Animal parasites and human disease

Preface

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. Scientists 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 compilation." 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 compilation " than for the addition of new facts to scientific knowledge, 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 vi PREFACE

progress. Having the courage of his convictions along these lines, the writer has spent much time which he might otherwise have spent on original research in the compilation and popularization 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 parasitologist, 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 important; 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 instrumental 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

PREFACE Vll

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 encumbering 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 investigators. It obviously would be impossible to give references, or even to mention more than a small per cent of the thousands 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 important 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 anyone 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 consistently 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 viii PREFACE

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 4 than can a photograph. The author has received valuable advice regarding the illustrations from Mr. A. J. Stover, scientific illustrator 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," Win. Wood and Co.; of Dr. A. Alcock, author of "Entomology for Medical Officers"; of Professor Win. A. Riley and Dr. Johannsen, authors of " A Manual of Medical Entomology," and of Dr. A. W. Sellards, who, in the absence of Dr. Strong, lent photographs taken in Pern 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 illustrations 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

PREFACE ix

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 information 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 book.

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. Professor 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 Protozoa, " 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.

Table Of Contents

Chap. Pages

I. Introduction 1-1 1

II. Parasites in General 12-25

Part I. Protozoa

III. Introduction to Protozoa 26-37

IV. Spirochetes 38-73

Relapsing Fever 42-48

Syphilis 48-62

Infectious Jaundice 65-69

Rat-bite Fever 69-70

Other Spirochete Diseases 70-73

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

Ciliates 126-127

VIII. Amebe 128-146

Amebic Dysentery 130-137

Mouth Amebse 139-146

IX. Malaria 147-167

X. Other Sporozoa, and Obscure or Invisible Parasites 168-195

Coccidians 170-173

Rhinvsporidium 173-174

Sarcosporidia 174-176

Oroya Fever 176-181

xi xii CONTENTS

Chap. Pages

Yellow Fever Group 182-188

Yellow Fever 182-186

Phlebotomus Fever 188

Spotted Fever Group 189-192

Rocky Mountain Spotted Fever 189-191

Chlamydozoa 192-195

Part II. "worms" •

XI. Introduction to the "Worms" 196-205

XII. The Flukes 206-230

Blood Flukes 21 1-220

Lung Flukes 220-224

Liver Flukes 224-228

Intestinal Flukes 228-230

XIII. The Tapeworms 231-253

Family Taeniids 239-245

Family Dibothriocephalidse 245-247

Larval Tapeworms in Man 247-253

XIV. Hookworms 254-269

XV. Other Intestinal Roundworms 270-285

XVI. Trichina Worms 286-297

XVII. FlLARLE AND THEIR ALLIES 298-314

Filaria bancrofti 299-307

Other Species of Filarise 307-314

XVIII. Leeches 315-321

Part III. Arthropods

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-follicle Mites 346-348

Tongue-Worms : 348-351

XXI. Ticks 352-369

Ticks and Disease 359-363

Other Troublesome Ticks 364-369

CONTENTS xiii

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 Dermatobia 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 (Chironomidse) 473-477

Blackflies or Buffalo Gnats 478-484

Gadflies (Tabanidae) 484-490

Tsetse Flies 490-504

Stable-Flies, Stomoxys, and Their Allies 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

ANIMAL PARASITES AND HUMAN DISEASE

Chapter I Introduction

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 ourselves from two other phases of it, war and disease. We have some reason for hoping that after the present world-wide conflagration 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 understood, 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, throughout the histoty 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 knowledge 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.

IMPORTANCE OF PARASITIC DISEASES 3

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 housefly!

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; hookworms 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 widespread 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 physicians of the old school have been so busy or so unprogressive that they have never attempted to add to or modify the knowledge 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 authoritative 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 buzzards 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 exaggeration 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 existence 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 prevalence 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!

EXOTIC DISEASES 5

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 parasitic 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 importance except to inhabitants of the countries directly influenced or to travelers through these countries. That the importance of such parasitic diseases is far greater than this is obvious from the fact that, with modern facilities for communication 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 inspection of immigrants is not made. In the port of San Francisco 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. Billings 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 infected 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 examination.

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 distribution 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 unfamiliar 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 parasitology in its broad sense, including bacterial and fungous parasites 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, Leeuwenhoek, actual observation of microscopic organisms became possible, and this famous pioneer in science observed, in 1675, " animalculse " 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 controversy 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

HISTORY 7

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 roundworms, 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 tapeworm by Bilharz in Egypt in 1851; Filaria (larvae) by Demarquay 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 discovered and recognized as such was the ciliate, Balantidium coli, a cause of dysentery, discovered by Malinsten in 1856. The spirochete 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 Dutton in 1901 ; the Leishman bodies of kala-azar by Leishman, and independently by Donovan, in 1903; the spirochete 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 r61e 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 Dutton 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 role of crabs as second intermediate hosts of lung flukes by Nakagawa in 1916.

The evolution of knowledge concerning the treatment of parasitic diseases has proceeded along two distinct lines, one, destruction of the parasites by drugs which are more or less specifically poisonous to them, the other by vaccination or immunization. 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 spirochetes, 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, previously 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 specific for all Leishmania diseases.