dissolved off in the stomach, and the little parasite (Fig. 63L) 
wends its way up the bile duct to the liver, there to begin again 
the reproduction of eggs and start a repetition of the entire cycle. 

Such is the life history of the liver fluke. In some flukes this 
strange life is further complicated by the invasion of a third host 
by the cercarise. In some fluke parasites of frogs, for instance, 
the redise inhabit certain snails, while the cercarise inhabit insect 
larvse, and infect their ultimate host by being eaten with the 
insects. Several human flukes, including the lung fluke, Para- 
gonimus ringeri (westermani) have a life history of this type. 
The encysted cercarise of the lung fluke are found in the tissues 
of several species of fresh-water crabs and in the earlier stages 
are believed to be parasites of a snail on which the crabs feed. 
The Chinese liver fluke, ClonorcMs sinensis, parsisitizes succes- 
sively a snail, a fish and a mammal. 

In some species of flukes daughter sporocysts are formed in- 
stead of redise, and in some the sporocysts give rise to cercarise 
directly. The known types of life histories of flukes are graphi- 
cally shown by the following diagram, copied from Leiper: 



Intermediate Host 





in mollusc 



Sporocyst. . . 

. . . Daughter Sporocyst 

in crustacean 

(or ciliated 

Sporocyst. . . 

.. Redise 


in insect 



Sporocyst. . . 

. . Redise, Daughter 


in fish 

on vegetation 

[ Free-swimming . 


tube of an aquatic animal, another in the conjunctival sac in 
the eyes of birds. 

The flukes which infest man may be divided for convenience 
into four groups, the blood flukes, the lung flukes, the liver 
flukes and the intestinal flukes. Altogether over 20 different 
species have been found in man, but only those which are com- 
mon or important will be considered in the following pages. 

Control. In all known cases freshwater snails act as inter- 
mediate hosts for the flukes which infest man and domestic animals. 
A practical and efficient method of destroying these snails would 
make the ultimate eradication of fluke diseases, in spite of the 
difficulty in treating them, a matter of brigher prospect than the 
eradication of hookworm and other intestinal parasites, in which 
sanitary disposal of faeces must be relied upon. 

Recent experiments by Chandler show that copper salts exert 
a powerful effect upon snails, even in very high dilution, appar- 
ently acting by inhibition of necessary enzymes. In experi- 
ments on a number of snails of six different families, including 
members of all the families of which species are known to act as 
intermediate hosts for pathogenic flukes, it was demonstrated 
that copper sulphate in proportions of one part in from 500,000 
to 2,000,000 parts of water destroys the snails in all cases within 
48 hours. From the point of view of expense, harmlessness 
and convenience in use, copper sulphate is preferable to any other 
substance which has been tried or suggested for destroying snails. 
In the dilute solutions which are necessary the water is not in- 
jured either for human or animal consumption, for bathing, or for 
agricultural purposes. It is destructive to very few other or- 
ganisms in the water, except algse. It is, however, injurious to 
some species of fish, especially the young, and its use may be 
objected to for this reason in some places where fluke diseases 
are prevalent, e.g., in oriental countries, where fish are extensively 
kept in the snail-infested waters and form an important part of 
the native diet. The eggs of the snails are not destroyed by the 
copper salts. With government aid and supervision, the work 
being carried out under the direction of scientifically trained 
men or commissions, it seems entirely possible that whole states 
or countries, at least in the vicinity of towns or villages, could be 
freed of human fluke diseases. 





Blood Flukes 

The most important flukes parasitic in man are three species 
of Schistosoma (or Bilharzia) which live in the large bloodvessels 
of the abdominal cavity. 

Schistosoma is one of the few genera of flukes in which the sexes 
are separate. The relation of the sexes is one of the most remark- 
able in nature. The mature 
male worm (Fig. 64) has a 
cylindrical appearance due to 
the fact that the sides of the 
flat body are folded over to 
form a ventral groove . In this 
groove, projecting free at each 
end but enclosed in the middle, 
is the longer and slenderer fe- 
male, safe in the arms of her 
lord. While young the sexes 
live apart, but as soon as sex- 
ual maturity is attained they 
couple together and spend the 
rest of their lives in this man- 

Unlike the liver flukes, the 
blood flukes do not develop 
great numbers of eggs all at 

once, but instead develop them Fig. 64. Blood fluke, Schistosoma fuBrna^ 

one by one and have only a ^^^^^^j male ( $ ) carrying female ( 9 ) in 

J. . ,, '^ A. J. ventral groove; int., intestine; gyn. c, 

lew m the oviduct at any one gynecophoric canal or ventral groove; m., 

time. Such a method of re- f °"*^' ^' «•• central sucker, x 8. (After 

1 • • ^ •!• 1 /. Looss.) 

production is facilitated, of 

course, by the constant juxtaposition of the male and female 
worms. The blood flukes live correspondingly much longer than 
the liver flukes, often persisting for many years. 

Schistosoma haematobium. — The most important species 
from the pathogenic point of view is Schistosoma hoematobium 
(Fig. 64). This parasite is common in the countries surrounding 
the eastern end of the Mediterranean, southern Asia and many 
parts of Africa, especially the east coast. In Egypt over half 



the population is said to be infected, and in an examination of 
54 boys in the village of El Marg, near Cairo, 49 were found 

These flukes, about one-half inch in length, abound sometimes 
in hundreds in the abdominal veins of their host, living especially 
in the portal vein and its various branches. The eggs of the 
worms, which are oval with a stout spine at one end (Fig. 65 A), 
and about 0.16 mm. (jJ-q of an inch) long, are carried to the small 
vessels on the surface of the urinary bladder. By means of the 
sharp spine they penetrate to the wall of the bladder and are 
voided with the urine. As the eggs enter the bladder they cause 
a certain amount of bleeding, resulting in a bloody urine. From 
this symptom the disease caused by infection with Schistosoma 
hcematohium is often called '* parasitic hsematuria." Except 

Fig. 65. Eggs of Schistoma; A, terminal spined egg oi S. ncematobium from 
urine; B, lateral spined egg of *S. mansoni from faeces; C, egg of S. japonicum, with 
only rudiment of spine ; note developed embryos in all. X about 200. (A and B 
after Looss, C after Leiper.) 

in severe infections no serious symptoms appear, but when nu- 
merous the worms cause much pain and give rise to a great va- 
riety of abnormal conditions of the bladder. The damage they 
do is partly the result of blocking of the veins, and partly the 
result of inflammation and bleeding of the bladder caused by its 
penetration by the spined eggs. Sometimes the kidneys, ureters 
and other urino-genital organs are attacked and seriously affected. 
In addition there can be little doubt but that the worms excrete 
poisonous matter into the blood, as practically all parasitic worms 
do to some extent, and this probably accounts for part at least 
of the anemic and debilitated condition so common in infected 


people. Recent experiments by Fairley seem to corroborate this 
view. It is reported that of 625 British soldiers who became 
infected with blood flukes in South Africa during the Boer war, 
359 were still on the sick list in 1914 exclusive of those perma- 
nently pensioned. The cost to the British government for per- 
manent and " conditional " pensions for these soldiers amounted 
to nearly S54,000 a year. 

The life history of Schistosoma hcematobium has only recently 
been worked out by Leiper, of the British Army Medical Corps, 
in Egypt. It was long known that a ciliated embryo or mira- 
cidium developed inside the egg shells, even before they left the 
body of the host, and that these embryos hatched out and swam 


Fig. 66. Egyptian snaJIs which serve as intermediate hosts for blood flukes; A, 
Bullinus contortus, an intermediate host for Schistosoma hcematobium; B, Planorbis 
boissyi, an intermediate host for Schistosoma mansoni. (After Leiper.) 

about when the eggs were immersed in water, but beyoud this 
point the life history could only be conjectured from analogy with 
the liver fluke. Leiper, who had already made some investi- 
gations in regard to the life history of S. japonicum in China, 
worked on the life history of this species, chiefly at El Marg, 
near Cairo, Egypt. He found that Schistosoma embryos are 
attracted by several species of fresh-water snails and that they 
penetrate the bodies of three species, Bullinus contortus (Fig. 
66 A), B. dyhowskii and Planorbis boissyi (Fig. 66B). Here they 
undergo transformation into sporocysts, from which daugh- 
ter sporocysts bud off (Fig. 67). After leaving the mother cyst 
the daughter sporocysts migrate into the tissue of the liver and 
grow rapidly. They become greatly elongated and eventually 
ramify throughout the organ, so increasing its bulk and color 
that an infected snail can be detected at a glance. The sporo- 



cysts move by wriggling movements, and absorb nourishment 
directly through the body wall. When they become over-dis- 
tended with the cercariae developing within them the wall ruptures 
and the cercariae are set free in the snail. The cercariae are dis- 
charged from the mollusc in '' puffs," a number being periodically 
shot into the water. 

Examination of molluscs which were collected in the El Marg 
canal resulted in finding 17 species of cercariae, among them the 
cercariae with forked tails and no bulb in the oesophagus, the 

Fig. 67. Larval forms of blood flukes teased from liver of Planorbis; J., 
sporocyst containing daughter sporocysts; B, daughter sporocysts in liver tissue; 
C, cercaria. Note forked tail, characteristic of Schistosoma cercariae. (After 

typical form of Schistosoma cercariae (Fig. 67C). Infected mol- 
luscs may continue to liberate cercariae for several weeks. Leiper 
later found that S. hcematobium developed only in the species 
of Bullinus, the cercariae from Planorbis belonging to another 
species, S. mansoni. In Natal and the Transvaal a small 


dark-colored snail, Physopsis africana, acts as an intermediate 

When fully developed the cercariae escape from the snails and 
swim about in water in search of a final host. They do not live 
at best as long as 48 hours, so a vast majority of the larvae must 
perish from failure to find a suitable host. It has been shown 
that not only man but also various species of monkeys and ro- 
dents may be infected by the cercariae. 

Infection may occur in two different ways: by drinking water 
containing cercariae, or by bathing in it, since the cercariae are 
able to penetrate either the mucous membranes or the sound 
skin, migrating through the body until they reach their desti- 
nation in the abdominal veins. The natives of some parts of 
Africa realize that infection may result from bathing, but from 
the nature of the disease they believe that infection takes place 
by way of the urinary passages and therefore employ various 
mechanical devices to prevent infection in this manner. There 
is little doubt, when infection occurs from drinking water, that 
the cercariae adhere to the walls of the mouth and throat and bore 
through them, since passage through the acid juices of the stom- 
ach is apparently fatal for them. 

The disease usually develops in from two to four months after 

Treatment and Prevention. — Recent work by Christopherson 
has shown that tartar emetic has a specific action on both the 
worms and the eggs, and leads to a rapid improvement in the 
condition of the infected individuals. The drug is given in the 
form of intravenous injections on alternate days beginning with 
J grain in 40 to 50 minims of saline solution, and increasing the 
dose by | grain with each injection until a dose of 2 to 2 J grains 
is reached The injections are continued until all of the voided 
eggs are sterile and show evidence of deterioration. Usually the 
total amount of tartar emetic required is between 20 and 30 
grains. Christopherson's work has been confirmed by a number 
of other investigators. The dead eggs imbedded in the tissues may 
continue to cause inflammation for a time, but the symptoms 
gradually disappear. Even without reinfection some of the 
worms, if the disease is left untreated, may continue to live and 
produce eggs for years, but in most longstanding cases reinfec- 
tion probably occurs frequently. 

216b the flukes 

Now that the life history and modes of infection are known, 
definite preventive measures can be taken. Prevention of con- 
tamination of drinking water by infected urine is, of course, the 
ideal preventive measure, but in countries where the disease is 
most prevalent, as in Egypt, cooperation of the natives in such 
a matter is more than can be expected. Leiper has pointed out, 
however, that the disease can be eradicated without such coop- 
eration by other means, depending upon local conditions. In 
large towns and cities it is practical to destroy the free-swim- 
ming infective stage of the worm by filtering or impounding 
water, while in rural districts the worm must be deprived of 
its intermediate host. Cairo, for example, obtains its water 
supply from the Nile, part of it being unfiltered. Water used 
for irrigation purposes above Cairo, and frequently contaminated, 
is turned back into the river and is probably the chief source of 
infection at Cairo, where 10,000 children are said to become in- 
fected annually. In towns where filtering is impractical the 
water could be rendered uninfective by impounding it in protected 
reservoirs for 48 hours, since the cercarise die in this time. The 
objection to this is that the water loses valuable sediment, but 
it is doubtful whether the agricultural loss from lowered vitality 
resulting from Schistosoma infection is not greater than is the 
loss in fertility from impounding water. 

It seems very probable that the use of copper sulphate for 
destroying snails in ponds or irrigation ditches in agricultural 
districts, as outlined on p. 211, will prove to be an effective means 
of controlling the disease. At present a preventive measure used 
in Egypt is the intermittent flow of water in irrigation canals, 
under government control. The snails which serve as inter- 
mediate hosts for Schistosoma are said to die if the water in which 
they live is dried up. It is customary for water to be turned out 
of most irrigating canals for periods of 15 days at a time, which 
Leiper says would be sufficient to destroy molluscs in them except 
in puddles left by an uneven floor, which must be treated by 
chemicals, or the floors leveled. However, in view of the remark- 
able resistance which most snails have to drouth and to other 
adverse conditions, this conclusion ought to be proven by eirtensive 
experimentation. Infected water to be used for washing can be 


rendered non-infective by the addition of one part of cresol in 
10,000 parts of water. 

Leiper's work shows that transient collections of water are not 
sources of infection after recent contamination, whereas all per- 
manent collections of water, as in rivers, canals and marshes, 
are dangerous if inhabited by a suitable intermediate host. 
The removal of infected persons from a given body of water 
would have no immediate effect in reducing its infectiveness, 
since the snails discharge cercarise into the water for a prolonged 
period. The preventive measures briefly outlined above were 
worked out by Leiper for the special conditions existing in the 
infected parts of Egypt but in a broad way they are applicable 
wherever Schistosoma hcematohium occurs. 

Other Species. — There are two other species of Schistosoma 
which are pathogenic to man. One, S. mansoni, was long con- 
fused with >S. hcematohium, the only apparent differences having 
been observed in the eggs. The eggs of S. mansoni (Fig. 65B) 
are provided with a lateral instead of a terminal spine, and are 
voided in the digestive tract and its appendages, whence they are 
liberated with the faeces, instead of making an exit from the body 
by way of the urinary organs. By experimental infections of 
mice Leiper showed that cercarise from the snail Planorhis hoissyi 
(Fig. 66B) developed into worms somewhat smaller than those 
from the species of Bullinus, with certain distinct differences in 
anatomy. The cercariae from Planorhis produced only lateral- 
spined eggs which were voided with the faeces, thus showing that 
S. mansoni was really a distinct species and not merely an abnor- 
mal type of S. hcematohium. This parasite occurs in common with 
the foregoing species in many parts of Africa and is also common 
in the West Indies, Venezuela and perhaps other parts of tropi- 
cal America. Like the hookworm, it was probably introduced 
from Africa in the slave days. The intermediate host in Ven- 
ezuela has recently been shown by Iturbe and Gonzales to be 
the snail Planorhis guadelupensis, whereas in Brazil Lutz has 
shown P. olivaceus to be the intermediate host. 

The anemia and debility caused by S. mansoni is similar to that 
caused by S. hcematohium. The irritation and inflammation of 
the urinary organs is replaced, however, by similar symptoms of 
the intestine, and a kind of dysentery often results. 

The manner of transmission of the parasite is similar to that 


of Schistosoma hcematohium except that infected faeces instead of 
urine contaminates water inhabited by a suitable intermediate 
host, as Planorhis hoissyi. 

A third species of Schistosoma, S. japonicum, is endemic in 
parts of Japan, China and the PhiHppine Islands, and perhaps 
in many other oriental countries. It is slightly smaller than 
the other species (about two-fifths of an inch in length) and pro- 
duces eggs (Fig. 65 C) which do not have the spine that is so 
characteristic of the other species of Schistosoma, but only a 
rudiment in the form of a little lateral knob. The eggs of S. 
japonicum, like those of S. mansoni, are voided from the intestine 
with the faeces. They also frequently become lodged in the 
liver gall bladder, walls of mesenteric bloodvessels, spleen, pan- 
creas, and sometimes other organs, not even the brain being 
exempt. The female worm must in some way deposit her eggs 
outside the bloodvessel in which she lives since they are ap- 
parently carried to their destination by the lymph streams. 
Severe infections with this parasite usually prove fatal sooner or 
later, and post-mortem examinations show many of the organs 
of the body to be badly affected. Infection with S. japonicum 
is associated with a skin disease known to the natives as " ka- 
bure," and probably caused by the burrowing of the cercariae 
in the skin. According to Laning of the U. S. Navy, it is not an 
uncommon thing for large per cents of the crews of patrol gun- 
boats in the Yangtze River to be completely disabled by infection 
with this parasite. Laning divides the disease caused by S, 
japonicum into three stages. The first stage, lasting from three 
to six weeks, is marked by high afternoon temperatures, slow 
pulse, respiratory troubles, transient oedema and rash on the 
skin and mucous membranes, abdominal pains, digestive irregu- 
larities and sometimes mental disturbances. The second stage 
is marked by enlarged liver and spleen, dysenteric symptoms, 
anemia and irregular fever. The third stage, which does not 
always occur, but may appear in from three to five years where 
there are constant reinfections, is marked by diseased liver, 
oedema of legs and arms, emaciation, anemia and dysentery, 
and death from exhaustion is not uncommon. 

The life history and mode of infection in the case of S. japonicum 
is undoubtedly very similar to that in other species of Schistosoma. 
Miyairi, a Japanese investigator, found reproductive stages of 


S. japonicum in a species of Ldmncea in Japan. Miyairi and 
Suzuki, in further work on the Hfe history of this fluke, found 
that after sporocysts have developed in the tissues of infected 
snails redise are produced, 50 or more from each sporocyst. 
The long, coiled rediae crowd the liver and produce cercariae, the 
latter reaching maturity in about seven weeks. If in autumn 
the cercarise have become fully developed but have not left 
the snails they remain in their hosts over winter. 

Leiper obtained development of the characteristic fork-tailed 
cercarise in another small snail, Blanfordia (or Katajama) noso- 
phora, common in the rice fields of Japan. There is an interest- 
ing tale connected with 
Leiper's experiments on 
infection with these para- 
sites. With great care this 
investigator experimented 
with the infection of snails 
which he had imported 
from Japan to work on in 
his laboratory at Shanghai. 
After having succeeded in 
obtaining infection of the 
snails, he teased out the 
livers in water to liber- 
ate the cercarise. Four 
laboratory-bred mice, 

which are difficult to ob- Fig. 68. Mesentery of mouse with blood- 
tain in the Orient, were r'^^^\ ^^^^"^^^ ^^*^ Schistosoma. (After 
' Leiper.) 

immersed in the water 

in which the cercarise had been liberated, and a start was made 
for England. But alas! a woman in a neighboring stateroom 
objected to the presence of the mice so near and demanded their 
relegation to the butcher's cabin, where three of them died. At 
Aden the few remaining infected molluscs were sacrificed and 
the last mouse was subjected to infection. A month later when 
the animal was examined in the laboratory of the London School 
of Tropical Medicine many blood flukes, males and females in 
couples, were found in the portal bloodvessels (Fig. 68). 

It should be remarked in concluding this discussion of the 
blood flukes that many snails, including members of the genera 


Planorbis and Limncea, which could very probably act as inter- 
mediate hosts as well as the species in which the development 
has actually been observed, are abundant in the United States, 
and there is great danger that if once introduced, at least in the 
warmer parts of the country, these blood flukes might become 
endemic. Careful examination of immigrants from endemic 
countries and exclusion of Schistosoma-irSected persons is impor- 
tant if the infection is to be kept from becoming established. 
An ounce of prevention in this country is worth a pound of cure. 

Lung Flukes 

In Japan, China, the Phihppines, and other oriental countries, 
a region which seems to be particularly afflicted with fluke dis- 
eases, there occurs a very serious lung disease caused by a species 
of fluke, Paragonimus ringeri (westermani) (Fig. 69). It is also 


Fig. 69. Lung fluke, Paragonimus ringeri. Abbreviations as in Fig. 74. 
X about 7. (Partly after Looss, partly after Leuckart.) 

found in dogs. In some parts of Formosa fully 50 per cent of 
the population is infected. A closely alHed species, P. kellicotti, 
occurs in hogs in the United States, and probably in other parts 
of the world. 

The lung fluke is about half an inch in length, reddish brown 
in color, and relatively very broad. The adult lives most fre- 
quently in the lungs of its host, where it produces cavities an 
inch or two in diameter. The cavities become filled with various 



Fig. 70. Eggs of lung fluke in 
contents of cyst in lung of hog. X 
about 50. (After Stiles and Hassall.) 

tissues through which the parasite tunnels out its burrows and 
in which it deposits its eggs (Fig. 70). These excavations in the 
lung connect with the bronchial tubes, through which the blood, 
parasite eggs and other products are voided, thus causing the 
characteristic blood-spitting. The 
expectorations, resembling those 
of pneumonia, are of a pecuUar 
brownish red color, due in part 
to the blood corpuscles present 
and in part to the dark brown 
fluke eggs, which are often very- 

Occasionally the lung fluke bur- 
rows in other organs and glands 
of the body, such as the liver, 
spleen, muscles, intestine and 
brain. Musgrave found in the Philippines that sometimes many- 
parts of the body are infested at once, and in one case he found 
over a hundred mature parasites in a muscular abscess. When 
they burrow in the brain they cause epileptic fits and usually in 
time cause death. 

The eggs of the lung fluke (Fig. 71 A) when immersed in fresh 

water for several weeks develop 
within themselves typical ciliated 
embryos or miracidia (Fig. 71B). 
The latter burst away the little 
cap at the end of the egg and 
emerge as free-living animals. 

Nakagawa has recently shown 
that if these miracidia are placed 
in water with certain species of 
snails, particularly Melania liher- 
tina, the miracidia swarm about the snails and burrow into them, 
shedding their cilia as they go. The entire cycle of development 
in the snail has not been worked out but it is probably very similar 
to that of Schistosoma. Sporocysts of various sizes occur in the 
liver and other tissues of the snail, and it is probable that these 
produce the cercariae directly. 

Nakagawa discovered the encysted cercarise of this species, 
proved to be such by experimental infection of animals, in three 

Fig. 71. A, freshly passed egg 
of lung fluke; B, egg of lung fluke 
with fully developed embryo. X 
250. (After Katsurada.) 



species of crabs in Formosa, and Yoshida, another Japanese in- 
vestigator, acting on the discovery of his countryman, found the 
larvffi in a fourth species of crab in Japan. The crabs most com- 
monly infected are Potamon ohtusipes, a coarse-shelled, chestnut- 
colored crab about one and a 
half inches in diameter, and 
P. dehaanii, a slightly smaller 
,^, . ^^ ^ ^^ ^ species, grayish black or red- 

^^&^^P^ dish in color. Both these 
>':'<^/iii^^^^^% ^^^t)S bound in the shallow 
waters of mountain streams, 
and the former species is 
sometimes used as food. An- 

FiG. 72. A common fresh-water crab other implicated SpecieS, 
of Japan, Eriocheir japonicus, which serves jH^rrochcir idVOTlicU^ TFis" 72^ 
as a host for lung fluke. (After Yoshida.) . i • n i 

IS abundant m all plams rivers 
in Japan and is a common article of diet throughout the country. 
It is a larger crab, reaching a diameter of three inches, and has 
large hairy claws. The fourth species, Sesarma dehaani, is of 
medium size, dark in color with light reddish claws, and inedible. 
Miyairi has shown that in Korea another crab, Astacus japonicus, 
is the intermediate host. 

The lung fluke cercarise encysted in these crabs (Fig. 73A) 
were found chiefly in the liver while young, but when older they 



Fig. 73. A, encysted cercaria of human lung fluke, Paragonimus ringeri, from 
gill of crab; B, larva emerging from cyst. o. s., oral sucker; int., intestine; ex. v., 
excretory vesicle; v. s., ventral sucker. X 50. (After Yoshida.) 

occur in the gills. They vary in number from a few to several 
hundred. In some localities a very high per cent of crabs are 
infected, Nakagawa reporting that practically 100 per cent are 
infected in one district in Formosa where the lung fluke is very 
common. The cysts containing the cercarise are nearly round, 
0.5 mm. (sV of an inch) or less in diameter, and have relatively 


thick walls. The enclosed cercaria lies straight, unlike most 
encysted cercariae, and the body is entirely covered by short 
spines. In fully-developed specimens the suckers, digestive 
tract and other parts of the anatomy of the enclosed cercarise can 
be seen (Fig. 73 A) . While still in the cysts the cercariae are fairly 
resistant to unfavorable environmental influences, but are easily 
destroyed after hatching. 

When an encysted cercaria is swallowed by a susceptible ani- 
mal the cyst wall is dissolved off in the intestine, the active 
liberated larva (Fig. 73B) bores through the intestinal wall, 
wanders about in the abdominal cavity for some time, then 
bores through the diaphragm into the pleural cavity, whence it 
eventually penetrates the lungs from the outer surface. It 
becomes mature in about 90 days. Occasionally the worms 
apparently get lost and bore through the abdominal wall and 
muscular connective tissues. It is probably in this way that 
other organs than the lungs are penetrated by the flukes. 

There are two ways in which man may become infected, namely, 
by eating infected crabs which are not thoroughly cooked, or 
by drinking water containing cysts discharged from infected 
crabs. As already remarked, the mature cysts make their way 
to the gills, whence they can easily be removed, and whence 
they probably escape readily under natural conditions, thus 
becoming free in the water. Here they may remain alive for 
some time, probably 30 days or more. Yoshida states that the 
cysts sink to the bottom, in which case human infection could 
occur only rarely if ever from infected water. Nakagawa, how- 
ever, observed that 20 per cent of the larvae when freed float 
on the surface of the water. 

Prevention of infection consists either in the destruction of the 
snails which act as the first intermediate host by the use of copper 
sulphate, as outlined on p. 211, or by abstinence from the use of 
raw crabs as food and in avoidance of water for drinking which 
may possibly be infected. Whether or not other animals may 
serve as hosts for the cercariae is unknown, but if the allied Para- 
gonimus kellicotti is truly endemic in the United States, where no 
fresh-water crabs are found, some other animal must serve as an 
intermediate host, possibly certain species of crayfish. The fact 
that the lung fluke is not known as an endemic human parasite in 
this country suggests that the intermediate host may be an animal 



which is not used as food and the habits of which give Httle oppor- 
tunity for the parasites to gain access to the human body. The 
disease is said to have increased in Peru, having been introduced 
there by Japanese and Chinese laborers. If this is true some 
Peruvian animal, probably a fresh-water crab, must serve as an 

intermediate host. This suggests that 
the disease if once introduced might 
flourish in other countries, especially 
where fresh-water crustaceans are eaten. 
Lung fluke infection is evidently an- 
other disease for which a quarantine 
should be established. 

Liver Flukes 

Although the liver fluke of the sheep, 
Fasciola hepatica, and other flukes of 
herbivorous animals are occasionally 
found in man, they cannot be looked 
upon as usual human parasites. Adult 
liver flukes are sometimes accidentally 
eaten with raw liver, in which case 
they attach themselves to the mem- 
branes of the throat, causing irritation, 
congestion, a buzzing in the ears, 
difficult breathing, and other quite 
no. 74. The chin'II^ fluke, alarming symptoms Vomiting to ex- 
Clonorchis sinensis. X 3|. pel the worms usually gives immediate 

m., mouth in oral sucker; ph., pplJAf 

pharynx; gen. p., genital pores; ' . 

V. s., ventral sucker; sh. gl., so- There are Several species of flukes, 
called vitteiiine or yolk glands however, which are apparently espe- 

really shell glands; ut., coiled ' ... ^ 

egg-filled uterus; int., intestine; cially adapted for parasitizmg carnivo- 
sp. d., sperm duct; ov., ovary; j.^^^ animals, and which are common 

sem. rec, seminal receptacle, . . 

where sperms for fertilizing eggs human parasites m some countries. 
aretemporariiy8tored;t.,testis; Japan, China, the Philippines and other 

Gxc. C.J GxcrGiiory CRiiBdj cxc. p») 

excretory pore. (After Stiles.) Oriental countries are especially aflflicted 

by these flukes. The commonest species 
in man is the Chinese fluke, Clonorchis sinensis (Fig. 74) which 
is found in all of southern Asia from India to Korea. In some 
parts of Japan about 60 per cent of the population are said to 
harbor it in their livers, sometimes in hundreds or even thousands. 



-TTV.**" 1/ 

. ._ int.- m 



— -noisizr- 


In some districts in Korea 80 per cent of the inhabitants are said 
to be infected. Leiper found it common in both dog and man in 
the vicinity of Shanghai. It is also found in the liver ducts of cats, 
hogs, and probably other flesh-eating animals. It is from one-half 
to three-quarters of an inch in length, and nearly four times as long 
as wide. The ventral sucker is very small, and is situated on the 
anterior third of the body. Some authors believe that a small 
variety of this fluke found in Japan constitutes another species, 
C. endemicus, but this view is assailed by recent investigations. 
In Europe there occurs 
a species, Opisthorchis 
felineus (Fig. 75A), 
which is very common 
in domestic cats and 
dogs and is by no means 
uncommon in man; 
there is one record of its 
having been found in 
eight or nine out of 124 
post mortem examina- 
tions in Siberia. A very 
closely related species, 
0. pseudofelineus (Fig. 
75B), has been found in 
cats and coyotes in the 
central parts of the 
United States. From 
its similarity to the Old 
World species it would 
not be surprising to find 
it occasionally parasitic 
in man. 


rp, -J-, . FiQ. 75. A, Cat fluke, Opisthorchis felineus; 

i ne JiiUropean species, B, American cat fluke, O. pseudofelineus. Abbre- 
viations as in Fig. 74. x about 5. (A, after 

Stiles and Hassall; B, after Stiles.) 

Opisthorchis felineus^ is 
usually a little less than 
half an inch in length, and shaped very much like Clonorchis 
sinensis. The American 0. pseudofelineus is somewhat longer 
and slenderer than the European species. Another species of 
the same genus, 0. noverca, occurs commonly in pariah dogs 
in India, and occasionally in man. It differs from the Euro- 
pean species chiefly in having the skin thickly beset with spines. 



Little is known . of the life history of any species except the 
Chinese fluke, C. sinensis. The eggs (Fig. 76A) are of charac- 
teristic shape, and hatch in water into miracidia (Fig. 76B). 
The encysted cercarise of this fluke (Fig. 77A) have been found 

in the subcutaneous tissues and 
muscles of 12 different species 
of fresh- water fish. The cysts, 
which are very small, measuring 
only about 0.14 by 0.10 mm. (^ 
by 250 of an inch), are usually 
more abundant in the superfi- 
FiG. 76. Egg and ciliated em- cial than in the deeper tissues. 

bryo of Chinese fluke, (^ Monorchia a ^.Y.r...^U pv'^f^ po^. Kp fniinH in 
sinensis. X 700. (After Katsurada.) ^^^^"OUgn CySlS Can De lOUUQ m 

fish throughout the year, the 
younger ones are more frequently met with in late summer and 
early autumn. 

When infecte fish are eaten, according to experimenrs re- 
cently made with animals by Kobayashi, the larval flukes escape 
from the cysts (Fig. 77B) within three hours, and in fifteen hours 
they may already have 
reached the bile duct and gall 
bladder. The parasites reach 
maturity and eggs are found 
in the faeces of the host within 
26 days. The young flukes 
have a spiny cuticle until 
nearly mature, but the spines 
finally disappear. 

Muto recently found cer- 
carise in the snail Bythinia 
striatula var. javonica which ^""^"^ ^^^^' ™" "^^^^^ ^"^ ^'"''^ sucker; v. s., 

. v?ntral sucker; ex. v., excretory vesicle; 

encyst m fish of various ph., pharynx; int., intestine. 

species. When these fish 

are fed to dogs and mice, infection with Clonorchis sinensis results. 
On the other hand, controls fed with fish parasitized by cercarise 
from the snail Melania lihertina, which Kobayashi believed to be 
the first intermediate host, developed infections with Meta- 
gonimus only. Sporocysts develop in Bythinia about three weeks 
after infection with the miracidia. 

It is probable that the European liver fluke, 0. felineus, and its 

Fig. 77. Larvse of Chinese fluke; A, 
cercaria encysted in fish; B, larva freed 


Indian and American allies all have histories very similar to that 
of the oriental species. Their occurrence in man in countries 
where fresh-water fish is a common article of diet, and their 
frequency in animals which eat raw fish, strongly suggest fishes 
as intermediate hosts. 

These liver flukes, like the sheep fluke, live chiefly in the gall 
bladder and bile ducts where they often cause much mechanical 
obstruction on account of their large numbers. Severe infections 
such as occur in countries like Japan where raw fish is commonly 
eaten cause symptoms of a very serious nature. One of the most 
prominent of these is enlargement of the liver accompanied by 
more or less bloody diarrhea; the latter becomes more and more 
constant as time goes on. The liver sometimes becomes pain- 
ful, and jaundice is a frequent symptom. The patient becomes 
anemic, emaciated and weak, and is ready prey for other diseases. 
There are often periods of partial recovery followed by relapses, 
probably due to reinfections, and the patient ultimately becomes 
exhausted and succumbs to a cold, an attack of malaria, or other 
ailment from which one would ordinarily recover readily. 

There is no specific treatment for the disease. The only meas- 
ures that can be taken are to remove the patient from any possible 
source of reinfection and to keep him in the best possible general 
health, with wholesome diet, good air and proper exercise. How 
long the flukes persist in the liver is not known. 

Means of prevention of the disease are suggested by what is 
known of the life history of the parasites. The most important 
measure is unquestionably the suppression of the habit of eating 
uncooked fish in places where the disease is endemic. Kobayashi 
has shown that while the larvae of C. sinensis are killed at once on 
exposure to a boiling temperature and in a short time when ex- 
posed to considerably lower temperatures, they are not de- 
stroyed by exposure to vinegar for five hours, nor by refrigeration. 

Much could also be done by destroying the snails which act as 
the first intermediate hosts by means of copper sulphate, as sug- 
gested on page 211. Another measure, which is far less reliable, 
is the prevention of contamination of water in which fish live. It 
is impossible to prevent some contamination of water by the lower 
animals which carry the infection, and it is nearly as difficult to 
prevent contamination by human faeces. The almost universal 
use of night soil (human faeces) for fertilizer in oriental countries 


is a serious hindrance to the sanitary disposal of such infected 
material. Leiper suggests that this problem may be solved by a 
chemical treatment of night soil which would destroy all parasite 
eggs or cysts and yet not injure its value as a fertilizer. 

Intestinal Flukes 

There are several species of flukes which appear to be common 
parasites of the human intestine in certain parts of the world, 
especially in the oriental countries where the other human flukes 
abound the most. Many of these flukes are very small, but they 
may occur in great numbers, producing practically the same effects 
as do tapeworms, — anemia, emaciation and general debility. 
Many species are probably only accidental human parasites, 
normally living in some other host but occasionally finding their 
way into the human intestine with food or water and establishing 
themselves there. 

The smallest fluke parasitic in man is Yokagawa (or Metagonimus) 
yokagawa, named after a Japanese parasitologist. It is widely 
distributed in Japan, Korea, Formosa, parts of China, and prob- 
ably other oriental countries. It infects mice and dogs as well 
as man. Muto infected fish with the encysted cercerise by feed- 
ing to them cercaria-infected snails, Melania Ubertina. Encysted 
cercariae occur in a number of Japanese fresh-water fishes which 
are commonly eaten raw, particularly the ''ayu". The cysts are 
most numerous in the connective tissue under the skin and about 
the fins, especially early in the season, indicating that the fish 
become infected by free-swimming cercarise which bore through 
the skin, and not by cercarise eaten with another host. The 
encysted cercarise closely resemble those of Clonorchis sinensis. 
The development in the final host is said to take only from seven 
to ten days. Y. yokagawa inhabits the upper portion of the small 
intestine, sometimes in considerable numbers, but it never seems 
to do enough damage to cause more than a slight intestinal catarrh. 
It is remarkable for the lack of a ventral sucker and is only about 
1 mm. (about ^V of an inch) in length, and about half as broad. 
Its body is covered with a great many microscopic spines. 

A very similar fluke, Heterophyes heterophyes (Fig. 62), only 
slightly larger, occurs from Egypt to Japan in a variety of 
animals and occasionally parasitizes man. Two species of Echi- 



nostoma normally parasitic in other animals occur occasionally 
in man in the Malay countries. They are distinguished from 
other flukes by the crown of spines around the mouth sucker. 
One species, E. ilocanum, about one-fifth of an inch long, was 
found endemic among some Filipinos in a prison in Manila. 
The other, E. malayanum, about two-fifths of an inch long, oc- 
casionally parasitizes man in the Malay countries. 

Gastrodiscoides hominis (Fig. 78) is a species which is character- 
ized by the expansion of the posterior end of the body into a great 

Fig. 78. Gastrodicoides hominis. A, ventral view, showing disc-like expansion 
and posterior position of ventral sucker; B and C, dorsal views; D, lateral view; 
E, eggs. A-D, X 3; E, X 65. (After Lewis and McConnell.) 

concave disc. It is a small reddish brown parasite a little over 
one-fourth of an inch in length, which inhabits the cecum and 
large intestine of hogs, and occasionally of man, in India. A 
closely allied species occurs in horses and 
asses in many parts of Africa. Watsonius 
watsoni (Fig. 79) is a related species, also l^^m^^^'^ 
reddish brown in color, found in the small 
intestine of West African negroes. A closely 
related species, Paramphistomum cervi, is 
found in the stomach of sheep and cattle in 
Egypt and has a life history almost identical 
with that of the sheep liver fluke. This or a Fig. 79. Watsonius 
very similar species occurs in the stomach of ZnrgenZi^lper^rl 
cattle in the United States. (gen. ap.) and large 

Several large flukes of the genus Fasdolopsis sJ^keAv! s.). x about 
occur occasionally in man, especially F. buski 35. (After Shipley, 
(Fig. 80), found in many East Asian countries. ^ZZ^^^' ^""^ ^''^^' 
This species reaches a length of over an inch 
with a width of about half an inch, and has the ventral sucker 
very close to the mouth. It normally inhabits the small intestine 
of the hog but occasionally parasitizes man. Goddard found it 
in 5.5 per cent of all dispensary patients at Shaohing, China, 
during 17 months, and in 28 per cent of 304 cases admitted to the 



hospital. According to Goddard there are three stages in the 
disease caused by this parasite. There is first a period of latency 
during which there is some asthenia and mild anemia. This is 
followed by a period of diarrhea, in which there is more or less 

intestinal disorder; there is however? 
no blood in the diarrheal stools. 
There is always noticeable anemia, 
and this may be extreme. A com- 
bination of chronic diarrhea and an- 
emia is said to be characteristically 
the result of Fasciolopsis infection 
in Shaohing. Often the abdomen is 
protuberant in children. The third 
stage is characterized by increased 
anemia and a distressing amount of 
oedema, which affects the abdominal 
cavity first, then the legs, and finally 
the upper portions of the body. It 
gives the affected parts of the body a 
very characteristic puffy and swollen 
appearance. Goddard believes that 
the infection is derived from eating 
imperfectly cooked snails, some 
species of which may act as the in- 
termediate host. This would imply 
that a second intermediate host was 
not necessary in the life history. 
On the other hand it has been claimed 
that the cercarise encyst in shrimps, 
but Leiper had no success in infecting hogs with the cysts which 
he found in shrimps. 

The full life history of none of these intestinal parasites is 
known, and we can only guess at them by analogy with more or 
less closely related parasites about which we have more knowledge. 
None of them do enough damage to cause more than slight in- 
testinal irritation or catarrh, and sometimes light dysenteric 
symptoms. They are susceptible to most of the drugs used for 
expelling tapeworms and roundworms. Some species are said 
not to be affected readily by santonin, though they an? ex- 
pelled by thymol and naphthalene, and presumably by oil of 

Fig. 80. Fasciolopsishuski, i 
large intestinal fluke of man. x 2h 
Abbreviations as in Fig. 74. (Af 
ter Odhner.) 



General Structure. — Even more 
peculiar and remarkable in their 
structure and life than the flukes 
are the tapeworms. A mature tape- 
worm is not an individual, but a 
whole family, consisting sometimes 
of many hundreds of individuals one 
behind the other like the links of a 
chain (Fig. 81). In some respects 
the tapeworms are more degener- 
ate than flukes, due to their in- 
variably parasitic life in the digestive 
tract of their hosts. Being continu- 
ally bathed in semi-digested fluids 
in the intestine they can readily 
absorb food all over the surface of 
their bodies, and have no need for a 
digestive system of their own. The 
digestive tract, therefore, is entirely 
lacking, not even a vestige of it 
remaining as an heirloom from less 
dependent ancestors. 

In general form the majority of 
tapeworms are very long tapelike 
organisms which attach themselves 
to their host's intestinal walls by a 
" head " or scolex at what is really 
the posterior end of the chain of 

segments. This scolex is furnished Fig. 81. Beef tapeworm, Taenia 

with suckers and often hooks as well gradTatchlnge in°s*LTpmgiot- 

(Fig. 82). Next to the head there tids, and irregular alternation of 

ii t J) sides of genital apertures. (After 

IS a narrow region or neck stiles.) 
which continually grows and forms 

segments as it grows, each new segment thus produced pushing 
forward the segments previously formed. This process eventu- 




ally produces the characteristic chain of segments, each of which 
is known as a proglottid. Obviously the oldest proglottid is the 
one at the end of the chain, those just back of the neck being 

young and immature. The nervous 
system, which is developed into a 
primitive brainlike mass in the scolex, 
grows forward as two longitudinal 
nerves which run continuously through 
all the proglottids in the chain. The 
muscles and excretory canals also run 
continuously through the chain. Each 
proglottid, however, possesses com- 
plete reproductive systems of both 
sexes, fully as complex as in the 
flukes, if not more so (Fig. 83). The 
female system consists of an ovary, a pair of shell glands (usually 
spoken of as yolk glands), a seminal receptacle for receiving and 
holding the sperms until used for fertilization, a vagina for the 


Fig. 82. Armed and 
armed tapeworm ' ' heads 
scoleces; A, unarmed head of 
ToBnia saginata; B, armed head 
of Tcenia solium. X 10. 


Fig, 83. Sexually mature proglottid of beef tapeworm, Tcema sa^mato; exec, 
excretory canal; n., nerve cord; ut., uterus; ov., ovary; sh. gl., shell gland, 
usually called yolk gland; vag., vagina; gen. p., genital pore; sp. d., sperm duct; 
t., testis. X 7. (Partly after Leuckart.) 

entrance of the sperms, and a uterus for the storage of the mature 
fertilized eggs. The male system consists of a number of scat- 
tered testes for production of sperms, all connecting by minute 
tubes with the sperm duct. The latter, near where it opens at 
the surface of the body, enlarges into a '' cirrus pouch " where 



the mature sperms are temporarily stored. The sperm duct 
ends in an extensible copulatory organ for conducting the sperms 
into the vagina of the same or another proglottid. Though 
hermaphroditic, i.e., with both sexes in a single individual, a 

Fig. 84. Ripe proglottids of various tapeworms of man, drawn to scale accord- 
ing to average measurements: A, Toenia saginata (after Leuckart). B, Tcenia solium 
(after Stiles). C, Dipylidium caninum (after Diamare). D, Tcenia confusa (after 
Guyer). E, Dibothriocephalus latus (after Leuckart). F, Diplogonoporus grandis 
(after Ijima and Kurimoto). G, Dibothriocephalus cordatus (after Leuckart). H, 
Tcenia africana (after von Linstow). /, Hymenolepis diminuta (after Grassi). 
/, Hymenolepis nana (after Leuckart). 

proglottid does not necessarily always fertilize its own eggs, 
but cross-fertilization may often occur. This is generally in- 
sured by the fact that the male reproductive system usually 
becomes mature before the female. In the pork tapeworm, 


for instance, the male reproductive system reaches maturity 
when the proglottid has been pushed back to about the 200th 
position, whereas the female system does not mature until it 
has been pushed 200 or 300 proglottids farther back. Copulation 
then takes place by the doubhng back of the chain of proglottids 
on itself, bringing the young mature male segments into contact 
with the older mature female segments. 

After copulation, when the mature fertilized eggs begin to form, 
great changes take place in the proglottid. The uterus begins 
to enlarge and branch until it nearly fills the segment, crowding 
aside and absorbing the other organs. Segments thus distended 
with eggs are spoken of as '' ripe " proglottids and are ready to 
break loose from the chain to be voided with the faeces of the host. 
Ripe proglottids of a number of species of tapeworms found in 
man are shown in Fig. 84. 

Life History. — The life histories of all tapeworms are much 
alike. Usually before the ripe proglottids become detached and 

pass out of the host, the 
eggs develop, inside their 
tough shell, into little 
round embryos with six 
hooks (Fig. 85 A). In 
order to continue their 

Fig. 85. A, egg of beef tapeworm, T. saginata; ^ i + V. 

— note contained embryo and external filaments; development SUCn em- 

B, freed six-hooked embryo. X 300. (After bryOS mUSt be eaten by 
Leuckart.) ,i • <• • i 

another species of animal 
which acts as an intermediate host. Most often the adult 
form of the worm occurs in carnivorous animals, while the in- 
termediate host in which the larva develops is a herbivorous 
animal, but there are numerous exceptions to this. There is no 
active search for a new host on the part of the tapeworm embryo 
as there is by the embryos of flukes, but instead merely a 
passive transfer. 

When eaten by a suitable intermediate host, the shell enclosing 
the six-hooked embryo is dissolved off, and the embryo is re- 
leased (Fig. 85B). It migrates into the organs and tissues of 
the body, aided by the blood and lymph circulation of the host, 
some species having preference for certain organs, others es- 
tablishing themselves with equal readiness in any parts which 
they happen to reach. 



Having reached the organ or tissue in which it is destined to 
develop, the embryo loses its hooks and grows into some form of 
bladderworm, that is, the body undergoes a series of transfor- 
mations which usually result in the formation of a bladder-like 
body filled with a watery fluid. Into the bladder there grows 
an invagination and at the bottom of this, pushed inside out into 
it, there develops a head or scolex. There are different types 
of bladderworms which go under different names, as follows: 

(1) the cysticercus (Fig. 86 A), the simple type described above; 

(2) the cysticercoid (Fig. 86B), in which the bladder part of the 

Fig. 86. Types of tapeworm larvae: A, cysticercus of Toenia solium with head 
and neck evaginated, X 3; B, cysticercoid of Hymenolejns nana, X 12; C, plerocer- 
coid of Dibothriocephalus latus, with head invaginated. (A, partly after Stiles, B, 
from several figs, by Grassi and Rovelli; C, partly after Braun.) 

worm is poorly developed; (3) the coenurus, in which multiple 
heads form in the single bladder; and (4) the hydatid, in which 
the bladder buds into multiple daughter cysts, each with multiple 
heads (Fig. 95). The larvae of the tapeworms of the family 
Dibothriocephalidce are quite unlike the bladderworms of other 
tapeworms. They grow as long wrinkled wormlike bodies with 
the head invaginated in a little projection at the anterior end. 
Such a larva is called a plerocercoid (Fig. 86C). 

When the organs or tissues in which the larval stages are 
developed are eaten by an animal of the kind from which the eggs 
originally came, all but the scolex of the bladderworm is digested 
off, the latter turns right side out, attaches itself to the wall of 
the small intestine with the aid of its suckers and hooks, and be- 
gins to bud off proglottids of another generation. Tapeworms 
are usually looked upon as inert animals, but in reality they are 
quite active, and their movements can often be felt. 


Damage to Host. — The amount of damage which adult 
tapeworms do to their hosts is a much disputed question. There 
are those who beheve that the presence of an adult tapeworm is 
more or less of a joke and as such is to be gotten out of the sys- 
tem but not to be taken seriously. The experience of physicians 
who have had wide dealings with tapeworms does not ordinarily 
bear out this idea. The mere mechanical obstruction of the 
intestine which a large tapeworm may cause must be consider- 
able. The amount of food taken from the host for nourishment 
of such a worm might well be compared with the food absorbed 
by a growing embryo, and it usually produces a ravenous appetite. 
The injury to the wall of the intestine caused by the adhesion 
of the worm by its suckers and hooks is often the cause of serious 
conditions, allowing the entrance of bacteria and sometimes 
resulting in destructive ulceration. The waste products and 
other toxic substances given off by tapeworms must be very con- 
siderable and their poisonous properties cannot be doubted. 
Only recently there came before the notice of the author a case 
of tapeworm infection illustrating the toxic effect of the worms. 
A patient came to a local physician for treatment, thinking he 
had tuberculosis and having been so diagnosed by another doc- 
tor. He was in an extremely anemic condition and was very 
weak and easily exhausted. His cheeks were sunken, his eye 
staring and he was subject to occasional mental disturbances. 
Within a fortnight after the worm had been expelled he was prac- 
tically a new man although he had been suffering for over a year. 

Abdominal pains, anal itching, disordered appetite and di- 
gestion, emaciation, anemia and many types of nervous derange- 
ments, as giddiness, partial paralysis, false sensations and epilep- 
tic fits, are common symptoms of tapeworm infection. The 
degree to which each of these symptoms is felt varies remarkably 
in different individuals. The nervous symptoms are all due to 
intoxicating substances liberated by the worms. Sometimes 
a partial immunity to the toxic effects of worms is acquired by 
infected people, and in such cases the worms may be present 
unnoticed for years. 

The damage done by bladderworm stages of tapeworms is 
often more serious, especially in the case of hydatids, the large 
multiple bladderworms of Echinococcus granulosus. The bladder- 
worms which occur in man most commonly develop in the lung 


or liver, but may attack other parts of the body such as the 
muscles, eye and even the brain. They do injury both by me- 
chanical interference with the organs and tissues, and by the 
accumulation of poisonous waste products which may be ac- 
cidentally liberated. Only by surgery can such bladderworms 
be removed, and surgery is often impossible on account of the 
numbers and positions of the bladders. 

Treatment. — Preparatory to treatment for adult tapeworm in- 
fections the patient is put on a light diet and his bowels cleared out 
so that the parasite may meet with no obstruction in its passage 
through the intestine. The drugs which have been found most 
useful in expelling tapeworms are male fern, pelletririne and 
thymol. These drugs are dangerous if not taken properly, and 
none should be taken without the supervision of a physician. 
Thymol, for instance, while ordinarily quite harmless since it is 
not absorbed by the intestine, is soluble in alcohol and certain other 
substances and may cause death if taken along with these things. 
Oil of chenopodium, which has recently come into great favor 
for expelling hookworms and is even more efficient for certain 
other nematodes, has been found valuable for expelling dwarf 
tapeworms, Hymenolepis nana, and would probably be equally 
effective for other species. 

After the drug is administered a purgative is given which tends 
to drive the parasite out. The latter should be passed into a 
vessel of warm water, since sudden contact with cold stimulates 
the nervous system of the worm and causes it to contract sud- 
denly, thus often breaking it before it has been completely ex- 
pelled. A careful search for the head should be made, and if 
not found the treatment should be repeated in the course of a 
week or ten days. 

Prevention. — Prevention varies, of course, with the species of 
tapeworm and its intermediate host, but since infection with all 
the common human species, with the exception of the species 
of Hymenolepis, occurs from eating raw or imperfectly cooked 
meat of some kind in which the bladderworms have devel- 
oped, the exclusive use of thoroughly cooked meat is the best 
preventive measure. Experiments show that pork bladder- 
worms are killed when heated to 127° F. and beef bladderworms 
to 120° or even less, but the difficulty of heating the center of a 
large piece of meat even to this point is shown by the fact that 



in an experiment to test the penetration of heat, a ham cooked 
by boiUng for two hours had reached a temperature of only 
115° in the center. When roasted, pork should always be cut 
into pieces weighing no more than three or four pounds to insure 
thorough penetration of heat. Beef which has lost its red or 
" rare " color is quite safe. 

Since bladderworms are unable to survive the death of their 
host for more than a limited time, they are eventually destroyed 
by ordinary cold storage — within three weeks in the case of the 
beef bladderworm, Cysticercus hovis, but not always so soon in 
the case of the pork bladderworm, C. cellulosce. According to 
Dr. Ransom temperatures of about 15° F. kill beef bladder- 
worms within five days. Thorough curing or salting of meat is 
also destructive to the parasites. 

Infected persons should be careful not to contaminate the 
food or water of domestic animals with their faeces, bearing in 

Fig. 87. Heads of some adult tapeworms found in man, drawn to scale; A, 
beef tapeworm, Tcenia saginata; B, pork tapeworm, T. solium; C, fish tapeworm, 
Dibothriocephalus latus; D, heart-headed tapeworm, Dibothriocephalus cordatus; 
E, African tapeworm, T. africana; F, double-pored dog tapeworm, Dipylidium 
caninum; G, dwarf tapeworm, Hymenolepis nana; H, rat tapeworm, Hymenolepis 
diminuta. X 10. 

mind the various ways in which the eggs may be disseminated 
— by streams, rain, flies, etc. 

The eggs of the dwarf tapeworm, Hymenolepis nana, are 
thought to be able to develop through the bladderworm stage 
to the adult in a single host, and should therefore be guarded 
against by different measures (see p. 243). The larvae of other 
species of Hymenolepis develop in insect larvae such as mealworms, 
and are therefore subject to still different means of prevention. 

The tapeworms of man belong to two quite distinct families, 
the Taeniidae, in which the scolex is rounded and furnished with 
four cup-shaped suckers (Fig. 87, A, B, E, F, G and H), and the 



Dibothriocephalidse, in which the head is flat and possesses two 
sUthke suckers (Fig. 87C and D). The latter family also differs 
from the Taeniidse in having eggs with lids like those of the 
flukes (Fig. 88 A), and without developed embryos when passed 
in the faeces. 


Family Taeniidae 

Beef Tapeworm. — The commonest human tapeworm in most 
parts of the world is the beef tapeworm, Tcenia saginata. 
adult of this species as it occurs in the 
human small intestine consists of over 
1000 proglottids, and grows to a length of 
15 or 20 feet; cases have been reported 
of specimens of this tapeworm which 
measured 35 to 40 feet, though in some 
of these cases there were probably several 
tapeworms infesting a single person. 
When two or more worms are expelled 
in pieces it would naturally be easy to 
measure them as parts of a single one. 

The scolex of the beef tapeworm (Fig. 
82 A) is hardly larger than the head of a 
pin. It possesses four small suckers for 
adhering to the wall of the intestine, but 
there is no crown of hooks. The suckers 
are apparently quite sufficient for main- 
taining a hold, if one should judge from 
the difficulty experienced in dislodging the 
worm from the intestine. 

The proglottids gradually increase in 
size as they get farther from the scolex (Fig. 81), and the organs 
contained in them develop slowly. The general form of a sexu- 
ally mature proglottid and the appearance and arrangements of 
the organs are shown in Fig. 83. Shortly after sexual maturity has 
been reached and the sperms for fertilizing the eggs have been 
received, the uterus begins to grow and develop lateral branches 
to accommodate the rapidly forming eggs. When fully developed 
the gravid proglottid enlarges, becoming three or four times as 
long as when sexually mature, and resembles a pumpkin seed 
in shape. The greatly developed uterus, distended with eggs, 

Fig. 88. Gravid segment 
of Tcenia saginata. X 4. 
(After Stiles.) 


occupies practically the whole segment, while nearly all the other 
organs degenerate (Fig. 88). 

A man infested by a beef tapeworm expels several hundred 
proglottids a month, each one gorged with many thousands of 
eggs. Fortunately the majority of these never get an opportunity 
to develop further but it is easy to see how some of the eggs may 
reach their intermediate hosts, cattle, if the people who harbor 
the worms are at all careless. Disseminated by rain water, 
washed by streams into drinking troughs, carried about on the 
feet of flies, adhering to the heel of a boot, and in many other 
ways the eggs passed with the faeces may be transferred to the 
grass or water eaten by cattle. In India, where this tapeworm 
is common, cattle are said to devour human excrement if they 
have access to it. 

When eaten by cattle or other ungulates, as the pronghorn 
antelope, giraffe and llamas, the six-hooked embryos (Fig. 85) 
escape from the eggs and migrate into the muscles of the new 
host, attacking especially the muscles of mastication. Here in the 
course of from three to six weeks they grow into bladderworms, 
Cysticercus hovis, about one-third of an inch in length. They are 
grayish white in color with a little yellow spot where the head is 
invaginated. The fact that the cysts lack any marked contrast 
to the muscle tissue, and if not very numerous may be obscured 
by it, causes them to be overlooked frequently. If present they 
can usually be found most readily in the muscles of mastication 
or in the heart; these are the portions of the carcass regularly 
examined in meat inspection. Beef which contains bladder- 
worms is said to be " measly." 

Infection of man results, of course, from eating measly beef 
which is raw or only partially cooked. In Abyssinia the Moham- 
medans, who are forbidden by rehgious law to eat raw meat, are 
practically free from tapeworm infection, whereas practically 
all the non-Mohammedans are infected. The ripe proglottids 
begin to appear in the faeces, several at a time, in the course of 
two or three months after infection, and may continue to be 
developed for years. 

Pork Tapeworm. — Common in some parts of the world, but 
very rare in the United States, is the species Tcenia solium, 
which passes its bladderworm stage in hogs. Wherever raw or 
imperfectly cooked pork is eaten, infection with this tapeworm is 



likely to occur. The infrequence of these tapeworms in the 
Philippines where the bladderworms are very common in hogs 
is worthy of note. 

The adult Tcenia solium differs from the beef tapeworm chiefly 
in the form of the scolex, which in addition to four suckers is 
armed with a double row of hooks, arranged on a conical pro- 
jection or " rostellum " at its apex (Fig. 82B). The worms are 
usually of less length than beef tapeworms, seldom exceeding 
from six to ten feet; they consist of about 800 or 900 segments. 
The ripe proglottids (Fig. 84B) can in most cases be distinguished 
from those of the beef tapeworm by their ufiually smaller size 
and fewer branches of the uterus (compare Figs. 84A and B). 

The eggs, passed in the ripe proglottids with the faeces, develop 
into bladderworms when eaten by hogs or cer- 
tain other animals. The usual filthy way in 
which hogs are housed and fed gives ample 
opportunity for infection if the infested people 
are at all careless in their personal habits, or 
if privies are built so that they leak and the 
hogs have access to the surrounding ground or 
outflowing streams. Young pigs are especially 
hkely to become '' measly " from eating tape- 
worm eggs. 

As soon as the eggs reach the intestine 
the six-hooked embryos are liberated from of measly pork. (After 
the enclosing capsule and make their way 
through the wall of the intestine, to be carried by bloodvessels 
to the place where they are to develop. They may develop 
in almost any or all of the muscles or organs of the hog's body, 
but they especially favor the tongue, neck and shoulder muscles, 
and, next in order, certain muscles of the hams. Sometimes 
the bladderworms, technically known as Cysticercus cellulosce, be- 
come so numerous as to occupy over one-half of the total volume 
of a piece of flesh examined, i.e., several thousand to a pound. 
They appear as small elliptical bladders from 6 to 18 mm. (one- 
fourth to three-fourths of an inch) in length (Fig. 89). They 
have a whitish spot at about the middle of the length, in the center 
of which is the opening where the head is invaginated. 

Unlike the beef tapeworm, Tcenia solium can pass its bladder- 
worm stage in a number of animals, namely hogs, man and dogs. 

Fig. 89. Fragment 


They have been reported in a considerable number of other 
animals also but the cases are very doubtful. The fact that the 
larval stage can develop in man makes the species particularly 
dangerous on account of possibility of self-infection, either by 
contaminated hands or by a reversal of the peristaltic movements 
of the intestine which throws the ripe proglottids of the worm back 
into the stomach where the embryos in the eggs are liberated by 
the gastric juices. This is discussed further on p. 251. 

The Dwarf Tapeworms. — The dwarf tapeworm, Hymenolepis 
nana (Fig. 90A), is the smallest tapeworm found in man, but 

it often occurs in such numbers as to 
cause much irritation in the intestine. 
It is a common parasite in Italy, and 
occurs throughout the warm parts of 
Europe, Asia, Africa and America. It 
is probably much more common in the 
United States than is generally sup- 
posed, since it can easily be overlooked 
unless the faeces are microscopically 
examined for eggs. It is probably a 
common parasite of rats and mice as 
well as of man, though the rodent par- 
FiG. 90. A, dwarf tapeworm, ^site is believed by some parasitolo- 
Hymenoiepis nana, X 7 (after gists to be a distinct species,i?.m2^nna. 
Wter kfi^m)"' "' """"' "" '"^ Utiles considers the rodent parasite a 

sub-species, H. nana fraterna. 
The adult worm, which consists of from 100 to 200 proglottids, 
is usually little over an inch in length and less than one mm. (-^ 
of an inch) in width. The scolex (Fig. 87G) has four tiny suckers 
and a crown of little hooks. The ripe proglottids (Fig. 84J) 
differ from those of the large tapeworms in being much wider 
than long, with the enlarged uterus in the form of a solid mass, 
partially divided into compartments instead of being branched. 
As regards life history, the dwarf tapeworm is commonly be- 
lieved to pass both its larval and adult stages in a single host, 
contrary to what occurs, so far as is known, in any other tape- 
worm. The eggs (Fig. 90B), eaten by a rat or man, liberate six- 
hooked embryos in the small intestine, where they enter the villi 
and transform into cysticercoid bladderworms (Fig. 86B), which 
in turn fall into the cavity of the intestine, attach themselves 



by the armed head, and become adult. It is said that eggs of 
this parasite can be found in the faeces within a month after an 
egg of the preceding generation has been swallowed. Self- 
infection with these eggs rarely occurs, since the eggs will not 
develop unless acted upon by the gastric juices. There is still 
room for doubt as to whether an insect is not commonly involved 
as an intermediate host as in other species of Hymenolepis; in 
fact, several investigators have found cysticercoids in rat fleas 
which they ascribed to this 
species. Ransom thinks 
there is room for doubt 
as to whether the larvae of 
Hymenolepis found in the 
intestinal villi of rats and 
mice break out and become 
mature in the lumen. 

The common presence 
of this parasite or a variety 
of it in rats and mice indi- 
cates that infection in man 
may occur from accident- 
ally swallowing the '^ pills " 
of these animals infected 
with the eggs or ripe pro- 
glottids of the worm. 
Since a single mouse " pill " 
might contain hundreds 
of eggs, each of which 
could develop into an 
adult in another rat or 
mouse, or in man, it is 
not difficult to understand the great numbers of this worm which 
are often found in a single intestine. 

The unique life history of this species, if true, makes it subject 
to entirely different preventive measures from those used against 
most other tapeworms. Since infection results not from eating 
bladderworm-infected meat, but probably from swallowing egg- 
infected faeces, especially the " pills " of mice and rats, and pos- 
sibly also from swallowing infected insects which are acting as 
intermediate hosts, prevention consists in the elimination of 

Fig. 91. 
nuta, from 

Rat tapeworm, Hymenolepis dimi- 
house mouse in Oregon. Natural 



rats and mice from the household and in keeping food out of 
their reach, and in guarding against the accidental ingestion of 
such possible intermediate hosts as fleas. 

A closely allied species, H. diminuta (Fig. 91), occurs rarely 
in man. It closely resembles the dwarf tapeworm but is of 
larger size (four to 24 inches in length) and has no hooks on the 
scolex (Fig. 87H). The eggs develop in the larvae or adults of 
the mealworm, Asopia farinalis, and in other insects, forming 
cysticercoids. When these are eaten by rats, mice or man they 
transform into adults. In an experiment on man the eggs of 
the adult worm were found in the faeces 15 days after the eating 
of an infected mealworm. The larvae of a number of species 
of fleas also become infected when they ingest the eggs. It is 
evident that prevention consists in guarding carefully against 
the accidental swallowing of mealworms with cereals or other 
foods, and in cautioning children against putting beetles or 
other insects into their mouths. Although 
the worm is rare in man it is common in 
rats and mice in many parts of the world, 
and occurs in nearly all parts of the United 

Other Tapeworms (Taeniidae). — A con- 
siderable number of other tapeworms of this 
family have been found in man, acciden- 
tally occurring in him, or having a very 
hmited distribution. 

Of those with limited distribution should 
be mentioned two species of Davainea. One, 
D. madagascariensis (Fig. 92), is a small 
tapeworm reaching a length of ten or twelve 
inches. It is found, chiefly in children, in many tropical countries, 
especially. in islands and seaports and on ships. The suggestion has 
been offered that the intermediate host, so far unknown, may be 
the ubiquitous sea-going cockroach. This tapeworm is interesting 
in that there is not only a crown of hooks on the head, but there 
are hooks on the suckers also. The other species of Davainea 
is D. formosana, recently described by Akashi from children in 
Formosa and Tokyo. It differs from the preceding species in 
its larger size, lack of hooks on the suckers, larger size of egg 
masses in the ripe proglottids and in other minor details. 

Fig, 92. Davainea mad- 
a^a^cariensis; A, head and 
neck, B, gravid proglottids. 
X 8. (A, after Blanchard, 
B, after Daniels.) 


The African tapeworm, Tcenia africana, is a species found in 
German East Africa. It is about four feet in length with no 
hooks on the scolex (Fig. 87E) and with an unusual fanUke ar- 
rangement of the uterus in the ripe proglottids (Fig. 84G). Von 
Linstow, who described the worm, suggests that the zebu may 
be the intermediate host since its flesh is eaten raw by the 

A medium-sized tapeworm, TcBuia philippina, reaching a 
length of about three feet, has been found among prisoners at 
Manila. It very much resembles the African tapeworm but has 
smaller proglottids. Other species have been described from 
various parts of the world, especially southern Asiatic Russia, 
but they are of such rare occurrence, some having been found 
only once, that they need no description here. 

Two specimens of the species Taenia confusa (Fig. 84D,) were 
found by Ward in Nebraska many years ago, and recently another 
specimen was reported by Chandler from Texas. It probably has 
been endemic in the central states in the meantime, but confused 
with other species. It is possibly identical with T. hremneri of 

Of the accidental tapeworms of man there should be mentioned 
especially the dog tapeworm, Dipylidium caninum. This species 
is abundant in dogs, and sometimes cats, in all parts of the 
world. It is a species about a foot in length, with three or four 
rows of hooks on the rostellum (Fig. 87F), and a double set of 
reproductive organs in each proglottid (Fig. 84C). The larva, 
a cysticercoid, occurs in lice and fleas. It is stated that the eggs 
of this tapeworm cannot be sucked up by the dog-infesting fleas, 
but that they are readily swallowed by flea larvae. The eggs hatch 
in the intestine of the flea larvae, the embryos pass to the body 
cavity and the cysticercoids remain through the metamorphosis 
of the larvae to the adult fleas. Children who play with dogs 
are occasionally infested by this worm, probably by accidentally 
swallowing lice or fleas or by crushing them and then putting in- 
fected fingers into the mouth. 

Family Dibothriocephalidae 

The tapeworms of this family, as remarked before, are charac- 
terized by a flattened head with two slitlike suckers (Fig. 87C 
and D). The larvae, which usually develop in fishes, are of the 



plerocercoid type, i.e., they have long wormlike bodies with an 
invaginated head at one end (Fig. 86C). 

Fish Tapeworm. The common fish tapeworm of man, 
Diphyllobothrium latus, is an important species in the districts 
in which it occurs. It is found in all countries where fresh- water 
fish is extensively eaten, and especially in countries where it is 
commonly eaten raw. In the Baltic countries, Switzerland, 
Russia, Japan, and about the Central African lakes this parasite 
is particularly common. Relatively few cases have been re- 
ported in the United States, though the larvae are said to be found 
frequently in fish from the Great Lakes. 

The fish tapeworm is a large species and commonly reaches a 
length of from six to 30 feet, or even more, 
with from 2000 to 4200 short, broad pro- 
glottids, only the terminal ones of which 
are as long as broad. The scolex (Fig. 87C) 
is almond-shaped. Unlike the tapeworms 
of the family Tseniidse, the genital openings 
are near the middle of the under surface of 
the proglottids, instead of at one side. In 
the ripe proglottids (Fig. 84E) the uterus 
is in the form of a rosette near the center 
of the segment. The proglottids do not 
usually retain the eggs until they break off 
from the chain, but void them, as do flukes. 

Fig. 93. An egg of fish through the genital pore. The empty pro- 
tapeworm, Z). /a^ws, — note lii-j 1 1 jj.-i.j ui 
segmented condition and glottids, shrunken and twisted, are broken 

operculum; 5, ciliated em- off in short chains from time to time. 
300? UfTe^Looss.)^ ''''* The eggs (Fig. 93 A), which are large and 
brown with a lid at one end as in fluke 
eggs, contain six-hooked embryos which are furnished with a 
covering of cilia (Fig. 93B). The eggs hatch in water in from eight 
to fifteen days, and the embryos swim about by means of their 
cilia, though they often slip out of their ciliated envelope and 
creep on the bottom. The embryos have recently been shown 
by Rosen and by Janicki to develop in certain species of Cyclops 
and Diaptomus, copepod crustaceans, into larvsG which are 
called procercoids. In 12 to 15 days these larvae are about 0.4 
mm. (eo of an inch) in length, sausage shaped, with a spherical 
caudal appendage carrying the embryonic hooks. This append- 


age shrinks and a depression appears at the opposite end; a 
large portion of the body is occupied by a pyriform central mass. 
The full development is reached in two or three weeks, the larvae 
being then about 0.5 mm. long. Small trout fed on the infected 
cope pods were successfully infected. The passage through the 
intestine and body cavity of the fish is slow; it requires about six 
days for the larvae to reach the liver in young fish, and in older 
fish it may take from two to four weeks. In the fish the worms 
develop into plerocercoid larvae in the muscles. Pike, perch and 
other carnivorous fish are most frequently infected. 

When eaten by a susceptible host in raw or imperfectly cooked 
fish, the larva, except the head, is digested, and the head, at- 
taching itself to the wall of the small intestine, begins to grow 
into an adult worm at the rate of about 31 to 32 proglottids a 
day. The mature eggs begin to appear in the faeces within a 

The fish tapeworm is especially active in the production of 
toxins which cause intense anemia. Its head has been found 
to produce oleic acid, a substance which has blood-destroying 
properties. Often the nervous symptoms produced by this 
species are also very marked. 

Two other species of Dibothriocephalidae have been found in 
man. One of these, Diphyllobothrium cordatus (Figs. 84G and 
87D), occurs in dogs, seals and other fish-eating animals in Green- 
land. It only accidentally establishes itself in man. Diplo- 
gonoporus grandis is a very large species, found in Japan, in 
which there is a double set of reproductive organs. The genital 
openings are arranged in two longitudinal grooves on the ventral 
side of the worm (Fig. 84F). This species is rare in man. 

Larval Tapeworms in Man 

There are several species of tapeworms which inhabit the human 
body in the larval or bladderworm stage. Three types are found 
in man. Most important are the huge multiple cysts or " hyda- 
tids " of Echinococcus granulosus ^ a small tapeworm of dogs. 
Second, there are the bladderworms of the common pork tape- 
worm, Tcenia solium, which often occur in large numbers, and 
may be of very serious nature if located in important organs. 
And, finally, there are two species of Sparganum. This is not 


a true genus but is a collective group of larval tapeworms of the 
plerocercoid type which cannot be definitely classified because 
the adult is unknown. 

Echinococcus hydatids. — In some parts of the world infection 
with the hydatids or larvae of Echinococcus is very common, 
especially in children. In Iceland, where there is very close asso- 
ciation between the human and the canine population, two or 
three per cent of the inhabitants are afflicted, and in certain dis- 
tricts as high as ten per cent. In Australia, also, this tapeworm 
is common in dogs and its larvae occur in a considerable pro- 
portion of human beings as well as in stock. In the United 
States, especially in the southeastern states, it is fairly common. 
The adult of Echinococcus (Fig. 94) is a minute tapeworm 
found in dogs and sometimes in other carnivorous animals. It 
measures only from one-tenth to one-fifth of an inch in length. 
The mature worm consists of a tiny scolex with four suckers and 
a double crown of hooks, followed by an unsegmented neck and 
three gradually larger proglottids, the ultimate 
one of which is larger than all the rest of the 
worm and contains about 500 eggs in the uterus. 
Echinococcus may occur in hundreds or even 
thousands in the intestine of dogs, though it 
often escapes notice on account of its small size. 
The eggs of the worm, dropped in pastures 
with the faeces of infected dogs, ordinarily de- 
velop in sheep, cattle or other herbivorous 
animals. Human infection usually results from 
too intimate association with dogs, and children 
especially are liable to infection by allowing dogs 
Fig 94 Ech' _ ^^ " ^^^^ " them or Hck their faces with a tongue 
coccus granulosus which, in view of the unclean habits of dogs, 
(After^Leuck^t^)^ ^^^ ^® ^^ efficient means of transmission for 
the tapeworm eggs. 
The hydatids develop in many different organs of the body. 
The liver is the favorite site, after which, in order of frequency, 
come the lungs, kidneys, spleen, intestinal walls, membranes 
lining the body cavity, heart, brain and various muscles. Some- 
times a single host is invaded by the hydatids in several different 
The development of the embryos is very slow indeed. In a 


month after reaching their destination in the hver or other organs 
they are in the form of Httle globular bodies, enclosed by a cap- 
sule produced at the expense of the host. A cyst measures about 
one mm. (2^5 of an inch) in diameter. By the end of the fifth 

Fig. 95. Diagram of portion of small Echinococcus cyst showing daughter cyst 
(d.c), brood capsules (br. cap.) and invaginated heads (h.). X about 5. 

month it has grown to the size of a walnut. The membrane of 
the bladderworm itself is very delicate, but the capsule formed 
by the host is thick and tough. The enclosed fluid is transparent 
and nearly colorless, and is composed of various materials which 
have permeated in from the blood and tis- 
sues of the host, and of the waste products 
produced by the growth of the parasite. 

When the hydatid has reached this stage 
in its development (Fig. 95) there grow 
into its cavity from the inner surface little 
vesicles or brood capsules, on the inner sur- 
face of which in turn there grow a number of 
little heads or scoleces. Each of the heads 
has the power ultimately to grow into an 
adult worm. As there may be a dozen or 
more of the scol ex-bearing brood capsules in cyst from liver of steTr.^f 
a single hydatid, and from six to 30 heads nat.size. (After Ostertag 
in a single vesicle, the number of heads of ^°™ 
scoleces produces may be enormous. Sometimes there may be 
still further multiplication by the development of secondary cysts 
either inside or outside of the original hydatid which may develop 
a whole series of scolex-bearing vesicles of their own. 

Sometimes instead of forming the usual large vesicles and 
secondary vesicles, the growth results in the formation of a great 
mass of small separate vesicles (Fig. 96), varying in size from a 



pinhead to a pea, with few and scattered heads. These masses 
of vesicles, known as '' multilocular " cysts, may be six inches 
or more in diameter; they are most frequently found in the liver. 
Unless surgically removed they usually prove fatal sooner or later. 
The fact that the " multilocular " cysts are not found in Ice- 
land or Australia where the ordinary cysts are so common, and 
that they occur to the almost total exclusion of the ordinary 
kinds in some countries, especially in parts of Germany, suggests 
that they may belong to a different species indistinguishable 
from E. granulosus in the adult state. 

The great size to which hydatids may grow makes them danger- 
ous on account of the mere mechanical damage they may do, 
especially if they occur in such organs as the heart, brain, kid- 
neys or liver. The liver of an ox containing hydatids has been 

known to reach ten times its normal 
weight, and to be of such large size 
as to cause much mechanical injury 
to neighboring organs. But more 
dangerous than the mechanical injury 
is the possibility that the vesicles, 
hemmed in by restraining tissues, may 
burst and liberate into the tissues the 
poison-bearing liquid which fills them. 
Hydatids may grow persistently for 
many years. There is one case on 
record where a swelling had gradually 
developed during 43 years over a large 
Fig. 97. Echinococcus cyst portion of the face of a woman, and 
in liver of man. (After Huber ^^s as large as a child's head. When 

from Stiles.) , , , . , , . 

removed by an operation, this was 
found to be a hydatid. Ordinarily growth does not increase 
beyond the size of a baseball. The only treatment is a surgical 

The conditions which exist in places where hydatid disease in 
man is common gives us an idea of what to avoid in order to pre- 
vent infection. In Iceland from 30 to 100 per cent of the dogs in 
different regions are said to be parasitized by Echinococcus. A 
large proportion of the sheep and many cattle are infested with 
the hydatids. The dogs are fed on the uncooked entrails and 
waste meat of slaughtered animals, and the dogs in turn are 


allowed to run at will over the pastures, dropping the egg-laden 
proglottids with the faeces in places where the water or food of 
the stock may be infected. Dogs are allowed the free run of 
the houses, are given unbounded liberty in playing with children, 
and not infrequently eat from the same dish as their human 
companions. The resulting prevalence of Echinococcus in both 
dogs, stock and man is hardly to be wondered at. 

The precautions which should be taken to prevent the spread 
and to bring about the control of this disease may be summar- 
ized as follows: (1) avoidance of too great familiarity with 
dogs, (2) exclusion of dogs from shores of lakes or reservoirs from 
which drinking water is taken, (3) extreme cleanliness in handling 
of food, (4) prevention of dogs from eating the entrails or meat 
scraps of animals which may be infected with hydatids. 

Cysticercus of Taenia solium, — The fact that the bladder- 
worms of the pork tapeworm, Tcenia solium, sometimes occur in 
man has already been mentioned. Since self-infection with the 
eggs of the worm is a dangerous possibility, the presence of a 
pork tapeworm in the intestine is to be looked upon much more 
seriously than infection with other tapeworms. 

The bladderworms, technically named Cysticercus celluloses 
(Fig. 86 A), develop from the six-hooked embryos which are 
freed from t»he enclosing egg-shell by the gastric juices. The 
embryos bore through the intestinal wall and migrate to various 
organs and tissues to develop. 

The effect of Cysticercus infection depends entirely upon the 
number present and upon their location in the body. A few of 
them in the muscles or in the connective tissue under the skin are 
quite harmless. In the eye, heart, spinal cord, brain or other 
delicate organs their presence may be very serious, the symptoms 
being due chiefly to mechanical injury. Infection of the brain 
is usually accompanied by epileptic fits, convulsions and other 
nervous disorders. There is no treatment except a surgical 
operation, and this is often obviously impossible, both on account 
of the number and position of the parasites. Moreover, in a 
great many cases a correct diagnosis of this infection is made only 
in a post-mortem examination. 

Sparganum. — The group name Sparganum has been given to 
plerocercoid larvae of tapeworms of the family Dibothriocepha- 
lidae, of which the adult form is unknown and the true genus there- 
fore indeterminable. 



The most common type of such tapeworm larvae is Sparganum 
mansoni (Fig. 98), an elastic worm three to 14 inches in length. 
It is not segmented, but appears so since it is 
transversely wrinkled; there is an invaginated 
scolex at the broader end. These parasites are 
found coiled in the connective tissue of man 
and other animals, often causing tumors. The 
majority of human cases have occurred in Japan, 
but cases are recorded from many other parts 
of the world also, including Texas. 

Recently it has been shown that this worm 
is the larva of Diphyllobothrium mansoni of dogs 
and cats, which has a life history similar to that 
of D. latus. The first larva, or procercoid, 
develops in Cyclops leuckarti, but not in related 
copepods. The plerocercoid or sparganum stage 
develops in a large number of different animals, 
including man, but probably the normal second 
intermediate hosts are cold-blooded vertebrates, 
especially frogs and snakes, in which they are 
very common. When these animals are eaten 
by dogs or cats the parasite completes its de- 
velopment to the adult form. 

Another type of Sparganum, which has been 
termed S. proUferum, was discovered by a 
Japanese investigator, Ijima, in a Japanese 
woman in 1904. The skin on a large part of 
her body was much swollen and presented 
numerous hard pimples. Examination showed 
thousands of worms which were identified as 
larval tapeworms of the Sparganum type, 
imbedded in little oval capsules varying in size from less 
than one mm. (-^^ of an inch) in length to six or eight 
mm. (i of an inch). Young slender worms not yet encysted were 
also found. In 1907 a similar case occurred in a fisherman in 
Florida, and the parasites were believed by Dr. Stiles to be either 
identical with or closely related to the Japanese worm. Two 

Fig. 98. Spar- 
ganum mansoni; 
nat. size. (After 
Ijima and Mur- 



other Japanese cases, discovered in 1907 and 1911 respectively, 
have also been reported. In one of these the worms, most but 
not all of them in capsules, were found in countless numbers not 
only in the subcutaneous tissue but also in the muscles and through- 
out most of the internal organs, including even the brain. 

The worms of this species (Fig. 99) are in all cases white, flat- 
tened organisms of very variable shape and size. They usually 
vary from three mm. to 12 mm. (| to ^ an inch) in length, and 
from 0.3 mm. to 2.5 mm. (go to lo of an inch) in width, but in 
one Japanese case they were uniformly larger, reaching a length 
of three inches. Their peculiarly irregular shape is due to the 
unique method of proliferation by the growth of buds or super- 
numerary heads. These apparently 
become detached, leave the cyst, and 
become encapsuled themselves after 
migrating in the subcutaneous tissue. 
This explains the increasing num- 
bers of acne-like spots or nodules 
containing worms, which were re- 
ported by the patients. 

Attempts made by Ijima to pro- 
duce adult worms by feeding the 
larvae to various domestic animals 
failed, and nothing is known of the 
life history or mode of infection be- 
yond a suspicion that the eating of 
raw fish is responsible for it. Dr. 

^ , ,. 1 J.1 T-n "J Fig. 99. Sparganum proliferum, 

Gates, who discovered the l^lorida from man in Florida. Much en- 
case, reported that there was probably larged. (After stiles.) 
a similar case in Florida a few years 

before, the patient having moved to California where he died 
*' eaten up with worms." 

The rare occurrence of this peculiar and serious parasitic disease 
is evidence that the mode of infection is unusual. The suspicion 
that it results from eating raw fish is sufficient reason for discrim- 
ination against c^his kind of food even in places where this or other 
human para sites which come from raw fish are not positively 
known to occur. 


History. — For many years it was customary in the United 
States to look upon the shiftless people to be found in our South 
as the product of wanton laziness and an inborn lack of ambition. 
For decades the more fortunate Northerners considered the 
" poor whites " of the South a good-for-nothing, irresponsible 
people, worthy only of scorn and of the sordid poverty and ig- 
norance which they brought upon themselves as the fruits of 
their own shiftlessness. When it became known, largely as the 
result of investigations by Dr. C. W. Stiles, of the U. S. Public 
Health Service, that these hopelessly incapable and pitifully 
emaciated and stunted people were the victims, not of their own 
unwillingness to work or learn, but of the attacks of intestinal 
worms which sapped their vitality, poisoned their systems, and 
stunted both their mental and physical growth, and that over 
two million people in our own southern states were the victims of 
these parasites, the " poor whites " and " lazy niggers " of the 
South became objects of pity and help rather than of scorn. 

The hookworm, which is the cause of this deplorable condition, 
is by no means a newly discovered parasite. A close cousin of 
the American hookworm was discovered in Italy over 75 years 
ago, and has subsequently been found to be prevalent in parts of 
every warm country in the world, in some places infesting nearly 
or quite 100 per cent of the inhabitants. It would probably be 
well within the truth to say that over half a billion people in the 
world are infected with hookworms. The disease caused by 
hookworm, which has recently come to be used as a symbolism 
for laziness, was known for ages before the cause of it was dis- 
covered, in fact it was probably one of the ailments most familiar 
to the ancient Egyptians, and descriptions of symptoms probably 
representing hookworm disease appear in the medical papyrus 
of 3500 years ago. The disease has gone by many names: 
malcoeur or mal d'estomac in the West Indies, tuntun in Colombia, 



opilag9o in Brazil, tunnel disease and miner's itch in Europe, 
and chlorosis in Egypt. 

The American hookworm, Necator americanus, was probably 
introduced into America from Africa by slaves. In many parts 
of the latter continent as well as in parts of Asia, especially 
Ceylon, this hookworm is very common. It occurs in the 
gorilla as well as in man. In the United States it is occasionally 
found in all but the most northern states, but is a great menace 
only in the southern ones — North and South Carolina, Georgia, 
Florida, Alabama, Mississippi, Louisiana and Texas. It also 
presents a serious problem in Cuba, Porto Rico and Brazil. In 
most other warm parts of the world a closely allied species, the 
Old World hookworm, Ancylostoma duodenale, is more prev- 
alent. It is impossible now to know what was the origin or 
natural distribution of either species, since both worms have 
been introduced by infected travelers into every quarter of the 
globe. In Europe Ancylostoma duodenale is far the more com- 
mon. It first attracted attention there as the cause of " tunnel 
disease " at the time of the building of the St. Gothard tunnel. 
The infected laborers, dispersing after the completion of the 
tunnel, spread the infection to all parts of Europe, and serious 
epidemics broke out in the coal-mining districts of Hungary, 
Germany and Belgium. 

The Parasites. — The two species of human hookworms are 
similar in structure; they agree in all important details of life 
history; and both produce the same symptoms, require the 
same treatment, and can be prevented in the same ways. They 
are round worms, belonging to the great group of nematodes, 
which as adults live in the small intestine of their hosts and suck 
blood. An allied species, A. ceylanicum, found in civet cats and 
dogs in southern Asia occasionally occurs in man. The American 
hookworm, Necator americanus (Fig. 100), is smaller than the 
Old World species, Ancylostoma duodenale, the measurements 
being about eight mm. (one-third of an inch) and ten mm. (two- 
fifths of an inch) respectively in the males, and ten mm. and 15 
mm. (three-fifths of an inch) respectively in the females. They 
are normally whitish in color but when gorged with blood they 
are reddish brown. The females, which are much more numerous 
than the males, have simple cylindrical bodies, largely occupied 
by the threadlike ovaries and egg-filled oviducts. In the Old 



World species the mouth (Fig. 101 A) is armed with a number of 
chitinous hooklike teeth, which in the American species are 
replaced by hard ridges or lips (Fig. lOlB). The male worms are 


Am. Hookworm 
not, size 

Qld World ttookwor/i* 

Fig. 100. American hookworm, Necator americanus, male {$) and female ( 9) ; 
b.c, buccal cavity; ph., pharynx; int., intestine; cerv. gl., cervical gland; t., 
testis; sp. d., sperm duct; b., bursa; ov., ovaries and oviducts; v., vulva or 
genital opening; a, anus. X 8. (Partly after Manson.) 

also cylindrical but instead of tapering at the tail end they possess 
an umbrella-like expansion known as a bursa, which is sup- 

FiG. 101. Buccal cavity and mouth of Old World hookworm (A), and American 
hookworm (J5), showing teeth in former and cutting ridges in latter. A, X 100; 
B, X 230. (After Looss.) 

ported by clawlike rays somewhat suggestive of the ribs of an 
umbrella (Fig. 102). The bursa is used for holding the female 
during copulation. It was the clawlike ribs of this '* umbrella '' 



which first suggested the name " hookworm " for the parasites, 
though the hookhke teeth in the mouth of the Old World species 
might just as readily have suggested the name. 

Fig. 102. Bursa of American hookworm. (After Stiles.) 


Fig. 103. Life history of hookworm; A, adults, female and male, in intestine; 
B, egg as passed in faeces; C, embryo hatching in ground, 24-48 hours later; D, 
fully developed larva, enclosed in sheath, ready to infect human being; E, larvae 
released from sheath, migrating in body of new host. 

Life History. — (Fig. 103.) The female worms produce an 
enormous number of eggs which are poured into the intestine of 


the host, usually in a continuous stream, but occasionally with 
intermissions, to be passed with the faeces. The thin-shelled 
eggs, which are about 60 /x by 35 ^ (4^ ^ by ^^^ of an inch) in size, 
and sHghtly larger in the American species, undergo the first 
stages of development while still in the intestinal canal, and by 
the time they are voided with the faeces they are segmented into 

from two to eight cells 

C£^) (Fig. 104). The segmented 

condition, together with 
the fact that they are clear 
and not yellow or brown 
from bile stain, distin- 
guishes the eggs from those 
of many other worms 
T, ,^, ^ ,, , . , found in the intestine. 

J^iG. 104. liiggs of hookworms in early stages -^,111 

of segmentation,— four-segmented type most Further development doeS 

common in faeces; A, Necator americanus; B, ^^^ ^^]^q ^I^^q ^^^^l ^^^ 

Ancylostoma duodenale. ^ 

faeces are exposed to air, 
when, if moisture is present and the temperature is moderately high 
(65° to 85° F.), the development continues and the embryo hatches 
in from 24 to 48 hours (Fig. 103C). Below 65° F. development is 
very slow, and above 85° F., although development is very rapid, 
the eggs and larvae are likely to die. The newly hatched worm is 
about 0.2 mm. (less than a hundredth of an inch) in length with a 
bottle-shaped oesophagus, a simple intestine, and practically no re- 
productive organs. The most favorable conditions for the devel- 
opment of the larvae, in addition to the temperatures mentioned, 
are a moderate degree of moisture, presence of air, plenty of food 
in the form of decomposing organic matter, and not too rapid 
putrefaction. According to Looss, the larvae will not develop 
well in faeces derived from a purely vegetable diet, a small propor- 
tion of animal matter being essential for food. Enough animal 
food for some development would always be provided by blood 
from intestinal hemorrhages. On the other hand a purely meat 
diet is unfavorable on account of the rapid putrefaction. If 
suitable conditions are present, the larva grows rapidly for four 
or j&ve days, shedding its skin at the end of the second day. In 
about five days, under ideal conditions, the skin begins to be- 
come detached again but is not shed. It is retained as a flexible 
protecting sheath for the larva, but does not hinder free motion 


(Fig. 103D). The larva has by this time grown to several times 
its original size, being over 5 mm. (sV of an inch) in length, and is 
now in the infective stage and ready to begin its parasitic life. 
No further food is taken but the parasite begins an active migra- 
tion in the neighboring soil or water. If even a trace of moisture 
is present in the soil the larvse are capable of traversing consider- 
able distances and may thus give rise to infection far from the 
place where the faeces were originally deposited. They are said 
to be able to travel through moist soil at a rate of probably not 
less than five feet per hour, which, if kept up constantly in a 
straight hne would mean a wandering of forty yards in twenty- 
four hours. While such continued travel in a straight line prob- 
ably would never occur, it is evident that a single infective stool 
would easily be able to infect the ground for several square yards. 
Complete drying up is fatal to both eggs and larvse in all stages. 

The larvae may remain just under the surface of moist soil or 
mud or in water for a long time, awaiting an opportunity to enter 
a human host. They have been kept alive in the laboratory 
in plain water at a temperature of about 60° F. for 18 months 
and unless attacked by predaceous insects or other animals 
would undoubtedly live fully as long under outdoor conditions. 
They are much more resistant to unfavorable conditions than 
are the eggs or newly hatched larvae. They can exist under de- 
privation of air for a long time and may survive burial in snow 
for at least six days. 

It was formerly thought that infection occurred by way of the 
mouth only, the larvae entering with impure food or water. It 
is now believed, however, that this means is not only not the 
usual one, but that direct infection by swallowing may never 
occur, since there is evidence to show that the parasites are un- 
able to resist the acid juices of the stomach before they have 
first passed through the blood and tissues of tKe body. It was 
discovered purely by accident that the hookworm larvae can 
readily penetrate the skin and bore through the tissues until 
they reach a vein. The feet of plantation laborers are often in 
a bad state of soreness and ulceration due to the boring of the 
larvae and to subsequent infection by bacteria. Walking on in- 
fected ground with bare feet is undoubtedly the mode of infection 
in the majority of cases. By the blood or lymph vessels the 
worms are carried eventually to the heart and thence to the lungs; 


from the lungs they pass by way of the trachea to the oesophagus, 
and thence to the stomach and intestine. Experiments show, 
however, that the larvae may reach the intestine by other routes, 
leaving the trachea and oesophagus out of the circle of migration, 
but in any case they follow a rather roundabout path in the 
bloodvessels. Probably in cases of infection by food or drink 
the worms bore through the mucous membranes of the mouth or 
oesophagus during the swallowing of the food and thus, even 
when eaten, reach their ultimate destination by an indirect route. 
The larvae shed their skins twice more after entering the human 
body, each time attaining more and more of the adult character- 
istics and growing in size at the expense of the blood and mucous 
membranes on which they feed. After the last moult the sexes 
are differentiated but the larvae are still less than a fourth their 
full size and require five or six weeks from the time of infection 
to become fully mature. The length of life of individual hook- 
worms in the intestine is variously estimated in months or years. 
The readiness with which reinfection usually occurs makes this a 
difficult point to determine. 

The Disease. — The disease to which hookworms give rise 
varies to a very great extent in different individuals, and is not 
always dependent upon the number of worms present. It was 
formerly supposed that the anemia and loss of vitality produced 
by hookworms was due solely to the loss of blood devoured by 
the parasites. In cases of severe infection, where perhaps several 
thousands of worms may be harbored by a single patient, the 
amount of blood devoured must be sufficient to account for a 
considerable degree of anemia. However, in cases of infection 
with relatively few worms the symptoms are sometimes fully as 
marked and cannot be explained on this basis. The injuries 
from hookworm infection result apparently from a number of 
causes which may be summed up as follows: (1) ulceration or 
infection of the skin from wounds made by the boring of the 
parasites, often giving rise to an extensive affection of the feet 
in the form of pimples or sores called *' ground itch,'' " water 
sores," etc., caused partly by entrance of bacteria into the wounds, 
and partly by the irritation produced by the boring of the worms; 
(2) loss of blood devoured by the parasites; (3) loss of blood from 
the bleeding of wounds into the intestines, sometimes very con- 
siderable, due to a secretion from the mouth of the worm which 


prevents the coagulation of blood; (4) the entrance of harmful 
bacteria and other microscopic organisms into the wounds made 
by the worms, resulting in the absorption of bacterial toxins and 
in the formation of dangerous lesions; (5) a thickening and de- 
generation of the mucous walls of 
the intestine; and (6) the secretion 
of poisonous substances or toxins 
from glands in the heads of the 
worms. These poisonous secre- 
tions, which have blood-destroying 
properties, probably account for 
more of the symptoms of hook- 
worm disease than does anything 
else, though apparently they have 
widely different effects on different 
individuals. Sometimes the pres- Fig. io5. American hookworm; 

. , « • J 1 1 section showing manner of attach- 

ence of eggs m the tseceS is the only ^ent to intestinal wall. (After 

indication of infection. Negroes as Ashford and igaravidez, from photo 

1 u f 1 4.-U-T4. ^y ^^- W- ^- Gray.) 

a class show tar less susceptibility 

to the poisons produced by hookworms than do the whites; this 
is especially well demonstrated in our southern states. The 
symptoms are more severe in summer than in winter, very 
probably due to the greater abundance of worms in the summer. 

Hookworm disease is almost always preceded by a case of 
ground itch, due, as remarked above, to irritation from the boring 
of the worms and to secondary infection with bacteria. The 
commonest symptom of the disease is anemia, usually accom- 
panied by some fever or dyspeptic trouble, though often in mild, 
cases there is no evident emaciation. The significant name " el 
palido " (the pale one) is applied to the hookworm victim on the 
coffee plantations of Porto Rico. In severe cases of long stand- 
ing the anemia and loss of vitality become extreme and so weaken 
the patient that he succumbs to the least unfavorable circum- 
stance; his unhappy career is usually ended by some slight illness 
which in normal health he could easily have resisted. In Porto 
Rico about 30 per cent of all deaths are attributed to hook- 

Both the mental and physical development become abnormal. 
A child of 12 or 14 years may have the degree of development 
which should belong to an average child of six or eight and a 


young man or woman of 20 may present the general development 
of a child of 12 or 14, though the face may appear either very 
childish or prematurely old. Girls who are affected from child- 
hood lack development of the breasts, but in general there is no 
marked loss of flesh. The face has a stupid bloated appearance, 
and the eyes have a hollow stare which is very characteristic. 
The bloating carried to the abdomen results in " pot-belly." 
The appetite, at first ravenous, diminishes with the progress of 
the disease, and frequently becomes perverted so that patients 
become dirt-eaters, i.e., have a mania for swallowing earth or 
mud, possibly a reaction involuntarily prompted by the irritation 
of the intestinal tract by the parasites. Over 25 per cent of the 
hookworm patients of one physician in our southern states con- 
fessed to '* dirt-eating." The diseased appetite, of course, only 
adds to the infection. The nervous symptoms, which are rather 
late in appearance, consist of dizziness, headache and profound 

The loss of efficiency from hookworm infection is startling, and 
the slow development of many countries may be largely attributed 
to the handicap placed upon the citizens by the hookworm. The 
effect of the disease can be appreciated from the following ex- 
amples: the managers of large coffee " haciendas " in Porto 
Rico state that hookworm reduces the average efficiency of the 
laborers from 35 to 50 per cent. On a cocoa plantation in 
Ecuador not over 33 per cent of the work which should have been 
obtained from 300 laborers was available, due to anemias of 
hookworm and chronic malaria. On a sugar plantation in 
British Guiana, after the laborers had been treated for hookworm 
on a large scale, the working power of the gangs increased 100 
per cent. Dr. McDonald of Queensland, Austraha, reports that 
hookworm " is sucking the hearts' blood of the whole com- 
munity." The loss of efficiency of the miners in a single Cali- 
fornia mine, due to hookworm, has been estimated at 20 per cent. 
Estimating only 50 per cent of the miners to be infected, the 
annual economic loss in this one mine would be $20,000 per year. 
The economic loss due to the infection of 2,000,000 or more people 
in the southeastern United States or to the infection of from 
60 to 80 per cent of the 300,000,000 people of India must be 
almost incalculable. 

The retarding effect of the disease in education and civiHzation 


is not less terrible. There are many families in our South where 
for at least four generations illiteracy and ignorance have re- 
sulted from disablement by hookworm disease. In many com- 
munities large proportions of the children are kept out of school 
on account of physical or mental disablement from this cause. 
Unlike many diseases, this one has no tendency to weed out the 
weak and unfit; it works subtly, progressively, undermining 
the physical and intellectual life of the community, each gener- 
ation handing down an increased handicap to the next. 

Treatment. — Treatment of hookworm disease consists, pri- 
marily, of the administration of a drug which will kill and expel 
the worms from the intestine. In severe cases this is followed 
by treatment with a tonic to bring back some of the lost health 
and vitality. Recently it has been shown possible to hasten 
recovery after expulsion of the worms by vaccinations prepared 
from bacteria which are found in abundance in the faeces. This 
indicates that some of the evil effects of hookworm disease are 
due to absorption of bacterial toxins through the injured intestine. 

Until recently the classical remedy for use against hookworm 
has been thymol. This is a drug which is poisonous to the 
human system but under ordinary circumstances is not absorbed 
by the digestive tract. It is, however, very soluble in alcohol, 
ether and various oils, so that certain precautions have to be 
taken in its use, and it should not be taken except under medical 
supervision. Thymol is not highly efficient except in repeated 
doses, taken some days apart, and this is a severe handicap in 
its use. During the five-year period from 1909 to 1914, however, 
the American Hookworm Commission, largely by the cooperation 
of local physicians, treated nearly 700,000 hookworm patients 
in southern United States with thymol. 

A few years ago oil of chenopodium came into favor in some 
parts of the United States as a remedy for hookworm, and is now 
rapidly supplanting all other remedies in all parts of the world. 
It is made from a common weed, usually called Jerusalem oak 
or goose-foot, and is therefore very cheap and the supply inex- 
haustible. It is more effective than thymol and is if anything 
less dangerous to the patient. According to Hall and Foster, 
oil of chenopodium is not entirely harmless, and among other 
effects is distinctly constipating. To hasten the elimination of 
the chenopodium as well as to counteract the constipating effect 


and the slow absorption through the intestinal walls, Hall and 
Foster strongly advise giving castor oil with the chenopodium 
and also afterward; this gives a maximum of both efficacy and 
safety. The usual method of giving oil of chenopodium is five 
to 15 drops at two hour intervals; each dose should be accom- 
panied by castor oil. 

A number of investigators have pointed out the superior effect 
of oil of chenopodium when given with chloroform. Hall and 
Foster, by means of extensive experiments on dogs, have demon- 
strated that chloroform itself is more efficient against hookworms 
than any other drug with which they have experimented, and they 
could find no evidence of superior efficiency of a combined use 
of both drugs, except in case of accompanying infection with 
Ascaris, against which oil of chenopodium is particularly effec- 
tive. Chloroform dissolved in castor oil can be given internally 
in from three to four gram doses with as great a degree of safety 
as can other drugs in common use for worms, its safety lying in 
its rapid elimination from the system. A dose of chloroform 
should not be repeated, however, in less than three weeks, since it 
does some temporary damage to the liver which may not be 
completely repaired in less than that time. 

Beta-naphthol is considered by some physicians better than 
thymol, especially when distributed to laborers for use without 
medical supervision, since there is less chance of bad results, and 
it can be taken safely by an ignorant person with a few simple 
directions. This drug is used for treatment of coolie laborers 
in Ceylon, and new consignments of coolies are treated with it 
whether infected or not, since a great majority of them are 

Male fern is sometimes used for expelling hookworms but is 
more dangerous than either thymol or beta-naphthol, is more 
expensive and is if anything less efficacious. Oil of eucalyptus 
has also been used with some success. It has the advantage of 
being less unpleasant and less dangerous than some of the other 
drugs in common use. 

Prevention. — Methods of prevention of hookworm disease 
are suggested by the mode of infection, namely, contact with 
soil or water contaminated by infected faeces. The ways in 
which such contact may be made are numerous, and vary with 
the habits, occupation and wealth of the inhabitants. Plan- 


tation workers on our sugar and cotton plantations and on the 
coffee plantations of Central and South America, and the coolies 
working on the estates of China, India and other tropical coun- 
tries, practically never wear shoes. The necessity for shoes is 
unknown, the discomfort of using them when the habit of going 
without them has been long established makes their use difficult 
to encourage, and there are very few who could afford such 
luxuries even if their value were appreciated. As shown above, 
the hookworm larva? in soil or water commonly gain access to their 
hosts through bare feet. The readiness with which infection may 
occur by contact with contaminated ground or water is shown by 
the case of a prominent American in Porto Rico who became 
infected by removing his boots and wading in a small pool. 
Kneeling bare-kneed or resting the bare hands on the moist 
ground beside a stream or pool to drink; drinking water which 
has been directly or indirectly polluted; dirt-eating, which is a 
common perversion of the appetite in intestinally diseased people; 
eating with soiled or dirty hands; the chewing of dirty finger- 
nails; in all these and a hundred other ways the agricultural 
laborer may become infected. 

Miners, working underground where they are continually in 
contact with earth, are exposed equally as much as agricultural 
laborers, and more so in relatively cold countries such as those of 
central Europe, since the warmth resulting from subterranean 
location allows the parasites to thrive where on the surface they 
would perish. Dirty hands, unsanitary habits and polluted 
water are the cause of the high percentage of hookworm infection 
in mines where no special preventive measures are practiced. 

Sanitation. — Prevention of hookworm disease, were it not 
for the inevitable ignorance and stupidity of many of the people 
to be dealt with, would be a relatively easy matter. The com- 
parative ease with which infections can be discovered, the read- 
iness with which the parasites, once discovered, can be expelled, 
and the ease with which heavy infection, even in badly infested 
countries, can be prevented by cleanliness, sanitation and care 
of exposed parts of the body are factors which should make the 
hookworm relatively easy prey for the hygienic reformer. But 
the hookworm has a valiant ally in the stunted brain and will of 
its victim and in the unsanitary habits, established by countless 
generations, which characterize the natives of almost every hook- 


worm-infested country, and for these reasons alone the eradi- 
cation of the disease has in many cases been a greater stumbling 
block to medical science than that of even malaria or yellow fever. 
Mosquitoes are easier to control than are the hopelessly ignorant 
and stupid victims of hookworm disease! 

The keynote in the prevention and eradication of hookworm 
disease is the prevention of pollution of the soil, in other words, 
proper sanitation. Not only the hookworm, but almost all of the 
true nematode parasites of the human intestine, are the direct 
outcome of unsanitary conditions. The early stages of develop- 
ment, so far as is known, are invariably passed in water or moist 
soil, and for this reason the sanitary disposal of faeces would 
forever put an end to such of these parasites as are peculiar to 
man. The difficulties involved in this simple hygienic principle 
are infinitely greater than the average civilized and cultured 
person would suspect. In southern United States, 68 per cent 
of the rural homes are estimated to be without privies of any kind. 
In many rural districts where privies do exist, their use is restricted 
to the women and children or to the family of the manager. 
In most tropical countries where coolie laborers are employed, 
practically all of whom carry infection, no attempt is made to 
provide any kind of place for defecation, not even a simple hole in 
the ground. The condition in this regard among the " jibaros " 
or plantation laborers of Porto Rico, for instance, is fairly repre- 
sented by this case — of 61 hookworm patients at Utuado, 55 
never had used privies of any kind, and of the six who did oc- 
casionally use them only two lived in rural districts! The ex- 
tent to which the unhygienic conditions may go, and the readi- 
ness with which infection with various intestinal worms may take 
place, is demonstrated by the occurrence in Brazil of three species 
of intestinal worms in a baby three months old. 

The time when the value accruing from proper sanitation will 
be realized to an extent sufficient to make man as careful con- 
cerning his personal habits as are some of his domestic animals is 
still in the future; but it is reasonable to hope that it will soon 
be at hand. It is a significant fact that the domestic cat, which 
sanitarily covers up its excreta, has, on the average, fewer intesti- 
nal parasites than the less careful dog. Dr. Stiles has recently 
tested the effect of sanitation and consequent reduction of in- 
testinal parasites, both protozoans and worms, by examination of 


school children from sewered houses and from houses with privies. 
The statistics compiled from the data obtained showed that the 
children from sewered houses possessed fewer parasites and aver- 
aged a higher grade in school than those from houses with privies, 
even though the difference was undoubtedly reduced by the fact 
that sewered homes suffered from proximity to the privies of 
unsewered homes and from consequent infection by flies and other 
agents of transmission. 

The most important and effective preventive measure against 
hookworm and other intestinal nematodes which can be inaugu- 
rated is the enforcement of the building of privies or latrines 
of some sort, if it be only a ditch which is occasionally covered 
with earth or disinfected, for the use of laborers on plantations 
and estates, and the placing of a penalty or fine for unnecessary 
pollution of the ground or water where there is any danger of 
spreading hookworm infection, especially along roads or on plan- 
tations. Naturally such practices as the use of night-soil (human 
faeces) for manure, which is extensively practiced in China, should 
be stringently forbidden, unless the material can be disinfected 
by chemical treatment, as suggested by Leiper. The faeces of all 
infected persons, as well as those of any suspected persons, should 
be carefully disinfected. The use of common salt as a disinfect- 
ant against hookworm has been found efficacious, but it must be 
used in rather large quantities. Nicoll, in Australia, in experi- 
ments recently conducted with hookworms, obtained rather un- 
satisfactory results with salt treatment of infected faeces, unless 
the salt was used in very large quantities and was very thoroughly 
mixed with the infective material. The spraying of the earth 
walls and floors of mines with a strong salt solution or other 
disinfectant, and a similar treatment of factories, yards, etc., 
which are known to be infected, is a preventive measure which 
is said to bring good results, but in the light of Nicoll' s experi- 
ments this should be reinvestigated. Wearing of boots or shoes 
by mine workers, agricultural laborers and all who work with 
brick, pottery, earth roofing, etc., is recommended as a protective 
measure by the boards of health in some countries. This cer- 
tainly is a good recommendation when it can be followed, but it 
should be remembered that many who need protection the most 
are unable to invest in such luxuries as shoes, and that at best 
little advance towards the final eradication of the disease is 


made by such measures. • If money sufficient to buy shoes and 
other protective garments were invested in improving sanitary 
conditions much more permanent good would result. This does 
not mean, however, that such protection as is gained by the use 
of shoes and spraying of ground is not well worth while for such 
individuals as can afford it and who are forced by occupation or 
other circumstances to come in contact with polluted soil. 

The isolation and treatment of infected persons is to be highly 
recommended, especially in case of immigrants or new arrivals 
from infected regions. In 1910 the Board of Health of San Fran- 
cisco made an examination of a shipload of Hindus which had 
just arrived and found 90 per cent to be infected, whereupon a 
quarantine was established, and has since been maintained, for 
hookworm patients. Every colony of Hindu coolies in California 
is a center from which hookworm disease is spreading. Had a 
hookworm quarantine been established years before, California 
would have been to a great extent free from this parasite. Quar- 
antine measures have been taken in Natal, where all infected 
immigrants are treated before being assigned to plantations. 
When the infection does appear in a mine or plantation the in- 
fected persons should be treated, and not allowed to return to 
work until their faeces are free from eggs. 

The treatment of hookworm disease is of such vital importance 
to the public of any endemic region that it should be supervised 
and aided by the government. Such aid should consist in the 
establishment of free dispensaries for hookworm patients, the 
supply of necessary drugs at cost for the treatment of hookworm 
disease, the appointment of inspectors to enforce sanitary regu- 
lations, and the distribution of information regarding the disease 
by free pamphlets, pubHc lectures and school instruction. In 
the United States this work has been done largely by the American 
Hookworm Commission, financed by a gift of 11,000,000 from 
John D. Rockefeller. In 1914 the Rockefeller Foundation ex- 
tended the work of hookworm eradication " to those countries and 
peoples where conditions invite." Such work has been begun in 
a number of West Indian islands. Central America and Egypt. 

It has been pointed out that demonstration as well as instruc- 
tion is necessary to impress the natives of hookworm districts 
with the advantages of sanitation and hygienic conditions. It 
is absurd to rely upon the ability of the average native, dwelling 


in a filthy environment in which he was born and brought up, to 
form a conception of community cleanUness, which he has never 
seen, resulting in public benefits which he has never known. The 
erection of schools, hospitals, residence sections, etc., which are 
models of simple but efficient sanitation, would go much further 
toward securing the cooperation of natives in duplicating such 
conditions than would any amount of instruction without such 
practical demonstrations. 


General Account. — As compared with the hookworms all the 
other intestinal roundworms, except trichina, which will be dis- 
cussed in the following chapter, sink into relative insignificance, 
but there are several species which are very common in some parts 
of the world and some which are of very wide distribution. The 
pathological effects of some of these worms appear to be slight 
or almost entirely negligible, — while others, at least in individual 
cases, cause severe symptoms and may even be a direct cause 
of death. Recently, as has been remarked in a preceding chap- 
ter, more and more suspicion is being aroused against various 
intestinal worms, especially those which habitually inhabit the 
ccecum and appendix, as playing a leading part in producing 
appendicitis. The relation of intestinal worms to bacterial in- 
fections is discussed on pp. 203-204. 

As regards the selection of a drug for treatment of any of 
these rarer intestinal parasites, certain general principles should 
be of value. As has been pointed out by Hall and Foster, 
" almost all anthelmintics {i.e., drugs used against worms) are 
poisons, intended to kill or stupefy or otherwise disable and re- 
move worms, while at the same time inflicting a minimum amount 
of damage on the host animal by virtue of the comparative 
insolubility of the drugs or their rapid elimination." For worms 
situated in the upper portions of the digestive tract, drugs such 
as chloroform, which are rapidly absorbed and eliminated, can 
be used, whereas for worms situated in the lower portions of 
the digestive tract, insoluble drugs would in general be better. 
That certain drugs have more or less specific action against 
certain species of worms is true, as evidenced by the case of oil 
of chenopodium against ascarids, and chloroform against hook- 
worm. It is quite probable, however, that this apparently spe- 
cific action may be due rather to a mode of life of the worm 
affected which makes it particularly easily reached by the drug. 
Hall and Foster, for instance, suggest that the striking efficiency 




Fig. 106. Intestinal nematodes of man, natural size. Male and female of each 
species shown, except Strongyloides, in which only the females is known. The 
female of (Esophagostoma is immature, the mature form being unknown. 


of chloroform against hookworms may be due to the fact that 
hookworms are blood-suckers and that the chloroform rapidly 
absorbed by the blood is ingested by the hookworms in amounts 
sufficient to cause stupefaction or death. 

The presence of intestinal worms of most species can be de- 
termined by the finding of the eggs in the faeces, and in most cases 
the eggs are characteristic enough to make a determination of 
the species fairly easy. It often facilitates the search for para- 
site eggs to concentrate them in the following manner: Mix a 
portion of the faeces the size of a walnut with 60 cc. of distilled 
water, strain through several thicknesses of wide-mesh surgical 
gauze and centrifuge at high speed for about ten seconds. Pour 
off most of the liquid, add more water, shake thoroughly and 
centrifuge again. The material thrown to the bottom of the 
tube contains the eggs, which can readily be found under a micro- 
scoper A bit of the centrifuged material is placed on a slide with 
a little distilled water. In two or three minutes the eggs will 
settle on the slide, and the excess liquid can be poured off. The 
eggs of parasitic worms vary in size, shape, color, surface mark- 
ings and state of development. Most eggs are colored yellow 
or brown from bile in the faeces but the eggs of the hookworms, 
Strongyloides, and a few others remain clear and colorless. The 
characteristics of the eggs of the commoner parasitic worms are 
shown in a comparative way in Fig. 61, p. 205. In the case of a 
few intestinal nematodes eggs do not appear in the faeces. In 
the pinworms, for instance, the adult female containing the eggs 
usually passes out entire, whereas in Strongyloides the eggs hatch 
before leaving the host. 

Preventive measures against practically all of the true nema- 
tode parasites of the intestine consist mainly in proper sanitation, 
a discussion of which will be found on p. 265. It is possible that 
some of the intestinal nematodes may occasionally, at least, 
utilize an intermediate host of some kind, but even if this were 
true sanitary disposal of human faeces would, as said before, be 
sufficient to exterminate such parasites as are peculiar to man. 
The nematodes which occur in other animals as well as man have 
to be guarded against by other means also. The spiny-headed 
worms, which are transmitted in the bodies of insects which 
serve as intermediate hosts, are, of course, subject to quite dif- 
ferent prophylactic measures. 


Ascaris or Eelworm. — Of greatest importance of these lesser 
intestinal parasites is the eelworm, Ascaris lumbricoides (Fig. 
106). Ascaris is one of the largest nematode parasites known^ 
the female averaging about ten inches in length, and occasion- 
ally measuring a foot and a half, while in diameter the body is 
about as large as an ordinary lead pencil. The males are usually 
several inches shorter. These worms are among the most fre- 
quent human parasites. They occur in all parts of the world 
and are found, especially in children, in the majority of temperate 
countries, even in countries as far north as Greenland and Fin- 
land. In the tropics they are abundant and are almost univer- 
sally present in children, each individual harboring anywhere 
from two or three to several hundred worms. 

Ascaris can be recognized immediately by its large size and 
robust form. The males (Fig. 107) can be distinguished by the 

Fig. 107. Ascaris, dissected to show anatomy; female above, male below. 
Note ribbon-like intestine (cross-barred) with pharynx at its anterior end; the 
coiled threadlike ovaries in female and testis in male; the large kinky oviducts in 
the female, uniting to form a vagina near the external opening on the anterior third 
of the body; and in the male the large sperm duct opening at the ventrally-curved 
posterior end of the body in common with the intestine. 

sharp downward curve of the posterior end of the body, the female 
(Fig. 107) having a straight and rather stumpy tail. Both 
sexes are more slender at the head than at the tail end. The 
sexual organs occupy the greater part of the body. In the female 
they consist of two coiled threadlike ovaries (Fig. 107) and a pair 
of large oviducts in the form of kinky tubes which open about 
one-third of the way back from the anterior end. In the male 
there is a single coiled threadlike testis and a single sperm duct 
(Fig. 107), the latter opening at a cloaca at the posterior end of 
the body. The size and simplicity of the organs makes Ascaris 
a favorite subject for class-room dissection. The human species, 


Ascaris lumbricoides, is now usually looked upon as a variety 
of the species which occurs in hogs in almost every country in 
the world, and which is sometimes known as A. suilla. 

The life history of Ascaris is usually thought to be very 
simple. The eggs, of which thousands are deposited by a single 
female, develop within the eggshell outside of the human body, 
in water, soil or manure piles, wherever the proper conditions of 
temperature can be found. The eggs (Fig. 108) are about 0.06 mm. 
long by 0.04 mm. wide (;f^(y by ^^(^ of an inch), elliptical in form 

with a thick transparent shell, 
usually bile - stained, covered 
over outside by irregular albu- 
minous coats which give them 
a rough warty appearance. 
When passed from the diges- 
o tive tract no sign of segmen- 
Fi: 108. Egg of Asmns;^, surface tation can be Seen. Under 

view showing warty albununous coat; . 

B, same in "optical section," i.e., with lavorable conditions ot Optl- 

microscope focused on center of egg in- ^^^ temperature (33° C), 
stead of on surface. . 

moisture, and oxygen supply 
the eggs develop in from 10 days to a month, but may be retarded 
for a long time by low temperatures, excessive dryness or in- 
sufficient oxygen. Although continued dryness at high tem- 
perature may be fatal to the eggs, yet under natural conditions 
in soil there is probably almost always sufficient moisture to 
allow development to proceed, and the developed eggs may live 
for several years. The eggs are extremely resistant to most 
chemical reagents, even when used in very strong dilutions, so 
that ordinary methods of disinfection would be of little value in 
destroying them. The use of human faeces (night soil) as a fer- 
tilizer undoubtedly results in wholesale contamination of vege- 
tables and other garden products. 

The eggs only rarely hatch outside of the body; ordinarily 
the larvae escape only after the eggs have been ingested and have 
reached the small intestine. Since eggs injected under Ixie skin 
will hatch it is evident that some other factor besides the digestive 
juices is influential in liberating the larvae. 

Stewart, in recent experiments in China, was the first to dem- 
onstrate that Ascaris might not develop directly in the intestine 
of its host. Subsequent experiments by Stewart and also by 
Ransom and Foster have fully corroborated Stewart's work. 


Ripe eggs ingested by rats and other rodents hatch in the 
small intestine. Some of the newly-hatched larvae may be elimi- 
nated in the faeces, but others penetrate the wall oi the intestine 
and go to the liver and lungs 
and occasionally other organs, 
including the abdominal cavity. 
The newly-hatched larvae mea- 
sure between 0.2 and 0.3 mm. 
in length, but during their 
migrations and during their so- 

journ in the lungs they grow W^ jB /\ y^ q 

rapidly, reaching a length of 
from 1 to 1.5 mm. by the tenth 
day, when ready to leave the , ^^«: ^^^i ^P^r^^'P/^^'^,^^^ ^*^,^T ""^ 

^ r V Ascaris; a, freshly hatched larva; o, larva 

lungs. They may reach the from lung of rat on tenth day after infec- 

liver as early as two days after *^o"- x ^^^\ (Adapted from Stewart.) 
infection, and the lungs on the 

third day. From the sixth to the tenth days the larvae pass from 
the blood-vessels into the air sacs and bronchial tubes of the lungs, 
and thence through the trachea to the mouth. Some larvae 
escape from the mouth, but the majority are swallowed and pass 
out with the faeces apparently dead, the host becoming free from 
parasites in about two weeks. It is not probable that, as at first 
suggested by Stewart, the rat normally acts as an intermediate 
host, but rather the development of Ascaris to the lung stage and 
failure to complete the development in the intestine may be con- 
sidered as a case of imperfect adaptability of the worm to this 
host. It was subsequently shown by Stewart himself and also by 
Ransom and Foster that a similar development in the lungs takes 
place in pigs and other animals as well as in rats, and it is rea- 
sonable to suppose that a direct development in a single host 
normally takes place. However, this has been shown to be uhe 
case only in a few instances, and in cases where a massive infec- 
tion would be expected from feeding enormous numbers of eggs to 
susceptible animals only a small number of Ascaris developed, 
and in some instances none at all. 

Both in the hog and in man, susceptibility to Ascaris infection 
decreases with age. The higher rate of infection in children is 
probably, however, due to careless habits as well as to greater sus- 



The symptoms produced by Ascaris infection vary greatly 
with different individuals. In some cases a great number of 
Ascaris may be harbored with practically no ill effects. Often, 
however, even when small numbers are present, peculiar mental 
and constitutional ailments occur, such as feverishness, anemia, 
restlessness, epilepsy, insomnia and deliriousness. In combina- 
tion with these nervous troubles there is usually some dyspeptic 
trouble, such as irregular appetite, nausea and stomach aches. 
The nervous and other constitutional symptoms are the result 

of poisoning or intoxication from sub- 
stances given off by the worms in the 
intestine, as explained in Chapter XI, 
p. 203. The worms occasionally creep 
forward into the throat or nose. Their 
wandering into other organs through 
ducts leading from the intestine or 
into the body cavity through the in- 
testinal walls often gives rise to serious 
abscesses which call for an operation 
and removal of the intruders. The 
production of a serious and often 
fatal pneumonia in rats, pigs and other 
animals by larvae developed from eggs 
experimentally fed to them leaves 
little room for doubt but that a sim- 
FiG. 110. Human whipworm, ji^r Condition is produced after human 

Trichuris trichiura: A, female; . » ^. ^ ,^ , a • i 

ov., ovary; ut., uterus; v., vulva; mfcction, and that Ascavis may be 
int., intestine; w., whiplike an- the cause of Certain lung troubles in 

terior end containing oesophagus. . 

X 3. B, egg; note barrel shape numau beingS. 

and pluglike bodies at ends. Santonin has been the classical 

drug for expelling Ascaris, but oil 
of chenopodium has recently been demonstrated to be considerably 
more effective. According to Hall and Foster oil of chenopodium, 
properly administered (see Chap. XIV, p. 264), is almost 100 
per cent effective for ascarids, and is more dependable than any 
other drug commonly used for worms. 

Whipworm. With the possible exception of the hookworms 
and Ascaris J the whipworm, Trichuris trichiura (Figs. 106 and 
110), is the most common worm parasitic in man. It is a nema- 


testine occupy the thicker posterior part of the body. The fe- 
male whipworms, which are always far more numerous than the 
males, are about two inches long, while the males are a little 

The human whipworm is found in almost every part of the 
world, but is especially prevalent in warm countries; it para- 
sitizes both man and monkeys. It usually makes its home in 
the coecum but occasionally establishes itself in the appendix 
or large intestine. It is usually said to transfix the wall of the 
coecum with its threadlike anterior portion, but there is some evi- 
dence to show that it merely buries its long head and " neck " 
between the folds of the intestinal wall. 

Usually the only evidence of the presence of whipworms is 
the appearance of the characteristic dark-colored, barrel-shaped 
eggs (Fig. HOB) in the faeces. These eggs, like those of Ascaris, 
develop in water or moist soil. The embryo-containing eggs are 
very resistant to adverse conditions and may live for years 
without losing their vitality. Infection, as far as known, occurs 
as in the case of Ascaris. The worms may attain maturity 
and produce eggs in less than a month after the eggs have been 
swallowed. Although the whipworm feeds on blood to some 
extent, and undoubtedly produces toxins, as evidenced by the 
increase in eosinophiles (see p. 203) in the blood which nearly 
always occurs in case of whipworm infection and by the occa- 
sional mental disturbances and other nervous symptoms, this 
worm usually produces very slight, in fact often unnoticeable, 
effects. It is, however, thought by some workers to be one of 
the intestinal parasites most frequently involved in causing 
appendicitis. It is very difficult to dislodge the whipworm by 
the usual methods used for expelling intestinal parasites, prob- 
ably due to its very firm attachment by the long slender " neck." 
Oil of chenopodium administered as for hookworm (see p. 264) 
is probably the most effective remedy. 

Pinworm. — One of the most frequent and widely distributed 
intestinal parasites of man is the pinworm, Oxyuris vermicularis 
(Figs. 106 and 111). This parasite occurs almost universally in 
children at one time or another in temperate as well as tropical 
countries; it inhabits the lower part of the small intestine and 
the coecum. 

The adult females (Fig. Ill 9 ) are whitish worms about two- 



fifths of an inch in length, and have about the diameter of an 
ordinary pin. The males (Fig. 111<J) are only about half as 
large and have the posterior end of the body rolled ventrally. 
The adult females filled with eggs leave 
the small intestine and coecum and wander 
back to the rectum whence they are 
passed out with the faeces or creep out 
of the anus, especially in the evening 
or at night, causing intense itching. 
These egg-filled females, or the free eggs 
which already contain coiled embryos, 
live in the moist groove between the 
buttocks, in girls sometimes creeping for- 
ward to the vagina. From the scratching 
and rubbing which results from the itch- 
ing in the vicinity of the anus the fingers 
and fingernails become infected with the 
eggs. The eggs may then be transferred 
to the mouth directly or indirectly, thus 
causing reinfection, or they may be trans- 
mitted from person to person by unclean 
hands. Infection may also occur by 
swallowing the mature egg-filled female 

o!^r^lJ^^9: ^°™^' •''• by ^^^ ^^^^^ °f '^^ vegetables 
female; $, male; ph., or other foods which have been polluted 

^vX^; ir'/utems-t!; by the eggs. As in the case of other 
anus; v., vulva; t., testis; parasite eggs, those of the pinworm may 
(Aftet-ciTuTfrom''Brau„'- ^Iso be Scattered by flies which have 
visited infected faeces. 

When first deposited, the eggs, often hanging together like 
short strings of beads, contain larvae which resemble tadpoles 
(Fig. 11 2 A). In the faeces or in the moist groove between the 
buttocks the larvae, still in the eggs, transform within a few hours 
into worms of typical nematode form (Fig. 112B). Later stages 
are shown in Figs. 112C and D. 

After infection, which probably nearly always occurs by way 
of the mouth, about two or three weeks elapse before sexual 
maturity is again attained and the eggs and females reappear 
in the faeces. 

While usually no inconvenience is felt from the presence of 



even large numbers of pinworms, since they do not suck blood 
and seldom cause intestinal lesions, yet they sometimes produce 
reflex nervous symptoms, probably by secretion of toxins, and 
they may interfere with the normal action of the bowels. As 

Fig. 112. Early development of pin worm, Oxyuris vermicularis. A, newly laid 
egg containing tadpole-like larva; B, egg 12 hrs. later with nematode-like larva; 
C, egg with fully developed embryo; D, newly hatched embryo. X 500, (A and 
B after Braun; C and D after Leuckart.) 

remarked elsewhere pinworms are believed to be sometimes, 
and perhaps frequently, the original cause of lesions in the ap- 
pendix which culminate in appendicitis. The intense itching 
which they produce by creeping in the vicinity of the anus is 
usually the most disagreeable effect of their presence. 

On account of their situation in the lower part of the intestine, 
treatment for pinworms should be by drugs which are not rapidly 
absorbed from the intestine but are relatively insoluble. Thy- 
mol, male fern and, best of all, oil of chenopodium are effective 

Strongyloides, — Another parasite of the intestine which is of 
wide distribution and locally very common is Strongyloides ster- 
coralis, sl very small worm about one-tenth of an inch in length 
which bores deep into the mucous membrane of the intestine. The 
female strongyloid (Figs. 106 and 113A), which is the only 
sex known, can be recognized by its small size, and microscopi- 
cally by the chain of six or eight eggs, lying near the middle of 



Fig. 113. Life history of Strongyloides stercoralis. A, adult female in intestine 
(note long pharynx, egg-containing uterus and vaginal opening on posterior third 
of body; B, newly born embryo as passed with faeces; C and D, adult female and 
male, respectively, of free-living generation; E, " rhabditiform " larva, from female 
of free-living generation; F, filariform larva, resembling grandparent, and formed 
by metamorphosis of E, ready to infect by boring through skin. X 75. (Partly 
after Looss.) 


the body, visible through the deUcate body wall. The eggs, 
which are deposited deep in the intestinal coat, normally hatch 
before leaving the digestive tract of the host and grow con- 
siderably, so that when the faeces of an infected person are ex- 
amined microscopically the active writhing larvae (Fig. 113B), 
250 /x (y^^ of an inch) in length, can be seen darting about in 
snakelike fashion. Further development of the larvae takes 
place in water of fairly high temperature, such as would be found 
under the burning rays of a tropical sun. Under such conditions 
the larvae attain a sexually mature form, male and female (Fig. 
113C and D), in which they are quite different from their parents. 
They now copulate, and the females lay 30 or . 40 eggs, all within 
two days. This second generation of eggs hatch into tiny free- 
living larvae (Fig. 113E) resembling the parents, but after their 
first moult they lose the parental characteristics and become 
like their grandparents (Fig. 113F). After having reached this 
stage, they soon die unless they gain entrance to the digestive 
tract of a human being again. An unusual phenomenon is 
shown by these worms in that the life cycle, under less favorable 
conditions, can be abridged, and the alternation of generations 
eliminated. If, for instance, the larvae in the faeces be exposed 
to the cooler water of a temperate country, they do not be- 
come sexually mature and reproduce, but transform directly 
into the parasitic type and reinfect without further repro- 

The method of infection is similar to that of the hookworms. 
While the larvae may occasionally gain entrance to their host 
with polluted water or food, they are able to bore through the 
skin as do the hookworm larvae, and it is probable that this is 
the more usual method. 

As a rule Strongyloides does not cause very serious ill effects 
from its pursuit of life and happiness in the intestine. Nearly 
all cases of diarrhea and dysentery, in which the strongyloids 
were formerly supposed to be the chief agent, can now be ascribed 
to some other cause, the strongyloids being more or less innocent 
bystanders. Barlow, however, reports that in 23 cases in 
Honduras, five of them uncomplicated, such symptoms as in- 
termittent diarrhea without blood or mucus in the stools, colic 
and certain nervous symptoms were in evidence. In many cases 
where a diseased condition of the intestine is brought about by 


some other causes, the strongyloids increase in number and un- 
doubtedly intensify the bad condition. 

The worms are not so readily expelled by drugs as are most of 
the intestinal parasites, being able, on account of their small size, 
to stow themselves away in the folds and villi of the intestine 
where drugs do not reach them. 

Since the strongyloid occurs in the same countries as do the 
hookworms, though more limited in distribution, and has a 
similar mode of transmission and infection, the same preventive 
measures which are used against hookworm are of service against 
this comparatively harmless companion of it. 

Other Species. — There are a great many other worms which 
occasionally make their home in the human digestive tract, some 
being locally common, others merely sporadic in their occurrence; 
some, in fact, are not truly parasites at all, but have merely 
established themselves temporarily after having been swallowed 
with infected food. Stephens lists 59 species of nematodes as 
having been observed in man. None of those not already 
mentioned can be considered of great importance, since they 
seldom cause serious ailments and are most of them rare. Only 
those which are true parasites and have been recorded from man 
more than once need be mentioned here. 

Belonging to the same family as Ascaris (Ascaridse) or to 
closely allied families are: Belascaris cati (or Ascaris mystax) 
(Fig. 106) and Toxascaris limbata (or Ascaris marginata), small 
Ascarids two or three inches in length, normally parasitic in cats 
and dogs respectively, found practically all over the world but 
only occasionally in man; and Physaloptera mordens (Fig. 106), 
a worm one and a half to two inches long, which appears to be 
not uncommon in negroes in central East Africa. 

Allied to the hookworms and having an expanded umbrella- 
like " bursa " at the posterior end of the male are several species 
of Trichostrongylus (or Strongylus). T. instabilis (suhtilis) (Figs. 
106 and 114) is a small worm from four to six mm. (one-fifth of 
an inch) in length, somewhat resembling a hookworm but much 
more slender. It is normally parasitic in the small intestine 
(duodenum) of sheep, camels, baboons and other animals and 
occasionally occurs in Egyptian " fellahs." A closely allied 
species, T. orientalis, is found in the duodenum of Japanese. 
Other species of this genus normally found in herbivorous ani- 



mals in Egypt occasionally parasitize man. The eggs of Tri- 
chostrongylus (Fig. 61Y) resemble those of hookworms, but they 
are a little larger and frequently contain more than four cells. 
The life history is similar to that of the hookworms. Ternidens 
(or Triodontophorus) deminutus (Fig. 106) is a worm about half 
an inch in length, normally found in the large intestine of monkeys 
in central East Africa, and not uncommon in natives; (Esopha- 
gostomum apiostomum (brumpti) is a parasite which forms tumors 
in the large intestine of monkeys and occasionally man, in 
central Africa and in the Philippines. It produces symptoms of 

Fig. 114. Trichostrongylus instabilis; 
A, female, showing pointed tail and 
vulva (v.) ; B, male, showing smaller 
size and bursa (b.). X 25. (After 
drawings and measurements by 


Fig. 115. (Esophagostoma stepha^ 
nostomum var. thomasi. A, immature 
female in cyst in large intestine of 
man in Brazil; B, same, removed 
from cyst. (After Thomas.) 

dysentery. An allied worm, 0. stephanostomum var. thomasi, 
a variety of a species normally found parasitic in gorillas in 
Africa, has been found once in man in Brazil. In this case there 
were 187 tumors (Fig. 115 A) in the small and large intestines 
each containing one worm (Fig. 115B). This species will prob- 
ably be found to be normally parasitic in some species of South 
American monkey. 

These and a number of still rarer human parasites are of little 
interest as far as man is concerned, except as medical curiosities. 

In connection with the intestinal nematodes there should be 
mentioned three species of spiny-headed worms (class Acantho- 



cephala) which occasionally have been found in man. These 
worms are not true nematodes but are distantly related to them. 
They are characterized by the presence, at the anterior end of 
the body, of a prolonged proboscis which 
is covered with thornhke, recurved spines. 
This proboscis is sunk into the walls of the 
intestine of the host to gain anchorage. Like 
the tapeworms, the spiny-headed worms are 
totally devoid of any digestive tract of their 
own. The common species of the hog, 
Gigantorhynchus hirudinaceus (gigas) (Fig. 
116), is said to occur in man in southern 
Russia. It is a large worm, the female ten 
to 12 inches in length and about one-fourth 
of an inch in diameter and the male about 
one-fourth as long. The larval stage is 
passed in certain species of beetles. 

A single case of infection with another 
ryhnchus hirudinaceus species, EcMnorhynchus hominis, which was 
'Zasf.''A!rnltur7^ze, ^nly one-fourth of an inch in length, has been 
B, X 5. (After Raiiiet recorded, also from Russia. A species which 
rom Neumann.) -^ probably more frequently a human para- 

site is Moniliformis (or EcMnorhynchus) moniliformis, normally 
parasitic in field mice, rats and marmots. The female worm is a 

Fig. 116. Giganto- 


Fig. 117. Development of spiny-headed worm of rats and mice, Monilifor- 
mis (or Echinorhynchus) moniliformis. A, proboscis, X 50; B, larva from cock- 
roach, X 23; C, egg, X 150. (After Grassi and Calandruccio.) 

little over three inches in length, the male about half this size. 
A species of cockroach serves as an intermediate host. Grassi 
and Calandruccio found by experimentation that the larvae in 
cockroaches (Fig. 117B) would develop apparently equally well 
in white rats and in man. An allied or possibly identical species, 


M. clarki, has been described by Ward from a squirrel in Illinois; it 
is a worm about four or five inches in length with a very minute 
proboscis. Ward believes that this species would also probably 
develop in man if the larvae were accidentally swallowed with 
some insect which presumably serves as an intermediate host. 
A Moniliformis which may be identical with M. moniliformis was 
found by the writer in about ten per cent of rats in Houston, 
Texas, and it has been reported in other parts of the United States 


Of quite a different nature from other intestinal parasites is 
the trichina worm, Trichinella spiralis. As far as the injurious- 
ness of its presence in the intestine is concerned it is much less 
serious than many of the other intestinal worms, since its length 
of life as an adult is relatively short. The serious and often 
fatal results of trichina infection are due to the peculiar life 
history of the worm and are concerned with the offspring of the 
infecting worms and not with these worms themselves. 

There can be little doubt but that this worm, with the pork 
tapeworm as an accompKce, was responsible for the old Jewish 
law against the eating of pork. It was, however, many thousands 
of years later, in A.D. 1828, that the worms were first dis- 
covered. A little over 50 years later, 1880-1891, the trichina 
worm was the cause of international complications between the 
United States and Germany, and during this time American pork 
was excluded from German markets on account of the alleged 
frequency with which it was found to be infected. The outcome 
of this trouble was the beginning of the present American system 
of government meat inspection. 

Prevalence. — Since the danger of infection from eating im- 
perfectly cooked pork has been given wide publicity, and has 
come about as near to being a matter of common knowledge as 
any fact of parasitology, the prevalence of the infection has been 
greatly reduced, but even now trichina embryos are found in 
from 0.5 per cent to 2 per cent of the inhabitants of most civilized 
countries, as shown by post mortem examinations. According 
to Dr. Ransom, of the U. S. Bureau of Animal Industry, statistics 
based on microscopic inspection of 8,000,000 hogs in the United 
States show only 1.41 per cent infection with live trichina worms, 
and a total of 2.57 per cent infection with live trichinae and 
trichina-like bodies. 



In some European countries the infection is somewhat less. 
Some of the great epidemics of trichiniasis (or trichinosis) in 
Europe have been attributed to American pork, but according 
to Ransom there have been no authentic cases of the disease in 
Europe from American pork up to recently, and, so far as known, 
none recently. Our slaughterhouses have been referred to as the 
great breeding centers of trichina, but this is true only as to 
slaughterhouses not under federal inspection. 

The r61e of the rat in the spread of trichiniasis can readily be 
appreciated when the statistics concerning the infection of these 
animals in slaughterhouses, stables, etc., are examined. Of 51 
rats captured in the Boston abattoir some years ago 39 (77 
per cent) were infected, and every one of 40 captured in a large 
exportation slaughterhouse in the same city was infected. Rats 
captured in stables where no hogs are kept, however, are usually 
less trichinized. Rats in localities where an epidemic of tri- 
chiniasis has recently swept through are usually extensively 

The prevalence of the disease in man is by no means parallel 
with its prevalence in other animals. The great controlling 
factor is the method of eating pork. Among such people as 
Americans, English and French, where pork is almost always 
eaten cooked, trichiniasis is rare and comes only from eating 
pork not thoroughly cooked, thus allowing a few worms to escape, 
though ordinarily not enough to cause serious disease. On the 
other hand very fatal epidemics have occurred among the Ger- 
mans, Austrians and Italians, who are very fond of raw pork, 
especially in the form of sausage or " wurst." Nearly all the 
epidemics in America have been among the Germans or Italians 
who still cling to their native habits. 

According to statistics compiled by Dr. Ransom in the five- 
year period from 1909 to 1914, 320 cases occurred in the United 
States, with 6 per cent fatality. The majority of all cases are 
reported as being caused by raw sausage or raw ham, and usually 
home-made or prepared in meat shops on a small scale. As stated 
by Ransom, '' no cases of trichinosis have been reported which 
trace back to sausage prepared in establishments conducted on 
a large scale. While it is not impossible that such cases might 
occur, the chances seem very remote, for the reason that in such 
establishments any one lot of sausage is invariably made up of 



small portions from a large number of hogs, and the infection, 
if any be present among the hogs involved, is necessarily greatly 
diluted, with the result that no individual consuming the sausage 
is at all likely to ingest a sufficient number of trichinae to produce 
an appreciable effect, even though the parasites should happen 
to survive the curing processes to which the commercially pre- 
pared sausage is usually subjected." 

Life History. — The trichina worm, Trichinella spiralis, occurs 
in quite a large number of animals, but the readiness with which 

infection occurs in dif- 
ferent species of ani- 
mals varies greatly. 
In America hogs are 
most commonly in- 
fected, and infection is 
common in rats which 
have access to waste 
pork; in Europe dogs 
and cats commonly 
show a higher percent- 
age of infection than 
hogs in a given local- 
ity. Man is highly 
susceptible, in fact so 
susceptible that he 
cannot be considered 
a normal host of the 
parasite. Rats and 
mice are sometimes 
thought to be the pri- 

FiG. 118. Larvse of trichina worms, Trichinella V> + f +V> 

spiralis, encysted in striped muscle fibers in pork, ^l^^ry noStS 01 tUe 

Camera lucida drawing of cysts in infected sausage, worm, but the fact that 
X 75 

these rodents succumb 
easily to infection while the parasites are still in the intestinal 
stage tends to show that rats are not normal hosts. Rabbits 
and guinea-pigs are easily infected when fed meat containing 
the worms, and a number of other mammals can occasionally 
be infected artificially. 

The worms gain entrance to the digestive tract as larvae en- 
cysted in meat (Fig. 118). In the intestine of the host they are 




freed from their cysts and take refuge among the villi and folds 
of the mucous membrane of the small intestine. Here they 
mature and copulate as early as the third day after being swal- 
lowed. The female worms (Fig. 119) are from three to four mm. 
(J to J of an inch) long, whitish in color, slender and tapering 
from the middle of the body toward the anterior end. The 
digestive tract of the worm consists of a long muscular pharynx, 
followed by a simple intestine. The forepart of the intestine has 
a very characteristic cross-barred ap- 
pearance. The reproductive system in 
both sexes is single, i.e., with only one 
ovary or testis, and occupies a large 
portion of the body. The arrangement 
is different in the two sexes, the male 
reproductive system opening at the 
posterior end of the body with the anus 
while the female system opens on the 
anterior third of the body. The male 
worms (Fig. 119) are only about half 
the size of the females. The adult 
intestinal worms are essentially short- 
lived, the males usually passing out of 
the intestine soon after mating, and 
the females as soon as they have given 
birth to all of their offspring. The 
adults usually disappear within two or 
three months after infection. 

^ . , . V • J.U ^ Fig. 119. Adult 

iricnina worms are peculiar m that worms, THchineiia 
they bring forth living young, free of ^^^^ (^) ^^^ female (9); 

,, ^ ^^ rr^^ ^ , • i V., vulva; emb., embtyos in 

the eggshell. They do not nourish oviduct; ov., ovary; t., testis, 
their young within the body as do truly ^ ^- ^^^^^r Claus, from 
viviparous animals, but merely retain 

the eggs in the uterus until they hatch. Sometimes the young 
worms begin to be born within a week after the parents have 
been swallowed by the host. They are most numerous in the 
circulating blood between the eighth and 25th day after infection, 
though the greatest invasion occurs on the ninth and tenth days. 
When born they are scarcely 0.1 mm. (^j^^^ of an inch) in length. 
The mother worms usually burrow into the walls of the intestine 
far enough so that the young can be deposited directly into a 





lymph or bloodvessel rather than into the lumen of the intestine. 
The larvae are carried in the blood or lymph stream, and are 
distributed to nearly all parts of the body. They leave the 
capillaries in the striped muscles and penetrate into the fibers. 
Although young migrating larvae may accidentally be carried 
to other tissues, and have even been found in the cerebrospinal 
fluid and in the mammary glands and milk of a nursing woman, 
they are apparently incapable of developing in any tissue except 

Fig. 120. Larvae of trichina worms burrowing in human flesh before encyst- 
ment. From preparation from diaphragm of victim of trichiniasis. X 75. 

voluntary muscle. They may settle in the heart muscle, but 
degenerate there without continuing their development. The 
muscles particularly favored by the worms are those of the dia- 
phragm, ribs, larynx, tongue and eye, which, as noted by Staubli, 
are among the most active muscles and the muscles with the 
richest blood supply and largest amount of oxygen. According 
to Flury trichinae have a high glycogen content, and probably 
subsist on the glycogen stored in the striped muscles; in fact 
the abundance of glycogen may account for their location in 
these muscles. 



When the larvae have arrived at their destination in the muscles 
they thread their way between the fibers towards the ends of the 
muscles (Fig. 120), ultimately penetrating the individual fibers 
where they coil up into loose spirals, constantly coiling and un- 
coiling as much as their close quarters will permit. When worms 
which are still boring are teased out of the flesh and warmed to 
blood heat, they can be seen constantly tightening and loosening 
their coiled form, reminding one of a fist being alternately clenched 
and unclenched. After entering muscle fibers the worms grow 
rapidly in size to a length of one mm. ( jV of an inch), ten times their 
original size, and become sexually differentiated. The inflam- 
mation caused by the movements and waste products of the 
animals results in the degeneration of the enclosing muscle fibers 
and in the formation, beginning about a month after infection, 
of connective tissue cysts around the young worms. The cysts 
(Fig. 118), which are completely developed in from seven to nine 
weeks, are lemon-shaped, from 0.25 to 0.5 mm. (y^^ to yV of an 
inch) long, lying parallel with the muscle fibers. As a rule only 
one or two worms are enclosed in a cyst but as many as seven in 
a cyst have been observed. When first formed the cysts are 
very delicate and can only 
be seen by careful focusing 
with the microscope, but 
they gradually grow thicker 
and more conspicuous, and 
after seven or eight months 
there begins a deposit of 
chalky calcareous matter 

(Fig. 121 A). This process Fio. 121. Stages in calcification of trichina , • 

, . , , 1+ ' +V» '^' ^^^^ calcified; B, thin layer of calcareous 

ultimately results in tne material over whole cyst, worm beginning to 

entire cyst becoming hard- degenerate; C, complete calcification. (After 

J . , 1 Ostertag.) 

ened into a calcareous 

nodule (Figs. 121B and C), and even the enclosed worm, 
which usually degenerates and dies after some months, becomes 
calcified after a number of years. There are cases, however, 
where the trichina worms do not die and disintegrate so soon, and 
the calcification process is much slower. There are records of 
these worms found living in cysts in hogs 11 years after in- 
fection and in man 25 to 31 years after, though it is doubt- 
ful whether in some of these cases a fresh infection did not 


occur unknown to the patient or to the observers who made 
the records. 

The larval worms, which, as pointed out by Ransom, on account 
of their advanced stage of development are comparable with 
the nymphs rather than the larvae of arthropods, when encysted 
in the flesh of some susceptible animal never develop further 
until eaten by another susceptible animal. If they are eaten the 
cyst is dissolved off in the intestine of the new host, the larvae 
are set free in the digestive tract, and within three days be- 
come sexually mature and copulate, to begin the performance 
all over. 

Obviously man usually if not always becomes infected from 
eating infected pork, whereas hogs may be infected not only 
by eating scraps of raw pork but also by eating the bodies of 
infected rats and mice. The latter animals are infected in 
a similar manner. The number of trichina worms which may be 
harbored by a single host is almost incredible. According to 
the writer's investigations, the sausage which was the cause of a 
recent epidemic in Portland, Oregon, contained over 2,000,000 
larvae to the pound at a very conservative estimate, and in a bit 
of human muscle from the diaphragm of an Italian who fell 
victim to the disease the number of worms was even greater. 

The Disease. — The disease caused by trichina worms is more 
fatal to man than to any other animal, the fatality sometimes 
rising to 30 per cent or more of the cases. Even in man the 
worms, if eaten only in small numbers, produce no serious or 
even noticeable effect. When eaten in great numbers, however, 
as would always happen in eating heavily-infected raw or under- 
done pork, the worms produce symptoms so much like typhoid 
fever that the disease is undoubtedly often diagnosed as such. 
The course of the disease, as described by Ransom, is somewhat 
as follows : the first symptoms of the disease — diarrhea, ab- 
dominal pains and intestinal catarrh — are the result of irritation 
of the intestine by the adult worms, especially the females, which 
burrow deep to deposit their young. Except in very light cases, 
a sort of general torpor is noticeable, accompanied by weakness, 
muscular twitching, etc. A very striking symptom, which ap- 
pears in about a week and lasts for a few days, is a marked puffi- 
ness or edema of the face and especially of the eyelids. As 
pointed out by Ransom, the gravity of the case cannot be judged 


from the severity of the first symptoms. In some of the worst 
cases the first symptoms are very mild. 

In nine or ten days or longer the second stage of the disease 
appears, accompanying the period of migration of the larvse. 
This is the period which is frequently fatal. The most pro- 
nounced symptoms are intense muscular pains and rheumatic 
aches, with disturbances in the particular muscles invaded, in- 
terfering with the movements of the eyes, mastication, respira- 
tion, etc., the respiratory troubles becoming particularly severe 
in the fourth and fifth weeks of the disease, in fact sometimes 
so severe as to cause death from dyspnea or asthma. Profuse 
sweating and more or less constant fever, though sometimes 
occurring in the first stage also, are particularly characteristic 
of the second stage. The fever is commonly absent in children. 
The third stage, accompanying the encystment of the parasites, 
begins about six weeks after infection. The symptoms of the 
second stage become exaggerated, and in addition the face again 
becomes puffy, and the arms, legs and abdominal walls are also 
swollen. The patient becomes very anemic, skin eruptions occur, 
the muscular pains gradually subside and the swollen portions 
of the skin often scale off. Pneumonia is a common compU- 
cation in the third stage. 

Trichinella is unique among worms in causing constant fever. 
It is probable that the fever as well as certain changes in the 
blood corpuscles and chemical changes in the invaded muscles 
is due both to poisonous substances given off by the worms and 
to poisonous substances resulting from destroyed muscle tissue. 
Such substances have been found by Flury and Groll and others 
in cases of Trichinella infection. They are substances which 
act on the muscles themselves, on the nervous system, and on the 
bloodvessels. It is quite evident, as pointed out by Herrick, that 
with the invasion of the blood and tissues by millions of larvae 
and with the breaking down of large amounts of muscle tissue 
a constant inoculation of the infected person with poisonous 
protein material is taking place, a condition which always gives 
rise to fever. Certain volatile acids are produced by the muscle 
degeneration, and these are considered by Flury to account for 
the muscular pains. Other toxic substances account for most of 
the other symptoms of the disease, e.g., the marked increase in 
certain kinds of white blood corpuscles, the eosinophiles. 


The duration and final outcome of the disease is variable, 
according to the heaviness of the infection. Death, as remarked 
before, may frequently result, and according to Ransom most 
commonly occurs from the fourth to the sixth week. It rarely 
occurs before the end of the second week or after the seventh. 
Recovery usually does not occur in less than from five to six 
weeks after infection, and often not for several months. Re- 
current muscular pains and weakness may continue for years and 
a stiffness may persist indefinitely in the invaded muscles. Com- 
monly cases in which a copious diarrhea appears early in the 
disease are of short duration and mild in type. Young children, 
due either to smaller quantities of pork eaten or to greater tend- 
ency to diarrhea, are likely to recover quickly. 

Treatment and Prevention. — The search for a specific remedy 
for trichiniasis has so far been futile. Even the adult worms in 
the intestine are much more difficult to dislodge or destroy than 
are other intestinal worms, since they bore so deeply into the 
intestinal walls that the ordinary drugs do not affect them. Even 
were it possible to drive out the adults readily, this often could not 
be done in time to prevent disease or death, since the infection is 
seldom recognized before the larvae are already produced and are 
migrating throughout the body. This is the critical stage of the 
disease; if the system can endure the irritation and inflam- 
mation produced by the burrowing of millions of worms and 
can withstand the effects of the toxins produced both from the 
worms themselves and from the destroyed tissues during the 
first and heaviest onslaught of the newly produced larvae, the 
danger is past. The fever, the muscular pains, amounting to 
agony for a time, and the intestinal disorders continue for weeks 
but gradually subside. The treatment employed during all this 
time can only be systematic and of general nature — efforts to 
reduce the fever, to permit sleep, to keep the digestive system 
in as good order as possible and to do all that can be done to keep 
up the vitality and general health. 

It is possible that if the trichina worms could be isolated and 
ground up, and injected into the blood, an active immunity 
could be built up as in the case of typhoid vaccinations. Passive 
immunity by injection of serum from a convalescent has been 
stated by Salzman to have some curative as well as preventive 
value, but this work needs confirmation. The disease, however, 


is not so prevalent or so difficult to prevent by otfier means as 
to make promiscuous immunization justifiable, even if possible. 
A more hopeful though so far unproductive line of research 
regarding the treatment of the infection lies in experiments 
with drugs or serum to kill either the adult worms in the intestine 
or the larvae before they begin destroying the tissues. 

Personal preventive measures against trichiniasis are easy 
and consist simply in abstinence from all pork which is not 
thoroughly cooked. Experiments by the U. S. Bureau of Animal 
Industry show that trichinae are quickly destroyed by a tem- 
perature of 55° C. (131° F.), since the body protoplasm is coagulated 
at this temperature, but pork must be cooked for a length of time 
proportionate to its weight in order to insure the permeation 
of heat to the center. Experiments show that at least 30 to 
36 minutes boiling should be allowed to each kilogram of meat 
(2^ lbs.). Hurried roasting does not destroy the parasites as 
long as red or raw portions are left in the center. Cold storage 
for 20 days or more at temperatures below 10° F. has been shown 
by Ransom to be destructive to trichinae. The regulations of 
the U. S. Bureau of Animal Industry, relative to pork prod- 
ucts customarily to be eaten without cooking, require freez- 
ing for 20 days at a temperature of not higher than 5° F., 
or curing in accordance with certain specified processes. 
Temperatures above 10° F. are more or less uncertain in 
their effects. Salting and smoking are not efficacious unless 
carried out under certain conditions. Thorough salting is effec- 
tive, provided the meat is left for some time for the salt to per- 
meate it. Large pieces of pork placed in brine have been known 
to contain living trichinae for over a month. The parasites in 
sausages are destroyed in 24 hours by hot smoking whereas they 
resist cold smoking for three days. 

Prevention of trichiniasis by meat inspection methods is at best 
only partial, and, while meat inspection might help to lessen the 
chances of the disease, it should not be implicitly relied upon. 
Probably in an ordinary meat inspection all heavy infections 
would be found, provided the inspector has been doing his work 
properly. The inspection usually consists in the microscopic ex- 
amination of a bit of muscle from tongue and diaphragm; if 
the examination is negative, the hog is passed. Obviously light 
infections must frequently escape notice, and the false sense of 
security which is the result of knowledge that meat has been 


'' inspected " may do much damage. There is no inspection 
for trichinae in force in the United States at the present time. 

Much could be done to prevent the prevalence of trichina in- 
fection in pork by preventing hogs from eating food which might 
be infected. Hogs should never be allowed access to the car- 
casses of other hogs or to the dead bodies of rats and mice, or 
to waste scraps of pork. Dead hogs or waste pork, if there is 
any possibility of their being infected, should not be thrown where 
rats and mice could prey upon them. If these principles were 
carefully followed out, there is no doubt but that trichiniasis 
could be reduced to a much greater extent than it has been. 

The symptoms of trichina disease in hogs are much less evident 
than in man, and there is no certain diagnosis of it in living ani- 
mals except by microscopic examination of the muscles for the 
detection of the larvae. When heavily infected, hogs show severe 
intestinal disorders, abdominal pains and stiff muscles, but there 
is nothing diagnostic in these symptoms. A farmer who drives 
sick hogs to market, however, in order to get rid of them, with- 
out giving proper warning of their condition which might make 
possible the discovery of trichina infection if present, should 
be considered guilty of criminal negligence, and punished in 
accordance with the damage done by this neghgence. This is 
particularly true if he feeds his hogs waste containing raw meat, 
or allows them to feed upon dead animals — a very common 

As has recently been pointed out by Stiles, there is no prac- 
tical or proper method of inspecting meat by which the absence of 
Trichinella can be guaranteed, and it is therefore unjust to hold 
a butcher responsible for cases of trichiniasis which may result 
from the eating of pork sold by him. There are laws which pro- 
vide that ^' diseased meat " shall not be sold and that an implied 
warranty of fitness for food goes with any sale of food. Neither 
of these laws, however, can be unreasonably enforced. Techni- 
cally all meat is diseased, since there are no market animals 
which are not parasitized in some way. As to the " implied 
warranty," this can go only with an implied guarantee on the 
part of the buyer that the food will be properly prepared before 
being eaten. Clams in the shell, unhusked corn and uncooked 
beans are guaranteed as being fit for food only when properly 
prepared. In like manner pork is sold with the understanding 


that it will be properly prepared, i.e., thoroughly cooked. Raw 
pork, since it is likely to contain Trichinelloe which may cause 
disease, and since the absence of these worms cannot be guaran- 
teed by any practical inspection now known, is unfit for food and 
therefore cannot be guaranteed if eaten raw. As Stiles has 
pointed out, great and unjustifiable loss may result from too 
stringent enforcement of the laws mentioned above. 


General Account. — One of the most interesting and puzzling 
groups of human parasites are the members of the nematode 
genus Filaria. They are extremely common parasites in all 
tropical countries, have a unique and extraordinary life history, 
are associated with many serious pathological conditions and 
have figured prominently in the history of medical science. 

Dr. Timothy R. Lewis first discovered these worms swarming in 
human blood, while working on tropical diseases in India. They 
had previously been observed in various bodily excretions but 
only in rare cases and in small numbers. They were found 
in enormous numbers in the blood, but only at night. The 
worms were evidently larvae and since they only rarely and ap- 
parently accidentally escaped from the body with excretions, 
the thought occurred to Manson that they must be liberated 
from the blood by some nocturnal blood-sucking insect. Man- 
son and others later proved this theory to be correct, and thus 
took the first step toward our present knowledge of the biologi- 
cal transmission of disease by insects, a step which marked the 
beginning of a new era in modern medicine. 

Many species of Filaria from human blood have been described, 
some of which undoubtedly are not valid species. Some species 
apparently produce no pathological conditions whatever, while 
others are associated with, and are usually considered to be the 
direct cause of, a large number of diseased conditions. Some of 
the species are of limited geographic distribution while others 
are of world-wide range, probably due to differences in the ex- 
tent of the distribution of the intermediate host. In some 
tropical localities 50 per cent or more of the population are para- 
sitized by these animals. In South China ten per cent of the entire 
population is said to be infected and in some South Sea Islands 
over half of the inhabitants are infected. Recently in an exam- 
ination of 949 natives from the Congo-Cameroon country of 



Africa, about 74 per cent of the men, 79 per cent of the women and 
33 per cent of the children were found to be filariated. 

The blood-dweUing filarise which are readily observed are, as 
remarked above, only larvae, the adults being much larger, long, 
slender worms which live in the lymphatic vessels, connective 
tissue or other tissues of the body. It is to these adult worms 
and not to the larvae that the so-called " filarial diseases " are 
supposed to be due; the blood-living worms apparently cause 
no serious symptoms. The larvae have been termed " micro- 
filariae " to distinguish them from the adult worms. 

Filaria hancrofti 

The most widespread species and most important from a 
medical point of view is Filaria hancrofti. This nematode occurs 
more or less abundantly in all warm climates of the world, north 
to southern United States and southern 
Europe and Asia, and south to southern 
Australia and Patagonia. 

Life History. — The adult Filarice 
were not discovered for many years pio. 122. Adults of Filaria 
after the larvae had been found in the hancrofti, female ( 9 ) and 

1 1 T . ,, • j.1. J male ($). Natural size. 

blood, smce they occur in the deep- ^^f^^j. Manson.) 
seated lymphatic vessels where they could 

be observed only on post mortem examinations. They are very 
long, slender nematodes (Fig. 122), the females three or four inches 
in length and hardly greater in diameter than a horsehair, and 

the males about half this size. In their 
normal habitat in the lymph vessels the 
males and females live coiled up to- 
gether, sometimes several pairs of them 
Fig. 123. Microfilaria of in a knot. The male worms, in addition 
~uteTu:t pai'e^rr to their smaller size, may be distin- 
rounded by delicate mem- guishcd from the females by the coiled 
brane. (After Bahr.) ^^.^ ^j^.^^ reminds One of a vine tendril. 

The greater part of the body of the female is occupied by a pair 
of uteri, which in the adult are always filled with eggs. 

The eggs (Fig. 123) usually hatch before they are laid so that 
living young swarm forth from the parent worm, but in excep- 
tional cases the eggs are deposited before hatching. The young 

c^ %^ 



worms reach the blood by way of the lymph stream and these 
grow to about 300 /x (a little over j^^ of an inch) in length. They 
are delicate colorless worms (Fig. 124A), blunt at the anterior 
end and tapering to a slender point at the tail end, and are 
entirely enclosed in a remarkably delicate transparent sheath, 
which, although it fits as tightly as a glove over a finger, is too 
long for the animal and can be seen projecting at either end. The 
sheath may be looked upon as a wonderful adaptation to prevent 

the worms from being able to 
bore through the bloodvessels 
and escape from the blood, in 
which case they would miss 
their chance for " salvation." 
The internal organs are in a 
very rudimentary condition. 
The most remarkable cir- 
cumstance connected with the 
life of these microfilariae is the 
periodical appearance and dis- 
appearance of them in the 
blood of the peripheral vessels. 
If the blood of an infected 
person is examined during the 
day few if any worms can be 
found, but as evening ap- 
proaches they begin to appear 
Fig. 124. Comparison of microfiiariffi ; and Continue to increase Until 

A mf. bancrofti (large with «heath) ; 5, ^^^^ midnight, after which 
mf. Persians (small, blunt tail, no sheath); ^ ' 

c, mf. loa (large, with sheath); D, mf. they decrease again until 

juncea (demarquaii) (small, sharp tail, no rnnrm'ncr "Hnrino- +V>p niaVit 

sheath). X75. (After Manson.) mornmg. uurmg tne nignt 

when they are most abun- 
dant there may be as many as 500 worms in a single drop of 
blood. If the parasites are assumed to be evenly distributed 
throughout the peripheral circulation, this would imply the 
presence of several milHon worms in the body. The periodic 
appearance and disappearance of microfilariae in the blood is not 
invariable. When an infected person is made to sleep in the 
daytime instead of at night, the appearance and disappearance 
of the parasites in the peripheral bloodvessels can be reversed, 
implying that the distribution of the parasites may be dependent 


on some physiologic condition of the host. Still stranger is the 
fact that in many of the South Sea Islands, Samoa, the Fiji 
Islands and the Philippine Islands, the microfilariae show no 
periodic disappearance, although if a person infected in a place 
where the parasites do show periodicity be transferred to one of 
the above-named islands, the periodic phenomena still persist. 
As stated before, Manson, the great English parasitologist, with 
characteristic ingenuity, suspected that this parasite, so abundant 
in the blood, must make use of some blood-sucking insect as a 
means of transmission, and further concluded that the night 
swarming of the parasites in the peripheral circulation might be 
an adaptation to the nocturnal habits of an intermediate host. 
Working on this hypothesis, he discovered that certain mosquitoes 
acted as the liberating agents for the parasites. The fact that 
in those islands where no periodicity is shown the usual inter- 
mediate host is a diurnal mosquito Aedes (or Stegomyia) pseudo- 
cutellaris, certainly bears out the adaptation hypothesis. On the 
grounds of the apparently distinct habits and different adaptation, 
the non-periodic microfilariae have been separated into a distinct 
species, or at least subspecies, to which the name Filaria philip- 
pinensis was applied by Ashburn and Craig in 1906. Zoologists 
are coming more and more to realize the importance of physio- 
lologic as well as morphologic characteristics as a basis for sepa- 
rating species and subspecies. The case of these filariae is by no 
means unique in the organic world. Physiologic and biochemical 
reactions are the main basis for the classification of the Bacteria, 
and some Protozoa can be distinguished better by their patho- 
genic effects and biochemical reactions than by their morphology. 
To continue their development the larval worms must be 
sucked up by the females of certain species of mosquitoes. A 
considerable number of species of mosquitoes of several different 
genera, including Anopheles, Aedes and Culex, may serve as 
intermediate hosts for F. bancrofti (see p. 449). The commonest 
and most widespread transmitting agent is the house mosquito 
of the tropics, Culex quinquefasciatus (fatigans), a species which 
also transmits dengue. A few hours after being swallowed by 
a susceptible mosquito the microfilariae (Fig. 125 A) become rest- 
less and endeavor to escape from their sheaths. This they 
eventually accompUsh by butting against the anterior end, 
having gained as much impetus as their close quarters will allow. 



Once free, the little larvae (Fig. 125B) move actively about in 
quite a different manner from the ineffective wriggling in which 
they indulged while enclosed in the sheath, and by means of which 
they were unable to " get anywhere." The active liberated 

worms make their way 
to the thoracic muscles 
of the mosquito, where 
they He between the 
muscle fibers and par- 
allel with them. The 
body, growing rapidly, 
by the fourth to tenth 
day becomes thick and 
sausage-like (Fig. 
125C), with a short, 
pointed tail, but it later 

Fig. 125. Development of Filaria bancrofti in increases greatly in 

mosquito; A,aswithdrawnwithblood(first24hours^ j^^^j^ ^^^ decreases 
in stomach; B, form found m tissues just outside ^ 

stomach (48 to 72 hours after ingestion) ; C, form slightly in thickueSS, 

found in muscles on fourth day; i) mature larval thuS becoming long and 
lorm, ready for transmission, in proboscis (two or . . 

more weeks after ingestion). X 150. (After Lewis slender again (Fig. 

from Nuttaii.) 125D). Meanwhile the 

internal organization of the animal undergoes a great change. 
The central core of cells gradually becomes differentiated into a 
digestive tract, separated from the body wall by a true body 

Fig. 126. Mature larvae of Filaria bancrofti in thoracic muscles and prob 
of mosquito. (After Castellani and Chalmers.) 

cavity. By the time the larva has reached its full size — about 
1.5 mm. {^^ of an inch) in length — the digestive tract is a com- 
plete tube with both mouth and anal openings. While these 
changes are taking place, the larval worm, though capable of 
activity, remains at rest between the muscle fibers (Fig. 126), 


but it now becomes active again and migrates into the connective 
tissue of the anterior parts of the body of its host, and ultimately 
into the proboscis (Fig. 126). Here the worms lie in pairs, or 
several pairs together, awaiting an opportunity to re-enter a 
human host. 

The length of time required for the metamorphosis and de- 
velopment in the mosquito varies from about two weeks under 
ideal conditions to several weeks under less favorable circum- 
stances. When the infected mosquito bites a human being, the 
worms emerge from the proboscis and bore through the skin 
in the immediate vicinity of the wound, though not directly 
through the puncture. Experiments have shown that the larvae 
can not be deceived into entering vegetable tissue, such as a 
banana, even though for many days they have been at the tip 
of the proboscis, ready to emerge when the mosquito bites into 
warm-blooded flesh. 

It is possible that these parasites may occasionally find entrance 
to the human body by other paths than the mosquito's bite but 
this has not yet been proved. The popular belief that bad water 
is the cause of filarial infection is probably due to the effect of 
stagnant water on the abundance of mosquitoes, and not to the 
emergence of the larvae from the bodies of mosquitoes into water. 
Bahr has shown that the larvae will live in water only seven 

Once back in a human body from this period of " purgatory " 
in the body of a mosquito the larvae migrate to the lymphatic 
vessels, there to attain sexual maturity, copulate and reproduce. 
The larvae of the next generation escape again to the blood as 
microfilariae, and the cycle is complete. The adult worms may 
five for many years and even the microfilariae are able to live for 
a considerable time, as shown by their continued presence after 
the death of the parents. 

Filarial Diseases. — The disease symptoms which are asso- 
ciated with Filaria hancrofti can all be traced to interference 
with the lymphatic system. In many cases there are no ill 
effects of the infection felt for many years, or perhaps never, 
though sooner or later there is usually produced anemia, en- 
largement of the spleen and fever. More serious are the effects 
produced by obstruction of the lymphatics. This causes great 
enlargement of the lymph vessels and the diversion of the lymph 



from its normal channel, and results in varicose lymph glands 
(Fig. 127C) and vessels and in distended lymph sacs which may 
burst into the kidneys, bladder or body cavity. Often the 
microfilariae disappear from the blood, probably on account of the 
death of the parents, but the obstruction of the lymphatics 
continues to exist, as do the evil effects resulting therefrom. 

Fig. 127. A few extreme cases of elephantiasis; A, of legs and feet; B, of 
scrotum; C, varicose groin gland; Z), of scrotum and legs; E, of mammary glands. 
{A and B sketched from photos from Castellani and Chalmers; C, D and E from 

One of the most frequent results of a blocking of the lymph 
vessels is an enormous enlargement of the part of the body 
in which the blocking occurs, known by the suggestive name, 
"■ elephantiasis " (Fig. 127). In most cases the lower Hmbs and 
scrotum are the parts affected, though almost any portion of 


the body may occasionally become enlarged. In some South 
Sea Islands 50 per cent or more of the population are thus affected. 
The disease begins by repeated attacks, at intervals of from a 
month to a year, of '' elephantoid " or filarial fever in which 
chills and high fever accompany a painful swelling of the parts 
affected. These attacks, also known as lymphangitis, end in an 
emission of lymph and a partial subsidence of the swelling. 
But each attack leaves a little more permanent tissue, so that in 
time the growth, which is hard and unyielding, develops to enor- 
mous proportions. Sometimes an affected leg may reach a diam- 
eter of several feet. In one case recorded by Manson, a scrotum 
affected by elephantiasis reached a weight of 224 pounds, though 
it must be admitted that this is unusual. 

Another condition resulting from filarial infection is the escape 
of the contents of lymph vessels into the kidneys or bladder, a 
condition technically known as " chyluria." The urine is milky 
and coagulates after standing a short time. This condition lasts 
for a few days or weeks, then ceases and returns at irregular 
intervals. It produces severe anemia and a general feeling of 
ennui, and saps the vitality. 

Occasionally the presence of dead filarise in the body leads to 
the formation of abscesses which sooner or later discharge. If 
on any of the appendages, no further trouble results, but such 
abscesses in the internal regions of the body may have serious or 
fatal effects. 

Though very probably some of these so-called " filarial dis- 
eases " are caused directly by the filarise, the exact relation of 
F. bancrofti to all of the pathological conditions associated with 
its presence in the body is far from settled. Dutcher and Whit- 
marsh, of the United States Army, in investigations of filarial 
diseases in Porto Rico recently obtained pure cultures of a certain 
type of bacterium from the blood or serum of 15 patients, all 
but one of whom was affected by some form of filarial disease, 
whereas in unaffected individuals, with one exception which was 
looked upon as a " carrier," the cultures from the blood remained 
uniformly sterile. In a few cases in which filarial diseases were 
present the bacterium was not found but it was believed that 
either the infection was so light that the cultures did not happen 
to become contaminated, or that the infection had died out. 
A number of other observers have obtained cultures of bacteria 


from blood and tissues of elephantiasis cases. Others, however, 
have found the blood quite sterile. It is worth noting in this 
connection that the number of cases of elephantiasis or other 
filarial diseases in which microfilariae are not present in the blood 
is considerably greater than those in which the larval parasites 
are present. This is usually explained by assuming that the 
parent filarise have died or that the larvae cannot reach the blood 
on account of a blocking of the lymph channels by fibrous growths. 
Cruickshank and Wright, for instance, in 130 cases of elephantiasis 
in Cochin, found only 12 with microfilariae in the blood. The 
observations recorded above are certainly significant and may 
revolutionize our ideas in regard to filarial diseases. However, 
even if some of the " filarial diseases " were found to be due to 
bacteria, the filariae might still be incriminated as carriers of 
the bacteria, and therefore as an indirect cause of the diseases. 
Treatment and Prevention. — So far there is no widely-ac- 
cepted treatment by which the parent filariae, and with them the 
microfilariae, can be destroyed. The number of the larvae is 
reduced, however, by injections of thymol, ichthyol and other 
drugs, and such injections might prove to be a useful preventive 
measure. McNaughton has recently reported five cases of 
filarial infection successfully treated by injections of salvarsan; 
one case was of ten years' standing. Usually the only course 
of the physician is to relieve as far as possible the abnormal 
conditions associated with the presence of the worms. Such 
relief, of course, varies greatly with the diverse pathological 
conditions which may arise. Varicose glands and vessels, un- 
less causing great discomfort, are usually left alone, since they 
are lymph channels substituted for the normal ones in the body 
which have been blocked, and it is therefore dangerous to inter- 
fere with them. In cases of elephantoid fever the only treat- 
ment is such as would tend to relieve the pain in the swellings 
and the fever, and perhaps in severe cases the pricking of the 
swollen part to allow the exudation of the collecting lymph. 
In chyluria the treatment consists in rest and in making the 
pelvic regions as comfortable as possible to prevent pressure 
which would tend to burst the lymphatics and force the lymph 
into the kidneys or bladder. Elephantiasis, the commonest 
expression of filarial disease, is seldom completely recovered 
from. Formerly the only treatment was temporary reduction 


of the swellings and prevention of further growth by care of the 
general health, avoidance of violent exercise, massage and tight 
bandaging. In severe cases of elephantiasis of the leg physicians 
sometimes cut off great masses of the elephantoid tissue, grafting 
on new pieces of skin to cover the parts operated on. Removal 
of enlarged growths of the scrotum can usually be accomplished 
successfully. Another method which has been used with some 
success is an operation for the draining of the lymph from the 
tissue all the way into the bone or even from the bone itself. 

Castellani has recently found a method of reducing elephantoid 
tissue which will probably supplant all of the above methods. 
This consists in the injection into the diseased tissues of a drug, 
fibrolysin, which, as its name implies, has the property of destroy- 
ing fibrous connective tissue. Elephantoid swellings are re- 
ported to have been cured by this method in a few months. 

Prevention of filarial diseases can best be accomplished by 
anti-mosquito campaigns. As far as is known at present mos- 
quitoes are the only means of transmission which the parasites 
have. The same preventive measures, therefore, which serve 
as preventives against malaria, serve also against Filaria han- 
crofti, and since the former disease is found practically every- 
where that the filarise are found, it is possible to prevent the 
two diseases with one effort. People who carry filariae in their 
blood should be prevented, as far as possible, from exposing 
themselves to mosquitoes. In the places where the micro- 
filariae are periodic and the transmitting mosquitoes are nocturnal 
this should be perfectly possible, although in such localities as 
the Philippines and Samoa, where the intermediate host is largely 
diurnal, it would present almost insuperable difficulties. In 
places where Filaria is abundant and mosquitoes are not ex- 
terminated the carrying at night of a bottle of disinfectant, as 
alcohol or dilute lysol, for immediate application to mosquito 
bites would be well worth while. 

Other Species of Filaria 

There are, as previously stated, a number of other species of 
Filaria which inhabit the human body. Filaria (or Acantho- 
cheilonema) perstans is extremely common in the natives through- 
out Central Africa and also in parts of northern South America; 


it is confined to regions of heavily forested tropical swamps. 
In some districts in Uganda it has been found in 90 per cent of 
the inhabitants. The microfilariae of this species (Fig. 124B) 
are smaller than those of F. hancrofti, have a blunt tail and 
lack the sheath which is so characteristic of F. hancrofti. Fur- 
thermore they show no tendency to disappear periodically from 
the peripheral vessels. The adult worm, which has rarely been 
found, is smaller than F. hancrofti (about three inches in length) 
and occurs in the connective tissue of the abdominal and peri- 
cardial cavities. The normal transmitting agent, probably some 
species of mosquito, is not certainly known. No disease symp- 
toms which can be correlated with the presence of the parasite 
have yet been demonstrated. 

Another species, F. juncea (demarquaii), of which the larva 
(Fig. 124D) is small and without a sheath, as in F. perstans, but 
with a sharp tail, occurs in the West Indies and northern South 
America. It is not known to cause any diseased conditions. 
The adults live in the mesenteric tissues. In many Indians in 
British Guiana F. perstans and F, juncea occur together in the 
blood, and in some cases the presence of F. hancrofti compli- 
cates the matter still more. 

F. magalhaesi is another species about which very little is 
known. A pair of adult worms were found only once, in the 
heart of a child in Rio de Janeiro. They were of unusually large 
size, the female measuring over six inches in 
length and the male about three and a half 
inches. Nothing is known of the life history 
or pathological effects. 

The Lea Worm. — Of somewhat different 
nature from the above species of Filaria is F. 
loa or Loa loa (Fig. 128), a parasite found on 
Fig. 128. Adult ^j^^ ^^g^ ^^^g^ q£ Africa, especially in Congo, 

loa worms, female _ . 

(9) and male {$). which, as an adult, creeps in the connective 

Looi's'f '''^' ^'^^^'' ^iss^e ^f i^^ ^ost just under the skin. The 
female varies, probably with age, from two to 
two and one-half inches in length, and is semi-transparent and very 
slender. The male resembles the female, but is only from one to 
one and one-half inches in length. Both sexes are characterized 
by numerous irregularly distributed pimple-like elevations of the 
skin. The loa worm shows a special preference for the connective 



tissue in and about the eyes, but may also be found creeping 
under the skin of fingers, breast, back, etc. A loa is said to travel 
at the rate of about an inch in two minutes, and to become 
especially active in the presence of direct warmth on the skin, 
as before a fire. The migration of the worms causes itching and 
a " creeping " sensation, and in some unexplained way gives rise 
to temporary swellings, from half an inch to four inches in diame- 
ter, known locally as " Calabar swellings." These swellings 
may shift their position an inch or more a day, and may disap- 
pear to reappear somewhere else. Thi^ relation of Loa to Cala- 
bar swellings has not been definitely proved but there is strong 
evidence for it. In one case Manson succeeded in finding 
great numbers of microfilariae of Loa in lymph taken from one 
of these swellings, a fact which gives color to Hanson's hypothe- 
sis that the swellings might be due to the emission of larvae from 
the parent worm into the connective tissue. The larvae of the 
parasite (Fig. 124C), very closely resembling the microfilariae 
of F. hancrofti, occur in the blood in great numbers, but they 
have a periodicity di- 
rectly opposite to that 
of the latter species in 
that they swarm in the 
peripheral blood in the 
daytime and withdraw 
to the larger vessels at 
night. The living 
larvae of the two species 
cannot readily be dis- 
tinguished from each 
other in fresh blood, 

1 J. •_ J • J ^« J ^4.„,' ^j Fig. 129. Comparison of killed and stained speci- 

but m dried and Stamed mens of M^crofilar^a bancrofti and mf, loa. A mf. 

preparations the dead hancrofti, — note graceful curves; B, mf. loa, — note 

oro-ani^rYmpflnPnmlvhp irregular scrawl-like curves; C, tails of m/. Zoa; D, 

organisms can easny Oe ^^^^ ^^ ^^ hancrofti. (After Manson.) 

identified. The micro- 

filaricB hancrofti are found lying in smooth graceful curves (Fig. 
129 A), while the microfilarice loa die in ungraceful and irregular 
scrawl-like positions (Fig. 129B), with the tail nearly always 
sharply turned back (Fig. 129C). 

There is much evidence that the intermediate hosts of L. loa 
are mangrove flies of the genus Chrysops, which belong to the 



horsefly family, Tabanidse, and resemble our deerflies (see p. 489 
and Fig. 227). Leiper succeeded in obtaining a development of 
microfilaria loa in two different species of Chrysops. In recent 
investigations in a heavily infested district of Africa, Kleine 
found over five per cent of 600 Chrysops infected with larval filarise, 
which he took to be Loa loa. The worms were found developing 
in the fatty connective tissue surrounding the tracheae in the 
abdomen of the insects and later making their way forward toward 
the proboscis. In two cases larvse were induced to emerge from 
the fly's proboscis into a few drops of salt solution. That these 
worms were really the larvse of L. loa is entirely probable, but 
there is no definite proof of it. 

The development of the parasites after they have been re- 
turned to a human body is extremely slow, in fact the evidence 
indicates that full sexual maturity is not reached for a number of 
years. The length of life of the worms is unusual; there are 
cases recorded in which these parasites were abstracted from 
patients who had been away from endemic regions for ten or 15 
years. Microfilariae are not invariably found in the blood of 
infected persons. Children, especially, are prone to infection 
with the creeping worms, usually sexually immature, without 
having any larvae in their blood. Even sexually mature para- 
sites apparently do not liberate larvae constantly. 

Surgical removal of the parasites when they present themselves 
in the eye or subcutaneous tissue is the only remedy so far known. 
Many of the parasites probably do not expose themselves at all, 
but remain in the deeper tissues and organs of the body. When 
they die in the tissues they probably become calcified as do the 
adults of other filariae. 

Onchocerca volvulus. — Closely related to the filariae is 
another parasite of the subcutaneous connective tissue, Oncho- 
cerca volvulus. It occurs over a large portion of the west coast 
and central portion of Africa. Three cases of infection with the 
same or a closely alhed species has recently been reported by 
Th6z6 from French Guiana. The adult female is several inches 
in length, and slender as a hair; the male is stouter, and little 
over an inch in length. The adults lie in couples in fibrous tumors 
which can be seen readily under the skin. The tumors vary in 
size from about one cm. (| of an inch) in diameter to the size 
of a pigeon's egg, and are found most commonly on the hip, 



sides of the chest and upper part of the back, and sometimes 
in the arm and knee pits and on other parts of the body. Each 
sweUing consists of dense fibrous tissue in which several pairs of 
parasites are imbedded, and contains small cystlike spaces into 
which project the posterior end of the male 
with its copulatory organs, and the anterior 
end of the female with its vaginal opening. 
These cystlike spaces are usually swarming 
with sheathless microfilariae. The latter are 
believed by some authors to leave the tumors 
and to find their way ultimately to the blood- 
vessels, whence they can be liberated by some 
blood-sucking insect. The intermediate host 
is unknown, but the stable-flies, Stomoxys, and 
tsetse flies, Glossina, have been suspected. 
The tumors are of long duration in man, and 
in some adults are said to have been present 
since childhood. It is significant that prac- 
tically all cases of elephantiasis in the Welle 
district of Congo, where Filaria bancrofti is said 
not to occur, are accompanied by infection 
with Onchocerca volvulus. Recently Robles 
has described Onchocerca ccecutiens causing 
subcutaneous nodules on the heads of natives 
in parts of Guatemala, and suspects certain 
species of Simulium as carriers. 

The Guinea-worm. Another connective 
tissue parasite, more distantly related to the 
filariae, is the guinea-worm, Dracunculus medi- 
nensis (Fig. 130). This is a frequent parasite 
in many parts of tropical Asia and Africa and 
has been known for a very long time. The Fig. 130. Guinea- 
" fiery serpents " which molested the Israelites Z^neL^'le^u 
by the Red Sea and were mentioned by Moses Natural size. (After 
were probably guinea-worms. These parasites ^^^^^kart.) 
creep in the deeper layers of the subcutaneous tissue where they 
can be more readily felt than seen, but the females always come 
to the surface of the skin to give birth to the myriads of wriggling 

The adult female worm, which is the only sex certainly known, 



may attain a length of four feet or more, though the average 
length is about three feet, while the diameter is less than jV of an 
inch. The body is smooth, cylindrical and milky-white in color, 
with the tip of the tail sharply hooked. The male worms are 
believed to be much smaller than the females. When ready to 
bring forth her young, the guinea-worm is instinctively at- 
tracted to the skin, especially to such parts as are likely to, or 
frequently do, come in contact with cold water, such as the 
arms of women who wash clothes at a river's brink, or the legs 
and backs of water-carriers. The worm pierces the lower layers 
of the skin with the front end of her body and the outer layers 
of the skin form a blister over the injured spot. The blister 

eventually breaks, revealing a 
shallow ulcer, about as large 
as a dime, with a tiny hole in 
the center. When the ulcer is 
douched with water a milky 
fluid is exuded directly from 
the hole or from a very deli- 
cate, transparent projected 
structure which is a portion 
of the worm's uterus. This 
fluid is found to contain hordes 
of tiny coiled larvse with char- 
acteristic straight projecting 
tails. The larvse (Fig. 131) are 
from 0.60 to 0.75 mm. (about gV 
of an inch) in length. An hour or so later a new washing with cold 
water will bring forth a fresh ejection of larvse and so on until the 
supply is exhausted, a little more of the uterus being extruded each 
time. After each ejection of the larvse the protruded portion of the 
uterus dries up, thus sealing in the unborn larvse. This process 
can be looked upon only as a wonderful adaptation for the pres- 
ervation of the race. As we shall presently see, the tiny larvse 
utilize various species of Cyclops (Fig. 132), small fresh-water 
crustaceans, as intermediate hosts. If the larvse were not de- 
posited in water, or if they were all poured at once into any bit 
of water with which the skin of the host came in contact, the 
chance of their reaching a suitable Cyclops would be very small. 
The result would usually be family suicide and eventually race 

Fig. 131. Cross section of guinea- 
worm showing uterus filled with em- 
bryos. X about 30. (After Leuckart.) 


suicide. The repeated birth of a Hmited number of progeny 
each time the skin of the host comes in contact with water is 
therefore a successful solution to a problem which to a blind 
burrowing unmeditative worm must otherwise present insuper- 
able difficulties. When 
all her young have been 
deposited, under the stim- 
ulus of contact with water, 
the parent worm shrivels 
and dies and is soon ab- 
sorbed by the tissues on 
which she formerly preyed 
and through which she 

The embryo worms, 
safely deposited in water, 
unroll themselves and be- fig. 132. Cydops sp. (?), some species of 

gin to swim about in a which serve as intermediate hosts of guinea- 
r 1 • T i ii worms. X about 25. 

fashion pecuhar to them- 
selves. Their bodies are somewhat flattened and they have a 
slender tail. They swim by a few quick sculling motions of the 
tail, followed by a pause, then a few more strokes, etc., in the 
manner of a tadpole. In turbid water they remain alive for 
two or three weeks but eventually perish unless they come in con- 
tact with a Cyclops, into the body of which they make their way. 

They usually enter by way of the mouth, sometimes as many 
as six or ten entering a single Cyclops. In a day or two they 
leave the stomach of Cyclops and enter the body cavity. In 
spite of the relatively large size of the worms the crustaceans 
seem to feel very little inconvenience, and seldom succumb 
even to very heavy infection. 

The young guinea-worms become fully developed in Cyclops 
in from four to six weeks, according to the temperature, mean- 
while having undergone one and perhaps two moults. They are 
then about one mm. {-^ of an inch) in length, and ready to in- 
fect a new host. Entrance to the new host is probably accom- 
plished by the accidental drinking of a Cyclops with unfiltered 
water. The female worms become adult in their new host in 
about a year so the larvae can again be deposited at about the 
time that Cyclops becomes abundant. 


The guinea-worm, though annoying and to one of fine sensi- 
bihties extremely disgusting, is not in any way dangerous if not 
interfered with. Should she come to an untimely end, however, 
or fail to pierce the skin, she may give rise to troublesome ab- 
scesses, though more often the body becomes calcified and may 
be felt for years as a hard twisted cord beneath the skin. The 
crude method of abstraction of the worm which is frequently 
practiced is the chief source of danger from infection with it. 
This extraction consists in winding out the extruded part of the 
worm around a stick, drawing it forth a little further each day. 
Sometimes this method is successful but frequently it results in 
the snapping in two of the worm beneath the skin, and the 
consequent liberation into the tissues of thousands of young 
worms with the fluid contents of the uterus. This gives rise 
to inflammation, fever, abscesses and even death from blood- 

A much more effective and rational method of treatment is 
to bathe the part of the body occupied by a mature worm at 
frequent intervals until she has emptied her uterus, a process 
which takes two or three weeks. When the birth of embryos 
ceases, gentle pulling is likely to bring the worm forth, but if 
not her body is quickly absorbed by the tissues. A more re- 
cent and quicker method of dealing with a guinea-worm is to 
inject her body, or the tissue in which she is coiled, with a very 
weak solution of bichloride of mercury. This kills her and usu- 
ally makes her extraction easy after a few hours. Promising 
results have recently been obtained by arsenobenzol injections 
into the host. 

Prevention of guinea-worm infection consists obviously in 
keeping drinking water clear of Cyclops, or in thoroughly filtering 
it, or, if these measures are impracticable, in preventing infected 
persons from bathing in or otherwise contaminating rivers or 
other bodies of water from which drinking water may be taken. 
It has been suggested that portable steam generators be used to 
heat the water in wells, water holes, etc., in which infected 
Cyclops live, since these crustaceans succumb at a slightly ele- 
vated temperature. Addition of small quantities of potash to 
water is also effective in destroying Cyclops. The difficulty 
connected with an attempt to exterminate Cyclops locally is 
that the eggs resist desiccation and are blown about freely by 
the wind, so that a new colony is likely to spring up at any 


The annelids as a group are not of such primary importance 
as parasites as are the two other great groups of '' worms." 
In fact only one class, the Hirudinea or leeches, contain species 
which are parasitic on the higher animals. 

No boy who has ever experienced the unbounded delights of 
hanging his clothes on a bush and immersing his naked body 
for a swim in a muddy-bottomed river or pond is unfamiliar 
with leeches or " bloodsuckers." Still more familiar with them 
is any tourist who has journeyed on foot through the jungles of 
Ceylon or Sumatra, or any explorer who has walked through 
the warm moist valleys of the Himalayas or Andes, and who has 
been attacked by hordes of bloodthirsty land-leeches which in- 
fest these places. Nor is it likely that the thirsty traveler in 
North Africa or Palestine who stops to gulp a few mouthfuls of 
water from a pool or stream and who accidentally inbibes one of 
the leeches which infest such waters will not always remember 
the bleeding and unpleasant sensations, and perhaps dangerous 
symptoms, which follow the settlement of the leech in the mouth 
or nasal passages. 

General Anatomy. — The leeches are segmented worms be- 
longing to the phylum Annelida, in company with earthworms, 
kelp worms, etc. They are distinguished from other annelids 
by the absence of any bristle-like outgrowths from the body 
(setse) and by the presence of two suckers, one at the mouth for 
sucking food, and a large one at the posterior end for adhering 
to surfaces. The rings of the body as seen on the surface do not 
correspond to true segments of the body as they do in other 
annelids; there are several rings to most of the segments. The 
bodies of leeches are extremely elastic, and can be stretched at 
will to several times the contracted length. In fact the usual 
method of locomotion, other than an undulating mode of swim- 
ming, is by alternately expanding and contracting the body, 



adhering first by the large posterior sucker, then by the smaller 
oral sucker and so forth. 

Nearly all leeches feed exclusively on blood. The digestive 
tract (Fig. 60C, p. 197) is pecuHar in that the oesophagus is sup- 
plied with a series of " crops" or side pockets in which blood can 
be stored up as a reserve supply to be gradually drawn back into 
the stomach and intestine and digested as needed. Since some 
leeches can fill up with three times their own weight in blood, 
and can live on this supply for a year or more, meals are few and 
far between. The saliva of the leech has the power of prevent- 
ing the coagulation of blood, and therefore blood continues to 
flow for some time after the leech has " got his fill " and let go. 
Like other annelids, leeches have a true blood system and a 
series of nephridia, little coiled tubes, a pair in each segment, 
which function as primitive kidneys. There are no special gills 
or other respiratory organs; oxygen is absorbed directly through 
the skin which is constantly kept moist. 

Leeches are hermaphroditic, i.e., both sexes are represented 
in the same individual, but the egg of one leech is always ferti- 
lized by a sperm from another. In most leeches the eggs are 
deposited in a stiff mucous cocoon which is secreted by a por- 
tion of the body. When the eggs are laid the cocoon is slipped 
over the head like a jersey, the ends closing together to form 
a capsule. After a little manipulation with the oral sucker the 
mother leech imbeds the cocoon in moist soil, near the edge of 
water in the case of aquatic species. 

Importance as Parasites. — The ordinary pond and river 
leeches which adhere to bathers are of little or no economic im- 
portance as human parasites. Of these the well-known medici- 
nal leeches, Hirudo, used for sucking out infections or bad 
blood, are the best known examples. They are furnished with 
powerful suckers and sharp-pointed pincer-like jaws, and can 
therefore easily penetrate the skin and suck blood from any part 
of the surface of the body. They can usually be persuaded to 
release their hold when removed from water. 

With the weak-jawed members of the genera Limnatis and 
Hcemopis, commonly known as horse leeches, it is quite dif- 
ferent. These animals seek to penetrate the natural openings 
of the body and fasten themselves to the mucous membranes, 
especially in the mouth and nasal cavities, where they may cause 


such extensive bleeding as to bring about the death of the host. 
Of perhaps even greater importance, because more difficult to 
avoid, are the bloodthirsty land-leeches which have already been 
mentioned as infesting many tropical countries. Leeches serve 
as intermediate hosts for many species of trypanosomes of fishes 
and other aquatic animals, and it is not impossible that they may 
be found to transmit some species to man. 

Leeches in the Mouth or Nose. — The leeches which habitu- 
ally settle themselves in the mouth or nasal cavities of men or 
animals are inhabitants of muddy-bottomed ponds, ditches, 
reservoirs, troughs, etc., and enter the mouth or nose of their 
host while he is drinking. According to Masterman, leeches of 
the species Limnatis nilotica become so abundant in northern 
Palestine in late summer and autumn that almost every horse 
and mule passing through these parts has a bleeding mouth. 
The Nile leech, Limnatis nilotica, is the most plentiful species 
around the shores of the Mediterranean, but leeches of the 
genus Hoemopis, with similar habits, also occur over a large part 
of Europe. Troublesome aquatic leeches have been reported 
by travelers in the lake regions of central Africa also, and in 
some other warm countries, especially Formosa. 

The young leeches, which are usually the ones which enter 
the mouth or nose during drinking, are only a fraction of an inch 
in length, but the adults reach a length of several inches. The 
average length of Limnatis nilotica is about one inch or less. 

A person while drinking from infected pools, especially in 
dusk or at night, is very likely to suck in one or more of these 
leeches. During the process of swallowing the parasites attach 
themselves to the walls of the mouth or pharynx and may mi- 
grate into the nose or larynx. Seldom, if ever, are the leeches 
completely swallowed, and even if they should reach the stomach 
they would probably be killed at once and digested. It is a 
peculiar and indeed unfortunate fact that, while the leeches 
which attack the surface of the body fill with blood and then 
let go, those which settle on the mucous membranes keep their 
hold for days or weeks, though they shift their positions, leaving 
the old bites to continue bleeding. As already stated, the loss 
of blood from the wounds made by the leeches is often sufficient 
to cause an extreme or even fatal anemia, though the hemor- 
rhages of clear blood are never great in quantity at any one time. 


The blood flows out of the nose or into the throat or trachea, in 
the latter cases being constantly " hawked " up. Masterman 
describes the case of a man in Palestine, attacked by leeches, who 
for nearly a week had been " spitting blood " and had a spittoon 
full of practically pure blood by his side, every few minutes adding 
more. His lips were blue, and he was unable to speak above 
a whisper. Every few minutes he had a short cough. Often 
when the leech is attached in the larynx beside the vocal cords, 
the body flops back and forth during breathing, and has been 
known to cause asphyxiation by blocking the trachea. Cases are 
on record where leeches, having fallen into one of the bronchi, 
have died and disintegrated, and thus caused destructive bac- 
terial infections to set in. The presence of leeches in the mucous 
membranes is often accompanied by severe headaches. Some- 
times leeches which have settled in the nose have the revolting 
habit of protruding themselves from the nostrils and allowing a 
portion of the body to wander over the upper lip. They are, 
however, so elusive that they can be captured only with great 

The treatment employed for leech infestations of the nose 
or mouth varies greatly in different countries. According to 
Masterman the natives of Palestine transfix the leech, if within 
reach, with a thorn from a native tree, and muleteers extract 
leeches from mules' mouths with packing needles. When the 
parasite is beyond reach of this transfixing process these people 
smear some of the thick deposit which collects in their tobacco 
pipes on a splinter of wood and endeavor to touch the leech with 
it; this is said to cause the leech to lose its hold. Masterman 
found the most successful means of removing a leech to be either 
to seize it with a suitable forceps, or to paralyze it with cocaine. 
Much difficulty is often experienced in seizing the writhing, 
slippery creature with a pair of forceps even when it can be seen 
clearly with a mouth mirror, partly on account of the spasmodic 
contractions of the larynx and the frequent coughing. The 
paralyzing of the worms with cocaine is a very successful method ; 
it is done by touching the worm with a 30 per cent cocaine solu- 
tion on a bit of cotton. The worm becomes paralyzed in a few 
minutes after being touched, and releases its hold. To avoid 
the possibility of the leech falling into the trachea the patient is 
made to lie on a couch with his head hanging over the edge. 


Land-leeches. — Of perhaps greater importance, because far 
less easy to avoid, are the attacks of the land-leeches of many 
tropical countries. These leeches are found in Ceylon, Japan, 
Sumatra, Philippine and East Indian Islands, Australia, and the 
humid mountain meadows of the Himalayas in India and of the 
Andes in South America. Sir J. Emerson Tennent in his book 
on ''The Natural History of Ceylon" writes as follows: "Of 
all the plagues which beset the traveler in the higher grounds of 
Ceylon the most detested are the land-leeches, Hcemadipsa 
ceylonica. They are not frequent in the plains, which are too 
hot and dry for them, but among the rank vegetation of the 
lower hill country, which is kept damp by frequent showers, 
they are found in tormenting profusion. They are terrestrial, 
never visiting ponds or streams. In size they are about an inch 
in length and as fine as a common knitting needle, but they are 
capable of distension till they equal a quill in thickness and at- 
tain a length of nearly two inches. Their structure is so flexible 
that they can insinuate themselves through the meshes of the 
finest stocking, not only seizing on the feet or ankles, but ascend- 
ing to the back or throat, and fastening on the tenderest parts 
of the body. In order to exclude them the coffee planters who 
live among these pests are obUged to envelope their legs in 
" leech garters " made of closely woven cloth. The natives 
smear their bodies with oil, tobacco ashes or lemon juice, the last 
serving not only to stop the flow of blood, but also to expedite 
the healing of the wounds. In moving, the land-leeches have 
the power of planting one extremity on the earth and raising the 
other perpendicularly to watch for their victim. Such is their 
vigilance and instinct that, on the approach of a passerby to a 
spot which they infest, they may be seen amongst the grass and 
fallen leaves on the edge of a native path, poised erect, and pre- 
pared for their attack on man and horse. Their size is so in- 
significant and the wound they make is so skillfully punctured 
that both are generally imperceptible, and the first intimation of 
their onslaught is the trickling of the blood or a chill feeling of 
the leech when it begins to hang heavily on the skin from being 
distended with its repast. Horses are driven wild by them and 
stamp the ground in fury to shake them from their fetlocks, to 
which they hang in bloody tassels. The bare legs of the palankin 
bearers and coolies are a favorite resort, and as their hands are 



too much engaged to pull them off the leeches hang like bunches 
of grapes round the ankles. Both Marshall and Davy mention 
that during the march of troops in the mountains when the 
Kandyans were in rebellion in 1818, the soldiers, and especially 
the Madras Sepoys, with the pioneers and 
coolies, suffered so severely from this cause 
that numbers perished. 

One circumstance regarding these land- 
leeches is remarkable and unexplained: they 
are helpless without moisture, and in the hills 
where they abound at all other times they 
entirely disappear during long droughts; yet 
reappear instantly at the very first fall of rain, 
and in spots previously parched, where not one 
was visible an hour before, a single shower is 
sufficient to reproduce them in thousands. 
Whence do they reappear! May they, like 
rotifers, be dried up and preserved for an 
indefinite period, resuming their vital activity 
on the mere recurrence of moisture? " 

Similar reports come from travelers in other 
tropical countries. Alfred Wallace encountered 
land-leeches in Sumatra where he found them 
infesting the leaves and herbage by the side 
of the paths through the forests. At the 
approach of a traveler as indicated by foot- 
steps or a rustling of leaves, the leeches stretched 
themselves out at full length and attached 
themselves to any part of the passerby which 
they happened to touch. Their presence and 
FiQ. 133. Japa- -^j^g jQgg Qf blood was Seldom felt during the 

nese land-leech, . ^ n • i i i 

Hoemadipsa japoni- excitement of Walking, but a dozen or so had 
Sft^rwht^ ^ ^ ^^ ^® picked off every evening. Dean C. 
Worcester in his book on the Philippines 
says " the moist earth swarmed with leeches which crawled 
through my stockings and bit my ankles until my shoes were 
soaked with blood." One species, H. japonica (Fig. 133), is 
common in parts of Japan. The land-leech of Australia belongs to 
a different genus, Philcemon. 

In any of the localities infested by land-leeches it is advisable 


to bind the feet and legs in leech-proof cloth, this being preferable 
to various ointments which are supposed to discourage the leeches 
from their meal. In a tropical cUmate where so many diseases 
and unfavorable conditions beset one on every side, it is impor- 
tant to take every precaution to keep in perfect health. The 
loss of blood from the attacks of leeches, and the portal given 
for entrance of bacteria and other organisms in the wounds made 
by them, might make all the difference between life and death 
in the struggle for existence in these disease-plagued chmes. 




To the average person it is astonishing to learn that the insects 
and their alhes, constituting the phylum Arthropoda, include 
probably more than four times as many species as all other 
animals combined. In this vast horde of animal forms are 
included some species which are distinctly valuable to the human 
race, such as bees, the silkworm, the thousands of insects (Dip- 
tera and Hymenoptera) parasitically destructive to injurious 
species and the predaceous beetles; a great number which are 
indifferent as regards their economic importance serving, perhaps, 
only to arouse admiration for their beauties or disgust for their 
loathsomeness; and many which are of great importance as 
crop pests or as annoyers of domestic stock or of man himself. 
Only relatively very few, a mere handful, are injurious to man as 
parasites or as disease carriers, but these few are of almost in- 
calculable importance. As mere parasites the parasitic arthro- 
pods are of minor importance, but it is in their capacity as inter- 
mediate hosts of other parasites or as mechanical carriers of 
disease germs that these animals have to be reckoned with as 
among the foremost of human foes. Every arthropod, para- 
sitic or otherwise, which habitually comes in direct or indirect 
contact with man must be looked upon as a possible disease car- 
rier. The role of arthropods in the dissemination of disease is a 
matter about which practically nothing was known 35 or 40 
years ago. A French physician. Dr. Beauperthuy, in 1853 was 
one of the first to express a belief in the dissemination of various 
diseases by mosquitoes and in the role of the housefly in the 
spread of pathogenic organisms. In 1879 Manson first proved 
insects to be intermediate hosts of human parasites, in the case 
of Filaria and the mosquito. Since that time many of the most 
important human diseases have been shown not only to be trans- 



mitted by arthropods but to be exclusively transmitted by certain 
species or genera. In the latter category, as far as we know at 
present, are malaria, by some physicians rated as the most im- 
portant human disease; typhus fever, the unseen dragon of death 
which hovers over every war camp in the world; yellow fever, 
which formerly haunted South and Central America; sleeping 
sickness, the scourge of Central Africa; Chagas' disease of 
South America; relapsing fever; Rocky Mountain spotted fever; 
dengue; phlebotomus fever; Japanese flood fever; filarial dis- 
eases; guinea-worm infection; lung fluke infection; some tape- 
worm infections; and others of less importance. Some other 
important diseases, such as kala-azar and oroya fever, are be- 
lieved to be transmitted by arthropods but the transmitting 
agents have not yet been discovered. 

There are many other diseases which, although they may be 
transmitted in other ways also, are commonly disseminated by 
insects, often in a more or less mechanical way. Such are plague, 
tuberculosis, leprosy and others. In the case of some of these 
diseases, e.g., plague, the intestines of the transmitting arthro- 
pods serve as culture tubes for the disease germs, whereas in 
other cases, e.g., amebic dysentery, the arthropods are merely 
passive carriers of disease germs which adhere to their feet or 
bodies. It is evident that any insect may serve as a disseminator 
of disease in this mechanical way in direct proportion to the ex- 
tent that it associates with man and that its habits bring it in 
contact with disease germs. 

Relationships. — The insects and their allies, constituting the 
phylum Arthropoda, are the most highly organized of inverte- 
brate animals, and stand at the head of their particular line of 
evolution. They find their nearest allies in the segmented worms 
or annelids, i.e., earthworms, leeches, etc., but most of them show 
a great advance over their lowly cousins. Like the annelids 
they have a segmented type of body, though in some types, such 
as the mites, all the segments become secondarily confluent. 
Like the annelids, also, the arthropods are protected by an ex- 
ternal skeleton which usually consists of a series of horny rings 
encircling the body. The most obvious distinguishing character- 
istic of the arthropods is the presence of jointed appendages in 
the form of legs, mouthparts and antennae. Internally they are 
distinguished from other invertebrates in that the body cavity, 


SO conspicuous in the annelids, has been entirely usurped by a great 
expansion and running together of bloodvessels so that in the 
place of the usual body cavity or ccelom there is a large blood- 
filled space. Within this space are bloodvessels and a so-called 
heart, which retained their individuality while the other vessels 

Classification. — The phylum Arthropoda is divided into five 
classes. One of these, the Onychophora, includes only a single 
genus of animals, Peripatus, which is very primitive, and helps 
to bridge the gap between the more typical arthropods and the 
annelids. Peripatus is a free-living wormlike animal and of no 
interest here. The remaining four classes are the Crustacea, 
Arachnida, Myriapoda and Insecta. 

The Crustacea, including crayfish, water fleas, etc., are pri- 
marily arthropods of the water. They are geologically of great 
antiquity and among them are the most primitive of the typical 
arthropods. Their appendages are usually numerous and, taking 
the group as a whole, show a wonderful range of modifications 
for nearly every possible function. Crustaceans breathe by gills. 
Although many are parasites of aquatic animals, none can be 
considered as parasites of man or other land animals. In two 
cases Crustacea are known to serve as the intermediate hosts of 
human parasites, namely Cyclops as a host for the guinea-worm 
(see p. 312), and the Japanese land crabs as the second inter- 
mediate hosts of the lung fluke (see p. 222). 

The Arachnida, including spiders, scorpions, mites, etc., are 
for the most part highly developed arthropods, representing the 
terminus of a separate line of evolution. They probably had a 
common origin with the Crustacea, but have become adapted 
to terrestrial life. The members of this class have four pairs of 
legs as adults, two pairs of mouthparts and no antennae. They 
breathe by means of invaginations of the body which contain 
gills arranged like the leaves of a book, whence the name " book 
lungs." Some of the higher arachnids also have a system of 
branched air tubes or tracheae in the body similar to those found 
in the insects and myriapods. Two orders of Arachnida contain 
parasitic species, namely the Acarina, or mites and ticks, and 
Linguatulina, or tongue-worms. Many ticks are disease carriers. 

The Myriapoda, including centipedes and millipedes, are 
terrestrial arthropods which breathe by tracheae. The body is 



furnished with a distinct head, followed by a considerable num- 
ber of similar segments, each bearing one or two pairs of legs. 
There is a single pair of antennae. Although some of the centi- 
pedes are poisonous, none of the myriapods are parasitic, nor 
are any of them known to be disease carriers. 

The Insecta, or insects, represent the zenith of invertebrate 
life. They are terrestrial arthropods which, like the myriapods, 
breathe by tracheae. Their appendages, however, are reduced 
to one pair of antennae, two pairs of mouthparts and three pairs 
of legs with usually the addition, if not secondarily lost, of two 
pairs of wings. The wings are really mere outgrowths or folds 
of the integument or " skin " of the insect, between the two layers 
of which are branches of the tracheae, represented by the " veins" 
in the wings of adult insects. There is a fundamental plan of ar- 
rangement of the veins which is variously modified in different in- 
sects, but absolutely fixed in any given species. The venation 
of the wings is often of great value in the identification of genera 
or species of insects. An insect is always readily divisible into 
three parts, the head, thorax and abdomen. The head, in addi- 
tion to the antennae already mentioned, bears two compound eyes 
sometimes of relatively enormous size, usually several simple eyes, 
and the mouthparts. 

Mouthparts of Insects. — Incredible as it may seem at first 
thought, the mouthparts of all kinds of insects, from the simple 
chewing organs of a grasshopper to the highy modified piercing 
and sucking organs of biting flies and mosquitoes and the great 
coiled sucking tube of butterflies and moths, are modiflcations 
of a single fundamental type. This type is represented in its 
simplest form in the chewing or biting type, as found in grass- 
hoppers and beetles (Fig. 134). The mouthparts in these in- 
sects consist (1) of an upper lip or labrum (Fig. 134, Lbr.); 
(2) a lower lip or labium (Fig. 134, Lbm.), really formed of a 
pair of organs fused together, each bearing a segmented appen- 
dage, the labial palpus (Fig. 134, Lab. p.); (3) a pair of hard, 
horny, toothed mandibles or jaws (Fig. 134, Mand.) lying just 
under the lower lip, which chew up food by a horizontal instead 
of vertical movement; (4) a pair of maxillae (Fig. 134, Max.), 
lying between the mandibles and lower lip, each bearing a seg- 
mented appendage more or less like those on the lower hp, and 
caUed the maxillary palpus (Fig. 134, Max. p.) and (5) the 



hypopharynx (Fig. 134, Hyp.), a short fleshy organ lying in the 
midst of the other organs, and comparable in both form and 
function with the tongue of vertebrate animals. In addition to 
these parts there is a horny lining of the upper lip and roof of 


Fig. 134. Simple mouthparts of a chewing insect (Stenopalmatus) ; Ibr., la- 
brum, or upper lip; mand., mandible; hyp., hypopharynx or tongue; max., maxilla; 
max. p., maxillary palpus; lbm., labium or lower lip (really a second pair of maxillse 
fused together); lab. p., labial palpus. 

the mouth cavity known as the epipharynx. This structure 
is usually closely associated with the upper lip, so that the com- 
bined organ is spoken of as the " labrum-epipharynx." 

The extent of the modifications which these mouthparts may 
undergo is wonderful, especially in insects where they are modi- 
fied for sucking or piercing. In the true bugs the mandibles 
and maxillse are prolonged into needle-like organs, the maxillae 
often armed with sawlike teeth at their tips, and the lower lip 
is developed into a thick, fleshy, jointed proboscis, grooved on its 
upper side to form a sheath for the piercing organs (Fig. 164). 
The labrum is a short movable flap, and the hypopharynx is very 
sHghtly developed. In the Diptera, which include the mos- 
quitoes, gnats, blackflies, tsetse flies and other biting flies as 
well as houseflies and blowflies, there are several different types 


of modifications. In mosquitoes the mouthparts (Fig. 191) are 
much as in bugs, but the labrum-epipharynx and hypopharynx 
are also modified into long piercing organs, and the latter is 
fashioned into a true hypodermic needle for injecting salivary 
secretions. In blackflies and tabanids (Figs. 220 and 225) the 
parts are similar but the piercing organs are shorter and more 
bladelike, resembUng daggers rather than needles. In the 
tsetse flies and stable-flies (Figs. 220 and 225) the lower lip itself 
is the chief piercing organ, the labrum-epipharynx and hypo- 
pharynx contained in it being needle-like and capable of forming 
a sucking tube by apposition with each other. The mandibles 
and maxillae are much reduced or rudimentary, but the maxillary 
palpi are conspicuous, and in tsetse flies form a perfect sheath 
for the proboscis. In the houseflies and their non-blood-sucking 
allies the mouthparts are most modified, being all molded to- 
gether to form a fleshy proboscis especially fitted for lapping 
up liquid foods. In fieas the mouthparts (Fig. 178) are somewhat 
as they are in the biting flies, but the mandibles are not modified 
as piercing organs but as protective flaps, and the sheath for the 
piercing organs is formed from the labial palpi instead of from 
the labium or lower lip itself. The mouthparts of sucking lice 
(Fig. 171) are still not thoroughly understood but the piercing 
and sucking organs, whatever parts they really represent, can 
be retracted into a blind pouch under the pharynx. The mouth 
parts of such insects as moths, bees, wasps, etc., are also remark- 
able examples of structural adaptations, but they do not concern 
us here. 

General Anatomy. — The digestive tract of insects (Fig. 135) 
is often highly developed and differentiated. The blood-sucking 
insects have a muscular pharynx in the head which acts like a 
suction pump. In the bedbug, for instance, the powerful muscles 
which are used to expand the pharynx and thereby produce 
suction occupy a considerable portion of the inside of the head, 
and the area on top of the head to which they are attached is 
distinctly visible on the outside. The pair of salivary glands 
open into the floor of the pharynx, but they themselves are 
usually situated in the thorax. Often they are very highly de- 
veloped. In the true bugs they have connected with them 
accessory salivary glands, which in some species may serve at 
least in part as storage vats for holding the secretion temporarily. 



In mosquitoes (Fig. 189) the salivary glands consist of three 
lobes, one lobe being noticeably different in appearance and 
secretion from the others. The pharynx connects with the 
stomach by a slender oesophagus. Various means are used by 

blood-sucking insects to increase 
their capacity. In the bugs 
(Fig. 135) the stomach is ex- 
tremely distensible and serves as 
a storage reservoir. In fleas and 
many biting flies there is an ex- 
pansion of the oesophagus an- 
terior to the true stomach, called 
the proventriculus; in mosqui- 
toes there are capacious pouch- 
like food reservoirs or outgrowths 
from the oesophagus in addition 
to the proventriculus (Fig. 189). 
Just behind the true stomach at 
the beginning of the intestine 
there open a number of long 
slender tubes, the ''Malpighian 
tubules" (Fig. 135, malp. t.). 
These are the excretory organs, 
corresponding to the kidneys of 
vertebrate animals. Their func- 
tion is to collect the waste 
matter of metabolism from the 
blood and pour it into the in- 
testine, whence it can ultimately be voided through the anus. 
The length of the intestine varies, being usually longer in vege- 
table-feeding insects than in carnivorous ones. It often has a 
marked expansion, the anal pouch, at its posterior end. 

The tracheae of insects, as already intimated, are really a ven- 
tilation system consisting of air tubes ramifying all through the 
body even to the tips of the antennae and legs. They open by a 
series of pores along the sides of the insect known as spiracles, 
which function as do the nostrils of higher animals. The prin- 
ciple of oil sprays for insects is to form a film of oil over the 
spiracles, so that the insects will suffocate. 

The nervous system of insects is very highly developed for 



Fig. 135. Digestive tract of a Re- 
duviid bug; ace. sal. gl., accessory- 
salivary gland; conn, d., connecting 
duct between salivary glands; int., in- 
testine; malp. t., malpighian tubules; 
oes., oesophagus; rect., rectum; sal. gl., 
salivary gland. (Partly after Dufour.) 


invertebrate animals. In some species the instincts, especially 
those connected with providing for their offspring, simulate care- 
ful and accurate reasoning, and it is difficult not to look upon 
them as animals endowed with a high degree of intelligence. 

Life History. — As regards life history, three different types 
can be recognized among insects. In the primitive order Thy- 
sanura alone there occurs " direct development " in which the 
newly hatched insect is nearly a miniature of its parent, and 
merely increases in size. The two common types of development 
are by incomplete and complete metamorphosis. Insects which 
have an incomplete metamorphosis are those which differ more or 
less from their parents when hatched, but which gradually assume 
the parental form with successive moults or sheddings of the 
skin. The young or '' nymphs " of such insects invariably lack 
wings, and often have other characteristics different from their 
parents. In such insects as lice, in which the wings are absent in 
the adult, there is very little difference except in size between 
the young and adult forms. Insects which have a complete 
metamorphosis are those in which, as in butterflies, the newly 
hatched larva is totally different from the parent, and does not 
gradually assume the parental form. Instead, it retains its worm- 
like larval characteristics until full grown and then transforms, 
during a resting and more or less quiescent period of relatively 
short duration, into the adult form. This transformation, which 
may amount to nothing short of a complete remodeling of the 
entire body and all its organs, is sometimes accomplished in an 
amazingly short time. Many maggots transform into adult flies 
in less than a week, and some mosquito larvae transform into 
perfect mosquitoes in less than 24 hours. 

The length of life of insects in the larval and adult stages 
varies with almost every species and with environmental con- 
ditions. The larval stage may occupy a small portion of the 
life, as in the case of many mosquitoes and flies, or it may con- 
stitute the greater part of it. There are some mayflies, for 
instance, which live the greater part of two years as larvae but 
exist as adults not more than a few hours. As a rule male in- 
sects are shorter lived than the females; the length of life of the 
latter is determined by the laying of the eggs — when all the 
eggs have been laid the female insect has performed her duty 
in fife and is eUminated by nature as a useless being. The result 


is the paradoxical fact that ideal environmental conditions 
shorten the life of these insects, since they facilitate the early 
deposition of the eggs. 

Classification. — The classification of insects is based mainly 
on three characteristics: the type of development, the modifi- 
cation of the mouthparts, and the number, texture and venation 
of the wings. All blood-sucking insects have mouthparts 
adapted in some way for piercing and sucking, but the types 
vary greatly in different groups. Many of the more thor- 
oughly parasitic insects, e.g., lice, bedbugs and " sheep ticks," 
have secondarily lost their wings entirely, or have them in a rudi- 
mentary condition. In the whole order of Diptera the second 
pair of wings is reduced to inconspicuous club-shaped append- 
ages known as halteres. 

The only orders of insects which contain species of interest as 
human parasites are the Hemiptera (Rhynchota), or true bugs; 
the Siphunculata, or sucking lice; the Siphonaptera, or fieas; and 
the Diptera, or two-winged flies. These four orders may be 
briefly summarized as follows: 

Hemiptera (suborder Heteroptera) : metamorphosis incom- 
plete; mouthparts fitted for piercing and sucking, the piercing 
organs being ensheathed in the jointed lower lip; first pair of 
wings, unless reduced, leathery at base and membranous at tip; 
second pair of wings, when present, membranous with relatively 
few veins. Human parasites: bedbugs, cone-noses, kissing bugs. 

Siphunculata: metamorphosis incomplete; mouthparts fitted 
for piercing and sucking, and retractile into a pouch under pharynx; 
wings secondarily lost. Human parasites: sucking lice. 

Siphonaptera: metamorphosis complete; mouthparts fitted 
for piercing and sucking, the piercing organs being ensheathed 
in the labial palpi, and the mandibles modified as protective 
flaps; wings secondarily lost. Human parasites: fleas, chiggers. 

Diptera: metamorphosis complete; mouthparts fitted for pierc- 
ing and sucking, for sucking alone, or rudimentary; first pair 
of wings (absent in a few species) membranous with few veins; 
second pair of wings represented only by a pair of clubshaped 
organs, the halteres. Human parasites: Sandflies, mosquitoes, 
midges, blackflies, gadflies, tsetse flies, stable-flies, maggots of 
various species. 


General Account. — The mites and ticks, which constitute the 
Order Acarina of the Class Arachnida, are only slightly known by 
the majority of people. Popular knowledge of them is usually 
limited to a few species of ticks, chicken mites, and perhaps two 
or three other species of mites. Yet the group includes a large 
number of species, varying in size from some ticks which are half 
an inch or more in length to mites barely visible to the naked eye. 
The variety of body form is great and some species when magnified 
appear ridiculously grotesque. The majority of the species are 
more or less round or oval, with head, thorax and abdomen all in 
one piece, but many have the cephalothorax (head and thorax 
fused together) distinctly marked off from the abdomen, while 
a few are quite wormlike in form. Many mites are free-living 
and prey upon decaying matter, vegetation, stored foods and 
the like; some are predaceous and feed upon smaller animals; 
some are aquatic, even marine; and many are parasitic on other 
animals during all or part of their life cycle, and some of these 
serve as intermediate hosts for, and for dissemination of, danger- 
ous disease germs. 

Like other Arachnida (spiders, scorpions, etc.) the mites and 
ticks usually have two pairs of mouthparts and four pairs of 
legs, though the last pair of legs is not acquired until after the 
first moult. The first pair of mouthparts or chelicerae are some- 
times needle-like, sometimes shaped like a grapnel hook, and 
very often pincer-like, the pincers often being at the tip of a 
long exsertile needle-like structure. The second pair of mouth- 
parts, or pedipalps, are simple segmented palpi. In many kinds 
of Acarina the anterior end of the ventral side of the body is 
produced as a sort of chin or lower lip, the hypostome, which 
may be needle-like or barbed and rasplike (Fig. 152). 

The digestive tract is in most cases well developed. Waves 
of muscular contraction make a very efficient sucking organ of 



the pharynx. The stomach has pouches opening from it which 
act as food reservoirs (Fig. 149), so that one meal may last for 
a long time. The intestine is usually short and the excretory 
organs, malpighian tubules, open into it not far from the anus. 
The reproductive organs, as in other Arachnida, open on the ventral 
surface of the abdomen but at different places in different species. 
The nervous system is largely concentrated into a great mass, 
the " brain," lying near the anterior end of the body and pierced 
by the oesophagus. Many mites possess tracheae, similar to 
those of spiders and insects, for breathing, while others, soft- 
skinned forms, simply absorb oxygen through the surface of the 

Life History. — The life histories of mites and ticks are some- 
what variable, but usually there are four stages in their develop- 
ment: the egg, the larva, the nymph and the adult (see Fig. 157). 
The eggs are usually laid under the surface of the soil or in crev- 
ices, or, in some parasites, under the skin of the host. After a 
varying period of incubation, which depends on climatic con- 
ditions, the larva hatches in the form of a six-legged creature, 
often quite unUke the parent. After a single good feed of blood 
or plant juices the larva rests, sheds its skin and appears with 
an additional pair of legs and a body form more closely resem- 
bling that of the parent but without developed sexual organs. 
The nymph thus produced feeds again, sheds its skin from one 
to three times and finally, after another period of rest during 
which its body is remodeled for the second time, moults again 
and comes forth as a fully adult male or female, ready for the 
reproduction of another generation. There are all sorts of modi- 
fications of this order of development, due to the slurring over of 
one phase or another. One of the most aberrant species is the 
louse-mite, Pediculoides. In this form the eggs develop within 
the parent's body and the adult males and females issue forth 
from the brood chamber improvised for them out of the abdomen 
of the mother (Fig. 139). 

The popular opinion that all mites are parasitic is, as remarked 
before, far from being true. Over half of the known species are 
not parasitic at any stage in their life history, while many others 
are parasites only during part of their life cycle. 

Parasitism. — The mites are an interesting group for the study 
of the origin of parasitic habits since, as Ewing has shown, para- 


sitism has apparently arisen independently in different families 
and genera at least eleven times. Nathan Banks in his treatise 
on the Acarina, after giving a number of interesting examples of 
peculiar parasitic habits, writes as follows: '' We can only explain 
these remarkable habitats by the fact that mites, especially in 
their immature stages, have an incontroUable desire to go some- 
where, and get into every cavity and crack they discover in their 
wanderings. When hungry they test their locality for food, and 
if not too different from their previous diet this new habitat may 
result in new species and genera." 

A few species of mites have become adapted to live as internal 
parasites, but all the species normally infesting man are either 
external or subcutaneous in their operations. A few of the 
species which are not averse to human beings as food are 
troublesome and irritating enough to bring their whole tribe into 
disrepute. The families of mites which contain species annoying 
to man are the Ixodidce and Argasidce, the ticks; Trombidiidce, the 
harvest mites and " red-bugs "; Parasitidce {Gamasidoe) , including 
the chicken mites; Tarsonemidce, including the louse-mite; Ty- 
roglyphidce, including the cheese and grain mites; Sarcoptidce, the 
itch mites; and Demodeddce, the hair-follicle mites. For con- 
venience we may include with the mites the very aberrant arach- 
nid forms known as tongue-worms, now usually placed in a 
distinct order, Linguatulina. Since the ticks are popularly looked 
upon as quite distinct from other Acarina, and form a very im- 
portant group of the order on account of their role as disease 
carriers, they will be considered in a separate chapter. 

Harvest Mites 

The six-legged larvae of the harvest mites, family Trombidiidae, 
known as red-bugs or chiggers, are very annoying pests, and one 
species, the Japanese '' akamushi " or kedani mite, has been 
proved to be the carrier of a dangerous disease, kedani or flood 
fever. Harvest mites are little scarlet-red animals, and their 
larvae are tiny pale-colored creatures barey visible to the naked 
eye (Fig. 136). According to one writer who had evidently 
experienced them a red-bug is a " small thing, but mighty; a 
torturer — a murderer of sleep; the tormentor of entomologists, 
botanists and others who encroach on its domains; not that it 



bites or stings — it does neither; worse than either, it just 

The adult harvest mites (Fig. 137) are law abiding members of 
the community, and attack only such animals as plant-lice, cater- 
pillars and other insects. They hibernate in soil or sheltered 
crevices and in the spring lay their eggs, several hundred apiece, 

in the ground or among dead 
leaves. The eggs are very 
small, round and brownish in 
color, and were once classified 
O as fungous growths! The 

Fig. 136. European red-bug, Leptus au- 
tumnalis, larva of a Trombidium usually 
thought to be T. holosericeum. X 150. 
(After Hirst.) 

Fig. 137. An adult of the 
kedani mite, a Trombidiid. 
X 40. (After Nagayo et al.) 

newly hatched six-legged larvae creep up on blades of grass 
or plant stems and await an opportunity to attach them- 
selves to an insect. If successful in finding a host, or rather in 
being found by a host, the mites gorge themselves with the 
juices of the insect, then drop to the ground, crawl to some snug 
hiding place and undergo a transformation. The whole inside 
of the body is remodeled, a fourth pair of legs is acquired, and 
after a few weeks the skin is shed and an adult trombidiid mite 
crawls forth. 

It is while the larval mites are hungrily awaiting the arrival 
of an insect upon which to feed that they attack human beings or 
animals which may pass their way. They are so small that 
they can easily pass through the meshes of ordinary clothing 
and reach the skin, where they set up a severe irritation and 


intense itching. Some authors claim that the mites burrow in 
the skin and produce inflamed spots, but ordinarily they do not 
go beneath the skin except sometimes to explore their way into 
the long tubes of the sweat glands. The habit of attacking 
warm-blooded animals is evidently abnormal, (and the love of 
blood proves ruinous to those individuals which get an opportu- 
nity to indulge it, since they soon die victims of their own per- 
verted appetites. How like some human beingsIN 

The irritation caused by the mites is probably due to a spe- 
cific poison secreted by the mites rather than to any wounds that 
they make. The inflammation of the skin may not be felt for 
12 or even 24 hours after infection by the mites. When the in- 
flammation does commence there appear large red blotches on 
the affected parts of the body which itch intensely and are made 
worse by scratching. After a day or so the red blotches blister 
and finally scab over. Red-bug rash is most frequent on tender- 
skinned people and on those parts of the body which are most 
exposed, though it may spread over the whole body and torment 
the victim unbearably. Laborers who are continually exposed 
to these mites seem to develop an immunity to the mite poison, 
and suffer little or none from them. Herrick states that one of 
the severest infestations he ever knew was contracted by a 
delicate-skinned person who sat down on the ground for a few 
minutes on some golf links which had recently been laid out on 
an old pasture where there was still much long grass. This 
person's body became covered with large inflamed spots even to 
the neck. The torture was intense for a week, and the infection 
persisted for a still longer period. A Mexican species, known by 
the Aztec name " tlalsahuate," meaning " grain of earth," shows 
a decided preference for the eyelids, armpits, groins and other 
thin-skinned portions of the body, where it induces itching and 
inflammation, and even ulceration when scratched. The " b^te 
rouge " or '' Colorado " of the West Indies and Central America 
is a similar if not identical species. 

Sprinkling sulphur on the legs and inside the stockings is a 
necessary preventive measure for those who are seriously affected 
by red-bugs, and who have to walk through tall grass or brush 
where these pests abound. A hot bath shortly after infection, 
with soap or with soda in it, gives much relief. To allay the itch- 
ing weak ammonia or baking soda applied to the affected parts is 


good, and alcohol, camphor and other cooUng applications are 
also useful. 

Since in many instances the adults are unknown, the larval 
harvest mites are, for the sake of convenience, placed in a col- 
lective group, Leptus, and the name is used in the manner of a 
generic name. The common red-bug of Europe, for instance, 
which is supposed to be the larva of Trombidium holosericeum is 
known as Leptus autumnalis. The most abundant species of 
red-bug in the United States is Leptus irritans. It occurs through- 
out the southern United States and as far north as New Jersey 
and the upper Mississippi Valley. An allied species, Leptus 
americanus, also occurs in many parts of southern United States. 
On the northern border of its range this mite does not appear 
until the latter part of June and becomes especially annoying 
during August, but its season becomes earlier and earlier the 
farther south it occurs. 

The European harvest mites, the commonest of which is Leptus 
autumnalis (Fig. 136), are well known pests throughout Europe, 
especially in Central and Western France, where they are known 
as the " b^tes rouges " or " rougets." They are said to attack 
small mammals, such as rodents, by preference. Unlike the 
American species, the European harvest mites become espe- 
cially abundant in the fall of the year. Japanese investigators 
have recently cast doubt on the commonly accepted belief that 
Trombidium holosericeum is the parent of Leptus autumnalis since 
in Japan the parent of the kedani mite (Fig. 137), which very 
closely resembles L. autumnalis^ is quite different from T. holo- 
sericeum, whereas an adult mite which very closely resembles 
the latter, produces larvae quite different from L. autumnalis. 

The Japanese harvest mite, larva of Trombidium akamushi, 
known locally as the akamushi (red-mite), tsutsugamushi (sick- 
ness mite) and kedanimushi (hairy mite), has been proven to be 
the carrier of a typhus-like disease known as kedani or flood 
fever. These larval mites occur in countless numbers on the 
local field mice, Micromys montebelloi, living especially on the 
inside of the ear. They frequently attack the farm laborers 
who engage themselves in harvesting and handling the hemp 
which is raised on the flood plains of certain Japanese rivers. It 
is among these people that the kedani or flood fever occurs, 
always following the bite of a mite. The bite, usually in the 



armpits or on the genitals, is at first painless and unnoticed, 
but the mite remains attached at the wound from one to three 
days before dropping to the ground to transform to the nymphal 
stage. The bite of the mite is said to develop into a tiny sore or 
inflamed spot in the region of which the lymph glands become 
swollen and painful and flood fever follows. The nymphs and 
adults of this mite have recently been found by Nagayo and his 
fellow-workers in Japan. 

The transmission of kedani by this mite is the only positive 
instance of human disease carried by Acarina other than ticks. 

Other Occasionally Parasitic Species 

There are many species of mites, of several different families, 
which under abnormal circumstances or by sheer accident may 
become troublesome parasites of man. Nearly all mites secrete 
salivary juices which have 
a toxic effect when injected 
into the blood; therefore 
any mite which will bite 
man under any circum- 
stances may become a pest. 
In nearly all cases the symp- 
toms of attacks by mites are 
similar — hivelike or rashlike 
eruptions of the skin, in- 
tense itching and in severe 
attacks fever. 

most important of the occa- 
sionally parasitic mites is 
the louse-mite, Pediculoides ventricosus (Fig. 138), belonging 
to the family Tarsonemidse. This is a very minute species, 
barely visible to the naked eye, which is normally parasitic 
on grain-moth caterpillars and other noxious insects, and there- 
fore beneficial. These mites live in stubble, stored grain and 
beans, cotton seeds, straw, etc., attacking the various insects 
which infest these products and becoming numerous in pro- 
portion to the abundance of their prey. The female has the 
remarkable habit of retaining the eggs and young in her abdomen 

Fig. 138. Louse-mite, Pediculoides ventri- 
One of the cosus; 9. unimpregnated female; $, male, 
X 150. ( 9 . after Brucker from Webster; 
$ , after Banks.) 



until they have become fully developed males and females. Her 
abdomen in consequence becomes enormously distended so that 
the rest of the body appears as only a tiny appendage at one side 
of it. A gravid female (Fig, 139) fully distended may reach a 
diameter of 1.5 mm. (^V of an inch) whereas normally she measures 
only 0.2 mm. {j^s of an inch) in length. Under the most favorable 
conditions only six days may elapse from the time the young 
females emerge from the mother before they reproduce a brood of 

their own. The brood varies 
in number from a few dozen 
to over 200. 

Like many other beneficial 
things, these predaceous little 
mites may become a distinct 
nuisance, and many serious 
outbreaks of infestation of 
human beings by them are on 
record, especially among the 
grain threshers of the central 
portion of the United States 
and among laborers who handle 
stored grains and other dry 
foods. In our Middle West 
their attacks have often been 
^^«^ attributed to harvest mites. In 
Italy the rash produced by 
louse-mites is called " miller's itch." Several outbreaks have 
occurred in the United States due to the use of new straw mat- 
tresses. The transformation of all the grain-moth caterpillars 
into moths leaves the mites with their normal food supply cut 
off, and they are then ready to feed upon any flesh to which they 
may have access in an effort to prevent starving to death. 

The itching rash produced begins about 12 to 16 hours after 
exposure to the mites. At first they produce pale hivelike spots, 
which later become red and inflamed, and itch unbearably. 
Little blisters, the size of a pinhead or larger, appear at the sites 
of the bites and these later develop into httle pustules. Scratch- 
ing results in the formation of scabs, and when these fall off 
dark spots which are slow to fade are left on the skin. The 
rash and itching normally disappear within a week unless fresh 

Fig. 139. Louse-mite, gravid female 
X about 75. (After Brucker 


detachments of mites are constantly acquired. In severe in- 
festations the irritation and poisoning is sufficient to cause 
constitutional symptoms such as fever, high pulse, headache, 
nausea, etc. 

Since the mites cannot thrive on human blood, and remain 
attached to the skin for only a short time, no treatment for 
destroying them is necessary. Remedies to relieve the itching, 
such as the application of soda or soothing ointments, or warm 
baths with a little soda, are called for. To prevent infection 
when handling infected produce, Dr. Goldberger, of the United 
States Public Health Service, suggested a greasing of the body, 
followed by a change of clothes and a bath after working with 
the infected material. Riley and Johannsen suggest the use of 
powdered sulphur as a preventive in view of its efficiency against 
harvest mites. Control of the mite consists largely in keeping 
grain and other dry produce as free as possible from the insects 
on which the mites feed. Burning stubble in winter and threshing 
wheat directly from the shock would tend to lessen the worms in 
stored wheat and with them the mites. 

Grain Mites. — The family Tyroglyphidse, including many 
species of mites which normally feed on grain, flour, sugar, dried 
fruits, cheese and other foods, contains 
several species which become annoying to 
man and produce an itching rash on people 
who handle infested goods. 

According to Banks all the members of 
this family are pale-colored, soft-bodied 
mites, with prominent pincer-like chelicerse 
and no eyes. Their bodies are about 
twice as long as wide and are furnished 
with a few scattered long hairs (Fig. 140). 

The life history of some members of the Tymgiylhus lonj^^ x 3o! 
family is quite remarkable in that there is (After Fumouze and 
added a phase of existence which does not 

occur in other mites. All the species scatter their eggs haphazard 
over the infected material. Upon hatching the larvae have six 
legs and acquire a fourth pair after moulting, in orthodox mite 
style. Some now develop directly into adults, while others go 
through what is called a " hypopus " stage. The hypopus (Fig. 
141) is very different from the nymph from which it develops; 


the body is hard and chitinous, there is no mouth or mouthparts, 
the legs are short and stumpy, and there is usually a raised area 
on the ventral surface with a number of tiny sucking discs. By 
means of these suckers the hypopus attaches itself to insects or 
other creatures and is thus transported to 
new localities, the entire object of the 
hypopus stage apparently being to secure 
passage to new breeding grounds. After 
dropping from its unwilling transporter 
the hypopus moults into an eight-legged 
nymph again, which, after feeding, develops 
into an adult. 

The Tyroglyphidse are all quite similar 
Fig. 141. Hypopus or -j^ appearance, and the characters which 

traveling stage of Tyro- , , , 

glyphus, ventral view. Separate the species, and even the genera, 
Much enlarged. (After ^j.^ f^^ ^^d minute. A considerable num- 

Banks.) » . 

ber of species may attack persons who 
handle infested materials, and they are the cause of " grocers' 
itch." This affliction is caused especially by various species 
of Glyciphagus and Tyroglyphus. Of historical interest is a 
case of dysentery apparently due to a Tyroglyphus, T. longior, 
(Fig. 140) which occurred in one of Linnaeus' students. The 
mites were abundant in his faeces, and were found to live and 
multiply in a juniper-wood cup which he used. As shown by 
Castellani, an itching rash known as '' copra itch," occurring 
among the laborers in the copra mills of Ceylon where cocoanut 
is ground up for export, is caused by a variety of this mite, called 
T. longior castellanii. Copra itch occurs also among stevedores 
who handle copra in London. Another species, Glyciphagus 
huski, was taken from beneath the skin on the sole of the foot 
of a negro in England; it had caused large sores. The negro 
attributed the affliction to the wearing of a pair of shoes loaned 
him by a similarly affected negro from Sierra Leone, Africa. 
Another species, Rhizoglyphus parasiticus, which lives on roots, 
bulbs, etc., in India, produces a skin disease among coolies work- 
ing on tea plantations. It begins with blisters between the toes 
and spreads to the ankles, causing very sore feet. 

Other Species. — A few species of the family Tetranychidse, 
including the '' red spiders " or spinning mites, occasionally 
become troublesome to man, although they are normally vege- 



table feeders and may do much damage to cultivated plants. 
One species especially, Tetranychus molestissimus, which lives 
on the undersides of leaves of a species of cockle bur, Xanthium 
macrocarpum, in Argentina and Uruguay, attacks man during 
the winter months from December to February. It produces 
symptoms similar to those of the louse-mite, with intense itching 
and some fever. The common " red spider," T. telarius, an 
almost cosmopolitan species, also is reported to attack man oc- 

The common chicken mite, Dermanyssus gallinae, belonging 
to the family Parasitidae (Gamasidse), frequently causes much 
irritation and annoyance to those who come in contact with it. 
Although it can thrive and multiply only on certain kinds of 
birds, it sometimes remains on mammals for some time, causing 
an eczema or rashlike breaking-out on the skin, attended, as in 
other mite infections, by intense itching. Except in cases of 
constant reinfection chicken mites are usually troublesome to 
man for only a few days at most. Since these mites can live 
for several weeks without feeding on their normal hosts, places 
formerly frequented by fowls may be infective after the removal 
of the birds. The mites remain on their hosts only long 
enough to fill up on blood, usually at night, spending the rest of 
the time in cracks and crevices in and about the coops. Various 
sprays of sulphur, carbolic solutions and oils are used to destroy 
them. An allied species, Holothyrus coccinella, living on geese and 
other birds on Mauritius Island, attacks man, causing burning and 
swelling of the skin, and frequently proves quite dangerous to 
children by entering the mouth. 

A very small mite, Tydeus molestus, belonging to the family 
Eupodidae, attacks man in much the same manner as do the 
harvest mites. It is common on some estates in Belgium, ap- 
parently having been imported many years ago with some Peru- 
vian guano. It appears regularly each summer on grass plots, 
bushes, etc., in great numbers, disappearing again with the first 
frost. It causes great annoyance in red-bug fashion, not only to 
man but to other mammals and birds as well. 



Itch Mites 

The itch mites, belonging to the family Sarcoptidae, are the 
cause of scabies or mange in various kinds of domestic and wild 
animals, and of " itch " in man. This disease is one which has 
been known for a very long time but was formerly supposed to be 
caused by " bad blood " or other constitutional disorders such 
as cause the growth of pimples. Even at the present time the 
true cause of the disease is not understood by the majority of 

The Parasites. — The itch mites (Fig. 142) are minute whitish 
creatures, scarcely visible to the naked eye, of which the females 

Fig. 142. 

Human itch mite, Sarcoptes scabiei; 9 » female ; $ 
100. (Partly after Banks.) 

male. X about 

burrow beneath the skin and lay eggs in the galleries which they 
make. They are nearly round and the cuticle is delicately 
sculptured with numerous wavy parallel lines, pierced here and 
there by stiff projecting bristles or hairs. There are no eyes 
or tracheae. The cone-shaped mouthparts are covered over by 
the shieldlike upper lip. The legs are short and stumpy and are 
provided with sucker-like organs, called ambulacra, at their 
tips. In the female the two posterior pairs of legs terminate 
in a simple long bristle, whereas in the male only the third pair 
of legs terminates in bristles. The human itch mite, Sarcoptes 
scabiei, is only slightly distinguishable from the itch mites which 
cause scabies and mange in many of our domesticated animals. 
Each infected species of mammal has its own variety of itch 



mite, but many of them can be transferred readily from one 
host to another. In the common human species the male is 
only about 0.25 mm. (y^^ of an inch) in length, while the female is 
about 0.4 mm. (^V oi an inch) in length. A variety of this mite, 
S. scahiei crustosce, causing the so-called '' Norwegian itch," is 
found in northern Europe and occasionally in the United States, 
but is always rare. The disease caused by it differs in some re- 
spects from ordinary itch. Still another species, Notoedres cati, 
which causes a very persistent and often fatal disease in cats, 
temporarily infests man, but is apparently unable to breed in 
human skin, since the infection dies out in a week or two. 

The impregnated females of itch mites excavate tortuous tun- 
nels in the epidermis (Fig. 143) especially on such portions as 

Fig. 143. Diagrammatic tunnel of itch mite in human skin, showing female 
depositing eggs. X about 30. (Adapted from Riley and Johannsen.) 

between the fingers and toes, on the groins and external genitals, 
and in the armpits, where the skin is delicate and thin. The 
tunnels are anywhere from a few millimeters to over an inch in 
length, and are usually gray in color from the eggs and excrement 
deposited by the female as she burrows. The daily excavations 
of a mite amount to two or three millimeters. 

The eggs (Fig. 143) vary in number from 15 to 50. They are 
laid in groups of from two to four, the mite resting after each 
oviposit ion. After they are all laid the female dies, usually at 
the end of a single tortuous burrow. The eggs hatch in from three 
to six days into six-legged larvae. The latter transform in two or 
three days into nymphs. The nymphs commonly build burrows 
for themselves and moult twice, the second time becoming adult 


male and female mites. . -l^he duration of the two nymphal periods 
is from three and one-half to six days, the entire development of 
the mites therefore requiring from' nine to sixteen days. The 
mites are not necessarily nocturnal as was formerly supposed, 
but wander about on the surface of th^ skin when the latter is 
warm, which is most frequently tht& ease when the host is in bed. 
Copulation takes place on the surface of the skin, and apparently 
the males do not burrow or enter the burrows made by the fe- 
males, but merely hide under superficial dead cells of the 
epidermis. Since they die very soon after copulation, they are 
seldom found. The young impregnated females soon begin 
fresh excavations, and produce more eggs. Fifteen or twenty 
eggs each generation, of which approximately two-thirds are 
females, and a new generation about every four weeks, results 
in an enormous rate of increase. In less than six months the 
progeny of one pair of itch mites theoretically would number 
several millions! 

The Disease. The " itch " is a disease which in the past has 
swept over armies and populations in great epidemics, but it has 
decreased with civilization and cleanliness, and is fortunately 
less common now, at least in civilized communities. 

As its name implies, the disease is characterized by itching of 
the most intense kind where the mites burrow in the skin. The 
itching is probably due only to a very slight extent to the me- 
chanical irritation in the skin, but is induced rather ]3y poisonous 
substances secreted or excreted by the mites. Injection of fluid 
containing crushed mites produces an eruption and irritation 
similar to that caused by the burrowing of the living mites. 

The excretions of the mites as they feed in their burrows form 
little hard pimples, about the size of a pinhead or a little larger, 
containing yellow fluid. When these are scratched, as they are 
almost certain to be on account of the unbearable itching, they 
frequently become secondarily infected and may give rise to 
larger sores. Ultimately scabs form over them. 

Since the entire life history of the parasites is passed on a 
single host, generation after generation may develop from a 
single infection, and although the infection apparently may dis- 
appear temporarily, it persists recurrently for many years. Since 
the mites are sensitive to cold the infected areas of skin not only 
do not spread but may become restricted during the winter, to 

ITCH 345 

spread with renewed vigor with the corning of warm weather. 
So persistent is the infection that it is doubtful whether it ever 
spontaneously dies out. " Norwegian itch," caused by Sar copies 
scahiei crustosce, is even more persistent, and, unlike ordinary itch, 
may occur on the face aiid scalp as well as on other parts of the 
body. Gigantic crusts form b^r the infected parts. 

Infection can result only from the passage of male and female 
mites, or of an impregnated female, from an infected to a healthy 
individual. Normally this takes place by actual contact, rarely 
in the daytime on account of the secretive habits of the mites, 
but commonly at night, especially from one bedfellow to another. 
Gerlach experimented to determine how long the mites could 
live away from their hosts and found that in the dry warm air of 
a room they lost vitality so rapidly that they could not be re- 
vived after three or four days. In moist places, on the other 
hand, such as in the folds of soiled underwear or bedcloths, they 
survived as long as ten days. From this it is evident that in- 
fection may take place by means of bedding, towels, underwear 
or other cloth which may come in contact with infected skin. 
The author once witnessed an epidemic of itch arising from the 
use of an infected wrestling mat in a college gymnasium. ( It is 
also possible for infection to be derived from mangy animals, 
though the mites, once adapted for several generations to a 
given host, do not survive a transfer to a different species of host 
more than a few days.^ 

Treatment and Prevention. — The treatment of itch before 
the nature of the malady was understood was considered very 
slow and difficult, and even at the present time it is looked upon 
by many people as a disease which can be recovered from only 
after prolonged treatment. The fact that the mites burrow 
beneath the skin to lay their eggs makes careless superficial 
treatment almost as inefficient as the internal medicine which 
was once taken to " purify the blood." The most effective 
treatment for the itch is as follows: the patient rubs himself 
vigorously with green soap and warm water for about 20 minutes, 
and follows this with a warm bath for half an hour or more, dur- 
ing which the soapy massage continues. In this manner the 
skin is softened, the pores opened and the burrows of the mites 
soaked so that the application of mite poison which is to follow 
will penetrate more readily. When the skin is thus prepared 


some substance for destroying the mites is applied. Sulphur 
ointment made by mixing one-half an ounce of sulphur to ten 
ounces of lard, is excellent; its virtue lies in the formation of 
hydrogen sulphide in contact with the skin, sulphur itself being 
inert. A still more efficient though more expensive remedy is 
•a beta-naphthol ointment, prepared as follows: beta-naphthol, 
75 grains; olive oil, 2 J fluid grams; sulphur, 1 oz.; lanolin, 1 oz.; 
green soap, 1 oz. One of these applications, or some other, is 
unsparingly rubbed into the skin of the infected portions of the 
body, and of a considerable area around them. When rubbed 
in for 20 or 30 minutes the patient goes to bed, leaving the oint- 
ment on his body until morning when it is washed off with another 
bath. Meanwhile the soiled underwear, bedclothes or other 
possibly infected articles are sterilized by boiling or baking. 
Since this course of treatment does not destroy the eggs it is 
repeated in about ten days in order to destroy any mites which 
may have hatched in the meantime. 

For delicate-skinned individuals the treatment described above 
is too severe and may, of itself, give rise to inflammation of the 
skin not unlike that caused by the mites. In such case balsam 
of Peru may be used satisfactorily instead of sulphur ointment, 
but should be rubbed in several times at intervals of a few hours. 
It does not cause any irritation. 

Prevention of this annoying infection consists merely in avoid- 
ing contact with infected individuals, and of shunning public 
towels or "soiled bed linen. A single infected individual in a 
logging or railroad camp may be a means of infecting the entire 
camp. Means should, therefore, be taken to guard against 
such individuals whenever possible, and to prevent the spread 
of infection from unsuspected individuals by care as regards the 
use of towels and bed clothes. 

Hair Follicle Mites 

The hair follicle or face mite, Demodex folliculorum (Fig. 144), 
of the family Demodecidse, is a species which is most strikingly 
adapted for its parasitic life. It is a wormlike creature, very 
unmite-like in general appearance, which lives in the hair follicles 
and sebaceous glands of various mammals. In man it occurs 
especially on the face. 



The wormlike appearance of the adult mites is due to the great 
elongation of the abdomen which is marked by numerous fine 
lines running around it. The beak is short and broad, and the four 
pairs of legs, all similar, are short, stumpy, three-jointed append- 
ages. The female mites are .35 to .40 mm. 
long (about ^ of an inch), while the males are 
a little smaller. 

The multiplication of these mites is slow. 
The eggs hatch into tiny six-legged larvae in 
which the legs are mere tubercles. It requires 
four moults to bring the larvae to sexual 

In most cases these parasites cause no incon- 
venience whatever and their presence is not 
even suspected. In Europe a large proportion 
of people are said to be infected, but in Amer- 
ica, according to Riley and Johannsen, there is 
reason for believing that the infection is far 
less common than is usually supposed. Since 
"generation after generation may be produced 
on a single host the infection is potentially 
indefinite in its duration. When the mites 
become numerous in the hair follicles 
sebaceous glands they sometimes cause " black 
heads " by causing a fatty accumulation to be produced, but 
they are not the only or even the usual cause of "black-heads.'' 
The skin disease known as '' acne " has also been attributed to 
these mites, but probably erroneously. Follicle mites have been 
suspected also of spreading leprosy. 

The method of transmission of the mites to another host is 
not definitely known but it is probable that the adults wander 
on the surface of the skin at times, and may then be transmitted 
by direct contact or by towels, as are itch mites. In dogs, 
where the follicle mite, possibly a different species, causes a very 
severe and often fatal form of mange, transmission from dog 
to dog takes place in a very irregular manner, and there are 
frequent instances cited of infected dogs associating for a long 
time with uninfected ones without spreading the disease. Ex- 
periments with transmission of the canine follicle mite to man 
have invariably failed. Little is known about treatment of 

Fig. 144. Hair- 
follicle mite, Demo- 
dex folliculorum. X 
or 200. (After Meg- 


Demodex infection, but it is probable that sulphur applications 
in some form would reach and destroy them. 


Related to the mites, but now placed in a distinct order, Lin- 
guatulina, are the tongue- worms. These animals have become so 
modified by parasitic life that the adults have lost nearly all re- 
semblance to the other members of their group, and have become 
so wormlike, both in form and life history, as 
to have been classified by older writers with 
the tapeworms (Fig. 146A). Only the larval 
stage gives a clue to their real relationships. 
Their long bodies are either flattened or 
cylindrical, and distinctly divided into rings 
or segments as in leeches. There is no dis- 
tinct demarcation between head, thorax and 
abdomen. On either side of the mouth are 
of^Porocephaius a^mif- ^^o hooks which can be retracted into grooves 
latus. X 3. (After like the claws of a cat (Fig. 145) . These are 
^^ usually looked upon as the vestiges of some of 

the appendages. At the bases of the retractile hooks there open 
a number of large glands, the secretion of which is believed to have 
blood-destroying power. The internal organization of the body 
is degenerate in the extreme; there is no blood, no respiratory 
system, no special sense organs, no organs of locomotion; little 
more than the barest necessities of racial existence — a simple 
nervous system, a digestive tract and a reproductive system. 
The sexes are separate. 

The adult worms live in the nostrils, trachse or lungs of car- 
nivorous reptiles and mammals, where they produce their myriads 
of eggs. The latter are voided with the catarrhal products of 
the respiratory system caused by the presence of the parasites. 
The egg-laden mucous excretions from the nose of an infected 
animal are dropped on vegetation and eaten by herbivorous ani- 
mals, whereupon the eggs (Fig. 146B) develop into larvae in the 
new host. These larvae (Fig. 146C), hatched out in the stomach, 
are far more mitelike than the adults, inasmuch as they possess 
two pairs of rudimentary legs and primitive arthropod mouth- 
parts. The larvae migrate to the liver, spleen or other organs 



and there encyst (Fig. 146D). After a series of moults a second 
larval stage is entered upon, this time with a wormlike appear- 
ance much more like that of the adult (Fig. 146E). 

At this stage a " wanderlust " seizes the tongue- worm and it 
begins an active migration in an endeavor to reach a more satis- 
factory site for adult life. The mites may settle in the res- 


Fig. 146. Life history of tongue- worm, Linguatula rhinaria; A, adult female 
from nasal passage of dog; B, egg containing embryo; C, larva from sheep, man or 
other animals; D, encysted larva; E, 2nd larval stage, from liver of sheep or man. 

piratory tract of their original host, or may abandon their host 
by way of throat or anus to take chances on being snuffed up or 
taken into the mouth cavity of another animal. Having gained 
access to their final habitat in the nostrils or lungs, they attach 
themselves by their hooks, moult, copulate and reproduce. 

While both larval and adult stages of tongue-worms are oc- 
casionally found in man, the larvae, as liver parasites, are more 

The tongue-worm most frequently observed in man is Lingua- 
tula rhinaria. The male of this species is a small worm, whitish 
in color, about three-fourths of an inch in length, whereas the 
female (Fig. 146 A), which is yellowish or brownish due to the 
eggs in her body, reaches a length of from three to five inches. 
The adults occur most commonly in the nasal passages of dogs 
(Fig. 147). The eggs (Fig. 146B) are dispersed with mucus 
during the violent fits of sneezing to which the presence of the 
parasite gives rise. The swallowing of food or drink, especially 
grass or vegetables, soiled by this infective mucus, results in the 
access of the larva-containing eggs to the intermediate host, which 
is most frequently sheep, goats, rabbits, etc., but occasionally 



man. In the course of five or six months the larvae (Fig. 146C), 
having migrated to the Hver or lymph glands, transform to the 
second larval stage (Fig. 146E), reach a length of about one- 

FiQ. 147. Head of a dog split in half to show three tongue-worms, Linguatula 
rhinaria, (a) in the nasal cavity. Reduced in size. (After Colin, from Hall.) 

fourth of an inch, and consist of from 80 to 90 rings or segments, 
each one with very fine denticulations on the hind margin. For 

a long time this larva was looked 
upon as a distinct species. L. rhinaria 

is nowhere abundant, even in its 

normal hosts, though in some parts of 
Europe about ten per cent of dogs are 
said to be infected. The majority 
of human cases reported have been 
in Germany. 

Another species which is occasion- 
ally found as a parasite in man dur- 
ing its larval stage is Porocephalus 
nrmillatus (Fig. 148). Unlike Lingua- 
tula, this worm has a cylindrical body, 
only about 18 to 22 rings of segments 
and a total length of about one-half 
an inch. The segments have no fine 
denticulations as they have in Lingua- 
tula. This species is said to spend its 
adult life in the lungs of the African python, the larvae occurring 
occasionally in man, but more frequently in giraffes, monkeys and 
other African animals. Sambon thinks the eggs escape from the 

Fig. 148. Porocephalus armil- 
latus; 9' female; $, male. 
Natural size. (After Sambon.) 


nostrils of pythons into water, and that infection occurs through 
drinking. The return of the larva from the intermediate host 
to the python probably takes place by the intermediate host 
being eaten. The larvae as they occur in man or other animals 
may either be encysted or freely migrating in the tissues or body 
cavities. Such symptoms as emaciation, bronchitis, pleurisy and 
offensive discharges from the lungs may be present. From 75 
to 100 larvae have been known to be expectorated by a single 
patient. Recently Mouchet reports finding Porocephalus in over 
22 per cent of post mortem examinations made at Leopoldville, 
in Belgian Congo. 

A more slender species, P. moniliformis, bright yellow in color, 
occurs as an adult in pythons in southern Asia and the East 
Indies, and in two cases human infection has been reported. 
One case of human infection with a Porocephalus in Montana in 
1876 is of interest, since, as pointed out by Sambon, it may have 
been the larva of P. crotali of rattlesnakes. 


While mites as a group are extremely annoying pests, with one 
exception they are not dangerous as disease carriers. The ticks, 
on the other hand, are not only annoying but dangerous. Several 
important diseases of domestic animals are transmitted solely by 
ticks, and several human diseases are likewise dependent on 
ticks for dissemination, especially African relapsing fever or 
*' tick fever " and Rocky Mountain spotted fever. In addition 
to this, tick bites, at least those of some species, give rise to a 
serious form of paralysis, especially in children, which may end 
in death. Tick bites also frequently give rise to dangerous 
ulcerating sores which may result in fatal blood poisoning. The 
economic importance of ticks as parasites of domestic animals is 
not for consideration here, but it would not be amiss to state 
that the annual loss in the United States from cattle ticks alone 
is estimated at from $40,000,000 to $50,000,000. It is evident 
that ticks should be looked upon as worthy candidates for ex- 
termination wherever this is possible. 

Although the ticks constitute only one of several divisions of 
the order Acarina, they are so readily distinguishable and so 
well known that in the popular mind the ticks are looked upon as 
a group quite distinct from all other mites, and equivalent with 
them. They are of relatively large size and usually exceed all 
other Acarina in this respect even in their larval stages. Some 
species when full grown and engorged are fully half an inch in 

General Anatomy. — The body of a tick is covered by a 
leathery cuticle which is capable of great expansion in the fe- 
males as they engorge themselves on their host's blood, fiUing the 
numerous complex pouches of the digestive tract (Fig. 149). 
When not engorged ticks are flat and oval or triangular in shape 
(Fig. 154), usually tapering to the anterior end, but after en- 
gorgement they resemble beans or nuts of some kind (Fig. 158). 




Fig. 149. Digestive tract of Argas persicus; an., anus; ch., chelicera; int. c, 
intestinal coeca; oes., oesophagus; ph., pharynx; sal. gl., salivary glands; st. 
stomach. X about 20. (Adapted from Robinson and Davidson.) 

.- ^yp- 


bas. p. 

Fig. 150. Head or capitulum of tick; 
hyp., hypostome; chel., chelicera; pal., 
palpus; bas. p., basal piece. (Partly after 

Fig. 151. Tip of chelicera of a tick, 
much enlarged; cut. p., articulated 
cutting part; shaft, shaft; sh., sheath; 
fi. t., tendon of flexor muscle; ex. t., 
tendon of extensor muscle. (After 
Nuttall, Cooper and Robinson.) 



Most ticks have a little shield or " scutum " on the dorsal sur- 
face, quite small in the females, but nearly or quite covering the 
back in the males (Fig. 156). Attached to it in front is a little 
triangular piece, the capitulum or " head " which bears the 
mouthparts (Fig. 150). The latter consist of a quite formidable 
piercing organ, the hypostome, a pair of chelicerse or mandibles 
which are armed with hooks (Fig. 151), and a pair of blunt palpi 
which are probably tactile in function. The hypostome is a 
rasplike structure, beset with row after row of recurved teeth 
(Fig. 152). So firmly do these hold in the flesh into which the 

proboscis is inserted that 
forcible removal of a tick 
often results in the tearing 
off of the body from the 
capitulum which remains at- 
tached to the host. Like 
other Arachnida, ticks have 
four pairs of legs. These 
are quite conspicuous when 
the body is empty but are 
^ hardly noticeable after en- 
gorgement. The breathing 
ticro'S«''^^r*ZrJo™f^J;.«: apparatus consists of a sys- 

nymph; B, Argas persicus, adult; C, Ixodes tem of tracheffi which open 

7^\:^!Zt^l SZ.rt^. by a pair of spiracles in the 

male; G, Omithodorus mouhata, nymph; H, vicinity of the fourth pair 

r^a*:^TuenhS;:rN^u;ifr'^'" ^f l«g«- The shape of the 

plates which cover the spir- 
acles are sometimes used in distinguishing species. The ventral 
surface has two openings, the genital pore just back of the pro- 
boscis, and the anus some distance from the posterior end of the 
body (Fig. 154). 

Habits and Life History. — All ticks are parasitic during some 
part of their lives. The majority of them infest mammals, 
though many species attack birds and some are found on cold- 
blooded animals. A very decided host preference is shown by 
some species, whereas others appear to be equally content with 
any warm-blooded animal which comes their way. In many 
species the hosts or parts of hosts selected by the adults are not 
the same as those selected by the immature forms. 



The life histories of all ticks are more or less similar. After 
several days of mating the female ticks engorge and soon after 
drop to the ground and begin to lay their eggs (Fig. 153). These 
are deposited on or just under the surface of the ground. Some 
of the family Argasidae engorge several times, laying a batch of 
from 20 to 50 eggs after each gluttonous repast. All of the 
Ixodidse, on the other hand, lay their eggs after a single engorge- 
ment. The eggs number from a few hundred in some species 
to upwards of 10,000 in others and are laid 
in rather elongate masses in front of the 
female. Each egg as it is passed out by the 
ovipositor is coated with a viscid substance 
by glands between the head and dorsal shield 
of the tick and is then added to the mass in 
front. The process of egg-lajdng occupies 
several days, as not more than several hun- 
dred eggs can be passed out and treated 
with the viscid coating in the course of a 

The eggs develop after an incubation p>eriod 
which varies with the temperature from two -pia 153 Texas 
or three weeks to several months. Eggs de- fever tick, Margaropus 
posited in the fall 'do not hatch until the fol- (^tt^Grkybi^^^^ 
lowing spring. 

The larval ticks which hatch from the eggs are much smaller 
than the adult ticks and have only six legs (Fig. 157B). They are 
popularly known as " seed ticks." The seed ticks soon after 
hatching climb up on a blade of grass or bit of herbage and assume 
a p>oUcy of watchful waiting until some suitable host passes with- 
in reach. Seed ticks must be imbued with almost unlimited 
patience, since in many if not in the majority of cases long delays 
must fall to their lot before a suitable host comes their way like 
a rescue ship to a stranded mariner. The jarring of a footstep 
or rustle of bushes causes the ticks instantly to stretch out to 
full length, feeling with their clawed front legs, eager with the 
excitement of a life or death chance to be saved from starvation. 
If success rewards their patience, even though it may be after 
many days or weeks, they feed for only a few days, becoming 
distended with blood, and then drop to the ground again. Re- 
tiring to a concealed place they rest for a week or more while 

356 TICKS 

they undergo internal reorganization. Finally they shed their 
skins and emerge as eight-legged but sexually immature ticks 
known as nymphs (Fig. 157C). The nymphs climb up on bushes 
or weeds and again there is a period of patient waiting, resulting 
either in starvation or a second period of feasting. Once more 
the ticks drop to the ground to rest, transform and moult, this 
time becoming fully adult and sexually mature. In this condition 
a host is awaited for a third and last time, copulation takes place, 
sometimes even before a final host is reached, and the females 
begin their final gluttonous feeding which results in distending 
them out of all proportions. In some species, especially those 
which live on hosts which return to fixed lairs, copulation takes 
place ojff the host. When this occurs, as in many species of 
Ixodes, the male is often not parasitic at all, and may differ 
markedly from the female in the reduced structure of its hypo- 
stome (Fig. 152C, E and F). In all species the males die shortly 
after copulation. 

This, in general, is the life history of ticks, but it is, of course, 
subject to considerable variation in different species. In many 
species there are two nymphal periods instead of one. In some 
species, as in the Texas fever tick, Margaropus annulatus, the 
moulting takes place directly on the host, thus doing away with 
the great risk of being unable to find a new host after each suc- 
cessive moult. In a few species the first moult is passed through 
on the host, but the second is passed on the ground. The most 
important asset of ticks to counterbalance the disadvantage of 
having to find new hosts is their extraordinary longevity. Larvae 
of ticks have been known to live more than six months without 
food, and adults have been kept alive in corked vials for five 

There are two families of ticks, the Argasidse and the Ixodidse. 
The Argasidse include the bird ticks and their allies, which are 
distinguished from the Ixodidse by the absence of a dorsal shield 
and in having the head partially or entirely concealed under the 
overlapping anterior margin of the body (Fig. 154). The fe- 
males of this family do not become distended as do those of the 
Ixodidse, but take more moderate though more frequent meals. 
They are chiefly inhabitants of warm countries. Both nymphs 
and adults feed at night, usually dropping off their hosts im- 
mediately after a meal, and thus seldom being carried from the 



lairs or abodes of their hosts. The Ixodidae, on the other hand, 
inhabit the hosts rather than their lairs, and frequently remain 
attached for several days, or even longer. In the less capacious 
Argasidae the females lay their eggs in a number of installments 

Fig. 154. Comparison of dorsal and ventral view of Ixodid and Argasid females; 
A, dorsal view of Ixodid 9 I ^' ■> ventral view of same; B, dorsal view of Argasid 
9 ; B' , ventral view of same. An., anus; cap., capitulum; d. sh., dorsal shield; 
e.s., eye spot; gen. op., genital opening; sp., spiracle. 

after successive feeds, and the total number of eggs may be 
counted in hundreds instead of thousands. The reason for this 
difference is readily accounted for by the difference in habits in 
the two families, since the progeny of the Argasidae, reared in 
the lairs of the hosts, have far better chances of finding a host and 
of surviving than do the progeny of the Ixodidae which live on 
their hosts and may drop off to lay their eggs almost anywhere 
in the wanderings of the host. 

Tick Bites. — The status of ticks as human parasites, as stated 
before, is one not to be passed over lightly. Aside from the 

358 TICKS 

transmission of diseases tick bites are dangerous to man in a 
number of ways. 

The wounds made by ticks, especially if the head is torn off in 
a forcible removal of the parasite, are very likely to become 
infected and result in inflamed sores or extensive ulcers, not in- 
frequently ending in blood poisoning. The author, as the result 
of the bite of a tick in northern California (probably Dermacentor 
occidentalis) , suffered from an ulcerating sore on his arm, over half 
an inch in depth and three-fourths of an inch in diameter. Blood 
poisoning set in early causing a very high temperature and great 
pain in the arm, and it was only a timely return to civilization 
and hospital care that saved his arm if not his life. Sanitary 
removal of ticks and cleansing of the wounds, as described on 
p. 367, would be well worth the consideration of every inhabitant 
or traveller in a tick-infested country. 

Tick Paralysis. — More serious than the painful wound made 
by ticks is a peculiar paralyzing effect of tick bites, known as 
tick paralysis. This occurs especially from tick bites on the back 
of the neck or on the head; it affects the legs first, but spreads 
forward in a few days to the arms and neck and may result in 
death. Paralysis in man and animals from tick bites has been 
reported from South Africa and Australia and in North America 
from the parts of Oregon and British Columbia inhabited by the 
spotted fever tick. Sheep are especially subject to tick paraly- 
sis, to such an extent in British Columbia as to present a serious 
problem. This peculiar effect of tick bites has been reproduced 
experimentally in sheep in places where it has not been known 
to occur normally, by allowing a spotted fever tick, Dermacentor 
venustus (Fig. 156), to bite along the spinal column. The bites 
of this tick are particularly likely to cause paralysis, though it is 
not yet known whether this is because of an especially toxic 
secretion produced by this species or because of its preference for 
biting along the spinal cord or on the head. There has been 
much controversy as to what really causes the paralysis, some 
authors believing that it is due to a microorganism injected by 
the tick, since it is usually six or seven days after the attach- 
ment of the tick before the effect is felt. The fact, however, 
that no such organism can be discovered, that inoculations of 
blood and other parts of diseased animals into healthy ones does 
not result in transmission of the disease, and that the paralysis 


is usually accompanied by little or no fever, makes this seem 
unlikely. A single attack of tick paralysis seems to confer 
immunity and it is probable that many children are naturally 
immune. The most reasonable explanation is that the ticks 
secrete a toxic substance, especially when rapidly engorging, 
which has a specific action on the motor nervous system. Pos- 
sibly the bite must pierce or come in contact with a nerve or 
nerve ending in order to produce the effect. 

Numerous cases of tick paralysis in children have occurred 
in British Columbia and in the Blue Mountains of Eastern 
Oregon. One doctor in the vicinity of Pendleton reported no 
less than 13 cases. The disease begins with paralysis of the 
legs and usually results in complete loss of their use; the paraly- 
sis ascends in the course of two or three days, affecting the arms 
and finally the thorax and throat. Unless the heart and respi- 
ration are affected, recovery follows in from one to six or eight 
days after removal of the ticks. The latter, often in pairs, are 
usually found on the back of the neck or along the middle line 
of the head, especially just at the base of the skull. If the ticks 
are not removed, the disease may result in death or in spon- 
taneous recovery after a few days or a week. 

Unfortunately in most of the cases of tick paralysis in chil- 
dren the ticks have not been identified, but it is well known 
that the spotted fever tick is the most frequent cause of paralysis 
in sheep and the only species by which such a disease has been 
reproduced experimentally. In South Africa, however, a similar 
paralysis in sheep results from the bites of Ixodes pilosus, and 
paralysis in children in Australia from the bites of other but 
undetermined species. The scrub-tick, Ixodes holocyclus, is said 
to be troublesome as a cause of paralysis in young stock in New 
South Wales. In the regions of Oregon and British Columbia 
where tick paralysis is especially prevalent there occur a number 
of different ticks, and there is no evidence that any tick which 
attacks man along the spinal cord or on the head may not cause 

Ticks and Disease 

The r61e of ticks as disease carriers has been well established 
since Button and Todd in 1905 proved that African relapsing 
fever was transmitted by a species of tick known as the tampan, 

360 TICKS 

Ornithodorus moubata (Fig. 155). A year later Dr. Ricketts 
showed that spotted fever in the United Stated was dependent 
upon a tick, Dermacentor venustus, for its transmission. It is 
now known that ticks serve as intermediate hosts for a consider- 
able number of disease germs of two different groups, the spiro- 
chaetes and the Piroplasmata. The various forms of relapsing 
fever of man are caused by spirochaetes, and it is possible that 
all the different types of this disease may be transmitted by 
ticks, though in some of the types other arthropods act as the 
usual transmitters. Many diseases of domestic animals are 
caused by organisms of the group Piroplasmata (see p. 182), 
including Texas fever of cattle in North America, East Coast 
fever of cattle in Africa, biliary fever of horses in Asia and Africa, 
and similar diseases of sheep, dogs, rats and monkeys. The only 
human disease positively known to be caused by an organism 
of this group is Oroya fever of Peru, caused by Bartonella hacilli- 
formis (see p. 178). Whether or not a tick is instrumental in 
transmitting this disease is not yet known. Rocky Mountain 
spotted fever was at one time thought to be caused by a member 
of the Piroplasmata, but the parasite of this disease is still un- 
known. The fact that it is transmitted by a tick suggests that 
it may be found to belong either to the spirochaetes or to the 
Piroplasmata. Ticks have also been suspected of carrying the 
East Indian form of kedani fever which in Japan is transmitted 
by a larval mite, but this has not been proved. 

Ticks and Relapsing Fever. — The fact that tick bites frequently 
give rise to serious fever and illness, now known as relapsing 
fever, which not infrequently result in death, has been well known 
in Africa for many years, in fact Livingston in his " Darkest 
Africa " speaks of this disease as resulting from tick bites. The 
implicated ticks, Ornithodorus moubata, known as " tampans " or 
'' carapatos," are very common pests in shaded places in the 
dirty thatched houses of the natives, and are difficult to avoid. 
They occur chiefly along the routes of travel, being readily 
carried and dispersed by caravans. They live also in the bur- 
rows of warthogs. A detailed account of the role played by 
the tick in harboring and transmitting relapsing fever spiro- 
chaetes and a description of the disease can be found in Chap. 
IV, p. 42. 

The tampan is a broad oval tick (Fig. 155), mud-colored, 


about five-eighths of an inch in length, belonging to the family 
Argasidse. Like the other members of the family it has no 
dorsal shield and has the margin of the body produced in such 
a way as to conceal most of the head and legs. Unlike most 
ticks the larvae are weak and do not feed 
but transform to nymphs very soon after 
the eggshell splits. The nymphs are 
said to produce more painful wounds than 
the adults and they can just as readily 
transmit relapsing fever. 

An allied species, 0. savignyi, occurs 
from Abyssinia through Arabia to India 
and Ceylon and attacks man, camels and 
horses. It is said to transmit the Indian 

- !• 1 • c • i 1 i • Fig. 155. The tampan, 

form of relapsmg fever m these countries, omithodorus mouhata. x 3. 
Like 0. mouhata it attacks its host in its 

resting place, hiding in the daytime in dust or sand in or around the 
squalid huts of the natives. Except in coastal towns, where it is 
abundant everywhere, it is found chiefly in camps of long stand- 
ing inhabited by men and animals. Burrowing to a depth of an 
inch in dusty soil it can live without food for months. In Persia 
0. tholosani is said to transmit African relapsing fever which has 
been introduced there. 0. talaje of Mexico and Central America 
has habits very similar to those of the tampan in Africa; it fre- 
quently occurs in the adobe houses and attacks the occupants 
at night. 0. turicata, the '^carapato" of Central America, is 
another very annoying species. Its bites are so severe that hogs 
are said to have been killed in a single night by its attacks. 
Though not proved it is very probable that one or both of these 
species may be instrumental in transmitting the milder American 
form of relapsing fever. It is almost certain also that another 
tick, the " miana bug " of Persia, is capable of transmitting 
European relapsing fever (see p. 364). 

Ticks and Spotted Fever. — The tick which is responsible for 
the transmission of Rocky Mountain spotted fever (see p. 191) 
is a wood tick, Dermacentor venustus (andersoni) (Fig. 156). This 
is a handsome reddish brown species, the male of which has the 
whole back marked with black and silvery-white lines, while 
the female has only the small dorsal shield marked with silver, 
the abdomen being deep reddish brown. This species is one 



which requires two different hosts to complete the Ufe cycle. 
The six-legged larvae (Fig. 157B), of which there are about 5000 
in a brood, attach themselves to any of the rodents which abound 

Fig. 156. Spotted fever tick, Dermaeentor venustus, male {$) and female (9)- 


Fig. 157. Development of spotted fever tick, Dermaeentor venustus; A, eggs; 
B, larva; C, nymph. X 30. 

in the country where the ticks occur, especially squirrels of 
various kinds. Usually the larvae, and the nymphs also, attach 
themselves about the head and ears of their host. After a few 
days the larvae drop, transform into nymphs (Fig. 157C) and 



again attack their rodent hosts. After dropping off these and 
transforming into adults they no longer pay any attention to the 
rodents but seek larger animals, especially preferring horses and 
cattle, though they readily attack other large wild and domestic 
animals and man. Their original wild hosts were probably the 
mountain goats, elk and other wild game of the region, but with 
the supplanting of these by domestic animals the latter have 
become the main host animals of the ticks. Unlike most ticks, 
this species may take two or even two and a half years to com- 
plete its life cycle under unfavor- 
able conditions. The winter is 
passed in either the nymphal or 
adult stages. 

Dermacentor venustus is found in a 
limited area in northwestern United 
States and British Columbia, east 
to eastern Montana and eastern 
Wyoming, west to the Cascade 
Mountains and south into Nevada 
and Colorado. This distribution 
somewhat exceeds the present dis- 
tribution of spotted fever (Fig. 58, 
p. 191). 

Several different species of ticks fig. 158. Spotted fever tick, 

have been found capable of trans- Dermacentor venustus; engorged 

mitting spotted fever from rodent 

to rodent under experimental conditions. Several species of ticks 
other than D. venustus are found in the spotted fever districts, 
but none of these can have any hand in the transmission of the 
disease to man since they do not attack him. A tick closely 
related to D. venustus, the Pacific wood tick, D. occidentalis, oc- 
curs west of the Cascades and Sierras in Oregon and California 
and frequently attacks man. There is little doubt but that if 
spotted fever once got a foothold in the territory occupied by this 
tick, the latter would act as an efficient disseminator. In southern 
and eastern states other ticks which attack man would probably 
disseminate the disease were it once introduced. For this reason 
it is of the utmost importance that the infection should not be 
carried to parts of the country which are not now infected. 
Measures for the prevention of this are discussed in Chapter X, 
under '* Spotted Fever." 



Other Troublesome Ticks 

Although there are a large number of species of ticks which 
will attack man, there are a few in addition to the disease-causing 
species named above which deserve special mention on account 
of the particularly bad effects of their bites. The family Argasidse 
includes a number of species which produce very venomous bites 
when they attack man. The various species of Ornithodorus, 
some of which have already been mentioned as carriers of relap- 
sing fever, produce very painful bites. Another species worthy 
of mention is the famous " miana bug," Argas persicus (Fig. 159), 
which is especially renowned in Persia, but which also occurs in 

many other parts of the Old 
World. This species is often a 
great tormentor of human be- 
ings, especially in dirty huts 
where it can breed readily. It 
is primarily, however, a parasite 
of fowls, and is believed to be 
identical with the American fowl 
tick, Argas miniatus. The bites 
of the miana bug are dreaded 
not only on account of their 
painfulness, but also because 
they are believed to be a means 
of transmission of European re- 
FiG. 159. Persian tick or fowl lapsing fever, in common with 

tick, Argas persicus. X 5. (After ,. , , -i • j_ 

Braun.) lice and perhaps other msects. 

A closely allied species, A. re- 
flexus, is a common parasite of pigeons in Europe and North 
Africa, and frequently attacks people who come in contact with 
infested birds or cotes. 

Another argasid tick which deserves special mention is the 
" pajaroello," 0. coriaceus of California. Herms states that 
" natives, principally Mexicans, in the vicinity of Mt. Hamilton 
fear this parasite more than they do the rattlesnake, and tell 
weird tales of this or that man having lost an arm or leg, and in 
one instance even death having ensued, as a result of a bite by 
the Pajaroello. There seems to be a suspicion in that region 
that three bites will result in certain death. The stories all 



agree in the essential detail that the bite results in an irritating 
lesion which is slow to heal and often leaves an ugly deep scar." 
The tick is about two-fifths of an inch in length, irregularly oval, 
with thick turned-up margins, roughly shagreened, and of a 
yellowish earthy color spotted rusty red. It occurs in the Coast 
Range mountains of California and in Mexico and according to 
Herms is most commonly found in the dry leaves under live 
oak trees where cattle or other animals are accustomed to lie 
in the shade. It passes through from four to seven moults to 
reach the adult state, occupying 
from one to two years to com- 
plete its life history, according 
to its success in finding suitable 
hosts. The bites of this tick 
produce sharp pain, accompanied 
by a considerable discoloration 
around the wound, and if on an 
arm or leg the whole limb may 
become greatly swollen as in the 
case of a snake bite. After scab- 
bing over, the wound may con- 
tinue to exude lymph and to be 
irritable for several weeks, and it 
is possible that infection and con- 
sequent blood-poisoning might 
readily occur, thus giving a basis 
for the tales mentioned above. ^^^ (ofo^SSL,°U- 

Another noteworthy member of nini. x lo. (After Marx from 
the Argasidae is the spinose ear 

tick, Otiobius (or Ornithodorus) megnini (Fig. 160), of south- 
western United States and Mexico, and now becoming common 
in parts of South Africa. It is very troublesome to man as well 
as to horses and other domestic animals. The nymphs, which 
develop from the larvae in the ears of their hosts, are peculiar in 
having very spiny bodies, quite different from the smooth larvae 
and adults. The nymphs remain attached to their hosts for 
months but finally drop off to transform into adults. The 
adults are not parasitic but lay their eggs without further feed- 
ing. The pain and annoyance caused by the spiny nymphs in 
the ears of domestic animals is sufficient to cause them to be- 



come ill-tempered and emaciated. Children sometimes suffer 
a great deal from their attacks, and have difficulty in dislodging 
the invaders from their ears. This can readily be done, however, 
by pouring olive oil or some other harmless oil into the ears. 

Although there are a large number of species of the family 
Ixodidae which may attack man, they do not as a rule prove as 
great pests or produce as severe bites as some of the Argasidse. 
The characteristics of some of the principal genera are given in 


Fig. 161. Diagrams of rostra or capitula of important genera of Ixodid ticks, 
useful in identification. (After Nuttall.) 

With long rostrum Other characteristics 

A, Ixodes Anal, groove in front of anus, no eyes, 

no festoons. 

B, Hyalomma eyes present, festoons present. 

C, Amblyomma eyes present, festoons present, ornate. 

Aponomma eyes absent, festoons present, ornate. 

With short rostrum 

D, Haemaphysalis eyes absent. 

E, Margaropus circular spiracles. 

F, Rhipicephalus . . .■ comma-shaped spiracles. 

G, Dermacentor eyes present, ornate. 

Fig. 161 and accompanying table. Only a few species need 
special mention here. Dermacentor venustus is, of course, of 
preeminent importance on account of its role as a transmitter 
of spotted fever and in producing tick paralysis. D. occidentalism 
the '' wood tick " of the Pacific slope of the United States, is 
another member of the genus which very commonly attacks man; 
its bites are particularly likely to cause ugly ulcerating sores. 
Experimentally, as said before, it has been shown to be capable of 
transmitting spotted fever, and it would probably act as an effi- 


cient disseminator if the disease were introduced into its terri- 
tory. The same might be said of D. variabilis, the dog tick of 
eastern North America, though this species less commonly 
attacks man. 

Of particular interest is the effect produced by the larvae of 
certain ticks in southeastern Africa, especially the bont tick, 
Amhlyomma hebrceum. Its larvae produce itching and painful 
wounds which may be followed in a week or so by fever, head- 
ache, skin eruptions and other general symptoms. The name 
*' tick-bite fever " has been applied to this malady. Whether it 
is caused by a microorganism is unknown. Immunity rapidly 
develops, so that usually only new arrivals are affected. In 
Europe one of the most troublesome species of Ixodidae, as far 
as man is concerned, is the common dog tick, Ixodes ricinis, 
which attacks a great variety of animals, and is evidently quite 
fond of human blood. A particularly obnoxious species in 
tropical America is Amhlyomma cajennense. Not only the 
nymphs and adults but also the larvae of this species are pests 
of man. 

Treatment and Prevention. — As shown above tick bites may 
be attended by a number of serious results, such as fever, ulcer- 
ating sores, paralysis or disease transmission. The treatment 
of the bites, therefore, may be of considerable importance. It 
has been shown that ticks, at least in the case of the relapsing 
fevers, do not ordinarily infect directly by biting, but by con- 
taminating the wound with infected excrement. It is obvious, 
therefore, that disinfection of the wound after removal of the 
tick would be a precaution of great value in places where ticks 
carry diseases to which human beings are susceptible. Such 
treatment would also prevent bacterial infections of various 
kinds from entering the wounds and causing ulceration or blood- 

Ticks should never be removed forcibly since if so handled 
the head is likely to tear off from the body and remain in the 
wound, held there by the ugly barbed proboscis. A drop of 
kerosene, creoline or some other oil on the head of the tick will 
cause it to withdraw its beak and drop off in the course of a 
minute or two. Disinfection of the wound with alcohol, weak 
carbolic, lysol or other disinfecting agent should follow imme- 

368 TICKS 

Precautions against tick bites where serious diseases are likely 
to result are of the greatest importance but very difficult. King, 
while investigating spotted fever, spent a whole season in the 
heart of the Bitter Root Valley in Montana where spotted fever 
infection was most dangerous. He wore high-topped shoes and 
cotton outer garments soaked in kerosene and had pieces of 
khaki cloth soaked in kerosene sewed to the tops of his boots or 
fastened by drawstrings higher up on his leg. A leg covering of 
oil-proof material with crude oil applied on the outside would 
be of benefit, according to King. In Abyssinia the attacks of 
Ornithodorus savignyi are prevented by rubbing the feet with 

Means of control of tick pests vary considerably with the dif- 
ferent species, depending on the hosts, their seasonal history, 
their varying life histories and other factors. 

Most of the species of ticks which attack man are normally 
parasitic on domestic animals, and therefore means of extermi- 
nating ticks on the latter would tend to reduce the human pests. 

Ticks on domestic animals may be destroyed either by hand 
treatment or by dipping, or by the elimination of ticks from 
pastures by starvation. The cattle tick, Margaropus annulatus, 
has been eliminated from many ranches by a skillful manoeuvering 
of the cattle, driving them from field to field in such a way that 
in the course of a number of months the ticks would all have 
dropped and perished from starvation. Such a plan is not 
feasible for many species since a variety of hosts may be 
utilized, and long periods of starvation can be endured without 

Dipping of infested animals is a good control method. An 
arsenical dip has been found best adapted for destruction of 
ticks on their hosts, a description of which, with me^ods of 
preparing and using, is given in Farmers' Bulletin lIH^. 378 
of the U. S. Department of Agriculture. 

Hand treatment with arsenical dip by means of rags, mops or 
sprays is sometimes found more practical. 

The systematic dipping of domestic animals in the spotted 
fever districts of Montana for a period of three years has been 
recommended by the U. S. Department of Agriculture for the 
elimination of the spotted fever tick from these regions. In 
this particular case supplemental means of control consist in the 


destruction of indigenous rodents in a wholesale manner, and 
the clearing away of brush land in tick-infested areas. 

Another means of destruction of spotted fever ticks has been 
found in grazing sheep on tick-infested lands. Range sheep have 
been found to destroy ticks in large numbers by the ticks becom- 
ing entangled in the wool and starved. Five hundred sheep were 
found to destroy 25,000 ticks in a season. 

Ticks which infest the lairs of their hosts, attacking only at 
night and for brief periods, can be more easily handled. In 
this case thorough disinfection by fumigation or by spraying 
with a disinfectant, and thorough cleanliness in stalls, coops, 
kennels, huts or other host homes will effectually destroy them. 
The disease-carrying tampan, Ornithodorus mouhata, of Africa is 
an example of a tick which can be controlled by such methods. 
Dirty, poorly kept native huts are the ideal habitats for tampans, 
which secrete themselves during the day in crevices, thatched 
roofs or debris, after the manner of bedbugs. Plastering houses 
with mud, building of smudges, fumigation and cleanliness are 
methods which usually succeed in keeping out ticks. Crevices, 
bed sheets and other places which might harbor ticks should be 
dusted with pyrethrum insect powder. 

The nearly allied 0. savignyi of Abyssinia, which conceals itself 
in dusty soil to a depth of one inch, can best be destroyed in in- 
fested camp sites, environs of wells, etc., by harrowing the sur- 
face of the ground, strewing dry grass and brush over it, and 
burning it from around the edge of the infested area toward the 
center. Spraying with antiseptics has been found practically 
useless, since even the total immersion of ticks in strong antisep- 
tics for an hour or more fails to kill them. 

The fowl tick or " miana bug," Argas persicus, and the Ameri- 
can hut-infesting species of Ornithodorus, 0. talaje and 0. turicata, 
can be controlled by methods similar to those used for the 



The Order Hemiptera. — The order of insects, Hemiptera (or 
Rhynchota), which includes the true bugs, contains a number 
of species which habitually or occasionally attack man. The 
most important of these are the bedbugs, which are found all 
over the world in temperate and tropical climates. There are 
few objects which are more disgusting than bedbugs to good 
housekeepers, yet there are few who, at one time or another, 
have not had to contend with them or at least guard against 
them. Belonging to an allied family are the cone-noses, larger 
than bedbugs and not devoid of wings, fiercer in disposition and 
capable of producing much more painful bites. A considerable 

number of species of these bugs 

are known and are found in all 

warm countries. The relation of 

bugs to disease is still very im- 

FiG. 162. A hemipteran wing perfectly known, but these para- 

^ ^^" sites are positively known to 

transmit at least one important disease, and are suspected of 

transmitting several others. 

The true bugs, order Hemiptera, are characterized by having 
piercing and sucking mouthparts contained in a jointed beak 
and by an incomplete metamorphosis, i.e., not undergoing a 
complete transformation from a larval to an adult form during a 
period of rest, as do such insects as butterflies, beetles, etc. The 
newly hatched young may differ quite considerably from the 
adult, but the mature characteristics are gradually attained with 
each successive moult. The order is divided into two suborders, 
only one of which, the Heteroptera, concerns us here. In the 
members of this group the first pair of wings, if present, have a 
thickened, leathery basal portion and a membranous terminal 
portion (Fig. 162). The second pair of wings are always mem- 
branous when present. 





General Account. — The bedbugs belong to the family Cimi- 
cidse. They have broad flat bodies, and are devoid of wings, 
except for a pair of spiny pads which represent the first pair of 
wings (Fig. 163). The first segment of the thorax has winglike 
expansions at the sides which grow forward and partially sur- 
round the small head. In the 
male the abdomen is quite 
pointed at the tip, whereas in 
the female it is evenly rounded, 
the contour of the abdomen 
being almost a perfect circle in 
unfed bugs. The eyes project 
prominently at the sides of the 
head, the flexible four-jointed 
antennae are constantly moved 
about in front of the head, 
and the jointed beak is folded 
under the head so that it is 
entirely invisible from above. 
The legs have the usual seg- 
ments, the tarsi being three- 
jointed. The greater part of 
the body is covered with bristles 
set in little cup-shaped depres- 
sions. These depressions are perforated at the bottom to allow 
for the passage of muscles which move the bristles. Murray 
describes having seen bugs raise the bristles upon meeting each 
other as cats raise their hairs or birds their feathers. The bristles 
are of two kinds, one a simple slender spine, the other with a 
stouter flattened end, with sawlike teeth along the thinner edge. 
In addition to both kinds of bristles, the legs also have a dense 
brush of hairs at the end of each tibia. When a bug is distended 
with blood a smooth shining band can be seen at the base of each 
abdominal segment where no bristles occur (Fig. 163). These 
bands are the portions of the segments which are not ordinarily 
exposed, being overlapped by the preceding segment. 

One of the most striking characteristics of bedbugs is the 
peculiar pungent odor so well known to all who have had to con- 

Fig. 163. 

Bedbug, Cimex lectularius, 
female. X 10. 



tend with these pests. Many other bugs are characterized by 
similar odors, as, for example, the common " stink-bugs." The 
odor is produced by a clear volatile fluid secreted by a pair of 

glands of very variable size which 
open between the bases of the hind 
pair of legs. Although in most 
''wild" bugs the stink glands are 
supposed to be distinctly bene- 
ficial in that they make the owners 
obnoxious to enemies which would 
otherwise prey upon them, they 
are a decided handicap to the do- 
mestic bedbugs in the struggle for 
existence, since the odor draws 

F,G. 164. Head and part of thorax attention to the presence of bugs 
of bedbug, ventral view. X 20. Note which might Otherwise escape 

jointed beak, eyes and stout spines. ^^^:^^q js^^r doeS the SCent ap- 
pear to be any protection to them against such enemies as cock- 
roaches and red ants. Murray suggests that it may be of some 
use to them in their social intercourse 
in the dark recesses in which they 
spend their lives. 

The nasty odor of bedbugs has 
evidently inspired some faith in their 
medicinal value. Seven bugs ground 
up in water was said by Pliny to 
arouse one from a fainting spell, and 
one a day would render hens immune 
to snake bites. Even at the present 
time there are places in civilized coun- 
tries where bedbugs are given as an 
antidote for fever and ague. 

There are a number of species of _, ,^^tj- v. ^u ^■ 

f IG. 165. Indian bedbug, Cimex 
bugs in the genus CimeX, but some hemij4erus(rotundatus),iemale. X 

of the species confine their attentions «• (^^^^^ Casteiiani and Chai- 

1 1 • 1 1 mers.) 

to poultry and other birds, bats, etc. 

There are two widely distributed species which attack man: one 
is the common bedbug, Cimex ledularius, found in all temperate 
climates; the other is the tropical or Indian bedbug, Cimex hemip- 
terus {rotundatus) , prevalent in many tropical countries, includ- 


ing southern Asia, Africa, the West Indies and South America. 
The tropical bug (Fig. 165) differs from the common one only in 
minor details, such as greater length of body hairs, darker color 
and more elongate abdomen. It is less dependent on human 
blood than its relative of temperate climates, and readily attacks 
not only rats and mice but also bats and birds. Both species are 
reddish brown in color, becoming deep red when gorged with 
blood. Another species, C. boueti, attacks man in Guiana. 

Habits. — Bedbugs are normally night prowlers, and exhibit 
a considerable degree of cleverness in hiding away in cracks and 
crevices during the daytime. When hungry they will frequently 
come forth in a lighted room at night, and have even been known 
to feed in broad daylight. Favorite hiding places are in old- 
fashioned wooden bedsteads, in the crevices between boards, 
under wall paper, and other similar places, for which their fiat 
bodies are eminently adapted. Like other animals which have 
long associated with man, bedbugs have developed much cun- 
ning in their ability to adapt themselves to his habits. Marlatt 
says " the inherited experience of many centuries of companion- 
ship with man, during which the bedbug has always found its 
host an active enemy, has resulted in a knowledge of the habits 
of the human animal and a facility of concealment, particularly 
as evidenced by its abandoning beds and often going to distant 
quarters for protection and hiding during daylight, which in- 
dicate considerable apparent intelligence." Their ability to 
gain access to sleepers at night is hardly less remarkable. Cases 
are reported of bedbugs creeping along ceilings and dropping down 
on beds in order to reach their hosts, but these may have been 

The bedbug makes himself a great pest wherever he occurs 
by the unsparing use of his piercing and sucking mouthparts. 
The latter consist of four needle-like organg lying in the long, 
jointed lower lip or beak, a pair of flattened sharp-pointed man- 
dibles and a pair of slightly shorter maxillae with serrated edges. 
The beak is grooved in such a way that the sides of the groove 
almost close together, thus forming a protective sheath for the 
stilettos inside. When about to indulge in a meal the beak is 
bent back, and the piercing organs, gliding up and down past 
each other, are sunk into the flesh of the victim (Fig. 166). A 
strong sucking motion of the .pharynx, into which a bit of sali- 


vary juice has already been poured, draws blood up through a 
tube made by the piercing organs, through a thickened '' bottle 
neck " ring to the oesophagus and then into the relatively enor- 
mous stomach. The muscles for dilating the pharynx in order 
to make a suction pump out of it occupy the greater part of the 
head. According to Cragg, who has worked 
on the alimentary tract and digestive proc- 
ess of bedbugs, there are about 70 pulsa- 
^^ tions of the pharynx per minute in young 
bugs, in which this can be observed through 

Fig. 166. Diagram the body wall. Bugs Seldom cling to the 
SrNotTJ^iilot «ki° while sucking, preferring to remain 
of proboscis. (After on the clothing. Since a fresh meal appar- 

"^^^^"-^ ently acts as a stimulus for emptying the 

contents of the rectum, the adherence to the clothing is a fortunate 
circumstance, inasmuch as it precludes to some extent the danger 
of bedbugs infecting their wounds with excrement, as do ticks. 

In the course of ten or 15 minutes a full meal is obtained and 
the bug, no longer flat but round and distended with blood, re- 
treats to his hiding place, having first deposited a bit of excrement. 
According to Cragg, in the case of C hemipterus (rotundatus) , a 
single meal, much of which is temporarily stored in the stomach 
which acts as a food reservoir as well as a digestive organ, is not 
fully assimilated for at least a week, although the bug is ready to 
feed again in a day or two, thus having parts of several meals in 
the stomach at once. This is quite a different condition from 
that found in most blood-sucking insects, where a meal is com- 
pletely digested before another is sought. Observations made 
by several authors on C. ledularius do not indicate that this 
species has similar habits. As in other bugs, the digestive juices 
change the absorbed blood into a dense black mass, described 
by Murray as almost like lamp-black. 

The bite of the bedbug seldom produces pain or swelling unless 
rubbed or scratched, a fact which indicates either that the saliva 
is not irritating or that it does not ordinarily reach the wound 
before sucking begins. In some people, however, a stinging, hard, 
white swelling is produced. 

Under normal conditions the common bedbug, C. ledularius, 
has only rarely been found feeding on anything but human blood. 
The bugs which infest the nests of swallows and other birds are 


of different species from the human pests, and are not known to 
annoy man voluntarily, although they occasionally enter rooms 
from the nests of chimney swifts. Bats are often accused of 
carrying bedbugs into houses, but they, too, are attended by 
their own particular species which does not attack man. The 
assertion that bedbugs can be found under bark and moss out 
of doors also arises from a misapprehension. These bugs are 
really the immature stages of certain other species of bugs which 
resemble bedbugs closely enough to be mistaken for them by a 
casual observer. 

Although human blood is their normal food, bedbugs are able 
to subsist on the blood of such animals as rats, mice, rabbits, 
cats, dogs and even chickens. It has also been shown that bugs 
will suck blood from freshly killed mice. By utilizing mice 
and rats as a food supply they are able to exist in deserted build- 
ings for a long time. Furthermore they are able to endure long 
fasts; they have been kept alive without any food whatever for 
a year. Murray has found that bugs which have been starved 
even for a long time pass unaltered blood corpuscles in their 
faeces, and suggests that a small quantity of food may be re- 
tained undigested in the rectum to be drawn upon very slowly in 
time of need, though when a fresh supply of blood is obtained 
the old store is cleared out. Bugs also store up a great deal of 
fat for use in time of famine. Sometimes, however, after a house 
has been deserted for some time, and their normal supply of 
food is cut off, the bugs migrate in search of an inhabited house. 
In cold weather bugs hibernate in a semi-torpid condition and 
do not feed, but in warm climates they are active the year around. 
The common bedbug, according to Marlatt, is sensitive to 
temperatures of 96° F. to 100° F. or more if accompanied by a 
high degree of humidity, and is killed in large numbers under such 
climatic conditions. According to Bacot, unfed newly hatched 
bugs are able to withstand cold between 28° F. and 32° F. for 
as much as 18 days, though they are destroyed by exposure to 
damp cold after a full meal. 

Life History. — The eggs of bedbugs (Fig. 167 A) are pearly 
white oval objects, furnished with a little cap at one end which 
is bent to one side. As in the case of lice, the eggs are relatively 
large, being about one mm. (^V of an inch) in length, and are 
therefore laid singly or in small batches. The ovaries hold about 


40 eggs at a time, all near the same stage of development, so 
they must undergo rapid increase in size shortly before being 
deposited. Girault, who has carried out extensive breeding 
experiments, saw one female lay 111 eggs during the 61 days 
that he had her in captivity, and another laid a total of 190 
eggs. Often a female returns to lay more eggs in the same 
place so that batches of 40 or more can be found in the crevices 
where the adult insects hide. 

The eggs hatch in from six to ten days during warm weather, 
but are retarded in their development by cold. A week of 

freezing temperature reduces the 
hatching to 25 per cent. The 
freshly hatched bugs (Fig. 167B) 
are very small, delicate and pale 
in color. After their first hearty 
meal they have a much more 
robust appearance, and grow 
rapidly. The skin is normally 
moulted five times before the final 
Fig. 167. Egg and newly hatched adult stage is reached, at least 

larva of bedbug. X 20. (After Mar- , , . r j t_ • 

1^1-^ ) one gluttonous teed bemg neces- 

sary before each moult in order 
to insure normal development and reproduction. Although 
apparently not necessary to its development, the bug may gorge 
itself several times between moults, at intervals of about one to 
six days. Marlatt found the average period of time between 
moults to be eight days. Allowing a similar length of time 
for the hatching of the eggs, the time occupied from laying of 
the eggs to maturity is about seven weeks. Girault has found 
the development from the hatching of the eggs to maturity to 
take place in as short a time as 29 days. On the other hand, 
starvation, cool temperatures and possibly other conditions may 
drag out the period of development to great length. Bacot 
found that the newly hatched larvae could live unfed four and a 
half months and with one feed for nine months. The several 
larval stages of the insect resemble each other quite closely except 
in the constantly increasing size and deepening color. The 
wing pads appear only after the last moult. 

Bedbugs and Disease. — The relation of bedbugs to human 
disease is a subject which, although a problem of the most vital 


interest in preventive medicine, is still very indefinitely known. 
Various authors have associated bedbugs with a number of 
human diseases but the evidence brought forth in support of 
these insects being the normal transmitters of the diseases in 
question rests on insecure foundations. Ordinarily bugs are 
handicapped in the extent to which they are able to spread 
disease by their non-migratory habits. Unlike many parasites 
they are not usually carried about by human beings, but remain 
permanently in places occupied by their hosts. It is obvious, 
therefore, that bugs are limited in the spreading of disease to the 
occupants of the infested place. Should this be a private home, 
spread of disease by bugs would be practically limited to a single 
family. In case of infested hotels, rooming houses, sleeping 
cars, boats, etc., conditions are ideal for the spread of disease by 
bugs, and it can hardly be doubted that it is in such places that 
most of the damage is done. 

One of the first accusations against the bedbug as a disease 
carrier was made by Patton, of the British Medical Service in 
India, who in 1907 brought evidence against this insect as a 
carrier of Indian kala-azar (see p. 79). Patton followed what 
he believed to be developmental stages of the parasite of kala- 
azar, a species of Leishmania, in the gut of the Indian bedbug, 
Cimex hemipterus (rotundatus) . Subsequent investigations, es- 
pecially recent ones by Cornwall, have shown that infection of 
bedbugs by feeding on kala-azar patients is very rare, and that 
the bugs cannot, apparently, transmit the infection either by 
biting or by means of infected faeces. The rare infectivity of 
bugs which have fed on kala-azar patients, however, may be 
correlated with the fact that the kala-azar parasites are rare in 
the peripheral blood. As pointed out by Price and Rogers, 
even if only a small per cent of bugs become infective, where 
they are as numerous as they are in this coolie huts in India, 
they would be able to spread the disease successfully. Donovan 
believes the kala-azar parasites may utilize the Malay bug, Tri- 
atoma rubrofasciatus (see p. 381), as an intermediate host, but 
retTent work is tending to throw doubt on the necessary in- 
strumentality of any insect in transmitting the disease. Bed- 
bugs have also been associated with another Leishmania disease, 
oriental sore, but it is doubtful whether the bugs act as more 
than mechanical disseminators of the parasite, if at all. Yaki- 


moff in Turkestan and Cornwall in India were unable to infect 
bedbugs with parasites of oriental sore even when the bugs were 
fed directly on the ulcers. On the other hand, the fact that one 
species of Cimex, C. pipistrelli, transmits a trypanosome disease 
of bats would lead one to suspect their ability to transmit a 
Leishmanian disease, since the two groups of parasites are 
certainly near relatives. Several workers have incriminated 
bedbugs as carriers of European relapsing fever, especially in 
Serbia and in the southeastern part of Europe, but there can be 
little doubt but that lice are the normal transmitters of the 
European as well as the North African form of relapsing fever. 
In Moscow, for instance, Bayon found that relapsing fever was 
practically unknown among the better class of people who were 
personally clean, even though living in bug-infested quarters, 
whereas the fever was very prevalent among the lower classes, 
most of whom were lousy, even though they were kept in hos- 
pitals where no bugs existed. On the other hand, Hagler, who 
worked with the American Red Cross expedition in Serbia in 
1915, points out that while typhus disappeared with the exter- 
mination of lice, relapsing fever continued to develop in the 
Belgrade hospital until the latter was fumigated for bedbugs. 
The Indian bedbug, C. hemipterus, is believed by some workers 
to be a common transmitter of Indian relapsing fever, though 
evidence points strongly to the instrumentality or lice and ticks 
in spreading the disease. Spirochceta carteri, the organism of 
Indian relapsing fever, has been observed to remain alive for 
from four to seven days in the alimentary canal of bugs which 
have fed on infected monkeys, but bugs seldom become infected 
from human cases. 

As remarked elsewhere, bedbugs have been found capable of 
acting as intermediate hosts for the trypanosome, T. cruzi, of 
Chagas' disease, but they usually remain infective for a much 
shorter time than do bugs of the genus Triatoma. Bedbugs have 
been found capable of transmitting the infection to guinea-pigs 
in from 21 hours to 77 days after an infective feed. 

That bedbugs may act as mechanical spreaders of various 
diseases is unquestionable. Experiments show that the bacilli 
of bubonic plague can develop in the gut of bugs, though more 
slowly than in fleas, and with a much higher mortality for the 
bugs. That they may act as transmitters of the disease is quite 


certain, and bugs have been found to remain infective for 48 
days if they did not early succumb to the disease. Leprosy also 
can probably be spread by bugs in a mechanical manner, and it 
is reasonable to believe that such diseases as tuberculosis and 
syphilis may likewise be carried by them. 

Other Parasitic Bugs 

Most of the other true bugs which may be looked upon as 
normally human parasites belong to the family Reduviidse. This 
is a large family of rapacious bugs, many of them bright colored, 
which are especially numerous in the tropics. Most of them 
prey upon other insects, but nearly all of them produce painful 
wounds when they bite man. Nearly all are active runners and 
good fliers. 

Triatoma, — By far the most important species are the mem- 
bers of the genus Triatoma (Conorhinus), popularly known as 
cone-noses, " big " bedbugs and by numerous local names. 
There are about 40 species, most of them in South and Central 
America. T. sanguisuga of southern United States is the well- 
known '' Mexican bedbug." It is a bug about one inch in length 
with a flat, dark brown body, the edges of which, not covered by 
the wings, are marked with pinkish bars. The long conical head 
is furnished with a strong beak. Its bite, like that of others of 
the family, is very painful and causes swelling, sometimes fol- 
lowed by effects which may last a year. 

The salivary secretion is evidently very poisonous and not 
unlike snake venom in the extensive swelling and irritation which 
it causes. The adult bugs attack not only man but other mam- 
mals also, while the nymphs often annoy chickens. Unhke the 
bedbug this insect can fly, and will readily enter rooms at night 
to attack sleepers unless screened out. The eggs are white, 
oval objects when first laid, soon turning yellowish and then 
brownish; they are laid in small batches under logs or stones 
outdoors. They hatch in about 20 days into young bugs which 
probably prey very largely on other insects. After four moults 
the insect reaches the adult winged condition in which it is 
most troublesome as an invader of houses. This species is re- 
placed by T. protracta in southwestern United States. 

The most important species of the genus are those which are 



naturally infected with Trypanosoma cruzi in South America. 
On account of its domestic habits, Triatoma megista (Fig. 168) 
is the most important species in the transmission of the disease 
to man. This bug is a large, handsome, black and red insect, 
locally known as the " barbeiro," which infests the dirty thatched 
houses of the natives in the state of Minas Geraes in Brazil. 
It is nocturnal in habit, coming forth from its hiding places in 
the thatch of the roof or in the debris of the floor to feed upon 

its human victims after the man- 
ner of bedbugs. The bugs are 
so active and hide so rapidly 
when a light is produced during 
their foraging in the dark that, 
they can seldom be caught. The 
details of the development of the 
trypanosome of Chagas' disease 
in this insect and the relation 
of the insect to the disease are 
described in Chapter VI, p. 110. 
Torres beheves the bugs almost 
invariably become infected by 
feeding on infected vertebrates, 
since Triatoma does not devour 
excrement of its own species, 
as does the allied Rhodnius pro- 
lixus, and cannibalism is rare 
among these bugs, except in young 
larvse which sometimes feed on 
each other. 

The life history of the barbeiro is quite hke that of other 
members of the genus, except that the eggs are laid in or about 
human habitations. The eggs hatch in from 20 to 40 days and 
the young pass through five moults to reach maturity, the whole 
life cycle occupying about a year. The females begin depositing 
eggs about a month after the last moult. These insects suck 
blood at intervals of from four days to several months. 

A number of other South and Central American species of 
Triatoma have been found to harbor Trypanosoma cruzi or a 
species indistinguishable from it. Triatoma geniculata, which 
inhabits the burrows of the armadillo and various rodents, is 

Fig. 168. The "barbeiro," Tria- 
toma megista. X l^. (After Chagas.) 


known to infect these animals in nature, and the armadillo is 
possibly an important reservoir of the disease. Triatoma chagasi 
which had fed on a rodent known as the '* moco," Cerodon 
rupestris, in an uninhabited desert region was found to be infected. 
T. vitticeps, occurring near Rio de Janeiro, T. sordida of Sao 
Paulo and T. dimidiata of San Salvador in Central America 
have been found infected with trypanosomes thought to be iden- 
tical with the species causing Chagas' disease, and these species 
have been shown to be capable of transmitting the infection to 
guinea-pigs. In Argentina, as well as throughout most of 
Brazil, T. infestans, the vinchuca or " great black bug of the 
Pampas," described by Darwin in his " Voyage of a Naturalist " 
as a vicious human pest, has been found to harbor a similar 
trypanosome, but whether or not Chagas' disease exists in 
Argentina is still in doubt. T. protrada of southwestern United 
States has been shown recently by Kofoid and McCulloch to 
harbor a trypanosome which exhibits only slight differences from 
Trypanosoma cruzi, and, as intimated by the discoverers, may 
possibly be merely a variety of the same species though named 
by them T. triatomce. The widely distributed T. rubrofasciata 
was shown by Neiva to become infected with trypanosomes after 
feeding on an infected guinea pig. From all this evidence, and 
from the fact that other species of bugs of different genera and 
families, including the bedbugs, are experimentally susceptible 
to the infection and capable of transmitting it to rodents, it is 
possible that all the species of Triatoma and alUed genera in South 
and Central America may be potential transmitters of the in- 
fection. CannibaHsm is common among many of these bugs, 
and may make possible a direct spreading of trypanosome in- 
fection from bug to bug. 

The *' Malay bug," T. rubrofasciata, of tropical Asia and some 
parts of Africa and Madagascar is a closely allied species. With 
its huge proboscis it produces a nasty sting which is followed in 
a few minutes by acute pain and swelling. Although it feeds on 
man by preference, it attacks a number of other mammals and 
even insects. Large nymphs or adults, which are an inch or 
more in length, are said to consume about one cc. of blood at 
a meal, and they feed at intervals of from three to six days. The 
breeding habits are similar to those of other cone-noses. In 
the islands of Mauritius and Reunion the stomach and intestines 


of this bug have been found to contain trypanosomes in all 
phases of development, and of very variable form, possibly 
representing several species. These trypanosomes can be 
inoculated into mice and rats and it is suggested that under 
certain conditions they or others living in the gut of the bug may 
cause disease in man. A number of cases are on record where 
irregular fevers have followed the bites of this insect. Since these 
fevers were shown to be non-malarial and showed symptoms of 
typical trypanosome infection, it is possible that such an infec- 
tion may really be transmitted to man by this bug as well as 
by its close relatives in South America. It is also possible that 
the bug may serve as an intermediate host for the kala-azar 

Other Species. — Several other species of bugs of this family 
occur in Africa. One, Acanthaspis sulcipes, has been thought 
to be the possible transmitter of a form of endemic goitre in 
tropical Africa. In North America the family is further repre- 
sented by the " kissing bugs," of the genus Melanolestes. The 
common kissing bug or " black corsair," M. picipes, became very 
abundant in the United States a few years ago and gave op- 
portunity for many startling newspaper stories. It is a large 
black bug with reddish marks on the back and legs. Its bite 
much resembles that of a wasp, though often much more serious, 
occasioning more than local symptoms and even vomiting. 
Allied bugs of the genera Reduvius, Rasahus 
and Melanolestes occur in the warm parts of 
North and Central America, and frequently 
attack man and other mammals, though 
their normal food in most cases is insects. 

In Venezuela and other parts of northern 
South America a very common bug which in- 
fests houses is Rhodnius prolixus, a species 
which has been found capable of transmitting 
Fig. 169. Pito bug, Trypanosoma cruzi. This species is not only 
(A^ter Akock.) ^^^ ^^ cannibalistic in habits, but also devours excre- 
ment of other bugs, thus suggesting the possi- 
bility of direct dissemination of trypanosomes from bug to bug. 
Of other families, there are many bugs which occasionally attack 
man but few which commonly do so. One which is worthy of 
mention is the malodorous pito bug, Dysodius lunatus (Fig. 169), 


of South America, belonging to the family Aradidse. It is a 
large broad bug which frequents houses and bites severely. 

All the species of bugs which infest houses may be destroyed 
by the fumigation methods described below, but all but the bed- 
bugs must be kept out by screening, since they are not handi- 
capped in their migrations by degeneration of the wings. 

Remedies and Prevention 

Prevention of " bugginess," at least in the case of bedbugs, 
consists chiefly in good housekeeping, but occasional temporary 
infestations are likely to occur in almost any inhabited building. 
A number of remedies for bugs have been advocated, of which 
the best is undoubtedly fumigation with hydrocyanic acid gas, 
as described below. Sulphur is also valuable for fumigation but 
is not so harmless to household goods as is hydrocyanic acid gas. 
When the infested parts of houses or rooms can be easily located, 
good remedies are kerosene, gasolene, turpentine or other coal-tar 
products painted into all the infested cracks and crevices, es- 
pecially in the woodwork of beds. An effective remedy of this 
nature is a mixture of one ounce corrosive sublimate, two cups 
alcohol, one-half cup turpentine. These substances should be 
applied several times at intervals of a week in order to destroy 
newly hatched bugs. Some housekeepers take infested beds 
apart and pour boiling water into the " buggy " parts, thus 
effectually killing both bugs and eggs in the bed but this does 
nothing against bugs which may hide elsewhere than in the bed. 
Bedbugs have a number of natural enemies, among which may 
be mentioned especially cockroaches, red ants and large preda- 
ceous bugs, but all of these are pests themselves, and are, there- 
fore, hardly to be encouraged as bedbug hunters, efficient as they 
might be in this capacity. 


Hydrocyanic Acid Gas. — Of the remedies for bugs mentioned 
above, fumigation with hydrocyanic acid gas is the most effective. 
This gas can be used with good success for fumigation of houses, 
mills, granaries, greenhouses or any other closed structure, 
against any kind of insect pest. But since the gas is extremely 


poisonous not only to insects but also to other animals and to man, 
its use must be accompanied by great care and precaution. A 
few deep breaths of the gas is sufficient to cause asphyxiation. 
On the other hand it has great advantages in that it is not in- 
flammable or explosive, and, unlike sulphuric fumes, does no 
damage to dry foods or to household goods, except to tarnish 
nickel slightly. Wet foods may absorb some of the gas and 
should be removed before fumigation. Care should also be 
taken that there is no possible avenue of escape for the gas into 
adjoining rooms or houses which are occupied. The character- 
istic peach-kernel odor, however, makes its detection easy, thus 
removing danger of asphyxiation without warning. 

The gas is generated by the action of sulphuric acid on potas- 
sium cyanide. The procedure as advised by Herrick is as fol- 
lows: Estimate the number of cubic feet in the room or house 
to be fumigated, and allow one ounce of potassium cyanide to 
every 100 cubic feet. Make the room or house as near air tight 
as possible, stopping all the large openings such as fireplaces and 
chimney flues with old rags or blankets. Seal cracks about win- 
dows and doors with strips of wet newspaper. Such strips when 
thoroughly wet can be applied quickly and effectively over cracks 
and will stick tightly for several hours, and can be removed easily 
after the operation. While the room is being made tight some- 
one should measure out the required ingredients for fumigation, 
allowing one fluid ounce of crude sulphuric acid and three fluid 
ounces of water to each ounce of potassium cyanide. The water 
first should be poured into a stone crock holding two gallons or 
more, i.e., large enough so that the reacting fluid will not spatter 
on floors or carpets. The crock had best be placed on several 
thicknesses of newspaper or on an old rug or burlap sack. The 
required amount of sulphuric acid should then be poured slowly 
into the water. Never pour the water into the acid. The cyan- 
ide should be weighed out and put into a paper bag beside the 
jar. All articles which might suffer from the gas or which will 
be needed before the operation is over should be removed from 
the room. When everything is ready the operator, holding his 
breath, should drop the paper bag of cyanide gently into the 
acid jar, and walk out shutting the door behind him. The time 
required for the acid to eat through the paper bag in order to 
reach the cyanide gives ample time to leave the room before the 



steamlike gas arises. If preferred, however, the paper bag may 
be suspended by a string passing through a screw eye in the 
ceiUng and through the key hole of the door (Fig. 170). The 
operator may then lower the bag into the jar after leaving the 
room. When stringing a room in this manner, care should be 
taken not to place the acid jar under the bag until everything is 
ready. The fumigation should extend over a period of five or 
six hours at least, a good method being to start the operation 
toward evening and let it run 
all night. Better results will 
be obtained at a temperature 
of 70° F. or above, than at 
a lower temperature. 

Two or three hours after 
the doors and windows have 
been opened the gas will have 
disappeared sufficiently to 
allow safe entrance into the 

,1 u -J. T_ ij 2. Fig. 170. A room "strung" for hydro- 

room, though it should not ^y^nic acid gas fumigation from outside. 

be occupied until the char- The bag of cyanide can be lowered into the 

.... J • rnv crock of sulphuric acid and water by means 

acteristlC odor is gone. The ^f the string. (After Herrick.) 

contents of the generating 

jar should be dumped in some safe place and the jar washed 
before being used again. When a whole house is to be fumigated 
each room should be made ready as described above and then 
set off in regular order beginning on the upper floor and working 
downward, since the gas is lighter than air and therefore rises. 
Herrick describes clearly and in detail the method which he 
has successfully used in the fumigation of large dormitories. 
For this account the reader is referred to Herrick's " Insects 
Injurious to the Household," pages 448 to 452. 

The effectiveness of this method of fumigation against bedbugs 
was proven by experiments conducted by Herrick. Bugs were 
placed in perforated pill boxes and wrapped in various manners, 
some with three inches of excelsior, some in two folds of a thick 
comforter, some in two inches of cotton batting and others in two 
folds of a woolen blanket. Others were placed in a cork stop- 
pered vial, the cork of which was punched twice with a pair of 
curved forceps. In each box several newly laid eggs were en- 
closed to determine the effect of the gas on their hatching. In 


every case every bedbug was killed and none of the eggs showed 
signs of hatching in 12 days. According to experiments made by 
the U. S. Public Health Service five ounces of powdered potas- 
sium cyanide per 1000 cubic feet is sufficient for the destruction 
of bedbugs, four ounces for mosquitoes, two and one-half ounces 
for fleas and ten ounces for lice. 

Sulphur. — The fumes of burning sulphur, sulphur dioxide, 
rank next to hydrocyanic acid gas as both a disinfectant and an 
insecticide, but they have a serious disadvantage in their tendency 
to bleach fabrics and to tarnish metals, especially in a humid 
atmosphere. Sulphur dioxide is considered the most effective 
remedy for mosquitoes in cellars, barns, etc., since it kills these 
insects even when very dilute, and it has remarkable penetrating 
power. The methods of sealing rooms or buildings are similar 
to those described for hydrocyanic acid fumigation. All dyed 
goods and metallic articles, however, must be removed or covered 
with vaseline. Two pounds of sulphur is used to 1000 cu. ft., 
more if the building cannot be tightly sealed. The sulphur is 
placed in some suitable dish with a little wood alcohol poured on 
it to make it burn more readily. In order to avoid danger of fire, 
the dish of sulphur should be placed on bricks or in a tub of shal- 
low water before igniting. After two hours the place may be 
opened and ventilated. 

Other Fumigants. — Another effective insecticide is the vapor 
of carbon bisulphide, a poisonous gas which is not nearly so 
virulent as hydrocyanic acid gas. As its vapor is heavy it 
settles rapidly. Its effect on many insects is less certain than in 
the case of the hydrocyanic acid gas and it has the additional 
disadvantage of being both inflammable and explosive. Re- 
cently cresyl or creolin, a very volatile substance, has come into 
favor as a fumigating medium, especially for destroying mos- 
quitoes. It is not injurious to higher animals in the strength 
used (125 cc. to 1000 cubic feet), does not injure household goods 
and is destructive to all exposed insects. It is volatilized by 
means of an alcohol lamp. Cresyl does not, however, have the 
penetrating power of hydrocyanic acid gas or sulphur, and is 
therefore of less value for such secretive insects as bedbugs, 
though highly valuable for exposed insects, such as mosquitoes, 
since they may be destroyed without having the rooms vacated. 
Formaldehyde, though a valuable disinfectant, i.e., active in 
the destruction of microorganisms, is not an effective insecticide. 


Although the disrepute of human Hce has grown with civiliza- 
tion and with the knowledge that lousiness and cleanliness are 
incompatible, lice are even yet among the most important of 
external human parasites. In former times the louse apparently 
was not an object of disgust and loathing even among the better 
class of people. In Herrick's entertaining book, '' Household 
Insects," the following quotation from Hooke, an English zoolo- 
gist of the 17th century, is given concerning the head louse. 
" This is a creature so officious that 'twill be known to everyone 
at one time or another, so busie, so impudent, that it will be in- 
truding itself into everyone's company, and so proud and as- 
piring withall that it fears not to trample on the best, and affects 
nothing so much as a crown; feeds and lives very high, and that 
makes it so saucy as to pull anyone by the ears that comes its 
way, and will never be quiet till it has drawn blood." 

Unfortunately, even at the present time, and in the face of 
present knowledge concerning the role of lice in the spread of 
disease, there are many individuals, many communities and even 
some races which make no effort to exterminate them. Still 
more unfortunate is it that there are many people who of neces- 
sity must associate with these unwelcome companions. In 
logging camps, jails, ships, railroad camps, etc., where close 
association with people who are dirty by nature is unavoidable, 
lice very often become prevalent. Most of all, however, are 
Hce associated with war. The deadly typhus fever, which has 
ravaged the armies of almost every war in the history of the world, 
as far as is known, apparently is spread exclusively by Hce. These 
parasites are the guerillas of war; they bring suffering and death 
not only to armies but also to the innocent non-combatant popu- 
lation of the war-stricken countries through which the armies 
have passed. This phase of the subject will be discussed in more 
detail under the section on " Lice and Disease." 





General Structure. — 

Lice are small wing- 
less insects constituting 
the order Siphunculata. 
They were formerly class- 
ified as a suborder of the 
Hemiptera or true bugs, 
but recent studies have 
shown the erroneousness 
of this grouping. The 
mouthparts are adapted 
for piercing and sucking. 
The piercing apparatus 
(Fig. 171B) consists of 

Fig. 171. Mouthparts of a body louse; A, four needle-like organs, 
longitudinal section through head ; 5, mouthparts „ u* u • 4.U ^ r 

from sac under pharynx and oesophagus; buc. t., 0^^6 01 Wnicn IS tne uell- 
buccal tube; m., mouth cavity; ph., pharynx; oes., ^ate Salivary duct, which 
oesophagus; retr. sac, retractile sack for mouth- , '^u j • + 

parts; prot. m., protractor muscles of pharynx; Can be Wltnarawn mtO 
ret. m., retractor; dil. m., dilators; d. p., dorsal ^ little pOUch Under the 

ventral piercer ; ^^,^ a\ 

(Adapted from pharynx (Fig. 171 A). 
This type of mouthparts 

piercer; sal. d., salivary duct; v. p. 
V. pi., ventral plate = labium (?). 



readily distinguishes the 
true lice from the bird 
lice, which constitute 
the order Mallophaga 
(Fig. 172). In the latter 
there are nipper-like 
mandibles fitted for bit- 
ing instead of sucking, 
and these parasites feed 
only on hair, feathers, 
etc., and not at all on 
blood. In other respects 
_,,,., ^ ,. , , the sucking Kce and bird 

Fig. 172. Head of bird louse (from golden ,. , • i t_i 

eagle); ant., antenna. Note breadth of head as hce ShOW a considerable 
compared with thorax, a feature which readily resemblance t O each 
distinguishes bird lice from sucking lice. 

other, and are now gen- 
erally believed to be closely related. These two orders of lice are 
sometimes combined in an order Anoplura. The feet of the true 
lice are armed each with a very large curved claw, quite gro- 



tesque m appearance in some species, which closes* back like a 
finger against a thumblike projection of the next segment of the 
leg (Fig. 173). There are not even rudiments of wings. 

The body of a louse is clearly divided into head, thorax and 
abdomen (Fig. 174). The thorax is always broader than the 
head, a characteristic 
which distinguishes at a 
glance a true louse from 
the broad-headed bird 
louse (Fig. 172). The 
abdomen is divided into 
segments, normally eight 
of them in the human spe- 
cies; the terminal one 
is indented in the female, 
but is rounded in the 
male with the large 
spikelike copulatory or- 
gan often projecting at 

its tin fFie" 174 n '^QO'l humanus. Note huge claw and thumb-like op- 

FiG. 173. Front leg of body louse, Pediculus 
bte huge claw and thumb 
posing process of next segment. X 100. 

The digestive tract, as in 
most other blood-sucking insects, is furnished with capacious 
pouches branching from the stomach, which serve as food reser- 
voirs. The tracheal system is well developed and opens by prom- 
inent spiracles on the sides of the abdomen. 

Most species of lice are quite closely limited to a single host, 
and sometimes even genera are thus limited. Kellogg has sug- 
gested that the evolutionary affinities of different birds and mam- 
mals may be demonstrated by the kinds of lice which infest them. 
The lice infesting man have generally been regarded as belonging 
to three species, each selecting a different portion of the body as a 
habitat; these are the head louse, Pediculus humanus (capitis), 
the body louse, P. corporis (vestimenti) , and the crab louse, Phthi- 
rius pubis. The head louse and body louse are now thought 
to be mere races or varieties of a single species, P. humanus. 
Both Pediculus and Phthirius are probably normally confined to 
human beings. 

Body Louse. The body louse (Fig. 174) is by far the most 
common, as it is the most important, louse infesting man. It 
closely resembles the head louse, but is often larger, more ro- 
bust and less active. Fertile offspring result from hybridization 




of these two' species. The females, which are somewhat larger 
than the males, reach a length of about one-eighth of an inch. 
Due to their dirty white or grayish color these lice are familiarly 
known as '' gray-backs." This species is known to be instru- 
mental in transmitting both 
typhus fever and European 
relapsing fever. 

As the name "body louse" 
implies, this species inhabits 
the trunk rather than the 
head. The German name 
'' Kleiderlaus ", meaning 
" clothes louse ", is still better, 
since this louse has so far 
adapted itself to its host as 
to have broken away from 
the custom, prevalent among 
all other species of lice, of 
living in the hair of the body, 
and to have established the 
habit of living on the cloth- 
ing. Just when, in the proc- 
ess of our evolution from a 
hairy ancestor, this louse 
shifted its position from the 
waning hair to the more and more habitually worn clothes would 
be interesting to know. Not unlikely both this louse and the 
closely allied head louse have evolved from a species which once 
roamed the hairy bodies of our forefathers, each species coping 
with the unfavorable circumstance of the developing hairless- 
ness of its host in a different way, the more conservative head 
louse withdrawing to the fine hair of the head, the body louse 
adapting itself to living on the clothing. 

A person infested with thousands of body lice may remove his 
clothing and find not a single specimen on his body. An exami- 
nation of the underwear will reveal them adhering by their long 
claws to the surfaces which were next to the body. Here they 
live and lay their eggs, leaving the clothing only long enough to 
suck a meal of blood, even then usually adhering to the clothes 
by their hind legs. 

Fig. 174. Body louse, Pediculus humanus, 
male; ant., antenna; e., eye; p., penis; sp., 
spiracles; th., thorax, X 25. 



— hciip 


Habits and Life History. — Although there has been very 
close association between lice and human beings probably since 
man's first appearance in the world, little definite knowledge 
concerning the life history of any of the three species was ob- 
tained until recently. The importance of lice in the great anti- 
German war has stimulated much research on them. 

One of the first experiments with the breeding of body lice was 
made by the great zoological pioneer, Leeuenhoek, in the 17th 
century. He placed two female lice in his stocking and tied 
them in; after six days he opened the brood chamber and found 
a cluster of 50 eggs beside one 
of the lice and another cluster 
of 40 eggs, probably laid by 
the other insect which had 
escaped. He found 50 more 
eggs in the remaining louse. 
He left the eggs in his stocking 
ten days more, when he dis- 
covered 25 young lice, where- 
upon he abandoned his experi- 
ment in disgust. 

The eggs of lice, commonly 
called ''nits," are oval, whitish 
objects fitted with a little lid at 
the larger end, through which 
the hatching takes place. The eggs of the body louse are about 
one mm. dV oi an inch) in length. They are glued to the fibers of 
clothing (Fig. 175B) especially along seams or creases, although 
in all other lice the eggs are glued to hair. Under experimental 
conditions the body louse will sometimes lay eggs on hairs, but 
it nearly always selects the crossing point of two hairs and shows 
less skill in attaching the eggs. The body louse shows a marked 
" homing " instinct in laying her eggs and shows a strong desire to 
lay eggs where others have been laid, until clusters of from 50 
to 75 or more have been formed. 

According to recent experiments by Sikora in Germany and 
Bacot in England, the number of eggs laid by the single female 
body louse may frequently reach 200 or more. Bacot obtained 
295 eggs from a single specimen in one case. During the first 
three or four days only two to four eggs are laid daily, the num- 

FiG. 175. A, egg of head louse, Pedi- 
culus capitis; B, egg of body louse, P. 
humanus. X 25. (After Cholodkowsky.) 

392 LICE 

ber gradually rising, until after a week or so of egg-laying seven 
to ten or more eggs may be laid each day. A day or two before 
the end of egg-laying and the death of the louse the daily number 
drops again. Eggs are laid whether copulation has occurred 
or not, but in no case have unfertihzed eggs been observed to 
develop. One copulation is not sufficient to fertihze all the eggs, 
but fertile eggs may be laid for at least 20 days after a single 
copulation. According to Sikora, copulation normally takes 
place at intervals of from one to three days. Egg-laying ceases 
at temperatures below 77° F. and a daily exposure to a tempera- 
ture of 60° F. for only two or three hours causes a marked faUing 
off in egg production. 

According to Sikora the eggs hatch in about six days at the 
optimum temperature of 95° F. At a temperature of 77° F. 
the incubation period is prolonged to 16 days, whereas at 68°, 
lowered from 42° to 60° F. during the latter part of the night, or 
at a constant temperature of 60° F., no hatching at all takes place. 
At temperatures above 95°, also, the eggs suffer a high mortaUty 
probably due to the difficulty in obtaining proper conditions 
of humidity rather than to the direct effect of the heat itself. 
Either excessive humidity or complete drying is fatal to the 
eggs. It is evident that in winter the laying off of the clothing 
at night in a cold room or the leaving of mattresses or bed clothes 
in the daytime is sufficient to prevent the laying of eggs or the 
hatching of eggs already laid, thus resulting in the extermination 
of the lice. 

The newly hatched lice are almost perfect miniatures of the 
adults, and are ready to feed almost as soon as they emerge from 
the egg; in fact, they usually die in less than 24 hours if not 
allowed to feed, though the adults can survive as much as five 
days of starving. According to Sikora, the rapidity of the 
development of lice is dependent on temperature and on amount 
of food. At a temperature of 95° F. and with as many daily 
feeds as would willingly be taken, namely six, the lice pass through 
their first moult in three days, the second in five or six days, and 
the third, which brings them to maturity, in eight or nine days. 
Reduction of daily feeds to two increased the period of develop- 
ment to nine or ten days, whereas reduction of temperature to 
75° F. by day and 95° F. by night, with two daily feeds, prolonged 
the development to from 13 to 15 days. 


According to observations by Sikora, copulation may take 
place within ten hours after the last moult has been passed, and 
Bacot also observed cases in which copulation took place on the 
day of reaching maturity. Egg-laying begins in from one to four 
days after the final moult and continues at the rate described 
on the preceding page until the death of the insect. The aver- 
age length of life for the females is about 35 or 40 days, and 
probably a little less for the males. 

According to Bacot, hungry lice do not show a tendency to 
wander on the skin, but proceed to pierce the skin and suck blood 
at once. Nor do they shift to make another stab, as fleas fre- 
quently do, if the first stab does not immediately furnish blood. 
They apparently place great reliance on the power of the sali- 
vary secretion, which is poured into the wound, to dilate the 
capillaries by its irritation and thus cause a flow of blood. Some- 
times blood is not drawn for several minutes after the puncture 
is made. Bacot states that lice fill their crops in from two to 
15 minutes, but Sikora observed that adult lice, if fed only twice 
daily, sucked for an hour to an hour and a half, and, if left in con- 
tact with the skin for several hours, have a tendency to pump 
blood intermittently with short pauses, meanwhile voiding ex- 
crement containing undigested blood corpuscles. Sikora also 
observed that hungry lice placed on the well-shaved skin of a 
puppy made repeated attempts to draw blood without success, 
and also that dog lice, HcBmatopinus ventricosus, tried in vain to 
draw blood from the human skin. He concludes therefrom 
that not only is it necessary for lice to penetrate the skin with 
their piercing apparatus, but that they must also produce an 
irritation by means of a salivary secretion, apparently specific 
in its action for certain kinds of blood, in order to cause blood 
to flow from the tiny puncture. Apparently the salivary se- 
cretion deteriorates in unfed lice, for though starved lice may 
still be able to drive their piercing apparatus into the skin, it 
takes them three times as long to draw blood. 

A fact of far-reaching significance, if found to be commonly true, 
has recently been reported by Hall in Texas. This author 
found that a female body louse taken from a Mexican baby, 
when placed in a bottle with a head louse taken from the same 
baby, devoured the head louse. Two head Uce were then fed 
to the body louse daily for three days, and the same louse was 

394 LICE 

induced to eat crab lice, small black ants, bedbugs, and raw beef. 
When body lice were placed in a bottle with head lice, bedbugs, 
and a piece of beef, they ate first the head lice, then the bedbugs 
then the beef, and finally became cannibals to the extent of the 
survival of the fittest! This would readily explain such facts 
as that body lice (according to Hall) can be found in empty box 
cars used to transport Mexican troops weeks before, and it 
would account for louse-borne diseases lying dormant in isolated 
places. A freight car once infected with typhus would be a source 
of danger for a longer period than the few days a louse can live 
without food. However, before insectivorousness can be ad- 
mitted as a usual habit of lice in the absence of normal food, 
further investigation is necessary. 

Digestion is very rapid. An entire two-hour feed may be 
digested in from eight to ten hours at 95° F., but digestion is 
slower at lower temperatures and the stomach contents remain 
unchanged for ten hours or more at 45° F. or below. At tem- 
peratures above 95° F. digestion is even more rapid, but there is 
a high mortality. 

It is evident from Sikora's experiments that 95° F. is the op- 
timum temperature for the development and reproduction of 
lice. The absence of lice from hot countries — observable in 
Mexico, for instance, where they are abundant on the central 
plateau above 5000 to 6000 feet, but absent from the hot coastal 
strips — is apparently not due to the high temperature but 
probably to the disastrous effect of profuse perspiration and 
consequent excessive humidity between the clothes and skin. 

The bites of the body louse produce itching red pimples which 
become covered by a brownish crust, the results of the action 
of the toxic salivary juices. Scratching produces characteristic 
white scars, surrounded by brownish pigment; in fact, large 
areas of the skin may take on a mottled bronze color. The color- 
ing of the skin is said to be due to the stimulation of pigment 
formation in the skin by toxins secreted by the louse. Many 
individuals develop an insensibility to the bites of lice, a fact 
which probably explains the indifference of some communities 
to them as, for instance, the people' of Russian Poland. 

Head Louse. The head louse, P. humanus capitis, is very 
closely related to the body louse, and is, in fact, thought by some 
workers to be a mere variety of the latter. Aside from its different 


habits, however, it differs very slightly from its relative. It is 
commonly smaller in size, and is more distinctly festooned along 
the sides, due to constrictions at the joints between the segments. 
Nuttall, however, has shown that all of the supposed morpho- 
logical and biological differences between these two kinds of lice 
are inconstant, and they should, therefore, be considered as 
races of a single species. The head louse assumes all the char- 
acteristics of the body louse when reared under conditions suit- 
able for the latter. 

The head louse although usually preferring the fine hair of the 
head as a habitat occasionally wanders to other parts of the body 
as well. It is found in every part of the world. Different vari- 
eties are said to occur on the different human races and to vary 
in color with the color of the skin on which they live. The 
lice which live on the white race are pale gray with a dark line 
along each side of the abdomen, those on negroes are blackish 
or brown, on Hindoos smoky brown, on Japanese and Chinese 
yellowish, and on American Indians dark reddish brown. What 
a wonderful case of protective coloration, except that, as in so 
many other cases of so-called protective coloration, there is no 
practical protection. A negro is as likely to scratch out a black 
louse as a white one! 

As in the case of the body louse reproduction is very rapid but 
the egg production is lower, due to the smaller capacity of the 
body, even taking into consideration the slightly smaller size 
of the eggs. The course of development is practically the same 
in both species. The average number of eggs, according to 
Bacot's observations, is from 80 to 100. Only one mature egg 
can be developed in the louse's body at a time, but the suc- 
cession of them is so rapid that eight or ten may be laid in a 
day. Each egg or " nit " is glued by the lower end to a hair 
(Fig. 175 A), the favorite " nests " being the vicinity of the ears. 
The young lice hatch in ten or 12 days and reach maturity in 
two or three weeks, and are then ready to reproduce again. At 
this rate of reproduction, allowing only a 50 per cent hatch, a 
single pair of lice theoretically could produce over three-quarters 
of a miUion offspring in the fourth generation, and in the course 
of less than three months! 

Although the bites of this species are not quite so irritating as 
are those of the body louse, yet the frequent piercing of the skin 
for a gory meal results in much scratching. Often the bites 
swell into pimples which may bleed when scratched or which 

396 LICE 

form a little pus, sufficient in very negligent individuals to make 
the hair mat together. According to Stiles, if this is allowed to 
run on, a regular carapace may form, called trichoma, in which 
fungous growths may develop, and under which the lice abound, 
and the head may exude a foetid odor. 

Crab Louse. — The crab louse, Phthirius pubis (Fig. 176), is 
quite distinct from the other two species of human lice. It has 
a very broad short body with long, clawed legs, presenting the 
general appearance of a tiny crab, from which it derives its name. 
The first pair of legs are smaller than the others and do not 

Fig. 176. Crab louse, Phthirius pubis, 9 . X 35. 

possess a *' thumb " in apposition to the curved claw. The 
abdomen is composed of six segments, and is markedly festooned 
along the sides. This louse is grayish white in color, with dark 
shoulder patches and slightly reddish legs. The females are 
about yV of an inch in length, the males somewhat smaller. The 
favorite haunts are the pubic regions and other parts of the body 
where coarse hair grows, as in the armpits and in the beard and 
eyebrows. Unlike the other human lice this species is almost 
exclusively confined to the Caucasian race. 

The females produce from ten to 15 eggs and glue them, one 
at a time, to the coarse hairs among which they live. A number 


of eggs may be glued to a single hair, and often at some distance 
from the skin. The eggs hatch in six or seven days, and the young 
become sexually mature in about 15 days. This species, even 
under favorable conditions, will live apart from its host only 
ten or 12 hours. The eggs are said not to develop except at 
temperatures between 68° F. and 86° F., which are approxi- 
mately the temperatures to which eggs attached to hairs beneath 
the clothing would be exposed. 

Lice and Disease 

The role of lice in the spread of disease has long been sus- 
pected in an indefinite and uncertain way. Only recently, and 
at the cost of the lives of several great investigators, has the 
whole portentous truth regarding the transmission by them of 
typhus and relapsing fever (North African and European types) 
been brought to light. Foremost among the investigators of 
louse-borne diseases stands the name of NicoUe and his associates, 
who in 1909 proved that typhus fever could be transmitted by 
the body louse, and in 1913 that the Algerian type of relapsing 
fever could be transmitted likewise. Two American investi- 
gators, Ricketts and Wilder, working independently of the French 
workers, proved in 1910 that the body louse was instrumental 
in transmitting typhus (tarbardillo) in Mexico, and in 1912 
Anderson and Goldberger showed that the head louse could also 
transmit it. Opinions differ as to whether the infection can be 
transmitted through the eggs to the lice of the succeeding genera- 
tion. In 1918 an American commission under Dr. R. P. Strong, 
and a British committee under Sir David Bruce and Major Byam, 
working under field conditions on the war front in France, dem- 
onstrated that trench fever is a louse borne disease. 

There is every reason to belive that typhus fever is normally 
transmitted exclusively by lice. Wherever the hording together 
of promiscuous crowds of people becomes necessary and when 
scrupulous cleanliness, either of necessity or of choice, is not en- 
forced, there the lice will thrive and sooner or later the dread 
disease will break out. The organism which is believed to be 
the cause of typhus fever, Rickettsia prowazeki, is discussed on 
p. 186. NicoUe and his fellow workers have shown that lice which 
are fed on infected patients do not become infective until the 
eighth and usually the ninth or tenth day afterward. The same 

398 LICE 

results were obtained both in experiments with crushed Hce and 
with the excrement of the hce. 

Epidemics of typhus usually occur in winter and in cold coun- 
tries, due to the huddling together of people in warm, poorly 
ventilated houses where lice thrive, and where the unhygienic 
conditions lower the vitality of the people. Typhus has fol- 
lowed in the wake of nearly every army which has ever been 
assembled. During the present great European war typhus 
has been largely absent from the armies and population of Brit- 
ain, France and Germany, due solely to the intensive anti-louse 
measures which have been enforced by these countries. The 
less scientific and less cleanly nations have suffered enormous 
losses. An epidemic began in Serbia in January, 1915, among 
some Austrian prisoners who were allowed to disperse all over 
the country. The disease spread with them, and for a time raged 
almost at will in that war-stricken country. The majority of 
the small number of Serbian doctors were affected, no sanitary 
measures for the suppression of lice were understood or enforced, 
and no adequate accommodations for the sick could be provided. 
The epidemic continued to rise, and reached its height in April, 
when there were estimated to be 9000 deaths per day. It was 
largely through the heroic efforts of the American Red Cross 
expedition that the epidemic was finally checked, after having 
destroyed over 150,000 people. In December, 1916, another 
epidemic was reported to be raging in Syria with over 1000 deaths 
per day. Milder epidemics have occurred in Austria, Bulgaria 
and Russia, all countries where science and cleanliness have 
not been worshipped as they have in the greater nations of Eur- 
ope. Mexico has suffered also; in December, 1915, 11,000 
cases of typhus were reported in Mexico City and its environs. 

The role of lice in the transmission of the European and North 
African form of relapsing fever has long been suspected but was 
not proved until 1913, when NicoUe and his fellow- workers 
scientifically demonstrated it in Tunis and Algeria. Noting 
that the louse was the only constant factor affecting the occur- 
rence of the disease, these French workers undertook extensive 
experiments which resulted in proving that the body louse, and 
probably also the head louse, serves as a medium for the develop- 
ment of the spirochaetes of relapsing fever, and that these insects 
transmit the disease not by biting but by inoculation of the 


wounds which they make with the infected contents of their 
bodies when crushed. 

Nicolle and his associates also showed that sometimes, at least, 
the spirochsetes, probably in the granule stage, are hereditarily 
transmitted through the eggs to the young of the next generation, 
as is the case with the African relapsing fever parasites in the 
tick. Experiments on the transmission of the relapsing fever of 
Algeria with other parasites such as bedbugs, fleas, biting flies 
and ticks were negative. Some observers, however, believe that 
in Europe other insects also, notably bedbugs, may be instru- 
mental in transmitting relapsing fever. The evidence furnished 
by the epidemiology of the disease is, however, very strongly in 
favor of lice as the normal transmitters. The Indian form of 
relapsing fever is also probably transmitted by lice. Further 
details of the development of the spirochsetes in the lice are 
given in Chapter IV, p. 44. 

Being transmitted by lice, relapsing fever shows the same pe- 
culiarities of occurrence as does typhus; epidemics always rage 
fiercest in winter, and usually break out during war times. Ser- 
bia, which was so stricken by typhus, was held in the grip of an 
epidemic of relapsing fever earlier in the war. 

The demonstration of the relation of lice to the transmission 
of trench fever in 1918 by American and British Commissions 
working under war conditions was a very brilliant piece of medical 
research carried out successfully in spite of adverse conditions. 
For the two years preceeding the beginning of the investigation 
concerning the transmission of the disease, trench fever is said 
to have occasioned more sickness among the troops in France 
than any other infectious disease. The work of the Commissions 
showed that trench fever is naturally transmitted by the body 
louse, and that this is the important and common means of trans- 
mission. The louse may transmit the disease by its bite alone, 
or by infection of abraded sink by the excrement. A discussion 
of Rickettsia quintana, the probable cause of trench fever, and its 
occurrence in infected lice will be found on p. 187. 

Lice may also serve as mechanical transmitters of still other 
diseases. The bacilli of bubonic plague have been found alive 
in both body lice and head lice taken from victims of the disease, 
and both this species and the body louse have been experimen- 
tally proved to be able to transmit plague from rodent to rodent 
in Java. De Raadt in Java infected rodents with plague by in- 


400 LICE 

jecting them with ground bodies of head Hce taken from plague 
patients. The practice among some natives of kiUing Hce by 
mashing them against the head of the host, accompanied by the 
frequent scratching due to irritation from bites, may well be a 
frequent cause of plague infection if there has been any oppor- 
tunity for the lice to migrate from an infected to a healthy person. 

There is no reason why syphilis could not be transmitted in 
a similar manner, especially during the second stage of the dis- 
ease, when the spirochaetes are present throughout the blood. 
The readiness with which spirochaetes of other kinds will live in 
insect or tick bodies makes it reasonable to believe that the 
spirochaetes of syphilis might live in the bodies of human lice, 
at least long enough to be conveyed from person to person. 

Prevention and Remedies. — The prevention of lousiness con- 
sists primarily in personal cleanliness. However, no amount 
of personal hygiene and cleanliness will prevent temporary 
lousiness if there is association with unclean and careless com- 
panions. Lousiness and human wretchedness and degradation 
have always been companions, but this does not imply that lice 
have any inherent abhorrence of a clean body if they can get 
access to it. From the nature of their habitats the common 
modes of infection of the three different species of human lice 
vary somewhat. Any of them will spread by contact or close 
association, but each has its own special means of finding new 
hosts. The head louse depends largely for distribution on a 
promiscuous use of combs and brushes or borrowed hats and 
caps, and on the free-for-all trying on of head gear in haberdash- 
eries and millinery shops. The body louse is dispersed by cloth- 
ing and bed linen and finds fresh hunting grounds by night 
migrations from one pile of clothes to another. The crab louse 
frequently utilizes public toilets for dissemination. Where men 
are crowded together in prisons or war camps lousiness is almost 
sure to develop unless particularly guarded against, since some 
uncleanly persons are nearly always in the aggregation, and con- 
ditions are such that the infestation is given every opportunity 
to spread. There are, however, many ways in which lice may 
be dispersed among clean people in ordinary life. Stiles reports 
a case where a large number of girls in a fashionable boarding 
house in eastern United States developed lousiness shortly after 
traveling from Chicago to New York in a Pullman sleeper. 


In Washington and other cities where negresses do much of the 
laundering the family wash is a common source of infestation. 
Closely packed street cars, school cloak rooms, unclean rooming 
houses — all these and many other means may serve to start 
a new colony of lice. 

Perfect cleanliness will usually result in their quick elimination. 
A shampoo with warm water and soap, frequent baths, clean 
underclothes, pressed suits, and other items of personal care are 
inimical to the welfare of the unwelcome visitors. Certain 
remedies are, however, useful in the quick destruction of these 
pests. Head lice can best be destroyed by a thorough washing of 
the head with a two per cent carbolic acid solution or a kerosene 
emulsion (equal parts kerosene and olive oil). When one of 
these remedies has been thoroughly rubbed into the hair the 
head should be covered with a cloth. After several hours the 
ointment is washed off in warm water and ^oap and the dead 
lice removed with a fine-tooth comb. In long hair this treat- 
ment is applied by having the patient lie down with the hair 
hanging over the edge of a bed into a pan of the carbolic solution 
or kerosene emulsion, the hair being sluiced backward and forward 
for ten minutes until thoroughly saturated. The treatment may 
have to be repeated after about ten days to destroy lice which 
have hatched in the meantime, but usually the eggs are des- 
troyed as well as the adult lice. Crab lice can be destroyed best 
by the use of mercurial ointment applied to the infected parts, 
accompanied by washing with soft soap and warm water. A 
close clipping of the hair in the infested regions is the safest and 
quickest method of getting rid of the nits. 

Eradication of body lice is in some respects simpler than that 
of other lice, since it is the clothes instead of the body which are 
to be treated. Much work has been done since the outbreak of 
the war in Europe on testing the effect of various chemicals and 
methods of treatment on lice. This problem is recognized as 
one of the most important minor considerations in war. 

The methods usually employed for getting rid of body lice are 
to sterilize the clothes, either by steam, by fumes of carbon bi- 
sulphide or sulphur dioxide (if no wool is present), by dry heat of 
160° F., or by treatment with volatile odorous substances, such as 
kerosene, naphthaline, ether, anise oil, oil of turpentine, oil of 
eucalyptus or anisol (methylphenylether). The last is a new 


402 LICE 

remedy reported by Frankel, and is said to stun lice in four 
minutes and to kill them in ten minutes. Soaking for one hour 
in a 1 J per cent cresol solution is said to destroy all lice on clothing. 
The eggs are not so easily destroyed as are the adults, but they 
succumb to heating, to exposure to carbon bisulphide (100 grams 
per cubic meter), or to immersion in any of the oils mentioned 
above. Ammonia gas destroys the eggs on clothing in a closed 
receptacle. On the Mexican border of the United States a mix- 
ture of vinegar and kerosene is used for dipping louse-infested 
clothing. The French soldiers are said to have kept largely free 
of lice by the simple expedient of having a hot iron run along the 
seams of the underwear when laundered, to kill nits. 

Preventive measures against lice, simple as they are under 
ordinary conditions, often constitute a very difficult problem, 
especially in army camps. Common methods employed are the 
treatment of the clothes with odorous or poisonous substances, 
the use of underclothes with smooth inner surface, such as silk 
or oil cloth, to which lice cannot attach their eggs, or the dusting 
of naphthaline powder into the shoes, stockings and underwear. 
A substance which has been found most efficient by the British, 
and has been used extensively on the western front in France is 
the now famous NCI, a powder consisting of 96 per cent com- 
mercial naphthaline with two per cent creosote added to increase 
the toxicity and to give lasting qualities and two per cent iodoform 
to increase the adhesiveness of the powder when dusted on the 
inside of the clothing. The shepherd people of the Carpathians 
are said to protect themselves against lice by saturating their 
underclothes in melted butter which prevents the lice from 
fastening their eggs to the fibers of the clothes, and probably the 
fatty acids of rancid butter are also directly deleterious to the 

When louse prevention is undertaken on a large scale, as it 
has been as never before in the present war, enormous difficulties 
are encountered, largely due to the fact that the soldiers, es- 
pecially of the less enlightened nations, do not cooperate with 
the officials. Germany, menaced by louse-borne diseases more, 
perhaps, than any others of the principal warring nations, due to 
the constant contact of her troops with the less efficiently cared- 
for troops of Russia and of the Baltic nations, has largely solved 
the problem by the erection of '' disinfection stations." In 


October, 1915, there were eight of these on the Polish front, 
and more were being built. Through these stations men are 
passed as clothes might be passed through a laundry. Enter- 
ing at the " unclean side," dirty, lousy and unhygienic, they 
emerge from the '' clean side " fresh, clean and free from ver- 
min. Each institution consists of eight separate buildings, 
grouped around a central power house in which 200 tons of coal 
are burned daily to supply steam for disinfection, light, power, 
etc. Laundries, kitchens and administrative quarters are also 
provided. Each of the eight buildings consists of a clean and 
an unclean part, with a chief surgeon in charge, and each has a 
capacity of 500 men every eight hours, a total of 12,000 per 24 
hours for the entire institution. At the entrance on the unclean 
side each man receives a net for whatever apparel he may have, 
such as boots, helmets, etc., which must be sterilized by dry heat, 
and a smaller net to receive his valuables, such as notebooks, 
tobacco, etc. A check number is hung about his neck, and a 
similar number placed on his belongings. He is now given a 
pair of slippers, and enters a large waiting room where he disrobes, 
placing his clothes in another net which has been given him, to 
be sterilized by steam. If in need of it he is given a hair-cut and 
is then subjected to a fifteen minute shower bath with soap, after 
which he is presented with a towel, clean slippers and clean under- 
wear. He is then allowed to pass to the clean side of the build- 
ing where he is given his own disinfected clothing, given a meal 
and conducted to disinfected railroad coaches. The greatest 
disadvantage is the non-cooperation of Russian prisoners, who 
by all sorts of subterfuges try to avoid being *' laundered." 
However, Germany has, by this method, practically converted 
her whole eastern front into a huge filter to guard against lice 
and lice-borne diseases. Without such radical measures Ger- 
many could never have kept herself as free as she has from the 
diseases of war. 


David Harum says, '' A reasonable amount of fleas is good 
for a dog. They keep him from broodin' on bein' a dog." A 
goodly supply of fleas might likewise keep man from brooding over 
anything deeper than the presence of these fleas, but in many 
cases this in itself is a rather serious thing to brood over. Not 
only are fleas very annoying pests and a common cause of in- 
somnia, but they may also serve as the disseminators of a number 
of serious human diseases, among which the terrible bubonic 
plague stands foremost. 

General Structure. — Fleas are insects which are more or less 
distantly related to the Diptera or two-winged flies, but which 
have become so specialized by their particular mode of life as 
external parasites as to necessitate their segregation into a dis- 
tinct order of their own, the Siphonaptera. Their bodies are 
ordinarily much compressed to facilitate gliding between the 
hairs or feathers of their hosts. The head is broadly joined to 
the thorax, which is relatively small. The abdomen is large and 
much compressed from side to side; it consists of ten segments, 
the first seven of which are simple rings, each protected by two 
horny plates, a dorsal " tergum " and a ventral " sternum " 
(Fig. 177). The last three segments are modified differently in 
the male and female in connection with the sexual organs. In 
both sexes the " tergum " of the ninth segment has a pitted area 
covered with little bristles which is called the pygidium, and is 
probably sensory in function. All parts of the body are furnished 
with backward-projecting bristles and spines which aid the flea 
in forcing his way between dense hairs and in preventing him from 
slipping backward. The efficiency of these spines is apparent 
when one attempts to hold a flea between his fingers. Many 
fleas have specially developed, thick, heavy spines arranged 
in rows suggestive of the teeth of combs and therefore known as 
ctenidia or " combs " (Fig. 179). Such a comb may be present 



either along the ventral margin of the head or along the hind 
edge of the pronotum (the dorsal plate covering the first segment 
of the thorax) or in both places. The presence or absence of 
these combs and the number of teeth in them is of considerable 
use in identification of species. 

The legs of fleas are very long and powerful, and at first glance 
seem to possess one more segment than do the legs of other in- 

FiG. 177. The Indian rat flea, Xenopsylla cheopis, male. X 50. (After Jordan 

and Rothschild.) 

sects. They really consist of the usual number of segments, 
however, but are pecuHar in the enormous development of the 
first segments of the legs (coxae), which in most insects are quite 
insignificant (Fig. 179). The shape of the sternal plate to which 
the coxae are attached is suggestive of still another segment. 
The great development of the coxae as well as of the other seg- 
ments of the leg gives unusual springiness and consequently 
enormous jumping power. The human flea, Pulex irritans, has 
been observed by Mitzmain to jump 13 inches horizontally and 
seven and three-fourths inches vertically. An equivalent jump 
for a man of average height would be over 450 feet horizontally 
and over 275 feet vertically! The jumping power must over- 
come to some extent the disadvantage of winglessness and render 
migration from host to host comparatively easy. All the legs 

406 FLEAS 

are furnished with rows of stout spines and are armed at the 
tip with a pair of large stout claws. 

Eyes are present in some species of fleas but not in others. 
The antennae are short and club-shaped, and when not in use are 
folded back into special grooves for them on the sides of the 
head (Fig. 178, ant. gr.). The mouthparts (Fig. 178) are fitted 
for piercing and sucking. In the normal resting position they ap- 
pear to consist of a long jointed proboscis, blunt at the tip, with 


Fig. 178. Head and mouthparts of a flea (squirrel flea, Ceratophyllus fasciatus) ; 
ant., antenna; ant. gr,, antennal groove; cox., coxa of 1st leg; cten., ctenidium; 
hyp., hypopharynx; lab. palp., labial palpi, which together form a tube for pro- 
tecting the lancets; mand., mandibles; max., maxilla; palp., maxillary palpi; 
prothor., prothorax; st. pi., sternal plate of skeleton with which leg is articulated. 

a pair of stout triangular flaps at either side at the base. The 
triangular parts are the maxillae and each is provided with a 
stout four-segmented palpus, which might easily be mistaken for 
an antenna. The proboscis really consists of a pair of segmented 
gouge-shaped structures, the labial palpi, which fit together to 
form a more or less perfect tube, in which lie three piercing 
organs. The latter consist of a pair of thin bladelike mandibles 
serrated on each edge, curved at the tip, and provided with a 
longitudinal groove, and a single bristle-like organ, the epiphar- 
ynx. In piercing the skin of the host the epipharynx first bores 



a tiny puncture, and then the serrated mandibles enlarge the 
hole by an up and down sawing motion. As these organs are 
sunk into the flesh of the host the labial palpi bend back like a 
bow under the flea's head. The two grooved mandibles, placed 
in apposition, form a tube for the outflow of saliva, while the 
epipharynx, which is also grooved, forms a tube with the man- 
dibles for the inflow of blood. The digestive tract is provided 
with a pharynx which acts like a suction pump, and a very large 
and distensible stomach. 

Classification. — Several hundred species of fleas have already 
been described and it is probable that many more species will be 
found. Although some authors split the fleas into a consider- 
able number of families, it is more usual to recognize only two 

Fig. 179. Heads of common fleas, showing distribution of ctenidia or " combs"; 
A, human flea, Pulex irritans, without combs; B, dog flea, Ctenocephalus canis, 
with combs on both head and pronotum ; C, rat flea, Ceratophyllus fasciatus, with 
only pronotal combs, 

well-defined families or groups — the Pulicidae and the Sarcopsyl- 
lidse. The former family includes all the "ordinary" fleas, whereas 
the Sarcopsyllidae is a very specialized group of fleas with a much 
shortened thorax, which appears as if mashed between the head 
and abdomen, with slender anterior and middle legs, and with 
feeble labial palpi of only three segments. Whereas all of the 
Pulicidae lay their eggs singly, or in small groups, and develop- 
ment of the embryos occurs after the eggs are deposited, in some 
of the Sarcopsyllidae the eggs, during their early development, 
are retained in the abdomen of the female, which swells up to 
such a size that the head and thorax appear as a small append- 
age at one end of it. 

408 FLEAS 

The exact identification of fleas, especially if the host is un- 
known, is difficult, being based largely on such minute charac- 
teristics as relative lengths of different segments of the legs, 
number and distribution of spines, etc. Most species of fleas, 
however, are quite closely confined to their respective hosts, only 
a few species being able to thrive on a number of different hosts. 
Some of the commoner species of the fleas which are of most im- 
portance to man can be fairly closely identified, if the host and 
geographic locality is known, by the presence or absence of the 
'^ combs " on the head and thorax. The common human flea, 
Pulex irritans (Fig. 179A), and the Indian rat flea, Xenopsylla 
cheopis (Fig. 177), have no combs, the common rat and squirrel 
fleas of temperate climates (Figs. 179C and 178) have only the 
thoracic comb, while the cat and dog fleas (Fig. 179B) have both 
facial and thoracic combs. 

Life History and Habits. — The life history of all fleas is 
quite similar. Like the Diptera, or flies, they pass through a 

complete metamorphosis, 
i.e., undergo a complete 
reorganization from larval 
to adult form during a 
resting pupal stage. The 

Fig. 180. Larva of Indian rat flea, Xenop- eggS are OVal, whitish in 
sytta^cheopis. X 12. (After Bacot and Ride- ^^^^^ ^^^ relatively large, 

often one-third the length 
of the parent flea, and are laid singly, except in the chiggers, 
being dropped at random in the fur of the host or in the lairs or 
habitations of the hosts. The human flea, for instance, lays its 
eggs in the dust and debris in cracks in floors, under carpets, 
etc., whereas the fleas of most mammals lay their eggs loosely in 
the fur of the host, whence they drop off when the animal shakes 
himself or prepares to sleep. The time required for the eggs to 
reach the hatching stage varies with the species and with climatic 
conditions from two or three days to over two weeks. 

The larvae (Fig. 180) are tiny cyUndrical maggot-like creatures 
with neither legs nor eyes. They have small brown heads and 
whitish bodies composed of. 13 segments, which are provided with 
rather sparse bristly hairs to aid in crawhng. The last segment 
is terminated by a pair of tiny hooks. 

The larvae squirm about actively in the dirt or debris of the 


lairs or rubbish piles in which they hatched, avoiding light and 
feeding upon what bits of organic matter they can find, such as 
mouse pills, crumbs, hairs, epidermal scales from their hosts and 
the excrement of adult fleas. Some species, if not all, devour their 
shed skins after moulting. According to Bacot and Ridewood, 
who have recently made observations on the larvae of a number of 
species of fleas, the larvae become very excited and impatient 
when disturbed. They sometimes lie quiet, coiled like a watch 
spring, for repose or concealment, but when about to moult they 
stretch out at full length. They crawl by alternately expanding 
and contracting the body like an earthworm, first securing a hold 
with the hooks at the posterior tip of the body, then with the 
head which is bent under to hook over some irregularity on the 
surface. The duration of the larval stage varies with the tem- 
perature and humidity and to some extent also with the species. 
Under favorable conditions, i.e., at rela- 
tively low temperatures and high humid- 
ity and with plenty of food, the larvae of 
some species pass through their two 
moults and enter the pupal stage in a 
week, whereas under unfavorable condi- Fia. I8i. Cocoon of 
tions the duration of the larval existence ^ T2 ^ ^^' ^ ^^ *^^ 
may be drawn out to over three months. 

When ready to undergo their transformation into adults, the 
larvae spin little silken cocoons which are somewhat viscid, so 
that particles of dust and lint readily adhere to them and give 
them a dirty, dingy appearance (Fig. 181). According to Lyon 
the adult insects may emerge from the cocoons of the cat flea, 
Ctenocephalus felis, in from two to 14 days, but in most species 
at least a week is required for the transformation to take place, 
and this time may be greatly increased by unfavorable climatic 
conditions. Strickland, in his work on the rat flea of England, 
Ceratophyllus fasdatus, found that the average pupal existence 
was 17 days and was extended to four months or more by low 
temperatures, the fully formed adult insect remaining dormant 
within the cocoon until exposed to a temperature of about 70° F. 
There is much probability that the winter in temperate climates 
and the hot dry season in tropical climates is tided over by fleas 
in the cocoon, the emergence of the adults coinciding with the 
advent of moderately high temperatures and humidity. 

410 FLEAS 

The adult fleas, according to Strickland's work on the rat flea, 
do not become sexually mature for some days after they escape 
from the cocoon, and copulation does not occur until this time, 
nor, in the case of the rat flea, until after a feed of rat's blood, the 
latter apparently acting as a stimulus to reproduction. Soon 
after copulation the eggs begin to be laid. 

In the dog flea, Ctenocephalus canis, the entire cycle from egg to 
adult is said to be passed through in a minimum of two weeks, in 
the human flea, Pulex irritans, in 19 days (in southern Europe) 
and in the rat fleas in about three weeks. Ordinarily, however, 
the life cycles occupy a considerably longer time, the average 
being from one to three months. 

The length of life of adult fleas depends largely on food supply, 
temperature and humidity. Unfed fleas, unless allowed to bury 
themselves in rubbish, usually die in less than a month, though 
when buried in debris they may be kept alive many months. 
Well fed rat fleas kept at low temperatures (about 60° F.) and high 
humidity may live for nearly a year and a half, according to 
Strickland's experiments. The optimum climatic conditions and 
normal length of life probably vary a great deal with different 

Unlike most blood-sucking insects, fleas usually feed at fre- 
quent intervals, usually at least once a day, and sometimes much 
oftener than this. The frequent biting is due to the fact that 
fleas are very easily disturbed while feeding and seldom complete 
a meal at one bite. Moreover, the capacity of the stomach is 
not so great as in many other blood-sucking insects. The human 
flea and some others are mainly nocturnal, visiting their hosts 
chiefly at night, whereas others, such as the cat and dog fleas, 
remain in the fur of the host nearly all the time. Some species 
show a decided preference for certain parts of the body of their 

Fleas and Disease. — Like most other blood-sucking parasites, 
fleas are intimately connected with the spread of disease. The 
most serious charge against them in this connection is the dis- 
semination of bubonic plague, which as a human scourge ranks 
with such diseases as smallpox and leprosy. In fact, few diseases 
have ever ravaged the human race with more terrible destruc- 
tiveness than plague when it breaks forth as an epidemic and 
becomes rampant. It is estimated that in the epidemic of the 


14th century in Europe one-fourth of the population of that 
continent, or 25 miUion people, died of the disease. Superstition 
and unreasoning terror led to horrible persecution and torture of 
innocent people who were supposed to cause the plague. At 
present the disease is practically confined to tropical countries, 
and is especially prevalent in India, where an average of about one 
million deaths a year are caused by it. The practical disappear- 
ance of plague from Europe is thought by some authors to be 
associated with a change in the rat fauna of Europe, the do- 
mestic and gregarious black rat, Epimys rattus, being replaced 
by the wilder and more scattered brown rat, Epimys norvegicus. 
The disease, however, has often been introduced from the tropics 
into other countries, and there is constant danger of this wherever 
the strictest preventive regulations are not enforced. In 1900 
the disease was introduced into San Francisco, and there is every 
reason to believe that had knowledge of preventive medicine 
been at the point where it was 300 years ago, the United States 
would have been swept as was Europe in the 14th century. In- 
stead, knowing that rats were the chief reservoir of the disease, 
and that rat fleas were instrumental in transmitting the disease 
from rat to man, the U. S. Public Health Service took hold of the 
situation and instituted an anti-rat campaign such as had never 
been thought of before. Over a million rats were caught, ex- 
amined and destroyed in the city of San Francisco. The infec- 
tion spread, however, and became established in the ground 
squirrels of several counties in California. From July 1, 1913, to 
November, 1914, over 20,000,000 ground squirrels were destroyed 
in infected districts in California. So strenuous were the efforts 
to stamp out the disease before it could get beyond control that 
only 187 cases of the disease in man occurred in California, 
with none since 1914. New Orleans has also had a taste of plague, 
and infected rats have been taken in the vicinity of the water 
front in Seattle. 

The steps which have made possible an intelligent fight against 
plague were the discovery of the plague germ. Bacillus pestis, 
by Yerson in 1894, the establishment of the identity of the disease 
with that of rats by the same worker, the discovery of the mul- 
tiplication of the plague germs in the gut of rat fleas, Xeno- 
psylla cheopis, by Liston in 1905, and finally conclusive experi- 
mental proof by the British Plague Commission in India in 

412 FLEAS 

1906 that the rat flea was the principal means of transmission of 
the bubonic form of the disease. 

As far as is known the plague bacilli live only in the digestive 
tract of the fleas and do not infect either the saliva or the body 
cavity. From this fact it is evident that the germs are inoculated 
into the wound made by the flea, either with the excrement which 
is commonly voided while sucking blood or with regurgitated 
blood. It has been pointed out that a rat flea's stomach will 
hold about one-half a cubic centimeter of blood and could there- 
fore take 5000 germs with a single feed from an infected animal. 
These often multiply to such an extent as to form a solid mass of 
organisms, blocking the digestive tract of the insect (Fig. 182). 
It has been stated that when the stomach and 
intestine of a flea are plugged with plague 
germs the normal action of the valves of the 
digestive tract is lost, and the pumping move- 
ments of the pharynx result in regurgitating 
infected material into the wound instead of 
sucking fresh blood from it. Fleas were found 
by the British Plague Commission to remain 
infective for 15 days during the height of an 
_. epidemic, though during the non-epidemic 

Fig. 182. Diges- ^ •j.-ji -j-rx- r 

tive tract of flea season no mdividual remamed mfective tor 
plugged with solid ^QYQ ^]^an seven days. In Java the Indian 

growth (in black) of ■ • t- .- 

plague bacilli. (After rat fleas have been found to remain infective 
Manson.) fQj. 33 days and Bacot has found the European 

rat flea, Ceratophyllus fasciatus, to remain infective, when kept 
away from a host, for 47 days. 

The Indian rat flea, Xenopsylla cheopis (Fig. 177), is the species 
most intimately associated with plague transmission. This spe- 
cies has been introduced with rats on ships into all parts of the 
tropics, and into seaports in many temperate countries, especially 
such ports as San Francisco, which trade extensively with the 
Orient. This species, however, is by no means the only one 
which can serve in the transmission of plague. It is probable 
that any species which will attack both man and other sus- 
ceptible animals, such as rats and ground squirrels, may transmit 
the infection. Thus in India the human flea, Pulex irritans, 
and the European rat flea, Ceratophyllus fasciatus, have been 
proved experimentally to be plague carriers, and in California 


the squirrel fleas, Hoplopsyllus anomalus and Ceratophyllus acutus, 
also have been shown to carry the infection. It is evident also 
that other animals besides rats and man are susceptible to the 
disease. Ground squirrels, Citellus beecheyi, guinea-pigs and 
monkeys have been shown to be susceptible. A marmot or 
ground hog, Arctomys hobac, common in Manchuria, is thought 
to have been the chief reservoir of the disease in the Manchurian 
epidemic in the winter of 1910-11, the flea Ceratophyllus silan- 
tiewi being the transmitting agent. 

Doubtless any fleas which attack these animals and which 
also attack man may be instrumental in spreading the plague to 
human beings in direct proportion to the willingness with which 
they will bite man, and to their opportunities for doing so. It 
must not be inferred that only fleas can transmit the disease. 
The pneumonic form of plague, which is relatively uncommon, 
is transmitted by particles of sputum or mucus from the mouth or 
lungs. The bubonic plague may also be transmitted by bedbugs 
and perhaps by other parasitic insects. A head louse taken from 
a plague patient was found to be infected. There can be no 
doubt, however, that the rat fleas are by far the most important 
spreaders of this terrible disease. 

A similar but milder disease of rodents, transmissible to man, 
occurs in western United States. It is caused by Bacterium 
tularense and is known as tularemia. Deerflies and certain lice 
have been shown to be transmitting agents, but the role of fleas 
is only conjectured. 

Another disease which is commonly believed to be transmitted 
by fleas is the Mediterranean or infantile form of kala-azar 
(see p. 83). This is prevalent in dogs throughout many of the 
regions bordering the Mediterranean, especially in parts of Italy 
and North Africa, and is the cause of a high mortality in the 
numerous cases which occur among children. A number of 
authors have carried on experiments to prove the instrumentality 
of the common dog flea, Ctenocephalus canis, and also of the 
human flea, Pulex irritans, with varied results. (See Chap. V, 
p. 83.) The role of fleas in the transmission of this disease is 
still uncertain but there is enough evidence against the fleas to 
warrant their being looked upon with extreme suspicion until 
definitely proved innocent. 

Another instance of the instrumentality of fleas in the trans- 

414 FLEAS 

mission of disease is their relation to the spread of certain species 
of tapeworms, especially the common dog tapeworm, Dipylidium 
caninum. The larval stage of this tapeworm is passed in the body 
cavity of the dog flea, Ctenocephalus canis, the eggs of the parasite, 
adhering to hair in the vicinity of the anus, being ingested by the 
flea. Occasional infection of human beings, especially young 
children, occurs by the accidental swallowing of infected fleas, a 
thing which could easily happen in cases of too great intimacy be- 
tween children and their pet dogs. As many as 50 larvae of Dipy- 
lidium have been found in a single flea. The larvae can also de- 
velop in the human flea. The rat flea, Xenopsylla cheopis, has 
been found to harbor the larval stages of tapeworms of the genus 
Hymenolepis, as many as nine cysticercoids having been found 
in a single specimen. These tapeworms are normally parasitic in 
rats and mice but occasionally parasitize man also. 

The relation of fleas to other diseases is suspected. A German 
writer has put forth the theory that fleas are instrumental in 
the transmission of typhus. If typhus is purely a bacterial 
disease, its spread by fleas and other parasites as well as by lice 
would be quite possible, but if it should be found to be caused by 
an organism which requires a true intermediate host, it would 
be doubtful whether such widely different insects as lice and 
fleas could both function in the same manner. That fleas 
might act as mechanical transmitters of such diseases as tuber- 
culosis and syphilis is quite possible, though it is doubtful if 
this often occurs. 

Important Species 

Human Flea. — The only species of flea which is known to be 
a parasite of man primarily, with the exception of the chigger, 
is the appropriately named human flea, Pulex irritans, though 
in many places man is annoyed more by certain other species 
which are primarily parasites of his domestic animals. The 
human flea is not exclusively a parasite of man. It also attacks 
badgers, skunks, dogs and other carnivores, occasionally occurs 
on rats and mice, especially in houses and ships, and has been 
taken on the blacktail deer, Odocoileus columhianus} It is now 

1 Specimens of fleas taken in considerable numbers on deer in northern 
California by F. C. Clarke, of the California Fish and Game Commission, 
were identified by Prof. R. W. Doane of Stanford University as Pulex irritans. 
On account of the distinctive habits of these deer fleas, Clarke (in Htt.) 
believes that they should be considered a variety of P. irritanSy for which he 
proposes the name P. irritans cervi. 


cosmopolitan in distribution, probably having originated in 
Europe, whence it was introduced with Europeans to all parts 
of the world. This flea is the species which has made California 
as famous for its fleas as is New Jersey for its mosquitoes. The 
relatively cool humid summer climate combined with a mild 
wet winter make the Pacific Coast of the United States an ideal 
place for this pest. Though more or less of a nuisance through- 
out the year in mild cHmates, this flea is less troublesome in 
winter, due to relative inactivity, to slower reproduction, and 
to the fact that small mammals are more commonly attacked at 
this time of year. 

The human flea is readily distinguished from most common 
species in temperate climates by the absence of any combs, 
either on the head or thorax. From the Indian rat flea, Xeno- 
psylla cheopis (Fig. 177), it is diflSicult to distinguish, the essential 
difference being the presence in the rat flea and absence in the 
himian flea of a vertical chitinous thickening of the mesoster- 
num, i.e., the plate to which the middle leg is artiijulated on 
either side. The antennae of the human flea are shorter and 
more knoblike than are those of Xenopsylla. 

The human flea secretes itself in crevices and cracks of houses, 
in floors, rugs, bedding, etc., coming forth chiefly at night to 
pierce the flesh and suck the blood of its hosts. The suscep- 
tibility of different individuals to flea bites is variable. The 
irritation that is normally produced, probably chiefly as a result 
of the injection of the insect's salivary secretions into the wound, 
causes the formation of a reddish pimple with more or less swell- 
ing. Some people, however, are apparently entirely immune to 
flea bites and feel no pain from them. The writer is one of these 
fortunate individuals. On his first visit to California he had 
been fully warned concerning the ravages of the fleas but found to 
his pleasant surprise that the only discomfort felt from fleas was 
the tickling occasionally caused by their movements beneath 
his clothing. A college roommate, however, was attacked to 
such an extent as to be unable to sleep, and spent a considerable 
part of many nights in pursuit of the wily fleas and in violent 
massaging of painful wounds. 

As has been noted, the human flea may act as a transmitter 
of plague, infantile kala-azar and tapeworm {Dipylidium) in- 
fection, though it is not the chief villain in the spread of any one 
of these diseases. 

416 FLEAS 

Dog and Cat Fleas. — Next in importance to the human flea 
as a parasite of man is the dog flea, Ctenocephalus canis, and the 
closely alUed cat flea, C. felis. In the southeastern United States 
where the flea scourge is as great if not greater than in Cali- 
fornia, the dog flea is the species usually met with. During the 
moist hot summers this species becomes exceedingly abundant. 
Although primarily a parasite of dogs this flea wilhngly includes 
man in its bill of fare if opportunity offers, and also attacks 
cats, rats and other mammals. The usual fleas of cats, how- 
ever, are now generally considered to be specifically distinct from 
the dog flea. The cat flea is the only one of the two species 
found in India, where it is a common parasite of dogs as well 
as cats. The cat flea has a longer and more slender head than 
its near relative. Both species can readily be distinguished 
from any other common species with similar habits by the pres- 
ence of two conspicuous combs, one along the ventral margin of 
the head, the other on the pronotum (Fig. 179B). 

The eggs of dog and cat fleas are usually laid loosely in the fur 
of their host, whence they readily fall out when the host shakes 
himself or is settling himself for a nap. They develop in the 
dust and dirt of kennels, woodsheds, house floors or other places 
where infested animals are likely to go. Houses, of course, be- 
come infested through the agency of infested animals, and since 
the fleas, once in houses, encounter man more readily than they 
do the original hosts, man is very likely to suffer from their at- 
tacks. Patton and Cragg found the inside of a hat, in which a 
kitten had slept overnight, so full of flea eggs that it looked as if 
it had had sugar sprinkled in it from a sifter. Another author 
collected a teaspoonful of eggs from the dress of a lady who had 
held a kitten in her lap for a short time. The writer has been 
able to flnd a similar quantity of eggs by dusting a smooth hard- 
wood floor after an infested dog had indulged in one vigorous 
shake. With these instances in mind one can readily understand 
how houses into which infested pets are admitted become over- 
run with fleas. 

The dog flea, from its habits, is the species most frequently 
imphcated in the transmission of kala-azar (see p. 83), and is 
the species usually instrumental in transmitting tapeworm 
{Dipylidium) infection to children. Since this species will feed 
on rats there is no reason for doubting that it may act as a trans- 


mitter of bubonic plague, though its preference for dogs or cats 
would preclude a frequent occurrence of this. 

Rat and Squirrel Fleas. — The various species of rat and squir- 
rel fleas are only accidental parasites of man. They readily at- 
tack him if opportunity offers but do not remain adherent to him 
as they do to their normal hosts. If it were not for their enormous 
importance in the spread of bubonic plague, they would hardly 
need special consideration. 

From its intimate connection with the spread of bubonic 
plague, the Indian rat flea, Xenopsijlla cheopis (Fig. 177), is of 
prime importance. Though other members of the genus are 
confined to Africa and Asia, this species has now a world-wide 
distribution, having accompanied its normal host, the rat, to all 
warm seaports in both the Old and the New World. It is a 
rather short, stout flea, resembling the human flea in the absence 
of combs. Although the normal hosts of Xenopsylla cheopis are 
rats of various species, the domestic habits of these rodents 
bring the fleas into close association with man, and they will 
readily feed upon him if hungry. Furthermore, deRaadt has 
recently demonstrated that these fleas do not remain constantly 
in the fur of their normal hosts, but that 80 per cent drop off in 
the course of 48 hours. This species is not migratory and sel- 
dom reaches anyone but the inhabitants of the house in which its 
host occurs, unless carried by the rats themselves. Swellen- 
grebel states that in Java this flea will wiUingly bite man on the 
first day of fasting. In many tropical countries the Indian rat 
flea is the commonest flea found in houses; in Egypt 96 per cent 
of fleas caught in plague-infested houses were of this species. 

The European rat flea, Ceratophyllus fasciatus, is a species 
having habits quite similar to those of Xenopsylla cheopis. It 
replaces the latter species in temperate climates except in sea- 
ports, where the Indian rat flea is often more common. The 
common rat flea of China and Japan is Pygiopsylla ahalce. The 
larvae of C. fasciatus develop best under cool humid conditions 
in an abundance of rubbish. Strickland, who has worked out 
the biology of this flea in detail, found that it would actually 
attack man in preference to rats, although a feed on the blood of 
rats seemed to be necessary before any eggs were laid. Another 
species of the same genus, C. gallinoB, attacks chickens in Europe, 
and has been introduced into several parts of the United States. 

418 FLEAS 

It is said to be very annoying to man also. The common squir- 
rel flea in North America, C. acutus, is found on a number of 
species of wild rodents, and also occasionally on rats and mice. 
It does not attack man so readily as does C. fasciatus, but is 
nevertheless not averse to human blood. This species has 
come into great importance in California as the transmitter of 
plague from rats to ground squirrels. It is probable, how- 
ever, that other species of this genus and of allied genera 
may quite as readily transmit plague, depending only on the 
extent to which their habits bring them in contact with infected 

Chiggers. — The chigger, chigoe, jigger or sand flea, Derma- 
tophilus (or Rhynchoprion) penetrans (Fig. 183), as it is vari- 
ously called, is one of the most de- 
spised pests of tropical countries. 
It is a very small flea of the family 
SarcopsylUdse, about one mm. in 
length, with no comblike spines 
and relatively slender legs. It has 
a very comical pointed forehead, 
like a helmet worn with the point 
forward. The males and virgin 
females of this species are similar 

Fig. 183. Chigger or burrowing , ,^ n ' i ^ -, ^ ji j 

flea, Dermatophilus penetrans, un- ^0 O^^^r fleaS m hablts, eXCept that 

impregated female. X 30. (After they attack a wide range of hosts. 

Karsten from Riley and Johannsen.) -,/r ■ ,^ • • i i j n ,^ • 

Man IS the prmcipal host of this 
particular species, but pigs are also very commonly attacked. 
Chiggers occur especially in sandy regions where there is much 
underbrush, and here they lie in ambush on the vegetation, dead 
leaves or sandy soil, ready to attack any host which may come 
their way. The particular importance of this flea lies in the 
fact that the impregnated females have the aggravating habit 
of burrowing into the skin especially in such tender spots as under 
the toe nails, where, nourished by the blood of the host, the eggs 
develop and cause the abdomen to swell into a great round ball 
as large as a pea, leaving the head and legs as inconspicuous 
appendages (Fig. 184). Only the two posterior segments of the 
abdomen do not enlarge; these act as a plug for the hole made in 
entering the skin. The eggs, up to a hundred in number, mature 
in about a week and are then expelled by the female through the 



Chigger or burrowing flea, Der- 
X 18. 

protruding end of the abdomen. Sometimes the entire female 

is expelled with her eggs by the pressure of the inflamed tissue 

which surrounds her. The 

eggs, which fall to the 

ground, soon hatch into 

typical flea larvae (Fig. 185). 

These, if they happen to 

fall on sandy soil under 

conditions suitable for 

their development, grow 

to maturity, pupate in a 

cocoon and emerge as adult 

insects in the course of ten 

days or two weeks. fig. 184. 

The wounds made by the ^^f^^ophilus penetrans, gravid female 
, . , , . (After Moniez.) 

burrowmg female in the skm 

become much inflamed and very painful. Frequently the dis- 
tended abdomen of a flea is crushed and the eggs released in the 
wound. In such cases the inflammation is greatly increased un- 
less the crushed body and eggs are immediately expelled. As 
soon as the eggs are laid, or even before, the skin surrounding the 
wound ulcerates and pus is formed. The empty female flea is ex- 
pelled. The sore which is left 
is very liable to infection by bac- 
teria and frequently results in 
the loss of toes or even whole 
limbs through blood-poisoning. 
Quiros has recently pointed out 
that in Central America, where chigger infection is very common, 
especially in boys who play barefooted in the streets along which 
infected hogs are driven to public market, deaths from tetanus 
and gas gangrene from chigger wounds are very common. 

Although usually only a few chiggers are present at a time, 
there are cases where hundreds infest a person at once, literally 
honeycombing the skin and making the feet or other parts of 
the body so sore that the victim is rendered a complete invalid. 
This obnoxious flea formerly existed only in the tropical por- 
tions of America, especially in the West Indies, but it was intro- 
duced to the West Coast of Africa in 1872, and has since become 
abundant throughout the tropical parts of that continent and 

Fig. 185. Larva of chigger, Dermatoph 
ilus penetrans. (After Newstead.) 

420 FLEAS 

in the neighboring islands. It has also been introduced by coolies 
into India, but does not seem to thrive there as it does in tropical 
America and Africa. 

The treatment of chigger wounds formerly consisted in the 
destruction of the fieas while imbedded in the wounds. This was 
done by applying various insecticides or pricking with a needle, 
the dead insect being removed after ulceration. A much better 
method is to enlarge the entrance hole of the flea with a clean 
needle and remove the parasite entire. The wound should then 
be carefully dressed and protected until healed. An ointment 
recommended by Quiros consists of 23^ grams salicylic acid and 
10 grams ichthyol in 10 grams of yellow vaseline. Bathing of 
infected parts with kerosene oil is also recommended. 

Chiggers can be avoided to a large extent by the use of high 
boots, or shoes and leggings. Walking barefooted in chigger- 
infested regions is almost sure to result in attacks by these pests. 
Houses, yards, etc., in chigger regions should be kept carefully 
clean of dust, dirt and debris which might favor the develop- 
ment of the parasites. In Central America Quiros recommends, 
as one of the best preventive measures, a prohibition against 
driving hogs affected with chiggers through the streets, along 
with regulations for treating affected hogs where they are raised. 
According to Penschke, in German East Africa, attacks by chig- 
gers can be prevented by thoroughly rubbing the feet every two 
or three days with vaseline to which has been added a few drops 
of lysol or cresol soap (15 drops to 3 J oz. of vaseline). 

Sticktight Flea. — The " sticktight " flea, Echidnophaga galli- 
nacea (Fig. 186), is another member of the family Sarcopsyllidse 
which may be a human pest. It is a small dark-colored flea which 
very commonly attacks chickens in nearly all tropical and sub- 
tropical countries, including the southern United States in 
America. Although the normal host is the chicken, other poultry, 
dogs, cats, domestic rabbits, rats and other animals, as well as 
man, are attacked. This species gets its name from the tenacity 
with which it adheres to its host. It is gregarious, collecting in 
dense masses on the heads of poultry (Fig. 186), in the ears of 
mammals and in other places. It is not averse to attacking 
man, especially children, but since it is not so active as other 
fleas it can easily be found and removed. No disease is known to 
be transmitted by this flea. 


Prevention. — Strict cleanliness in private homes or public 
buildings prevents fleas from breeding in them. Uncared-for 
carpets and straw mattings afford excellent breeding grounds 
for the human flea, as do dusty cracks 
between floor boards, unswept corners 
under sinks, and any other place where 
the eggs and young, undisturbed, may 
obtain enough moisture to keep them 
from drying up. The use of bare hard- 
wood floors with rugs which can readily 
be taken up and swept and thorough 
sweeping in corners and under pieces 
of furniture, sinks, etc., do not give 
fleas an opportunity to breed in the ^^\^\^ 
home or in pubHc buildings, and are pj^^ igg. Head of chicken 
therefore valuable preventive measures, infested with chicken flea, 

Oj. ,, r J. r -jj- Echidnophaga gallinacea. 

ne of the best means ot riddmg an (^fter Bishopp.) 

infested house of fleas is to sprinkle 

the floors with naphthaline and close the rooms for a day or 
two. This will effectually kill all adult and larval fleas, and the 
eggs may then be destroyed by washing the floors with hot soap- 
suds, a five per cent formalin solution or one-tenth per cent 
solution of corrosive sublimate. It is claimed that alum swept 
into carpets or a solution of alum soaked into carpet paper pre- 
vents fleas from breeding. 

Fleas are very susceptible to fumigation with hydrocyanic 
acid gas. Experiments by the U. S. Public Health Service show 
that fleas succumb to the amount of gas generated by two and 
one-half ounces of potassium cyanide in 1000 cubic feet of space. 
Fumigation with sulphur is also effective. Details of methods 
of fumigation with these substances will be found on p. 383. 
Sodium fluoride in the form of a crystalline powder scattered 
on floors or blown about by means of a dust-gun will probably 
prove effective against fleas, as it has against cockroaches 
and other insects. It is inexpensive and not dangerous to 

Various traps for the capture of adult fleas have been devised, 
one of the simplest and most effective being to clothe the legs in 
sticky fly paper, and wander about in the infested rooms. A 
badly infested building in Cornell University was cleared of fleas 



in this manner. Another device, used by the Chinese, is a rod 
of bamboo, smeared with bird Hme, fitted inside of a larger piece 
of bamboo which has holes cut in it. A trap 
of similar type may be constructed by fitting a 
piece of broomstick wrapped with sticky fly 
paper inside a wire cylinder (Fig. 187). Such 
a '' flea stick " can be roUed about on floors or 
in beds and will collect a large proportion of 
the flea population. Another trap consists of 
a glass of water with about an inch of oil on 
the top of it fitted with a little wick in the 
center of a floating piece of cork. This is 
placed in the center of a dish of strong soap- 
suds and lighted at night. The light attracts 
the fleas, which leap headlong into the soap- 

The destruction of fleas, especially cat and 
dog fleas, on domestic animals is often neces- 
sary in order to do away with a flea scourge. 
Dogs and cats, or other hosts, may be cleared 
of fleas by washing them in two or three per 
broomstick wrapped cent solution of creolin (about one tablespoon- 

with sticky fly paper, p -i , xr x\ a.T_ 

fitted in a cylinder ^ to a quart of Warm water), or some other 
derivative of creosote, or a similar solution of 
potassium sulphide. According to Bishopp, 
the solution should be worked into the hair with a brush, 
and care should be taken to wet the fleas which crowd 
toward the head of the animal. After about ten minutes 
the solution should be washed off with warm water and soap, 
at least in delicate-skinned animals such as cats, to avoid a 
burning effect. Another method of treatment is to rub 
powdered moth-balls (naphthaline) into the fur. This causes 
the fleas to emerge from the fur in a stupefied condition in 
which they are easily captured and destroyed. Except to sicken 
cats slightly for a day or two this treatment has no ill effect 
on the host. 

Of temporary value in flea-infested places is the use of repel- 
lents, such as oil of pennyroyal, eucalyptus oil, etc., smeared on 
shoes or clothing, or between bed sheets. Beds may be isolated 
by elevating them to some distance from the floor, or by sur- 

FiG. 187. A 
modification of the 
Chinese flea trap. 
Constructed of a 

of wide-meshed wire 
net. (After Bishopp.) 


rounding them with a band of sticky fly paper 12 to 14 inches 
wide. Where perfect protection from fleas is desired, as in a 
plague-smitten city, all of these protective measures, as well as 
fly-paper wrapped legs, and any other means which may come to 
mind should be made use of. These should be followed up by 
the more permanent measures leading to the extermination of 
both larval and adult fleas. 



Importance. — Of all existing insect pests mosquitoes are the 
greatest enemies of mankind. The mere annoyance which the 
enormous numbers of them cause by their constant attacks and 
painful bites is sufficient to have made some parts of the world 
practically uninhabitable. There are rich pieces of country which 
have remained absolutely unsettled on account of this pest alone. 
Some of the choicest hunting and camping grounds in North 
America, and in other continents also, are practically closed to 
the camper by the countless millions of mosquitoes which trans- 
form a camper's Paradise into an intolerable hell, and drive any 
bold human invader to frenzy. When travel through such places 
is necessary no comfort can be hoped for without the presence 
of a dense smudge or without almost constant application of 
" mosquito dope," and even then the unceasing '' zangs " of the 
mosquitoes as they threateningly approach is hardly less trying 
on the nerves than are the actual attacks. Unlike most insect 
pests the mosquitoes of cold northern countries are if anything 
more abundant than they are in the tropics. The far northern 
mosquitoes do not, however, act as carriers of disease; terrible as 
they are, they wage clean warfare, whereas tropical mosquitoes 
have their spears poisoned with death-dealing disease germs. 
The northern mosquitoes bite, suck their fill of blood if they can, 
and are through; the tropical mosquitoes often leave months or 
years of suffering and disease, or even death, in their wake. No 
less than four different diseases are believed to be transmitted 
by mosquitoes exclusively, namely, malaria, yellow fever, dengue 
or breakbone fever and filariasis, while a fifth, a form of myiasis 
in South America, is believed to be transmitted sometimes by 
mosquitoes. Mosquitoes have been suspected of complicity in 
the transmission of still other diseases, but their relation to the 
first four diseases mentioned above is sufficient to brand them as 
the greatest insect enemies of the human race. 




General Structure. — Mosquitoes are members of the great 
insect order Diptera, to which so many human pests belong. 
Their nearest relatives, outside the mosquito family itself, are 
the midges (Chironomidse), craneflies (Tipuhdse), sandflies 
(Phlebotomus), and blackflies or buffalo gnats (Simuliidae) . The 
members of the mosquito family, Culicidae, can be distinguished 
from other Diptera which look more or less like them by the 
characteristic and quite conspicuous fringe of scales on the hind 

FiG. 188. Diagram of adult female mos- 
quito (Aedes sollicitans); abd., abdomen; 

Fig. 189. Digestive tract of a 
mosquito; d. f. res., dorsal food 
reservoirs; malp. t., malpighian 
tubules; ph., pharynx; prov., pro- 
ventriculus; rect., rectum; sal. d., 
salivary duct; sal. gl., salivary 

ant., antenna; e., eye; halt., haltere; palp., gland; st., stomach; v. f. res., ven- 

palpus; prob., proboscis; th., thorax. 

tral food reservoir. 

margin of the wings. Most of the CuUcidae have a long promi- 
nent proboscis containing needle-like organs for piercing and 
sucking, but in two subfamilies, including the midges of the 
genus Dixa, and the so-called phantom midges, Corethra (Fig. 
192), the adults of which resemble true mosquitoes and are often 
mistaken for them, there is no long proboscis. 

The general appearance of adult mosquitoes is so well known 



as to need no description, but the details of their structure is as 
little known by most people as are those of the structure of other 
insects. The diagram on page 425 (Fig. 188) illustrates the 
details of the parts of a mosquito which are of most use in iden« 
tifying and classifying. The sexes can be distinguished most 
readily by the antennae; in the female (Fig. 190 A) they are long 
and slender with a whorl of short hairs at each joint, whereas in 
the male (Fig. 190B) they are shortened and have a feathery 
appearance, due to tufts of long and numerous hairs at the 
joints. In many mosquitoes the palpi also furnish a means of 

Fig. 190. Heads of female (9) and male (q) mosquito, Culiseta incidens: 
ant., antenna; b. j. ant,, basal joint of antenna; label,, labellum; palp., palpus; 
prob., proboscis. 

distinguishing the sexes; they are usually long in the males 
but short in the females, but in Anopheles they are long in both 
sexes, and in some mosquitoes, e.g., Uranotcenia, they are short in 

The proboscis, which is the most fearful part of a mosquito, 
also differs in the sexes, and fortunately is so constructed in the 
male that a mosquito of this sex could not pierce flesh if he would. 
At first glance the proboscis appears to be a simple bristle, some- 
times curved, but when dissected and examined with a micro- 
scope it is found to consist of a number of needle-like organs 



lying in a groove in the fleshy lower lip, which was the only part 
visible before dissection. In the female mosquito there are six 
of these needle-hke organs the nature and names of which are 
shown in Fig. 191. The " labrum-epipharynx " and " hypo- 
pharynx " act together to form a tube for drawing up blood into 
the mouth. A tiny tube runs down through the hypopharynx, 
opening at its tip, through which saliva is poured into the wound 
as through a hypodermic needle to prevent blood from coagu- 
lating. The ensheathing lower lip does not itself penetrate the 
wound, but bows back as the mosquito bites, the flexible tip or 



Fig. 191. Side view of head of female Anopheles showing mouthparts; ant., 
antennae; clyp., clypeus; ceph. s., cephalic scales; hyp., hypopharynx; lab., 
labium; label., labellum; labr. ep., labrum-epipharynx; mand.; mandibles; max., 
maxillae; palp., maxillary palpi. X 20. (After Nuttall and Shipley.) 

*' labella " acting as a guide for the piercing organs as they are 
sunk into the flesh. In male mosquitoes the piercing organs are 
much degenerated, only the suctorial part of the apparatus being 
well developed. 

Besides the variations of the parts mentioned already, mos- 
quitoes vary as regards the form, distribution, color and other 
characteristics of the scales which clothe much of the body and the 
edges and veins of the wings; the details of the male reproductive 
organs at the tip of the abdomen; the relative length of parts of 
the leg; and in other respects. 

All mosquitoes have good '* capacity " as far as the digestive 
tract is concerned, having three food reservoirs connected with the 



oesophagus, in addition to a large stomach (Fig. 189). Connected 
with the proboscis is a pair of sahvary glands consisting of three 
lobes each. One of these lobes in each gland differs from the 
others and instead of secreting ordinary saliva is thought to secrete 
the poisonous substance which prevents coagulation of blood and 
produces the inflammation and pain attendant upon a mosquito 

Fig. 192. Larva and adult of Corethra, a member of the Culicidae which is not 
a bloodsucker, but is often mistaken for a mosquito. The larvae prey on mosquito 
larvae and other aquatic organisms. Note anterior and posterior "floats" in the 
larva, and mosquito-like appearance of adult, except for lack of proboscis. (Larva 
after Howard, Dyar and Knab; adult after Smith.) 

bite. Schaudinn, however, has adduced some experimental evi- 
dence that it is the contents of food reservoirs which cause the 
inflammation. It is in the salivary glands that the malaria para- 
sites, and probably the parasites of dengue and yellow fever also, 
collect, and whence they are poured with the secretions of the 
glands into the wounds. 

Life History. — Mosquitoes, like other Diptera, pass through 
a complete metamorphosis in the course of their life history, i.e., 
they undergo a transformation from larval to adult stages during 
a period of rest. In a general way the life histories of all mos- 
quitoes are much alike, but in details there is much variation 



among them. Without special adaptations in habits and physi- 
ology to meet the exigencies of their diverse environment there 
would be little chance for the mosquitoes of the frozen north 
or of the parched tropical deserts to meet successfully the struggle 
for existence. A great store of interesting facts concerning the 
life history and habits of mosquitoes has been collected by 
Howard, Dyar and Knab in Part I of their '' Monograph of the 

Fig. 193. Eggs of mosquitoes; A, Culiseta inornatus; B, Mansonia perturbans, 
C, Aedes calopus; D, Anopheles punctipennis, dorsal view; D', same, ventral view. 
X 75. (After Howard, Dyar and Knab.) 

Mosquitoes of North and Central America and the West Indies " 
and much of the information incorporated into this chapter 
has been taken from their work. 

The eggs of mosquitoes (Fig. 193) are usually oval, with vari- 
ous surface markings, and in Anopheles with a peculiar '' float " 
of air cells. The number of eggs laid by a single female mos- 
quito varies from 40 or 50 to several hundred. Some species 



lay their eggs singly (Fig. 194) while others lay them all at one 
time in little boat-shaped rafts called egg-boats, the individual 
eggs standing upright (Fig. 195). The fact that the eggs are a 
little larger at the lower end makes the whole egg-boat slightly 
concave, thus making it difficult to overturn. Most of the com- 
mon mosquitoes of temperate climates lay their eggs on the 

open surface of water or at- 
tach them to some partially 
submerged object; a few 
species lay eggs which sink. 
Many species, however, 
especially those of the far 
north and of the tropics, lay 
their eggs in dry places which 
are likely subsequently to 
be covered with water. In 
^ ,„, ^ , , ^ , J . most mosquitoes of temper- 

FiG. 194. Eggs of Anopheles quadrxmacu- ^ i i 

latus on surface of water. X 13. (After ate climates the eggS hatch 

Howard.) jj^ ^ fg^ days, or even within 

24 hours. In the species of the far north the eggs probably 
never hatch until the following spring, being laid in depressions 
on the ground which are usually not immersed until the melting 
of the winter snows. Such hibernating eggs are said not to hatch 
unless they have been exposed to freezing temperatures. On the 
other hand the mosquitoes 
of dry hot countries lay 
eggs which are highly re- 
sistent to desiccation and 
do not lose their vitality 
during months of dryness. 
Such species must almost 
''live while the rain falls," 

and to win in the struggle against an unfavorable climate they 
must be prepared to utilize the most transitory pools for the 
completion of their aquatic immature stages. In such cases 
the embryo within the egg shell develops to the hatching point, 
so that it is ready to begin the larval existence almost with the 
first drop of rain. Such mosquitoes further fortify their race 
against the unkind environment by laying their eggs in a number 
of small batches instead of in a single mass, as is the habit with 

Fig. 195. Egg boat of Culex floating on 
water. X about 8. 


mosquitoes where water is plentiful. Just as a man runs less 
risk of ruin if he deposits his money in a number of insecure 
banks rather than in a single uncertain one, so it is with mos- 
quitoes and the places where they deposit their eggs. The 
gamble for life in a dry climate would be too risky if all eggs were 
deposited in one place, and species with this habit have probably 
long since been weeded out in the struggle for existence. An- 
other remarkable adaptation of dry-climate mosquitoes is the 
variation in the hatching periods of the eggs in the same batch; 
not all hatch with the first drops of moisture, but some lie 
over until subsequent immersions, thus insuring a much better 
chance that some of them, at least, will not waste their life on 
the desert air with too little water to enable them to reach 

The eggs of mosquitoes never hatch except in the presence of 
water. The larvae, which are always aquatic, are very active 
wormlike creatures, well known as " wrigglers " or " wriggle- tails" 
(Fig. 196). When first hatched they are almost microscopic, 
but they grow rapidly to a length of from a quarter of an inch to 
almost an inch. The bunches of long bristly hairs on the body 
take the place of legs, and aid the larva in maintaining a position 
in the water. The '' rotary mouth brush " is a brush of stiff 
hairs which is used to sweep small objects toward the mouth; 
in predaceous species these are sometimes modified into rakelike 
structures or into strong hooked bristles for holding prey. The 
trumpet-shaped breathing tube (Fig. 196 A) is present on all 
mosquito larvae except Anopheles (Fig. 196B), in which it is 
undeveloped. It is used to pierce the surface film of the water to 
draw air into the air tubes or tracheae inside the body, for, al- 
though aquatic, mosquito larvae are air breathers, and make 
frequent trips to the surface to replenish their air supply, re- 
maining suspended by the breathing tube from the surface of the 
water while breathing. The leaf like " tracheal gills " on the last 
segment of the abdomen differ from true gills in that air tubes 
or tracheae instead of bloodvessels ramify in them. In one 
species of mosquito, Mansonia, the larvae absorb air from the air- 
carrying tissues in the roots of certain aquatic plants, piercing 
them with the apex of the breathing tube and thus avoiding the 
necessity of rising to the surface of the water. In well-aerated 
water the larvae can live without surface air for a long time by 



using their tracheal gills, but they die within a few hours if 
shut in water without dissolved air. 

Mosquito larvae, unless suspended from the surface film by 
means of the breathing tube, have a tendency to sink and they 
rise again only by an active jerking of the abdomen, using it as 

Fig. 196. A, Larva of tropical house mosquito, Culex quinquefasciatus; ant., 
antennae; br. t., breathing tube or siphon; m. br., mouth brushes; th., thorax; 
8th s., 8th abdominal segment; 9th s., 9th abdominal segment; tr., tracheae; 
tr. g., tracheal gills. B, Larva of Anopheles punctipennis; note absence of breath- 
ing tube, and starlike groups of scales on abdominal segments; m. br., mouth 
brushes; br. p., breathing pore; other abbrev. as on Fig. A. X 10. (After 
Howard, Dyar and Knab.) 

a sculling organ. Some species are habitual bottom feeders, 
others feed at the surface; some live on microscopic organisms, 
others on dead organic matter, and still others attack and devour 
other aquatic animals, including young mosquito larvae of their 
own and other species. 

The larvae shed their skins four times and then go into the 


resting pupal stage. Mosquitoes of temperate climates usually 
take from five days to two weeks to complete the larval existence, 
depending almost entirely on temperature. In the mosquitoes 
adapted to take advantage of transitory rain-pools the larvje may 
transform into pupse within two days and the pupal stage is a 
mere matter of hours. On the other hand, some mosquitoes 
habitually pass the winter as larvae. 

The general form of the pupa can be seen in Fig. 197. Alcock 
has aptly described this stage of a mosquito as resembling a 
tiny lobster deprived of ap- . 

pendages and carrying its 
tail bent. The pair of ear- 
like breathing tubes on the 
cephalothorax (head and 
thorax fused) take the place 
of the trumpet-like tube of eye -• 
the larva and are used in 
the same manner. Unlike 
the larva the pupa is lighter win9.c.' 

than water, and requires 

muscular effort to sink in- ^ig. 197. Pupa of house mosquito, Culex 

pipiens: ant. c, antennal case; br. t., breath- 
Stead 01 to rise. Ing tubes; leg. c, leg cases; pad., paddles; 

As remarked before, the ^^^s «- ^^^s ^^s^- x ^o. (After Howard, 

Dyar and Knab.) 

transiormation into the 

adult during the pupal stage may be a matter of a few hours in 
the case of the dry-climate mosquitoes, but in most species it re- 
quires from two days to a week, depending on the temperature. 
The adult mosquito emerges head first through a longitudinal 
slit along the back of the thorax. After its exit it rests for a 
moment on the old pupa skin, stretches and dries its wings, and 
then takes flight. 

Habits of Adults. — Adult mosquitoes vary to a remarkable 
degree as regards habitats, feeding habits, mode of hibernation, 
choice of breeding grounds, and other habits. The knowledge, 
only recently gained, that each species of mosquito has habits 
and habitats more or less peculiar to itself, is of great economic 
importance, since it does away with useless expenditure in com- 
bating harmless or relatively harmless species, and aids in the 
fight against particularly noxious ones. The fact, for instance, 
that one of the commonest summer mosquitoes of northeastern 


United States, Culex territans, does not annoy man does away 
with the necessity of combating this species, and obviates the 
necessity of destroying larvae in certain kinds of marshes and 
pools where this is practically the only breeder. Again, the 
fact that mosquitoes breeding in crab holes do not annoy man 
eliminates the necessity of attempting the almost impossible 
task of destroying such breeding grounds in order to be free of 
mosquitoes. The fact that a certain species of Anopheles, A. 
malefactor, which is a tree-hole breeder, is not a malaria carrier, 
saved thousands of dollars in the anti-malarial fight in the 
Canal Zone. 

Habitats. — A classification of mosquitoes according to habi- 
tats and breeding grounds has been attempted by some authors. 
Dr. J. B. Smith, for instance, divides the mosquitoes of New 
Jersey into four ecologic groups, the salt marsh, house, swamp, 
and woodland mosquitoes. However, almost as many different 
ecologic groups could be made as there are species of mosquitoes 
or possible breeding and foraging places. There are species 
which breed in reedy swamps, woodland pools, eddies of rivers, 
slow-flowing streams, holes in trees, pools of melted snow, salt 
marshes, tide pools, crab holes, pitcher plants and other water- 
bearing plants, or in broken bamboo stems filled with water. 
There are species which have become " domesticated " and occur 
almost always in the vicinity of houses, laying their eggs in 
water troughs, street gutters, rain barrels, water-filled cans in 
garbage heaps, flower vases, water bottles, and any other col- 
lection of water in or about human habitations. Some species 
show almost no preference as regards breeding places, others, 
especially those breeding in such specialized places as in water- 
holding plants, are very closely limited ; some species prefer pure 
clear water, others filthy water, while still others are apparently 

Migration. — That mosquitoes are seldom found far from 
their breeding grounds is another fact, only recently recognized, 
of great economic importance. The evidence points to the fact 
that most kinds of mosquitoes seldom stray more than from half 
to three-quarters of a mile from their birthplace, and usually not 
over a few hundred yards. The supposition that mosquitoes 
utilize a strong wind to carry them long distances is entirely false, 
since mosquitoes are so delicate as to be unable to fly at all with a 


strong wind but remain hidden away at times when such wind 
storms occur. Some mosquitoes are able to resist moderate winds, 
but nearly always fly against them instead of with them. The salt 
marsh mosquitoes are apparently an exception to the sedentary 
nature of mosquitoes, as shown by Smith's work in New Jersey. 
These mosquitoes commonly migrate for a number of miles and 
may go as much as 40 miles inland from the salt marshes which 
bred them. The common salt marsh mosquito, Aedes sollicitans 
(Fig. 188), the mosquito that made New Jersey famous, breeds in 
enormous numbers in the extensive coastal marshes of New 
Jersey, whence it migrates inland, and sometimes crosses the 
Hudson River and invades New York City in hordes. The 
author has seen mosquitoes (not positively identified as this 
species) literally in clouds on the roofs of buildings in the down- 
town section of New York, where the day before not a mosquito 
was to be found. With the exception of a few of the salt marsh 
species, however, an abundance of mosquitoes can almost al- 
ways be looked upon as evidence of the existence of breeding 
places within a mile, and usually within a few hundred yards. 

Although most species are not migratory, railroad trains, 
street cars, ships and other conveyances are efficient means of 
transfer for mosquitoes. Hawaii is said to have been free of 
these pests until they were introduced with sailing vessels, in 
which mosquitoes can usually find plenty of water for breeding. 
The great number of trains daily running inland in New Jersey 
from the marsh-studded coast is undoubtedly a factor in keeping 
more distant suburban towns stocked. Well established cases 
are on record of places once free of mosquitoes becoming infested 
after the advent of railroad train or boat service. 

Time of Activity. — Although mosquitoes are usually looked 
upon as strictly nocturnal, and though this is true of most of 
the common species of temperate climates, it is by no means 
characteristic of the whole group. Many species, including all 
Anopheles, are active chiefly at twilight, in the evening, or early 
morning. Knab found that the mosquitoes of northern prairies, 
where the nights are too cold for them, are active throughout the 
day only. A large proportion of forest-Hving tropical species, 
at least in America, are said to be diurnal. Some of the mos- 
quitoes of the northern woods are apparently ready to bite 
when a victim approaches, whether it be day or night. The 


widely distributed yellow fever mosquito, Aedes calopus (or 
Stegomyia fasciata) (Fig. 201), feeds by preference in the early 
morning or late afternoon. Here again a knowledge of the 
habits of particular species is of importance, since it may aid in 
the intelligent avoidance of particular disease-carrying forms. 

Food Habits. — Heretical as it may sound, mosquitoes feed 
mainly on plant juices, honey, etc. It is doubtful if the males 
of any species normally suck blood, and even the females of some 
species are strict vegetarians. On the other hand, the females 
of many species have a voracious craving for warm blood. Some 
species indiscriminately attack any warm-blooded or even cold- 
blooded animal, while others show strong preferences. The 
yellow fever mosquito normally feeds chiefly on man, and even 
discriminates against the black race. The other " domestic " 
mosquitoes apparently have a strong liking for human blood also, 
and it is not unlikely that their domestic habits are the result 
of their taste for human blood. Knab found that Aedes spenceri 
of the Saskatchewan prairies would fly toward any large object. 
On the prairies such an object would usually be a large animal 
and the mosquitoes would fly toward it instinctively in the 
hope of satiating the craving for food. 

Hibernation. — The method employed by mosquitoes for 
passing the winter in cold climates, and the dry season in the 
tropics, varies with the species. Many of the mosquitoes of 
temperate climates and many in the tropics hibernate or pass the 
dry season in the adult stage, the females stowing themselves 
away in hollows in trees, caves, crevices in rocks, cellars, barns, 
etc., to come forth and lay their eggs in the spring. A few species 
hibernate in the larval stage, the larvae of one species, Wyeo- 
myia smithii, becoming enclosed in solid ice in the leaves of the 
pitcher plant in which they live. Most hibernating larvae retire 
to the bottom of their breeding pools during cold weather and 
do not survive freezing. The majority of temperate- and warm- 
climate mosquitoes and all of the northern ones pass the un- 
favorable season in the egg state, and this may be looked upon as 
the common method of hibernation. 

Length of Life. — The length of life of mosquitoes varies with 
the species and with the sex. Male mosquitoes seldom live more 
than from one to three weeks; their duty in life is done when they 
have fertilized the females. The latter usually die shortly after 



they have laid their eggs but some species may live for four months 
or more. The species which lay all their eggs in a mass at one 
time are short lived, and have several generations a year, whereas 
those in which the eggs are laid in small lots, at intervals, live for 
several months. Species in which the females hibernate are still 
longer lived, but since they are not active in winter their effec- 
tive life is short. 

Classification. — Over 500 species of mosquitoes have been 
described, the majority of which belong in the tropics, although 
the north is richer in individuals. The task of classifying all of 
these species into subfamilies and genera is one which has taxed 
the wits of many scientists. The wide discrepancies in the work 
of different men as regards mosquito classification is the best 
possible proof of the difficulties in the way. As in many other 
groups of animals, intensive study has tended to magnify the 
value of certain characteristics as criteria of genera or subfamilies, 
the result being the breaking up of what would ordinarily be 
looked upon as a single group into a number of poorly defined 
and intergrading groups. Theobald, who has written a mono- 
graph of the mosquitoes of the world, separates the Corethrinae 
(forms without a long proboscis) from the mosquitoes, and 
divides the remainder of the family into ten subfamilies and a 
very large number of genera based largely on scale character- 
istics. On the other hand, Howard, Dyar and Knab, whose classi- 
fication is adopted here, recognize only two subfamilies — the Core- 
thrinae and the Culicinae, the latter including all the true mos- 
quitoes. The Culicinae are further divided into two tribes, the 
Sabethini, including chiefly forest-dwelling non-blood-sucking 
forms, and the Culicini. The genera of the latter are arranged 
in a series from the primitive forms of the genus Anopheles to 
such highly specialized forms as Megarhinus. 

The identification of species of mosquitoes, or even of genera, 
is often very difficult for anyone but a specialist. Fortunately 
some of the most important disease-carrying species are so 
marked that they can quite readily be distinguished even by 
a novice. Only a few of the disease-bearing species can be 
separately described here. 



Mosquitoes and Malaria 

As was shown in Chap. IX, malaria is one of the most important 
and one of the most deadly of human diseases. This being true, 
the mosquitoes, which are the sole means of transmitting the 
disease, must be looked upon as among the most important and 
most deadly enemies of the human race. The role of mosquitoes 
in causing disease, especially malaria, has been suspected by 
various peoples as far back as any records go. The steps which 
led to the proof of the relation of mosquitoes to malaria are briefly 
outlined on pp. 148-149. 

Fortunately not all mosquitoes are malaria carriers; in fact, 

only one genus, Anopheles, com- 
prising a number of more or less 
well-defined subgenera which have 
been considered genera by some 
workers, is known to be able to 
transmit the human malarial dis- 
eases, and not even all of the 
species of this genus are incrimi- 
nated. As will be seen below, 
some species of Anopheles are able 
to transmit one type of malaria, 
but not another. A species of 
Culex has been shown to be instru- 
mental in transmitting a disease 
of birds which is allied to malaria. 
The role of the mosquito in the 
A.aibimanus. Drawn to scale. (After spread of malaria and the develop- 

Howard, Dyar and Knab.) ^ . . , 

ment of the parasites in the mos- 
quito's body have been discussed in Chap. IX, pp. 154-156. Suffice 
it to repeat here that the sexual phase of the life history of all 
malaria parasites occurs in the digestive tract of mosquitoes, after 
which a rapid multiplication of the germs takes place, resulting 
ultimately in the collection of large numbers of the parasites in 
the salivary glands of the insect, whence they are poured into the 
capillaries in the skin of the subsequent victims of the mosquito. 
Identification of Anopheles. — The Anopheles mosquitoes, 
fortunately, are fairly easy to identify in all stages of their de- 
velopment except as pupae. They represent a primitive group 

Fig. 198. Wings of American 
Anopheles; A, A. crucians; B, A. quad- 
rimaculatus; C, A. punctipennis; D, 



of mosquitoes, and in many respects are less specialized than 
other members of the family. The different species of the 
genus vary a great deal as regards choice of breeding places, 
habits and appearance, so that it is necessary in any malarial 
district to determine, if possible, which species are malaria 
carriers, how they may be identified, where they breed, and what 
their habits are. The majority of the species have mottled or 
spotted wings, and the arrangement of the markings is a good 
means of identification (Fig. 198). 

The following comparative table (Fig. 199) shows in a graphic 
way how Anopheles may ordinarily be distinguished from other 
common mosquitoes, such as Culex, Aedes, etc., in their different 

Malaria-Carrying Species. — Over a hundred species of Anoph- 
eles have been described and they occur all over the temperate 
and tropical parts of the world. Although not more than about 
half of these species have been proved to be able to harbor ma- 
larial parasites and nurse them to the weaning point, the num- 
ber of incriminated species is constantly growing, and it is the 
safest plan to look upon any Anopheles as a potential malaria 
carrier until proved otherwise. The fact that a given species 
of Anopheles may transmit one type of malaria but not another 
complicates the task of determining the role of a species, and has 
caused discrepancies in the results of workers. A. quadri- 
maculatus (Fig. 200) in North America, for instance, may carry 
tertian and quartan malaria, but not the more deadly aestivo- 
autumnal type. A. crucians, on the other hand, carries sestivo- 
autumnal malaria but only rarely carries tertian malaria. The 
third common North American species, A. punctipennis, has 
recently been proved to be able to nurse and transmit tertian 
and quartan malaria, but not nearly so readily as does A. qua- 
drimaculatus. The situation among these American species 
fairly illustrates what is found elsewhere — considerable differ- 
ences among the species of Anopheles as regards their ability to 
nurse the several types of malaria and the readiness with which 
they may do so. In most countries, though there may be several 
species which transmit malaria, there is usually one species which 
is especially responsible for the disease. In North America it is 
A. quadrimaculatus and in the southern states A. crucians and 
quadrimaculatus ; in tropical parts of America, A. alMmanus and 




Culex, Aedes, etc. 

Eggs laid singly on surface of water; Eggs laid in rafts or egg-boats, or 

provided with a partial envelope, more singly on or near water, or where water 
or less inflated, acting as a "float." may accumulate; never provided with 

a "float." 


LarvfiB have no long breathing tube or 
siphon; rest just under surface of water 
and lie parallel with it. 

Larvae have distinct breathing tube 
or siphon on 8th segment of abdomen; 
hang from surface film by this siphon, 
except in Mansonia, which obtains air 
from aquatic plants. 

Pupae have short breathing trum- Pupae have breathing trumpets of va- 

pets; usually do not hang straight down rious length; often hang nearly straight 
from surface of water. down from surface of water. 

Palpi of both male and female long Palpi of female always much shorter 

and jointed, equaling or exceeding the than proboscis, those of male usually 
proboscis in both sexes. long, but sometimes short. 


Adult rests with body more or less at 
angle with surface, the proboscis held 
in straight line with body. 

Adult usually rests with body parallel 
to surface, though sometimes at an 
angle. Proboscis not held in straight 
line with body, giving " hump-backed " 

FiQ. 199. 


argyrotarsus ; in Europe, A. maculipennis ; in Africa, A, costalis and 
funesta; in India, A. culidfacies, stephensi and listoni; in Malay 
countries, A. umbrosus and willmori; in China and Japan, A, sinen- 
sis and listoni; in the East Indies, A. ludlowi; and in Australia, 
A . hancrofti. These species are only a few of the most widely dis- 
tributed and commonest of the 
malaria carriers. Many other spe- 
cies may be locally more important. 
Habits of Anopheles. — Be- 
sides the ability to nurse the 
parasites of malaria, an efficient 
malaria spreader must have habits 
which will insure the use of such 
ability. The important malaria 
carriers are, therefore, species 
which readily attack man, and 
especially those which are more 

or less ''domesticated." Nearly Fig. 200. The common North 
n . f> A 77 , . American malarial mosquito, Anoph- 

all species of Anopheles are active ^i^, quadHmaculatus. 
only at twilight, and forage out- 
doors neither in bright daylight nor in the darkness of night, 
though such species may bite at any hour of the day inside houses. 
Different species are known to come forth at different times 
in the evening, some with the first shade of the late afternoon, 
others not until almost dark. A few species, e.g., A. hraziliensis, 
are diurnal, and many forest species will readily bite in the day- 
time if disturbed. Nearly all Anopheles hibernate as adults, 
but a few, notably A. bifurcatus of Europe, hibernate as larvae. 
Anopheles may breed in almost any standing water providing 
it contains microscopic organisms on which to feed. Dr. Smith, 
of New Jersey, says he has found no pool so insignificant and 
no stream so rapid that Anopheles could not breed in it some- 
where. He says '' no other mosquito has as wide a range of 
breeding places as have the species of Anopheles.'^ Nevertheless, 
it is apparently true that each species has its favorite breeding 
grounds and some species are quite particular. A. willmori 
of the hilly parts of Malay, for instance, will breed only in swift- 
running streams, the banks of which are cleared, whereas A. 
umbrosus of the coastal plains of the same country breeds only 
in jungle-edged streams; A. eiseni of Central America breeds 


only in tree holes; A. cruzi of Brazil breeds in accumulations of 
water in the leaves of certain tropical plants. A number of 
species of Anopheles will breed in brackish water, and some in 
pure or even concentrated sea water. A. ludlowi of the Philip- 
pines is believed to breed only in sea water. Some of the coral 
islands of the East Indies are practically uninhabitable for new- 
comers on account of the prevalence of malaria which is carried 
by Anopheles that breed in quiet pools within the coral reefs. 

The larvae of Anopheles are chiefly surface feeders. Some feed 
upon anything floating on the surface of the water which is 
small enough to enter the mouth. Others, however, reject many 
things after they have been swept into the mouth by the mouth 
brushes, and some feed exclusively on vegetable matter. Only 
a few species are predaceous. 

Apparently neither the eggs nor larvae of Anopheles are resistant 
to drying, though they may live on moist mud for some time. 
Eggs of Anopheles laid in such mud develop to the hatching point 
but do not hatch until immersed, and die if the mud dries to the 
extent of losing its glistening surface. 

Anopheles are not rapid in development as compared with 
some mosquitoes. At Washington, D. C, in early summer, A, 
quadrimaculatus was determined by Dr. Howard to develop in a 
minimum of 24 days — three for the eggs, 16 for the larvae, and 
five for the pupae. In some species the development may be 
more rapid, but about two weeks is probably a minimum. Ac- 
cording to observations by Kulagin near Moscow, Russia, in 
1906, there was but one generation of Anopheles in a year, the 
females always resting over winter before depositing their eggs. 
This point of the number of generations of Anopheles deserves 
further local study everywhere. 

It is important to note that Anopheles mosquitoes are verj'' 
sedentary in habit, and seldom fly more than a few hundred 
yards from their birthplace, and usually not this far. As a 
group, the insects of this genus are physically incapable of as long 
flight as are most other mosquitoes. It is frequently reported 
that Anopheles is found several miles from its nearest breeding 
places, but the difficulty of knowing with certainty that no 
water-filled hoofprint or tin can exists in the intervening area is 
obvious. That an Anopheles may occasionally wander half a 
mile or more from its breeding ground is unquestionable, but not 


enough individuals do this to make it necessary to look for 
breeding places more than three or four hundred yards from the 
infested locality. The conveyance of mosquitoes in trains, 
boats, etc., must, however, be taken into account. 

The effect of smti- Anopheles campaigns on the prevalence of 
malaria is discussed in Chap. IX, pp. 165-167. 

Mosquitoes and Yellow Fever 

Following upon the heels of the discovery of the relation of 
mosquitoes to malaria, and second only to it in importance, came 
the discovery of a similar relation to yellow fever, in 1900. As 
in the case of malaria, some physi- 
cians suspected the instrumentality 
of mosquitoes in the dissemination of 
this disease before there was any 
proof of it. The proof came as the 
result of the illustrious work of the 
American Army Yellow Fever Com- 
mission, composed of Doctors Reed, 
Carroll, Lazear, and Agramonte, at 
the cost, indirectly, of the lives of 
three of them. What is known of 
the nature of yellow fever, and of 
the role of the mosquito in trans- 
mitting it, is discussed in Chap. X, 
pp. 182-185. It should be repeated 
here, however, that the ''germ" of the 
disease is still unknown, though be- 
lieved to be a protozoan. The blood 

of a patient can infect a mosquito Fig. 201. Yellow fever mos- 
ij. j.T-£j.j.T_ 1 r quito, Aedes calojms, female. 

only durmg the first three days of (After Doane.) 

illness, and the mosquito cannot 

transmit the disease in less than 12 days later. In one case, 

hereditary transmission of yellow fever from an infected mosquito 

to its offspring has been shown to occur. 

The Transmitting Species, Aedes calopus. Unlike the condi- 
tion as regards malaria, yellow fever can be transmitted by only 
one species of mosquito, Aedes calopus (or Stegomyia fasciatus) 
(Fig. 201). This is a small black mosquito, conspicuously 
marked by white bands on the legs and abdomen, and a white 



Fig. 202. Head of Aedes 
calopus, male. (After Gold- 

lyre-shaped design on the thorax. The female, which, of course, 
is the only sex connected with the transmission of disease, since 
the males do not suck blood, has very short palpi which are white 
at the tip. The wings are clear and somewhat iridescent. 

Habits of Aedes calopus. — The yellow fever mosquito is the 
most thoroughly " domesticated " species known. It is seldom 
found except in the vicinity of houses and shows a decided pre- 
ference for human blood. As a rule it 
seldom leaves the rooms of houses ex- 
cept to find a suitable place to lay its 
eggs. Long familiarity with man has 
made this mosquito one of the most 
elusive and well-adapted pests .of the 
human race which nature has ever 
evolved. Its stealthy attack from be- 
hind; its habit of crawling up under the 
clothing to bite in preference to attack- 
ing the exposed ankles; the suppres- 
sion of the characteristic mosquito 
"song," so that its bite comes silently 
and without warning; its habit of concealing itself in pockets, 
folds, etc., of garments; its hiding behind pictures, under chairs, 
etc.; the wariness of its larvae; — all these are the result of 
lessons learned from long and close association with man. 

Aedes calopus is principally a diurnal mosquito, and becomes 
particularly hungry in the early morning and during the after- 
noon. It will bite in lighted rooms, but will never bite in the 
dark. The French Yellow Fever Commission in Rio de Janeiro 
stated that Aedes calopus is nocturnal. The evidence for this 
conclusion, which is at variance with the observations of other 
workers, has been shown by Howard, Dyar and Knab to be very 
inadequate and faulty. The danger of sleeping in an infected 
place, and the comparative freedom from danger enjoyed by 
persons who visit infected places only in the daytime, is thought 
to be due to the fact that most of the mosquitoes obtain a meal 
very early in the morning, just after daybreak. 

Breeding. — A edes calopus never lays eggs until it has had a 
meal of blood and when water or moist surfaces are available. 
According to recent experiments by Bacot a single male mosquito 
may fertilize a number of females. Fertile eggs are usually 


laid from four to seven days after a blood meal. The nearest 
allies of this species are tree-hole breeders, but the yellow fever 
mosquito has become domesticated to such an extent as to much 
prefer a rain barrel or water-filled tin can in a garbage heap, or, 
even better, a water-pitcher or flower-vase indoors. Churches 
in Central America are usually well supplied with yellow fever 
mosquitoes which breed in the holy-water fonts. 

Fig. 203. A yellow fever center in Panama in the pre- American days. (Drawn 
from photo from Thompson.) 

The eggs (Fig. 193C), up to 150 in num