UNIVERSITY OF CALIFORNIA wCFARTMENT OF CIVIL ENGINEERING BERKELEY. CALIFORNIA Civil Engineering Dept, Engineering Library RERKEUF-Y, CAU THE SOURCES AND MODES OF INFECTION BY CHARLES V. CHAPIN, M.D., Sc.D. \\ SUPERINTENDENT OF HEALTH, PROVIDENCE, R. I. AUTHOR OF "MUNICIPAL SANITATION IN THE UNITED STATES" SECOND EDITION REVISED AND ENLARGED TOTAL ISSUE FOUR THOUSAND NEW YORK JOHN WILEY & SONS, INC. LONDON: CHAPMAN & HALL, LIMITED 1916 CiT Engineering Library COPYRIGHT, 1910, 1912, BY CHARLES V. CHAPIN Stanbopc ]pteft . H. OILSON COMPAMV BOSTON. U.S.A. PREFACE. THIS volume is intended to indicate the principles which should guide sanitary practice, and to show how recent labo- ratory work and the epidemiological study of disease have modified these principles. When I began work as health offi- cer in 1884 the filth theory was still in favor, 'and it was generally believed that the germs of disease commonly grew in decaying organic matter. Yet contagion was recognized as an important factor in the spread of disease, and the isola- tion of the sick was more and more insisted upon. Fifteen years ago probably most health officials believed that the contagious diseases could be completely stamped out if only all persons sick with them could be isolated. The air was thought to be the chief medium for their transmission, and fomites the mechanism for their passage from place to place. Sanitary practice was based on these premises. My own views concerning these matters became greatly modified year by year, partly owing to the rapidly accumu- lating knowledge of bacteria and other disease-producing organisms, and partly owing to direct observations on the manner in which the infectious diseases are disseminated, and on the effect of preventive measures. It now appears that the growth of disease germs outside of the body is not frequent enough to be an important factor in the causation of disease, but their growth in the body with- out causing sickness, their latency as it were, often for many months, is a factor of very great significance. We know now that direct contact with the sick, or with healthy carriers of disease germs, is an exceedingly frequent mode of transmis- sion, and that infection by means of the air, or from infected articles, is not nearly as common as was formerly believed. iii iv PREFACE We are now better able than ever before to attribute to water and milk their proper share in the distribution of infection. The recent discovery of the transmission of disease by insects gives us entirely new and most effective means of combating disease. It is time that sanitary measures directed against the infectious diseases should be modified to correspond with existing knowledge. Present-day theories and present-day practice are maintained largely by tradition, and to facilitate the adaptation of practice to the facts as we now know them, is the purpose of this book. Some modifications of sanitary practice are suggested, but no attempt is made to discuss details; rather are general principles presented, which it is believed ought to guide administrators in their work. While some of the following pages may seem rather radical to many, I believe that practically all laboratory workers will agree with the contents of the first chapter, and that a large number of bacteriologists and health officers are convinced of the great importance of " carriers " and mild unrecognized cases. The tendency among many, too, is to lay less emphasis on infection by fomites, though perhaps few are ready to give up routine terminal disinfection for the common infec- tious diseases. So also there are very many careful observers who are attributing more and more importance to what is generally called contact infection. The public health administrator is placed at great disad- vantage because he is obliged to base his acts on knowledge which is far from exact. The laboratory workers have accu- mulated a vast mass of quite exact data in regard to the caus- ative relation of bacteria and protozoa to disease, and no one appreciates this more than the writer, but there are many problems which the laboratory men cannot solve, and many others which they have failed to solve. The epidemiologist must study in the field the way in which disease is caused. He must use the statistical method, and the application of statistical methods to epidemiology is more difficult and attractive than laboratory experiment. PREFACE V We need to measure more carefully the relative importance of different sources of disease and different modes of infec- tion. It is not so important to know that typhoid bacilli live in water for weeks, as it is to know that 99 per cent die in one week. It is not enough to discover that diphtheria bacilli can be recovered from articles in the sick-room; we must learn how often they are found and how often disease is traced to such a source. We have for years been much alarmed because tubercle bacilli are found in milk, but since a serious effort has been made to measure the actual danger, the alarm has greatly diminished. Doubtless the house fly has been the cause of typhoid fever, but in what percentage of cases we are profoundly ignorant. Healthy carriers of diphtheria have certainly transmitted the disease to others, and we should earnestly try to determine the amount of diphtheria caused in this way. The attempt is made in the following pages to estimate roughly, with the very imperfect material now available, the relative importance of different factors in the extension of infectious diseases. The conclu- sions must to a large extent be merely tentative, and as indicating lines for further study. I am under great obligations to my friends Dr. H. W. Hill and particularly Prof. F. P. Gorham for many suggestions and criticisms, but neither is to be considered at all responsible for any of the views presented. The book is intended primarily for health officers and phy- sicians, but it is hoped that many others will find some parts interesting and suggestive. CHARLES V. CHAPIN. PROVIDENCE, April, 1910. PREFACE TO SECOND EDITION. So much new material has accumulated since the appear- ance of the first edition that it has been thought best to re- write several parts of the book. Thus, recent experiments and particularly the observation that bacteria fresh from the body are usually less resistant than are " cultured" germs, indicate that the life of bacteria outside- the body is even shorter than was supposed. It is in regard to carriers that literature has been accumulating most rapidly and several comprehensive articles, as well as very numerous reports of carrier infection, leave no room for doubt that in many diseases, as diphtheria, cholera, typhoid fever and cerebro-spinal meningitis, the carrier is a very important, if not the most important, factor in the spread of the disease. Also recent work has shown that contact with carriers is quite likely to be the key to the epidemiology of poliomyelitis. New evidence has been presented concerning the carriage of infection by milk and also by water, but I cannot see that the reality of the Mills-Reincke phenomenon, which depends upon the influence of water on so many forms of disease, has yet been established. Much work during the past two years has been devoted to insects as carriers of infection and several additional diseases have been shown probably to be so transmitted. One of the most interesting of these is typhus fever, and, if recent work is substantiated, much light will be thrown on its epidemiology. While there is more evidence than there was that the fly is a factor in the spread of the fecal-borne diseases, there does not as yet seem to be much warrant for the rather sensational literature with which the public is deluged. Studies in hospitals and elsewhere have confirmed the belief that air is of minor vi PREFACE TO SECOND EDITION vii importance in the spread of disease. The views presented in the first edition in regard to the inutility of isolation under many conditions, and in regard to the small importance of fomites, were somewhat novel and it was suspected that they might be subjected to considerable criticism, but such does not seem to have appeared, and I still believe that, while isolation and bedside disinfection will in the future continue to be, when scientifically applied, of the utmost importance, much of the routine practice of health officials needs to be profoundly modified. CHARLES V. CHAPIN. Providence, July, 1912. CONTENTS. CHAPTER I. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY. PAGE Review of evidence of growth of disease germs outside of the body, anthrax, black leg, tetanus. Typhoid bacilli in soil, feces, water, ice, oysters, milk. Epidemiological evidence relating to typhoid fever. Evidence relating to cholera, Mediterranean fever, plague, dysentery, bacteria of suppuration, diphtheria and various other diseases. Reasons for former belief in " filth theory " of disease. Epidemiological evidence against soil infection. Conclusions. Relations of these views to public sanitation 1 CHAPTER II. CARRIERS AND MISSED CASES. Importance of the subject. Evidence of the occurrence of carriers and missed cases, and reference to disease caused by them in typhoid fever, cholera, dysentery, cerebro-spinal menin- gitis, diphtheria, glanders, influenza, pneumonia, gonorrhea, tuberculosis, leprosy, suppuration, tetanus, scarlet fever, small- pox, measles, protozoan diseases such as cattle fever, malaria, sleeping sickness, nagana, syphilis, amebic dysentery, poliomye- litis and yellow fever. Review of evidence. Conclusions. ... 33 CHAPTER III. LIMITATIONS TO THE VALUE OF ISOLATION. The number of carriers and missed cases. Not realized by health officials. Failure of isolation in Providence. Hospital- ization has not materially lessened infectious disease. Less isolation followed by less diphtheria in Providence. Failure of isolation in institutions. Failures in the isolation of measles, of cerebro-spinal meningitis, of smallpox. Failure due to carriers and missed cases. Difficulties in the isolation of diphtheria. Absolute isolation not possible. Moderate isolation sufficient. Infection not so easy as was believed. Isolation effective at the beginning of an outbreak, rarely later. The more carriers the less effective is isolation. True value of isolation hospitals. Details of home isolation. Summary 133 ix X CONTENTS CHAPTER IV. INFECTION BY CONTACT. PAGE Transmission of gonorrhea by indirect contact. Of syphilis in the same way. Typhoid fever spread by contact. Reasons why contact infection has been disregarded. Mode of contact infection in typhoid fever. Contact infection in dysentery. Cholera. Anchylostomiasis. Gonorrhea. Transfer of nasal and oral secretions by contact. Presence of germs in secretions and on various objects. Diseases do not spread from family to family in tenements. No cross infection in hospitals except by contact. Contact infection in tuberculosis. Protection from contact infection a personal matter. Need for urging personal cleanliness 164 CHAPTER V. INFECTION BY FOMITES. Definition. Fomites and yellow fever. Examples of alleged foinites infection. Infection by clothing, rooms, rags, money. Fomites infection in tetanus, anthrax, typhoid fever, diphtheria, plague. No evidence that fomites are of much importance. Reasons for belief in fomites. Effect of drying on bacteria of different kinds. The finding of bacteria on fomites. Drying of vaccine and smallpox virus. Summary of bacteriological evi- dence. Experimental work with yellow fever, plague. Results of abandoning disinfection after scarlet fever and diphtheria in Providence. Disinfection in other diseases. School disinfec- tion. Views of other writers. Conclusions 212 CHAPTER VI. INFECTION BY AIR. Alleged aerial transmission of smallpox, scarlet fever, diph- theria, typhoid fever, influenza, measles. Hospital experiments in aerial transmission. Transmission of typhus fever and plague. History of surgical technique shows that air-borne infection is of little moment. Air-borne anthrax. Bacteria not given off from moist surfaces. Bacteria carried in dust. Dust and the germs of typhoid fever, diphtheria, plague. Dust and tubercle bacilli. Finding of tubercle bacilli in dust. Other bacteria in dust. Droplet infection. Finding of bacteria in air. Experimental work with tuberculosis, Mediterranean fever, anthrax, plague. Conclusions 259 CONTENTS XI CHAPTER VII. INFECTION BY FOOD AND DRINK. PAGE The Broad Street well. North Boston well. Typhoid fever due to water. Cholera, dysentery, diarrhea. The Mills- Reincke phenomenon. Malaria and yellow fever. Purification of water. Ice. Milk, number of outbreaks. Mode of infec- tion of the milk. Typhoid fever, scarlet fever, diphtheria. Ice cream. Butter. Streptococcus sore throat and milk. Tuberculosis and milk, evidence of infection. Bacilli in market milk. Amount of tuberculosis due to milk. Mediterranean fever, anthrax, foot-and-mouth disease, rabies. Diarrhea. Infection by meat. Infection by shellfish. Crawfish. Watercress. Celery 316 CHAPTER VIII. INFECTION BY INSECTS. Insects as biological and as mechanical carriers. Pioneer work of Smith and Kilborne in cattle fever. Malaria. Modes of control: quinia, isolation, screening; mosquito reduction; practical results. Yellow fever carried by mosquitoes, not by fomites. Control of yellow fever; quarantine, isolation; mos- quito control; practical results. Filariasis, sleeping sickness, kala-azar, dengue, pellagra, opilacoa, pappataci fever, oriental sore, typhus fever, relapsing fever, Rocky Mountain fever. Bubonic plague and fleas. Anthrax. Carriage of bacteria on the bodies of insects. Cockroaches and other insects. Flies, experimental work. Bacteria found on flies. Habits and species. Transmission of disease, murrina, tuberculosis, cholera, dysentery, diarrhea. Flies and typhoid fever, local and seasonal distribution. Evidence against theory. Epidemiological evi- dence in favor of causal relation. Privies, flies and typhoid fever. Conclusions 380 THE SOURCES AND MODES OF INFECTION. CHAPTER I. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY Former Theories. From time immemorial miasms, ma- larias, vapors and emanations, gaseous or otherwise, have been believed to be the frequent cause of disease. These miasms were thought to arise from stagnant marshes, decay- ing vegetation, putrid animal matter, and indeed filth of every kind. This belief in the extra-corporal origin of disease reached its widest acceptance about the middle of the nineteenth century. The rise of the germ theory greatly strengthened it. The discovery of bacteria and of their wide distribution and almost universal growth in dead organic substances, and the theory that these bacteria were the real cause of disease, led men to look for the source of disease outside of the body, and chiefly in dead animal and vegetable matter. With the passing of the germ theory as a theory, and with the demonstration of the parasitic nature of so many of our most important and dreaded diseases, the opportunity was afforded for studying in detail the bacteria and protozoa which are the specific causes of these diseases. Much has been done by laboratory workers to unravel the life history of these minute forms, and it is well for us to examine the knowledge thus gained, and also the newer epidemiological observations on the spread of the infectious diseases, and in the light of these data question the belief that these diseases have their origin in the outer world rather 1 2 THE SOURCES ''AN'ti tiOpES OF INFECTION than in th& bodies (jf men or animals. Let us consider some of these diseases in detail. Anthrax is not common in the United States, but it is of much interest from a scientific standpoint. It was the first disease definitely proved to be caused by bacteria. It is of particular interest in this connection because a relation to the soil has been better established for this than for any other disease. Practically all writers are agreed that the soil may become infected with anthrax, and remain so for a long time, and that animals pastured upon such soil con- tract the disease by taking the bacteria in with the food, or inspired air, or through abrasions of the skin. That this soil infection is not the sole, or perhaps even the most com- mon source of infection, and that danger from this source has perhaps been somewhat exaggerated, is probably true. Thus Delepine 1 from studying recent outbreaks in Great Britain is convinced that the disease is perpetuated by a more or less direct contact, chiefly with unrecognized or concealed cases, and that there is no necessity for supposing a long continued soil infection, and no direct evidence for it as the principal source of the disease. McFadyean 2 can- not trace anthrax in Britain to the soil, and thinks it im- probable that it grows there, or it would be more common. Moreover it does not grow well under 60. Legge 3 notes that animal anthrax does not increase in the summer as it would be likely to if it were due to growth in the soil. Moore 4 does not think the bacillus maintains a saprophytic existence. In Louisiana 5 the extensive outbreak in the latter years of the nineteenth century was believed to be due to some extent to food infection, and to a large extent to direct inoculation Delepine, Pub. Health, 1904-5, XVII, 491. McFadyean, J. Comp. Path, and Therap., Edinb. and Lond., 1903, XVI, 35. Legge, Lancet, Lond., 1905, I, 695. Rep. Comm. of Agric. N. Y., 1907. Louisiana Agricultural Experiment Sta., Bull. No. 60, 2d. s. f 1900. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 3 by a species of horsefly, Tabanus lineola. Outbreaks of anthrax have occurred every few years in Louisiana for over half a century, and persistent soil infection has been alleged as their source. Very likely it is so to a certain extent, but on the other hand there is no doubt that the interval be- tween the outbreaks may well be bridged over by a more or less direct connection between sporadic and unrecognized cases occurring in the interval. That such cases really occur is shown by Delepine's investigations of similar conditions in England. Nevertheless almost all veterinary and medical writers are agreed as to the long continued soil infection of certain areas. Evidence of this is forthcoming from France, Germany, England 1 and the United States. In England such infective areas are said to be the most numerous where refuse from mills using foreign wools is used for manure. In this country anthrax is believed to have been traced to morocco factories on the Delaware River using large numbers of foreign skins. 2 Some of the infected Delaware farms had new tenants with new cattle each year, but infection recurred. All the evidence pointed to persistent infection of the soil. Similarly infected farms or fields are reported from New Jer- sey, 3 from the Genesee valley 4 and from Louisiana. 5 Law reports that 200 cases in cattle, and 3 in human beings re- sulted in the space of two weeks, from the soil infection of a limited area. Dr. Leonard Pearson wrote me that the evi- dence is conclusive that soil infection with anthrax has existed in a number of places in Pennsylvania. Two instances have recently been reported which seem to show pretty conclu- sively that anthrax bacilli do grow in small ponds under 1 Poore, The Earth in Relation to the Preservation and Destruction of Contagia, Lond., 1902, 9-21. 2 Delaware Agricultural Experiment Sta., Bull. No. 32, 1896, 6. Rep. St. Bd. Health, N. J., 1904, 5. 4 Law, Text-Book of Veterinary Medicine, Ithaca, 1902, IV, 195. 6 Louisiana Agricultural Experiment Sta., Bull. No. 60, 2d s., Insert opp. 345, and 357. 4 THE SOURCES AND MODES OF INFECTION natural conditions. Dr. J. Sinclair Holden, health officer of Sudbury, Co. Suffolk, England, writes that in 1905 the waste water from a horsehair factory was discharged into a small pond. There was evidently some seepage from this pond to another about 20 feet distant. The second pond, in the fol- lowing year, was found to be so abundantly filled with the bacilli of anthrax that it seemed that there must have been free reproduction. Hastings l also reports that he examined a pond which had received anthrax-infected tannery refuse, and that this was teeming with the vegetative forms of the bacillus. While there is a good deal of evidence, apparently conclu- sive, that soil may remain infected with anthrax for years, there also is evidence that the infection after a time disap- pears. Pasteur records instances of the infection dying out after a lapse of some years, 2 and in Delaware infection did not persist on all the infected farms. 3 The fact that anthrax has appeared at so many isolated points in England and the United States, and though in the majority of cases soil inocu- lation must have taken place, nevertheless the fact that the disease has never become widespread or long persistent locally is sufficient reason for the conclusion that its virus does not, in these countries at least, find a suitable soil. If it increases at all in the soil it is only for a time, and the tendency is for it to die out. In other words, the history of this disease is best explained on the hypothesis that the soil is infected chiefly if not exclusively by the spores, which may retain their virulence for years, but which rarely germinate in the earth. Charbon Symptomatique. Another animal disease known as black-leg, or in Europe as charbon symptomatique, is 1 Hastings, Paper read at meeting of Society of American Bacteri- ologists, 1908. * Poore, The Earth in Relation to the Preservation and Destruction of Contagia, Lond., 1902, 13. 3 Delaware Agricultural Experiment Sta., Bull. No. 32, 1896, 7. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 5 quite prevalent among cattle in this country. Like anthrax it is caused by a bacillus that forms spores. Veterinarians are agreed that soil areas become infected with black-leg and may remain so for some time. Undoubtedly this infection may be explained, as is the infection by anthrax, as due simply to the resistance of the spores, and does not necessarily re- quire the actual multiplication of the germs in the soil. Tetanus or lockjaw, even before it was known to be due to a bacillus, was believed to occur with exceptional fre- quency in limited areas. It has been stated by numerous writers that there is a strip of land near Red Bank, New Jersey, where tetanus is decidedly endemic. The disease was also said to be formerly extremely common, especially among animals, on the eastern end of Long Island, but that it has now become quite rare in that locality. This alleged local prevalence on Long Island has been, in this country at least, one of the most frequently used arguments in sup- port of soil infection, but Overton 1 has shown that the published statements cannot be verified, and that the disease has not been especially prevalent in that locality. I have corresponded with various officials in New Jersey, but have never been able to obtain any evidence of the alleged local infection at Red Bank. Tetanus is more common in the southern than in the northern parts of the United States, and is a very important cause of death in the West Indies. Before the organization of the present efficient health depart- ment in Havana there were often 200 deaths or more annually from infantile tetanus, due to infection of the navel. It has long been recognized that tetanus follows wounds in which dirt is forced deep into the tissues, and that garden earth is especially dangerous. Even well-established evidence of per- sistent local infection does not prove growth in the soil. It might be due to a great variety of causes. Thus it has been explained that the bacilli of tetanus are very widely distributed because these bacteria are natural 1 Overton, Long Island M. J., Brooklyn, 1907, I, 176. 6 THE SOURCES AND MODES OF INFECTION inhabitants of the healthy intestines of domestic animals, particularly the horse. Hence they are found in profusion wherever the manure from these animals falls, and soiled skin and clothing are not likely to carry them. Theobold Smith, 1 however, says that there is no evidence that the tetanus bacilli are normal inhabitants of and multiply in the intes- tines of animals. He inclines to the view that their home is in the soil. Vincent 2 after introducing tetanus spores into the stomach of a rabbit could find no evidence of multipli- cation, and he, too, thinks a saprophytic existence probable. The tetanus bacillus forms spores which may retain their vitality for 16 years, so that it is not surprising that lands have been known to remain infected for several years. 3 These spores, or the bacilli, are said to have been found in gelatine, 4 in blank cartridges, 5 and on balls of lamp wick used in Havana for tying the umbilical cord. 6 While the soil, and dirt gener- ally, contain tetanus bacilli or their spores, there is no direct evidence to show that they are propagated outside of the body. The fact that they do not grow in the presence of air would indicate that this is not the case, and the distribution of the disease and its comparative rarity would also lead to this conclusion. It is not, of course, to be denied that the tetanus bacillus may lead a saprophytic existence. It is very pos- sible that it may do so, but it certainly can be affirmed that at present we have no proof that it does so, and all observed facts relating to the bacillus, or the disease caused by it, may be explained without assuming any such hypothesis. It is suggestive that the pathogenic bacteria which are ofteaest assumed to grow in the soil are the very ones the Theobold Smith, J. Am. Ass., Chicago, 1908, L, 929. Vincent, Compt. rend. Soc. de biol. Par., 1908, LXV, 12. Villar, J. Comp. Path, and Therap., Edinb. and Lond., 1897, XX. Tuck, J. Path, and Bacteriol. Edinb. and Lond., 1904, IX, 38. Dolley, J. Am. M. Ass., Chicago, 1905, XLIV, 466. Junta Superior de Sanidad de la Isla de Cuba, Suplemento y Noto Adicional, 1902-3, 4. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 7 spores of which may retain their vitality for years. Is it not more likely that it is persistence of spores, rather than growth of the bacilli themselves, that in most instances maintains the soil infection ? Typhoid Bacilli in Soil. It has been amply demonstrated that water, milk, soil and various other materials are, when sterile, suitable media for the growth of the typhoid bacillus. But this fact is of little practical importance, as sterile mate- rials are not ordinarily found in nature, but on the contrary almost everything which could possibly be considered a cul- ture medium for typhoid and other disease germs is swarming with bacteria, mostly of entirely harmless varieties. There has been much painstaking work to determine whether ty- phoid bacilli actually do grow, or even retain their vitality, in or on a great variety of substances. The difficulties in this sort of experimentation are considerable, and not the least is that of picking out the typhoid bacillus from among other forms. Robertson 1 and Firth and Horrocks 2 seem to have made the most elaborate experiments in regard to its growth in soil, and to have worked under more natural con- ditions than most observers. Robertson found that by moistening soil from time to time with bouillon he could keep the bacillus alive for 11 months, and even cause it to grow. Firth and Horrocks did not find any evidence of increase in soil under a great variety of conditions. When conditions were favorable it could be recovered up to 74 days. In peat it could only be recovered after 13 days. More recently Mair 3 has been able to recover the bacillus from un- sterilized soil in large numbers, for 20 days, and in small numbers, up to 70 or 80 days. He found no evidence of increase. Great care was taken not to introduce any nutri- tive medium with the bacilli. Unlike most observers, Mair found that in sterile soil the bacilli disappear more rapidly, 1 Robertson, Brit. M. J., Lond., 1898, I, 69. 1 Firth and Horrocks, Brit. M. J., Lond., 1902, II, 936. 3 Mair, J. Hyg., Cambridge, 1908, VIII, 37. 8 THE SOURCES AND MODES OF INFECTION in 11 days in fact. He believes that this is due to the chem- ical composition of the particular soil used. Smith 1 working with similar soil, unsterilized, could not recover the organism after 25 days, and the average duration in the soil was 15 days. Calvagno and Calderini 2 spread upon the soil some typhoid excreta. It was found that the bacilli could be recovered from the surface of the soil for 12 to 20 days and from the deeper portions, 20 centimeters, for 40 days. Most observers, as Koch, 3 Karlinski, 4 Uffelmann, 5 Martin, 6 Pfuhl 7 and others agree that it does not grow in soil, though it may retain its vitality at times for months. Savage 8 found that it died rapidly in tidal mud, though a few bacilli could be recovered after five weeks. Klein 9 could not find the organism in dead animals buried in earth, after 20 days, but Loesner 10 found it after 96 days. Typhoid Bacilli on Vegetables. Recently Creel n has investigated the chance of vegetables becoming infected with typhoid bacilli. He planted radishes and lettuce in soil which was watered two or three days later with a fecal emulsion mixed with a 24-hours-old agar culture of the typhoid bacillus. Some of the plants were grown in- doors and some in the open air more or less exposed to sunshine. The leaves and stems were examined every 3 1 Smith, Rep. on Occurrence of Typhoid Fever in Belfast, 1902, quoted by Mair. 2 Calvagno and Calderini, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1908, LXI, 188. Koch, Die Bekampfung des Typhus, Berl., 1903, 14. Karlinski, Arch. f. Hyg., Munchen u. Leipz., 1891, XIII, 302. Uffelmann, Centralbl. f. Bakteriol. [etc.], Jena, 1894, XV, 133. Martin, Rep. Med. Off. Local Gov. Bd., Lond., 1900-1901, XXX, 508. Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. Savage, J. Hyg., Cambridge, 1905, V, 146. Klein, Rep. Med. Off. Local Gov. Bd., Lond., 1898-9, XXVIII, 363. 10 Loesner, Arb. a. d. k. Gsndhtsamte, Berl., 1896, XII, 448. 11 U. S. Pub. Health and Mar. Hosp. Serv., Pub. Health Rep., 1912, XXVII, 187. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 9 days for the bacilli, and they were found, but not constantly, for periods varying from 10 to 31 days. The author con- siders that these experiments demonstrate the possibility of the transmission of typhoid fever by means of uncooked vegetables grown in infected soil, and so they do. Yet it often happens that the soil is manured a long time before the seed is planted, so that the bacilli have a chance to die out, and doubtless often the conditions are less favorable than in the experiments, owing to excessive rains, or pro- longed drought, or very hot weather; and it is also true that the use of fresh night soil as a fertilizer in the more civilized countries is rapidly diminishing, so that it is not unlikely, after all, that raw vegetables are only occasionally a source of typhoid fever. If, too, as now seems probable, bacilli in feces are less resistant than those from cultures, the danger would be less than at first sight appears from these experiments. There can, however, be no doubt that this is a real source of danger, and that human excrement should not be used for fertilizing vegetables and low-growing fruits which are to be eaten raw. The futility of attempting to cleanse them by ordinary washing or rinsing is shown by Creel, who without success tried to cleanse a lettuce leaf by three washings with a pipette and by stirring in water. Typhoid Bacilli in Feces. According to Park, 1 typhoid bacilli soon die out in feces, usually in a few hours, but he has recovered them up to the tenth day. He suggested that this variation may depend on the constitution of the feces. On the other hand, Levy and Kayser 2 note the persistence of typhoid bacilli in a cemented privy vault up to 5 months, and Pfuhl 3 recovered them after 3 months from feces mixed with garden earth. Dele*pine 4 states that typhoid bacilli 1 Park, J. Am. M. Ass., Chicago, 1907, XLIX, 852. 2 Levy and Kayser, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1902, XXXIII, 489. Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 556. 4 DelSpine, Rep. Health of Manchester, 1907, 82. 10 THE SOURCES AND MODES OF INFECTION will survive in a privy for a year. His investigation was made in 1898, 13 months after the use of the privy by a patient. Meanwhile the vault had been disinfected several times. Apparently, however, its use by a carrier was not excluded. Calvagno and Calderini recovered typhoid ba- cilli from a privy vault for 30 days and from a barrel for 25 days. Morgan and Harvey l could not recover typhoid bacilli from a privy vault later than 18 days. Semple and Greig 2 found that urine containing 60,000,000 bacilli per cubic centimeter kept at 80 F. was free from them in 72 hours, and that feces under similar circumstances lost them* in 9(Thours. Mosebach 3 sought for typhoid bacilli in privy vaults belonging to houses where carriers resided but where there had been no frank case of typhoid fever for years, and had no difficulty in recovering the germs. Johnstone 4 in studying the Janet Hill outbreak, which was probably due to carriers, could find no bacilli in 6 samples of soil from the yard of a house where there had been persistent typhoid fever. Rogers 5 found that the bacillus lived only a few days in filtered septic tank effluent. Typhoid Bacilli in Water. Jordan and Russell 6 imitated natural conditions by enclosing inoculated water in colloidal sacs to permit of osmosis, and these were placed in the Chicago River, a sewage-polluted stream. They could recover the bacilli for from 3 to 7 days only. Russell and Fuller 7 repeated these experiments with substantially the same results, though they kept the bacillus alive in lake 1 Morgan and Harvey, J. Roy. Army Med. Corps, 1909, XII, 587. 2 Semple and Greig, Sc. Memoirs, Med. and San. Dept., Gov. India, 1908, XXXII, 40. 3 Mosebach, Centralbl. f. Bakteriol. [etc.], I Abt., Jena, 1909, LII, Orig., 170, 773. 4 Johnstone, Rep. Med. Off. Local Gov. Bd., Lond., 1909-10, XXXIX, 166. 6 Rogers, Brit. M. J., Lond., 1903, II, 639. 6 Jordan and Russell, J. Infect. Dis., Chicago, 1904, I, 641. 7 Russell and Fuller, J. Infect. Dis., Chicago, 1906 [Suppl. No. 2], 40. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 11 water from 8 to 10 days. Houston 1 has made some careful quantitative studies of the life of the typhoid bacillus in raw London tap water. In eighteen series of tests the average reduction during the first week was 99.9 per cent, but a few could be recovered up to the eighth week. More recently Houston 2 has compared the bacilli fresh from a carrier with the same strain after cultivation and he found that while the former usually lived over 5 weeks, the latter in 9 tests died in 1 week, in 3 tests in 2 weeks and in 1 test in 3 weeks. He also drank, without bad results, on 10 different days a half pint of water to each half pint of which had been added, from 23 to 28 days previously, fresh urine from the carrier containing 218,000,000 bacilli. Morgan and Harvey 3 came to a similar conclusion as regards the comparative viability of typhoid bacilli from cultures and from excreta. They consider that cultures are worthless for practical tests of the viability of the bacillus. As most of the tests have been made with cultures, it seems highly probable that the persistence of the typhoid bacillus outside of the body is not as great as many of the experi- ments would indicate. Houston 2 has made careful search for typhoid bacilli in raw Thames and Lea waters which are more or less polluted with sewage. From 215 samples of water aggregating 116,900 cubic centimeters, 20,771 colonies were isolated for study, but only 2 proved to be typhoid bacilli. These examinations continued through the year. Wilson and Dickson 4 report that they have developed a new method for isolating the typhoid bacillus from water by which they can recover a single bacillus from 100 c.c. of water. They claim that they can, by their method, show the presence of the bacillus when other methods fail to 1 First Rep. on Research Work, Met. Water Bd., Lond. 2 Seventh Rep. on Research Work, Met. Water Bd., Lond. 3 Morgan and Harvey, J. Roy. Army Med. Corps, 1909, XII, 587. 4 Wilson and Dickson, J. Roy San. Ins., Lond., 1911, XXXII, 9. 12 THE SOURCES AND MODES OF INFECTION reveal it and that conclusions as to the rapid disappearance of the bacillus, based on other methods, are consequently erroneous. They found that the typhoid bacillus could be recovered from water up to the twenty-third day. But it may be that a single bacillus in 100 c.c. is so extremely unlikely to cause infection that somewhat coarser methods may yield results more indicative of the practical danger. Field 1 found that typhoid bacilli would survive in sea- water for from 6 to 8 days, but that 50 per cent died in 24 hours. Herdman and Boyce 2 found no evidence of the mul- tiplication of the typhoid bacillus in sea-water but, on the contrary, it entirely disappeared in about 3 weeks, the larger part of the reduction taking place during the first few days. Recent careful observations have shown that in potable waters typhoid bacilli are able to survive much longer in winter than in summer. Ruediger 3 had noticed that the number of colon bacilli in the river supplying Grand Forks, N. D., was 4 or 5 times greater in winter than in summer. Believing that the excess in winter was due to the longer life of the bacilli at that season he tested the question by hanging in the river at different seasons celloidin sacs con- taining large numbers of typhoid bacilli. It was deter- mined that in the winter, when the river was covered with about 30 inches of ice, the typhoid bacilli lived 5 or 6 times as long as in the summer. In summer he floated down the river two dialyses containing large numbers of bacilli and after 54 hours only 0.11 per cent was left in one and 0.013 in the other. Ruediger attributes the greater longevity in winter in part to the inter-relation of different organisms and in part to the cutting off of the sun's rays by the ice. Houston 4 placed typhoid bacilli in tanks at different temper- 1 Field, Rep. Dept. Health, City of New York, 1904, I, 451. 2 Herdman and Boyce, Rep. Thompson Yates Lab., 1898-9, I. 3 Ruediger, J. Am. Pub. Health Ass., 1911, I, 411. 4 Seventh Rep. on Research Work, Med. Water Bd., Lond. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 13 atures and found that a reduction which took place in 2 weeks at 64.4 F. required 3 weeks at 50, 4 weeks at 41 and 5 weeks at 32. Wheeler finds that in well water with considerable pollu- tion, at room temperature, and with the exclusion of light, a considerable increase of typhoid organisms may take place. Konradi also claims that this bacillus can main- tain a saprophytic existence in water, but his methods have been criticised, and, in some experiments at least a good deal of nutrient material was added to the water with the organisms. The report on typhoid fever in the District of Columbia 1 quotes from Kubler and Neuf eld, and Stroezner and Tavel, instances of alleged longevity of the typhoid bacillus in well water or, in Tavel's case, in tap water, but secondary contact infection was not in any instance abso- lutely excluded. On the other hand, the infection in a reservoir in Scranton was proved to have died out within 8 weeks. 2 Pf uhl 3 found bacilli in tap water after 28 days, but not after 31 days. In artificially inoculated seltzer water it lived for 27 days. Hill, 4 however, could not recover it from various carbonated " soft drinks " after 14 hours. Typhoid Bacilli in Ice. Various writers have studied the life of typhoid bacilli in ice, and Prudden, 5 Winslow, 6 Park, 7 Jordan, Russell and Zeit, 8 Clark, 9 Smith and Swingle 10 and Wheeler 11 have shown that they tend to disappear gradually, U. S. Pub. Health and Mar. Hosp. Serv., Hyg. Lab. Bull. No. 35, 178. N. York M. J. [etc.], 1907, LXXXV, 1025. Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 55. Hill, Rep. Bd. of Health, Bost., 1904, 53. Prudden, Med. Rec., N. Y., 1887, XXXI, 341. Winslow, J. Mass. Ass. of Bds. Health, Bost., XI, 133. Park, J. Bost. Soc. M. Sc., 1899-1900, IV, 213. J. Infect. Dis., Chicago, 1904, I, 660. Clark, J. Mass. Ass. Bds. Health, Bost., XI, 124. 10 Smith and Swingle, Science, N.Y., 1905, n. s. XXI, 481. u Wheeler, J. Med. Research, Bost., 1906, XV, 269. 14 THE SOURCES AND MODES OF INFECTION somewhat as they do in the water from which the ice is obtained. It must also be remembered, when considering the possible danger from ice, that the experiments of Sedgwick and Winslow and Clark show that when water freezes 90 per cent of the contained bacteria are excluded from the ice. Typhoid and Oysters. Herdman and Boyce 1 found that in oysters artificially infected typhoid bacilli could be re- covered up to the tenth day. The bacilli did not increase in the oyster but probably perished in the intestine. In clean water the oysters freed themselves from typhoid bacilli in from 1 to 7 days. Gorham 2 has made extensive studies of the contamina- tion of oysters in Narragansett Bay which is considerably polluted by sewage. No attempt has been made to isolate the typhoid bacillus but attention has been devoted to B. coli. It has been found that while there is not much sea- sonal variation in the colon content of the water there is a very great variation in the colon content of the oysters which are quite free from these bacilli during winter weather. The same phenomenon has been noticed by Pease in New York and by Freeman in Virginia. Gorham believes that during the winter the oyster assumes a con- dition approaching hibernation and during this time the ciliary movement ceases, and with it the current of water over the gills, and feeding stops. No water is taken in from the outside and the bacteria in the oyster are grad- ually eliminated. Is it not safe to assume that the oyster is equally free from typhoid bacilli in the winter, at least in the northern United States? Field 3 found that when typhoid bacilli were planted in living oysters they rapidly died and none could be re- covered after the ninth day. When the oysters were dead 1 Herdman and Boyce, Rep. Thompson Yates Lab. 1898-9, I. 8 Gorham. Am. J. Pub. Health, 1912, II, 24. Field, Med. News, N. Y., 1904, LXXXV, 571. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 15 or dying, there was a very considerable increase. Klein 1 found that in oysters kept in sea water typhoid bacilli would live from 6 to 7 days, but if kept out of the water, for 1 1 days. In other shellfish their life was longer. Typhoid and Milk. Sterile milk serves as an excellent culture medium for the typhoid bacillus, but ordinary market milk is not favorable for its growth, owing to the rapid pro- duction of lactic acid. Bassenge 2 says that when milk has soured to the extent of 0.3-0.4 Soxhlet, and has continued in this condition for 24 hours, the bacilli are destroyed. Neu- feld 3 states that they usually disappear from ordinary milk in from 2 to 3 days. Pfuhl 4 found the bacillus persisting in the milk for 13 days. Rosenau and McCoy have studied this question and reviewed the literature. 5 They find that raw milk, when first drawn, has a feeble antiseptic action, and typhoid and dysentery bacilli, when added to it, decrease slightly at times, but within 48 hours their numbers increase enormously. Eyre 6 also states that the typhoid bacillus may increase in milk to enormous numbers, but as the milk he experimented with was drawn under careful aseptic precautions, it is quite likely that his findings would not obtain in ordinary milk, owing to the hostile influence of lactic-acid and other bacteria. If typhoid bacilli increase in number in ordinary market milk, extensive outbreaks ought to be expected in our large American cities, where the milk is handled by large dealers drawing their supply from many producers situated at long distances, so that the milk is from 48 to 72 hours old before 1 Klein, Tr. Path. Soc. Lond., 1905, LVI, 23; Med. Press & Circ., 1905, LXXIX, 264. 2 Bassenge, Deutsche med. Wchnschr., 1903, XXIX, 675, 697. 1 Neufeld, Kolle u. Wassermann, Handbuch [etc.] Jena, 1903, II, 213. 4 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. 5 U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 41, 449. 6 Eyre, J. State M. Lond., 1904, XII, 728. 16 THE SOURCES AND MODES OF INFECTION it reaches the consumer. Any dilution ought to be more than balanced by the alleged increase in the bacteria. But nearly all of the American milk outbreaks reported in Bulletin 41 of the Hygienic Laboratory were on small routes where the interval between infection and delivery was short. No outbreaks due to railroad milk were reported from Boston, New York, Philadelphia, Chicago, Buffalo, Baltimore, or St. Louis, and of one hundred and twenty- nine outbreaks in American cities only two instances were reported, namely in Washington, D. C., in which typhoid infection was brought in over a railroad. Boers, 1 Bruck 2 and Pfuhl 3 have demonstrated the persist- ence of typhoid bacilli in butter up to 27 days, but few if any outbreaks have been traced to this article of food. Mayer 4 states that paratyphoid bacilli will retain their vitality in dried human feces for a year and a half. No bacteria can grow except in the presence of moisture, so an increase of typhoid bacilli on clothing, furniture, wood- work, etc., is not to be looked for. The duration of life under such conditions is sometimes shorter and sometimes longer than it is in the presence of moisture. This will be discussed further in another connection. It must be confessed that the experimental evidence relat- ing to the growth and vitality of typhoid bacilli outside the body is by no means conclusive. The evidence seems to be, however, that they rarely if ever increase in numbers, and in most instances they tend to die off, and that quite rapidly, often in a few days, or even hours. Epidemiological Evidence. Soil. There is not much epidemiological evidence that typhoid bacilli retain their vitality outside of the body for more than a few weeks or 1 Boers, cited in U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 41, 24. 2 Bruck, Deutsche med. Wchnschr., 1903, XXIX, 460. 3 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. 4 Mayer, Munch, med. Wchnschr., 1908, LV, 2218. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 17 perhaps occasionally for a few months, and there seems to be no such evidence of their increase, except sometimes in milk. Westcott x reports an instance where a well continued infected for 20 months. It was claimed that the conditions were such that continuous infection could not have taken place, but this does not appear to have been the fact. The numerous instances given in the Report on Typhoid Fever in the Spanish War 2 as showing the growth of typhoid bacilli in the soil, are by no means conclusive. Infected soil was supposed to have caused outbreaks in various army corps, but other sources could not be in any case excluded, and the chances of other modes of infection in an army are very great. The infection was supposed to have remained many months, and it is possible that it may have in some instances done so. As a matter of fact 90 per cent of the volunteer regiments in the Spanish War sooner or later became infected whether encamped on a polluted site or not. Koch 3 believed from epidemiological as well as from bacteriological evidence that it is very rare for an out- break to be due to long continued soil pollution, and that the possibility of the growth of the bacillus outside the body may be neglected. In 1902, Koch undertook the investigation of the typhoid fever which had prevailed for some time in sev- eral villages in Trier. As a result of his labors, every typhoid case and typhoid carrier in four of the villages was isolated, and the outbreak ceased, showing that it was due entirely to contact infection and not to soil infection. Epidemiological Evidence. Water. Numberless out- breaks of typhoid fever have been traced to infected waters. In some instances the pollution of rivers is continuous, and the cities supplied from them suffer from a uniformly high 1 Westcott, J. State M. Lond., 1899, VII, 104. 2 Abstr. of Rep. on the Origin and Spread of Typhoid Fever in U. S. Military Camps during the Spanish War of 1898, Wash., 1900, 20&-209. 1 Koch, Die Bekampfung des Typhus, Berl., 1903, 14, 19. 18 THE SOURCES AND MODES OF INFECTION death rate from this disease. In most instances water out- breaks are of an explosive character, the onset is sudden and they often end suddenly, though sometimes the decline is gradual owing to the development of a certain number of secondary cases due to contact infection. A few days* or sometimes a single day's pollution is sufficient to account for the whole outbreak. Three outbreaks of this kind have occurred in Providence, and in one instance it was clearly traced to the throwing upon the banks of the river of the excreta from an infected family. The Providence watershed covers about ninety-six square miles, and had upon it in 1900 a population of some 35,000, a large part in villages along the banks, but some scattered in hamlets and farms over the whole area. The death rate from typhoid fever in Rhode Island is not less than 20 per 100,000 in the country districts, which means seven deaths per annum on the watershed. As the fatality is not over 10 per cent, there must be seventy cases, and if we add the "carriers/' the number of persons each year distributing typhoid bacilli on the watershed must be at least one hundred, and perhaps very much greater. It is also certain that disinfection of excreta is practiced to such a slight extent as to accomplish very little. The fact that for years the city has had no outbreak of disease, and no excess due to the water, as is shown by the typhoid death rate which for several years has varied from seven to twenty- six per one hundred thousand, indicates that the typhoid bacilli, which are being continually deposited on the water- shed, fail to multiply. Exactly similar conditions prevail on the watersheds of Pawtucket, Newport, Woonsocket, Hart- ford and New Haven, only to mention those cities in my neighborhood with which I am personally familiar. And the general testimony of all epidemiologists is that municipal water supplies are never continuously infected unless com- paratively fresh excreta from typhoid-infected persons pass directly and continuously into them. Nevertheless it is cer- tain that typhoid bacilli must be continually discharged onto LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 19 the soil, and we are justified in considering the freedom from infection of the surface waters coming from such areas a strong evidence that the growth of the typhoid bacillus out- side the V>r>Hy_ flnpg nnf. fftrnmonlv occur, and is a negligible factor in the causation of the disease. Cholera. Early investigators, as Nicati and Rietsch, working with sterilized soil and water, found that cholera spirilla would live outside the body sometimes as long as 2 months. But all the more recent workers agree that under natural conditions, in unsterilized materials, the life of the organism is quite short. Loesner 1 recovered the germs from dead bodies, which had been artificially injected, as late as the twenty-eighth day. Houston 2 says that they usually die off in the surface layers of the soil in 12 days, though they may be kept alive longer if the soil is watered with liquid manure. Though Heiser 3 states that the spirillum was found in the quiet water in the bends of the Passig river, no evi- dence was presented to show that it grew there. Gotschlich 4 states that the spirillum is rarely found in feces for more than three days, and quotes Abel and Draer, Claussen and Dun- bar, and refers to Koch, as stating that it dies in dirty canal water in 24 to 30 hours. In unsterilized milk it may live from 1 to 2 days, but dies as soon as the milk becomes sour. All these agree that there is not the slightest evidence that the cholera spirillum can increase in numbers outside of the body. On the other hand, Emmerich and Gemiind 5 claim that it does increase in numbers in the soil, and may be found for two and one-half months. Paladino-Blandini 6 also states Loesner, Arb. a. d. k. Gsndhtsamte. Berl., 1896, XII, 448. Houston, Rep. Med. OS. Local Gov. Bd., Lond., 1898-9, XXVIII, 413 Heiser, Philippine J. Sci. (Med.), 1908, III, 92. Kolle u. Wassermann, Handbuch [etc.], Jena, 1904, IV, 108. Emmerich and Gemiind, Miinchen med. Wchnschr., 1904, LI, 1089, 1157. 6 Centralbl. f. Bakteriol. [etc.], I, Abt. Ref., Jena, 1905, XXXVI, 53. UNIVERSITY OF CALIFORNIA LF>,et TIWENT OF CIVIL ENGINEER 20 THE SOURCES AND MODES OF INFECTION that it may grow in polluted soil. Koch 1 says that it grows only in the human body. Cholera and Soil. There is certainly a great deal of clin- ical evidence that it does not increase in the soil, but on the contrary speedily dies out. The epidemic of cholera in Europe in 1885 was very widespread in Italy and Spain. How extensively it prevailed and what a great number of towns and villages were infected are well shown in the excel- lent report prepared by Shakespeare. 2 Nevertheless by the succeeding year it had entirely disappeared from Spain, and largely from Italy. Turkey had a similar experience. 3 We know that with the sanitary conditions prevailing in those countries at that time the soil must have been infected with cholera in countless places. But cholera rarely recurred, and when it did, it was in large cities, where, the most probable explanation is, it was maintained during the interval by mild unrecognized cases or latent infections. The extensive epi- demic in the United States in 1873 was not followed by a recurrence in the succeeding year. Not only is epidemiologi- cal evidence strongly against the saprophytic existence of cholera in temperate climates, but it is equally so for tropical regions. The great outbreak in the Philippine Islands in 1902-3 attacked hundreds of villages, and soil infection was universal, yet the disease speedily died out all over the islands. 4 In 1905 there was a similar experience. In the Philippine Islands during the latter outbreak it was believed that the cooked food offered for sale in the streets was a frequent vehicle of cholera germs, and a num- ber of samples, particularly of boiled rice, were found to con- tain the spirilla. 5 The rice was probably contaminated by the 1 Koch, Die Bekampfung des Typhus, Berlin, 1903, 14. 1 Shakespeare, Rep. on Cholera in Europe and India, U. S. Gov. Print. Off., Wash., 1890. 1 Clemow, Tr. Epidemiol. Soc., Lond., 1904, n. s., XXIII, 223. 4 Woodruff, J. Am. M. Ass., Chicago, 1905, XLV, 1160. 8 Maus, Med. News, N. Y., 1902, LXXXI, 318. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 21 hands of sellers or purchasers. Whether the spirilla increased in numbers is not known. Mediterranean Fever. Mediterranean or Malta fever has long been recognized as endemic at various points on the shores of the Mediterranean, particularly on the island of Malta. It shows all the characters of " endemic " disease, being confined to certain areas and exhibiting little tendency to pass to other parts of the world, or to extend by contagion. The micrococcus, M. melitensis, which is its cause, was dis- covered by Bruce in 1887 and has been very carefully studied by an English commission acting under the supervision of the Royal Society. This commission, as have independent observers, has given much study to the vitality of the spe- cific organism of the disease outside of the body. The evi- dence seems to be that it tends, like other disease germs, to perish when removed from the body and deprived of nourish- ment and moisture and exposed to light and heat, but it may retain its vitality for weeks and even months under certain conditions, behaving in this respect much like the typhoid bacillus. 1 No direct experiments seem to have been made to determine whether it ever maintains a saprophytic existence in the soil, but its habits of life are such that it is a fair in- ference that it can rarely do so, and that such saprophytic growth, if it ever takes place, is of no greater practical impor- tance than is the saprophytic growth of typhoid germs. The micrococcus was carefully sought for in water and in dust, but was never found. 2 The disease is referred to in this con- nection because, on account of its localization and slight apparent contagiousness, it was believed by many medical men, as well as the laity, to spring from the soil. Yet the work of the English investigators has conclusively shown that the chief source of the disease is the herds of infected goats. It is by the infected milk of these that the disease is transmitted to human beings. It is barely possible that 1 Report of Commission of Royal Society, 1901, Pts. I and II. Bruce, Nature, Lond., 1908, LXXVIII, 40. 22 THE SOURCES AND MODES OF INFECTION the fever may be spread to some extent by contact with infected urine either of goats or of men, just as typhoid fever frequently extends by contact infection, but the fact that thousands of infected men have been invalided home to England without any extension of the disease in that country would indicate that such occurrence is extremely rare. Bubonic Plague. The germ of bubonic plague is not so resistant as is that of typhoid fever, nor yet is it of such feeble vitality as that of cholera. It is rather susceptible to disin- fectants, to high temperature and to drying, but in a moist condition, particularly at low or moderate temperatures, may remain alive for some months. 1 The endemicity of the dis- ease in many localities has led some to assume that it devel- ops in the soil, but the most careful students see no necessity for assuming soil infection to account for its diffusion, and there is ample positive evidence that plague is derived from other sources. Yet, in view of the fact that soil infection has been so much discussed, it is rather remarkable that so few actual experiments have been made to test the theory. Perhaps it is because such experiments are difficult and those who are most competent to make them have thought their time better occupied with work giving better promise of positive results. Elliot 2 found that soil naturally infected would cause the disease in rats after an interval of a month, and Watkins-Pitchford 3 in some careful experiments found that inoculated soil retained its virulence for four weeks, but not for five weeks. The soil was not sterilized. Gladin 4 found the bacillus alive in unsterile moist earth after 2 1 Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 4, 1901. See also Simpson, A Treatise on Plague. 2 Elliot, Lancet, Lond., 1905, I, 1562. 1 Watkins-Pitchford, Rep. Gov. Bacteriologist, Pietermaritzburg, 1903 [Report on Plague, 31]. 4 Gladin, Centralbl. f. Bakteriol. [etc.], I, Abt. Orig., Jena, 1898, XXIV, 588. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 23 months, and Rosenau l kept it alive a long time in cool moist garden earth, and the Indian Plague Commission, 1901, did the same in moist sterile cow dung. Other experiments by Mackie and Winter in Bombay, cited in the Journal of Hy- giene, 2 were with grossly infected cow dung from the floor of a native house. No pest bacilli were recovered by culture on inoculation after 96 hours. Further careful experiments have been made by the Indian Commission of 1905. Their con- clusions are as follows: "Floors of cow dung grossly contaminated with the bacillus of plague remain infective for 48 hours ; floors of a sort of na- tive cement for 24 hours, the infectivity being tested in each case by inoculation. The floors were infective to animals allowed to run on them for only half the above time." Thus there appears to be no bacteriological evidence that the bacillus of plague grows outside of the bodies of living animals, and a great deal of evidence that when separated from the body it tends to die off more or less rapidly and fre- quently very rapidly. The Indian Plague Commission con- siders that reports of soil infections are unworthy of credence unless continuous and careful observations on the presence of rats and fleas have been made. Dysentery Bacillus. One form of dysentery is caused by a bacillus belonging to the colon group, and it has a number of sub-varieties. It is not quite so resistant as the typhoid bacillus, but it has been known to survive all winter in damp earth. 3 It is said that in Japan local outbreaks often persist longer than do outbreaks of cholera, perhaps due to the higher resistance of the germ. 4 The bacilli appear to be easily de- 1 Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 4, 1901, 9. 2 J. Hyg., Cambridge, 1906, VI, 511. 3 Schmidt, Centralbl. f. Bakteriol. [etc.], I, Abt. Orig., Jena, 1902, XXXI, 522. * Eldridge, U. S. Pub. Health and Mar. Hosp. Serv. Pub. Health Rep., 1901, 1. 24 THE SOURCES AND MODES OF INFECTION stroyed by other bacteria, for they can rarely be found in feces after two days. 1 Dysentery Amebae. One form of tropical dysentery is caused by an ameba, a protozoan, not a bacterium. There has been much dispute concerning these amebse, but it is now, however, believed by the best observers that Entameba coli, commonly found in the intestines, and else- where, is a harmless parasite, but that E. histolytica and E. tetragena, and perhaps E. minuta and E. nipponica, are true parasites and pathogenic. Craig 2 in recent work shows that in all probability the amebae which cause dis- ease in man do not grow readily, if at all, outside of the body. As most convincing evidence he alleges the ina- bility to grow in cultures the pathogenic forms in regions where there are no saprophytic forms to contaminate the cultures and deceive the observer. Bacteria of Suppuration. The formation of pus in wounds, abscesses, or elsewhere, is practically always the result of infection by bacteria. Many varieties of bacteria may cause suppuration, but a few species such as the Micro- coccus aureus, M. albus and M. citreus, and Streptococcus pyogenes, are by far the most common cause of this proc- ess. According to a re*sume* given by Gotschlich 3 they are constantly found growing in the skin and on the mucous surfaces. References are of course given in his article to numerous original investigations, but among more recent ob- servations may be mentioned those of Ruediger, 4 Gordon 5 and Hess. 6 These bacteria are also found in the tonsils and Kruse, Deutsche med. Wchnschr., 1901, XXVII, 370, 386. The Parasitic Amoebae of Man, Phila., 1911, 58. Gotschlich, Kolle and Wassermann, Handbuch [etc.], Jena, 1902, I, 147. Ruediger, J. Am. M. Ass., Chicago, 1906, XLVII, 1172. Gordon, Rep. Med. Off. Local Gov. Bd., Lond., 1904-5, XXXIV, 387. 6 Hess, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1907, XLIV, 1. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 25 lymph glands, apparently remaining latent for long periods of time, i.e., not causing suppuration. Bacteria such as the above, which are the constant parasites, or perhaps rather commensals of man, are naturally to be looked for in the vicinity of man and on the surfaces of the body, on clothing, utensils, furniture; and the dust and dirt of all places fre- quented by human beings are found to contain more or less of them. They may also be found in polluted waters. But whether under natural conditions they are commonly able to maintain a saprophytic existence is another matter. Judg- ing from what I have read in the text-books I should suppose that the pus organisms are not so limited as to the conditions of their growth as are most disease-producing bacteria. They are not so dependent on a high and even temperature or on the composition of the medium on which they grow. I should suppose that they would be more likely to maintain a sap- rophytic existence than most other pathogenic organisms, yet I do not know that such existence for them has ever been demonstrated. In fact Gotschlich 1 says that they are not saprophytes. Bacillus pyocyaneus has, however, been found, by Gorham, growing in a heap of moist rags at a paper mill. Diphtheria. Diphtheria was not so very long ago believed to be a " filth disease," that is, its germs were supposed to have a habitat outside of the body in various forms of " dirt." This theory was common during my medical-school days, and when I began health-department work in 1884, I tried to fit the facts as I saw them to this theory. But they did not fit, and the impression continued to grow that diphtheria was a purely contagious disease. The life habits of the diph- theria bacillus indicate that while it is more resistant than some other disease-producing organisms next to be men- tioned, and somewhat easier to cultivate, it is very unlikely that it is able to propagate itself outside of the body, except at times in milk. Houston, 2 while he does not consider his 1 Gotschlich, Kolle and Wassermann, Handbuch [etc.], Jena, IV, 173. * Houston, Loc. Gov. Bd. Rep. of Med. Off., 1898-9, XXVIII, 413. 26 THE SOURCES AND MODES OF INFECTION experiments conclusive, believes that the bacillus of diph- theria dies off very quickly in unsterilized soils of various kinds. Graham-Smith 1 cites a number of writers concerning the vitality of the organism in water and milk. According to Seiler and Stoutz, it multiplies in sterilized water for a while, but Montefusco and D'Espine and Marignac found no evidence of multiplication even in distilled water, and in polluted water it dies in 6 days. Schottelius reported, con- trary to general experience, that the bacillus multiplies more rapidly in raw than in sterile milk, while Montefusco found no multiplication in raw milk after 3 days, and Rubinstein found that the bacilli died in 24 hours. Eyre showed that in milk drawn in as sterile a condition as possible the diph- theria like the typhoid bacillus undergoes rapid multiplica- tion. Kersten, 2 on the other hand, reports that diphtheria bacilli will persist in raw milk for 72 days, and though they undergo no increase at first, do so later. Montefusco found that they died in fresh bread in 24 hours. Except in fairly fresh milk at room temperature, it is unlikely that the bacilli of diphtheria multiply outside of the body. Other Diseases. Tuberculosis, pneumonia, influenza, cerebro-spinal meningitis, gonorrhea and syphilis are caused by organisms which are difficult to cultivate, and I think all bacteriologists agree that it is futile to seek for their habitat outside of the bodies of men or other animals. As for the protozoan diseases, such as malaria and sleeping sickness, such a habitat is still more improbable. It is only recently, and after laborious experiment, that any of this class of organisms have been cultivated in the laboratory. That they grow outside of the body under ordinary conditions is in the highest degree improbable. There is one protozoan, however, the dysentery ameba, which, if recent observations are cor- rect, does live outside of the body. But this organism belongs 1 Nuttall and Graham-Smith, The Bacteriology of Diphtheria, Cam- bridge, 1898, 171. 2 Kersten, Arb. a. d. k. Gsndhtsamte., Berl., 1909, XXX, 341. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 27 to an entirely different class from the blood parasites, and while the facts so far known render it not improbable that the ameba does grow outside of the body, the facts in regard to blood parasites are against any such hypothesis. Summary of Laboratory Evidence. It appears, then, that so far as experimental evidence is concerned there is no war- rant for assuming a source for the common infectious diseases outside of animal bodies. It is only with extreme difficulty that a few of the blood parasites belonging to the protozoa can be cultivated, and the cultivation of many bacterial forms is strictly limited, so that it is hardly possible to ima- gine their maintaining a saprophytic existence. It is true that the bacteria of typhoid fever and perhaps cholera, dysen- tery, and diphtheria may be conceived of as growing outside of the body under natural conditions, but such growth, if it ever occurs, must be rare. Lack of Epidemiological Evidence. Nevertheless during the larger part of the nineteenth century it was common to seek such an outside source for most of the infectious diseases. The filth theory of disease, the vogue of which was largely due to Chadwick, Murchison and Pettenkoffer, assumed that the specific poison of many of our common infectious diseases, and particularly of typhoid fever and cholera, developed in a contaminated soil, or in other forms of filth. There was at that time no knowledge of the micro-organisms which cause disease, and the theories of the origin of disease, so far as they had any basis at all, depended on clinical or epidemio- logical evidence. There was, it is true, some epidemiological evidence for believing that typhoid fever and cholera could develop in filth, for both of these are excrement-borne dis- eases, and it was difficult to decide without any knowledge of the bacteria which cause them whether they developed in filth or were merely transmitted in filth. But as regards typhus fever, smallpox, scarlet fever, measles, diphtheria and similar diseases, there is really no epidemiological evi- dence to suggest that they develop outside of the body. If 28 THE SOURCES AND MODES OF INFECTION a disease does have its source in the outer world, we should expect to find it localized, attached to a definite locality, endemic, as it was formerly called. The somewhat well-de- fined infected area we should expect to maintain its infection for some time, and we should expect persons coming into the area to become infected. But if we watch the outbreaks, especially the smaller outbreaks, of such diseases as measles, smallpox, scarlet fever, diphtheria, etc., which occur in dif- ferent sections of cities, or in villages, we find nothing to indicate place infection. A " pin map " of these diseases in a city shows first one or two pins, indicating infected houses, then more appearing day by day in the surrounding section, until there are ten or twenty or a hundred cases within the radius of a block or a few blocks or half a mile. The scattered groups of houses are of a somewhat circular form, a little denser nearer the center. The outbreak lasts a few weeks, or two or three months, and then disappears, only to reappear in another part of the city. In village outbreaks contagion is usually more clearly traced. The importation of the disease and the sequence of the earlier cases are often made out. The outbreak lasts only for a moderate time, and then the disease disappears, usually not to return for a con- siderable time, often for years. There is nothing to indicate soil infection. If these diseases really come from privy vaults, sink drains and garbage heaps, we should expect a very different distribution in the house from what is actually found. The ground floor is not oftener infected than the upper floor, nor (for some might say that rising currents carry disease germs to the top of the house) the upper than the lower. But what is most important, when one family in a house is attacked with such a disease as diphtheria, we should expect the other families to be usually attacked also, if the disease is a disease of locality. But in Providence statis- tics for the last twenty years show that in scarlet fever and diphtheria in only about seven per cent of the houses does the disease extend from one family to another. In most of LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 29 these cases of extension, direct contact between members of the families is shown to have taken place. In such important diseases as smallpox, measles and scarlet fever, the germs of which have not been isolated, as well as in typhus fever, diphtheria and whooping cough, epidemio- logical evidence of an extra-corporal origin is entirely lack- ing. Epidemiological and laboratory evidence are against the growth of disease germs outside of the body under ordinary circumstances. The notion still common, even among physicians and health officers, that these infectious diseases are filth diseases, as that term is ordinarily under- stood, is absolutely without foundation. Typhoid Fever and Cholera. Typhoid fever and cholera not infrequently appear in small contact outbreaks very similar to those of scarlet fever and diphtheria, but being excrement-borne, contact infection is not so common as in the latter, while infection by water and food is more common. Some outbreaks of typhoid fever may undoubtedly be inter- preted as due to soil infection, but they can also be explained otherwise, and the bacteriological evidence is so strongly against the soil hypothesis that we are not justified at present in assuming it. There is no evidence that cholera finds a habitat in the soil of temperate climates, and the most careful observers in the tropics are, I think, agreed that it is not different there. The same is true of bubonic plague. Yellow Fever and Malaria. There is a class of diseases for which there seemed, at one time, to be very strong evi- dence that the cause which produced them had its origin out- side of the body. I refer to yellow fever, malaria, sleeping sickness and the blood-parasite diseases of cattle. Malaria is one of the best defined, oldest, and best understood of diseases. I suspect that for twenty-five hundred years what has been known of malaria has decidedly colored prevailing views as to the nature and source of many other infectious diseases. Malaria is a typical endemic disease. Its localiza- 30 THE SOURCES AND MODES OF INFECTION tion can scarcely be better illustrated than in my own neigh- borhood. During the latter half of the nineteenth century the southern part of New England suffered from extensive outbreaks of malarial disease. The whole country was by no means affected, but well-defined limited areas of infection were to be noted all over the region, and in different portions of some of the cities. Infection in many of these persisted from year to year. People moving into them became sick, and malaria was escaped by moving away. Most of these areas were in close proximity to swampy land and marshes, others were some little distance removed, but usually in the direc- tion of the prevailing winds. Thus there was presented a perfect picture of place infection. We were justified, in the then existing state of knowledge, in assuming that the mala- rial poison developed in the wet and marshy places which were closely connected with these infected spots. We now know that this assumption was incorrect, though it was very near the truth, and that the germs of malaria do not develop in the marshes, but that the mosquitoes which carry the germs from one person to another do breed there. As far as sanitation was concerned the error was not serious. The new facts have simply enabled us to work more economically, by determining accurately just what wet places are dangerous. But the apparent certainty that the malarial virus developed outside of the body had enormous influence in encouraging the belief that other disease poisons also had an extraneous origin. The history of yellow fever is somewhat similar to that of malaria. It is eminently a place disease. So are sleeping sickness and Texas cattle fever and a number of other diseases. All of this group we now know are transmitted by insects, and it is the insects which have an extraneous existence and not the parasite of the disease. The mico-organisms which cause these diseases do not grow outside of the bodies of human beings or other animals which serve as hosts, or of the insects which serve as carriers. LIFE OF DISEASE GERMS OUTSIDE OF THE BODY 31 Review of Evidence. In reviewing this subject we are forced to the conclusion that while it is possible that the anthrax and tetanus bacilli and the pus-forming bacteria may develop in the soil, there is no evidence that they com- monly do so. It is also possible that the typhoid bacilli, and to a still less extent the bacteria of cholera, dysentery and plague, maintain a limited saprophytic existence, but this is probably very unusual. There is ample epidemiological evi- dence that in temperate climates such a source for these diseases must be an almost infinitesimal factor in their development. Probably the diphtheria bacillus never has a saprophytic growth of any significance, unless possibly very rarely in milk. As for tuberculosis, pneumonia, influenza, cerebro-spinal meningitis, scarlet fever, typhus fever, small- pox, whooping cough, gonorrhea and syphilis, malaria, yellow fever and sleeping sickness, there is not the slightest reason for supposing that they ever develop outside of the bodies of animals. Changes in Present Theories and Practice. If these facts are correct and I can scarcely believe that any will seriously contend that we have any evidence that an appreciable amount of our common infectious diseases arises in the exter- nal world prevailing notions as to the sanitary functions of the state should be decidedly modified. The laity and the lay press still believe that most of the infectious diseases have their origin outside of the body, in filth, or if admitting con- tagion, attach equal importance to external sources of infec- tion. And even very many health officials and some teachers and writers on sanitation hold the same view. Municipal sanitation and municipal cleansing are still synonymous terms to many health officers. It is true enough that two or three diseases, as typhoid fever and cholera, the germs of which are found in human excrement, have markedly dimin- ished as a result of improved methods of excrement disposal, or because of the introduction of water supplies uncontami- nated with human excrement. It is also doubtless true that 32 THE SOURCES AND MODES OF INFECTION whatever promotes municipal cleanliness tends to promote personal cleanliness, and real personal cleanliness, as we shall see, is doubtless an important factor in the preven- tion of contagion. Intelligent and effective control of excreta disposal, of the mosquito nuisance in certain regions, of the rat nuisance in the presence of plague, and perhaps of the fly nuisance, are of great importance in the preven- tion of certain diseases. In the northern parts of the United States typhoid fever and dysentery and perhaps diarrhea are the only diseases likely to be effected by nuisance inspection and only when it is directed along cer- tain lines. Except for a few diseases or except for very indirect effects, the cleansing of streets, alleys, and back yards, of dwellings and stables, the regulation of offensive trades, and the prevention of nuisances generally, have, so far as we can see, no effect on the general health, nor any value in the prevention of specific diseases. While munici- pal improvements such as the above are desirable, there is little more real reason why health officials should work for them than there is that they should work for free transfers, cheaper commutation tickets, lower prices for coal, less shoddy in clothing or more rubber in rubbers all good things in their way and tending towards comfort and health. CHAPTER II. CARRIERS AND MISSED CASES. A Recent Discovery. That there are occasionally seen mild cases of the infectious diseases difficult or impossible to recognize, has long been known. That such cases are rare has always been generally believed. That the germs of dis- ease can maintain themselves and increase in number in a person without causing any symptoms at all, was until recently scarcely thought possible, and the idea that such latent infections are extremely common would have been scouted as preposterous. Even to-day the facts are denied by many sanitary officials, and there are comparatively few who recognize the frequency with which mild atypical forms of disease and healthy " carriers " of germs are found, or realize the tremendous importance which such cases have in the spread of the contagious diseases. Undoubtedly the most fruitful medical discovery of the last century, and perhaps of all time, was the discovery of the parasitic nature of the infectious diseases. Probably the most important discovery bearing on preventive medicine since the demonstration of the bacterial origin of disease, is that disease germs frequently invade the body without causing disease. The succeeding pages will be devoted to a consideration of some of the data available concerning the existence of mild cases and carriers. The term ' ' carrier " is applied to those persons in whom patho- genic micro-organisms exist, but who, nevertheless, show no symptoms. Such carriers are rarely found by the health offi- cer, and the very mild cases also naturally escape notice and are hence called by the English " missed cases," i.e., cases which fail of recognition. 33 34 THE SOURCES AND MODES OF INFECTION Typhoid Fever not an Intestinal Disease. Bateriolo- gists and pathologists now consider typhoid fever essen- tially an infection of the blood, rather than a disease of the intestines. Houston l urged this view in his report of a urinary carrier in 1899, and it was also set forth by Horton- Smith in 1900. 2 The latter considers that the bacilli proba- bly pass through the intestinal wall without causing changes there and proliferate in the mesenteric glands, whence they pass into the circulation. Pyer's patches are secondarily infected from the blood stream. A number of instances are recorded in which the bacilli pass through the blood into the fetus, causing a systemic infection but without intes- tinal lesions. It is a fact that in adults the intestinal lesions are frequently slight, and often the bacilli are few in number in the feces, and sometimes they cannot be found at all. Semple and Greig 3 report a case of typhoid fever in which the bacilli were found in the blood from July 20th to September 20th, but were never once found in the feces or urine. 4 So far as we know, the typhoid bacillus may enter the lymph and blood from any portion of the alimentary canal, and Semple and Greig, Lentz, Forster, Kayser and others believe that it frequently enters through the tonsils; and Pratt, Peabody and Long 5 say that there is no more evidence of entrance through the intestines than through the tonsils. Indeed, Lentz 6 says that he has shown, by the finding of bacilli in the tonsils, that the latter may be the portal of infection. He states that tonsillitis is of common and early occurrence in typhoid fever and quotes Drigalski as finding it in 40 per cent of all cases. 1 Houston, Brit. M. J., Lond., 1899, I, 78. 2 Horton-Smith, Brit. M. J., Lond., 1900, I, 827. * Seinple and Greig, Sc. Memoirs, Med. and San. Dept., Gov. of India, 1908, XXXII, 9. 4 See also Opie and Bassett, cited by Pratt, Peabody and Long. 6 Pratt, Peabody and Long, J. Am. M. Ass., Chicago, 1907, XLIX, 846. Lentz, Brit. M. J., Lond., 1910, II, 1501. CARRIERS AND MISSED CASES 35 In any event, the bacillus is soon found in the blood, and continues in this fluid through the acute stages of the disease. Typhoid fever is, then, essentially a bacteremia. Audibert l has recently shown that this at times presents a subacute type. The bacillus may migrate from the blood to any organ. As has been shown by Pratt, Peabody and Long, a favorite habitat is the gall bladder. Pratt found it in the gall bladder in 21 out of 30 cases. Kelly 2 says that typhoid bacilli were found in 7 of 74 gall-bladder opera- tions, and he states that in many cases there is no evidence of intestinal infection. Primary cholecystitis has also been reported by many others. Recently Elmer 3 reports a case, occurring in a small milk outbreak, in which the only symp- toms were cholecystitis. The distended gall bladder was drained with immediate relief of the symptoms. The bacillus may also infect the bones, 4 kidneys, 5 ovaries and cerebro-spinal fluid. 6 It would appear from the pathology that typhoid infection deviating from the intestinal type is by no means uncommon. Typhoid Bacilli in the Feces. Typhoid bacilli were first sought for and found in the feces, and it was then thought that they freely developed in the intestinal contents. It is now believed that, while some of the bacilli in the feces may have their origin in the intestine itself or its contents, the greater number come into the gut with the bile. It was long known that they could be found in the bile, but the importance of this fact and the relation of these bac- teria to the gall bladder was not recognized until the car- rier question came to the front. From the evidence fur- nished by a considerable number of animal experiments, as Audibert, Le Processus Eberthien, Masson et cie, Paris, 1911. Kelly, Am. J. M. Sc., Phila., 1906, n. s., CXXXII, 447, 744. Elmer, Arch. Pediat., N. Y., 1911, XXVIII, 217. Sultan, Deutsche med. Wchnschr., 1894, XX, 675. Greaves, Brit. M. J., Lond., 1907, II, 75. Lavenson, Univ. Penn. Med. Bull., 1908-9, XXI, 55. Silber- berg, Berl. klin. Wchnschr., 1908, XLV, 1354. 36 THE SOURCES AND MODES OF INFECTION well as by pathological studies on human beings, it seems probable that the bacilli reach the gall bladder by way of the blood stream. Once there, they may merely lead a sap- rophytic existence, increasing to enormous numbers in the bile and passing with it into the intestine, whence they are discharged in the feces. At other times the mucosa of the gall bladder is attacked and becomes inflamed, and nests of bacilli are found in the tissue. Such nests are not con- fined to the gall bladder but are found in the hepatic ducts, which fact must be taken into account when it is proposed to cure intestinal carriers by the washing out or removal of the gall bladder. Indeed, Ledingham refers to cases in which this operation did not prevent the subse- quent discharge of bacilli in the feces. Loele 1 opened the gall bladder in a convalescent typhoid case which was excreting bacilli, but no trace of them could be found in the gall bladder. Typhoid bacilli are not rarely found in gallstones and it is thought by some that they make their way into the stones after they are formed, but the general opinion is that they are the nuclei around which the stones develop. The bacilli are by no means constant in the intestines, even during the course of the disease, and indeed they are sometimes entirely absent, as in Semple and Greig's case previously mentioned. With improvements in technique they are more frequently found than formerly. The fol- lowing figures from Gaehtgens and Bruckner in 1910 2 give the highest percentages. Cases. Bacilli found. Percentage. 1st week . . 21 12 57 2nd week . . . 32 17 53 3rd week . . 13 10 77 4th week 4 2 50 5th week 2 2 100 1 Loele, Deutsche med. Wchnschr., 1909, XXXV, 1429. Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1910, LIII, 559. CARRIERS AND MISSED CASES 37 Typhoid Bacilli in Urine. Typhoid bacilli were noted in the urine as early as 1886 by Hueppe, 1 and similar find- ings were reported in succeeding years by many other ob- servers. The first extensive study of this condition was made by Richardson in 1898. 2 The bacilli are usually not found in the urine until the later stages of the disease, but are occasionally observed earlier, as by Connell, 3 on the seventh day. They are usually in large numbers and often in pure culture. Richardson found them present in about 23 per cent of all cases examined, and earlier and later observers give about the same figures. Thus Connell tab- ulated 621 reported examinations, of which 24 per cent were positive. The bacilli generally continue in the urine for a while after recovery, but usually disappear within three months. Oftentimes the presence of the bacillus is not accompanied by symptoms referable to the urinary tract. Often, however, cystitis develops, which may persist an indefinite time, accompanied by the presence of the bacilli in the urine. The pelvis of the kidney may also be attacked by the bacilli, and foci of infection may be found in the kidneys themselves. As early as 1889 Konzajeff 4 reported finding in the kidneys infarctions containing typhoid bacilli. Marchildon 5 has recently reported two cases in which the presence of typhoid bacilli in the urine was due to their growth in the seminal vesicles and the prostate, and Gould and Quails 6 found the bacilli in the prostatic fluid of 1 of 19 convalescents. Typhoid Bacilli in the Sputum. Pratt, Peabody and Long, previously quoted, cite several observers as finding 1 Hueppe, Fortschr. d. Med., 1886, IV, 448. 2 Richardson, J. Exper. M., N. Y., 1898, III, 349; 1899, IV, 19. Connell, Am. J. M. Sc., Plula. and N. Y., 1909, n. s., CXXXVII, 637. < Konzajeff, Centralbl. f. Bakteriol. [etc.], Jena, 1889, VI, 672. 6 Marchildon, Am. J. M. Sc., 1910, CXL, 74. 6 Gould and Quails, J. Am. M. Ass., Chicago, 1912, LVIII, 542. 38 THE SOURCES AND MODES OF INFECTION the bacillus in the bronchial secretions of typhoid fever patients, and state that Dieudonne found it for seven weeks after recovery. Richardson l also reports finding it in the sputum on three successive days. That this is not a common condition is probable from the investigations of Tenney, 2 who examined 53 typhoid fever patients without finding the bacilli in the sputum. A few of the cases had bronchial symptoms. He found that the bacilli would grow and survive in sputum for 125 days. Typhoid Carriers. Though typhoid carriers seem to have been first observed in England, their epidemiological importance was not realized until, under the direction of Koch, the active campaign against the disease in south- west Germany was begun in 1903. During the next few years extensive observations of carriers were made in this and other portions of Germany. Since the first edition of this book appeared, J. C. G. Ledingham 3 has published a most valuable study of ty- phoid carriers, and in addition to the data presented in my first edition, I have made free use of his material in the following pages. A typhoid " carrier " is a person without signs of illness in whom typhoid bacilli are living and increasing in num- bers. Some of these carriers have had typhoid fever, others so far as can be learned have not. In a large proportion of cases the carrier condition follows convalescence and lasts only for a few weeks or months. Some cases, on the other hand, become chronic carriers. Again, persons may be car- riers for a period, perhaps usually short, before the disease develops. Various names have been applied to the differ- ent kinds of carriers, both by the Germans and by the French, and a formal classification has been suggested. In 1 Richardson, J. Bost. Soc. M. Sc., 1897, II, 21. 1 Tenney, Bost. M. & S. J., 1910, CLXIII, 124. 8 Ledingham, Rep. Med. Off. Local Gov. Bd., Lond., 1909-10, XXXIX, 249-384. CARRIERS AND MISSED CASES 39 Germany carriers who excrete bacilli for less than 3 months are generally called Bazillentrdger, and those who remain carriers over that time are Dauertrdger. The English equivalents are " temporary " or " transitory " carriers, and " chronic " carriers. Sacquepee l names the excretors of bacilli in the incubation stage as " precocious " carriers, those who have had the disease and who continue to ex- crete bacilli for less than 3 months as " convalescent " carriers, those who excrete them over three months as " chronic " carriers, and those who have never been sick as " healthy carriers," or " well carriers." For the present purpose interest attaches chiefly to the fre- quency of the carrier state, the length of time it continues and the liability of carriers to cause disease in others. Some carriers excrete bacilli in the feces, some in the urine, and some in both. Only one sputum carrier has been reported. Carriers during Incubation. Cler and Ferazzi, 2 during a food outbreak, found 6 of 39 persons who had eaten the food and who, though exhibiting no symptoms, were carry- ing the bacilli in their intestines. These " precocious " carriers may become sick later, and sometimes the period of incubation, so called, may be three or four weeks, or even longer. 3 Indeed, it is not rare to find typhoid bacilli in the feces during the period of incubation. Conradi noticed this, and considers it an important factor in the spread of the disease. 4 Ravenel and Smith 5 have reported an out- break of forty cases due to contact with a case before the symptoms had developed. Prigge 6 discovered 3 carriers who developed the disease, 18, 19 and 20 days afterwards. 1 Sacquepee, Bull, de 1'Inst. Pasteur, Paris, 1910, VIII, 1, 49. 1 Cler and Ferazzi, Centralbl. f. Bakteriol. [etc.], Jena, I Abt., Ref. 1905, XXXVI, 479. J Griffith, Med. Press and Circ., 1905, LXXIX, 208. 4 Conradi, Deutsche med. Wchnschr., 1907, XXXIII, 1684. 8 Ravenel and Smith, J. Am. M. Ass., Chicago, 1909, LII, 1635. 6 Prigge, Klin. Jahrb., Jena, 1909, XXII, 245. 40 THE SOURCES AND MODES OF INFECTION G. Mayer l reports 3 cases. One of these was a boy whose stools contained the bacilli 8 days before the symptoms arose. According to Ledingham, Klinger concluded that of 812 cases of contact infection studied by him, 33 acquired the disease from a case in the first week of incubation and 150 during the second week. He assumes two weeks as the average period of incubation, though he found it in 60 cases, in which its duration was pretty well determined, to vary from 5 to 45 days, the average being 16 days. During the Spanish war many cases of typhoid fever were attrib- uted to exposure to cases in the incubation stage. 2 Convalescent Carriers. Drigalski 3 was the first to study the persistence of typhoid bacilli in the feces of con- valescents. Of 64 patients, he found that 7, or 11 per cent, continued to excrete them from 8 to 10 weeks, and 3 for over 3 months. One of these was later, at 9 months, found to be still a carrier. Klinger 4 at Strassburg examined 482 cases of typhoid fever during convalescence and 63, or 13.1 per cent, were carriers, of whom 8, or 1.7 per cent, con- tinued so for a period of over 6 weeks. Later 5 he reported that of 604 convalescents, 80, or 13.2 per cent were tempo- rary carriers, 70 intestinal and 10 urinary. G. Mayer 6 found that 232, or 24.9 per cent, of 930 typhoid fever cases became carriers during convalescence. Graham, Over- lander and Dailey 7 found the bacilli in the feces of 11, or 16.9 per cent, of 65 patients after defervescence and pre- vious to their discharge from the hospital. Including the 1 Mayer, Centralbl. f. Bakteriol. [etc.], Jena, I Orig., 1910, LIII, 234. 5 Abst. of Rep. on Origin and Spread of Typhoid Fever in U. S. Military Camps during Spanish War of 1898, Wash., 1900, 178. 8 Drigalski, Centralbl. f. Bakteriol. [etc.], I Abt., Jena, 1904, XXXV, 776. 4 Klinger, Arb. a. d. k. Gesundhtsamte., Berl., 1906, XXIV, 91, 6 Klinger, Arb. a. d. k. Gesundhtsamte., Berl., 1907, XXV, 214. 6 Mayer, Centralbl. f. Bakteriol. [etc.], Jena, I Abt. Orig., 1910, LIII, 234. 7 Graham, Overlander and Dailey, Bost. M. & S. J., 1909, CLX, 38. CARRIERS AND MISSED CASES 41 urinary carriers there were 15, or 23 per cent. Semple and Greig 1 report that 16, or 18.8 per cent, of 86 typhoid con- valescents continued to excrete bacilli after 'their tempera- ture became normal. Ledingham 2 gives a table and chart taken from Klin- ger's account (1909) of the anti-typhoid work in Germany, which shows the age and sex distribution of transitory and chronic carriers. Of 211 of the temporary carriers, 35 were between 5 and 10 years of age, the period showing the maximum number of cases. The age period of greatest incidence for the 220 chronic carriers was between 40 and 45, at which period there were 30 cases. Among the trans- itory carriers the proportion of females to males was 1.4 to 1, while among the chronic carriers it was nearly 5 to 1. Prigge 3 shows two diagrams, on one of which the maximum age of female cases is given as 15 to 20 years and the aver- age age of female carriers as 40 to 45 years. Chronic Carriers. The larger number of convalescent carriers cease excreting bacilli at varying intervals after their recovery. A certain number remain carriers for an indefinite period, sometimes for many months, sometimes for years, and perhaps occasionally for a long lifetime. The earliest and most extensive series of observations as to the number of typhoid fever patients who become chronic carriers was made by the men carrying on the campaign against this disease in Germany. According to Ledingham, of 6708 typhoid fever cases observed during the years 1904 to 1906, 166, or 2.47 per cent, became chronic carriers. Of 3867 cases in 1906 and 1907, 38, or 1 per cent, proved to be chronic carriers. In the Bavarian Pfalz from 1904 to 1907, there were observed 930 cases, of which 78, or 8.1 per 1 Semple and Greig, Scient. Mem., Med. and Surg. Dept., Gov. of India, 1908, XXXII, 9. 2 Ledingham, Rep. Med. Off. Loc. Gov. Bd., Lond., 1909-10, XXXIX, 267. 8 Prigge, Klin. Jahrb., Jena, 1909-10, XXII, 245. 42 THE SOURCES AND MODES OF INFECTION cent, continued to excrete bacilli for over three months. Park l examined the feces of 52 cases eight months after recovery and found bacilli present in 2; in one of them, however, it was present in only one of three tests. Of 16 other persons who had the disease six months previously, 2 were carriers. He thinks that 2 per cent of all typhoid fever cases became permanent carriers, and these may be found in the population at the rate of about one to five hun- dred. Bruckner 2 states that of 316 persons who had the disease, 12, or 3.8 per cent, became carriers, or omitting the 104 children, only 1 of whom was a carrier and who rarely become such, 5.2 per cent continued to excrete bacilli. Semple and Greig, before referred to, found nearly 4 per cent of typhoid patients remained carriers for over three months. Aldridge, 3 also working in India, reports that 6 of 190 convalescents, or 3.1 per cent, remained carriers for longer than six months. Tsuzuki 4 found 3 of 51 convales- cents, or 5.8 per cent, to be chronic carriers. Recently Hamilton, 5 following out the suggestion of Gaehgtens, tested the opsonic index of 25 persons who had gall-bladder trouble and found 7 with an abnormally high index. All 7 proved to be carriers. She hopes that this will prove a simple means of discovering carriers. In Washington 6 380 persons who had had typhoid fever during the years 1904 to 1909 were in 1909 examined and 8, or 2.8 per cent, found to be carriers. Klinger found that of 220 chronic carriers 30, or 13.6 per cent, had gallstones. There is no doubt that the presence of typhoid bacilli in the bladder and gallstones are defi- nitely associated. 1 Park, J. Am. Ass., Chicago, 1908, LI, 981. 8 Bruckner, Arb. a. d. k. Gesundhtsamte., fieri., 1910, XXXIII, 435. * Aldridge, J. Roy. Army Med. Corps, Lond., 1909, XIII, 221. 4 Tsuzuki, Arch. f. Schiffs-u. Tropen-Hyg., Cassel, 1910, XIV, 147. 6 Hamilton, J. Am. M. Ass., 1910, LIV, 704. U. S. Pub. Health and Mar. Hosp. Serv., Hyg. Lab. Bull. No. 77, 171. CARRIERS AND MISSED CASES 43 There is little doubt that the percentage of carriers both convalescent and chronic is considerably larger than is indicated by the above figures. Owing to the very marked intermittency with which bacilli are excreted in the feces of many carriers, an intermittency which is also shown by the urinary carriers, though to a lesser extent, it is certain that more extended examination of the excreta would dis- cover many more carriers. It must be remembered that most studies of this subject have been based on not more than two or three examinations. Carriers among Contacts. Persons brought into inti- mate relation with the sick may become infected without exhibiting any symptoms whatever. Drigalski and Con- radi * found the infection in 4 well persons in contact with typhoid cases, Liefmann and Nieter 2 found 7 carriers out of 252 persons examined in an insane asylum, some of whom it was believed were carriers and the causes of the out- break in the institution, but some of them, however, were true contacts. Scheller 3 examined 40 persons who drank milk which had been handled by a typhoid carrier. Of these 5 were sick, and 13 others, who had no symptoms, were yet found to be excreting typhoid bacilli in either feces or urine or both. All of them became free from germs within a few weeks. Ledingham states that at the St. Brieuc garrison in 1909, Billet and others found 1 carrier among 53 men who lived in rooms where the cases had been most numerous. Typhoid Bacilli in Persons Never Sick. Not only are persons who have had typhoid fever found to be " carriers " of the germs, but persons who have never had the disease, and who give no history of contact, may be infected. 1 Drigalski and Conradi, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XXXIX, 283. * 2 Liefmann and Nieter, Miinchen med. Wchnschr., 1906, LIII, 2097. 3 Scheller, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1908, LXVI, 385. 44 THE SOURCES AND MODES OF INFECTION Allowance must, however, be made for failure to recognize and remember mild atypical attacks, and some of the chronic carriers who are said never to have been sick may have forgotten an attack of " grip " or " malaria " years before. Soper's case so far as known had never had the disease. Houston's case, which had the bacilli in the urine for three years, had not been sick. One of the carriers, the source of several cases, discovered by Semple and Greig, had never had typhoid fever so far as known. Roscoe 1 reports an outbreak of twelve cases in an insane asylum due to contact with a carrier who had never had the disease. Jundell 2 notes a series of twenty-two cases on an estate in Sweden occurring at intervals since 1854. The grand- mother of the family, who had never had typhoid fever, was shown to be excreting the bacilli from 1904 until the time of the report, 1908. According to Ledingham, Prigge found that 8 of 84 carriers studied by him had never had the dis- ease. Of 431 carriers reported by Klinger, 163 gave no history of having had typhoid fever. Carriers among the Public. There have been a few studies to determine the number of carriers in the general population. Minelli 3 found 1 carrier in 250 prisoners in Strassburg. The most extensive investigation has recently been carried on in Washington, 4 where the feces from 986 well persons were examined bacteriologically. Only one test was made for each person, and 3 carriers were found. These were subsequently re-examined and two proved to be negative. Much more evidence is needed as to the number of car- riers to be found, both among the general public and among 1 Roscoe, Lancet, Lond., 1909, II, 1137. 8 Jundell, Abst. J. Am. M. Ass., Chicago, 1909, LII, 388. 3 Minelli, Centralbl. f. Bakteriol. [etc.], Jena, I Abt. Orig., 1906, XLI, 406. 4 U. S. Pub. Health and Mar. Hosp. Serv., Hyg. Lab. Bull. No. 52, 145. CARRIERS AND MISSED CASES 45 contacts. Extensive investigation ought to be made in dif- ferent parts of the world and among different classes of people. Duration of Infection. The bacilli may be found in the urine and feces of carriers, often in enormous numbers, for years. Not so very many cases have been followed bacte- riologically for a great length of time, though in one in- stance the positive examinations lasted four and one-half years. Tsuzuki followed several cases over a year. Mayer, before referred to, reports the following duration of infec- tivity: for 6 months, 56; 6 months to 1 year, 38; 1 year to 2 years, 16; 2 years to 4 years, 17. There is, however, epidemiological evidence for assuming a much longer continuance of the infection. Dean 1 reports the case of a medical man who had had typhoid fever twenty-nine years before, and had since then frequent attacks of biliary colic. Typhoid bacilli were recovered from his feces. It was believed that no one had contracted the disease from him, but he had always been very careful in his personal habits. Huggenberg 2 noted thirteen cases in a household extending over a period of thirty-two years. One woman who had the disease in 1877 was shown to be a carrier in 1908. Scheller 3 reported thirty-two cases ex- tending over a period of fourteen years, all probably due to a carrier who had been sick seventeen years before. Gregg 4 found a woman whose blood gave a positive Widal reaction, and in whose feces bacilli were found, and who had had typhoid fever fifty-two years before. She had presumably infected seven persons. JundelPs case reported above was infectious perhaps for fifty-four years. Chal- mers' case 5 had had the disease sixteen years before. Dean, Brit. M. J., Lond., 1908, I, 562. Huggenberg, Cor.-Bl. f. Schweiz. Aerzte., 1908, XXXVIII, 622. Scheller, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1908, LXVI, 385. Gregg, Boston M. & S. J., 1908, CLIX, 80. Chalmers, Rep. of Med. Off. Health, Glasgow, 1907, 61. 46 THE SOURCES AND MODES OF INFECTION Frosch l reports that evidence was presented to the com- mission appointed by the Prussian Government to study this subject as follows: That fourteen carriers had been in- fective four to nine years, six for ten to twenty years, and five for from twenty-one to thirty years. Soper's case has now been infectious for ten years, and a number of other writers report instances of carriers who were presumably excreting bacilli more or less constantly for periods of from four to eight years. Intermittent Excretion. From what has been said about the carrier state and the existence of nests of typhoid bacilli in the tissue of the gall bladder, the hepatic ducts and in the tissues of the urinary tract, it might be surmised that ex- cretion of bacilli is not in all cases continuous. That there have been reported considerable periods in which the feces and urine of carriers remain free from bacilli is not sur- prising. G. Mayer 2 claims to have been the first to note this intermittent excretion in 1905, but the matter did not receive much consideration until Davies and Hall 3 called attention to the marked intermittency of bacillus excretion in their case, reported previously by Davies, and which will be again referred to. This patient had been infectious at times for four years, particularly in the spring, and on one occasion she was herself sick. Davies and Hall laid considerable stress on this presumed seasonal intermittency, but Ledingham, who with Thompson afterwards followed up their case and also six others, con- siders that the evidence is not convincing, though certainly their carriers gave many more positives during the first than during the last half of the year. Semple and Greig report 18 instructive cases which they followed daily for a considerable period. One of their cases gave only negative 1 Frosch, Klin. Jahrb, Jena, 1908, XIX, 537. 8 Mayer, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1909- 10, LIII, 234. 8 Davies and Hall, Lancet, Lond., 1908, II, 1585. CARRIERS AND MISSED CASES 47 tests for thirty-one days, followed by a positive, another carrier remained free from bacilli, as shown by daily exam- ination, for a period of seventy-five days, and other cases for lesser periods. Scheller noted considerable intermit- tency in the excretion of bacilli. Of 108 examinations of urine and feces from 18 carriers, 48 only were positive. Instances of marked intermittency have been noted by others, as Bruckner, Kayser, Nieter & Liefmann, Eccard and Prigge. The latter, according to Ledingham, noted intermittent periods lasting from one to two and one-half years. Eccard, in an effort to check typhoid fever prevail- ing in an asylum, discovered three carriers who were effec- tually isolated. The disease, however, continued, and on three subsequent examinations, made several months apart, fresh carriers were found who before had given only nega- tive results, in one instance five times. The disease ceased on the isolation of this carrier. This experience of Eccard illustrates how greatly intermittency interferes with all pre- ventive work based on the discovery and control of carriers. An instructive table showing the marked intermittency of carriers in an insane asylum is given by Neisser. 1 Carriers Cause Disease by Contact. Perhaps one of the most convincing instances of contact infection from a carrier is the celebrated case of " Typhoid Mary," so well investigated by Soper. 2 Between August 27 and Septem- ber 3, 1907, 6 cases of typhoid fever developed in a banker's family of 11 persons at Oyster Bay. All the usual routes of infection were most carefully investigated by Soper and discarded because of the lack of evidence. Convinced that some peculiar event must have occurred in the family about August 1, he sought for it, and the only change that he could discover was a change in cooks. But the cook had left and no trace of her could at the time be found. Soper concluded that she was, in view of the evidence, the most 1 Neisser, Berl. klin. Wchnschr., 1910, XL VII, 2142. 8 Soper, J. Am. M. Ass., Chicago, 1907, XLVIII, 2019. 48 THE SOURCES AND MODES OF INFECTION likely source of the trouble, and he made every effort to locate her, but was unsuccessful until she had figured in two more outbreaks. No information was ever obtained from her as to her wanderings, but in various ways Soper learned that a case developed in a family in Mamaroneck where she lived in 1900, another case in a family in New York in 1901, 7 in a family of 9 persons at Dark Harbor, Me., in 1902, 4 in a family at Sands Point in 1904, and 7 cases at Oyster Bay in 1906. After leaving Oyster Bay she went direct to Tuxedo, N. J., a locality free from ty- phoid fever for several years, but where the laundress de- veloped the disease fourteen days after the cook's arrival. " Mary " went to a family in New York in December and within a few weeks 2 cases developed in this family. No wonder that with this evidence extraordinary means were taken to obtain specimens of her excreta, and it can be no surprise to any epidemiologist that she proved to be a carrier. She was confined in a hospital in New York for a long time and her release was refused by the courts, but she was after a while discharged, though still a carrier, and has recently brought suit against the city for $50,000. I am inclined to the opinion that few even of the scoffers at the " carrier theory " would care to employ Mary Wallon as cook. Hilgermann l narrates an instance in which new servants coming to a certain house soon developed typhoid fever. Cases were reported in 1895, 1900, 1902, 1903, 1905 and 1907, in all 15 cases. Suspicion fell upon a woman of 71 years who had had typhoid fever in 1894. She was found to be a carrier. This is the complement of Soper's case, where a moving carrier infected persons in successive houses. Here a stationary carrier infected a series of arrivals at her home. G. Mayer, before quoted, shows a genealogical tree of 195 cases occurring in a certain district in Bavaria during the course of about five years. In this tree are 13 carriers, 1 Hilgermann, Klin. Jahrb., Jena, 1908, XIX, 463. CARRIERS AND MISSED CASES 49 and from 8 of them the disease extended, that is, without them the " tree " would have had many less branches. Of these 13 carriers 2 had a recurrence of the disease. During the years in which his observations were made, of 495 endemic cases of typhoid fever 160 were traced to 91 darners. O. Mayer x has traced several " contact chains " from carriers. Sumacher, 2 after a careful investigation in the village of Crov, reported that he could trace 26.6 per cent of the cases to direct contact with carriers and 44.4 per cent to indirect contact. The following case came under my own observation in 1911: A girl 15 years old, whom we will call A, was re- ported as going to bed with typhoid, March 3. On April 12 the family went to their farm for a few days, and again they were at the farm on April 29 and 30. At this time two friends of A, Miss B and Miss C, were also of the party. There were no servants at the farm and the family prepared the food. On May 7 two other members of the family were taken sick with typhoid fever, and on May 6 Miss C went to bed with the same disease and on May 9 Miss B. On May 17 the father came down with typhoid fever, and a few days later the mother. The evidence pointed to infection at the farm, and of course the family suspected milk and water. The former was from the cow of a neighbor, where there had been no sickness, and the latter was found to be excellent. Further evidence acquit- ting the farm and farmer's family was furnished by the fact that another member of the family, a student at Bryn Mawr, had 6 of her college friends at the farm from March 22 to April 2 and none of them developed typhoid fever. On the other hand, every one of the party who went to the farm with the convalescent, April 29-30, later had the dis- ease. The city milk supply was beyond suspicion. I nat- urally suspected that the girl A, the one first sick, was a 1 Mayer, Miinchen. med. Wchnschr., 1908, LV, 1782. Sumacher, Klin. Jahrb., Jena, 1909-10, XXII, 263. 50 THE SOURCES AND MODES OF INFECTION carrier, and had infected the food at the farm on April 29 or 30, thus causing the sickness of her brother and sister and two friends. The sickness of father and mother might also have been derived from A, but more likely from the later cases which they helped to care for. No examina- tions were made of excreta until June 28, when A was found to be a carrier, as I at first suspected. Typhoid bacilli were again found in the excreta on July 29. Davies and Hall l report the case of a cook who, after discharge from a hospital, where she had had typhoid fever, went to her home, where 4 cases developed in the family. Besides these, 4 other cases occurred in three other loca- tions; in all 8 cases in about three years. Carriers Cause Disease in Institutions. Typhoid fever not infrequently appears in institutions; and in insane asy- lums especially, owing to the difficulty in controlling the habits of patients, such outbreaks are apt to occur. Some- times the source is to be found in a sick person and some- times in a carrier. A. & J. C. G. Ledingham 2 report an instructive and long-standing institutional infection of this kind. The asylum in 1908 held 92 male and 53 female patients. Cases of typhoid fever had developed in every year between 1893 and 1907, except four. In all there were 31 cases, of which 24 were women. Drainage and water supply could be eliminated as causes. All of the female patients were examined and 3 carriers were found. These were isolated in November, 1907, and since then no cases of the disease have developed in the institution.. Ledingham quotes Eccard in regard to typhoid fever in a large asylum at Frankenthal. Most of the cases, how- ever, occurred in a female block containing 110 " unclean, stupid and noisy women." From 1901 to 1906 there had been 21 cases. Repeated search for carriers was made in 1 Rep. Med. Off. Health, Bristol, 1909, 61. - A. & J. C. G. Ledingham, Rep. Med. Off. Local Gov. Bd., Lond., 1909-10, XXXIX, 304. CARRIERS AND MISSED CASES 5] 1903 and in 1906 and 1907. In the latter years some were discovered whose examination in earlier years had been negative, owing probably to intermittent excretion. Since 1906 no cases of typhoid fever have developed. Other in- stances of asylum typhoid due to carriers have been re- ported by Liefmann and Nieter, Levy and Kayser, Friedel, Dehler, 1 C. Neisser, 2 Roscoe 3 and Ledingham. 4 Dehler \ removed the gall bladder from two carriers who were found to be the cause of the outbreak, and their feces were after- wards free from bacilli. A very convincing instance of carrier infection was re- ported by Davies 5 of Bristol, England. A woman, Mrs. H, 50 years old, had had typhoid fever in 1901. In May, 1904, she went to a home for girls at Brislington to work in the kitchen. From that time until September, 26 per- sons in the institution developed typhoid fever. From September, 1904, to March, 1905, Mrs. H was in private service. She was then cook in a children's home for some months. The one case which developed here may have had no significance. In April, 1906, she was employed in the kitchen of the Inebriate Reformatory in Bristol. In the autumn of that year 4 cases developed among users of institution milk. There was no typhoid fever in the neigh- borhood, nor had there been any in the institution since it was opened. There was another outbreak in May, 1907, and up to November 4 of that year there had been 23 cases. Apparently the milk was at fault, and if so was infected after sterilization. Evidence pointed to Mrs. H, who handled the milk after it had been sterilized, and it was discovered by Davies that she was a carrier. She was then removed from contact with the food and there were 1 Dehler, Munchen. med. Wchnschr., 1907, LIV, 779, 2134. 2 C. Neisser, Psychiat.-neurol. Wchnschr., Halle, 1908-9, X, 37. Roscoe, Lancet, Lond., 1909, II, 1137. 4 Ledingham, Brit. M. J., Lond., 1908. I, 15. 6 Davies, Proc. Roy. Soc. Med., 1908, I, Epidemiol. Sec., 175. 52 THE SOURCES AND MODES OF INFECTION no more cases. Davies and Hall l by following up this case showed that the excretion of bacilli was markedly intermittent. They report also that the woman had what might be called a slight relapse in May, 1908, probably a cholecystitis, and in July a woman with whom she shared her lunch developed typhoid fever. Carriers Cause Disease through Milk. In typhoid out- breaks due to milk, water or food, the large number of cases, massed closely together in point of time, often fur- nish far more certain evidence as to causation than do smaller and less marked outbreaks due to contact infec- tion. There have now been quite a number of milk out- breaks reported as due to carriers, and some of these are very striking. The following outbreak was reported by Lums- den and Woodward. 2 Fifty-four cases of typhoid fever were reported on the routes of two milk dealers in Washington during the autumn of 1909. The outbreak was localized in that part of Washington still known as Georgetown. This section of the city was served by about thirty milk dealers. Of the 54 patients, 33 took milk from dealer A and 21 from dealer B. Dealer A, it was found, received 40 gallons of milk daily from the farm of Mrs. X, and dealer B received 20 gallons daily from the same source. The rest of Mrs. X's milk was peddled direct to eleven families nearby. Among these were 3 cases, not seen by a physician, which quite likely also were typhoid fever. The age distribution of the cases and all the other features of the outbreak pointed to milk infection, with its source on the farm of Mrs. X. No recognized cases of typhoid fever, or illness likely to be mistaken for it, had occurred on the farm, and naturally a search was made for carriers. Mrs. X herself was found to be excreting typhoid bacilli in her feces, and conditions were such that infection of the milk from her was very possible. If a well-defined case of 1 Davies and Hall, Lancet, Lond., 1908, II, 1585. 2 Lumsden and Woodward, J. Am. M. Ass., Chicago, 1909, LII, 749. CARRIERS AND MISSED CASES 53 typhoid fever had been found on this farm, it is improb- able that any epidemiologist would for a moment hesitate to attribute the outbreak to that case, even if no examination were made to show the presence of the bacilli in the ex- creta. When now a person is found actually discharging bacilli in large numbers, I can see absolutely no reason for not considering her in all probability the source of the trouble. The fact that the woman had typhoid fever as long as 18 years before, and had not, so far as known, previ- ously been a cause of disease, is urged by some as a reason for not admitting her to be the source of infection at this time. We know in the first place that many carriers are markedly intermittent in the excretion of bacilli, and, what is more to the point, it is by no means as easy to cause infection of persons or things as has generally been be- lieved. Plenty of cases of typhoid fever have occurred on milk farms without doing harm, and numberless cases of scarlet fever, diphtheria and smallpox, as well as of typhoid fever, are most carelessly cared for, yet fail entirely to spread disease. Bigelow 1 reports that in Worcester in 1910 there were >nly 295 reported cases of typhoid fever. Of these, 204 were the customers of a single dealer. The facts pointed to four farms as possible sources. No cases of the disease were found on the farms, and blood tests gave a positive Widal test from only one person, who daily assisted in the milking. He had had typhoid fever 26 years before, and about two weeks before the outbreak he had a slight attack of diarrhea with a little blood in the stools, and accompanied by some headache. He was on two occasions shown to be a urinary carrier. During February, 1910, there was an outbreak of typhoid fever in New York City in a section corresponding to the route of a large milk dealer. Of the 48 cases, 41 used this milk. The infected milk was traced to a distant farm in 1 Bigelow, J. Am. M. Ass., Chicago, 1911, LVII, 1418. 54 THE SOURCES AND MODES OF INFECTION Vermont, where a carrier who was doubtless the source of the trouble was found. It is worthy of note that a labora- tory assistant while pipetting a culture of the bacillus from this carrier drew some of it into her mouth and two weeks later developed a typical attack of typhoid fever. 1 Bolduan and Noble 2 report an outbreak of several hun- dred cases in New York City in 1909 which was traced to that portion of the milk of a large dealer which came from Camden, N. Y. There had been a case of typhoid con- nected with a creamery there, and also a case on farm X, the milk from which was supposed not to go to the cream- ery, both cases becoming sick at about the time of the city cases. But it was found that farmer X did send a part of his milk to the creamery and thence to New York. It was also learned that there had been much typhoid in Camden for several years, and that of 27 cases in 1908-09, 20 were on the milk route of X. It was also found that on the farm of X during the years 1878 to 1909 there had been 7 cases of what was probably typhoid fever. Mr. X him- self had had typhoid fever in 1863-64. He was, on two occasions, a month apart, found to have typhoid bacilli in his feces. The Abundance of Evidence. Only a very few though striking instances of the rise of sickness from carriers have been selected for the purpose of illustration. Within the past three or four years a great mass of similar material has appeared in the medical press, material already too abun- dant for satisfactory compilation. Articles are constantly appearing in the medical journals of all lands reporting instances of apparent infection by carriers. It is true that in many instances the evidence is by no means conclusive, often, indeed, only warranting a surmise. In many cases, on the other hand, and the number is rapidly increasing, the evidence which leads to the discovery of the carrier is 1 Bolduan and Noble, N. York M. J. ( 1911, XCIV, 1313. * Bolduan and Noble, J. Am. Med. Ass., Chicago, 1912, LVIII, 7. CARRIERS AND MISSED CASES 55 as good, and often better, than that on which, with un- questioning confidence, outbreaks are traced to recognized cases. The evidence which implicates the carrier is the same, and is as convincing as that which determines the contagiousness of the disease. Evidence against Carriers. While the evidence is thus seen to be very strong that typhoid carriers are an impor- tant factor in the spread of this disease, some facts are pre- sented which apparently point the other way. Thus Linos- sier 1 says that at least 10,000 persons with biliary lithiasis must visit Vichy each year. From what is known of this condition, it seems probable that a large proportion of these must be typhoid carriers, though no systematic exam- inations have been made to determine this. If this is so, typhoid fever ought to prevail in Vichy, but as a matter of fact there is very little. Linossier explains this as perhaps due to the fact that most visitors to Vichy are beyond the age of marked susceptibility to the disease, and in part also because they are mostly well-to-do and of cleanly habits. T. Thomson 2 also finds the conditions after extensive water outbreaks somewhat puzzling. He says that in Worthing after the outbreak of 1893, in which 8 per cent of the population of 17,000 were attacked, there was, for some years, less typhoid fever than before. After the out- break in Maidstone in 1897, involving 6 per cent of 33,000 persons, there was somewhat more typhoid fever for about four years; and in Lincoln, after the outbreak in which 2 per cent of 52,000 persons were sick, the amount of typhoid fever remained about the same. As we could expect the outbreaks to have left 39, 57 and 30 chronic carriers in the three towns respectively, Thomson says that one would naturally look for an increase in the disease over the pre- epidemic years. Such, however, does not seem to have 1 Linossier, Bull. Acad. de m6d., Par., 1909, 3 S. LXII, 627. 1 Proc. Roy. Med. Soc., Lond., 1910-11, IV, Epidemiol. Sect., 1. 56 THE SOURCES AND MODES OF INFECTION taken place. While this is somewhat paradoxical, the problem is so complicated by the development of acquired immunity, and the generally falling incidence of typhoid fever, that the apparent innocuousness of hypothetical car- riers under such conditions should not be allowed to weigh too heavily against the very clear and abundant evidence on the other side. Neisser 1 calls attention to the danger of attributing too much importance to the reports from certain insane asy- lums that endemic typhoid fever has ceased after the iso- lation of carriers. He shows that in other institutions typhoid-free years have occurred without any control of carriers. He also states that in four institutions where there were outbreaks involving 79 cases, 21 attendants were attacked, while of the attendants on carriers he can find only 3 attacked. He considers the danger from car- riers less than is generally believed, yet he thinks it suffi- cient to warrant the examinations of all newcomers at Benzlau and their isolation under the care of immune attendants. Atypical Typhoid Fever. There can be no question that mild unrecognized cases of typhoid fever are extremely common. Greater care in diagnosis has made an apparent increase in the number of reported cases of this disease, and a decrease in fatality. Thus in my own city the reported fatality from typhoid fever has during the last twenty years been reduced from 50 to 12 per cent; and it is prob- ably really considerably less than that. I have noticed that in milk and water outbreaks, when public attention is directed strongly towards the disease, the case fatality is often very low, which merely means that most of the cases have been recognized. In the Spanish War the com- mittee of investigation believed that the number of cases actually existing amounted to 20,738, while the number reported by the army surgeons was only 10,428. 1 Neisser, Berl. klin. Wchnschr., 1910, XL VII, 2142 CARRIERS AND MISSED CASES 57 Recently Bates l has reported a series of mild atypical typhoid fever cases in Panama Canal Zone, and states that such cases are quite common there, and are the chief factor in the extension of the disease. At the time Koch made his investigation of the four Trier villages there were 8 recog- nized cases, but a thorough bacteriological investigation of suspects discovered 64 more. Of these 49 were children. 2 These mild unsuspected walking typhoid cases not rarely result in death. Velich 3 notes 36 such cases, and a number of others are reported by Curschmann, and they also have been seen by the writer. I have recently investigated two milk outbreaks, in one of which the cause was apparently a mild unrecognized case, and in the other either a con- valescent or a carrier associated with him. Neufeld 4 de- votes considerable space to this class of cases. Lemoine 5 for three years examined the blood of every case'of gastro-intestinal disturbance and jaundice in his ser- vice at the military hospital at Val-de-Grace and found ty- phoid bacilli in 40 per cent, although there was little to lead him to suspect typhoid fever. Ledingham quotes Billet, etc., who report an outbreak of typhoid fever of 142 cases in a regiment at St. Brieuc. Besides these, there were 57 other atypical cases which doubtless would not have been recognized except for the epidemic. Bruckner 6 reports three outbreaks, all originating in mild missed cases. He finds that children are very susceptible, the most suscep- tible age being 11 to 15 years, and that in them the disease is apt to run an atypical course. More recently 7 he has reported an outbreak in an institution for boys in which 1 Bates, J. Am. M. Ass., Chicago, 1908, L, 585. 8 Koch, Die Bekiimpfung des Typhus, Berl., 1893, 14-15. 3 Velich, Arch. f. Hyg., Munchen u. Leipz., 1904, XLIX, 113. 4 Kolle u. Wassermann, Handbuch [etc.], Jena, 1903, II, 271. 6 Lemoine, Presse meU, Par., 1910, XVIII, 113. Bruckner, Munchen med. Wchnschr., 1910, LVII, 1213. 7 Bruckner, Munchen., med. Wchnschr., 1911, LVIII, 1008. 58 THE SOURCES AND MODES OF INFECTION three-fourths were attacked, many cases running an atyp- ical course and only discovered by the use of the ther- mometer. Chamberlain 1 says that a third of all cases among both American and Philippine soldiers can only be detected by laboratory methods. The Spanish War investigation showed that most of the volunteer regiments were infected when they came to camp, that is, they must have contained carriers or mild cases, and it was by extension from these that most of the true typhoid fever later developed. 2 The distinction between a case of true typhoid fever of mild type and a carrier often cannot in practice be made. There is no sharp line of demarcation, but infection by typhoid bacilli may result in a series of cases presenting gradation from the most severe symptoms to none at all. It is most unwarranted to assume, as some appear to do, that a mild unrecognized walking typhoid case may start up an outbreak, but that a true carrier cannot do so. Paratyphoid Fever. It is generally admitted that ag- glutination does not afford a reliable means for differenti- ating the various members of the typhoid group of bacilli. Recent English writers, however, as Dean, Bainbridge and Firth, believe that this can be satisfactorily accomplished by means of complement fixation. According to Bainbridge, 3 B. suipestifer, B. enteritidis (Gartner), B. partyphosus A and B. paratyphosus B can be differentiated in this way. The first two of the above-mentioned bacilli are connected with disease in the lower animals or are at least found in such animals and have been definitely connected with out- breaks of sickness in man due to the use of infected food. B. paratyphosus A, on the other hand, is said by Bainbridge 1 Chamberlain, Philippine J. Sc., 1911, VI, Med., 299. 2 Abst. of Rep. on the Origin and Spread of Typhoid Fever during the Spanish War of 1898, Wash., 1900, 168-175. 8 Bainbridge, Proc. Roy. Soc. Med., Lond., 1911. IV, Epidemiol. Sect., 51; Lancet, Lond., 1912, I, 705. CARRIERS AND MISSED CASES 59 to be a human parasi-tc, just as is B. typhosus (the ordi- nary typhoid bacillus). The disease caused by B. paratypho- sus A is said by Firth l to be very common in India. It is milder in type, with a more irregular fever and a more sudden onset, and is accompanied by more headache. It may very frequently be recognized clinically. Grattan and Wood 2 say that one-third of all cases of uncertain fever are due to this bacillus. This type of enteric is not, according to these authors, and to Bainbridge, common either in Eng- land or the United States, though perhaps its apparent rarity is due partly to lack of careful investigation. Grat- tan, 3 however, could not find this bacillus in 48 cases of enteric fever studied by him in London. But in India Grattan and Wood studied 157 cases of this disease. Of these 10 became carriers, but in only one case did the bacilli persist for as long as 5 months. They believe that these acute carriers are a greater factor in the spread of disease than are typhoid carriers in ordinary typhoid fever. These authors 4 report an outbreak of 9 cases of this type of paratyphoid fever in barracks at Benares, prob- ably due to a man who was discovered to be a carrier. A similar outbreak of 8 cases due to a carrier was reported by Grattan. 5 B. Paratyphosus B. Bainbridge and O'Brien 6 consider that B. paratyphosus B as well as A has its habitat in man. Carriers are frequently found, and such may infect food and thus cause food outbreaks of the disease. They did not find this bacillus in 300 typhoid convalescents, but 1 Firth, Roy. Army Med. Corps., Lond., 1911, XVII, 136. 2 Grattan and Wood, J. Roy. Army Med. Corps., Lond., 1911, XVII, 143. 3 Grattan, J. Roy. Army Med. Corps., Lond., 1910, XIV, 385. 4 J. Roy. Army Med. Corps., Lond., 1911, XXII, 131. * Grattan, J. Roy. Army Med. Corps, Lond., 1911, XVI, 9. * Bainbridge and O'Brien, J. Hyg., Cambridge, 1911, XI, 68; also Brit. M. J., Lond., 1910, II, 1503. 60 THE SOURCES AND MODES OF INFECTION they did find it in 6 cases of fever in which it was appar- ently the causative agent, also in 4 convalescent carriers and in 3 healthy persons. According to Bainbridge, car- riers of B. paratyphosus B were first noted by Lentz and later by Hamilton, Gaehtgens, Bruckner, Mayer and Prigge and Sachs-Miike. But if Bainbridge's contention is cor- rect, and if these Germans, as he states, have not made use of complement fixation to differentiate the bacilli, their data cannot be relied upon. It is not unlikely, however, that some of these were really carriers of B. paratyphosus B. Of those noted by Prigge and Sachs-Miike, 1 4 were in con- nection with a food-poisoning outbreak. One of the car- riers was under observation in a hospital for 2 years. Another, a well person, was found to be a carrier during a food-poisoning outbreak, and 6 months later, after an in- termission of excretion for 3 months, finally became sick and the bacilli were found in the feces. Bainbridge and Dudfield 2 report a contact outbreak of 13 cases in a boarding house at Paddington. It was thought probable that it was due to a carrier, but none was found. At Wrexham in 1910 over 100 cases of food poisoning oc- curred which were traced to pork pies. The meat was not infected when received, as other portions sent to other places did no harm. Apparently infection took place dur- ing the making of the pies. It was found that the head cook, who did not eat the pies and who was not sick, had the bacilli in the feces and was therefore presumably the carrier who infected the pies, though she claimed not to have had anything directly to do with the making of the pies. She had another typhoid-like bacillus in her urine, and these too were found in the pies. Sacque*pee* and Bellot 3 also report the case of a cook who had an abortive attack and while continuing at work infected 19 persons in 1 Sachs-Miike, Klin. Jahrb., Jena, 1909-10, XXII, 237. 2 Bainbridge and Dudfield, J. Hyg., Cambridge, 1911, XI, 24. Sacque>ee and Bellpt, Prog. meU, Pax., 1910, 3. s. XXVI, 25. CARRIERS AND MISSED CASES 61 a garrison of 250. G. Mayer J writes of a man who became a carrier from eating meat and later caused the infection of another. An outbreak of 38 cases was due to eating vegetables fertilized with the contents of a privy vault used by a man with " liver trouble," who had paratyphoid B bacilli in his feces. Cholera Spirilla in Convalescents. Usually the germs of cholera disappear from the feces early in convalescence, and until recently chronic carriers were unknown. Pfeiff er 2 reviews the literature, and cites Simond's observation that the average duration of infection is only about 6 days, and that the longest seen by him was 18 days. Of 117 cases reported to Rumpel, not one carried the germs over 24 days. Abel and Claussen found the average of 17 cases to be 5 or 6 days, and Pfeiffer the average of 39 cases 10 days, though in 2 the infection persisted 23 days. Other writers have made similar observations. Zirolla 3 found 29 convalescents excreting bacilli from 6 to 40 days. Zlatogoroff 4 followed 255 cases until three negative examinations were made. In 134 the spirilla dis- appeared by the fourteenth day, and in 22 they persisted after 21 days, in one case lasting for 56 days. Burgers 5 found the average duration of infection in a small outbreak was about 3 weeks from the beginning of sickness, but in one case the spirilla persisted for 69 days. According to Kolle, 6 cholera spirilla are sometimes found in the intestines of con- valescents as long as 48 days. Rommelaere 7 reported a 1 G. Mayer, Centralbl. f. Bakteriol. [etc.], Jena, I Abt. Orig., 1910, LIII, 234. 2 Pfeiffer, Klin. Jahrb., Jena, 1908, XIX, 483. 8 Abst., Med. Officer, 1911, VI, 84. 4 Zlatogoroff, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1911, XLVIII, 14. 6 Burgers, Hyg. Rundschau, Berl., 1910, XX, 169. 6 Kolle, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1895, XVIII. Rommelaere, J. de meU, Brux., 1892, XCIV, 837. 62 THE SOURCES AND MODES OF INFECTION case retaining the infection 47 days. Forrest x found the germs remaining 6 weeks. Kirchner 2 says that the spirilla are sometimes carried for weeks or months. Zlatogoroff says that Jakowleff found the germs in the feces 56 days after the attack, and Zeidler 93 days. Zlato- goroff himself found them for 56 days. Chronic and Intermittent Carriers. Until recently it was thought that cholera carriers were always of the " temporary " type, and that propagation of the spirilla was confined to the intestinal contents. It was believed that they did not invade the gall bladder or other organs as do typhoid bacilli. Observations by Kulescha, however, show that the spirilla can be found in the gall bladder in 10 per cent of the cases, sometimes producing lesions and propagating in the biliary passages. Consequently it is not surprising that Kulescha reports a case which was dis- charged from the hospital in January, 1909, after having had the spirilla in the feces for 57 days, and which re-entered the hospital in October of the same year with hepatic trouble and soon died. Cholera germs were found in the biliary passages. McLaughlin, 3 who takes these facts from Kulescha, states that Gaffky reports a cholera convalescent who was a carrier for 6 months. Adami, Vallee and Mar- tineau 4 have published notes of a case which arrived in Quebec from Russia 16 November, 1910. The man had perhaps had a slight attack of cholera on the steamship. At any rate cholera germs were found in his feces, and he remained a carrier until the next May. The spirilla were identified by agglutination. Intermittent Excretion of Spirilla. Intermittent excre- tion, which at first was not suspected, is now known to occur. Zirolla states that 2 cases observed by him showed 1 Forrest, J. Trop. M. [etc.], Lond., 1908, XI, 321. - Kirchner, Klin. Jahrb., Jena, 1908, XIX, 483. 8 McLaughlin, Boston M. & S. J., 1911, CLXV, 561. * Adami, Valle"e and Martineau, Canad. M. Ass. J., 1910, I, 697. CARRIERS AND MISSED CASES 63 a germ-free period of 1 month and 20 days jrespectively. During such a period attacks of indigestion or the admin- istration of salts caused the spirilla to reappear in the feces. Creel 1 reports the case of a carrier under observation at quarantine in New York for 54 days. Of 12 examinations of the feces, 6 were positive and 6 negative. Spirilla in Healthy Persons. Dunbar 2 was the first to note the occurrence of cholera spirilla in the feces of healthy persons. He discovered 28 healthy carriers in Hamburg in 1892-93. Rommelaere noted such a carrier in 1892, and carriers are by Koch considered an important factor in the spread of the disease. In 1905 cholera seemed to have been brought down the rivers from Russia into Germany by raftsmen, and Kirchner says that of 27 persons on one raft 2 were carriers. Pfeiffer states that in this outbreak there were 174 cases of the disease, and that 38 other car- riers were discovered. He cites Frosch as discovering 16 carriers, of whom 12 were children, and Friedheim as find- ing 51. In one family observed by Pfeiffer 4 died, 1 was very sick, 1 was mildly sick, and 2 were carriers. He says that there are very many mild cases of the disease which can only be recognized bacteriologically. Burgers 3 dis- covered 6 carriers connected with an outbreak of 30 cases in East Prussia. In Madeira in 1910, 4 of 600 contacts, 37 proved to be carriers. Of these, 12 later developed the dis- ease. The average duration of infection was 6 to 8 days. In a convalescent it continued for 5 weeks. McLaughlin 5 found 17, or 6.44 per cent of 264 prisoners in Manila, to be carriers, and in the city 27, or 7.18 per cent of 376 persons examined. During the summer of 1911 there was some cholera in Creel, J. Am. M. Ass., Chicago, 1912, LVIII, 187. Dunbar, Mod. Med., Osier, Phila. & N. Y., 1907, II, 720. Burgers, Hyg. Rundschau, Berl., 1910, XX, 169. Franca, Bull. Soc. path, exot., Par., 1911, IV, 358. McLaughlin, J. Am. M. Ass., Chicago, 1909, LII, 1155. 64 THE SOURCES AND MODES OF INFECTION the Philippines but only 1 case in Manila. Of 7 persons brought in close contact with this case all were shown to be carriers. 1 While during an outbreak, as stated above, 6 per cent of the population may be found to be carriers, McLaughlin 2 states that between outbreaks thousands of stools may be examined without finding a single carrier. That carriers increase as the number of cases increase is a phenomenon common to other diseases as well as cholera. It will be shown in the following pages to be true for cerebro-spinal meningitis and for diphtheria. Jakowleff, Zabolotny, Zlatogoroff and Kulescha 3 state that in St. Petersburg the feces from 2440 apparently well persons were examined, all of whom had been more or less in con- tact with cholera cases. Of these 125 showed the cholera spirillum, of whom 40 proved to be mild unrecognized cases, 25 were incubating the disease, and 60 were true carriers. During nearly four months of the summer of 1911, while cholera was prevailing in certain parts of Italy, bacterio- logical examination of the feces of immigrants was largely made use of to prevent the introduction of the disease into the United States. A sharp watch was kept by the steam- ship companies and by the United States officials on the other side to prevent the embarkation of possibly infected persons, and indeed all immigrants from infected districts were kept under observation for five days. Many also were subjected to bacteriological examination. According to a letter from Dr. John F. Anderson, of about 20,000 so examined in Italy, 41 were found to be carriers. Of about 25,000 immigrants examined at American ports, 27 were shown to be carriers. All of these were discovered early 1 U. S. Pub. Health and Mar. Hosp. Serv., Pub. Health Rep., 1911, 1493. * McLaughlin, N. York M. J., 1911, XCIII, 115. * Jakowleff, Zabolotny, Zlatogoroff and Kulescha, Bull. Soc. path, exot., Par., 1909, II, 276. CARRIERS AND MISSED CASES 65 in the season while the control of embarkation was not so strict. Gotschlich 1 examined pilgrims returning from Mecca, and though cholera had not so far as known prevailed among them, he found several Russian and Turkish pil- grims who proved to be carriers of the spirilla. Accord- ing to Pfeiffer, these spirilla of Gotschlich have been carefully studied by a number of observers and show slight variations from the type, and have probably lost their virulence. Atypical Cases of Cholera. While perhaps most cases of cholera are readily recognized, atypical and mild cases occur, and they are particularly frequent among children. McLaughlin 2 says that cholera in children simulates acute and chronic enteritis and meningitis, and is often thus wrongly diagnosed by practicing physicians. By means of examination of the feces he raised the proportion of cholera cases reported among children from 22 to 35 per cent of the total cases. Cholera Derived from Carriers. Cholera spirilla from carriers have according to Zlatogoroff and others been shown to be as virulent for animals as those from cases, but this perhaps ought not to be taken as an indication of their virulence for man. While Pfeiffer gives several in- stances in which cholera was spread by carriers, the num- ber of definite cases recorded in medical literature is not large. A very striking one, however, is reported by Mac- rae. 3 In a hospital in Calcutta, 10 nurses, 3 patients and a sweeper developed cholera within 4 days. An examina- tion of 127 articles of food and drink demonstrated spirilla in 14 samples of water and milk, all of which had been handled by the servants. An examination of 12 servants 1 Gotschlich, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1906, LIII, 281. 2 McLaughlin, Philippine J. Sc., Manila, 1909, IV, Sec. B, 363. Macrae, Indian M. Gaz., Calcutta, 1909, XLIV, 361. 66 THE SOURCES AND MODES OF INFECTION showed that 2 were carriers, and spirilla were recovered from their hands. Since the possibility of the spread of cholera by carriers has been recognized, outbreaks of the disease have occurred in Russia and Germany, and both Russian and German ob- servers consider that carriers afford the best explanation of many of the phenomena of cholera outbreaks. The re- peated occurrence of the disease in the Philippines, since the occupancy of the islands by the United States, has given a splendid opportunity for the study of cholera epi- demiology, which has been well taken advantage of by our officials. Heiser and McLaughlin are firmly convinced that carriers are a most important factor in the spread of the disease. Indeed, McLaughlin says that their importance can hardly be overestimated. He has no doubt that chol- era is often spread from village to village by carriers, and that intervals between local outbreaks are bridged over by the same means. There is no evidence that the spirilla maintain a saprophytic existence in the soil or water of the islands. Chantemesse 1 says cholera was introduced into Italy in 1910 by a party of gypsies who arrived at Brindisi, July 27, from Batum. They then went to Trani, where the disease developed August 7. None of the party were sick. Cases developed in October in Marseilles after the arrival of im- migrants from the East, though there was no recognized sickness among them. On October 7 cholera developed on a ship which carried Russian emigrants from South- ampton 30 days after the latter had left Russia. The bag- gage in all these cases had been disinfected and the emi- grants themselves had been examined several times by physicians, who failed to find recognizable cholera. In 1911 there were five cases of cholera in the United States, of which only one had any connection with a pre- vious case. Shall we assume that dried and dying germs 1 Chantemesse, Bull. Acad. de m6d., Par., 1911, LXXV, 113. CARRIERS AND MISSED CASES 67 on clothing caused them, or living germs from a carrier? In 1893, at a time when a cholera ship lay in the harbor several miles from New York, a number of unconnected cases occurred in that city. Were they caused by flies, by floating mattresses or clothing, as was then supposed, or were they derived from a carrier from some other ship? Similarly, " sporadic " cases occurred in England at the same period. In 1873, at least three local outbreaks in the United States were traced to immigrants recently arrived from Europe at points in the interior. Then it was thought that the germs were brought in the baggage. To-day do not carriers seem a more likely explanation? In 1866, New York was the starting place of an extensive epidemic. From May to July there were only a few cases in the city not directly connected with any imported cases, nor often with each other. The epidemiologists of the day attrib- uted these cases to fomites, or the feces of recovered cases. Our present-day knowledge shows us how much more likely the latter is as a cause than the former, and vindi- cates the judgment of the men of that day who without the help of bacteriology surmised the existence of the " carrier." McLaughlin x says that in the Bilibid prison at Manila the food and water were so well controlled that the only entrance for cholera was by means of carriers. As soon as carriers were sought for and isolated the disease was stamped out. Bacillary Dysentery. There are two forms of dysen- tery, one caused by bacilli, the other by amebae. The dys- entery bacilli form a group of closely allied types, as the Shiga, the Flexner and the Harris types. Certain of the group are called pseudo-dysenteric but yet are pathogenic. What is commonly called dysentery may be caused by a number of different pathogens, and the dysentery bacilli may cause diarrheal symptoms quite different from typical dysentery. For the present purpose the whole dysentery 1 McLaughlin, N. York M. J., 1911, XCIII, 115. 68 THE SOURCES AND MODES OF INFECTION group of bacilli may be referred to without distinction. Collins 1 and Goodwin 2 have studied the occurrence of the bacillus in well persons. According to Collins, Flexner, Wollstein and others failed to find it in healthy persons. Duval 3 found it in 2 instances, and Charlton and Jehle 4 in 2 of 10 cases examined. Collins found it in 2 of 30 normal persons, and in 1 three weeks after an attack of dysentery, and in another child who had had a few raucous stools. Goodwin found the Flexner-Manila type of the bacillus in 1 of 59 well persons examined. Kruse 5 says that all types of the bacilli have been found in well persons, and that these carriers are an important cause of the disease. Though carriers have fewer bacilli in their feces, which are also less in volume, they come in contact with a larger number of persons than do the sick. There are also many mild atypical cases. Kruse has found the bacilli in relapses after two years, 6 and says that Drigalski and Lentz have made similar observations. He also cites Ford as finding 10 carriers among 50 persons examined. In an asylum outbreak Heuser 7 found 3 carriers. Conradi, 8 while study- ing a contact outbreak near Metz, found several carriers. Kuster 9 isolated bacilli from a carrier who had probably been excreting since an attack years before. Kruse cites Kriege as saying that about 4 of 36 cases of dysentery become chronic, but usually the infection lasts only 2 to 6 weeks. Conradi found- that in 4 of 27 cases the bacilli persisted up to the end of the fourth week, while in 11 cases they disappeared by the middle of the second week. Collins, Rep. Dept. Health, City of New York, 1904, I, 428. Goodwin, Rep. Dept. Health, City of New York, 1904, I, 423. Duval, Studies from Rockefeller Inst., 1904, II, 42. Charlton and Jehle, Tr. Ass. Am. 'Physicians, 1904, XIX, 405. Kruse, Med. Press & Circ., 1908, LXXXV, 175. Kruse, Klin. Jahrb., Jena, 1908, XIX, 529. Heuser, Deutsche med. Wchnschr., 1909, XXXV, 1694. 8 Conradi, Festschrift v. Robert Koch, 1903, 555. 9 Kuster, Miinchen med. Wchnschr., 1908, LV, 1833. CARRIERS AND MISSED CASES 69 Shiga 1 says that the bacilli generally remain 1 or 2 weeks, and that perfectly normal persons sometimes harbor the germs. Aveline, Boycott and McDonald 2 failed to find the bacillus in 27 contacts in an asylum. Cameron 3 also, and Macalister, 4 rarely found bacilli in perfectly healthy contacts. The latter writer found that 26 per cent of the cases studied by him in a certain asy- lum developed a mild chronic state or had relapses, and that these conditions only could be regarded as dangerous. These he considers as practically carriers, and says their importance cannot be overestimated. O. Mayer 5 has reported finding entirely healthy carriers, and one of these later became sick. The bacillus found was of the " pseudo- " type Y. In convalescents he found them persisting up to 202 days. The average persistence is 3 to 7 months. In healthy persons they were not found over 30 days. Intermittency of excretion was noted in both convalescent and healthy carriers. Chronic Plague in Rats. Bubonic plague is a disease which attacks not man alone but many other species of animals, particularly the rat. In fact it may be considered primarily a rat disease, and without doubt the rat is the most important agent in its diffusion. That mild cases and chronic cases exist among rats which superficially ap- pear not to be sick, seems to be proved. Simpson 6 says chronic plague was observed in some of the animals experi- mented on in Hong Kong, and by Albrecht and Ghon in guinea pigs, and in rats for months by Kolle and Martini. The Indian Plague Commission (1905) 7 found eleven of the 1 Shiga, Philippine J. Sc., Manila, 1906, I, 485. 2 Aveline, Boycott and McDonald, J. Hyg., Cambridge, 1908, VIII, 309. 3 Cameron, Brit. M. J., Lond., 1911, I, 973. 4 Macalister, Brit. M. J., Lond., 1910, II, 1506. 5 Mayer, Munch, med. Wchnschr., 1910, LVII, 2566. 6 Simpson, A Treatise on Plague, Cambridge, 1905, 129. 7 J. Hyg., Cambridge, 1907, VII, 379. 70 THE SOURCES AND MODES OF INFECTION rats which they had fed with plague bacilli to be infected, although they appeared to be perfectly well. While chronic plague has been seen in laboratory animals, several observers in Bombay and Sydney have failed to find it under natural conditions, as also did Blue in San Francisco. 1 But Hunter found rats with chronic plague in Hong Kong, and the In- dian Plague Commission (1905) found a number of rats in- fected with plague at a time when no rats with acute plague could be discovered, and when there was no outbreak among human beings. The infected rats showed no sign of sick- ness. 2 Later observations discovered similar instances of chronic rat infection in animals caught in a number of dif- ferent places. The pathological conditions indicated a slowly resolving rather than a true chronic process. Wat- kins-Pitchford 3 found the bacillus in convalescent rats and guinea pigs. It is evident that such chronic " carriers " may be an important factor in the maintenance and exten- sion of the disease. Atypical Human Plague. Among human beings mild cases of the glandular type are by no means uncommon. But fortunately these are rarely dangerous, for without suppuration there is no escape of bacilli. But in certain in- stances, later suppuration may take place, or lung symp- toms develop, so that the individual may become a focus of infection. 4 Rat " carriers/' on the other hand, are always dangerous, for they may at any time suffer accidental death, and their carcasses may then readily infect other animals and even man. Plague Bacilli in Convalescents. In the pneumonic type in human beings the bacilli are thrown off in large numbers 1 Blue, J. Hyg., Cambridge, 1909, IX, 1. * J. Hyg., Cambridge, 1906, VI, 530-535; 1907, VII, 373. 8 Watkins-Pitchford, Rep. of Bacteriologist, Pietermaritzburg, Natal, 1903 [Rep. on Flague, 31]. 4 Gotschlich, Kolle u. Wassermann, Handbuch, Jena [etc.], 1904, IV 1 , 69. CARRIERS AND MISSED CASES 71 from the lungs. Martin, 1 Gotschlich 2 and others have found them in the sputum up to 76 days after the attack, or 42 days after recovery. Gaffky 3 cites Vagedes as reporting pul- monary infection lasting 2 months in a case in Oporto, and bacilli in an abscess persisting more than 2 months, and Vages one lasting 4 weeks in Paraguay. The latter also isolated the bacilli from a man who later became sick with the disease. Shottelius found the germs in the bronchial secretion of mild ambulant cases. It is thus very probable that mild cases and true carriers among both rats and human beings may play a considerable part in the dissemination of this disease. White Diarrhea of Chicks. One form of diarrhea com- mon among young chickens appears to be due to a bacillus, B. pullorum. The nature and mode of spread of this dis- ease were well worked out by Rettger and Stoneburn. 4 It affects young chickens three or four days old and spreads among them by contact or infection of their food with excreta. Many of the survivors become carriers of the bacillus until after they have become mature hens. Such hens show few or no symptoms. The eggs which these carriers lay become infected in the oviduct, and chicks hatched from them develop the disease, though they never come in contact with frank cases. Similar observations have been made by Gage. 5 Note is made of this disease here not because it is transmissible to human beings, for so far as is known it is not, but because it is an excellent illustration of latency, and shows how efforts to suppress a disease are doomed to failure unless account is taken of the part played by carriers. No amount of isolation of chicks sick with this form of diarrhea can ever be successful in stamping out the disease. 1 Martin, Ann. de 1'Inst. Pasteur, Par., 1900. 2 Gotschlich, Ztschr. f. Hyg. Infectionskrankh., Leipz., 1899, XXXII, 402. 3 Gaffky, Klin. Jahrb., Jena, 1908, XIX, 491. 4 Rettger and Stoneburn, Storrs, Agric. Ex. Sta., Bull. 60 and 68. 6 Gage, J. Med. Research, Bost., 1911, n. s., XIX, 491. 72 THE SOURCES AND MODES OF INFECTION It is also interesting to note the analogy to ophthalmia neonotorum, which in many cases is due to mild, long- standing and unrecognized infection of the genital tract of the mother with the gonococcus. Mediterranean Fever. Mediterranean fever, like plague, appears to be a disease of the lower animals, only secondarily affecting man. The germ which is its cause may, like so many other pathogenic organisms, develop in the body with- out giving rise to symptoms. Goats appear to be the chief source of human infection. In 1905 there were 363 cases among the garrison at Malta, but in 1906, presumably owing to the cutting off of the supply of goat milk, there were only 35 cases; * and in 1907 it was practically exterminated. 2 An interesting account is given of an outbreak of the disease on a steamship, among persons who drank the milk of a herd of goats that were being brought to America. 3 The goats were not sick. Horrocks 4 shows that probably one or more animals in every herd are excreting the germs in the milk and urine, and that 50 per cent give evidence by serum reaction that they are, or have been, infected. Other in- vestigations show that as high as 10 per cent of milch goats have the germs in their milk, although they present no symptoms of the disease. Carriers are also common among human beings. Shaw 5 found that 10 of 525 well persons were excreting the germs in the urine. Ross, 6 of Port Said, found the bacillus not constant in either milk or blood. Meningococcus in Nose. While the germ of epidemic cerebro-spinal meningitis (Micrococcusmeningitidis) has been 1 Hewlett, Practitioner (Lond.), 1908, LXXX, 222. 2 Bruce, Nature, Lond., 1908, LXXVIII, 39. 3 U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 41, 203. 4 Horrocks, Rep. of Commission of Roy. Soc., 1905-6, Pts. Ill, IV. 6 Shaw, J. Roy. Army Med. Corps, Lond., 1906, VI, 638. Ross, J. Roy. Army Med. Corps, Lond., 1911, XI. CARRIERS AND MISSED CASES 73 known for many years, it is only very recently that any ex- planation has been forthcoming as to the mode of infection. The finding of the organism in the nose of patients suggests the possibility that infection may pass to the brain from this point. It is theoretically possible for infection to take place through the cribriform plate of the ethmoid bone, or, as sug- gested by Westenhoeffer, 1 by the lymphatics from the pha- ryngeal tonsils, or as some think, by absorption from the alimentary canal and passage through the lymph channels or the general circulation. The organism is certainly found in the blood in a considerable number of cases. 2 What the exact route to the brain is, however, has not yet been determined. That the germ of this disease is found in the nose of the sick is now generally recognized, though considerable doubt has been thrown on the accuracy of some of the earlier obser- vations, as this organism is not readily distinguished from the cocci frequently found in the normal nose. Culture and agglutination tests are now recognized as the only valid methods of differentiation. Among those who have certainly isolated it in a considerable number of instances from the nasal mucous membrane of cerebro-spinal meningitis cases may be mentioned Dunham, 3 Weichselbaum and Gohn, 4 Lin- gelsheim, 5 Goodwin and von Sholly 6 and others. Causes Rhinitis. That thismicrococcus is frequently found in the nose of contacts, and other persons showing no symp- toms of the disease, is now well established. An interesting case is that of Kiefer, 7 who while working with a culture in the laboratory developed a severe rhinitis and succeeded in Westenhoeffer, Berl. klin. Wchnschr., 1905, XLII, 737. Birnie and Smith, Am. J. M. Sc., Phila., 1907, CXXXIV, 582, and Simon, J. Am. M. Ass., Chicago, 1907, XLVIII, 1938. Dunham, J. Infect. Dis., Chicago, 1906 [Suppl. No. 2], 10. Weichselbaum and Gohn, Wien. klin. Wchnschr., 1905, XVIII, 625. Lingelsheim, Klin. Jahrb., Jena, 1906, XV, 373. Goodwin and von Sholly, J. Infect. Dis., Chicago, 1906 [Suppl. No. 2J, 21. 7 Kiefer, Berl. klin. Wchnschr., 1906, XXXIII, 628. 74 THE SOURCES AND MODES OF INFECTION recovering the micrococcus from his nose. A similar case was reported to me by P. E. Rauschenbach, at the time working in a hospital at Newark. Ford 1 also had a case of this kind. Meningococcus in Contacts. Among those who have found the organism in well persons may be mentioned Weich- selbaum and Gohn, 2 who obtained it in 3 of 24 persons exam- ined. Ostermann 3 found it in 17 of 24 contacts in Breslau, but his methods of employing the agglutination test have been called in question. One well child in whose nose the germs were found was taken sick three days later and died the next day. Many of the carriers had pharyngitis and rhinitis. Of 49 children in schools where these carriers at- tended, 2 showed the meningococcus, and one of these had been playing with a carrier. Ostermann failed to find it in 50 persons who had not come in contact with cerebro-spinal cases. Goodwin and von Sholly, in New York, obtained it in 5 of 45 contacts, and a similar coccus which did not agglu- tinate, in 2 of 55 medical students not contacts. Bolduan 4 found the organism in 10 per cent of 150 contacts. Lingels- heim, 5 during an extensive outbreak in Beulen, Prussia, found the organism in the nose of 26, or 9 per cent of 289 contacts. Later he found it in 4 of 56 school children, but all 4 came from families where there had been cases of the disease. In 2 of the 4 cases no agglutination test was applied. In the cases of the disease examined by Lingelsheim the micrococcus dis- appeared by the fifth day in 66 per cent, and by the sixth to tenth day in 24 per cent. In 4.39 per cent of the cases it per- sisted over three weeks, and in 1 case it was found three months from the beginning of the attack. 1 Quoted by Councilman, J. Am. M. Ass., 1905, XLIV, 999. 2 Weichselbaum and Gohn, Wien. klin. Wchnschr., 1905, XVIII, 625. 3 Ostermann, Deutsche med. Wchnschr., 1906, XXXII, 414. 4 Bolduan, Med. Times, N. Y., 1908, XXXVI, 193. 6 Lingelsheim, Deutsche med. Wchnschr., 1905, XXXI, 1017, 1217; Klin. Jahrb,, Jena, 1908, XIX, 519. CARRIERS AND MISSED CASES ^5 Infection in the Family. Bruns and Hohn 1 found that the proportion of carriers decreased as the outbreak decreased. This is shown in the following table: Reported Cases. No. of Families No. of Well Persons Examined. No. of Carriers. Per cent of Carriers. March 148 7 23 14 61 April 278 39 135 67 50 May 327 42 172 81 47 June 188 23 93 34 36 July . 146 21 67 18 27 August 68 22 119 10 8 5 They found that of the fathers in these families 60 of 113 carried the germs; of the mothers, 39 of 114; of children in the families, 118 of 360; and of other members of the families 7 of 22 were carriers. Persistence of Infection. Bruns and Hohn give for the duration of the infection the following: For 8 days 28 2 weeks 18 3 weeks 13 4 weeks.. 10 For 5 weeks 4 cases 6 weeks 3 7 weeks 3 8 weeks 1 case Selter, in Bonn, 2 has observed a very much longer persist- ence of the infection. In the case of a mother and daughter who recovered from the disease, the cocci persisted from February 3 to June 4. The father in this family, who had not been sick, yielded positive findings in May, June, July and August, and had in all probability been infective for seven months. In another family where the disease ap- peared, the 6 well persons were carriers at one time or another from February 18 to June 5, during which period 1 Bruns and Hohn, Klin. Jahrb., Jena, 1907-08, XVIII, 285. Selter, Klin, Jahrb., Jena, 1908-09, XX, 457. 76 THE SOURCES AND MODES OF INFECTION they were examined twelve times. Sometimes the examina- tions were positive and sometimes negative, which is just what occurs in the examination of typhoid and diphtheria carriers. This apparent intermittency may be due in part to faulty technique, and in part to the temporary absence of the bacteria. In the 69 examinations of the family above referred to, 49 were positive and 20 negative. Selter could find no difference between the cocci found in the sick and in the carriers, but he was not able to trace a case of sickness to any of his known carriers. Kirchner, 1 in Hamburg, found 22, or 9.7 per cent, carriers, out of 237 well members of infected families, but in 3 families all the mem- bers were carriers, and in 10 other families 75 per cent were. Most of these were adults. In two instances the infection persisted 44 and 66 days respectively. Vagedes 2 reports 3 cases in barracks at Charlottenburg. Of 58 hospital attend- ants, etc., there, 4 were carriers, and of 593 of the soldiers 10 only were carriers. On a second examination five days later 1 only was found, and nineteen days later none. By the iso- lation of carriers the disease was " stamped out," but it will be noticed that the infection was not widely diffused before it was recognized. Bochalli, 3 in certain barracks where the disease prevailed, found 10 of 16 roommates of the sick, or 62 per cent, to be carriers. Of 485 in other companies, 42, or 8.6 per cent, were infected. Usually the germs quickly dis- appeared, but in one case they persisted for four and a half months. In another instance a nurse, going to a district where there was no meningitis, was attacked about one month later. Similar observations have been made in several places during the recent outbreak in Scotland. Buchanan, 4 in Glas- gow, found the micrococcus in 81, or 26.3 per cent of 308 con- 1 Kirchner, Klin. Jahrb., Jena, 1908, XIX, 473. 2 Vagedes, Deutsche mil.-arztl. Ztschr., Berl., 1907, XXIII, 647. Bochalli, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1908, LXI, 454. 4 Buchanan, San. Rec,, Lond,, 1907 n, s,, XI, 245. CARRIERS AND MISSED CASES 77 tacts in 74 families. Most of them were over fifteen years of age. In 14 families he obtained it from more than one person, in 2 instances from five. In 4 instances it was found in the nose two years, one year, one year, and three months, respectively, after an attack. He quotes Arbuckle, medical officer of health of Partick, as finding 23.1 per cent of 230 contacts infected. In Leith, Fraser and Comrie 1 found it in 10, or 14 per cent, of 69 contacts. Of these 5 were adults whose children were sick, and all of whom had worked on a ship in the air of whose engine room meningococci were found. Bethge, 2 immediately after the appearance of the first case in a certain institution, found that of 187 persons 66 were carriers. Found only in Those near Sick. The micrococcus which is the cause of this disease, while frequently noted in contacts, is rarely found in those not exposed to the disease. Oster- mann, when there were no cases about, failed to find the germ in 50 children and in many adults. Bolduan did not find it in 150. Kolle and Wassermann 3 recovered the germs from 2 of 114 persons, but one had been in contact with the disease, and the other shortly became sick. Bochalli found none in 40 men in a non-infected regiment, Lingelsheim 4 none in 129 persons otherwise sick, and none in 184 non-exposed chil- dren, and he cite.s Droba and Kucera as finding none among 210 children living where there was no meningitis. In 23 per- sons not exposed to the disease and examined by Fraser and Comrie none of these organisms were found. Arkwright 5 failed to find them in 54 well persons, and Flexner 6 could find none in 50 persons in Philadelphia at a time when the disease was not present in the city. Fraser and Comrie, Scot. M. & S. J., Edinb., 1907, XXI, 18. Bethge, Deutsche med. Wchnschr., 1910, XXXV, 66. Kolle and Wassermann, Klin. Jahrb., Jena., 1906, XV, 507. Lingelsheim, Klin. Jahrb., Jena, 1906, XV, 373. Arkwright, J. Hyg., Cambridge, 1907, VII, 145. Flexner, J. Exper. M., N. Y., 1907, IX, 105. 78 THE SOURCES AND MODES OF INFECTION As Lingelsheim says, it appears that the nearer we approach cases of the disease the more numerous carriers are, and the more extensive the outbreak the more numerous they are. Adults are more commonly infected than children. Fliigge thinks that carriers are ten to twenty times as numerous as cases, and that is doubtless true. Infection by Carriers. That carriers are the chief source of the disease is the opinion of those Germans who have lately had experience in severe outbreaks, and it is shared by the Scotch health officers. Lingelsheim says that there is no bacteriological or epidemiological evidence to show that the sick are more dangerous than the well, otherwise tire cases would occur in groups. On the contrary the carriers mingling freely with the public are the most dangerous. Jehle x states that 23 cases occurred in children in the families of miners. None of the miners were sick, but when they were transferred to another mine, children there soon began to develop the disease. Their parents were doubtless carriers. Meyer 2 reports an instance where carriers gave rise to three cases. At Leith, Buchanan 3 says that the first few cases could be traced to carriers, and Thomson 4 makes a similar statement regarding the early cases in Lanarkshire. Flatten 5 gives the details of numerous instances of the transmission of the dis- ease by well persons. Carriers explain Spread of Disease. Previous to the dis- covery of the presence of the specific organism of cerebro- spinal meningitis in the nose, and particularly in the nose of contacts, the mode of extension of the disease was a mystery. Though certainly an infectious disease, and appearing in epi- demics, often quite severe, it was apparently only slightly if 1 Jehle, cited by Warrington, J. Roy. San. Inst., Lond., 1907, XV, 656. 2 Meyer, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1909, XLIX, 305. 3 Buchanan, Brit. M. J., Lond., 1907, II, 852. 4 Thomson, Med. Press & Circ., Lond., 1908, n. B., LXXXVI, 344. 6 Flatten, Klin. Jahrb., Jena, 1906, XV, 265. CARRIERS AND MISSED CASES 79 at all contagious. Personally, out of over a hundred cases, I have only twice seen two cases in the same family, and have, except in those instances, never been able to trace connection between any two cases. Cases are frequently treated in con- siderable numbers in general hospitals all over the world, and infection of others has rarely, if ever, taken place. In New York a greater degree of contagiousness has been noted than in most places. 1 Of 1500 consecutive cases, 112, or 7 per cent, were secondary cases in the family. It is said that when more than one case occurs in a family they all are usually taken sick at about the same time, 2 but this was not so in New York. The following shows the date at which the secondary cases appeared in that city: Where First Cases were removed to Hospital. Where First Case remained at Home No. of Secondary Cases. Interval. No. of Secondary Cases. Interval. 14 1-7 days 3 Iday 5 1-2 weeks 4 2 days 4 2-3 " 1 3 " 3 3-4 " 1 5 " 2 4r-5 " 1 6 " 3 5-6 " 4 7 " 2 7-8 " 1 9 " 1 3mos. 1 11 " 34 1 21 " 1 30 " 18 The 34 cases which developed after the removal of the primary case to the hospital indicate either that the germ of the disease remained in the house, on fomites, which is highly improbable, as its powers of resistance are extremely 1 Am. Pub. Health Ass. Rep., 1905, XXXI, 359. 1 Bolduan and Goodwin, Med. News, N. Y., 1905, LXXXVII, 1222. 80 THE SOURCES AND MODES OF INFECTION slight, or that unrecognized carriers, persons with the coccus growing in the nose, remained behind, a supposition which is entirely in accord with bacteriological findings. In Glas- gow, 1 of 194 cases, 7, or 4.1 per cent, were secondary cases in the family. Some of these occurred after disinfection. It is not unlikely that the more extensive the outbreak the more numerous will be the " secondary " cases in the family. In Oppeln, where there was a very severe outbreak, Flatten 2 found the number of secondary cases as follows in successive months of the outbreak: No. of Families. No. of Cases. January 71 79 February 143 163 March 257 296 April 310 368 May 349 414 June 374 439 If, as appears, the meningococcus is frequently found in the nose of sick persons and of contacts, the mode of exten- sion of the disease becomes apparent. Observations indicate that a very considerable number of persons who come in con- tact with cases of this disease carry the organism on their mucous membrane. Yet very few of these persons ever be- come sick. It appears that the development of the cerebro- spinal symptoms, that is the disease as we know it, is really a rather unusual accident of a not uncommon harmless infec- tion of the nasal passage. We can therefore understand how the disease, though apparently showing little contagiousness, is nevertheless a strictly contagious disease. It extends almost entirely through the agency of carriers. Sometimes, as was previously stated, these carriers can be discovered, particu- 1 Rep. Med. Off. Health, Glasgow, 1906, 89. Flatten, Klin, Jahrb,, Jena, 1906, XV, 228. CARRIERS AND MISSED CASES 81 larly early in an outbreak. The appearance of cases in dif- ferent localities in a community, and at varying intervals, is readily explained by, and is almost a proof of, the existence of a considerable number of undiscovered carriers. Meningitis an Accident of Infection. The growth of the germs in the nose cannot properly be considered the "incu- bation" of the disease. Inoculation experiments 1 indicate that the nervous symptoms develop in a very few hours after the specific bacteria are injected into the meninges. There is much evidence, as given above, to show that the germs may grow on the surface of the nasal mucous membrane for days, weeks and perhaps months, but when they once gain access to the meninges the symptoms of the disease speedily develop. Meningitis also occurs as a result of infection by the pneu- mococcus. The disease thus caused is not essentially different from the epidemic form. The number of well carriers of the pneumococcus is enormously greater, and is much more con- stant than is the number of carriers of the meningococcus, and the chance of the former invading the meninges and caus- ing sickness is small, very much less than the chance of the latter doing so. In either case it may be considered an unfor- tunate accident of a usually benign infection. Inutility of Isolation of Meningitis. If these views are correct, little can be done by means of isolation to prevent the spread of the disease. When an outbreak occurs, there is certain to be a large number of carriers that cannot be found or isolated. To isolate the sick, and even those in immediate contact with the sick, will probably never make any appreciable difference in the progress of the disease, that is if the findings of to-day are confirmed by more extended observations. By the time several cases have developed in a community, there will probably usually be a considerable number of carriers who cannot be found. Stringent isola- 1 Lingelsheim, Deutsche med. Wchnschr., 1905, XXXI, 1017, 1217; Flexner, J. Exper. M,, N. Y., 1907, IX, 142. 82 THE SOURCES AND MODES OF INFECTION tion of the families of known cases will accomplish little, will work much hardship and injustice. v^iflUit ^^ Diphtheria Bacilli in Well Persons. Loeffler ^himsel^in 1884 found diphtheria bacilli hi a person who was not sick, and in 1889 Roux and Yersin 2 called attention to the per- sistence of diphtheria bacilli on the mucous membranes of convalescents, and their observations were at intervals sub- stantiated by others. In 1894 Park and Beebe 3 examined the throats of 330 healthy persons who had not, so far as known, been in contact with diphtheria cases, and found diphtheria bacilli in 24, or 7.3 per cent, but of these only 8, or 2.4 per cent, of the 330 were virulent. These authors minimized the dan- ger to be apprehended from these carriers, and although for some time similar observations were reported, they were gen- erally, and are even now by many, considered of little impor- tance. It seems to me otherwise, and therefore a considerable number of these observations are here summarized. Muller 4 examined in routine 92 children sick with diseases other than diphtheria, in Heubner's clinic, and reported that 12, or 13 per cent, were infected with diphtheria, but only 6 of the 12 were tested on guinea pigs. Later 18 children in the same institution, who had negative cultures on admission, were found to harbor the bacilli. Kober 5 in Breslau found that of 600 school children 2.5 per cent were carriers of diphtheria bacilli, but in only 0.83 per cent of the 600 were they virulent. At Baltimore, 6 in 1899, during an exceptional prevalence of diphtheria in a number of schools, cultures were taken from 4068 pupils apparently well, and of these 157, or 3.8 per cent, 1 Loeffler, The Bacteriology of Diphtheria, Nuttall and Graham- Smith, Cambridge, 1908, 31. Roux and Yersin, Ann. de 1'Inst. Pasteur, 1890, IV, 385. 3 Park and Beebe, Med. Rec., N. Y., 1894, XLVI, 385; Sci. Bull. 1, Dept. Health N. Y. City, 1895. 4 Muller, Jahrb. f. Kinderh., 1896, XLIII, 54. 6 Kober, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXXI, 433. c Baltimore, Rep. Com. of Health, 1899, 96; 1900, 85. CARRIERS AND MISSED CASES 83 showed diphtheria bacilli. The next year, of 351 examined, 23, or 6.6 per cent, were positive. Varieties of Bacilli found. Reports of the finding of diph- theria bacilli in well persons would have more value if it were made clear what was meant by the term diphtheria bacilli. The bacillus varies greatly in form, and those who have studied it most carefully are by no means agreed as to what should or should not be properly so called. Fortunately Wesbrook's classification of all these varieties, both admitted and questioned, renders it possible to interpret properly the reports of all who will take the trouble to use his nomencla- ture, and it is to be regretted that more do not use it. Again, diphtheria bacilli are quite as frequently found in the nose as in the throat, but few observers state whether the cultures were taken from throat or nose or both. For the purpose of securing definite data from a large number of cases, a col- lective investigation was undertaken by the Massachusetts Association of Boards of Health. 1 The number of persons examined was 4250 in different parts of the United States. Most of them had probably not been directly exposed to diph- theria except in Minnesota, where most of the cultures were taken from schools and institutions where there had recently been cases of the disease. The majority of the persons ex- amined were adults, and cultures were taken from both throat and nose. Of all persons examined, 2.89 per cent had " granu- lar " forms of diphtheria bacilli, i.e., those showing polar staining with methylene blue. 'If " barred " and other aber- rant types are to be considered as diphtheria bacilli, as they are by some, the number of cultures to be reported positive would have been more than doubled. Referring only to the typical granular types, 1.46 per cent of all persons showed throat infection (either with or without concurrent nose infec- tion) and 2.07 per cent showed nose infection (either with or without concurrent throat infection). In the different cities the percentage of infected persons varied from 0.43 in Provi- i J. Mass. Ass. Bds. Health, Boat., 1902, XII, 74. 84 THE SOURCES AND MODES OF INFECTION dence, where particular care was taken to avoid contacts, most of the cultures being taken from schools where there had been no diphtheria for at least two years, to 3.66 in the Willard State Hospital, and 6.03 in Minnesota, in both of which localities there had recently been diphtheria in the institutions examined. There were 47 tests for virulence, of which 8, or 17 per cent, were positive. Recently cultures were taken from school children in Brighton (Boston) by Slack. 1 Of over 4000 children examined by throat and nose culture on two occasions, 1.93 per cent showed diphtheria bacilli. Of these 8 were tested for virulence, of which all proved to be non- virulent. Most of these children were excluded from school until free from bacilli, but all of them had, of course, been carrying bacilli in school for a longer or shorter period. No case of clinical diphtheria was traced to any of these carriers, either in school or out of school. These facts have been ad- vanced as evidence that the danger from such carriers is a negligible factor in contrast with the danger from conva- lescents whose bacilli are usually virulent. But in Providence in 1908, 73 convalescents carrying diphtheria bacilli were admitted to school, and it is not known that they were in any instance the source of new cases in the school, and in all but two or three instances it is certain that they were not. Forbes 2 cites Meikle as reporting 27 carriers discharged from the hospital without any return case. These facts merely in- dicate that the amount of danger from a single focus of infection is much less than is generally believed. Value of Bacteriological Findings. Neumann 3 could not find any diphtheria bacilli in 111 perfectly normal throats and noses, but did find them in 8 of 95 cases suffering from catarrhal inflammation of the mucous surfaces. He does not think that they are found in normal throats, but certainly all who have had any experience in taking cultures have seen 1 Slack, Arms, Wade and Blanchard, J. Am. M. Ass., 1910, LIV, 951. 2 Forbes, Brit. M. *J., 1909, II, 522. 8 Neumann, Ztschr.f.Hyg.u. Infectionskrankh., Leipz., 1902, XL, 33. CARRIERS AND MISSED CASES 85 numberless cases where diphtheria bacilli were found in throats which, so far as appearances go, were perfectly nor- mal. When diphtheria bacilli are found on a reddened or slightly inflamed mucous surface, the abnormal condition may not in every individual case be due to their presence, for certainly " catarrhal " inflammations of nose and throat, due to other causes than the presence of diphtheria bacilli, are extremely common. The evidence is that at present, in cities, from 1 to 2 per cent of the population are infected with diphtheria bacilli. The presence of diphtheria bacilli in an inflamed throat may be, then, in 1 or 2 per cent of the find- ings merely a coincidence. It is safe to assume that in all but 1 or 2 per cent the presence of diphtheria bacilli stands in causative relation to the inflammation of the surface on which they are found. Diphtheria Bacilli in Children. In Bristol, Heaven 1 ex- amined 704 children (throat and nose) connected with schools where there had been considerable diphtheria, and found diphtheria bacilli in 24, or 3.4 per cent. Of 758 cultures taken from schools in London where there had been occasional cases of diphtheria, 58, or 7.6 per cent, showed the bacilli. 2 Pen- nington 3 examined 375 well children in Philadelphia schools, in some of which there had been more or less diphtheria, and of 37 positive cultures from these, 24 were more or less viru- lent. Of 125 pupils from four other schools 10.4 per cent gave positive cultures, about half of which were virulent. But Pennington found that of 25 cultures from convalescents 22 were virulent. In the city of Mexico, of 300 school children 10, or 3.3 per cent, showed diphtheria bacilli. 4 Von Sholly 5 examined 1000 tenement-house children in New York, taking cultures only from those whose throats appeared normal. The Heaven, Pub. Health, Lond., 1902-03, XV, 516. Rep. Med. Off. Health, Lond., 1904, Appendix III, 25. Pennington, J. Infect. Dis., Chicago, 1907, IV, 36 Fabela, Rep. Am. Pub. Health Ass., 1906, XXXII, Pt. 2, 199. Von Sholly, J, Infect, Dis,, Chicago, 1907, IV, 337. 86 THE SOURCES AND MODES OF INFECTION children for the most part were those brought to hospitals and dispensaries for treatment, but all cases were excluded which had any suggestion of sore throat, nasal discharge, etc. Of these 1000 cases 5.6 per cent showed diphtheria- like organisms, of which, however, only 1.8 per cent (of the 1000 cases) proved to be virulent. In 50 of the cases nose cultures also were taken, and one of these proved to have virulent bacilli. During a very severe outbreak of diph- theria in Christiania, Ustvedt 1 examined 4277 school children, and found diphtheria bacilli in 191, or 4.5 per cent. Of these, 10 afterwards developed diphtheria. Of 7 cultures tested for virulence 4 were positive. In one school in which the per- centage of positive cultures was 9.2 during the outbreak, it was 3.2 some months later. In a school in the country where there had been no diphtheria for years, no bacilli were iso- lated from 86 pupils. Ruediger 2 found diphtheria bacilli in 3 of 51 normal throats. Gross 3 took two throat and nose cultures from 314 children (without diphtheria) on admission to the Children's Hospital in Boston, and isolated diphtheria bacilli from 26, or 7.9 per cent. Five were tested for viru- lence, 4 of which were positive. Hewlett and Murray 4 found that 58, or 15 per cent, of 385 children on admission to the Victoria Hospital for Children in London, were diphtheria carriers, and that in children under two years of age the per- centage was 21. Cobbett 5 at Cambridge reported diphtheria bacilli in 2.9 per cent of 650 well persons, many of whom were contacts. Some had mild sore throat. Diphtheria Bacilli in Scarlet Fever. While the presence of diphtheria bacilli in scarlet fever cases sheds little light on their prevalence in normal throats, it is of much interest 1 Ustvedt, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1906, LIV, 147. 2 Ruediger, J. Am. M. Ass., Chicago, 1906, XLVII, 1173. Gross, Univ. M. Mag., Phila., 1896-7, IX, 45. 4 Hewlett and Murray, Brit. M. J., Lond., 1901, I, 1474. 6 Cobbett, J. Hyg., Cambridge, 1901, I, 242. CARRIERS AND MISSED CASES 87 from an epidemiological standpoint. The exudation which frequently covers the tonsils in scarlet fever is often mistaken clinically for a sign of diphtheria, and such cases are, before the appearance of the eruption, often reported as diphtheria, so that there is a popular impression among physicians that the two diseases are frequently combined, and that the presence of scarlet fever predisposes to diphtheria. While bacteriolog- ical examinations tend to show that diphtheria infection on scarlet fever is not so common as is often assumed, and that many cases reported as a combination of the two diseases are not really such, yet diphtheria bacilli are frequently found in cases of scarlet fever, more frequently than they are found in the general public from whom the scarlet fever cases come. In Providence during the past four years cultures have been taken from 92 scarlet fever cases in their homes, of which 6, or 6.5 per cent, were positive. Of 245 cultures in the hospital, 26, or 10.6 per cent, were positive. During the pre- ceding three years 116 cultures were taken, but it was not recorded whether they were from hospital or home cases, and of these, 5, or 4.3 per cent, were positive. The excessive per- centage of positive findings in the hospital was due to infec- tion after admission. Both throat and nose cultures were taken in nearly every case. In the Western Fever Hospital of London, 1 of 1019 throat swabs taken from the same num- ber of scarlet fever patients on admission, 7.86 per cent were positive; at another hospital 5.41 per cent of 203 cases, and at another 6.8 per cent of 87 cases. Of the 939 cases at the Western Hospital which did not have diphtheria bacilli on admission, 6 later developed diphtheria, ranging from the ninth to the fiftieth day after admission, and 28 more acquired diphtheria bacilli without being sick. Of the 80 cases that entered infected, 4 developed clinical diphtheria on the fourth, fifth, seventh and thirty-first days. Soerensen 2 found that of 1 547 scarlet fever cases examined on admission, 38, or 1 Cumpston, J. Hyg., Cambridge, 1907, VII, 598. J Soerensen, Ztschr. f. Hyg. u. Infectionskrankh., 1898, XXIX, 250. 88 THE SOURCES AND MODES OF INFECTION 2.5 per cent, carried diphtheria bacilli. During a service of two years 32 cases of diphtheria occurred in the scarlet fever wards among about 1500 patients, and 208 others were found to be infected but not sick. Ruediger 1 found diphtheria in 4 of 75 scarlet fever throats, or 5.3 per cent. Garratt and Wash- bourn 2 found diphtheria germs in 8, or 1.2 per cent, of 666 scarlet fever cases. In Croydon, 3 37, or 17.3 per cent, of 213 cases of scarlet fever were shown to be infected with diph- theria bacilli on admission to the hospital. In Brighton, 4 in 1905, 33, or 25.9 per cent, of 166 cases of scarlet fever had diphtheria bacilli present, and all but one were infected on admission; in 1907, 21 of 340 were infected. In Bristol, 5 of 202 scarlet fever patients in the hospital in 1904, 75 per cent had positive cultures on admission. In 1905, of 476 cases, 21 , or 4.4 per cent, were positive, besides 3 others which showed symptoms of the disease. In Philadelphia, of 700 scarlet fever admissions, 11 per cent showed diphtheria bacilli. Percentage of Diphtheria Carriers. The evidence thus far adduced tends to show that diphtheria bacilli are quite widely distributed in the urban population of Europe and America. Perhaps on the average 1 or 2 per cent harbor the germs of this disease in mouth or nose; but observations also indicate that the less diphtheria there is in a community, and the farther removed the persons examined are from cases of the disease, the less likely they are to be infected. Thus in Christiania during an outbreak, 9.2 per cent of the pupils in a certain school were infected, while some months later the ratio was only 3.2. The Massachusetts Association of Boards of Health report an infection of 6.03 per cent of the school children recently exposed to diphtheria in Minneapolis, while in schools in Providence where there had been no diph- 1 Ruediger, J. Am. M. Ass., Chicago, 1906, XLVII, 1173. 2 Garratt and Washbourn, Brit. M. J., Lond., 1899, I, 893. 1 Rep. Med. Off. Health, Croydon, 1904, 68. 4 Rep. Med. Off. Health, Brighton, 1905, 42; 1907, 22. 6 Rep. Med. Off, Health, Bristol, 1904, 100; 1905, 71. CARRIERS AND MISSED CASES 89 theria for a long time the ratio was only about one-half of 1 per cent. Percentage among Contacts. There are numerous obser- vations made on persons brought more or less closely in con- tact with the sick, which show that under such conditions Percentage of Carriers in Diphtheria Families, Providence, 1897-1901. Ages. Persons ex- amined. Number of Carriers. Percentage of Carriers. Under 1 year .... 119 17 14.2 1 " 112 15 13.3 2 years 97 23 23.7 3 M ..... 112 25 22.3 4 " 116 31 26.7 5 " 120 17 14.1 6 " 137 42 30.6 7 " 130 30 23.1 8 " 119 25 21.0 9 " 113 23 20.3 10 " 139 26 18.7 11 " 79 11 13.9 12 " 127 28 22.0 13 " 86 15 17.4 14 " 88 13 14.7 15 " 70 5 7.1 16 " 64 9 14.0 17 " ' 57 9 15.7 18 " 57 6 10.5 19 " ..... 45 4 8.8 20 " 34 4 11.7 Adults 2505 277 11.0 Totals . . . 4526 655 14.4 the number of carriers may be very high. For several years in Providence l cultures were taken from all the wage earners in the family at the time the case was reported, and from all the members of the family for release, that is, to determine Rep. Supt. Health, Providence, 1901, 44. 90 THE SOURCES AND MODES OF INFECTION the end of isolation. Only throat cultures were taken. Of 4526 such contacts examined 14.4 per cent were found to be infected. If nose as well as throat cultures had been taken, and if cultures had been taken from the whole family about midway in the course of the disease, I imagine the percentage would have been several times greater. The preceding table shows the percentage infected at different ages. The women in the family were infected very much oftener than the men. It was noticed that in about 10 per cent of the cases some well member of the family remained infected after the patient was entirely free from germs. In Glasgow, 1 of 2305 contacts in infected families 9.2 per cent were carriers. Percentage of Carriers in Infected Schools. In a certain school in Minnesota, 2 of 263 well children, 129, or 49 per cent, were infected with the granular and barred types of the bacil- lus. In Bristol 3 during a school outbreak in 1907, of 190 well children, 12.5 per cent were carriers. At the Willard Hos- pital for the Insane during an outbreak, of 1423 well persons, 189, or 13 per cent, were carriers. At the State Hospital in California, 11.6 of 1115 persons were infected. 4 In Provi- dence during an outbreak of diphtheria in an infant asylum, of 175 children and adults, 116 or 66.2 per cent, proved to be infected at one time or another, but this was only after many repeated cultures extending over a period of some months. Many of them were persistent carriers, one of them remaining infected for twenty-two months. Crowley 5 in a school out- break found 42 of 93 children infected, or 45 per cent. In Bermondsey, London, 6 the children in diphtheria families have a single throat culture taken, and of 597 children so Rep. Med. Off. Health, Glasgow, 1908, 71. Wesbrook, St. Paul M. J., St. Paul, Minn., 1900, II, 219 [p. 6 of reprint]. Rep. Med. Off. Health, Bristol, 1907, 51. Rep. Calif. St. Bd. Health, 1906-08, 201. Crowley, J. Roy. San. Inst., 1904-05, XXV, 807. Rep. Med. Off. Health, London, 1904, 31. CARRIERS AND MISSED CASES 91 examined 64, or 10.8 per cent, were found to be infected. Of 115 well children in an institution in Minneapolis, Corbet 1 found 29, or 25.2 per cent, infected. In several instances the bacilli presented atypical forms, but many of these were viru- lent. In a school in the same city, where there had been some diphtheria, he found that 20, or 14.3 per cent, of 140 cultures showed the presence of typical bacilli. 2 Ustvedt, 3 in Chris- tiania, found 17 per cent of contacts infected. In a school at Oakland, California, 4 25 per cent of the pupils were carriers. In Glasgow, 5 of 322 well members of diphtheria families 10.5 per cent were infected. In the Duke of York's school, Lon- don, of 536 well pupils 117, or 20 per cent, showed diphtheria bacilli, and of these 10 later had diphtheria, while only one of the " free " boys developed it. Of 13 cultures from the well boys, 7 were virulent, though mildly so, but the bacilli from the sick also showed a low virulence. It is worthy of note that the disease recurred in this school for two or three years. 6 von Sholly 7 found bacilli in 20 of 202 contacts, or about 10 per cent, and of these 14 were virulent. Buchanan 8 in Glasgow found that the bacilli were virulent in 66 per cent of 21 healthy carriers, and that bacilli recovered from 56 cases of the disease proved virulent only in 74 per cent. Aaser 9 found 19 per cent of contacts in cavalry barracks in- fected, and 20 per cent of children in a scarlet fever ward. Hellstrom 10 in Stockholm, of 786 soldiers who had been more 1 Corbet, Rep. Com. Health, Minneapolis, 1905, 7. 2 Rep. Com. Health, Minneapolis, 1903, 16. 3 Ustvedt, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., 1906, LIV, 147. 4 Bull. Calif. St. Bd. Health, November, 1906. 6 Rep. Med. Off. Health, Glasgow, 1906, 135. 8 Arkwright, J. Hyg., Cambridge, 1908, VIII, 48 ; Rep. Med. Off. Health, Lond., 1906, 36. 7 von Sholly, J. Infect. Dis., Chicago, 1907, IV, 337. 8 Buchanan, Brit. M. J., Lond., 1909, II, 519. 8 Aaser, Deutsche med. Wchnschr., 1895, XXI, 357. 10 Hellstrom, cited by Kober, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXXI, 433, and by Fibiger, Berl. klin. Wchnschr., 1897, XXXIV, 753, 92 THE SOURCES AND MODES OF INFECTION or less in contact with diphtheria, found 151, or 19.2 per cent, infected. Goadby, 1 in 586 pupils in a school where there had recently been 21 diphtheria cases, found that 190, or 34.1 per cent, were carriers, and he quotes Meade Bolton as finding 45.5 per cent of 214 contacts infected. Of the children ex- amined by Goadby 262 had enlarged tonsils and 196 abnor- mal throats. In another school where there had been no reported cases, 18 of 100 were infected. Berry and Washbourn 2 report 17, or 11.9 per cent, of infected contacts in a school of 142 girls. Lister 3 found 48 per cent of 125 contacts in Shadwell Hospital infected. Twenty-four of them had nasal discharge. Park and Beebe 4 in a foundling asylum obtained virulent bacilli* and one non- virulent form from 5 of 55 contacts. Fibiger, 5 during a school outbreak of diphtheria, recovered the bacilli in 22, or 16.4 per cent, of 134 children. Denny 6 found 11 per cent of 200 chil- dren infected, in a school where there had recently been 4 cases of diphtheria, and Graham-Smith, 7 10.4 per cent of 519 school children. Gabritschewsky 8 in the Russian military service found, during the prevalence of diphtheria, that 20 per cent of the well persons examined were carriers, and in a school in Moscow, at a time when there was much diphtheria, 21 of 66 well children showed diphtheria bacilli. Atypical Diphtheria. The old notion was, and I fear that very many physicians and not a few health officers so believe to-day, that diphtheria is a well defined disease with charac- teristic symptoms. They cannot imagine diphtheria without 1 Goadby, Lancet, Lond., 1900, I, 236. 2 Berry and Washbourn, Brit. M. J., Lond., 1900, I, 198. 1 Lister, Erit. M. J., Lond., 1898, II, 1338. 4 Park and Beebe, Med. Rec., N. Y., 1894, XLVI, 385. 6 Fibiger, Berl. klin. Wchnschr., 1897, XXXIV, 753. 8 Denny, Bost. M. & S. J., 1900, 515. 7 Graham-Smith, J. Hyg., Cambridge, 1903, III, 216. 8 Gabritschewsky, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1901, XXXVI, 45. CARRIERS AND MISSED CASES 93 serious illness. There always have been, however, some acute clinicians who thought otherwise. Jacobi in New York was among the foremost. He recognized that the disease often presented a mild type and that diagnosis was impossible. He said in 1884 1 1 "The symptoms are often but few. A little muscular pain and difficult deglutition are, perhaps, all that is complained of. Women will quietly bear it; men will go about their busi- ness. . . . There is as much diphtheria out of bed as in bed; nearly as much out of doors as indoors. Many a mild case is walking the streets for weeks without caring or thinking that some of his victims have been wept over before he was quite well himself. . . . Diphtheria is contagious. Severe forms may beget severe or mild forms. Mild cases may beget mild or severe cases." Under Jacobi's teaching I early learned to look for such mild cases, and I remember seeing an outbreak in a children's home during the early eighties, in which there were many very mild sore throats and walking cases. Mild diphtheria of this type does not usually come to the notice of a physician, and when it does is frequently not recognized. How fre- quent such cases are it is difficult to determine, but they must be very numerous. In a general hospital at Chelsea 2 (Lon- don), where there had been considerable trouble from out- breaks of diphtheria, it was determined to take cultures from all patients admitted who showed any symptoms of sore throat. Of 815 persons so examined 65, or 7.3 per cent, gave positive cultures. In New York City 3 the school inspectors were directed to take cultures from all children showing slight redness of the throat or hypertrophied tonsils." -Of 11,451 cultures 757, or 6.7 per cent, were positive. Thefc,j children were not in any sense considered as ill, yet the percentage 1 Quoted by Solis-Cohen, J. Am. M. Ass., Chicago, 1907, XLIX, 32. 2 Parkes, Pub. Health, Lond., 1902-03, XV, 538. 3 Letter from Dr. Cronin, N. Y. Bd. Health, Sept. 23, 1904. 94 THE SOURCES AND MODES OF INFECTION infected is certainly much higher than would be looked for among the general school population. In Hartford 1 during the years 1900-1903 cultures were taken from 2038 mild sore throats seen in the schools. Of these, 591 , or 29 per cent, were positive. These children might be said to have a decided sore throat, though they were all well enough to be in school. They were all excluded from school. During the same period there were reported in Hartford 1537 cases of diphtheria, so that the cases found in the manner described equaled one- third of the total cases. In Indianapolis, 2 at a time when there were 60 reported cases of diphtheria in the city, a dili- gent search for, and taking of cultures from, sore throats among the school children revealed the presence of 46 other cases. Every one knows how extremely common sore throat and tonsillitis are, and even if only a very small proportion, much less than 29 per cent, of these, are true diphtheria, the number in the aggregate must be very large. I think I am well within bounds when I assume that for every recognized case of diphtheria there is at least one sore throat which is also diph- theria though unrecognized. Judging from the proportion of mild cases in institution outbreaks, the proportion of unrec- ognized, mild, but yet clinical cases, must be much greater than that. Careful medical inspection often discovers that these missed cases have been the source of reported cases. For example, the Report on the Health of the City of Man- chester (England), 1906, gives a list of 29 cases caused in this way during that year. Rhinitis and Otitis. Diphtheria sometimes assumes a chronic form with few symptoms. Indeed some, as Neumann, believe that long persistence of diphtheria bacilli in throat and nose is always accompanied by local disturbance. That such is often the case in the nose, and that subacute chronic rhinitis may be a form of diphtheria, and may give rise to typical pharyngeal cases, is generally recognized. 1 Reps. Bd. Health, Hartford, 1900 to 1903. 2 Rep, Dept. Pub, Health & Charities, Indianapolis, 1908, 8. CARRIERS AND MISSED CASES 95 Park, 1 Abbott, 2 Ravenel, 3 Schaps, 4 Treitel and Koppel, 5 DeStella, 6 Ballin 7 and many others report cases of chronic rhinitis due to the presence of the diphtheria bacillus. The middle ear sometimes suppurates in diphtheria, as it does in scarlet fever, though less frequently, and this discharge may remain virulent for long periods. 8 I happen to have such a case under observation at the present time. A Real Danger. There can be no doubt, then, that mild and unrecognized cases of diphtheria are very common, that convalescents long harbor the bacilli, and that contacts and other carriers are very numerous; in fine, that these sources of infection far outnumber the cases of recognized sickness. But are these really sources of infection, or are they, as so many believe, an imaginary danger evolved in the brain of the laboratory worker ? It is well again to emphasize the fact that long before Klebs and Loeffler identified the bacillus of this disease a few able clinical observers like Jacobi be- lieved that evidence pointed clearly to the great danger of these unrecognized sources of infection. The bacteriologists have not raised the bugaboo of carrier infection, they have simply explained the facts which observing men have long recognized. Carriers cause Disease. A little perusal of medical liter- ature will show that many cases are reported of what is apparently the distribution of diphtheria by carriers. Peck 9 reports an instance where a young man who was 1 Park, Med. Rec., N. Y., 1892, XLII, 121. 2 Abbott, Med. News, Phila., 1893, LXII, 505. Ravenel, Med. News, Phila., 1895, LXVI, 537. Schaps, Arch. f. Kinderh., Stuttg., 1905, XL, 80. Treitel and Koppel, Arch. f. Kinderh., Stuttg., 1895-96, XIX, 107. DeStella, Arch, internat. de laryngol. [etc.], Par., 1903, XVI, 970. Ballin, Jahrb. f. Kinderh., 1903, LVIII, 412. Newsholme, Rep. Med. Off. Health, Brighton, 1906, 13; Address at Victoria Univ., Manchester, March 9, 1904, 21. '.Peck, Brit M. J.. Lond., 1895, I, 971. 96 THE SOURCES AND MODES OF INFECTION perfectly well but was a carrier, probably gave diphtheria to another young man with whom he slept. In 1897 a mother whom I saw, stayed for a few days in a house on a neighboring street taking care of a diphtheria case. Soon after her return home her son was taken sick with diphtheria, and when cultures were taken from her throat she also was found to be infected. 1 In 1905 a child who was sent to the hospital for some surgical lesion developed scarlet fever and was removed to the scarlet-fever ward. Three days after his return home another child in the family was taken sick with diphtheria, and a few days later a culture taken from the first child was positive. 2 Wesbrook 3 reports: " Two always well children carrying bacilli sent home. Diphtheria broke out shortly after their arrival. No other source of infection discovered. One always well girl carrying diph- theria bacilli went to her home. Stepmother and children developed diphtheria within a few days. This family was practically isolated in the country." Hellstrom, 4 during a diphtheria outbreak in a cavalry regi- ment, noted two instances in which perfectly well soldiers who had diphtheria bacilli on their mucous membrane car- ried the disease to others. Aaser 5 reports a child with diph- theria germs taking the disease home from a scarlet-fever ward where there was a diphtheria outbreak. In 1906 at Birmingham 6 there was a milk outbreak of diphtheria of 13 cases due to infection of the milk by the milk handlers, who had diphtheria bacilli in their throats, but were not sick. As soon as they were isolated the outbreak ceased. Similar milk outbreaks caused by infected well per- 1 Rep. Supt. Health, Prov., 1897, 21. 2 Rep. Supt. Health, Prov., 1905, 32. 3 Prelim. Rep. on Diphtheria in Well Persons, J. Mass. Ass. Bds. Health, Bost., 1901, XI, 10. 4 Hellstrom, cited by Fibiger, Berl. klin. Wchnschr., 1897, XXXIV, 753. 5 Aaser, Deutsche med. Wchnschr., 1895, XXI, 357. 6 Rep. Med. Off. Health, Birmingham, 1906, 40. CARRIERS AND MISSED CASES 97 sons have been reported from Fitchburg, 1 Lowell, 2 Brookline, 8 Montclair, N. J., 4 Oroville, Cal., 5 Australia 6 and other places. At the Willard State Hospital 7 a watchman, who lived with his son-in-law in the village, who had diphtheria, was never sick but was a carrier. He played cards with two clerks, and they all drank from the same pitcher. The clerks, who had not been exposed to diphtheria, were a week later taken sick with the disease. Four other instances of infection by carriers occurred during the same outbreak, and a similar instance some years before. In Lagrange Co., Ind., 8 in 1902, there were three outbreaks in a school, apparently caused by the teacher, in whose nose diphtheria bacilli were found, and who had shown no symp- toms but a slight cold. In Boston 9 a boy who had recovered from diphtheria, escaped from isolation and went to Brock- ton, and within four days three clinical cases developed in the house where he visited. Fischer 10 reports an outbreak traced to a restaurant in which were several carriers and mild sore throats. Solberg 11 had a boy who caused several cases of the disease. He had been kept in the hospital for several months, but was finally discharged with the bacilli present. Cob- bett's 12 outbreak in Cambridge was due to a boy apparently 1 Prelim. Rep. on Diphtheria in Well Persons, J. Mass. Ass. Bds. Health, Bost., 1901, XI, 9. 2 Rep. Bd. Health, Lowell, 1904, 24. 3 Prelim. Rep. on Diphtheria in Well Persons, J. Mass. Ass. Bds. Health, Bost., 1901, XI, 9. 4 Pediatrics, N. Y., 1901, XII, 366. 5 Rep. St. Bd. Health, Cal., 1906-08, 198. 6 Armstrong, Austral. M. Gaz., Melbourne, 1908, XXVII, 350. 7 Report of Epidemic of Diphtheria at Willard State Hospital by Russell and Salmon [Rep. State Com. on Lunacy, XVI], 35 of Reprint. 8 Letter from Dr. H. N. Hurty, Sec. Ind. St. Bd. Health, 1907. 9 Prelim. Rep. on Diphtheria in Well Persons, J., Mass. Ass. Bds. Health, Bost., 1901, XI, 9. 10 Fischer, Miinchen med. Wchnschr., 1906, LIU, 250, 314. 11 Solberg, quoted in Pub. Health, Lond., 1902-03, XV, 515. 12 Cobbett, J, Hyg., Cambridge, 1901, I, 229, 98 THE SOURCES AND MODES OF INFECTION well, but who for some weeks had had a slight nasal discharge in which diphtheria germs were present. Williams 1 notes a case in which a teacher was infected with clinical diphtheria by the nasal discharge of a pupil containing atypical bacilli. 2 Newsholme 3 saw a case of diphtheria in February, 1901, which had ear discharge for a short time only. Suppuration recurred April, 1904, and diphtheria germs were present. Three cases of the disease occurred in the family soon after. The ear again discharged in March, 1906, with bacilli pres- ent, and a sister apparently contracted the disease from this source. Newsholme had a similar case in 1907. Vance* states that a nurse had diphtheria in June, and after one negative culture from the throat, went home and infected 3 persons. In August she returned to the hospital and infected 4 other persons, at which time a culture from throat and nose was negative. Subsequent cultures proved positive, and continued so until late in November. Strain 5 also reports a nurse in whose nose diphtheria bacilli were found intermit- tently for nine months, but they were never present in the throat. Edsall 6 notes five outbreaks due to carriers, and Solis-Cohen 7 seven such outbreaks. Cameron 8 reports that in 70 instances cases of scarlet fever discharged from the Lon- don hospitals carried diphtheria to their homes, and that in many of these carriers diphtheria bacilli were shown to be present. Similar cases in which clinical diphtheria is apparently con- tracted from perfectly well convalescents or carriers, or from slight unnoticed sore throat, or from rhinitis, are found scat- 1 Williams, J. Laryngol., Lond., 1905, XX, 591. Wesbrook's W. Newsholme, Rep. Med. Off. Health, Brighton, 1906, 13. Vance, Intercolon. M. J. Australas., Melbourne, 1908, XIII, 152. Strain, Lancet, Lond., 1908, II, 1143. Edsall, J. Am. M. Ass., Chicago, 1909, LII, 125. Solis-Cohen, J. Am. M. Ass., Chicago, 1909, LII, 111. Cameron, Rep. to Asylums Bd. on Return Cases of Scarlet Fever in London, 1901-02, 41. CARRIERS AND MISSED CASES 99 tered through medical literature, and a number of such have been collected by the Massachusetts Association of Boards of Health, 1 .Nuttall and Graham-Smith, 2 Newsholme, 3 Sit- tler, 4 Niven, 5 Schneider, 6 myself 7 and others. Chronic Diphtheria. Diphtheria sometimes assumes a chronic form, with few constitutional symptoms, and little that is noticeable, and nothing that is characteristic in the fauces. This condition may continue for months, and is sometimes accompanied by considerable antitoxin in the blood. Such cases may cause typical diphtheria. 8 Glanders. According to veterinary writers 9 the infec- tion of glanders often remains latent, and also many mild chronic cases occur which are the source of considerable out- breaks. The Bureau of Animal Industry 10 reports an instance where a horse was apparently infectious for eight years with- out manifesting any symptoms which would lead even an expert to suspect the infection. Another instance was given of a year-long infection of an apparently well animal. Influenza. The rapidity with which epidemic influenza spreads, its sudden contemporaneous appearance at many distant points, and the difficulty of tracing the route of infec- tion, render it almost certain that there must in this disease be many mild atypical cases, and many persons infected, but showing no symptoms. That the disease is not carried by 1 Prelim. Rep. on Diphtheria Bacilli in Well Persons, J. Mass. Ass. Bds. Health, Host., 1901, XI, 9. 2 Nuttall and Graham-Smith, The Bacteriology of Diphtheria, Cam- bridge, 1908, 311. 3 Newsholme, Address at Victoria Univ., Manchester, Mar. 9, 1904, and Med.-Chir. Tr., Lond., 1904, LXXXVII, 549. Sittler, Miinchen med. Wchnschr, 1906, LIII, 863. Niven, Rep. on the Health of Manchester, 1908, 204. Schneider, Ztschr. f. Med.-Beamte, Berl., XX, 698. Rep. Supt. Health, Prov., 1897, 19; 1898, 23; 1905, 32. Neisser and Kahnert, Deutsche med. Wchnschr., 1900, XXVI, 525, and Neisser, Deutsche med. Wchnschr., 1902, XXVIII, 719. 9 Law, Text-Book of Veterinary Medicine, Ithaca, 1902, IV, 235. 10 U. S. Dept. Agric., Bu. An. Ind., Circ. No. 78, 4. 100 THE SOURCES AND MODES OF INFECTION the air over long distances, as has been urged by many, but is invariably transmitted by persons, has been shown by Par- sons, Schmid and others. That these persons often show no symptoms, and are not suspected of being carriers, also seems certain. There is some bacteriological evidence of this, but the bac- teriologists have not given to the study of this disease the attention which it deserves. Finkler found the bacillus in the sputum a year after the beginning of an attack. Lord, 1 during non-epidemic periods, in examining cases of what appeared ordinary cough, found influenza bacilli present in 60 per cent of the cases. Later, 2 in 186 non-tuberculous cases, mostly bronchitis, he found the bacillus frequently present, often in almost pure culture. Boggs 3 has also found chronic cases somewhat simulating tuberculosis, in one instance last- ing for a year. Holt, 4 in the Babies' Hospital in New York, obtained 112 positive cultures out of 312 taken from 198 persons. Of 48 healthy persons 16 yielded positive cultures. I have found scarcely any other reports of the examination of well persons for this organism, but the frequency with which it is found in those sick with other diseases is evidence of the widespread distribution of the bacillus. Wollstein, 5 by swabbing the throat, found the bacillus in 16 of 37 cases of pneumonia, in 11 of 34 of bronchitis, in 8 of 18 cases of measles, in 8 of 16 of tuberculosis, but only 5 times in 65 cases of other diseases. Davis 6 found influenza-like bacilli in normal throats, and in 61 of 68 cases of whooping cough and in 13 of 23 cases of measles. Inoculated on the mucous surface of a healthy young man, fever and catarrhal symptoms devel- oped. Both Davis and Wollstein consider that the so-called 1 Lord, Boston M. & S. J., 1902, CXLVII, 662. 2 Lord, Boston M. & S. J., 1905, CLII, 574. 3 Boggs, Am. J. M. Sc., Phila., 1905, n. s., CXXX, 902. 4 Holt, Am. J. Obst., N. Y., 1909, LX, 343. 6 Wollstein, J. Exper. M., N. Y., 1906, VIII, 681. 6 Davis, J. Am. M, Ass., Chicago, 1907, LXVIII, 1563. CARRIERS AND MISSED C'AgES 101 pseudo-influenza bacilli in their different forms are of the same " species " as the typical forms. Others have found the bacillus in other infectious diseases, as Leibscher l and Auerbach, 2 the latter of whom obtained it in 5.4 per cent of 700 cases of diphtheria, scarlet fever, etc. The Coccus of Pneumonia. That the pneumococcus is present in the saliva of normal mouths was early recognized by Pasteur, Sternberg, Welch and others, and is, of course, a now well-established fact. Recently a number of careful observations have been made to determine the frequency of its occurrence, its virulence, and variations in form and habits of growth. Buerger 3 found it present in 50 per cent of 78 normal mouths, and in 34.8 per cent of 204 normal throats not so carefully examined. He also found that it could be recovered for weeks from convalescents. Of the cultures from normal mouths 79 per cent proved virulent. Hiss 4 found it in 14 of 22 persons, and Duval and Lewis 5 in all of 24 per- sons about the laboratory. Longcope and Fox 6 obtained it in 40 per cent to 50 per cent of mouths examined. It was more often found and more virulent in winter. Frost, Divine and Reineking 7 found it in 36 per cent of healthy mouths, 23 per cent in autumn, 43 per cent in winter and 50 per cent in the spring. The organism may persist in the same individual for months. Park and Williams 8 report the pneumococcus as prevalent both in city and country, as do others, but note that germs from normal mouths are less virulent for rabbits 1 Leibscher, Prag. med. Wchnschr., 1903, XXVIII, 85. a Auerbach, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1904, XLVII, 259. Buerger, J. Exper. M., N. Y., 1905, VII, 497. < Hiss, J. Exper. M., N. Y., 1905, VII, 547. 6 Duval and Lewis, J. Exper. M., N. Y., 1905, VII, 473. Longcope and Fox, J. Exper. M., N. Y., 1905, VII, 430. 7 Frost, Divine and Reineking, J. Infect. Dis., Chicago, 1905 fSuppI. No. 1], 298. 8 Park and Williams, J, Exper. M,, N, Y., 1905, VII, 403, 102 THE SOURCES' ''AWJJ 'MODES OF INFECTION than those from cases of pneumonia. Wells 1 found pneu- mococci in the throat or upper respiratory passages in 45 per cent of 135 persons, and Besser 2 found them in 14 per cent of the noses of 57 well persons, and Hasslauer 3 in 24 of 111 normal noses. Ruediger 4 got positive results in 90 per cent of 51 normal throats, in 91.4 per cent of 71 scarlet fever throats, in 12 of 14 cases of measles, and in 8 of 9 cases of tonsillitis, or pharyngitis. Gonorrhea. That gonorrhea assumes a latent form in both men and women, showing no signs whatever for con- siderable periods, and relapsing into a subacute or even acute condition after it was supposed to be cured, has long been known. But it is only since the discovery of the gonococcus that the latency of this infection, as well as its persistence, has been fully appreciated, just as it has only been the rec- ognition of this coccus which has shown the serious patho- logical changes in important organs which often follow gonorrhea. There has also been demonstrated recently the frequent innocent transmission of the disease among young children. All the text-books and monographs dealing with gonorrhea dwell on these facts, and refer to the finding of the germ in cases long supposed to be well, and to its per- sistence for long periods of time. 5 A physician told me of a case lasting from the third year of life to the twenty-eighth. Some striking instances of the latency of gonorrhea are given by Chapman, 6 and he has shown me records of many more in which unsuspected infection had lasted for many years. The same author states that the gonococcus may be encysted 1 Wells, J. Am. M. Ass., Chicago, 1905, XLIV, 361. 2 Besser, Beitr. z. path. Anat. u. z. allg. Path., Jena, 1889, VI, 331. 8 Hasslauer, Centralbl. f. Bakteriol. [etc.], 1st Abt. Ref., Jena, 1905, XXXVII, 1. * Ruediger, J. Am. M. Ass., Chicago, 1906, XLVII, 1171 6 Wertheim, Arch. f. d. Geburtsh., Jena, 1902, XLII, 192. 6 Chapman, Fiske Fund Prize Essay, Providence, 1905, The Sequel of Gonorrhea, etc., 31. CARRIERS AND MISSED CASES 103 Or dormant in tubal or ovarian tissue indefinitely. Rathbun and Dexter 1 from a clinical and careful bacteriological study of cases show that infection often persists long after the patient is apparently cured, and that such uncured cases are far more common than is generally believed. Hamilton 2 refers to the difficulty of demonstrating the coccus in mild and chronic cases, and states that such cases are very com- mon. Nottshaft 3 followed 120 cases of gonorrhea and ob- tained the gonococcus from 73 per cent during the second six months. During the fourth six months the percentage fell to 18, and in the third year the gonococci still per- sisted in 6 per cent of the cases. This latency is the chief cause of innocent marital infections. It is also one reason why the medical supervision of prostitution can never have much effect in restricting the disease. No practicable amount of inspection would ever guarantee freedom from infection. Tubercle Bacilli in Mouth and Nose. There are two conditions under which tubercle bacilli may exist in human beings without appreciable symptoms. First, they may be found on the mucous surfaces of mouth, throat, or nose. Straus 4 examined the nose of 29 well per- sons, orderlies, nurses and physicians about tuberculosis wards, and recovered tubercle bacilli from 9. .Cornet found them in his own nose. 5 Jones, 8 by inoculating animals with mucus from the nose of 31 persons not brought into par- ticularly close contact with consumptives, demonstrated the presence of tubercle bacilli in 11. Similar results have been 1 Rathbun and Dexter, N. York M. J. [etc.], 1909, XC, 241. 2 Hamilton, J. Infect. Dis., Chicago, 1908, V, 134. 3 Nottshaft, Die Chronische Gonorrhea der Mansliche Harnrohre, Leipzig, 1905. 4 Straus, Arch, de med. exper. et d'anat. path., Par., 1894, VI, 633. 5 Cornet, Nothnagels Encyclopedia, Phila. and Lond., 1907, Tuber- culosis, 152. Jones, Med. Rec., N. Y., 1900, LVIII, 285. 104 THE SOURCES AND MODES OF INFECTION reported by Moller l and Bernheim. 2 Persons in the vicinity of consumptives must, unless great care be taken, receive a certain number of tubercle bacilli upon their mucous sur- faces. Whether they increase in numbers in such a location is not shown by the observers quoted, but unless they do it seems rather surprising that they can be demonstrated in such a proportion of cases. On the other hand, it does not seem likely that conditions in the mouth and nose are favor- able for the growth of this bacillus, and the weight of evi- dence seems to be that the tubercle bacillus does not, to any extent at least, develop on the normal mucous membrane of the throat or nose of well persons. Blair 3 reports finding tubercle bacilli in the nose of various wild animals in captivity. Latent Tuberculosis. That the tubercle bacilli invade the tissues and, creating little disturbance, remain latent for a considerable period of time, has been amply demonstrated. While there are not many who believe that this latency is so universal or so persistent as does von Behring, yet it is certainly not a rare phenomenon. L. Rabinowitsch 4 in a recent article gives a short resume* of the work of various observers, and Harbitz 5 has also discussed it in an article on tuberculosis of children. Harbitz, in 142 autopsies of chil- dren who were clinically free from tuberculosis, and in whose glands no macroscopic or microscopic signs of the disease could be seen, nevertheless was able by inoculation to dem- onstrate the presence of virulent tubercle bacilli. Rabino- witsch reports four cases of virulent bacilli in lymph glands that had undergone calcareous degeneration, thus indicating a long-standing latency. Many similar observations by other 1 Moller, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXXII, 205. 2 Bernheim, Clinique, Brux., 1905, XIX, 346. 3 Blair, J. Comp. M. & Vet. Arch., 1903, XXIV, 278. 4 Rabinowitsch, Berl. klin. Wchnschr., 1907, XLIV, 35. 6 Harbitz, J. Infect. Dis., Chicago, 1905, II, 143. CARRIERS AND MISSED CASES 105 writers are given by those just quoted, and Gaffky * has recently reported finding the glands of 11 per cent of 246 well persons as containing living bacilli, demonstrated by inocu- lation tests. Tubercle bacilli are found in the tonsils as well as in the lymph glands. Lartigau and Nicoll 2 found infected adenoids in 12 of 75 healthy children, and Weichselbaum and Bartel, 3 Goodale 4 and Cornet 5 report similar findings. Leprosy. Sticker says that lepra bacilli often remain latent in the nose for long periods. Bacteria of Suppuration, Latency. As has been stated on page 20, pus bacteria are normal inhabitants of the skin and mucous surfaces, and may even invade the glands and other deeper tissues and remain latent for long periods of time. They may later, as the result of traumatism, be carried by the circulation to distant organs, there causing suppuration. 7 Among those who have demonstrated the latency of infection with pus-forming bacteria may be mentioned Manfredi and Viola, 8 Kalble, 9 Perez 10 and Hess. 11 Conradi 12 seems to have employed an improved technique in his work, and has demon- strated bacteria in 72 of 162 apparently healthy organs taken 1 Gaffky, Konferenz Internat. f. Tuberk., Wien, 1907. 2 Lartigau and Nicoll, Am. J. M. Sc., Phila., 1902, n. s., CXXIII, 1031. 8 Weichselbaum and Bartel, Wien klin. Wchnschr., 1905, XVIII, 241. 4 Goodale, Boston M. & S. J., 1906, CLV, 278. 6 Comet, Nothnagels Encyclopedia, Phila. and Lond., 1907, Tuber- culosis, 158. 6 Sticker, Arb. a. d. k. Gesndhtsamte., Berl., 1899, XVI, Anlage I. 7 Soprano, Centralbl. f. Bakteriol. [etc.], 1st Abt. Orig., Jena, 1906, XLI, 601. 8 Manfredi and Viola, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXX, 64. 9 Kalble, Miinchen med. Wchnschr., 1899, XLVI, 622. 10 Perez, Jahresb. u. d. Fortschr. . . . d. path. Mik. Baumgarten, 1897, XIII, 894. 11 Hess, Centralbl. f. Bakteriol. [etc.], 1st Abt. Orig., Jena, 1907, XLIV, 1. 12 Conradi, Miinchen med. Wchnschr., 1908, LV, 1523. 106 THE SOURCES AND MODES OF INFECTION from 150 healthy animals. Ford 1 and Dudgeon 2 also report finding bacteria, especially pus-forming types, lying latent in healthy organs. Bardley 3 found bacteria pathogenic for rabbits in 196 of 200 atrophied tonsils, and in 101 he demon- strated Streptococcus pyogenes. Latent Tetanus. Canfora 4 and Vincent 5 have both shown that tetanus spores may be injected into the body and remain latent for some time. Tetanus occasionally develops in an inexplicable manner after surgical opera- tions and under certain other conditions, as following the administration of hypodermic injections of the salts of quinia. Semple 6 has recently studied this subject in a most careful manner. He finds that washed spores of tetanus when injected into test animals do not cause the disease, and may remain latent and virulent for as long as 7 months. Injections of the salts of quinia will in such animals give rise to tetanus by the injurious effects of the solution upon the tissues. It may be that surgical opera- tions may sometimes operate in the same way to favor the development of latent spores. It has been suggested that the relapses which are sometimes noted in tetanus are due to the persistence of foci of latent infection. Semple found tetanus bacilli in the intestines of 4 of 10 healthy human beings, and in 3 they proved virulent for guinea pigs. Likeness of Scarlet Fever and Diphtheria. Unfortunately we do not know the nature of scarlet fever virus, hence many important matters relating to the causation of this disease 1 Ford, J. Hyg., Cambridge, 1901, I, 277. 2 Dudgeon, Lancet, Lond., 1908, II, 1651. 3 Bardley, Johns Hopkins Hosp. Bull., Bait., 1909, XX, 88. 4 Canfora, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1907, XLX, 495. 8 Vincent, J. de physiol. et de path. g6n., Par., 1908, X, 664. 8 Semple, Sc. Memoirs, Med. and San. Dept., Gov. India, 1911, XLIII. CARRIERS AND MISSED CASES 107 are in doubt. There are many points of resemblance between this disease and diphtheria, such as the degree of infective- ness, the apparent variation in the period of incubation and duration of infection, the very brief incubation in some cases, the persistence of infection in some instances long after recov- ery and the contrary fact of the early loss of infectivity in many instances, the prominence of the initial throat symp- toms, and the occurrence of albuminuria and middle ear inflammations. We are justified, I think, in looking for a bac- terial infection, and the probability is that scarlet fever is in the main, like diphtheria, a local disease of the mucous surfaces, chiefly of the throat and nose. We certainly see many mild atypical cases of scarlet fever just as we do of diphtheria, probably fully as many, and we naturally expect to find also true carriers who exhibit no symptoms at all. Atypical Scarlet Fever. As the bacteriologist cannot help us, we have to rely on clinical evidence, which is much more uncertain and difficult to secure. The layman and the inex- perienced physician are apt to scoff at the suggestion of scarlet fever unless the patient has a high fever and is as red as a lobster. But all who have seen much of this disease know that it is exceedingly common to see cases with a scarcely discernible indefinite rash lasting for only a few hours, a rise in temperature of only a degree or two lasting also only a few hours, and the merest trace of sore throat. Sometimes the rash may be entirely absent and even the fever may escape the most careful observation. 1 In institutions and families, such cases, considered doubtful at first, or perhaps entirely neglected, prove to be the origin of typical symptoms in others. Every health officer will recall many such cases. They are the missed cases which are such a factor in the maintenance of this disease. There are many references to them in the reports of health officers and in medical litera- ture. Among others who report such atypical cases are News- 1 Caziot,Bull. et mem., Soc. med.d. hop. de Par., 1903, n.s., XX, 799; Semaine med., Par., 1903, XXIII, 205. 108 THE SOURCES AND MODES OF INFECTION holme, 1 Caziot, 2 Welch and Schamberg, 3 Cameron, 4 Butler, 5 Lesarge, 6 Thresh, 7 Corlett, 8 Ludke, 9 Kerley, 10 and Thorn- ton and Mader referred to below. In most of these missed cases there were some slight symptoms, though overlooked or misunderstood at the time. In Manchester, in 1906, there were discovered 229 missed cases, mostly of a mild character. From these 139 other cases had developed. 11 Number of Atypical Cases. It is difficult to estimate the number of atypical cases of scarlet fever. Probably it varies according to the extent and severity of the outbreak, and for other reasons. Newsholme 12 has reported a milk out- break in which the number of sore throats without the pres- ence of eruption was 215, while the number of typical cases of scarlet fever was only 38. Butler, 13 at Wellesden, studied the incidence of sore throat in families where there was re- ported scarlet fever, and found that 31.2 per cent of 1266 persons in such families had sore throats, while only 2.8 per cent of 1644 persons living in families where there was no scarlet fever had sore throat. In a school with 300 children Thornton 14 found 31 typical cases, 19 cases with no rash and slight sore throat, and 46 cases in which only desquamation * Newsholme, Tr. Med.-Chir. Soc., Glasg., LXXXVII, 549. 2 Caziot, Bull, et mem., Soc. meU d. h6p. de Par., 1903, n. s., XX, 799; Semaine med., Par., 1903, III, 205. 8 Welch and Schamberg, Acute Infectious Diseases, Phila., 1905, 390. 4 Cameron, Rep. on Return Cases of Scarlet Fever and Diphtheria to Asylums Bd., Lond., 1901-02, 38, 78. 6 Butler, Proc. Roy. Soc. Med., Lond., 1908, 1, Epidemiol. Sec., 225. Gaz. d. h6p., Par., 1909, LXXXII, 1471. 7 Med. Officer, 1910, IV, 5. 8 J. Am. M. Ass., Chicago, 1910, LV, 195. 9 Med. Klin., Berl., 1911, VII, 127. 10 Am. J. Dis. Child., 1911, I, 71. 11 Rep. on Health of Manchester, 1906, 43. 12 Newsholme, Rep. Med. Off. Health, Brighton, 1906, 48. 13 Butler, Rep. Med. Off. Health, Wellesden, 1907, 76. 14 Thornton, Brit. M. J., Lond., 1908, 1, 495, CARRIERS AND MISSED CASES 109 was noticed. Mader l observed 9 typical and 12 very atypi- cal cases in an outbreak in a home for epileptics. Ewart, 2 from an examination of 8000 school children at Middle- borough, estimates that there must be at least 3 missed cases annually for each 1000 children. True " carriers," that is, perfectly well persons, are sometimes reported. Thus I have noted an instance where a woman apparently in this way carried scarlet fever to her child. She had been taking care of another child, and after an entire change of clothing, bath and shampoo, visited the first-named child, who was taken sick two days later. Newsholme reports what he thinks are possibly, or even probably, similar cases. New- man, 3 of Finsbury (London), noted 5 carriers among school children, three of whom, though they had never had the disease, transmitted it to others. Kerr 4 also reports 5 such cases. When a diphtheria patient discharged from a hospi- tal carries scarlet fever home to his family, he must in most instances be considered a true carrier, for it is unlikely that symptoms of scarlet fever would often escape notice in the hospital. Ten of this sort of return carriers are reported by Simpson, 5 30 by Cameron 6 and 44 by Turner. 7 Smallpox. There is still doubt as to the specific cause of smallpox. The claims that have been advanced in favor of this or that micro-organism have not as yet been substan- tiated. Hence there is no " laboratory " evidence that car- riers of this disease exist, nor is there much clinical evidence 1 Mader, Cor.-Bl. f. schweiz. Aerzte, 1908, XXXVIII, 169. 2 Ewart, Pub. Health, Lond., 1910-11, XXIV, 275. 3 Newman, Rep. Med. Off. Health, Lond., 1904, 27. 4 Kerr, Rep. Med. Off. Education, Lond., 1907, 43. 5 Simpson, Rep. on Return Cases of Scarlet Fever and Diphtheria to Asylums Bd., Lond., 1898-99, 8. 6 Cameron, Report on Return Cases of Scarlet Fever and Diphtheria to Asylums Bd., Lond., 1901-02, 43. 7 Turner, Rep. on Return Cases of Scarlet Fever and Diphtheria to Asylums Bd., Lond., 1902-04, 3. 110 THE SOURCES AND MODES OF INFECTION that perfectly well persons transmit the disease. There are, it is true, scattered through medical literature numerous reports of instances of such transmission. These reports, as often in other diseases, are, as regards the evidence, rather unsatisfactory. There is usually a possibility of such trans- mission, no actual demonstration. Nevertheless it is quite possible that there may be true carriers of smallpox, and there may be a considerable number of them. Mild cases are often very numerous. This was well illustrated in the recent epidemic in the United States and England. In the United States in the year ending June 30, 1901, the fatality in 38,506 cases was only 1.79 per cent. At such a time great numbers of cases escape recognition. The patients often have no idea that they are sick with a dangerous disease. They may be at their work even during the prodromal stage. There may be only half a dozen, or even fewer, atypical pustules. I have in rather a limited experience seen several such cases. They are also reported by Welch and Scham- berg. 1 These authors also state that cases occur where there is no eruption at all. Davies 2 reports a nurse who was exposed to smallpox early in February and who had some fever and headache without any eruption or other symp- toms. Twelve days after she returned to her ward work, which was on February 28th, one of her patients in the ward developed frank smallpox. Davies from epidemio- logical evidence thinks that chronic carriers do not occur in this disease. The step from half a dozen points of eruption to none at all is so slight, and the extremely mild cases at times are so numerous, that a considerable number sine eruptione may reasonably be expected. Armstrong 3 re- cently reports three such cases with some fever and subjec- tive symptoms but no eruption. They occurred in infected families and subsequently proved refractory to vaccination. 1 Welch and Schamberg, Acute Infectious Diseases, Phila., 1905, 207. 2 Davies, Rep. Med. Off. Health, Bristol, 1909, 24. Armstrong, Arch. f. Diagnosis, 1909, II, 126. CARRIERS AND MISSED CASES 111 Measles. There is little clinical evidence that "carriers" of measles are common. Most health officers consider that measles is rarely carried by a " third person." It usually has a quite definite clinical picture. In Aberdeen, so Dr. Matthew Hay writes to me, judging from a census taken in certain schools, it was estimated that from 90 to 93 per cent of the children over ten years of age had had a recognized attack of measles. That such a high percentage of children had recognized attacks indicates that atypical cases cannot be very common. Mild, atypical and unrecognized cases of this disease must be far less numerous than are such cases in scarlet fever, diphtheria and typhoid fever. Levy at Richmond l investigated 2331 cases during an outbreak. They were all, without exception, traced to previous frank cases of the disease. Levy could find no evidence of in- fection from either carriers or fomites. His careful work in the study of this outbreak renders his conclusions of the highest value. Protozoan Diseases. Although the marks of distinction between animal and vegetable life as seen among the lower forms are ill defined and uncertain, yet it is generally agreed that though the group of organisms known as bacteria have characters belonging to both the vegetable and the animal kingdom, they are more nearly allied to the former, while an- other group, known as protozoa, are allied to the lower forms of animal life. Although one of the latter class was discovered to be the cause of malaria in 1880, at a time when most of the disease-producing bacteria were unknown, the bacteria have received far more study, and indeed it is only recently that the protozoa as the cause of disease have received much at- tention. It is known that a number of diseases both of men and of animals are caused by protozoa of various types. As has recently been emphasized by Daniels, 2 latency is a 1 Richmond Rep. Health Dept,, 1910, 38. 2 Daniels, Brit. M. J., Lond., 1909, II, 767. 112 THE SOURCES AND MODES OF INFECTION common phenomenon of protozoan infection, and is of the utmost importance from an epidemiological standpoint. Not only do the blood parasites maintain long continued in- fection with few symptoms, but such forms as Ameba, Balan- tidium and Lamblia live in the intestines indefinitely, repro- ducing themselves asexually. A number of the diseases to be referred to do not affect man, but they serve to illustrate the prevalence of latency in protozoan infections. Texas Cattle Fever. It has long been recognized that the Texas fever of cattle could be transmitted by apparently healthy animals. The explanation of this fact was not, how- ever, forthcoming until Smith and Kilborne's 1 classical re- searches in 1893 demonstrated that the disease was due to a blood parasite, a protozoan (Piroplasma bigeminum), not a bacterium, and also demonstrated that it is only transmitted from animal to animal by means of a species of tick (Boophi- lus annulatus) , in which the parasite passes through a cycle of changes necessary for the maintenance of the species. This work of Smith and Kilborne's was one of the most important steps in the development of our knowledge of the insect carriage of disease, a knowledge which has been of such inesti- mable value in connection with malaria, sleeping sickness, yellow fever and other blood diseases. It was soon deter- mined that animals which had recovered from Texas fever and were immune to it, carried the piroplasma in the blood for an indefinite time. In one instance it was known to have remained for thirteen years. 2 Reports from the Philip- pines 3 show that many of the cattle in those islands are in- fected with the parasites of Texas fever though showing no symptoms. Slightly different types of this disease occur among cattle in Europe and in Africa caused by different species of piroplasma and spread by carriers. 1 Smith and Kilborne, U. S. Dept. Agric., Bu. An. Ind., Bull. No. 1, 1893, 57. * U. S. Dept. Agric., Rep. Bu. An. Ind., 1904, XXI, 26. * Bull. 14, Bu. Gov. Lab., Manila, P. I., 1904, 11. CARRIERS AND MISSED CASES 113 Nagana. Nagana 1 is an African cattle disease which, like the sleeping sickness, is caused by a trypanosome, T. brucei, and is also transmitted by a tsetse fly, G. morsitans. Wild herbivora are very generally infected, but because of immunity, probably acquired, they show few or no symp- toms. These carriers are the real source of the disease. Dourine. This is a contagious disease of horses spread almost exclusively by the sexual act. It is caused by a trypanosome, T. equiperdum, found in the secretions, 2 blood and tissues. Although recovery may occur, the trypanosomes remain for months in the sexual organs of apparently cured animals and thus spread the disease. Malaria. The most important of the protozoan diseases is malaria. It had always been believed that this disease might remain latent for months and years, but what latency really meant could not be determined until after the dis- covery of the specific cause of the disease. Many of the protozoa pass through various metamorphoses, or fixed cycles of development, and it was found that in malaria the Plas- modium, which is its cause, may in certain stages persist in the blood or organs of the body without causing any charac- teristic symptoms, or indeed any symptoms at all. Then at any time, from one cause or another, its reproduction may again become active and more or less marked symptoms appear. Thus relapses may occur after a period of several years, when the bodily resistance is from any cause impaired. Thus fever after surgical operation is not rarely due to a latent malaria becoming active, the parasite being found in the blood and the symptoms yielding to quinia. As malaria is a strictly transmissible disease, the plasmodium which causes it being borne from one person to another by mosqui- toes, a latent case of the kind described may be, and doubt- less often is, the means of introducing the disease into hitherto 1 Minchin, Gray and Tullock, Proc. Roy. Soc., Lond., 1906; Nature, Lond., 1906, LXXVII, 57. 1 U. S. Dept. Ag., Bu. An. Ind., Bull. No. 142, 1911. 114 THE SOURCES AND MODES OF INFECTION uninfected localities. Unless such cases drift into hospitals, they are almost certain to be unrecognized. Craig 1 made a careful study of 424 such latent cases found among 1653 sol- diers examined in the Philippines. Since I first wrote this chapter Craig's book has appeared in which he discusses in much detail latency and recurrences. 2 He has noted an asex- ual conjugation of the parasites in the blood cells, which is followed by a resting stage, and which he believes has some relation to the latency of the infection. Where malaria pre- vails extensively, as in the tropics, it has long been noticed that a large part of the adult population is immune. It is now known that this immunity is to a large extent acquired, and is due to the invasion of the body in infancy by the parasites. This invasion, while sometimes causing symptoms and death, frequently gives rise to few or no symptoms, or if some reaction appears at first, it soon disappears, and the children may seem perfectly well though the parasites are constantly found in the blood. They disappear year by year and infection is rarely found after adolescence. Koch 3 in Africa found large numbers of children infected, even as high as 100 per cent. Plehn 4 found many adults infected though not sick. Christophers and Stephens 5 found the parasites in the blood of 90 per cent of infants examined in one locality on the Gold Coast in Africa, and the Thompson Yates ex- pedition to Nigeria 6 reports finding them in 63 per cent of children under 3 years of age. Ziemann 7 found that in the Cameroon country 37 per cent of children under 5 years of 1 Craig, J. Infect. Dis., Chicago, 1907, IV, 108. 2 The Malarial Fevers, N. Y., 1909, 228. 8 Koch, cited in Thompson Yates' Lab. Rep., 1900, No. 4. 4 Plehn, cited by Marchiafava and Bignani, Twentieth Cent. Prac- tice, XXI, 807. 6 Christophers and Stephens, Reports of the Malarial Commission of the Roy. Soc. (Eng.), 2nd Ser., 1900-03, 15. 'Thompson Yates' Lab. Rep., 1900, III, Pt. 2, 201. 7 Deutsche med. Wchnschr., 1900, XXVI, 399, 642, 753, 769. CARRIERS AND MISSED CASES 115 age were infected. In Panama Kendall 1 found 57 per cent infected of the natives of all ages examined in the village of Bahio, and 73 per cent of foreigners. While many of the latter were more or less sick, many were entirely well. Darling 2 in villages in the Panama Canal zone where there were no Anopheles, nevertheless found that 10 per cent of the laborers at work were infected though they were not at all sick. Among the families of the Spanish and the West Indians, the latent infection reached 30 per cent. It is this latent infection in the blood of the native population which is the cause of the malaria which so certainly attacks arrivals from non-malarial regions. The greater the distance that can be placed between the natives and the strangers the less the danger of the latter contracting the disease. Sleeping Sickness. African sleeping sickness has been shown to be due to a protozoan, Trypanosoma gambiense. This disease has been much studied of late, and it seems cer- tain that it is transmitted by means of the tsetse fly (Glossina palpalis) , though whether it is a purely accidental mechanical transference on the proboscis of the fly, or whether it passes through a part of its life history in the body of the fly, as the Plasmodium of malaria does in the mosquito, is still uncer- tain. In any event the parasite is frequently found in the blood of apparently healthy subjects, just as is the malarial parasite. According to Todd 3 it may remain in the blood for 15 years, causing no symptoms, and frequently remains for many months. The expedition from the Liverpool School of Tropical Medicine 4 found many natives infected, but who exhibited no symptoms, or only slight symptoms. The greater the prevalence of the disease the more common are these latent cases. In Gambia, where the disease is rare, not more 1 Kendall, J. Am. M. Ass., Chicago, 1906, XLVI, 1151, 1266. 2 Darling, J. Am. M. Ass., Chicago, 1909, LIII, 2051. 8 Todd, Tr. Epidemiol. Soc., Lond., 1905-06, XXV, 1. 4 Liverpool School Trop. Med. Memoirs, 1904, XIII; Med. News, N. Y., 1904, LXXXV, 526, 615, 116 THE SOURCES AND MODES OF INFECTION than one native in 1000 examined showed the parasites, while in the Congo 46 in 100 were infected, and in Uganda the percentage was still higher. Whether the disease is always transferred from man to man, or whether some of the lower animals also harbor the parasites and thus serve as a " reservoir " from which the human disease is derived, is as yet uncertain. Syphilis. The spirochete of syphilis has in one instance been reported as remaining latent in a healed lesion of that disease. 1 According to Bosquenet 2 the spirochetes are commonly found in gumma, where they may apparently remain latent for a long time. The fact that gumma have not been considered infectious has been urged as an~argu- ment against the pathogenicity of the spirochetes. It is now, however, generally thought that the spirochetes in these tumors are infective. Relapsing Fever. There are several types of relapsing fever having more or less well marked geographical limita- tions. The disease is characterized by well denned febrile " relapses " with equally well denned afebrile intervals. The different forms of the disease are caused by slightly dif- fering species of spirochetes, and, as will be referred to in the last chapter, these parasites are undoubtedly transmitted by insect carriers. According to Craig, 3 it has been demon- strated by Breinl and Kinghorn and by Button and Todd that though Spirocheta duttoni is not found in the blood during the afebrile period, the blood nevertheless is infec- tious. Mackie has shown the same for S. carteri, and Darling 4 has shown that the blood from the afebrile stage and from entirely recovered animals is still infectious. Darling's work was done in Panama. 1 Pasini, cited by Rosenberger, New York M. J. [etc.J, 1908, LXXXVII, 394. 2 Bosquenet, Spirochsetes, Phila., 1911, 51. 1 Craig, The Malarial Fevers, New York, 1909, 447. Darling, Arch. Int. Med., Chicago, 1909, 150. CARRIERS AND MISSED CASES 117 Vincent's Angina. It seems highly probable that this disease is caused by the spirochetes which are found con- stantly in the lesions. That many mild missed cases, and perhaps true carriers occur is probable. Farley, 1 in report- ing an institutional outbreak of this disease, says that a number of children were found without any constitutional symptoms, but with a slight exudation on the tonsils or with spongy gums, and that in these the spirochetes were found to be present. These cases were not discovered until a systematic examination was made of all the children and the outbreak ceased on their removal from the institution. Kerr 2 reports an outbreak in the Linden Lodge School in London, consisting of about 20 cases, and due apparently to unnoticed chronic and subacute cases which attracted no attention until they were sought for. Yellow Fever. The parasite which is the cause of yellow fever is still unknown, although fortunately for preventive medicine we have very accurate knowledge of the manner in which the disease is transmitted. As in scarlet fever, so in yellow fever lack of knowledge of the parasite renders diffi- cult the recognition of carrier cases if they exist. But there is abundant clinical evidence that many very mild and atyp- ical cases occur which it is impossible to recognize. It is in young children chiefly that this slight disturbance is pro- duced by the infection. A similar phenomenon is noted in malarial disease, and young children are the chief source of infection in both yellow fever and malaria. The fact of the mildness of these cases, their frequency, and the impossibility of making a diagnosis, has been insisted upon by Finlay, Gorgas, Guiteras, Carter, Agramonte, Marchoux and others. Even in adults, walking cases, which it is impossible to dis- cover by an ordinary examination, are not rare. Thus it was claimed that during an outbreak in Louisiana a single walk- ing case carried the disease to three different communities. 1 Farley, J. Am. M. Ass., Chicago, 1910, LIV, 1516. 2 Rep. Med. Off. of Education, Lond., 1909, 63. 118 THE SOURCES AND MODES OF INFECTION Amebic Dysentery. A number of observers have re- ported finding Entameba histolytica, which is the cause of this disease, in the intestines of healthy persons. It is now believed that most of these reports are based on error due to confusing the pathogenic species named above with harmless saprophytes. This is the view of Vedder J and Craig. 2 Although the laboratory evidence of the existence of carriers of dysentery amebae is uncertain or lacking, there is epidemiological evidence that these parasites are some- times found in persons for a long time after recovery, and may also be found in the feces before thq disease develops. Martini 3 reports a case in which the sickness lasted from the 15th of September to the 1st of December, 1907, but in which the amebae persisted until the last of January, 1908. Vincent 4 reports several instances in which persons were carriers for five months after their return to France from Tonkin. Lemoine 5 had under observation a man who con- tracted the disease in China in 1897 and returned to France and transmitted the disease to another in 1908. Cameron 6 reports a soldier returned to Scotland from the Boer War, and apparently well for 6 years, but who then developed a liver abscess in which amebae were found. Poliomyelitis. The disease known as acute anterior poliomyelitis, or infantile paralysis, has been, during the past fifteen years, occurring with increasing frequency. It usually appears in well-defined local outbreaks lasting from a few weeks to a few months. Except in .the largest cities the outbreaks are not often of long duration. " Spo- radic " or somewhat isolated cases also doubtless occur, Vedder, J. Am. M. Ass., Chicago, 1906, XLVI, 870. Craig, J. Infect. Dis., Chicago, 1908, V, 324; The Parasitic Amoebae of Man, Phila., 1911. Martini, Arch. f. Schiffs- u. Tropen-Hyg., Cassel, 1908, XII, 588. Vincent, Bull. Soc. path, exot., Par., 1909, II, 78. Lemoine, Bull, et m6m. Soc. med. d. h6p. de Par., 1908, 3d Ser., XXV, 640. 6 Cameron, Brit. M. J., Lond., 1911, I, 973. CARRIERS AND MISSED CASES 119 though it is not unlikely that some which are reported under this name may be due to a totally different cause from that which gives rise to the " epidemic " form, just as cases of cerebro-spinal meningitis, closely resembling the disease caused by the Weichselbaum diplococcus, may be produced by several other infective agents. For many years epi- demiologists have considered poliomyelitis as an infectious and contagious disease, though many have thought the evidence of communicability not to be entirely satisfac- tory. In fact, the epidemiological evidence of the conta- giousness of this disease, and of cerebro-spinal meningitis, is almost on a par. The contagiousness of both diseases is certainly not very marked ; that is, the chance of a frank case giving rise to another frank case, either in homes or in institutions, is very small. When an apparently contagious disease, yet one only slightly so, appears in well-marked outbreaks, it is pretty safe to assume the existence of large numbers of carriers or of mild atypical and unrecognized cases. The epidemiology of cerebro-spinal meningitis was inexplicable until the carriers of that disease were discov- ered. The explanation of its spread now involves no more difficulties than does that of scarlet fever or diphtheria. The epidemiological, and indeed clinical resemblance of cerebro-spinal meningitis and poliomyelitis led some, even before the work of Flexner and Clark, and Lucas and Osgood, to suspect the existence of carriers. The exist- ence of numerous " abortive " cases, as they have been called, had long been considered probable. Laboratory Studies. To determine definitely the ex- istence of either carriers or atypical cases of any infectious disease by means of epidemiological studies is extremely difficult, and to determine their number is entirely impos- sible. Fortunately experimental laboratory work, culmi- nating in the investigations of Flexner and Lewis, 1 have 1 Flexner and Lewis, J. Am. Med. Ass., Chicago, 1909, LIII, 1639, 1913. 120 THE SOURCES AND MODES OF INFECTION shown, by repeated transfers of the virus through monkeys, that poliomyelitis is in all probability due to a living con- tagium. Subsequent studies have shown that the virus is filterable; that it is found in various fluids and organs of monkeys including the nasal and pharyngeal mucous mem- brane, and presumably also in the mucus ; and that animals may be infected not only by injection into the central nervous system, but also by injection into the subcuta- neous tissue, and by application of the virus to the scari- fied and healthy mucous surfaces. The spinal fluid very early shows quite characteristic changes, and " immunity principles " (capable of neutralizing the virus in the test tube) are found in the blood of animals, and human beings who have had the disease. 1 Poliomyelitis Carriers. By means of the experimental methods rendered possible by this work, it has been shown that in monkeys, at least, the virus of this disease remains in the nose and throat after the clinical symptoms have subsided. Thus Osgood and Lucas 2 found the virus in the naso-pharyngeal mucous membrane of two monkeys 6 weeks and 5J months respectively after the acute symp- toms of the disease had disappeared, and Flexner and Clark found the virulence to persist 4 weeks in a monkey studied by them. Thus the existence of chronic conva- lescent carriers in inoculated monkeys is definitely proved. As the virus has been shown by Flexner and Clark 3 to exist in the tonsillar tissue of human beings during the dis- ease, just as it is found in the mucous membrane of monkeys, it seems reasonable to expect that it only needs further investigation to demonstrate the existence of human car- riers of this disease. Occasionally observers have, for epi- demiological reasons, suspected certain persons of being 1 Flexner and Lewis, J. Am. Med. Ass., Chicago, 1910, LIV, 1780. 2 Osgood and Lucas, J. Am. Med. Ass., Chicago, 1911, LV, 495. Flexner and Clark, J. Am. Med. Ass., Chicago, 1911, 1685. CARRIERS AND MISSED CASES 121 carriers. Thus Lovett 1 states that he has a number of such cases in his records, and in 11 instances the disease followed intimate contact with persons who had previously suffered from it. Such cases have also been reported by Krause. 2 Anderson 3 in Nebraska notes a number of in- stances in which the disease seems to have been carried by well persons. Thus a girl who had visited in Stromberg, where the disease prevailed, returned to a farm many miles distant and a few days later a case of poliomyelitis developed, followed by others on that and a near-by farm. In another instance a thresher apparently carried it from his own family to the place where he worked. In two other instances peddlers seemed to be carriers. Similar observa- tions have, in England, been made by Reece and Farrar. 4 Poliomyelitis : Atypical Cases. Ever since Wickman's studies in Sweden it has been believed that so-called " abor- tive " cases of this disease are quite common. These cases may show some slight symptoms referable to the nervous system, such as headache, pain, tenderness and rigidity of neck, hypersthesia and neuralgic pains; and some think that tonsillitis and gastro-intestinal irritation without ner- vous symptoms may be due to the same pathogenic agent. According to Frost, 5 Wickman found such abortive cases to equal in number 15 per cent of the frank cases. In Massachusetts in 1909 there were 49 possibly abortive cases observed in connection with 150 acknowledged cases. Frost himself in an outbreak in Hancock County, la., found 25 abortive cases and 5 frank cases. That some at least, and perhaps a large proportion, of these abortive cases are really poliomyelitis, is shown by the finding of 1 Lovett, Rep. State Bd. of Health, Mass., 1909. 2 Krause, Therapie der Gegenwart, 1911, LII, 145. 3 Anderson, Pediatrics, N. Y. & Lond., 1910, XXII, 543. 4 Reece and Farrar, Rep. to Local Gov. Bd. Lond., 1912, No. 61. 6 Frost, U. S. Pub. Health and Mar. Hosp. Serv., Pub. Health Bull. No. 44, 1911. 122 THE SOURCES AND MODES OF INFECTION 11 immunizing principles " in their blood. Anderson and Frost 1 state that Netter and Levaditi demonstrated a case in this way, and the authors themselves showed the presence of " immunizing principles " in the blood of 6 of 9 suspected abortive cases. In view of the epidemiological facts, and the experi- mental data, it seems not unsafe to surmise that, with the perfection and extended application of laboratory methods of diagnosis, carriers and mild atypical cases of poliomye- litis will be shown to be common, and it is not unlikely that they may prove, as in cerebro-spinal meningitis, many times more numerous than are frank cases of the disease. Latency a Common Phenomenon. The laity and not a few physicians are still incredulous that there can be diph- theria infection unless the patient is sick in bed and the throat choked with exudation, or that there can be scarlet fever without high fever and an extensive eruption. Still less are they willing to admit that perfectly well persons can carry and reproduce in their bodies the virus of the infectious diseases. It is difficult for many to realize that the virus of disease may remain latent in the body, for long periods, without causing symptoms. The facts pre- sented in the preceding pages have been gathered to show that latency is a common phenomenon, and for this pur- pose, besides many common human infections, a number of diseases have been referred to, not transmissible to human beings and of little interest to health officials, but which seem to illustrate this phenomenon. Infection without symptoms is no cause for surprise, but may be expected in any parasitic disease. There may be exceptions, as is said to be the case in relapsing fever and African East Coast cattle fever (caused by Th. parva). But these exceptions, rather than the existence of latency and atypical types, should be cause for surprise. 1 Frost, J. Am. Med. Ass., Chicago, 1911, LVI, 663. CARRIERS AND MISSED CASES 123 Laboratory Evidence of Carriers. Definite knowledge as to the existence and number of carriers must rest almost entirely upon evidence furnished by the finding in the body of the causative agents of disease, bacteria or protozoa, or the demonstration in the blood or tissues of an unknown infective principle, as in the case of poliomyelitis. Actu- ally, almost all such evidence depends upon the finding of disease-producing bacteria or protozoa in the bodies of healthy persons or animals. Those persons who do not believe that the causative relation between these minute forms of life and disease has been established with a rea- sonable degree of certainty will of course attach little weight to the bacteriological evidence of the existence of carriers. With such I cannot agree. On the contrary, the causation of certain diseases by bacteria seems to me to be one of the best-established truths of medical science, and it is conse- quently entirely legitimate to make use of bacteriological evidence in developing the theory and practice of preven- tive medicine. Many, while admitting that we have satis- factory evidence that some diseases are caused by specific bacteria or protozoa, are unwilling to admit that the evi- dence is conclusive as to the causative relation of certain other alleged pathogens and the diseases said to be due to them. Indeed, almost everyone takes this attitude towards some disease. It happens, however, that in the opinion of the majority of the most competent observers the evidence is especially strong as regards the causative agent of chol- era, typhoid fever, diphtheria, cerebro-spinal meningitis, sleeping sickness and malaria. And it is particularly for these diseases that we have abundant evidence as regards the numbers and importance of carriers. Laboratory Evidence of Atypical Cases. While acute clinical observers have at all times recognized many atypical cases which would have been overlooked by the average man, it was from the nature of things impossible to know how far or how often a disease could deviate from the nor- 124 THE SOURCES AND MODES OF INFECTION mal when the only criterion for the determination of the disease was the symptom complex of the normal type. It is only the discovery of the germ, and the ability to recog- nize it, which enables us to take a wider view of an infec- tious disease, and to see that it includes far more types and cases than was at first suspected. It is only the work of the laboratory that makes it possible to recognize the mild atypical cases of diphtheria, typhoid fever and malaria. The clinicians have been willing to accept, though, it must be confessed, with a little hesitancy, the teachings of the laboratory men in regard to prevalence of atypical cases. Some -are even emboldened to proceed along lines where the laboratory men cannot as yet go, and to recognize atypical scarlet fever which they would formerly have passed by, and to postulate the " abortive " type of polio- myelitis. Yet when the laboratory man points out the true carrier and suggests danger from him as well as from the atypical case, many a clinician, and not a few epidemi- ologists as well, hesitate to follow. Carriers Vary in Numbers. One of the important facts noticeable in the study of this subject is the great varia- tion in the number of carriers in different diseases. It ought to be determined by a sufficient number of observa- tions just how many carriers there are in different diseases among the general public and among contacts at different ages, at different seasons, and in different places. Un- fortunately the observations have not as yet been exten- sive enough to warrant any definite conclusions, though some quite striking differences are apparent. Probably the number of carriers is on the whole greater in pneumonia than in any other disease, including at times half the total population. In certain protozoan diseases the percentage of carriers may be even higher within limited groups, as among children in intensely malarious districts. So, too, carriers of the trypanosomes of sleeping sickness are at times very numerous. In the case of animal diseases, as CARRIERS AND MISSED CASES 125 Texas cattle fever, the proportion of infected animals is very large. Among human diseases it would appear that influenza carriers are very numerous, though the identity of the causative agent has not been so well determined, and the number of observations is not as large as for many other diseases. It is certain that cerebro-spinal meningitis car- riers are many times more numerous than the cases in the opinion of many, from ten times to twenty times as numer- ous. Under ordinary conditions, with a moderate preva- lence of the disease, diphtheria carriers equal about one per cent of the population, and during outbreaks the percent- age, particularly among children, is many times as great. Probably typhoid carriers are not so numerous as are diphtheria carriers, but there are not many data as to the numbers among either the general public or among con- tacts. In neither human nor rat plague do carriers appear to be either numerous or important. There is even less evidence of the existence of carriers, certainly of chronic carriers, of smallpox; and for measles the clinical evidence that there are no carriers is very strong. Relation between Number of Carriers and Infectivity. Here again data are too few to warrant more than a sugges- tion, but one cannot but be struck by the fact that the most infectious diseases show the fewest carriers, while some of the diseases which are only slightly contagious show very many more carriers than cases. Thus smallpox and mea- sles, considered perhaps the most contagious of diseases, are not certainly known to give rise to the carrier condition. Diphtheria is not so infectious as measles; that is, a case, brought in contact with susceptibles, does not so surely give rise to other cases ; and carriers of diphtheria are quite numerous. Cerebro-spinal meningitis exhibits many car- riers, and its ineffectivity, as measured by contagion in the family and institution, is small. Pneumonia has the most carriers of all and is the least contagious. 126 THE SOURCES AND MODES OF INFECTION Virulence of Germs in Carriers. The question of the infecting power of carriers is the crucial one of the whole subject. One way of testing this is by testing by animal experiment the virulence of the germs which the carrier is producing. Unfortunately, owing to insusceptibility of the lower animals, or the difficulties of the technique, or the cost of susceptible animals, like the apes, renders numerous observations out of the question. In one disease, diphthe- ria, in which experimentation is comparatively easy, it has been shown that in a varying percentage of carriers the bacilli are virulent, often exceedingly virulent, though there is a large number of carriers in which they are not virulent. The actual number of carriers of virulent germs is never- theless shown to be very large. The pneumococcus found in well persons is virulent for rabbits, though less so than are cocci from cases of pneumonia. Tests on the lower animals for the virulence of typhoid bacilli are of little value, but it is worthy of note that a case of typhoid fever in a human being has recently resulted from drawing into the mouth a culture of a typhoid bacillus derived from a carrier. In some of the diseases of the lower animals direct experi- ment has demonstrated the virulence of disease germs from healthy individuals. This has been abundantly proved in Texas cattle fever and in certain trypanosome infections. Carriers as a Source of Protozoan Disease. There seems to be little disposition in any quarter to question the importance of carriers of the malarial plasmodium in the extension of malarial disease. Yet so far as I know there are no experiments which demonstrate such transmission, and few if any clinical observations which would indicate such transmission. It is simply assumed that the numer- ous well persons carrying plasmodium must be a source from which oftentimes the mosquitoes get the infection which they transmit to others. Probably the reason why this view is so readily accepted without any demand for CARRIERS AND MISSED CASES 127 rigid experimental or epidemiological proof is that the mode of transmission of this disease is established on such con- vincing evidence. It seems certain that it is only trans- mitted by mosquitoes, and that mosquitoes obtain the parasites only by previously biting infected human beings. So, too, because the mode of transmission of sleeping sick- ness is definitely determined, no one looks for the origin of this disease outside the bodies of living beings, and as many human beings are shown to be " carriers " of the trypano- some, such persons are believed to be a principal source of the disease. Carriers as a Cause of Bacterial Diseases. In at least one bacterial disease, namely " white diarrhea of chicks," due to B. pullorum, it has been definitely shown that adult carrier hens infect their eggs and are thus the principal factor in the spread of the disease. In no other animal disease due to bacteria does the carrier question appear to have been so well worked out. While the existence of numerous carriers has been amply demonstrated in such diseases as cholera, typhoid fever, dysentery, diphtheria and cerebro-spinal meningitis, their importance in the spread of these and similar diseases has been questioned by many who never question the impor- tance of carriers in the spread of malarial disease. The reason for this, doubtless, is that the mode of transmission of these diseases is not so well understood because they do not readily permit the use of experimental methods. Every- one feels sure how every case of malaria is caused. On the other hand, we are often, perhaps usually, in doubt in cases of typhoid fever, cholera and diphtheria as to the mode of transmission of the infection and the source from which it comes. When there are many possible sources and modes of infection it is not easy to determine the right one. Evidence of Contagion the Same as for Cases. It is fair to claim that the evidence of the infectivity of carriers is the same as the evidence of the infectivity of cases. We 128 THE SOURCES AND MODES OF INFECTION believe that frank cases of diphtheria are contagious be- cause it very generally happens that persons exposed to them develop the disease, and, conversely, because a certain proportion of the recognized cases have been in relation to other cases. We believe that typhoid fever is contagious because a certain number of persons exposed to cases of the disease contract it, even though the proportion is smaller than in diphtheria. It is considered a further proof that many cases of typhoid can be shown to have had some connection with previous cases. When a con- siderable number of cases of typhoid fever are caused by the consumption of milk, and the milk is known to have been handled by a typhoid patient, or even to have come from premises occupied by such a patient, it is generally assumed that the contagion was derived from the patient. In precisely the same way it has been shown in the pre- ceding pages, and much more additional proof of the same kind is obtainable, that persons in contact with diphtheria carriers, and indeed the carriers themselves, not rarely develop the disease. It has also been shown that persons with diphtheria have often been in relation to carriers. The number, it is true, is not very great, and it cannot be so great as for cases; for while it is comparatively easy to recognize any frank case in the environment of any given patient, it is not possible to recognize any carrier there may be, except by cultures from every one with whom the patient has come in contact. In typhoid fever it is easier to find carriers because ty- phoid fever, more than any other disease, is spread through milk, water or food; and outbreaks so caused are often traced to some definite locality, often to a single house, so that the search for carriers becomes easier. Hence we have more definite proof that typhoid fever is caused by carriers than we have that any other human bacterial dis- ease is so caused. The outbreaks of typhoid fever which have been shown to have a definite relation to carriers CARRIERS AND MISSED CASES 129 afford as good evidence that carriers are the cause of this disease as there is that cases give rise to other cases. Lack of Statistical Evidence Alleged. Hamer l has urged that the mere association of a carrier and a case is no proof of a causative relation, and he says that the finding of carriers in connection with certain outbreaks of typhoid fever is of little importance unless we have some idea of the number of carriers in the general population. He does well to call attention to the lack of satisfactory data, but when only 1 carrier is found among 250 persons and 3 among nearly 1000, it is fair to assume that carriers are not very common. Carriers Often Appear not Dangerous. It is certainly a fact that carriers often appear to be non-infectious. Many carriers of typhoid bacilli and of diphtheria bacilli have been known to remain such for long periods of time with- out apparently infecting members of their families or others brought in close contact with them. As shown on page 84, diphtheria carriers have been followed in schools in Boston and Providence and no infection from them has been dis- covered. Diphtheria carriers have been discharged from hospitals and no cases have developed in their homes. These and similar facts certainly demonstrate that all car- riers do not at all times cause disease in those with whom they are brought in contact. Why this is so may be due to a variety of causes. Thus the excretion of bacteria is in many cases notoriously intermittent. There is also good reason for believing that the bacteria have in many cases lost their virulence. Perhaps sometimes they are produced in relatively small numbers. Again, many of the persons exposed are doubtless immune. Furthermore, we must bear in mind, as will be referred to in the following chapter, that the infecting power of even frank cases of disease is very much less than has generally been supposed. Such cases may often remain in close association with susceptible per- 1 Hamer, Proc. Roy. Soc. Med., 1911, IV, Epidemiol. Sect., 105. 130 THE SOURCES AND MODES OF INFECTION sons without the conditions being present for a transfer of an effective amount of infective material. One would expect this to happen still more often with carriers. On the other hand, there is much evidence which shows that carriers at times do cause disease. To most persons the evidence of this is conclusive. The question at issue merely is, How often does this occur? To what extent are carriers a factor in the maintenance of the infectious dis- eases? To the writer it appears that many things strongly point to carriers as a factor of great moment. The prob- ability of this is, I believe, sufficient to warrant our modi- fying our restrictive measures accordingly. I nevertheless freely admit that we are greatly in need of more statistical evidence. There are still many problems concerning the relation of carriers to disease which need further careful study, and it is not for a moment claimed that the " carrier theory," so called, satisfactorily explains every epidemiological phe- nomenon. There are many which it does not explain at all. On the other hand, some of the most important phe- nomena of the extension of the contagious diseases are far better explained by the newly discovered facts concerning carriers than by any of the theories of former years. We still have much to learn, but we are not on that account justified in neglecting the facts which have already been learned and in basing our practice on disproved theories of the sources of infection. No Sharp Separation between Varieties of Carriers. That typical cases of disease are the source of similar cases follows necessarily from the very definition of contagious- ness. That mild cases, even very mild and atypical cases, may give rise to typical as well as to other mild cases is recognized by everyone. Both clinicians and epidemiolo- gists have always believed that perfectly well persons may be the bearers of infection from the sick to others. It was believed by most, and is now by many, that such per- CARRIERS AND MISSED CASES 131 sons carry the infection in the hair or clothing or on the hands. The discovery that the germs of disease may grow in the body without causing symptoms has forced most rational persons to the belief that when well persons carry infection it is because they are " carriers," that is, are growers, of germs. It is probably true that all carriers are not dangerous, certainly not at all times, even when they are excreting bacilli. We know that in some diphtheria carriers the bacilli are not virulent for test animals and probably not for human beings. Certain observers of high standing have assumed that it is only the convalescent carriers and the carriers who are in immediate contact with the sick who are dangerous; that is, it is these only who carry virulent germs. If these can be controlled the carrier problem is solved, they think. I am willing to admit that the severe case is potentially more dangerous than the mild case, that the mild case may be more dangerous than the car- rier, and that the convalescent carrier may be more dan- gerous than the chance carrier found among the public at large. There is some evidence of this, and it is not im- probable that bacteria may tend to lose their virulence in passing through a succession of immune persons (as it is not improbable that they may increase in virulence by passing through susceptible persons) ; but I can see no ground at present for the assumption that virulent bacilli derived from a sick person may be carried by one well person but that when they pass to another well person they cease to be dangerous. There seems to be no ground for assuming that a virulent germ cannot pass from carrier to carrier. Conclusions. We are justified from the- evidence pre- sented in coming to the following conclusions: 1. Mild atypical and unrecognized cases of the infectious diseases are often extremely common. In many diseases they may be more numerous than the recognized cases. 2. Disease-producing micro-organisms, whether bacteria 132 THE SOURCES AND MODES OF INFECTION or protozoa, frequently persist in the body without causing symptoms. 3. Sometimes the germs remain only a few weeks or months after convalescence, and sometimes they may persist for years, perhaps for life. Sometimes these carriers give no history of ever having been sick. 4. While the bacteria found in carriers are sometimes lacking in virulence, many times they show the highest degree of virulence. 5. There is ample epidemiological evidence that healthy carriers as well as mild unrecognized cases are the source of well-marked outbreaks. 6. The number of carriers varies greatly in different dis- eases. From 20 to 50 per cent of the population are carriers of pneumococci. It seems probable that the influenza bacil- lus is as widely distributed. During outbreaks of cerebro- spinal meningitis the number of carriers may be from 10 to 30 times as numerous as the number of cases. Even when diphtheria is not prevalent 1 per cent of the population may be carrying the bacilli, and during outbreaks the number may be several times greater. Probably 25 per cent of all typhoid fever cases excrete bacilli for some weeks after con- valescence, and it is estimated that from 1 in 500 to 1 in 250 of the population are chronic carriers. What little evidence there is indicates that carriers are as numerous in dysentery and cholera as they are in typhoid fever. In yellow fever, sleeping sickness, and particularly in malaria, carriers are very numerous. There is evidence that there are not many carriers of measles or smallpox. 7. Any scheme of prevention which fails to take into ac- count carriers and missed cases is doomed to partial and perhaps complete failure, CHAPTER III. LIMITATIONS TO THE VALUE OF ISOLATION. Number of Mild Cases and Carriers. In the first chapter the attempt was made to show that pathogenic organisms do not usually develop outside of the body. Except for a few diseases, or under unusual circumstances, the saprophytic existence of disease germs is not to be looked for. Such sources of infection are much rarer than is generally assumed, and for most diseases may be entirely neglected. In the second chapter, evidence was presented that certain other sources of infection are very much more numerous than is generally believed, and it is here contended that no scheme of sanitation can have a scientific basis, or can have any possibility of success, which does not take full cognizance of them. It must be admitted by all that mild atypical cases of con- tagious diseases are very numerous. Every one who has had any experience with the last epidemic of smallpox in the United States and England must have had many unpleasant reminders of this. Health officers' reports are full of instances of the introduction of the disease into a community by per- sons unsuspected by any one of having the disease, and who often give rise to a whole series of cases. Similar experiences with scarlet fever are often reported. The most critical inves- tigation, such as that of our surgeons in the Spanish War, indicates that mild unrecognized cases of typhoid fever fully equal, if they do not exceed, the number of cases which are recognized and reported. Even with every facility for diagnosis, the amount of sore throat due to the diphtheria bacillus, but not so suspected, is fully equal to the amount of recognized diphtheria; and in many other infectious 133 134 THE SOURCES AND MODES OF INFECTION diseases these mild cases occur with varying degrees of frequency. Usually not Recognized. The extent to which these mild atypical cases escape recognition varies with the disease, the social condition of the people affected, the intelligence and conscientiousness of the physician, and the attitude of the health officer. That the majority of people will not consult a physician unless they are decidedly sick, is certain. That they will refrain from doing so if they expect to be reported to the health officer and to be placed under various restric- tions, is but in accord with human nature. A slight sore throat, or a fleeting rash, little suggestive of danger, will be lightly passed over, no physician will be called and no pre- cautions taken, and often there will be no thought of danger to others. It has always been known that a certain number of mild cases, difficult to recognize, could be expected in almost all infectious diseases, but it remained for the labora- tory worker to show how numerous they are in such diseases as typhoid fever, diphtheria, plague and malaria. The micro- scopic demonstration of the frequency with which clinically unrecognizable attacks of the above named and other diseases occur, had called the attention of clinicians and epi- demiologists to their probable occurrence in such other dis- eases as scarlet fever, smallpox, and yellow fever, the specific organisms of which have not as yet been discovered. So that at the present time the most careful epidemiologists, clinicians and laboratory workers begin to realize that very large num- bers of mild atypical and unrecognizable cases are bound to occur in most infectious diseases. But as yet few text-books on sanitation, clinical medicine, or even on bacteriology, lay sufficient emphasis on this fact. Nothing is more common than to find the young man just from the medical school, as well as the old practitioner, quick to deny the presence of scarlet fever, diphtheria, or typhoid jever because the symp- toms are not severe enough or because they deviate too much from the text-book description. But the large number LIMITATIONS TO THE VALUE OF ISOLATION 135 of the mild and aberrant cases, which usually remain " missed cases," and their importance in the extension of the infectious diseases, must now be admitted. Carriers Exceedingly Numerous. Still more numerous are the pure carriers, those persons in whose bodies the pathogenic bacteria and protozoa develop without causing symptoms. The recognition of this element of danger is due entirely to laboratory investigation, but, strange to say, most workers on bacteriology lay no more stress on this epidemio- logical factor than do the writers of treatises on hygiene or of text-books of medicine. In the preceding chapter sufficient evidence was presented to demonstrate the very great fre- quency with which these carrier cases occur. Their exist- ence and the virulence of the germs which they carry are now established facts. Numerous instances were given where such carriers appeared to have transmitted the disease to others. Indeed it is almost inconceivable that it should be otherwise. It is hardly possible that virulent typhoid bacilli or diphtheria bacilli produced in large numbers, as they fre- quently are in carriers, should not be equally as dangerous as those which develop in the bodies of the sick. That is, they are equally dangerous potentially; actually the well person moving freely about may be more dangerous to the com- munity than the sick person who is confined to the house. Approaching the subject from another standpoint, it is interesting to see how the discovery of these missed and car- rier cases has explained so much which we formerly did not understand. Effort to " Stamp Out " Disease. Twenty-five or thirty years ago we heard a great deal about "stamping out" the contagious diseases. That was the era of the building of hos- pitals for these diseases, of the organization of the sanitary service, of the discovery of pathogenic bacteria. The wonder- ful decrease in smallpox, the successful fight against cholera, the almost total disappearance of typhus fever, and the com- plete disappearance of plague, only foreshadowed, it was said, 136 THE SOURCES AND MODES OF INFECTION the extermination of typhoid fever, diphtheria, scarlet fever and measles. It was claimed that in those diseases which are exclusively contagious, if every case can be isolated until it is free from infection, the disease will be exterminated. It was believed that if people, and especially physicians, would take only a little more care, practically all cases of these diseases could be recognized and isolated. It was also thought to be not very difficult to control them until infection had disappeared. This confidence in the efficacy of isolation was in the then existing state of knowledge not unreasonable. Isolation and its Results in Providence. Previous to 1884 there had been in Providence no isolation to speak of in any of the contagious diseases except smallpox. In fact very many physicians did not consider that scarlet fever and diphtheria were very contagious, if contagious at all, but were inclined to look upon them as filth diseases. Restric- tive measures, including isolation at home and fumigation, began to be applied in 1884 and were quite steadily strength- ened during the next sixteen or seventeen years. I hoped, as did most health officers, that if scarlet fever and diph- theria could not be stamped out, they could be reduced to an insignificant remnant. But they were not stamped out in Providence, as they have not been in other cities. On the contrary, we had twice as many deaths in 1887 from scarlet fever as we had had during any year for seven years. Diph- theria from 1886 to 1890 also caused nearly double the num- ber of deaths that it had in the preceding four years. Of course we talked about epidemic waves, and noted that the mortality from the last wave was very much lower than from many that had preceded it, and congratulated ourselves that the outbreak was not so severe as in former years. But I began to ask myself what there was about epidemic waves that made restrictive measures of little use, and also to inquire if there was anything wrong about the restrictive measures. If we were limiting these diseases at all, it was certainly in a very moderate way. LIMITATIONS TO THE VALUE OF ISOLATION 137 Infection by Air and Fomites Thought Most Important. It was fully appreciated that in cities at least most cases of contagious disease cannot be traced to their source. Two theories have from antiquity been advanced in explanation. One is that most contagious diseases are easily carried by the atmosphere. Thus a person going by a house where there is scarlet fever, or passing an infected person in the street, might contract the disease. Such unconscious exposure might be quite common. But the principal source of the untraced cases of contagious disease was believed to be fo- mites. Walls and furniture were thought to become infected with the virus, and for weeks and months persons entering the room might contract disease through the breath. Books, toys, clothing and, in fact, every material thing, might readily become a source of infection and retain its virulence for months and years. These were perhaps not unreasonable a priori hypotheses, and they had some apparent backing of facts. At any rate they were the best theories we had. So health officers everywhere, including Providence, set about improving methods of disinfection. Sulphur fumigation was abandoned and the use of formaldehyde gas adopted in its place. Many cities set up a steam disinfecting plant, in Providence as early as 1887, and carpets, bedding and cloth- ing were disinfected by steam. Some cities, particularly on the continent of Europe, sent a band of uniformed disinfec- tors to wash and scrub everything in the infected house. Scarlet fever and diphtheria refused to be exterminated, though in Providence we did have rather less during the early nineties than we had had before. But I was not satisfied. It seemed to me that we were having too much of these diseases, that there must be a leak somewhere. Cultures Expected to Discover Much Diphtheria. Then for one disease a new weapon was put into our hands. Many had long recognized that the diagnosis of diphtheria was diffi- cult. It was suspected that many cases, because of this diffi- culty, escaped isolation entirely. When the culture method 138 THE SOURCES AND MODES OF INFECTION of diagnosis was devised I became enthusiastic and hopeful. We adopted it in Providence in January, 1895, and soon after required a negative culture before the patient was released from isolation. Hill has shown that without cultures the chance of error in the diagnosis of diphtheria is 50 per cent, which corresponds entirely with my frequently expressed opinion before the advent of the culture method. It is evi- dent, then, that the general use of cultures ought to bring to light great numbers of cases of diphtheria which were formerly unrecognized, and this it certainly does. If such an im- provement in diagnosis, and consequently in isolation, is brought about by the use of cultures, and if by the same means isolation can be maintained until the patient is certainly free from infection, there ought to follow a marked reduction in this disease. But it was quite otherwise. The deaths in Providence, which in 1894 had numbered 45, rose to 79 in 1895 and 125 in 1896, nearly twice as many in proportion to the population as there were in 1883, when there was no isola- tion, no disinfection and no antitoxin. The cases rose from 166 in 1894 to 386 in 1895 and 890 in 1896. The apparent reduction in the fatality rate from 27.71 to 14.07 indicates very plainly that the culture method of diagnosis had dis- covered a very large number of mild cases that would have previously been unrecognized, for antitoxin was only a minor factor in reducing the fatality, as it had been used in only a little over one-third of the cases. Isolation, disinfection, the use of cultures, and the opening of the contagious hospital had been accompanied by the greatest prevalence of the dis- ease for ten years. I do not mean to say that the adoption of the measures described had no effect upon the amount of diphtheria in Providence. I am sure that they had, and that this disease on the whole has been lessened, cases pre- vented and lives saved. But better results were expected. I was disappointed, and I think other health officers have been disappointed also. It seemed that the measures, car- ried out as they were, ought to have given better results. LIMITATIONS TO THE VALUE OF ISOLATION 139 It seemed that there was something which we did not understand. Failure of Hospital Isolation. One of the most effectual means of isolating cases of contagious diseases is by removal to the hospital. Certainly while in the hospital they can do no harm, and with reasonable care there is not much danger of their carrying infection back to their homes. Return cases do not occur in scarlet fever and diphtheria in more than about one to three per cent of discharges, and are not a factor of moment in the extension of these diseases. The idea that such hospitals would be a powerful factor in the extermina- tion of these diseases was not unreasonable. Smallpox hos- pitals have been in general use for a very long time, but they are not here under consideration, though it is questionable whether the hospital isolation of smallpox can ever accom- plish much alone and unaided by vaccination. But it is the hospitalization of scarlet fever and diphtheria that is par- ticularly instructive. English Hospitals. The use of hospitals for contagious diseases has been carried farther in England than elsewhere. Fifteen or twenty years ago the larger municipalities began building them on a considerable scale, and at present most of the English towns are provided with large hospitals for scarlet fever, and to a less extent for diphtheria. At the time when their construction was first strongly urged it was be- lieved that their use would result in the eradication of the diseases for which they were provided. The result has cer- tainly been disappointing, and there has recently been an active discussion as to whether they do an amount of good in restricting disease at all commensurate with their cost. 1 There is no doubt that the mortality from scarlet fever, both in 1 O'Connor, Geo. Wilson, Waddy and others, Brit.M. J., Lond., 1905, II, 630; Millard, Biss, Fraser, etc., Med. Press & Circ., Lond., 1904, LXXVIII, 215, 218, 241, 327, 377; Newsholme, Tr. Epidem. Soc. Lond., n. s., 1900-01, XX, 48; J. Hyg., 1901, I, 145; Millard, Pub. Health, 1901, XIII; J. T. Wilson, Pub. Health, 189&-97, IX, Sup., p. 21. 140 THE SOURCES AND MODES OF INFECTION England and the United States, has greatly diminished during recent years, but whether this has been due to restrictive measures or to lowered virulence has been disputed. The small death rate would indicate that the disease is really milder. This is also indicated by the fact that plural deaths, that is, more than one death in a family, are less frequent now than formerly. Again, local outbreaks of the old-time severe type occasionally appear. There was such an out- break in Providence in 1906-07, during which the case fatal- ity ran up to 12.85 per cent. Similar outbreaks have been noted in Keene, N. H., Haverhill, Worcester and Mont- real. The relatively lowered fatality in recent years has rendered it difficult to determine from the number of deaths just what influence restrictive measures, like hospital isola- tion, have had on the prevalence of scarlet fever, and increas- ing accuracy and care in reporting cases render it difficult to draw conclusions from the number of cases. But after all has been said it is clear that hospital isolation in scarlet fever has checked the disease very much less than was ex- pected, and sometimes appears to have had little effect. In Huddersfield, a city of nearly one hundred thousand people, from 1890 to 1899 the percentage of removals to the hospital was 90, yet the mean attack rate for the period was 4.3 per thousand. From 1900 to 1908 the removals to the hospital were 92.4 per cent and the attack rate 2.96. This is certainly a surprisingly high morbidity rate for a city where practically all reported cases have for twenty years been subjected to most excellent isolation. A similar state of things is noted in other cities. Some cities with a high per cent of removals to the hospital have more of the disease than do cities with no hospitals. The same is noted in rural communities. O'Connor, 1 medical officer of health of Leicestershire and Rut- land combined sanitary districts, reported -that in five par- ishes where the percentage of hospital isolation had for ten years reached 66 per cent, the attack rate was 6.2 per thou- 1 O'Connor, Brit. M. J., Lond., 1905, II, 630. LIMITATIONS TO THE VALUE OF ISOLATION 141 sand, while in five other parishes where hospital isolation was applied to only 14 per cent of the cases, the attack rate was 2.8. In another district, one parish which sent 60 per cent of its scarlet fever to the hospital, had three times as many cases as contiguous parishes which had little hospital isola- tion. Neech 1 says that in Cornwall from 1898 to 1907 there was practically no difference in the incidence of scarlet fever, in both urban and rural districts, connected with the use or failure to use isolation hospitals. Again, a city after it builds a hospital may have more of the disease than before. The aban- donment of hospital isolation may do no harm. In Leices- ter 2 the hospital was closed temporarily, and all the scarlet fever cases sent to their homes, with an actual decrease in number of reported cases. The hospital in other cities also has been closed without harm. I have thought it possible that at times hospital isolation might actually favor the spread of disease. When a case is removed to the hospital, comparatively little restraint is placed upon other members of the family, and if some of them are carriers, as they cer- tainly usually are in diphtheria, much harm may result. If, however, the case is kept at home, the rest of the family, particularly the children, are under considerable restraint for several weeks. Observations in Providence demonstrate that the retention of the case at home very rarely leads to the extension of the disease to other families in the house, and presumably to still less extension outside of the house. Why the Failure ? It may be admitted, and is doubtless true, that hospitals have prevented very many cases of dis- ease, and they may have been somewhat of a factor in its lessened prevalence. Nevertheless it must also be admitted that, notwithstanding the complete and excellent isolation secured in some cities like Huddersfield, scarlet fever has still prevailed to an alarming extent. When eighty to ninety per cent of the cases are removed to the hospital it is certain 1 Neech, Pub. Health, Lond., 1908-09, XXII, 296. * Rep. on Health of Leicester, 1902, 36. 142 THE SOURCES AND MODES OF INFECTION that the remainder will be so situated that home isolation will quite effectually prevent extension from them. In such cities almost all of the reported cases are thus effectively isolated, either in hospital or home. Yet the disease continues to pre- vail. There is evidently some source which escapes control. Newsholme has very clearly shown this. While admitting that isolation does prevent much sickness, he says that the disease still prevails and outbreaks still occur owing to some "epidemic influence." Now our purpose is to determine, if possible, what this "epidemic influence" is. What is the factor which is so powerful and continuous in its action that 90 to 95 per cent of perfection in the isolation of a contagious disease is unable to prevent a continued high prevalence and repeated epidemic waves ? American Hospital Experience. It is not merely English hospital experience which has shown the inefficiency of isola- tion. We have numerous instances in our own country. I have already referred to the experience of Providence, where increasing stringency in isolation was not followed by a decrease in contagious diseases. There has been much dif- ference between American cities as regards the strictness of enforced isolation. Some have been notoriously lax, while others have for years endeavored to secure a complete regis- tration of scarlet fever and diphtheria, and have adopted rigorous measures of isolation and disinfection, though in no American city has hospitalization been carried so far as it has in many English towns. But no one would be able, by study- ing mortality rates, to pick out the cities which pursue a rigorous policy of isolation. I collected data relating to the prevalence of scarlet fever and diphtheria in American cities for the decade 1890-1 899, 1 and it is surprising to note that the cities with the best sanitary administration frequently have a comparatively large amount of scarlet fever and diph- theria. During the period mentioned, Boston, in my opinion, had the best sanitary administration of any of the large cities, 1 Chapin, Municipal Sanitation, Providence, 1901, Table op. 480. LIMITATIONS TO THE VALUE OF ISOLATION 143 though New York stood high. The death rate from diph- theria in both cities was 84 per 100,000 living, from scarlet fever 25 for Boston, and 33 for New York. Certainly neither Chicago nor Cincinnati enforced such rigorous measures, yet the rates in these two cities were 72 and 71 for diphtheria and 17 and 7 for scarlet fever. Among the smaller Mas- sachusetts cities Fall River has usually had a rather ineffi- cient health service and little hospitalization, yet the death rate from diphtheria was 21 and from scarlet fever 15 per 100,000 living, while in Worcester the figures were 48 and 8, and this notwithstanding the fact that in Fall River the proportion of children is much greater than in most Amer- ican cities, and that the population is exceptionally ignorant as measured by illiteracy. Worcester has had a contagious- disease hospital since 1897, and has removed to it in some years as high as 63 per cent of its diphtheria cases. In general, Worcester secures an excellent registration of cases, and con- sequent isolation. Nevertheless Worcester has recently had, notwithstanding its increasing hospitalization and good home isolation, a severe outbreak of the disease. It seems a fair assumption that some factor much more important than the recognized cases of the disease has been at work in Worcester. If it were not so, the reported cases of the disease should not have risen from 132 in 1905 to 1178 in 1907. Diphtheria Isolation at Home. In Providence for some years previous to March, 1902, isolation in diphtheria was terminated only when a negative culture had been obtained from the patient. At that date a change was made, terminat- ing isolation ten days after the disappearance of exudation. This certainly liberated many cases still infectious, but this factor was of so little moment that the disease continued to decrease until on a certain day in August the city was entirely free from reported cases, a condition again nearly reached in 1907. Isolation in Institutions. It is by no means uncommon to see outbreaks in institutions lasting many months, al- 144 THE SOURCES AND MODES OF INFECTION though every case is promptly isolated and all persons in the institution are repeatedly examined by cultures from throat and nose. I have records of several such in Providence, and most health officers and managers of institutions have been through such unpleasant experiences. Here again we are forced to look for sources other than the recognizable cases. At a school in Owatonna, Minnesota, 1 there had been more or less diphtheria for years until a sharp outbreak in 1896 caused a very energetic effort to be made to stamp it out. Cultures were taken from everybody, and all persons in whom diphtheria bacilli were found were isolated, at first in a com- mon ward, but later each person in a separate room. Isola- tion was maintained until three successive negative cultures were obtained from throat and nose, and efficient disinfection was practiced. Still the disease persisted month after month, and some of the carriers, after release, were found to be still harboring the bacilli. One boy carried the bacilli for nineteen months. The attempt at the isolation of carriers was aban- doned, and several years later there was still more or less diphtheria in the institution. A still more notable failure of the isolation of diphtheria was at the Willard State Hospital for the insane in New York. 2 In this institution practically the same methods were adopted as at Owatonna, but nevertheless the disease persisted sev- eral years. Patients and carriers released from isolation after several negative cultures were still found to be carriers. If in an institution of this kind, where the strictest discipline is maintained, and where carriers can be isolated indefinitely, the most stringent measures of isolation and disinfection fail to stamp out the disease, what is to be expected of any such measures which can be adopted in an ordinary community? An outbreak in a hospital in California was managed in 1 St. Paul M. J., 1900, II, 223; Brit. M. J., Lond., 1898, I, 1008; Rep. St. Bd. Health, Minnesota, 1897-98, 465; Rep. Am. Pub. Health Ass., 1899, XXV, 546. 8 Rep. State Commission in Lunacy, N. Y., 1904, XVI. LIMITATIONS TO THE VALUE OF ISOLATION 145 the same way. 1 At first no effect seemed to be produced, and the outbreak lasted from April to August, but was as- sumed to have been finally checked by the same measures which failed at Owatonna and Willard. But as many out- breaks last even a shorter time, though no attention is paid to carriers, it is uncertain whether the outbreak was stamped out or died out. Sidney Davies 2 reports that at the Bostall- lane School in Woolwich diphtheria prevailed for three years notwithstanding repeated closures and bacterial examinations of the pupils. There is little doubt that at times a careful search for carriers and missed cases in schools and institu- tions and their isolation until two successive negative cul- tures from throat and nose are obtained, prove successful in checking outbreaks; there is no doubt, too, that outbreaks frequently die out of themselves; and it is shown by the exam- ples given above that it is at times impossible by any degree of isolation to stamp out an outbreak. How to manage such institutional epidemics cannot be determined until the con- trol of carriers is more carefully studied than it has been. Isolation a Failure in Measles. Measles is a disease which in cities it seems to be impossible to check to any appreciable extent by isolation. In Aberdeen 3 this was faith- fully tried for twenty years, 1883 to 1902, but no apparent effect was produced on the prevalence of the disease. Similar failures have been noted elsewhere. During the last half of this period in Aberdeen, when there was far more accurate registration and better control than before, the number of cases rose to 24,254, about fifty per cent more than in the first half of the period. A census of the children in certain schools indicated that from ninety to ninety-three per cent of children ' over ten years of age had had the disease. Restrictive meas- ures which protected only seven to ten per cent of the popu- lation from attack were then wisely abandoned. The very 1 Rep. State Bd. of Health, California, 1906-08, 201. 2 Rep. Med. Off. Health, Lond., 1908, 36. 8 Aberdeen, Report of Med. Off. of Health, 1904, 41. 146 THE SOURCES AND MODES OF INFECTION excellent report of the medical officer of health of Aberdeen discusses the subject very fully. In New York measles was first isolated in 1896, but not until 1902 were the regulations very rigorously enforced. The average death rate from 1895 to 1904 was 2.40, and the highest death rate since 1896 was reached in 1906, when it was 2.69. There is no evidence that the measures adopted in New York have had any more influence on the prevalence of the disease than did isolation and disinfection in Aberdeen. It seems in the highest degree probable that the disease prevails because of the unrecognized but infectious prodromal stage. No amount of isolation after the disease is recognized can atone for the harm done before the diagnosis is made. Isolation a Failure in Meningitis. Within a recent period the city of New York suffered from an exceptionally long and severe outbreak of cerebro-spinal meningitis. The attack rate was higher than in any of the other large American cities, and the outbreak lasted longer; and it lasted longer than it has in most of the German cities. On April 19, 1905, after the epidemic had continued for about two years, very strin- gent restrictive measures of isolation and disinfection were adopted. The outbreak was then declining, and that it would afterwards decline still more was to have been expected. But it was not "stamped out," for in 1907 there were reported 642 deaths and in 1908, 351. In Leith l great efforts were made to isolate all suspects and carriers, and the outbreak appeared to be checked, but in Edinburgh also it died out, though without such energetic measures. The experience in Germany seems to be that if in the beginning diligent search is made for carriers, and strict isolation is maintained, the outbreak may sometimes be checked, but after the disease has become established, and carriers are numerous, isolation is of little avail. These appear to be the views of Lingelsheim, Ostermann, Selter, Flatten and others. 1 Ker. Practitioner, Lond., 1908, LXXX, 66. LIMITATIONS TO THE VALUE OF ISOLATION 147 Isolation often a Failure in Smallpox. Smallpox is less likely to escape detection than is any other disease. Yet epidemics grow in the face of the most rigid isolation. Unrec- ognized cases, even in this disease, are so numerous that the isolation of the recognized cases often seems to be a complete failure. The State Board of Health of Minnesota, realiz- ing this, 1 has had the boldness to advise that no attempt be made to isolate, and that entire reliance be placed on vacci- nation. It was hoped that this would lead to more complete vaccination. There has been no alarming increase in small- pox in Minnesota, and Montana 2 is now following the lead of the former state. Why Does Isolation Fail ? The epidemiological evidence is conclusive that the isolation of recognized cases of con- tagious diseases often fails to check outbreaks which grow in spite of it; that it does not stamp out disease, and that it only reduces in a moderate degree the prevalence of the disease. We are forced to conclude that there is some defect in our procedures, or some other source of infection more important than the recognized cases. The error cannot be that isolation is too brief, for return cases and recurrences are not important factors. It is not that isolation is imper- fect, for isolation in the hospital is well-nigh complete, and careful observations in Providence indicate that the danger of extension outside the family from cases at home is very slight. Importance of Carriers and Missed Cases. As has been previously stated, two theories have been advanced to account for the appearance of untraced cases of contagious diseases: that of distant aerial infection, and that of the persistence of infection on things, i.e., fomites. In other chapters of this book it is shown that both of these modes of infection are of little moment, and in the first chapter it was shown to be 1 Resolution adopted July, 1906, to go into effect January, 1908, Am. J. Pub. Hyg., 1907, III, 227. 2 Am. J. Pub. Hyg., 1909, V, 815. 148 THE SOURCES AND MODES OF INFECTION unlikely that the specific organisms of our common diseases grow outside of the body. In the second chapter it was shown that they may grow in the body and yet produce few or no symptoms. It appears, then, highly probable that by far the most important factor in the causation of the con- tagious diseases are the "carrier" and " missed" cases. It is not for a moment suggested that the existence of carriers explains all epidemiological problems. There are, for instance, quite a number of contagious diseases which exhibit a varying degree of periodicity. We have as yet only the vaguest notions as to the causes of the variations in the prevalence of disease, its seasonal irregularities, and the rise and fall of epidemics. There is no reason to believe that these phenomena depend on the extra-corporal growth of pathogenic organisms, and it is probable that the seasonal distribution of such diseases as smallpox and scarlet fever is only in the most indirect manner dependent upon tempera- ture, rainfall, etc. It is not unlikely that the factors affecting the extension of these diseases are so numerous that their prevalence is really to a large extent a matter of chance. But whatever the factors may be, we must believe that they affect carriers as well as clinical cases. Why we have more carriers and more cases at one time than another, we cannot at present say. But it appears to be in the highest degree probable that in times of outbreaks, as well as in inter- epidemic periods, the chief factor in the extension of the disease is the existence of unrecognized infection in human beings or, in some diseases, in the lower animals. Need of Further Study. I would be the last person to assert that the views here set forth are unassailable and unal- terable. They doubtless will be modified; it may be that they are entirely erroneous. What is needed is further inves- tigation along the lines indicated, and a great deal of it. Unfortunately sanitary science is far from exact. We have few established truths, but many theories of greater or less probability, on which to base our practice. The probability LIMITATIONS TO THE VALUE OF ISOLATION 149 of each theory must be carefully weighed. Which is the most probable source of infection, the cesspool in the yard, the fomites that escaped disinfection, the patient who was re- leased too soon, or the unknown carrier ? The chances are greatly in favor of the last, and yet to-day sanitary practice almost completely ignores the carrier. It is not surprising that many health officers fail to appreciate the importance of the question which is here discussed. It is remarkable, however, that bacteriologists as a rule minimize the danger to be apprehended from carriers. Carriers not to be Ignored. It may be admitted that only 1 per cent of the population are diphtheria carriers, though as a matter of fact it must often be more than that; also that only 15 per cent of these carry virulent germs, though it is really often much greater. It may also be admitted that these bacilli are not usually so numerous as in the sick, though it is known* that they sometimes appear in pure culture; yet even admitting all this, there will be in inter-epidemic periods in a city of 100,000 people at least 150 well persons carrying virulent diphtheria bacilli. Why should the bacteriologist ignore these 150 sources of infection and insist on two throat and nose negative cultures from every reported patient ? Or why should he, as he occasionally does, recommend isolating the carriers in the family but ignore all other carriers ? Why neglect this whole question of carriers, and spend endless time in devising methods of liberating formaldehyde to kill the few bacilli that may remain about the house ? Why worry about the saliva that may have gotten onto a book, a coat, or the wall of a room, and neglect the reader of the book, the wearer of the coat and the dweller in the room, who is probably growing the germs in his throat and nose ? It is not easy to answer these questions, and so the bacteriologist withdraws to his laboratory and ingores them. But the health officer must answer them in one way or another. Principles of Diphtheria Isolation. To confine the dis- cussion for the moment to diphtheria, concerning which we 150 THE SOURCES AND MODES OF INFECTION have more accurate knowledge than we have for any other disease, there appear to be only two logical positions which the health officer can take in regard to its management. There is the possible policy of non-regulation. This the public would certainly not permit, and I think with very good reason. Or we can go to the other extreme and attempt to isolate every person carrying diphtheria bacilli, until they disappear from throat and nose, or until they are shown to be non- virulent. That is, of course, entirely impracticable except in small isolated communities or institutions, and it is often very difficult, and sometimes impossible then. In every large city there are hundreds of carriers who can never be detected, and who could not be controlled if they were. Virulent bacilli may remain for months, and the attempt to isolate for a pro- longed period prominent lawyers, business men, or physi- cians, would result in a breakdown of the whole system. As a matter of fact, such carriers escape from isolation while still infected. If cultures are taken daily, or every few days, it is usually not very long before the two negatives required by rule are secured and the patient is released, though sub- sequent cultures not infrequently reveal the bacillus. The ideal of health officers has been to keep up isolation until every spark of infection has died out, a very reasonable ideal, until it was learned that there are many hidden sparks scattered about the community, some of which are sure sooner or later to burst into flame. As it is impossible to attain the ideal of stamping out all infection, and as it is certain that many infected persons cannot be restrained at all, it is unrea- sonable to require restraint to the uttermost limit, of the recognized cases. It is often argued that the fact that all infected persons cannot be isolated, is no reason for not iso- lating all that can be found, anymore than the fact that many thieves escape is no reason for not imprisoning those thieves who are caught. But there is no true parallel here. The thief is a criminal, and his imprisonment is a punishment. The bacillus carrier is not a criminal, and he is isolated, not LIMITATIONS TO THE VALUE OF ISOLATION 151 as a punishment, but to protect the community. If the protection secured is not commensurate with the hardship inflicted, the procedure is unjust, and unwise from a socio- logical standpoint. A Compromise Necessary. But just as soon as we depart from the orthodox ideal, absolute isolation, we have to adopt some sort of compromise, a compromise which has no strictly logical defense. We are thus forced to follow one of three policies, either do nothing, which is unwise and would not be permitted, or attempt absolute isolation of all sources of infection, which is manifestly impossible, or employ a moderate degree of restriction, which, though not strictly logical, is nevertheless practicable, reasonable and to a con- siderable degree effective. Isolation of Real Value. While the most rigorous isola- tion does not stamp out diphtheria, we know that restriction does some good. The removal of a case to the hospital is shown by statistical evidence to prevent to some extent the development of secondary cases in the family. So too does good isolation at home. The warning sign on the house keeps out many people, some of whom would otherwise cer- tainly contract the disease. The regulation of school attend- ance prevents some school outbreaks, and others are checked by the prompt removal of the infecting child. The evidence points to an appreciable reduction in diphtheria prevalence in recent times, which I believe it is fair to consider as due, in part at least, to deliberate separation of the sick from the well under the direction of the sanitary authority or other- wise. Why more has not been accomplished by isolation is explained by the facts set forth in the preceding chapter. If because of the existence of so many unrecognized sources of infection, isolation can effect only a limited degree of pre- vention, could not substantially as much be accomplished by more moderate methods than are usually employed ? Why keep the patient indoors for six weeks when other mem- bers of the family with infected throats are going about ? 152 THE SOURCES AND MODES OF INFECTION Why keep from work the wage earners in an infected family when scores of other carriers are attending to their business without restraint ? Typhoid Carriers cannot be Isolated. The isolation of typhoid carriers is no more possible, just, or effectual in check- ing disease, than is the isolation of diphtheria carriers. As was shown in the preceding chapter, the number of carriers and convalescents excreting bacilli is probably much larger than the number of cases confined indoors. It seems to me useless to attempt to confine convalescents two or three months after their recovery. There certainly would be most energetic opposition on the part of the public, which probably would ultimately be sustained by the courts. The health officer who attempted to isolate convalescents until bacilli were no longer to be found in their urine, would be in an awkward position if he allowed chronic carriers to go at large, and he would be in a still more awkward position if he at- tempted to isolate all chronic carriers indefinitely. There are probably 200,000 cases of typhoid fever in the United States each year, and 3 per cent of these would be 6,000. To attempt to isolate 6,000 carriers would of course be futile. Not one-tenth of them could even be discovered. To isolate the small fraction of carriers who can be discovered is practi- cally useless, and therefore unjust. It may be, and probably is, wise to regulate the life of such carriers as may be dis- covered, and at times to forbid their engaging in certain occupations, such as those of cook, waitress and milk dealer, but to attempt their isolation under present conditions seems to me most unwise. Isolation too Rigorous. I believe that, on the whole, iso- lation in our prevailing contagious diseases is carried farther than is necessary; that less rigorous measures would accom- plish practically as much good, and that there would be less temptation to conceal cases and to interpret doubtful symp- toms in line with the patient's desires. It is impossible here to lay down in detail a scheme for the proper isolation of LIMITATIONS TO THE VALUE OF ISOLATION 153 contagious diseases. What are the best methods of dealing with these diseases is a matter for free discussion, and also for experiment. It is to call attention to the new facts, and to elicit discussion from the new viewpoints, that these pages are written. Degree of Contagiousness. Before considering some of the principles which should guide the application of meas- ures of isolation, we should consider what are, under the ordinary conditions of life, the chances of infection from a single individual. Until recently it has been believed to be very great. That smallpox hospitals are placed a mile or more from inhabited districts, that physicians clothe them- selves with gowns and caps and rubber boots on their visits to infectious cases, and that it is insisted that the ceiling of a room occupied by such a case be disinfected, indicate a belief that the virus of the contagious diseases is exceedingly diffusive and exceedingly virulent. Why such a belief is not well founded will be shown in succeeding chapters, and it will suffice here to call attention to the fact that the chance of an infected person transmitting the infection to another is not nearly so great as is generally supposed. This is a mathematical necessity. We now know that the number of infected persons is very much greater than was formerly believed, and that they often remain infected for much longer periods than was suspected. It necessarily follows that the danger to be apprehended from any one person at any one time is much less than was once thought. Factors Involved. The chance of an infected person giv- ing rise to the disease, or of transmitting the infection to others, varies greatly with the intensity of the infection, or the number of disease germs in the secretions or excre- tions, their virulence, the volume of the excretions, the care exercised, the occupation, and the surroundings generally. Conditions in the home and in institutions are usually much more favorable than elsewhere for the transmission of infec- tion. Yet in the home the chance of such extension of disease 154 THE SOURCES AND MODES OF INFECTION is not as great as has been supposed. In Providence, 1 the chance of persons contracting diphtheria from another mem- ber of the family who has the disease is only about 1 in 15. The chance of a child between two and six years contract- ing it is 1 in 5; of an adult, 1 in 40. The chance of a woman contracting the disease in the family is about three times as great as that of a man. For scarlet fever the figures are not very different. Every one must have noted repeated instances where only one of a family of children is attacked by scarlet fever or diphtheria, the rest of the family remaining well, though isolation may have been far from satisfactory. Danger Less outside Family. Outside of the family, in school, in factory and in ordinary social relations, except per- haps in the play of young children, the chance of transmitting the disease must be very much less. Instances are not rare where children, presumably in the infectious stage of scarlet fever, have mingled freely with others for many days, or perhaps weeks, with little or no extension of the disease. I have notes of an instance where a boy with scarlet fever in the sore-throat stage attended a Sunday-school festival, and no other case developed among the large number of children present. At an infant asylum a child was sick with mild scarlet fever for 17 days, mingling freely with about 75 chil- dren, mostly under 5 years of age, and only 3 other cases re- sulted. At a large school a girl returned at the end of the first week of an attack of scarlet fever, and continued her attendance for 20 days. Only 3 or 4 cases developed in that school. Similar and even more marked instances of appar- ently feeble infectivity are reported by others. I have made no attempt to collect such cases, but I happen to have before me three reported by Butler. 2 One child, taken sick Novem- ber 5, attended school from November 11 to November 19. Two other children, attacked December 26 and 27 respec- tively, attended different schools up to January 16. In only 1 Rep. Supt. of Health, Providence, 1909. 8 Butler, Proc. Roy. Soc. Med., Lond., 1908, I, Epidemiol. Sec., 225. LIMITATIONS TO THE VALUE OF ISOLATION 155 one of the three schools did even a single case occur. I have known of a teacher with virulent diphtheria bacilli in her throat from the first of January to the middle of April, who taught in a kindergarten all that time, but who did not trans- mit the disease to any one. Many of the instances of typhoid carriers which have been referred to, show that such persons may for long periods of time fail to infect any one, even though employed as cooks or handlers of milk. I have known of cases of smallpox remaining for several days in lodging houses or hospital wards, or traveling on railroads, without any one contracting the disease. Failure to infect may be due sometimes, perhaps, to intermittency in the excretion of germs, sometimes to lack of contact, and sometimes to lack of susceptibility on the part of the receiver of the infection. Whatever the cause may be, we must recognize that an infected person often mingles freely with the public without transmitting the infection to another. Carriers less Infective than the Sick. As has been stated, it is not improbable that the infectivity of a well car- rier may for several reasons be less than that of a person sick with the disease. It may then be argued that the danger from carriers has in the preceding pages been very much exaggerated. It is not to be denied that the probable danger from a single carrier is small. Their number, however, is large, so that the danger from all carriers is large, and is, I believe, a very considerable factor in the maintenance of the contagious diseases. Isolation should Vary. In applying isolation to the prevention of disease it must be kept in mind that different conditions require different procedures. Thus when an ordi- nary contagious disease first appears, after a considerable absence, in a small community, or in an institution, very rigorous measures of isolation are usually desirable, as expe- rience has shown that very often an outbreak is thus effec- tively checked in its beginning. Isolation in Villages. The efficacy of isolation under such 156 THE SOURCES AND MODES OF INFECTION circumstances is well illustrated by the history of outbreaks of the common contagious diseases in the smaller cities, town- ships and villages of Michigan. The data given in the annual reports of the board of health of that state are of great epi- demiological interest, and my discussion of the subject on another occasion is here given. 1 " Only those places are considered which have remained free from the disease for at least sixty days, and this unfor- tunately is never true of a city of any considerable size. The outbreaks reported are arranged in groups, one in which iso- lation and disinfection were both enforced, one in which they were both neglected, and one in which the reports did not state with sufficient exactness what restrictive measures were carried out. The following is a summary of some of the tables in the report : Number of Cases per Outbreak. Number of Cases per Outbreak. Restric- tive Meas- ures not Enforced. Restric- tive Meas- ures En- forced . Restric- tive Meas- ure? not Enforced. Restric- tive Measures Enforced. 2.22 1.71 2.53 4.67 3.80 Typhoid fever, 10 years . . Diphtheria, 14 years Scarlet fever, 14 years .... Measles, 1 1 years 5.82 11.12 11.95 48.30 3.13 2.11 2.32 3.03 1900 a 14 n 6.72 4.85 10.43 27.60 32.00 Smallpox Isolation Effective. - " Several things are to be noted in connection with these figures. In the first place, isolation and disinfection accomplish very much in preventing the extension of all these diseases. The number of facts is so great, the outbreaks of each disease running into the hun- dreds, and the difference between good and bad sanitation is so manifest in each one of the years for each one of the 1 J. Mass. Ass. Bds. Health, Bost., 1904, XIV, 226. LIMITATIONS TO THE VALUE OF ISOLATION 157 diseases, that the success achieved must be a very real one. It appears certain that isolation and disinfection as practiced in the smaller communities of Michigan reduce the cases of contagious disease in round numbers from forty-five to ninety- five per cent. In scarlet fever, diphtheria, measles and small- pox, isolation appears from the reports, as one would expect, to have very much more restrictive effect than disinfection. "As will be shown later, disinfection probably has little influence in restricting contagious diseases, but in view of existing ideas and practices it is probable that isolation and disinfection were not so distinctly separable as is indicated by the reports of the local health officers. One of the things which appeared most remarkable to the writer in these re- ports is the apparently great restriction of measles. It has certainly been the experience in all our larger cities that restrictive measures, no matter how energetic, have had very little effect in reducing the mortality from this disease. But in the smaller communities in Michigan it appears that where isolation and disinfection are well carried out there is nearly ninety-four per cent less cases per outbreak than where pre- cautions are neglected. Cause of Success. " But if one examines the original returns of the health officers it appears plain why such good results are obtained. If the first case of the disease coming to a community is early recognized and isolated the chances are good that the outbreak will be at once checked. The chances that such a case will be so recognized in a village are very much greater than in a city. If, however, the outbreak is not checked at its very outset, the chances are, even in the country, that its extension will be very considerable. As a matter of fact, a great many of the first cases coming to small communities are promptly recognized and isolated, and as a result an outbreak is prevented. It is because outbreaks are in rural communities so often nipped in the bud that the application of restrictive measures in such communities makes such a good showing. What is true of measles is true also 158 THE SOURCES AND MODES OF INFECTION of other diseases, particularly of scarlet fever and diphtheria. It is success in applying restrictive measures to the first case that is the principal cause of the apparent efficiency of these methods. If every appearance of contagious disease in these rural communities had gained some headway before restric- tive measures were applied, the showing would not be nearly so favorable. In fact, in the large cities in Michigan, where these diseases are always epidemic, restrictive measures, even of a very rigorous type, have not enabled the health officers to * stamp them out.' Thus in Detroit it was the custom for many years to l quarantine' absolutely every house where there was scarlet fever or diphtheria. No one was allowed to go out, and the inspectors visited the house twice a day and furnished provisions for the poor at an expense of thousands of dollars annually. Yet these diseases were no more 'stamped out' in Detroit than they have been in Chicago or other cities where milder methods have prevailed." Isolation in Common Diseases. When measles, diph- theria or scarlet fever appears in a town or institution which has for some time been free from the disease, the patient ought to be isolated until it is as certain as medical science can determine that he is free from infection. At least this should be attempted. If it should happen, as it sometimes does, that the diphtheria patient retains virulent bacilli for many months, or that the scarlet-fever patient has a discharging ear for a similar period, isolation will probably have to be abandoned. But isolation is worth trying, for in the majority of instances safety is secured in a few weeks. Contacts also should be carefully examined and isolated, or otherwise re- stricted as to their relations with the community. If after a reasonable time the disease is " stamped out " the health officer is to be congratulated. If it is not stamped out he may well temper the rigor of his restrictive measures. When a rare disease, as plague, leprosy, or cholera, appears in Europe or North America, equally stringent measures should be employed. At present smallpox belongs rather LIMITATIONS TO THE VALUE OF ISOLATION 159 to this class of rare diseases, and strict isolation of the first case and careful examination and supervision of contacts is desirable and useful. Many Carriers make Isolation Useless. The effective- ness of isolation, and the consequent reason for its practice, varies inversely as the number of carriers and missed cases. With the enormous number of carriers of pneumococci, it is entirely useless to enforce isolation of cases of pneumonia. Influenza belongs to the same class as pneumonia, in which compulsory isolation is useless. It is probable also that noth- ing which the health officer can do in the way of isolation will have any effect on the extent of outbreaks of cerebro- spinal meningitis. The enforced isolation of typhoid fever, owing to the number of carriers, will usually prove of little value. While it is probable that there are few carriers of measles, yet the long prodromal but extremely infectious stage renders ineffectual measures of restriction. If isolation of measles is attempted, little can be hoped for other than a slight postponement of the age of attack, and no measures should be adopted which inflict any great hardship. No one advocates the isolation, in the ordinary meaning of the term, of pulmonary tuberculosis. It is not attempted in this disease simply because infected persons are so numerous that it is impossible. If tuberculosis were as rare as leprosy, strict isolation would be, and should be, demanded. On the other hand, there are so few carriers of smallpox that, even with the mild type of the disease prevailing, strict isolation is often advisable. To discover the proportion of carriers to recognized cases, for each disease, is a matter of the greatest practical impor- tance. We must have a fairly clear idea of how many un- recognized human foci of infection there are before we can determine upon what methods of isolation, if any, are likely to prove effective. Yet the investigation of carriers has received comparatively little attention at the hands of bacteriologists. 160 THE SOURCES AND MODES OF INFECTION Value of Hospitals. Hospitals are useful for protecting the family, for checking outbreaks in institutions, for receiv- ing cases from lodging houses and hotels, for furnishing better medical service, and for relieving the overworked housewife in the families of the poor. It is an unnecessary expense to provide hospital accommodations for all cases of scarlet fever and diphtheria, or for ninety per cent or even eighty per cent. That half or two-thirds of the cases of these diseases can, for all practical purposes, be equally well cared for at home, is not unlikely. Home Isolation. In home isolation of scarlet fever, diph- theria and measles, the patient should, for the benefit of the public, be kept in the house. It does not seem reasonable to prolong isolation until all possible chance of infection has ceased. Exactly what the period should be in each disease should now be a topic for renewed discussion. Isolation in Providence. In Providence at present the period of isolation for scarlet fever is four weeks from the beginning of the case. Up to 1902 the period was five weeks. Since the reduction in the period of isolation, the attack rate has been about 33 per 100,000 living, although one of our largest epidemic waves occurred during this period, and regis- tration is certainly far better than formerly. From 1884 to 1901 the attack rate was about 34 per 100,000. In diph- theria, isolation is maintained for ten days after the disap- pearance of the membrane. The decrease in the prevalence of the disease which followed the adoption of less rigorous isolation has been previously alluded to. Family. When the attempt is made to isolate the patient in the family from the family, in order to protect other mem- bers, the duration of isolation may well be left to the dis- cretion of the family. It is the duty of the health officer to explain that the longer the separation of sick from well is maintained, the more likely it is to be effective. In scarlet fever there is no means of determining when the patient is free from infection. I am in the habit of recommending LIMITATIONS TO THE VALUE OF ISOLATION 161 separation from the family for six weeks, perhaps a somewhat shorter time if the case is a mild one, and longer if there is aural or nasal discharge. In Providence, scarlet-fever cases are usually sent home from the hospital in four or five weeks, if free from nose and ear discharge. No regard need be paid to desquamation, as the experience of English hospitals has shown that no danger is to be feared from that source. 1 It is absurd to isolate with strictness a diphtheria patient from the rest of the family unless cultures have shown that the rest of the family are free from the bacilli. If such home iso- lation is to be undertaken at all, it should be continued, if possible, until two or three successive negative cultures have been obtained. Hospital. Diphtheria cases in Providence are usually in the hospital until two, three or four successive negative cul- tures from the throat have been secured, the greater precau- tion being taken when the child is to return to an institution. Sometimes the patient is sent out while still harboring bacilli. The duration of isolation of the living cases is 19.65 days, and the percentage of return cases has been 1.9. In London 2 the period of detention of 6866 cases was 57.5 days, and the percentage of return cases was 1.2, about 0.5 per cent less than in Providence, although the period of detention was almost three times as long. The duration of stay in the Provi- dence hospital for scarlet fever, surviving cases, is 45.67 days, and the percentage of return cases is 3.4. In the London hospitals the period of detention is 64.9 days, 3 and the per- centage of return cases, 1902-04, was 3.22. 1 Metropolitan Asylums Board Report on Return Cases of Scarlet Fever and Diphtheria, 1902-04, 6. See also my discussion of this subject in FiskeFund Essay LII, published by R. I. Medical Society, Providence, 1909. * Metropolitan Asylums Board Report on Return Cases of Scarlet Fever and Diphtheria, 1901-02, 59, 62. 3 Metropolitan Asylums Board Report on Return Cases of Scarlet Fever and Diphtheria, 1902-04, 5, 23. 162 THE SOURCES AND MODES OF INFECTION School. School children in infected families should be excluded from school for a liberal period, for this works little hardship, and the state should make special effort to keep its schools free from disease. .Yet school exclusion may be, and often is, carried to excess. In Providence children living in a family where there is scarlet fever are excluded from school for four weeks from the beginning of the last case. In all except the poorer class of houses children living in other families in the house are permitted to attend school. In diphtheria, children in the infected family are not allowed in school .for four weeks, provided that if all the school chil- dren in the family yield two throat and nose negative cultures, they may attend school after the warning sign has been removed (which is ten days after the disappearance of the exudation). Children in other families in the better class of houses are admitted to school if one negative culture is ob- tained from throat and nose. After the expiration of a month, all children in families where there has been diphtheria are usually admitted to school whether or not they are carrying morphologically typical bacilli, and of course quite a number do go to school while infected. Doubtless these carriers may at times infect others in school, but even if two negative cul- tures were required before readmission, some children would probably still prove infectious. Absolute security is impos- sible, and the rule should be so framed as to accomplish a maximum amount of good with a minimum amount of an- noyance. Wage Earners. There is little reason for excluding wage earners from their work except in a few occupations. Most of the carriers we cannot restrain, and therefore why penalize those who have the additional misfortune of sickness in their families ? The most dangerous carriers are those who handle milk; hence milk producers and dealers living in infected families should be excluded from work. Judging from the number of reported outbreaks, the danger is probably greater for LIMITATIONS TO THE VALUE OF ISOLATION 163 typhoid fever than for any other disease. It is probably wise to regulate the occupation of all typhoid contacts who handle any kind of food that is eaten raw. Perhaps the same should be done with diphtheria contacts. Teachers and nurses may very properly be prevented from following their usual vocations if they live in infected families. It has been my custom also to exclude from work car conductors, post- men, barbers and department-store clerks. I doubt, however, whether this is always advisable. I am very sure that laborers, mill operatives and office clerks need not, under ordinary circumstances, be kept from their business. Summary. As regards the employment of isolation for the prevention of the spread of infectious disease we may fairly conclude: 1. The danger to be apprehended from a single infected person is much less than has been supposed. 2. Isolation is of far less value than was believed a few years ago. 3. The fewer the infected persons in any community or institution the more likely is isolation to be successful. Iso- lation in an extensive outbreak rarely accomplishes much. 4. The effectiveness of isolation varies inversely as the number of missed cases and carriers. 5. Hospitalization in such diseases as scarlet fever and diphtheria cannot be expected to exterminate them, and the majority of patients can be as well cared for in their homes. 6. In diphtheria, scarlet fever and measles there is rarely, and only in certain occupations, any necessity for interfering with the freedom of the wage earners of the family. 7. The isolation of school children should be more strict than that of adults, for less hardship results, and there is more danger in the mingling of children than in the inter- course of adults. CHAPTER IV. INFECTION BY CONTACT. Most Obvious Mode. Contact infection is the most obvious mode of transmission of the infectious diseases. For the sick to touch the well, and thus infect them, seems to be the most natural way of accounting for the spread of these diseases. If contact infection can explain epidemiological phenomena, there is no occasion for assuming the growth of pathogenic germs outside of the body, or of infection by fo- mites or infection by air, or any other similar theory, and no such theory should be adopted as a working hypothesis unless pretty strong evidence can be brought to its support. Venereal Diseases. Gonorrhea and S3^philis are univer- sally believed to be transmitted exclusively by contact, and almost invariably by a special kind of contact. This idea is so firmly fixed in the minds, of medical men and the laity, that no matter how many cases occur which it is impossible to trace to their source, no one ever suggests that these diseases are air-borne, or that their germs maintain a sapro- phytic life. No matter how much the patient may protest, it will still be held that the infection is due to contact, and in the vast majority of cases to contact involved in the sexual act. Gonorrhea, particularly, is believed to be almost never transmitted except by the most direct contact; yet there is at times as much reason for assuming that the gonococcus is air-borne, or clings to the walls of rooms and thence infects their occupants, as there is to assume the same for scarlet fever. Yet so firmly are we held by tradition that if any of us should suggest such an origin for gonorrhea it would pro- voke only a smile, while such sources of scarlet fever are accepted as well established. 164 INFECTION BY CONTACT 165 Gonorrhea in Babies' Hospital. The spread of gonococ- cus infection in institutions for children is very suggestive of the ways in which other infections are transmitted. A very interesting account of institutional infection is given by Holt. 1 At the Babies' Hospital in New York, from 1894 to 1898 inclusive, 64 cases of gonococcus vaginitis were admit- ted, and 16 cases developed in the hospital. In the summer of 1899, three children suffering from gonococcus vaginitis were inadvertently admitted to the country branch of the hospital, and though the danger was realized, and every effort was made to prevent the extension of the disease, by pro- viding separate nurses for the infected cases, by washing the napkins separately, and boiling and disinfecting them, never- theless 15 girls contracted vaginitis. In 1901 similar trouble was experienced, and notwithstanding the most vigorous measures qf isolation and napkin disinfection, 22 cases devel- oped in the one cottage to which the three original cases were admitted. The physicians were inclined to look upon general house infection as the only explanation of the origin of the cases. In November, 1902, a new hospital building was occupied for the first time, and it was hoped that it could be kept free from the disease, but 5 cases were unwittingly admitted during the first six months, and 29 cases of vagi- nitis and 8 of gonococcus arthritis developed in the institu- tion. During the year, 13 cases were admitted, and 66 were contracted in the hospital. Although the infected cases were all strictly isolated, on two occasions a child, even in another part of the hospital, developed the disease. For a time napkins were discarded and pads used, which could be burned; separate thermometers, baths and supplies were required for each child; wash cloths were burned, and tub baths forbidden. Bed clothing was disinfected with the greatest care. There was thought to be absolutely no opportunity for direct contact between child and child. When diphtheria or scarlet fever persists in an institution in 1 Holt, N. York M. J, [etc.], 1905, LXXXJ, 521. 166 THE SOURCES AND MODES OF INFECTION such a manner, it is at once attributed to persistent infection of the building itself, and it is suggested by Holt as a pos- sibility in this instance also. Carried by Nurses. But the gonococcus is an excep- tionally frail organism, and it is impossible to believe that persistent infection of a building or its contents can occur. Actually, in the Babies' Hospital, it was found that the nurse was the carrier of the germs from child to child, and the two cases which developed in distant wards, and which were sup- posed to be perfectly isolated and under the care of different nurses, were attended by the same night nurse who looked after the infected cases. Finally, when the strictest disin- fection had failed to check the disease, it was at last con- trolled by requiring that the nurses should practice a strict medical asepsis, and disinfect the hands in every instance immediately after bathing or changing the napkins of each child. Here was a disease which continued to spread after the erratic and persistent manner of scarlet fever and diph- theria, and which was shown to depend exclusively upon con- tact infection. Air-borne infection and fomites infection can have no part in institutional gonococcus infections, for the gonococcus dies so quickly that such modes of transfer- ence are impossible. Yet this infection is most persistent and troublesome in many institutions for the care of young children. Contact not always Direct. Gonorrheal infection is not only quite common in institutions, but it is often found in infants and young children in their homes. It is believed to result usually from the child sleeping with its parents, or to direct contact with the hands of the mother while washing or dressing the child. I have also known of cases of the direct transfer of the disease on instruments in a physician's office. It has thus been necessary to modify our conception of the mode of transmission of gonorrhea, and although it is still conceived of as due exclusively to contact infection, it is now recognized that the contact need not always be direct INFECTION BY CONTACT 167 between the sick and the well, but some infected person or thing may act as intermediary. Yet from what is known of the weak resistance of the gonococcus, the interval of time must be brief. The term contact infection as now employed means just that kind of transference of rather fresh infecting material from one to another. It does not necessarily imply actual contact between sick and well, but it does imply that there are no long intervals of time in which the infective materials may become dry and inert. The transfer of gonor- rheal pus from child to child on a syringe, or on the fingers of the nurse, are examples of contact infection. If the pillow used by an infected child were put away for a week or two, and when brought out caused ophthalmia in the infant who used it, it would be an example of fomites infection. The distinction between the two types of disease transference, though not sharply or accurately defined, is a reasonable and practical one. Thus every one admits that gonorrhea is fre- quently transferred by indirect contact infection, as it may be called, but it is never suggested that this disease is spread by fomites. Syphilis spread solely by Contact. While it appears to be pretty well determined that Treponema pallida is the cause of syphilis, we have as yet no data as to the cultivation of this organism or its persistence outside of the body. Its cultivation outside the body certainly is not easy, and it may be suspected that its life is short; but it is not impossible that the virus may retain its virulence for some days or weeks, as does that of rabies, variola and vaccinia. At present we have to rely solely on clinical evidence as to these points, and the universal opinion of this much studied disease is that the virus develops only in human beings (and some of the apes), that it is not very persistent, and that it is trans- mitted solely by contact. No one has ever suggested that syphilis is an air-borne disease in the ordinary sense, though one or two cases of droplet infection have been reported. 1 1 Buckley, Syphilis in the Innocent, N. Y. ; 1894, 176. 168 THE SOURCES AND MODES OF INFECTION No matter how obscure may be the origin of cases, no one would attribute them to aerial infection, or to dwelling in an infected house. Infection during the sexual act is undoubt- edly the cause of by far the larger proportion of the cases of this disease, yet in the aggregate a great number of cases are caused in other ways. Non-sexual Contact. Buckley in the work just quoted shows that probably ten per cent of the initial lesions are extragenital. Exceedingly infectious lesions at times are found in the mouth so that kissing is a not unusual mode of infection. At a party in Philadelphia, where there were kissing games, 8 persons were infected by a young man. One of these was a man who received his infection indirectly on the lips of a girl just previously kissed by the syphilitic. 1 Syphilis is often transmitted by nursing and the sucking of wounds. Mediate contact by all sorts of infected articles is common and Buckley has collected many hundreds of instances. Among the articles named are cups, glasses, spoons and other eating-utensils, pipes, toilet articles, underclothing, bathing suits, handkerchiefs, bed- ding, pins, string, wind instruments of all kinds, glass blowers' tubes, pencils, coins, nursing-bottles, sponges, syringes, surgeons' instruments, dentists' tools and barbers' utensils. Buckley's book is mainly taken up with an enumeration of these modes of infection. A perusal of these reports is extremely interesting, for though it is not claimed that every case narrated was caused in the man- ner assumed, yet it is evident that all such modes of trans- mission are possible, and one is greatly impressed by the vast number of ways in which fresh secretions may be passed from one to another. While the time during which the various articles retained their infection is unknown, or at least is not given in the reports of cases, it is apparent that almost none of the instances of mediate contact were the result of long persistent infection. Fomites infection is not an important 1 Shamberg, J. Am. M. Ass., Chicago, 1911, LVII, 783. INFECTION BY CONTACT 169 factor in the spread of syphilis. Buckley 1 says that the danger from soiled clothing, rags, or second-hand garments " is infinitely less than is commonly supposed, and relatively few instances have been recorded, and none of these are very clear or satisfactory." In the few instances which he gives, the infective material might well have been very fresh. Typhoid Fever by Contact. Of late years a great deal has been written about the transmission of typhoid fever by contact from case to case, and this mode of infection appears to have attained greater prominence in connection with this than with any other of the common infectious diseases. My attention was first drawn to the importance of contact infec- tion in typhoid fever by the vivid description given by Sedg- wick of an outbreak which he investigated in 1892 in Bondville, Massachusetts. He says: 2 "Children abound; and, as there are no fences, and because it is the custom, they mingle freely, playing together and passing from house to house. The families are of that grade in which food always stands upon the table ; meals are irregular except for those who must obey the factory bell. The children play awhile, then visit the privies, and with unwashed hands finger the food upon the table. Then they eat awhile and return to play. Or, changing the order of things, they play in the dirt and eat and run to the privy, then eat, play, and eat again, and this in various houses and in various privies. For them, so long as they are friendly, all things are common, dirt, dinners and privies; and, to illustrate exactly how secondary infection may go on, I may describe in detail one case which I personally witnessed. A whole family (of six or more) was in one room. Four of them had the ' fever.' Two of these were children in the prodromal stage. A table stood by the window covered with food, prominent among which was a big piece of cake. It was early September, and a very warm day; but every window was shut and the odor sickening. Flies innumerable 1 Buckley, Syphilis in the Innocent, New York, 1894, 156. 2 Sedgwick, Rep. Bd. Health Mass., Bost., 1892, 736. 170 THE SOURCES AND MODES OF INFECTION buzzed about, resting, now on the sick people, now on the food. A kind-hearted neighbor was tending the baby. By and by one of the children having the fever withdrew to the privy, probably suffering with diarrhea, but soon returning, slouched over to the food, drove away some of the flies, and fingered the cake listlessly, finally breaking off a piece, but not eating it. Stirred by this example, another child slid from his seat in a half-stupid way, moved to the table, and, taking the same cake in both hands, bit off a piece and swal- lowed it. The first boy had not washed his hands, and if the second boy suffered from secondary infection, I could not wonder at it. "This was one case; but I have seen so often the table of food standing hours long in the kitchen, and serving as one station in the dirty round of lives like these, that it is easy for me to understand how dirt, diarrhea and dinner too often get sadly confused. The privies had been obviously in bad condition, and, from some, filthy streams ran down between them and the houses. In and around these streams the chil- dren played. Given any original imported case, the infection might easily have reached these trickling streams. Children's fingers might thence carry the germs to the food, and thus the journey of the germs from one living intestine to another be completed. Or, again, given in such a community an imported case and no disinfection, as was the condition here at first. The importer, while in the early stages, handles with unclean hands food for others; or the clothing of such a per- son gets infected and is handled; there need be, then, no diffi- culty in completing the history. It follows as a matter of course." Contact Typhoid in Spanish War. Probably the report of Reed, Vaughan and Shakespeare 1 did more than anything else to call attention to the importance of contact infection in the epidemiology of this disease. This commission found 1 Abst. of Rep. on the Origin and Spread of Typhoid Fever in U. S. Military Camps during the Spanish War of 1898, Wash,, 1900. INFECTION BY CONTACT 171 that infected water played little part in the development of typhoid fever in the camps. They also found that probably every regiment brought into camp one or more mild unrec- ognized cases or carriers, and that these were the starting points of outbreaks. It was shown that the fever was not evenly distributed through the regiments, but was more or less localized in companies or squads (p. Ill et seq.). While they attributed a certain amount of the disease to carriage by flies and by dust, they considered contact infec- tion from man to man the most important cause. Of 1608 cases especially studied, and which were accurately located as to place and time, 35.01 per cent were directly connectible and 27.79 per cent indirectly connectible attacks; total con- nectible attacks, 62.80 per cent (p. 184). Owing to the unsat- isfactory methods, or lack of method, of excreta disposal, the shoes, clothing and hands of the men, as also the blankets and tentage, became more or less soiled with excreta, and infection of the men became easy, and in fact unavoidable. Men detailed as hospital orderlies were, after they had per- formed the duty of emptying bedpans, seen to go directly to their meals without washing their hands, and even to dis- tribute food to their comrades. In South Africa. Similar conclusions were arrived at by the surgeons who studied typhoid fever, which proved equally disastrous to the English, in the Boer War, but on the whole, however, the English, while recognizing the impor- tance of contact infection, did nol place so much stress upon it as did the Americans. 1 Contact Typhoid in Civil Life. Outbreaks in civil life have of late frequently been attributed largely to contact infection. Winslow 2 reported an outbreak in Newport, R. I., which probably had its origin in an infected well, but which 1 Col. Lane-Notter, Tr. Epidemiol. Soc., Lond., 1904, XXIII, 149; J. Roy. Army Med. Corps, Lond., 1905, IV, 587, 693; Tooth, Brit. M. J., Lond., 1901, I, 642. * Winslow, Technology Quarterly, 1901, XIV. 172 THE SOURCES AND MODES OF INFECTION was continued by contact infection. He coined the word " prosodemic " to describe this extension of the disease from case to case. Water-borne and milk-borne outbreaks of typhoid fever usually develop suddenly, a large number of cases being reported within a short time. That they do not end so suddenly but, even after the infected water and milk are eliminated, continue, decreasing gradually, is a phenome- non which becomes apparent from the examination of the charts of such outbreaks. This prolongation of the outbreak is due to the prosedemic infection of Winslow, and has been noted by Whipple l for water outbreaks, and by Trask 2 for milk outbreaks. During a water-borne outbreak at Lincoln, England, from 50 to 60 per cent of the cases were due to personal contact. 3 Municipal Outbreaks. Many local outbreaks have been believed to be due almost, if not quite, exclusively to contact infection. Such an outbreak was reported by Weston and Tarbett in Knoxville, 4 Jordan in Winnipeg, 5 Magrath in Springfield, 6 Noetel in Beuthen, 7 and Weil in Rathsweiler. 8 Freeman 9 states that the majority of the outbreaks in the smaller towns of Virginia appear to be due to contact infec- tion. The authority of Koch has done much to direct atten- tion to the importance of contact infection in the spread of typhoid fever in civil life. In a report on a village outbreak in Trier 10 he says that small country epidemics will usually 1 Whipple, Typhoid Fever, 1908, 209. 1 Trask, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 41, 38. 3 Pub. Health, Lond., 1905, XVIII, 129. 4 Weston and Tarbett, Am. Pub. Health Ass. Rep., 1907, XXXIII, Pt. 1, 63. 5 Jordan, Abst. in J. Am. M. Ass., Chicago, 1905, XLIV, 563. 8 Magrath, Am. J. Pub. Hyg., Bost., 1905, I, 467. 7 Noetel, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., 1904, XLVII,211. 8 Weil, Med. News, N. Y., 1904, LXXXIV, 467. 8 Freeman, J. Am. M. Ass., Chicago, 1909, LIII, 1263. 10 Koch, Die Bekampfung des Typhus, Berlin, 1903. INFECTION BY CONTACT 173 be found to be due to this mode of infection. In the particu- lar outbreak investigated all the cases were found to be due to contact, that is, to the direct transfer from person to per- son, and the source was in most instances unrecognized mild cases, often in children. He then describes conditions very much like those reported by Sedgwick. Fecal matter was observed in the dooryards where it could readily infect the children playing about, and would certainly be carried indoors on their shoes. Fulton, 1 Egbert 2 and others have shown that typhoid fever prevails far more extensively in the country than in the city. Formerly, when less was known about the etiology of the disease, polluted well water was believed to be the chief factor in its causation, but it now appears that it is far more likely to depend on contact infection. In Hospitals. Typhoid fever frequently develops in hos- pitals and other institutions, presumably by contact infec- tion. Occasionally explosive outbreaks due to infected milk or food are observed, but many institutional outbreaks are characterized by a slow and irregular development of cases. The disease chiefly attacks those who are brought in close contact with the sick, physicians and especially nurses. Fifty or sixty years ago few cases of hospital infection were re- corded. It is suggested that this may have been due to the fact that nurses in those days were usually women well along in years, and therefore not so susceptible to the disease, and usually immune. During recent years typhoid fever among nurses and ward tenders has been quite com- mon. It is stated that in 1902-6, of an annual aver- age of 322 nurses in six hospitals, 26 contracted typhoid fever and 12 of an average of 94 ward tenders contracted typhoid fever while on duty. It is said that in the Lon- don hospitals typhoid fever is twenty times as common 1 Fulton, J. Am. M. Ass., Chicago, 1904, XLII, 73. 2 Egbert, Am. Med., Phila., 1905, IX, 649. 3 Joslin and Overlander, Boston M. & S. J., 1907, CLVII, 428. 174 THE SOURCES AND MODES OF INFECTION among nurses as among women of the same ages in other occupations. 1 Goodall 2 says that during the years 1892- 1899 there were treated in the London hospitals 5913 typhoid patients, and 100 attendants contracted the disease. In four hospitals not admitting typhoid fever no cases developed. Schuder, 3 Neufeld, 4 McCrae, 5 Talayrach, 6 Edsall 7 and others have reported an excessive prevalence of typhoid fever among the attendants on cases of this disease in hospitals, and they have also noticed numerous instances in which it has devel- oped among other patients. Nurses and others infect their hands while caring for typhoid patients, and then without washing the hands, or after careless washing, infect their own mouths directly, or by handling their food and drink. Through the same carelessness they also infect other patients. Neufeld refers to the transfer of the germs on a thermometer and in a bath. Edsall has seen a nurse given the double duty of emptying the bedpans of typhoid cases and pre- paring special diet, and a patient was observed to empty a bedpan and then proceed to his dinner without washing his hands. Nurses also wipe out the mouths of patients with a bit of gauze on the finger, a procedure which was believed by Holt to be one of the means of spreading gonorrheal infec- tion in the Babies' Hospital. By introducing strict cleanli- ness Edsall was able to stop this transference of the disease. In Other Institutions. Sometimes quite marked out- breaks occur in institutions, due presumably to contact in- fection. Usually water, milk and other food as sources of infection can be excluded, and the irregular and slow devel- opment of the cases, and perhaps the discovery of carriers or Pub. Health, Lond., 1905, XVIII, 142. Goodall, Trans. Epidem. Soc., Lond., 1900. Schuder, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., XXXVIII, 251. Neufeld, Kolle u. Wassermann, Handbuch [etc.], Jena, 1903, II, 296. McCrae, Mod. Med. [Osier], Phila. & N. Y., 1907, II, 82. Talayrach, Arch. d. med. et de pharm. milit., Par., 1903, XLII, 393. 1 Edsall, Am. J. M. Sc., Phila., 1908, n. s., CXXXV, 469. INFECTION BY CONTACT 175 missed cases, renders the extension of the disease by per- sonal contact highly probable. In an almshouse in New Haven, 1 37 cases occurred during a period of some months. Mild cases were concealed and worked in the kitchen, and it was impossible to teach the inmates cleanly habits. At a soldiers' home at Lafayette, Indiana, there were 65 cases due to contact infection, probably chiefly from the physician. 2 At the State Hospital for the Insane at Trenton there occurred between April 8 and August 13, 1907, 80 cases with 16 deaths, due in all probability to contact infection, largely in the kitchen and pantry. 3 Ravenel 4 reports an outbreak in a boarding house at the University of Wisconsin, where 41 cases developed, probably as the result of a patient working in the pantry during the prodromal period of his illness. Sedgwick 5 reports the case of a chambermaid, and also of a laundress, who contracted typhoid fever from handling soiled linen. A waitress, also, who ate bread cut by the other two, developed the disease. Wolcott tells of the matron of a hospital who caught the disease from han- dling infected bedding and neglecting to wash the hands. McCrae 6 reports an instance of infection from careless han- dling of typhoid cultures in the laboratory, and a similar case occurred in an insane asylum at Northampton, Mass. 7 Dr. Mann tells me that a number of nurses eating at the same table in the Homeopathic Hospital in Boston con- tracted typhoid fever, probably from a waitress whose sister was sick with the disease, and who herself was perhaps a carrier. 1 Rep. Bd. Health, New Haven, 1905, 6. 2 Hurty, J. Am. M. Ass., Chicago, 1909, LIII, 1263. 1 Rep. St. Bd. Health, New Jersey, 1907, 149. < Ravenel and Smith, K. W., J. Am. M. Ass., Chicago, 1909, LII, 1635. 6 Sedgwick, J. Mass. Ass. Bds. Health, Bost., 1900, X, 148. 6 McCrae, Mod. Med. [Osier], Phila. & N. Y., 1907, II, 82. 7 Rep. Bd. Health, Mass., Bost., 1899, 762. 176 THE SOURCES AND MODES OF INFECTION Contact on Shipboard. Many of the instances of infec- tion by carriers referred to in Chapter II were almost cer- tainly the result of contact infection, and many more could be easily collected. Occasionally small outbreaks occur on shipboard, where it is possible to exclude all modes of infec- tion but contact. Thus, 9 cases on an Atlantic liner were traced to a saloon steward. 1 On the United States ship Con- necticut there were three outbreaks in 1907, almost certainly due to contact infection. 2 In the Family. During 1908 I noted three small out- breaks of typhoid fever in Providence, due apparently to con- tact infection. In one instance there were 10 cases in three closely related families, in another 8 cases in three such families, and in the third outbreak there were 7 cases in two families. Such family outbreaks are noticed in Provi- dence nearly every year, and they are referred to so often in current medical literature that it does not seem necessary to give additional references. Contact outbreaks in hotels and boarding houses, as well as in various public institutions, are also frequently reported. Hill in Birmingham, in 1898, traced 10 per cent of the typhoid-fever cases to contact with other cases. In Manchester in the same year about 13 per cent were traced in the same way, and in 1906, 36.8 per cent. Edsall attributed 27 per cent of 250 cases to contact, and Forster 117 of 386 cases, and McCrae 68 of 500 cases. It would be easy to prolong the discussion and show that med- ical men are everywhere attributing more and more impor- tance to contact infection in this disease. It is to be noted that in few of the reported instances of contact infection is there any direct and conclusive proof that the disease was caused in the manner alleged. The evidence is by no means so convincing as to mode of infection as it is in so many water-borne and milk-borne outbreaks, and from the nature of things it rarely can be so. 1 Rep. Med. Off. Health, Glasgow, 1907, 147. 2 McDonnold, Mil. Surgeon, Carlisle, Pa., 1908, XXIII, 29. INFECTION BY CONTACT 177 Evidence of Contact Infection. But when water and food as vehicles of infection are excluded, when the disease devel- ops in persons who are in contact with the sick or with car- riers, and when the fingers, possibly or perhaps evidently soiled with excreta, are seen to touch food, eating-utensils, and sometimes the lips, the probability of the development of the disease in this manner is so evident that observers are constantly seeing in contact infection the cause of family, institutional and community outbreaks of this disease. The importance now attributed to contact infection is the result of a careful estimate of probabilities. Amount of Contact Infection. In 1908 there were 11,375 deaths from typhoid fever in the registration area of the United States, which doubtless means considerably over 100,000 cases. The registration area includes about one-half the population of the country. While a certain amount of typhoid fever is caused by milk, it must be a very small fraction of the great total. As will be shown, milk outbreaks are usually well marked, and probably not a very great deal of milk-borne infection escapes notice. Again, while in some cities the larger part of the typhoid fever is due to infected water, it is not so in most cities, and certainly only a small part of the total typhoid fever in the country can be traced to such a source. It is not likely in my own city for instance that more than 20 per cent of the 4300 cases of typhoid fever during the past twenty-five years have been due to infected water or milk; and infected oysters, celery, etc., certainly play a very unimportant part in the causation of the disease. As we shall see, it is improbable that air-borne infection or dust infection is of any moment in civil life. The only other important source of typhoid fever which has been sug- gested is fly-borne infection. It will be shown also that infection by means of flies probably accounts for only a small part of our typhoid fever. By exclusion, then, we are led to the conclusion that contact infection is the chief source of our typhoid fever. 178 THE SOURCES AND MODES OF INFECTION Why should we not, in the absence of direct evidence as to other modes of infection, assume at once that contact, that is, the more or less direct transfer of infective material from person to person, is the principal source of contagious disease ? Why neglect the most obvious and direct mode of transfer in favor of more circuitous paths ? There are several reasons why contact infection in this disease has been neglected. Why Contact Infection has been Neglected. One reason has been the undue emphasis laid upon other modes of trans- mission. Formerly air infection was considered of great moment, and as this fell into disrepute, undue weight was attached to water and milk infection, partly, no doubt, because of the dramatic character of so many outbreaks. Another reason for doubting the importance of contact infection is the prevalent notion that typhoid fever is essentially an intes- tinal disease, and that it must be caused by infected food. It now appears that typhoid fever is not an intestinal disease, and in some cases the intestines are not involved and the feces are free from bacilli during the whole sickness. But the bacilli are found in the blood stream in the earliest stages, and it seems to be more likely that they enter the circulation through the upper part of the alimentary tract than through the intestines after running the gauntlet of the gastric secre- tions. Even if it be denied that the tonsils and stomach are the portals of entry of the typhoid bacilli, it is highly probable that bacilli taken into the mouth in small masses find their way to the lower part of the alimentary tract by means of the small quantities of saliva which are constantly swallowed. It has certainly been demonstrated that tubercle bacilli are swallowed and thus reach the intestines. People are not Cleanly. Then, too, contact infection in typhoid fever supposes an intimacy with the most offen- sive substances, which most persons would vehemently deny. Nevertheless it appears that the fingers of human beings, and secondarily everything that the fingers touch, are fre- INFECTION BY CONTACT 179 quently contaminated with excremental matter. The colon bacillus is for all practical purposes a good test for the pres- ence of excrement, and it is somewhat of a shock to learn that it is found on the hands of five to ten per cent of ordinarily cleanly people. Winslow * and Hall, 2 while studying the dis- semination of typhoid fever by carriers, recovered fecal bacteria from the finger nails and hands after the usual pro- cedures following the use of the closet and toilet. An inspec- tion of the privies or water-closets in railway stations, factories, shops and tenement houses shows that they usually present evidence of contamination with feces and urine, and in many instances are constantly in a horribly filthy condition. It is only in the better class of hotels and residences that these apartments are kept in even an apparently cleanly condition, and this is only by dint of constant vigilance and frequent cleansing. There can be no doubt that even very careful people frequently infect the seat, their fingers, the pull, the door, etc., and that in a large proportion of privies and water- closets the users almost certainly infect their fingers with at least traces of their own or others' excremental matter. Yet how many persons are there who invariably wash the hands after the use of a closet ? How many make it a rule never to put the fingers in the mouth ? Yesterday I saw a workman carrying a can of beer to his friends. His thumb was im- mersed a couple of inches in the beverage. Had he washed his hands after leaving the barroom water-closet ? At a recent sanitary convention I noticed the colored waiter stick his finger into a glass which he, however, did not remove, and which the speaker soon drank from. What was the recent history of that finger ? Does the fruit peddler wash his hands after using the tenement privy before he ventures to sort his fruit ? Do the waitress, the milk peddler, the candy seller, the Pullman porter, the soda-water clerk, the baker's boy, the delicatessen man always wash the hands before taking .. l Winslow, J. Mass. Ass. Bds. Health, Bost., 1903, XIII, 144. 2 Hall, Rep. Med. Off. Health, Bristol, Eng.. 1908, 27. 180 THE SOURCES AND MODES OF INFECTION up their work? Are the toilets in their places of business so cleanly that such a precaution is not necessary ? How- ever shocking it may seem, it is certain that it requires only a little observation to demonstrate that the path from intes- tines to mouth is not always a circuitous one. Contact with Carriers. Until recently it would have been argued that contact infection is not an important factor in typhoid fever because only a small proportion of the cases can be shown to have been in contact with this disease, and because the large proportion of cases of this fever are more or less isolated in their homes because of the sickness. But we now know that there are vast numbers of mild unrecog- nized cases, and most important of all, that the number of carriers is very great. There are doubtless 200,000 cases of this disease in the United States each year. If only 3 per cent of these become chronic carriers, and if a carrier remains such only three years, we should have a carrier population of 18,000 persons, practically all unknown and taking no pre- cautions against infecting others. If we add to these the 25 per cent of convalescents, who for some weeks are excret- ing the bacilli in their urine, it appears that there is a very respectable army of unrecognized sources of typhoid infection. At present we have no definite knowledge of the origin of the larger number of our cases of typhoid fever. In view of the almost universal careless habits of the people, and the great number of carriers, why not adopt as a working hypothesis the most obvious source of infection, infection by contact ? Danger from Privies. This view that contact infection is the most important factor in the causation of this disease, is borne out by the observation that the more promptly and effectively human excrement is disposed of, the less chance there is for contact infection and the less the disease prevails. When the disposal is exceptionally bad, as in army camps, lumber, mining and railroad camps, then this disease is al- most always very common, In thoroughly sewered and clean INFECTION BY CONTACT 181 cities, provided the water and milk are not contaminated, typhoid fever is comparatively rare. The privy vault stores up fecal matter on the premises and is rarely kept as clean as a water-closet, and the area around privies is often filthy also. It has often been noted that the removal of privy vaults has been followed by a decrease in typhoid fever. In Providence the disease fell off forty per cent after most of the privy vaults were abolished. Many other American cities in which typhoid fever is not maintained by a polluted water supply, show a steadily decreasing prevalence of this disease as privy vaults are gotten rid of. In England Pringle 1 has shown that in fourteen towns with middens the typhoid rate was 0.25 per 1000, while in fourteen water-closet towns it was 0.19. In Ipswich there was a marked decrease in typhoid fever following the removal of the middens. 2 A similar de- crease was noted in Oldham, Leicester 3 and other cities. On the other hand more " pail closets " remain in Nottingham than in most English cities, and to this Boobbyer 4 attributes the fact that typhoid fever has decreased less in that town than in the other great towns of England. Like reports of a decrease in the disease following removal of privies come from such widely separated places as Winnipeg 5 and Mel- bourne. 8 There are also numerous reports to the effect that in the same town typhoid fever is much more common in houses without water-closets than in those with them. This may be due in part to the storing of fecal matter on the premises of the former, and it may be due also to the fact that houses with privies are usually of a poorer class, and the inhabitants less cleanly in their personal habits, or to other reasons; but 1 Pringle, Pub. Health, Lond., 1902-03, XV, 630. 2 Pub. Health, Lond., 1908-09, XXII, 414. 3 Rep. Med. Off. Health, Leicester, Eng., 1908, 29. 4 Boobbyer, Rep. Health of Nottingham, 1908, 53. 6 Rep. Dept. Pub. Health, Winnipeg, 1908, 4. 6 Jamieson, J,, Australas. M; Gaz., Sydney, 1903, XXII, 56. 182 THE SOURCES AND MODES OF INFECTION these facts of typhoid distribution accord with the view that the disease is largely spread by contact from person to person. In Birmingham, 1 the incidence of typhoid fever in " pail " and water-closet houses was as 65 to 43, and there has been a steady decrease in the disease as the " pail closets " have been abolished. In Nottingham there was (in ten years) 1 case in each 37 houses with privies, and 1 in each 558 water-closet houses; in Salford it was 1 to 20 and 1 to 42 respectively, 2 and in Gorton the cases were two or three times as numerous in privy houses as in water- closet houses. 3 At Leigh, 4 typhoid fever was four times as prevalent among colliery workers as among the rest of the population, owing, in the opinion of the inspector, to the filthy mode of excreta disposal in the mines. In Glasgow 5 second- ary cases of the disease developed in 23 per cent of the cases in houses with privies and in 6 per cent of the cases in houses with water-closets. Every one who has had practical experience in sanitary inspection work knows that privy vaults not only serve as storehouses for excrement, but their presence encourages its careless disposal in the yards and on ash heaps. The filthy condition of the ground about the houses, leading to contami- nation of feet and hands of children, as reported by Sedgwick and by Koch, is rarely noticed on premises provided with water-closets. It may be urged that the excess of typhoid fever in privy towns is due to infection by flies rather than infection by contact, and this may be true to some extent; but if flies were the chief factor we should scarcely expect a great difference between water-closet and privy houses in the same town. So also the infection of miners, as noticed 1 Rep. Health of Birmingham, 1906, 49, and 1908, 49. a Pringle, Pub. Health, Lond., 1902-03, XV, 630. Martin, Pub. Health, Lond., 1904-05, XVII, 709. 4 Sweeting, Rep. Med. Off. Local Gov. Bd., Lond., 1907-08, XXXVII, 57. 6 Rep. Med. Off. Health, Glasgow, 1902, 97. INFECTION BY CONTACT 183 by Sweeting, cannot be due to flies. In Providence after the removal of privies the decrease in typhoid fever was as great in winter, when there were no flies, as during the fly season. Amebic Dysentery. There is no reason why amebic dysentery may not be transmitted by personal contact, but if, as is 1 generally believed, the ameba is quite widely dis- tributed in the soil, it is likely that in countries where the disease is endemic, man is the least common source of infec- tion. Nevertheless cases do develop from contact with t)ther cases. Lemoine 1 has reported such infections in France, in one instance at least, probably due to the use of the same bedpan, douche, etc. The infecting case was a carrier of ten years' standing. Allan 2 writes that in Charlotte, N. C., he observed four cases of amebic dysentery which he believed were due to contact with chronic carriers. Bacillary Dysentery. Bacillary dysentery, like typhoid fever, is a great scourge of military life, and outbreaks of a serious character are not rare in institutions such as hospitals for the insane. The bacillus is found in the feces of the patients and also in convalescents. There is every reason for believing that this disease, like typhoid fever, is frequently spread by more or less direct contact. 3 Conradi 4 described a village outbreak near Metz where 70 cases occurred during a period of three months. Several carriers were found in infected families, and conditions favoring contact infection were noted, very similar to those observed in the outbreaks of typhoid fever studied by Koch in Trier. Dodge 5 reports the case of a laboratory worker who got some of a culture of the dysentery bacillus hi his eye; the tears ran profusely and were swallowed, and in twenty-four hours an attack of 1 Lemoine, Bull, et mem. Soc. med. de hop. de Par., 1908, 3 s., XXV, 640. 2 Allan, Med. Rec., N. Y., 1910, LXXVII, 63. 3 Shiga, Mod. Med. [Osier], Phila. & N. Y., 1907, II, 781; Scheube, Diseases of Warm Climates, 2d Ed., Phila., 466. 4 Festschrift von Robert Koch, 1903, 555. 5 Dodge, Am, Pub, Health Ass. Rep., 1905, XXX, 310. 184 THE SOURCES AND MODES OF INFECTION dysentery developed. An outbreak of 49 cases, developing in the characteristic slow irregular manner of contact outbreaks, was reported in the Connecticut Hospital for the Insane. 1 Kruse 2 reports a similar outbreak in Germany, and two in Holland. Epidemic dysentery is quite common in hospitals for the insane, and its prevalence is explained as due chiefly to contact infection, for the carelessness of many patients and the impossibility of controlling their habits offer every opportunity for this sort of diffusion. 3 Cholera and Contact. If typhoid fever and dysentery are spread by means of contact infection, we should expect that cholera would be. That less is written about it is due probably to the fact that in recent years less attention has been, paid to cholera than to the more common diseases. The literature relating to typhoid fever has of late been many times more voluminous than that relating to cholera. Never- theless most writers attribute some importance to contact infection in this disease, and some consider it an etiological factor of very great importance. The filthy conditions of vil- lage life described by Sedgwick in America and Koch in Ger- many as giving rise to typhoid fever, are far surpassed in danger by the habits of vast numbers of the poorer people who dwell in cholera-infested countries. The opportunities for the direct transference of fecal matter from person to person are far greater in Asiatic countries than they are with us, and a number of writers have emphasized the part played by personal contagion in this disease. Gotschlich 4 refers to 1 Rep. St. Bd. Health, Connect., 1903, 234. 2 Kruse, Deutsche med. Wchnschr., 1901, XXVII, 370, 386. 8 See Reports of Commissioners in Lunacy (Eng.) since 1903; also Heuser, Deutsche med. Wchnschr., 1909, XXXV, 1694; Ryder, Boston M. & S. J., 1909, CLXI, 681; Haenisch, Ztschr. f. Hyg. u. Infections- krankh., Leipz., 1908, LX, 245; Mott, Tr. Epidem. Soc., Lond., 1901-02, and Arch. Neurol. Path. Lab., Lond. Co. Asyl., Lond., 1903,. II, 735; Prior, Australas. M. Cong. Tr., Victoria, 1909, III, 383. 4 Gotschlich, Kolle and Wassermann, Handbuch [etc.], Jena, 1904, IV, 108. INFECTION BY CONTACT 185 this factor, and a number of our officers in the Philippines have dwelt upon its importance. Woodruff l says that while infected water played some part in the great epidemic in Manila, the filthy habits of the people were the chief cause of the extension of the disease. He speaks of an outbreak of eighty cases in a provincial town due to food prepared in Manila by a caterer who soon died of cholera. Heiser 2 con- siders that the handling of foodstuffs and of the leaves in which the betel nut is wrapped, by dealers and prospective purchasers, is one of the chief ways in which cholera is spread, and McLaughlin 3 considers the " carrier " with filthy habits the greatest source of danger. He says that contact infection of visitors in the houses of the sick is a common means of disseminating the disease. Schumburg 4 reported several small outbreaks of cholera near Hamburg caused by contact infection. Shakespeare 5 reports several instances in which cholera was apparently caused by han- dling soiled linen, some of which might perhaps be considered rather as examples of fomites infection. Macrae 6 reports the infection of hospital nurses with cholera in a manner similar to the infection of nurses with typhoid fever. Heiser 7 says that in the Philippines, physicians and nurses who had been trained to aseptic methods did not contract cholera but untrained attendants frequently did through contact with patients. Diarrhea. Newsholme 8 believes that much infantile diarrhea is due to direct contact infection in the home, and he suggests that it is brought about by " sucking infective Woodruff, J. Am. M. Ass., Chicago, 1905, XLV, 1160. Heiser, J. Am. M. Ass., Chicago, 1907, XLVIII, 856. McLaughlin, J. Am. M. Ass., Chicago, 1909, LII, 1153. Schumburg, Ztschr. f. arztl. Fortbild., Jena, 1905, II, 567. Shakespeare, Rep. on Cholera in Europe and India, U. S. Gov. Printing Office, 1890, 81. Macrae, Indian M. Gaz., 1909, XLIV, 361. Heiser, Bull. State Bd. Health, N. Y., Sept., 1911. 8 Newsholme, J. Hyg., Cambridge, 1906, VI, 139. 186 THE SOURCES AND MODES OF INFECTION matter from dirty fingers, from dummy teats and in other ways." Naish ! and Niven 2 are largely in accord with this view. Sandilands, 3 in an extended article, cites others as reporting hospital and laboratory infection as well as evidence from house and neighborhood outbreaks. From his own study of multiple cases in houses, and of local dis- tribution, he is convinced that contact plays an important part in the causation of this disease. Doubtless the most complete epidemiological study of summer diarrhea has been made by Peters, 4 and it should be read by every one interested in the subject. Flies are considered as possible carriers of infection, and while no evidence against this theory is found, much positive evidence is presented to show that contact infection is an important factor in the causa- tion of this disease. Hook Worm Disease. The European type of the disease is caused by Anchylostoma duodenalis, while the American type is due to a slightly different species, Uncinaria ameri- cana. 5 The symptoms are caused by the growth of the worms, which are about half an inch long, in the intestine, where they fasten themselves to the intestinal wall, and not only suck blood themselves, but also cause considerable free bleeding from the wounds which they make. The eggs, which are laid in the intestine, do not there develop, owing to lack of oxygen, but hatch soon after the feces are voided, and the young worms then pass through several stages of growth in moist earth or mud. Until recently it was believed that human infection resulted from drinking water containing the young worms, or by get- 1 Naish, Pub. Health, Lond., 1909-10, XXIII, 168. 2 Niven, Proc. Roy. Soc. Med., Lond., 1909-10, III, Epidemiol. Sect., 131. 3 Sandilands, Proc. Roy. Soc. Med., Lond., 1909-10, III, Epidemiol. Sect., 95. 4 Peters, J. Hyg., Cambridge, 1910, X, 602. 6 Stiles, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 10, 1903. INFECTION BY CONTACT 187 ting them onto fingers or into food, and so into the mouth. It was first suggested by Looss in 1898 that infection might take place through the skin, and he believed that he had himself become infected in that way. In 1901 he proved the correctness of his surmises by experiments. Later Grassi, Fieri and Noe placed a few drops of water containing worms upon the skin, but only one of the three became infected. In 1902 Looss successfully repeated his experiments. It had meantime been noticed by Bentley and Boycott and Haldane that dermatitis was apt to be found in regions where the disease prevailed, and it was suspected that it might be due to the passage of the worms through the skin. Smith 1 showed that by placing infected earth on the arm, not only was infec- tion caused, but there resulted a dermatitis at the site of the application. Ashford, whose careful study of the disease in Porto Rico, and whose brilliant success in curing its vic- tims give his opinion great weight, believes that the skin is by far the most important avenue by which the worms infect the body. 2 Uncinariasis is, then, par excellence, a dis- ease due to contact infection. Fortunately the disease is usually easily curable under medical treatment, and the freeing of individuals from worms by this treatment is necessarily an important part of the prevention of the disease. It is evident from the mode of infection that the pollution of the soil with human feces is the principal factor in the spread of the disease. Properly constructed privies or water-closets, with the ultimate dis- posal of the fecal matter by deep burial, or some other means to prevent the pollution of the upper layers of the soil, are the essentials of prophylaxis. Contact Infection less Easy in Some Diseases than in Others. Gonorrhea is a disease in which the infecting secre- tion is not likely to be much handled, and when it occurs 1 Smith, C. A., J. Am. M. Ass., Chicago, 1905, XLV, 1142. 2 Ashford, Rep. of Commission on Study and Treatment of "Anemia" in Porto Rico, 1904, 37. 188 _ THE SOURCES AND MODES OF INFECTION in young children the secretion is often received on a diaper. Yet it has been shown in the preceding pages that infantile gonorrhea is spread exclusively by contact infection. Al- though the children themselves take little part in the spread of the disease in hospitals where they are isolated from one another, and although nurses and physicians have been shown the danger of carrying the disease, and have been instructed to take the greatest precautions, yet this disease may be maintained for months in an institution solely by means of infection borne on thermometers, syringes, etc., but particu- larly on the hands of attendants. In typhoid fever the bacilli are contained in the feces and urine, which even careless people are supposed to avoid touch- ing. Nevertheless it appears that the fingers of careful people, and even of trained nurses, are infected in this manner, and that transfer to the mouth with the subsequent development of typhoid fever results. There is much evidence that this mode of transference is an important, if not the most important, factor in the spread of this disease. Contact with Saliva. If contact infection is important in such diseases as gonorrhea, typhoid fever, dysentery and cholera, in which the infecting material is not constantly at hand, and is usually strenuously avoided, how much more important must this mode of transference be in diseases in which the specific germs are found in the secretions of the nose and mouth or in the sputum. Danger from Fingers. Probably the chief vehicle for the conveyance of nasal and oral secretion from one to another is the fingers. If one takes the trouble to watch for a short time his neighbors, or even himself, unless he has been par- ticularly trained in such matters, he will be surprised to note the number of times that the fingers go to the mouth and the nose. Not only is the saliva made use of for a great variety of purposes, and numberless articles are for one reason or another placed in the mouth, but for no reason whatever, and all unconsciously, the fingers are with great frequency INFECTION BY CONTACT 189 raised to the lips or the nose. Who can doubt that if the salivary glands secreted indigo the fingers would contin- ually be stained a deep blue, and who can doubt that if the nasal and oral secretions contain the germs of disease these germs will be almost as constantly found upon the fingers? All successful commerce is reciprocal, and in this universal trade in human saliva the fingers not only bring foreign secretions to the mouth of their owner, but there ex- changing them for his own, distribute the latter to everything that the hand touches. This happens not once but scores and hundreds of times during the day's round of the indi- vidual. The cook spreads his saliva on the muffins and rolls, the waitress infects the glasses and spoons, the moistened fingers of the peddler arrange his fruit, the thumb of the milk- man is in his measure, the reader moistens the pages of his book, the conductor his transfer tickets, the " lady " the fingers of her glove. Every one is busily engaged in this dis- tribution of saliva, so that the end of each day finds this secretion freely distributed on the doors, window sills, fur- niture and playthings in the home, the straps of trolley cars, the rails and counter and desks of shops and public buildings, and indeed upon everything that the hands of man touch. What avails it if the pathogens do die quickly? A fresh supply is furnished each day. Drinking Cups. Another important vehicle of transfer must be the common drinking cup. Davison 1 estimated that there were as many as 20,000 epithelial cells on a drinking glass that had been in use in a school for nine days, which well illustrates the amount of infection which may be thus carried. Cars, steamboats, hotels, schools, offices, factories, theaters, churches, all provide a common vessel from which large numbers of persons drink, thus furnishing an almost ideal method by which perfectly fresh saliva may be trans- ferred from one to another. Hundreds of thousands of persons must be each day in this manner exchanging the 1 Davieon, Tech. World Mag., Chicago, 1908, IX, 623. 190 THE SOURCES AND MODES OF INFECTION secretions of the mouth. When traveling in the steam cars I have noted the shocked expression on the face of passengers as a fashionably dressed woman was seen to allow her pug dog to drink from the common glass, not a pleasant thing, of course, but infinitely less dangerous than for the woman to drink from it. She might have tuberculosis, or carry diphthe- ria bacilli, or perhaps even have mucous patches on her lips. Other Kinds of Contact. Besides the moistening of the fingers with saliva and the use of the common drinking cup, the mouth is put to numberless improper uses which may result in the spread of infection. It is used to hold pins, string, pencils, paper and money. The lips are used to moisten the pencil, to point the thread for the needle, to wet postage stamps and envelopes. Children "swap" apples, cake and lollipops, while men exchange their pipes and women hatpins. Sometimes the mother is seen "cleansing" the face of her child with her saliva-moistened handkerchief, and perhaps the visitor is shortly after invited to kiss the little one. Children have no instinct of cleanliness, and their faces, hands, toys, clothing and everything that they touch must of necessity be continually daubed with the secretions of the nose and mouth. It is well known that between the ages of two and eight years' children are more susceptible to scarlet fever, diphtheria, measles and whooping cough than at other ages, and it may be that one reason for this is the great opportunity that is afforded by their habits at these ages for the transfer of the secretions. Infants do not of course mingle freely with one another, and older children do not come in such close contact in their play, and they also begin to have a little idea of cleanliness. Contact Dangerous because of Missed Cases. A little observation and reflection will show that the ways are num- berless in which fresh secretion of nose and mouth is passed from person to person. Enough has been written to demon- strate that the opportunities for contact infection are sufli- INFECTION BY CONTACT 191 ciently numerous to account for the spread of the contagious diseases without invoking any other mechanism. The chief objection to this view is that while it is true that there is much interchange of secretions, it is between well per- sons, and not between the sick and the well. That this objection is untenable is amply demonstrated by the evi- dence presented in Chapter II. There can no longer be the slightest doubt that there are large numbers of mild and un- recognized cases of infectious disease mingling freely with the public, and that in some diseases, and perhaps in most, there are also larger numbers of perfectly well carriers who also are unknown. These unrecognized foci are clearly numerous enough to cause, by their contact with others, the recognized cases. The transfer of the disease by fairly direct means is so obvious and easy that there is no neces- sity for invoking the agency of other and more circuitous modes of dissemination. Indeed it is sometimes said that the arguments here presented prove too much, and that if carriers were as numerous, and contact with them as fre- quent, as is here alleged, none could escape. But, as was stated in Chapter II and on page 153, infection does not take place so readily as is generally believed. This is demonstrated clinically, and the reasons are apparent. There are often long intervals in which carriers are not eliminating the pathogenic organism, and the saliva may not contain the germs, even when they are in the throat and nose. Germs are not evenly distributed through saliva, sputum or feces, and the particle transferred may be free from them. The .infective material is often small in amount and spread in a thin layer, and the contained organ- isms very speedily die. Lastly, small numbers of pathogens are often, perhaps usually, destroyed by the body. We must believe that usually continued or somewhat massive infection is necessary to cause disease, but that neverthe- less sometimes a single infection with a very small number of germs suffices. The number of unrecognized foci of 192 THE SOURCES AND MODES OF INFECTION infection in human beings, the opportunities for contact infection, and the natural obstacles to successful infection, appear admirably to explain many otherwise inexplicable phenomena of epidemiology. Bacteria on the Hands. Reference has already been made to this on page 179. Neumann, 1 by finding fecal bacilli on water-closet fixtures, showed how the hands are infected, and he also showed 2 how by another transfer on the hands they may infect bread, rolls, fruit, butter and milk. Colon bacilli have also been found on 3 of 12 roller towels. 3 Pus- forming organisms have their natural habitat on the skin, and the work of the surgeons has shown the tremendous importance of contact infection, which they have now learned most successfully to avoid. Danger from the Shuttle. As weavers habitually thread the shuttle by sucking the yarn through the eye, mouth bacteria may in this way be transferred from one to another. This has been alleged as a mode of infection in tuberculosis, and indeed Brown 4 claims to have traced three cases to this. Bacteria on Cups, Pencils. Vincenzi found diphtheria bacilli in the holy water in a church font. Kinyoun 6 found them in 2 of 85 swabbings from the woodwork and drink- ing glass of a railway car. They have also been found on glasses and cups by Albert and Boyd, 7 Perrow, 8 and in Chicago. 9 Forbes, in Rochester, found them upon a drinking glass which was believed to have been the cause of an out- break. This has been frequently referred to, and though I 1 Arch. f. Hyg., Miinchen. u. Leipz., LIX, 174. 2 Neumann, Deutsche med. Wchnschr., Leipz. u.Berl., 1910, XXXVI, 2046. Bull. Mass. State Bd. Health, Nov., 1911. Brown, Med. Officer, 1911, IV, 27. Vincenzi, Semaine me"d., 1898. Kinyoun, Med. News, N. Y., 1905, LXXXVII, 193. Albert and Boyd, Bull. State Bd. Health, la., Oct.-Dec., 1911, 37. 8 Perrow, Rep. Health Dept., Lynchburg, Va., Sept., 1911. 9 Bull. Dept. Health, Chicago, April 22, 1911. INFECTION BY CONTACT 193 i have not been able to find Forbes' original article, Dr. Goler, the present health officer of Rochester, informs me that the facts are as reported. Williams 1 recovered diphtheria bacilli from pencils moistened by the lips of children sick with the disease. The observations referred to in the chapter on fomites show that the germs of this disease are rarely found on fomites and then only on objects that have been recently and grossly infected. Tubercle Bacilli in Mouth. Not only are tubercle bacilli found in enormous masses in the true sputum, but they are often present in the saliva as well. Neild and Dunkley 2 found them in saliva from the tip of the tongue in 29 of 50 cases of pulmonary tuberculosis. Park found them in the saliva of 10 of 15 cases, 3 and refers to Moller recovering them in 3 of 20 cases. Le Noir and Camus 4 found virulent tubercle bacilli in the nose as well as from the mouth of tuberculous cases. Pathogenic Bacteria on the Hands. With the present habits of human beings these germs must be constantly trans- ferred to the fingers, and to a lesser degree to everything that the fingers touch. Graziani 5 found tubercle bacilli on the hands of 4 of 8 tuberculous patients, and on 3 of them 3 hours after washing with soap and water. He also obtained the bacilli from the hands of 4 out of 6 non-tuberculous patients. After shaking hands with tuberculous patients he was able several times to recover the bacilli from his own hands. Baldwin 6 found bacilli on the hands of patients in the Adirondack Sanatorium. They did not use handker- chiefs. Of 10 patients seen in private practice 8 had tubercle Williams, Scientific Bull. 2, 1895, Health Dept., N. Y. City, 14. Neild and Dunkley, Lancet, Lond., 1909, I, 1096. Park, Sixth Internat. Cong, on Tuberc., Wash., 1908, I, 157. Le Noir and Camus, Comp. rend. Soc. de biol., Par., 1908, LXV, 464. Graziani, Ann d' Ig. Sper., XV, 709, referred to by Rosenau, Sixth Internat. Cong, on Tuberc., Wash., 1908, I, 28. 6 Baldwin, Tr. Am. Climat. Ass., 1898, XIV, 202. UNIVERSITY OF CAUFORNIA 194 THE SOURCES AND MODES OF INFECTION bacilli on their hands. The other two were exceptionally careful. Preisich and Schiitz J found tubercle bacilli on the hands of children in a children's hospital at Budapest. Of 66 examinations of the dirt from under the finger nails 14 were positive under the microscope, but owing to the death of the animals from sepsis their virulence was not demon- strated. Of the 14 positive cases, 11 had tuberculosis, or were associated with it, while of the 52 negative cases only 5 were associated with tuberculosis. Dieudonne* 2 by inocu- lation demonstrated tubercle bacilli on the hands of 2 of 15 children. In this connection may be mentioned the experiment of Schumburg, 3 in which he rubbed an ose of a culture of bacteria on 'his hands, and recovered the germs after 15 and 16 handshakes. Ostermann, 4 on the other hand, does not consider contact infection of much importance in tuberculosis. While he recovered tubercle bacilli from the hands of 7 of 14 phthisical patients and from 1 attendant, he obtained them only 4 times from 42 children living in tuberculous families and 2 times from the floors occupied by these families. He does not find that bacteria are transferred from hand to hand as readily as have other observers. He also made a few cage experiments with guinea pigs to show that infection by contact is less effective than infection by air. It scarcely needed the experiments of Annett at Liverpool 5 and Higgins 6 at Birmingham to show that virulent tubercle bacilli may be found in the sputum on sidewalks, or those of Dixon 7 to demonstrate that they may be swept up on the skirts of ladies' dresses. 1 Preisich and Schiitz, Berl. klin. Wchnschr., 1902, XXXIX, 466. 2 Dieudonne, Munch, med. Wchnschr., 1901, XLVIII, 1439. 1 Schumburg, Ztschr. f. arztl. Fortbild., Jena, 1905, II, 567. 4 Ostermann, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., 1908, LX, 375. 6 Annett, Thompson Yates Laboratory Rep., 1901-02, IV, Pt. 2, 359. Higgins, Pub. Health, Lond., 1909-1910, XXIII, 100. 7 Letter from Dr. Samuel A. Dixon to author. INFECTION BY CONTACT 195 In Communion Cups. Anders 1 found tubercle bacilli in the dregs from communion cups in a Philadelphia church, and Moller 2 from the communion cup of a sanatorium chapel. Davison 3 found them on a glass used for some weeks in a high school. He also demonstrated pneumococci. Klein 4 obtained a positive tuberculous reaction once after inoculation of the swabbings of six telephones, although on twelve telephones on another occasion 5 he was unable to find either diphtheria or tubercle bacilli, and Rickards 6 was unable to find either bacillus on twenty-four mouthpieces of lung-testing machines in Boston. Hubs 7 found tubercle bacilli on napkin rings in the sanatorium at Stadtwald, but did not find them on the spirometer which was in daily use. Price 8 used some water in which sanatorium dishes had been washed to inoculate eight guinea pigs, all of which died of tuberculosis. Washings from dishes which had been first washed in the ordinary way showed no bacilli. Contact Chief Mode of Infection. Since it is true that pathogenic organisms begin to die or lose their virulence when thrown off from the body, we are forced to conclude that the closer the relationship in time and space with the bearers of the germs, the greater the chance of infection. Now that the number of unknown foci of infection and the opportunities for direct transfer of secretions have been demonstrated, the deduction is certainly permissible that contact infection is more important than the more indirect infection by fomites or by air. We are also compelled by inductive methods to place the greatest emphasis upon contact infection. In the chapter on Anders, J. Am. M. Ass., Chicago, 1897, XXIX, 789. Moller, Deutsche med. Wchnschr., 1905, XXXI, 548. Davison, Tech. World Mag., Chicago, 1908, IX, 623. Klein, Lancet, Lond., 1908, I, 1862. Ref. J. Am. M. Ass., 1905, XLIV, 1866. Rickards, Rep. Bd. Health, Boston, 1906, 91. Hubs, Ztschr. f. Tuberk. u. Heilstattenw., Leipz., 1906, IX, 396. Price, Sixth Internat. Cong, on Tuberc., Wash., 1908, I, 167. 196 THE SOURCES AND MODES OF INFECTION infection by fomites, and particularly in that on infection by air, much evidence is presented to show that infection usually does not take place unless contact is fairly close. The views here presented as to the great importance of contact infec- tion, and the comparatively slight importance of air infection and fomites infection, gradually developed after considera- tion of much experimental and epidemiological evidence. The two facts which more than all others have contributed to these views have been the restriction of scarlet fever and diphtheria to single families in the same house, and the suc- cess of certain hospitals in preventing cross infection, when contact infection is strictly guarded against. Disease Spreads in Dwellings only by Contact. The rarity with which scarlet fever and diphtheria pass from one family to another in the same house has already been alluded to, but it is worth considering again. Of 4306 other families in Providence living in the same house with a case of scarlet fever, only 295, or 6.8 per cent, were later invaded by the disease. This includes all families, whether careful or careless, and whether or not the initial case was removed to the hospital; but as less than 10 per cent of the cases have been removed to the hospital during the 23 years covered by the figures, hospital isolation can have been of little moment. This amount of infection is surprisingly small, and of itself indicates very strongly that close and intimate contact is usually necessary for the extension of this disease. A further study of the facts indicates this still more clearly. During the last 5 years, scarlet fever has extended to 118 of 1888 other families, or 6.3 per cent. In 54, or 22 per cent, of the cases infection occurred during the first two weeks, of which 37 were during the first week. Most of these cases during the first two weeks probably derived their infection from the first family before the disease was recognized. Only 24 second families developed their infection after the end of the second week and while the warning sign was on the house. This is the time when the patients are desquamating and INFECTION BY CONTACT^ 197 when the disease is popularly believed to be most infectious. These 24 cases are 1.3 per cent of the 1888 other families in the infected houses. As in a number of these cases there was known to be considerable communication between the fami- lies, it seems to be certain that in an ordinary tenement house scarlet fever is not readily carried from one family to another, and that effective isolation is comparatively easy. In fact, everything goes to show that two or more families may live in the same house, using hallways, doors, and even water-closets in common, without scarlet fever extending from one to the other. All that is necessary is that there shall be absolutely no visiting between the families, and that the children shall never meet in play. I do not know that similar data have been collected elsewhere, but Cameron 1 has shown by his study of " return" cases of this disease that in many instances the infecting case may remain in the family for some time, providing there is no direct contact with the well persons. Diphtheria is as little likely to extend from family to family without direct contact as is scarlet fever. During the last twenty-one years, in Providence, of 3667 other families living in a house with diphtheria, only 263, or 7.2 per cent, were invaded by the disease. During the five years 1904 to 1908, of 1648 other families, 114, or 6.9 per cent, have acquired the disease. Of these, only 38, or 2.3 per cent, were attacked after the first week of the initial sickness and before the warning sign was removed. As was shown above, many of these infec- tions are due to the fact that the first case is not recognized and hence the different families in the house continue to visit one another; or in some instances to the fact that persons in the second family carry the bacilli for a time without being sick. Probably a large part of the infections during the first week take place before the disease is recognized, so that it seems very probable that less than 2 and perhaps less than 1 Cameron, Rep. on Return Cases of Scarlet Fever and Diphtheria, Lond., 1901-02, 98. 198 THE SOURCES AND MODES OF INFECTION 1 per cent of families living in a house with a case of diph- theria contract the disease while the warning sign is on the house. I have given particular attention to the cases of diph- theria arising in other families in the house while the warning sign remained on the apartment where the disease first ap- peared, and almost always there is known to be direct inter- course between the families. Contact infection, then, seems to be necessary for the transfer of diphtheria from one family to another living in different apartments of the same house. Disease spreads in Hospitals only by Contact. Another strong reason for this view that contact infection is the chief mode of extension for the common contagious diseases is the success of certain hospitals in preventing cross infection by minimizing in every way the opportunities for infection by contact. The Parisian hospitals, particularly the Pasteur Hospital, have been leaders in demonstrating the success of this method. In most hospitals for contagious diseases great effort is made to prevent cross infection by separating the different diseases to a considerable distance, since the theory prevails that air-borne infection is the chief mode of spread. This view so dominates hospital practice that numberless ways escape notice by which disease is spread by very direct contact, with the result that in most hospitals cases of cross infection are continually developing. French Hospitals. The French seem to have been the first to appreciate the importance of guarding against contact infection, and an interesting account of the efforts made is given by Grancher, 1 who was one of the pioneers. Strict methods of "antisepsie medicale," as Grancher calls it, were introduced, and it was found possible to care for patients with different diseases even in a common ward with far less danger of transfer than before. He employed wire screens around the beds to impress upon the nurses the necessity for guarding against infection by contact. During the years 1 Grancher, Cong. Internal, de med., XIIL, C.-r. Par., 1900, Sec. de meU de 1'enf ance, 478. INFECTION BY CONTACT 199 1890 to 1900, 6541 patients were treated in Grancher's wards, and diphtheria was introduced 43 times, but only once did a case develop in the wards. Scarlet fever was introduced 19 times, and 7 cases developed in the wards. Less suc- cess was obtained in isolating measles, but infections were reduced two-thirds. Grancher was satisfied that even this disease was spread by contact. He believed that in clean wards infection is rarely air-borne; it is " objective," not " atmospheric." In several other French hospitals the impor- tance of preventing contact infection has been realized. In some of them isolation is made easier by placing the patients in separate rooms or cubicles; in some, partitions are placed between the beds. These partitions may be full height, or may stop short of the floor, and reach only just above the head. Sometimes screens only are used. In 1897 the Min- turn Hospital in New York, a small private hospital, was built to provide isolation in separate rooms for cases of scarlet fever and diphtheria. But the most notable example of the new method is the Pasteur Hospital in Paris, opened in 1900. The success of these various hospitals in preventing cross infection is correlated, not with the amount of isolation as ordinarily understood, but with the care with which aseptic measures are carried out by the attendants. The cubicles, partitions and screens certainly cannot prevent infection if the nurses without taking proper precautions pass from one case to another. This is shown by the constant development of cross infection in the ordinary hospital. It was in the Pasteur Hospital that the principles of medical asepsis were first fully appreciated and carried out in a practical manner. The hospital consists of two pavilions with about fifty beds each, designed ostensibly, one pavilion for scarlet fever and one for diphtheria; but, as is shown below, all sorts of cases are admitted. For the care of all these " other diseases " and mixed and doubtful cases, twelve single rooms are pro- vided in each ward, all opening into a common corridor, the doors of which are usually left open. The same nurses look 200 THE SOURCES AND MODES OF INFECTION after different diseases, often in adjoining rooms. The disci- pline of the hospital attempts to secure an entire avoidance of contact infection, and is remarkably successful. Yet the procedures are all very simple. The nurse always sterilizes her hands after waiting on the patient; she wears a gown, which is kept in the room, when anything is done which would be likely to infect her clothing. Nothing goes into the room except what is sterile, and nothing comes out without being at once sterilized. To train nurses sufficiently to take charge of a ward, two years are necessary, but the nurses whom I saw there were carrying out these details with the same precision and unconsciousness which are shown by the bacteriologist in his laboratory. English Hospitals. The principles of aseptic nursing as applied to contagious diseases have been employed in a num- ber of places in England, as, for instance, in the North Eastern, South Western and London Fever hospitals in London, at Walthamstow and Manchester, and doubtless in other places. The methods adopted in the Monsall Hospital at Manchester, and described by Gordon, 1 are as follows: "The patient's bed in the general ward is surrounded with a screen covered with sheets, which are kept constantly wet with a weak solution of some disinfectant. The main pur- pose of this screen is to serve as a label, and to remind the nurses that certain precautions must be taken for the patient behind it. At the same time, I think the wet sheets may pos- sibly arrest infective particles that are projected against them in the acts of coughing and sneezing. The only other requi- sites are two glass shelves fixed on the wall behind the bed, and a locker or portable cupboard made of metal, with an enameled surface, which can easily be disinfected and kept clean. " The precautions to be taken by the nurses in attending patients behind this screen or ' barrier ' are printed on a card fixed to the screen, and are as follows: 1 Gordon, Rep. on Health of Manchester, 1908, 154 INFECTION BY CONTACT 201 Rules in Manchester. " Precautions to be Observed in the Nursing of Barriered Cases. "(l) Rubber gloves are to be worn by the Nurse for all manipulations connected with the case, including the han- dling of clothes. The gloves are to stand in a bowl of 1 in 400 Izal solution. " (2) The following utensils are to be marked and kept on the glass shelves or in the locker provided: Spatula Nozzles Clinical Thermometer To be kept completely immersed in a 1 to 400 Izal solution. At least two bowls. All feeding utensils (plates, spoons, forks, etc.). "(3) A plentiful supply of wet swabs, with a bowl contain- ing Izal solution to receive these when used, is to be kept on the locker. Handkerchiefs or muslin squares are not to be employed. "(4) No toys or books that have once been used inside the barrier are to be taken outside it except to be destroyed. " (5) In every case a square of jaconette is to be placed on the pillow slip, and over this a piece of muslin; the latter is to be renewed whenever soiled. "(6) An overall is to be worn by the Nurse whenever either the patient or the clothes are handled. This is to be kept inside the barrier." The success of the methods described in the preceding pages is well shown by the published figures. At the Pasteur Hospital from October 1, 1900, to April 19, 1903, the following cases were received: Diphtheria 443 Scarlet fever 92 Sore throat 166 Erysipelas 163 Smallpox 524 Phlegmon of tonsil 20 Chicken pox 55 Other diseases 219 Measles.. 126 Mothers with infants. . 192 202 THE SOURCES AND MODES OF INFECTION Such a combination furnishes a remarkably fertile field for cross infections. During the next year about 750 cases were admitted. 1 During this whole period the only cases which developed in the hospital were 5 of smallpox, 2 of erysipelas and 1 of diphtheria. Dr. Loiseau writes me that since 1904 the per- centage of cross infections has been less than 0.1 per cent. At the Minturn Hospital in New York there has been no in- stance of infection in the hospital. At the Monsall Hospital in Manchester in 1908 a large number of persons admitted with mistaken diagnosis were cared for in the wards by the methods described without contracting the disease, and a number of cases of mixed infection were cared for in the open wards without infecting others, except in one instance when, owing to a mistake in orders, " barrier " isolation was not promptly instituted. A letter just received from Dr. Arnold, who has succeeded Dr. Gordon at Monsall, states that in order that the patient may see and be seen, and to avoid the dampness of the wet sheet, he has substituted a tape which as effectually prevents the mythical aerial flight of the germs, or, to speak literally, equally well reminds the nurse that she must be clean. Is Tuberculosis Air-borne ? It is assumed that tuber- culosis, as it occurs in human beings, is usually an air-borne disease, and as will be shown on another page, there is more reason for such an assumption concerning this than concern- ing most diseases. Yet there is in certain quarters a growing tendency to attribute to contact infection more importance than formerly. Yet it must be confessed that most writers on this disease lay no emphasis on contact infection, and some scarcely mention it. Cornet, 2 in speaking of kissing, the most direct means of contact infection, says that it is incredible that tuberculosis should be transmitted in this way, for the saliva is ordinarily germ free, and the germs if 1 Martin, Bull, med., Par., 1904, XVIII, 251. 2 Cornet, NothnagePs Encyclopedia, Tuberculosis, 187. INFECTION BY CONTACT 203 present would not be carried to the lungs. Cornet's first contention is certainly not correct, for Neild and Dunkley, as before mentioned, found tubercle bacilli on the tip of the tongue of phthisical patients examined during intervals of freedom from cough. They also report cases of lupus, due in all probability to inoculation with saliva, and refer to others reported by Wild. 1 There has been little experimental work to determine the part played by contact infection in tuberculosis. The work of Bartel and Spieler 2 indicates that guinea pigs exposed under natural conditions to contact with the members of a tuberculous family more often develop the disease than do animals exposed merely to the air of the room, while the experiments of Packard, though inconclusive, indicate little difference. Infection by Alimentary Tract. There seems to be evi- dence that the tonsils may be the seat of infection in many cases of tuberculosis. Harbitz 3 has very forcibly called atten- tion to the probability that tubercle bacilli frequently gain access to the body through the tonsils. He examined the tonsils and lymphatic glands of a large number of children, and found latent tuberculosis in many of the tonsils, and latent bacilli in the cervical glands in 17 instances, much more often than in the mesenteric glands. He thinks that a more careful study of the tonsils and lymph nodes would reveal much latent tuberculous infection, and he thinks that a con- siderable amount of infection takes place through the tonsils. Harbitz mentions Grawitz, 4 Aufrecht 5 and Beckmann as sup- porting this view. Ravenel and Reichel 6 review much litera- ,ture, and refer to Wood's experimental infection of swine 1 Wild, Brit. M. J., 1899, II, 1353. 2 Referred to in the chapter on infection by air. 3 Harbitz, J. Infect. Dis., Chicago, 1905, II, 143, and especially 198. 4 Grawitz, Deutsche med. Wchnschr., 1901, XXVII, 711. 6 Aufrecht, Verhandl. d. deutsch. path. Gesellsch., Berl., 1901-02, IV, 65. Ravenel and Reichel, J. Med. Research, Bost., 1908, XVIII, 1. 204 THE SOURCES AND MODES OF INFECTION through the tonsils, the course of the bacilli being apparently through the submaxillary and cervical glands. Benome l caused infection in animals through the mouth and pharynx. Bandelier 2 finds primary tuberculosis of the tonsils not so rare as is generally believed, but he does not consider the tonsils as a frequent starting point of phthisis. Mohler and Ravenel from experiments and observations consider the mouth as a frequent site of infection in the tuberculosis of hogs. Contact Infection in Tuberculosis. The nose also may be the seat of infection. Cornet, 3 by applying infective ma- terial by means of a feather to the nasal mucous membrane of guinea pigs, was able to produce disease of the nose and submaxillary glands. Renshaw 4 was able in the same way to infect seven of eight animals. As tubercle bacilli are nu- merous upon the hands of consumptives and upon various articles used by them, it is evident that fresh bacilli must be frequently carried to the mouth and nose of persons near by, and may either infect directly through the mouth, nose and pharynx, or may be swallowed and enter the circulation through the lower part of the alimentary canal. The only question is, How frequently does this happen? As was stated above, it is the opinion of many that it is a very common mode of infection. Moore 5 is of the opinion that in cat- tle tuberculosis is spread chiefly by the animals licking one another, and by their eating and drinking from the same vessels. Bartel 6 believes that infection by pharynx, stomach and intestines is more common than has been sup- posed, in which view he supports Weichselbaum, 7 Volland, 8 1 Benome, Ref. J. Am. M. Ass., Chicago, 1907, XLIX, 888. 2 Bandelier, Beit. z. Klin. d. Tuberk., Wiirzb., 1906, VI, 1. 3 Cornet, Nothnagel's Encyclopedia, Tuberculosis, 154. 4 Renshaw, J. Path, and Bacteriol., Lond., 1901, VII, 142. 6 Moore, Conference of Sanitary Officials, N. Y., 1907, 37. 6 Bartel, Sixth Internat. Cong, on Tuberc., Wash., 1908, I, 95. 7 Weichselbaum, Festsch. VI Konf. Internat. Tuberk., Wien u. Leipz., 1907. 8 Volland, Berl. klin. Wchnschr., 1899, XXXVI, 1031. INFECTION BY CONTACT 205 Kavacs 1 and Preisich and Schu'tz. 2 Among others who at- tribute much importance to contact infection may be men- tioned Wassermann, 3 Calmette and Landouzy. 4 Certainly the opportunities for the direct transfer of fresh moist infective material in the home of a phthisical patient must be very great, while the chance of the infective material becoming dried, pulverized and, while still virulent, being car- ried to the pulmonary alveoli, must be comparatively small. Unless there is some good reason to think otherwise, one would naturally attribute to contact infection the chief role in the extension of this disease, at least in the family. The only objection is offered by the pathologists, many if not most of whom affirm that the evidence points to direct infec- tion of the lungs by the inspired air. There are, however, many able experimenters who think otherwise, and who main- tain that tubercle bacilli may enter the body at various points and reach the lungs through the lymph channels. It is impos- sible for the writer properly to weigh pathological evidence, but that the question is still sub judice must be admitted. Under the circumstances it seems to be wise to assume as a working hypothesis that contact infection is a factor of great importance in the causation of human tuberculosis. It is certainly essential to guard against such infection in every way, and from a person who does thus conduct himself in a cleanly manner at all times, diffusion of the disease through the air would be impossible. Undue emphasis laid upon the invisible and therefore terrifying infection in the air has done more than anything else to develop the unfortunate phthisi- phobia which so often renders miserable the life of the tuber- culous, and seriously interferes with rational measures for the restriction of the disease. 1 Kavacs, Zeiglers Beitrage zur. Path. Anat., 1906, XL. 2 Preisich and Schiitz, Berl. klin. Wschnschr., 1902, XXXIX, 466. 3 Wassermann, Berl. klin. Wchnschr., 1908, Nr. 48. , * Calmette and Landouzy, Sixth Internat. Cong, on Tuberc., Wash., 1908, I, 110. 206 THE SOURCES AND MODES OF INFECTION Importance of Contact Infection. I have sometimes been told that I lay too much emphasis on contact infection, but if it is the principal way in which disease spreads, too much emphasis cannot be placed upon it, and it seems to me that the evidence is that it is the chief mode of infection. Even if it is not so important as is here alleged, every one must admit that it is of considerable importance, yet until recently very little attention has been paid to it. If contact infection is the chief mode of extension of the contagious diseases, then defense against them becomes more largely a personal affair than we have been taught. We do not have to rely exclu- sively on the municipality for our protection, awaiting forced isolation, hospital construction, disinfection and the like, but can largely protect ourselves by keeping our fingers out of our mouths, and also everything else except what belongs there. It may not be possible to prevent all contagious sick- ness in this way, but some can be avoided, and perhaps most of it. Contact infection is avoided by personal cleanliness, and personal cleanliness is demanded by decency, good man- ners and refinement, as well as by hygiene. It is not much trouble to be decently clean, and it is not very expensive. It is a serious mistake to build an expensive isolation hos- pital that does not check disease, or to construct a filter when it is not needed; but no harm would be done if the views here presented should be found to be erroneous and people should learn to wash their hands and keep their fingers out of their mouths to no purpose so far as disease prevention is concerned. It seems certain that much can be done to prevent the spread of disease in the family and in hospitals, schools and institu- tions, if only personal cleanliness be insisted upon. Yet such cleanliness or medical asepsis is sadly neglected by physicians as well as by nurses. Rather strong preaching is needed when, as was referred to on another page, a typhoid nurse is detailed for the double duty of washing bedpans and preparing food. It is certainly necessary to insist somewhat strenuously on reform when such occurrences as the following take place. INFECTION BY CONTACT 207 Disregard of Contact Infection. Thus, at one of the finest hospitals in this country, with separate wards for scarlet fever and diphtheria, a considerable number of cases have arisen in the general wards. The germs were supposed to be air- borne, as it was said there was no other possible avenue of infection. When I saw the head nurse lick her finger to facilitate turning the bedside charts of diphtheria patients, I suspected that the principles of medical asepsis had not been entirely mastered. Called to see a case of scarlet fever in a well-to-do family, I found the door of the sick-room carefully hung with a sheet to keep the infection from the other chil- dren. After examining the throat with a spatula I handed the latter to the mother. She took it into the hall and put it on an upholstered sofa, and with her saliva-infected hands opened the door of an adjoining room. The attending physi- cian meanwhile sat on the bed and handled the patient, an entirely unnecessary proceeding at that time, and except for the example set him, would have forgotten to wash his hands before leaving. A certain hospital determined to copy in one of its wards the cubicle system of the French, but had so missed its essential features that I found doctors and nurses going from cubicle to cubicle feeling the pulse, smoothing the bedclothes, and handling dishes without even stopping to wash their hands. Meanwhile the screen was supposed to prevent the microbes from passing from bed to bed, and we all carefully wore gowns and caps so that the wicked little germ might not jump into our hair and then jump off again onto the next patient. In another fine hospital for conta- gious diseases, where great stress is laid upon ample space between different diseases so as to prevent cross infection, the superintendent was observed freely to touch articles about the ward, and handle the patients, and then go to the public office without even washing his hands. Such incidents could be multiplied indefinitely. The superintendent of another hos- pital invited another visitor and myself to eat ice cream from the same spoon as himself, which spoon was then replaced 208 THE SOURCES AND MODES OF INFECTION in the freezer which was to supply the wards. I was most of all impressed with the fact that at the International Con- gress on Tuberculosis in 1908 a large number of the readers of papers moistened their fingers with their tongue when turn- ing the pages, and in each of the sections only one drinking glass was provided for all the speakers; and this continued without protest for a day or two. If the most distinguished investigators and health officials of the world, gathered to study the most important contagious disease, show no appre- ciation whatever of the importance of contact infection^ it is certainly tune for some one to be emphatic. Personal Prophylaxis. The discovery that disease germs are rarely able to maintain themselves outside of the body clouded the hopes of those who expected by municipal house cleaning to " stamp out the zymotic diseases," and the later discovery of numerous missed cases and carriers has shown that isolation of the sick controls infection far less than was believed. These somewhat discouraging facts are to a large degree offset by what has been learned of the modes of infection. Formerly air infection was chiefly feared; now it appears that contact infection is of prime importance. For- merly dependence was placed upon the state to isolate and disinfect; now it appears that the individual can protect him- self, and as easily protect others if he chance to be infected. It is usually comparatively simple so to live as not to allow the secretions of others to come in contact with one's own mucous surfaces, and it is easy, and should be considered immoral, to allow one's own secretions to be so placed that they may infect another. Personal cleanliness is less expen- sive than municipal cleanliness, and is within the reach of all. Need of Education. When one notes the utter disregard of medical asepsis shown in our hospitals and medical con- gresses, one is apt to feel that the education of the public in habits of personal cleanliness will take a very long time; but some encouragement is felt when it is remembered that it is not so very long ago that excrement was commonly thrown INFECTION BY CONTACT 209 into the street and garbage was tossed under the tables of the great. It is only a few years since our sidewalks were flecked with saliva, but now nineteen persons out of twenty are ashamed to be caught spitting on the pavement. Perhaps we may all soon learn to stop distributing our secretions so freely among our friends. Education in School. As the avoidance of contact infec- tion is chiefly a personal matter, the present need is for educa- tion. First of all, the teachers in the medical schools and the staffs of hospitals must learn to appreciate the importance of this mode of infection. It is not unreasonable to hope that in a few years the schools and the hospitals will place as much emphasis on medical asepsis as they now do on surgical asepsis, and it is to these centers that we must look for the education of physicians, health officers and nurses. To edu- cate the general public is a more difficult matter. Some years ago Dr. Theobald Smith called my attention to the desirabil- ity of teaching school children something about the require- ments of personal cleanliness, and since then I have each year distributed to each school child the following " dont's " REMEMBER THESE THINGS. Do not spit if you can help it. Never spit on a slate, floor, or sidewalk. Do not put the fingers into the mouth. Do not pick the nose or wipe the nose on the hand or sleeve. Do not wet the finger in the mouth when turning the leaves of books. Do not put pencils into the mouth or wet them with the lips. Do not put money into the mouth. Do not put pins into the mouth. Do not put anything into the mouth except food and drink. Do not swap apple cores, candy, chewing gum, half-eaten food, whistles or bean blowers, or anything that is put into the mouth. 210 THE SOURCES AND MODES OF INFECTION Never cough or sneeze in a person's face. Turn your face to one side. Keep your face and hands clean; wash the hands with soap and water before each meal. PROVIDENCE, May, 1901. An explanatory circular is sent to the teachers, and of late a short account of the sanitary reasons for personal clean- liness has been distributed to children above the primary grade. Large printed copies of the " don'ts " have been framed and hung in the schoolhouses. Much kindergarten work is of such a nature as to inculcate rather than discourage cleanly habits. Children work in common in moist clay and sand, use the same " gifts " and toys and are brought into close contact in the games. Miss Bessie M. Scholfield, late supervisor of these schools in Providence, succeeded, without any undue expense or violent change of methods, in employing kindergarten work as a means of teaching some of the principles of personal hygiene. Municipality should encourage Cleanliness. Besides efforts that are directly educational the municipality can do much indirectly to encourage habits of personal cleanliness and to prevent the distribution of the secretions and excre- tions of the body. The common drinking cup is a most efficient means of such distribution, and it should be abol- ished in all schools and other public institutions. This has been done in many places, and individual cups or specially designed drinking fountains substituted. The example is now being followed by some railways, factories and shops. The states of Kansas, Michigan and Mississippi were the first to forbid the use of a common drinking glass on rail- ways, and the Lackawanna and some other roads, and the Pullman Company advertise as an attraction free cups of paraffin paper for each passenger. 1 Since the above was 1 J. of Outdoor Life, 1909, VI, 371. INFECTION BY CONTACT 211 written a dozen other states have forbidden the use of the common glass. Hundreds of churches have adopted the individual communion cup. In the first edition, I said that " the roller towel should go the way of the common drinking cup." Since then Massachusetts and Connecticut and the cities of New York and Chicago have enacted statutes or adopted rules forbidding the use of a common towel in public places. People are more likely to keep clean if it is easy to do so. Hence the establishment of public baths may be con- sidered a real sanitary measure. While compulsion can have little share in the campaign for cleanliness, certain prohibitions are entirely reasonable and feasible. Thus ordinances against spitting on the sidewalks and the floors of public places have done much to teach people to take proper care of their secretions. Reference has already been made to evidence that the abolition of privy vaults results in a decrease in typhoid fever. Privy vaults cer- tainly encourage the improper disposal of excreta and general uncleanly habits. A good ^wftge system and the removal of vaults and cesspools do much to prevent con- tact infection, at least in the fecal-borne diseases. CHAPTER V. INFECTION BY FOMITES. Definition of Term. As was shown in the preceding chapter, it seems very probable that contagious disease may often be caused by the quite direct transference of the germs from one person to another on such objects as cups, pencils, pipes, the fingers, etc. This mode of transference should properly be considered a form of contact infection. The term contact infection, as commonly used at the present time, does not necessarily imply the immediate touching of two persons, but it does imply the comparatively direct transference of quite fresh material from one to another. Although almost any object may in this manner be the bearer of infection, it would not ordinarily be considered as fomites. By fomites are usually meant infected objects which retain the infection for some time. A toy used by a diphtheria patient and sent to a distant town and there giving rise to the disease, the dress of a scarlet-fever patient put away for weeks or months and brought out only to cause another case, a library book carrying the infection of smallpox from one household to another, blankets loaded with typhoid bacilli in South Africa transferring infection to England, infected hides from Asia causing anthrax in Philadelphia, blank cartridges as the bear- ers of tetanus germs, and the various objects in a room lately occupied by a case of any contagious disease giving rise to the same affection in newcomers, would all be recognized as fomites. The cup which carries the moist saliva from one school child to another, the borrowed pencil which transfers the fresh syphilitic virus from lip to lip, and the urine-moistened closet seat which infects the fingers and then the mouth of the next user, are not thought of as fomites but as the neces- 212 INFECTION BY FOMITES 213 sary media for that intimate mode of disease transference which is coming to be called contact infection. This dis- tinction between the two classes of bearers of infection is somewhat arbitrary, and not very definite, but is eminently practical. In this book, by infection by fomites is meant a transference of infecting material on objects under such con- ditions that considerable time elapses, days at least, usually weeks, sometimes months. Yellow Fever and Fomites. If one takes up the older text-books on yellow fever it will be found that fomites were considered the most important means in the extension of this disease. The invasion of cities and countries was usually attributed to this mode of carriage. This was the general view up to, and indeed after, the discovery of the role played by the mosquito, and numerous instances of such transference are given. Thus the federal inspectors 1 attributed the out- break at Brunswick, Ga., to ballast brought from Cuba. The disease was supposed to have been carried from New Orleans to Havana by means of second-hand oyster buckets. 2 Lice- aga 3 gives instances of the transmission of yellow fever by a shipload of grain from New Orleans, by cloth spread out on the grass to dry, by general merchandise, by bagging, by clothing, and by ballast. Horlbeck 4 says that two persons at Key West contracted yellow fever from sleeping on a mat- tress that was brought from Cuba. Never so Transmitted. In all these instances the evi- dence is the same : a locality has long been free from yellow fever, something is imported from an infected place and the disease develops. What could be clearer? The proofs that it is a fomites-borne disease were far more numerous and stronger for yellow fever than for almost any other disease. 1 Rep. Surg. Gen. U. S. Mar. Hosp. Serv., 1893, II, 33. a Report on Shipment of Merchandise, U. S. Mar. Hosp. Serv., Special Report, 1899, 9. 1 Liceaga, Am. Pub. Health Ass. Rep., 1898, XXIV, 122. 4 Horlbeck, Am. Pub. Health Ass. Rep., 1897, XXIII, 436. 214 THE SOURCES AND MODES OF INFECTION Yet we now know that yellow fever never was, nor could be, transmitted in any such way. Such a mistake, a mistake which cost millions upon millions because of the needless interrup- tion of commerce, and disinfection, should make us careful how on similar, but weaker, evidence we attribute importance to fomites as a means of infection in other diseases, and should lead us to inquire what proof there is that the long persist- ence of infection on things is a weighty factor in the trans- mission of disease. Smallpox. It does not require much search in medical literature to find numerous instances of the alleged trans- mission of disease by fomites. Recent text-books and jour- nals are full of them. Welch and Schamberg 1 state that smallpox was brought to Philadelphia on cotton from the South, but the only reasons for thinking so were that there was much smallpox in the cotton region and none in Phila- delphia, and that the patient handled cotton. Not long since the health officer of a western city reported that the principal source of smallpox in that city was lumber, his assumption being based on the facts that there was much of the disease in the lumber camps, that the rough lumber was well fitted to carry contagion, and that in most families the first person attacked was engaged in some sort of woodworking. The above are fair samples of the kind of evidence on which the theory of fomites infection rests. Smith 2 reports that a man from Paris died in London of what was probably malignant smallpox. Two people who afterwards slept in the same bed, on different days, developed the disease, as did the girl who sorted at the laundry the soiled linen from this hotel. Scarlet Fever. A recent writer in Public Health 3 reports six instances of house infection giving rise to scarlet fever, in one case nine months after the first patient was sick. The 1 Welch and Schamberg, The Acute Infectious Diseases, Phila., 1905, 160. ' Smith, Pub. Health, Lond., 1901-02, XIV, 211. 1 Trotter, Pub. Health, Lond., 1906-07, XIX, 745. INFECTION BY FOM1TES 215 only evidence was the recurrence of the disease in the house. Welch and Schamberg 1 quote from others reports of fomites infection in this disease. Boeck states that the hair of a scarlet-fever patient caused the disease twenty years after. Another physician caught the disease from a coat which he wore while attending a case a year and a half before. The health officer of Detroit 2 reports two cases due to infection from books which had been used by a patient some months before. Wende 3 states that quilts used by scarlet-fever patients in August, and put away without disinfection, caused the disease in November. The reports of the state board of health of Michigan 4 give instances of the per- sistence of the scarlet-fever virus for years in houses, letters, books, etc. Diphtheria. Buckley 5 quoted from the Newton, Vic- toria, Health Report an instance where a cornet used by a diphtheria patient was put away for four years, and was then found by some children, who contracted the disease from it. He gives another instance where the disease recurred in the house after a period of two years. At a time when Manila was absolutely free from diphtheria, an American child who had been there over a year received some Christmas presents from St. Louis, and was taken sick a few days later. Chris- tian 6 writes of the transmission of diphtheria on carpenters' tools which were sent from one shop to another. Cholera. A number of instances of the transmission of cholera by soiled clothing are given in the Report of the Marine Hospital Service for 1893. 7 In nearly every instance the clothing was brought from foreign countries. Because 1 Welch and Schamberg, The Acute Infectious Diseases, Phila., 1905, 344. 2 Rep. Bd. of Health, Detroit, for year ending June 30, 1903, 11. 8 Buffalo San. Bull, Nov. 30, 1908. Rep. St. Bd. Health, Mich., 1906, 134; 1907, 133. Pub. Health, Lond., 1906-07, XIX, 296. Bull. N. Y. St. Board of Health, June, 1907, 5. ' Rep. Surg. Gen. U, S. Mar. Hosp. Serv., 1893, Vol. II, 353. 216 THE SOURCES AND MODES OF INFECTION a company of soldiers had suffered from typhoid fever for two years, and the disease ceased on disinfecting the bar- racks, the outbreak was believed to have been due to room infection. 1 Before weighing the value of this evidence it is perhaps worth while to consider some of the things which are most often alleged to serve as fomites. Infected Clothing. From the time when the priest was directed how to detect leprosy in woolen and linen 2 to the present, clothing has been considered an important vehicle of infection. It is not to be doubted that disease germs may be carried on clothing. If clothing is soiled with a consider- able quantity of infected saliva, feces, urine or pus, and if while fresh, say within a few hours or days, it is brought in contact with susceptible persons, disease may result. If it is folded and put away in the dark, especially if it be in a damp place, it may remain infectious perhaps for months. But as bacteria as a rule die rapidly, and as there must be a sequence of gross infection, favorable conditions for survival, and con- tact with susceptible persons, it does not seem likely that disease is often caused in this way. Many instances are recorded, usually only of possible, rarely of probable, transference of disease by clothing. Of yellow fever more than of any other disease has this been alleged, yet we now know that such transmission of this disease is impos- sible. Many writers also report the spread of bubonic plague by means of clothing, but, as will be seen, the evidence is that plague is only under very exceptional circumstances carried by fomites. Typhus not carried in Clothing. When typhus fever appeared in New York in 1892, from sixty to seventy-five officers of the health department were, according to Doty, 3 1 Cited by Germane, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXIV, 404. 2 Leviticus, Chapter xiii, verses 47-59. 3 Doty, Med. News, N. Y,, 1905, LXXXVI, 730. INFECTION BY FOMITES 217 more or less in contact with the cases, often in intimate contact; gowns were not used, and the officials went freely between the patients and their own homes, and about their other business, yet no case of this disease could be traced to fomites infection. Butler l speaks of a parlor maid in a contagious-disease hospital who for six months had been in daily contact with nurses coming directly from scarlet-fever cases without change of clothes, but she did not contract the disease until exposed to an incipient case in the person of a nurse, when she promptly developed scarlet fever. This is only one illustration of many of the failure of supposedly infected clothing to infect. Physicians rarely carry Disease. In scarlet fever and diphtheria physicians are constantly passing from the sick to the well. Some of them take great precautions to avoid carrying the disease in their clothes, but the majority take few or none, or at least did not until very recently. Yet records of their transmitting disease are extremely rare. For many years I was on the lookout for this mode of transference, and only once or twice found any evidence that the physician was at fault. In such cases how much greater is the chance that the physician carries infection on his hands than in his clothes. Barlow 2 found that of 500 cases of scarlet fever in only 4 had the physician previously been treating the disease and these 4 cases were apparently traced to other sources. Infection by Clothing is Rare. If the gross infection of clothing is only in rare instances the cause of disease, how little must be attributed to slight infection ! A few droplets of tuberculous saliva, a slight smear of moisture from the lips of a diphtheria patient, will soon lose their virulence after exposure to light and air. But usually the visitor in a sick- room will escape all infection except the hypothetical floating 1 Butler, Proc. Roy. Soc. Med., Lond., 1908, 1, Epidemiol. Sect., 225. 2 Barlow, Med. Officer, 1910, III, 319. 218 THE SOURCES AND MODES OF INFECTION particles. The danger from this floating matter will be shown in another chapter to be a negligible quantity. It is the com- mon practice for physicians, nurses and visitors in a room occupied by a contagious case to wear a gown and cap. For physicians and nurses who are to move or lift the patient, or otherwise come into intimate contact with him, the gown is a reasonable protection against possible gross contamination. For the careless visitor too it may be useful. The cap is a useless frivolity. It is amusing to see how religiously it is worn, while no protection is given the feet, though Denny and Nyhen 1 have shown that infection by means of the shoes is bacteriologically possible, while the aerial infection of the hair has never been demonstrated and is highly improbable. More than once have I seen a physician don his cap to keep the germs from flying into his hair, and pass freely from one diphtheria patient to another, inspecting the throat, feeling the pulse or smoothing the bedclothes, and occasionally stroking his own chin or scratching his head, all without washing his hands. And physicians and nurses will continue to do such things as long as they fancy that air infection is all they have to fear, and forget that there is such a thing as contact infection. It has for some years been my custom not to wear a gown when called in consultation to cases of contagious disease, or when visiting hospital wards, unless I am to do much work about the patient. Under the condi- tions of a casual visit, even in smallpox, I do not wear a gown. It is not necessary to touch anything except with the hands, and these should be carefully washed before leaving. I have never carried infection to my home, or elsewhere so far as known, and I believe that there is no chance of my doing so. Laundries and Disease. If clothing can carry infection, sickness ought to make its appearance in laundries, to which enormous quantities of clothing go even while the infecting material is still fresh. Attempts have been made to show 1 J. Maes. Ass. Bds. of Health, Boat,, 1904, XIV, 109. INFECTION BY FOMITES 219 that disease is carried to laundry workers in this way, and it is probable that some of the alleged instances are true. Thus Sedgwick, and also Walcott, 1 report cases of typhoid fever where the evidence was very strong that the disease was contracted by handling soiled linen. Thorne-Thorne 2 also reports an interesting case of probable transmission of typhoid fever by clothing. That such accidents are common has never been shown. Certainly in Providence there is no excess of scarlet fever, diphtheria or typhoid fever among laundry workers. This cannot be due to the disinfection of the clothing, for much disinfection is not effective, and for six years there has been no disinfection after diphtheria, and moreover the linen from carriers and missed cases is nowhere subjected to disinfection. It is true that Landouzy, 3 after examining 1590 laundry workers in Paris, states that tuberculosis is twice as prevalent among them as among other workers, and he attributes it to infection from soiled clothing. But certainly other occu- pations show an even greater excess of this disease, and there is no suggestion that it is due to infection from the materials handled. There may be many other reasons why laundry workers should show an excess of tuberculosis, such as age distribution, poverty and overwork. Infection of Rooms. It is generally believed that the room, or rooms, which have been occupied by a case of con- tagious disease are a fertile source of danger to others. The germs of diphtheria, scarlet fever and smallpox are sup- posed to become attached, not only to books, playthings, bedding and furniture, but also to the walls and ceilings. It is true that anything which can be reached by the patient or attendant may possibly receive infection, the chance in- creasing according to the frequency with which the thing is 1 Sedgwick and Walcott, J. Mass. Ass. Bds. Health, Boston, 1900, IX, 145. 2 Thorne-Thorne, Clin. Soc. Trans., Lond., 1892, XXV, Suppl., 67. Landouzy, Presse med., Par., 1905, XIII, 633. 220 THE SOURCES AND MODES OF INFECTION handled. That parts of the room or its contents not touched should be infected by floating particles, is highly improbable. The secretions and excretions which in various ways become attached to the contents of the room are usually small in amount and thinly smeared on the surface. Such material usually rapidly loses its virulence by drying, so that, as is shown in these pages, virulent germs are recovered from the sick-room in only a small proportion of tests. Nevertheless if people should, after the termination of the sickness, crowd into the room, rub their moistened fingers over the various objects and put the fingers in the mouth, infection might sometimes result. But as the germs die rapidly, as probably not many persons enter the room, as even visitors would usually run little chance of taking up whatever pathogenic organisms might be there, we are, I think, justified in assum- ing that infection from the room or its contents is not very likely to take place. " Lung Blocks." The celebrated " lung block " in New York, bounded by Cherry, Catherine, Market and Hamilton streets, has had enormous influence on modern views con- cerning the transmission of tuberculosis. The great excess of tuberculosis in certain tenement houses has given rise to a strong belief in its causation by infection which remains attached to the interior of the dwelling. We even hear much loose talk about the germs of the disease developing in the filth and dampness of these dark houses. What an important factor house infection is believed to be in the causation of this disease is well illustrated by the exceedingly prominent place which is given to room disinfection. To judge from the attention, time and money bestowed on room disinfection after the removal or death of a consumptive, this practice is considered of equal importance with hospitals, sanatoriums, dispensaries or district nursing as a preventive measure. Let us see what is the evidence on which house infection is sup- posed to rest. It is apparently that cases continue to occur in the same house during successive years, This judgment INFECTION BY FOMITES 221 is based on the spot map. Thus in New York 1 during five years, 42 per cent of the deaths from tuberculosis occurred in 23 of the total houses infected, or in 5.25 per cent of all the houses in the city. In Ward IV, 55.8 per cent of the cases occurred in 10.5 per cent of the houses in the ward and in 28 per cent of the infected houses. In Ward VI, 44.7 per cent of the cases were in 7 per cent of the total houses and in 19 per cent of the infected houses. Many in other cities have noted the same phenomenon, but it has been especially well recorded by the New York Department of Health. But to say that these facts are to be largely explained by the per- sistence of the tubercle bacilli in the houses is no more rea- sonable than it would be to explain the recurrence of an excess of murders in certain areas to the persistence of a hypothet- ical microbe of homicide. It is true that the advocates of the importance of house infection point to numerous in- stances in which an apparently healthy family moving into a house recently occupied by a consumptive later develop the disease. That such should quite often happen merely as a coincidence is necessitated by the great prevalence of the disease. That in " lung blocks " exposure to living cases in the other tenements is a much more likely source of the disease than exposure to bacilli on the walls, is probable. To demonstrate the relation of the disease to house infection it would be necessary to go fully into the history of at least a large proportion of the cases, and that, particularly as we really know nothing about the latent period of the disease, is at present impossible. The excessive incidence of tubercu- losis on certain houses is no proof of house infection, and we are obliged to appeal to the facts of bacteriology and the general principles of infection to estimate the probable dan- ger from this source. When we consider the number of per- sons who are continually throwing off great numbers of tubercle bacilli, and the numberless chances there are, particu- larly in the crowded tenement districts, of coming in contact 1 Rep. Dept. Health, City of New York, 1896, 244. 222 THE SOURCES AND MODES OF INFECTION with fresh infective material, there seems to be no necessity of assuming that infection must be traced to the more or less feeble and scattered germs that may be clinging to the walls of a vacated apartment. What necessity or excuse is there for assuming that such infection plays more than an inap- preciably minute part in the causation of this disease ? Rags and Disease. Rags have often been considered an important vehicle of disease. At one time much attention was given to this subject in the United States, and great danger was apprehended from the importation of foreign rags, and stringent measures were taken to secure their disinfec- tion. Lengthy discussions of the matter, and references to a great volume of literature, may be found in a report for the New York City Board of Health by Smith in 1886, and in the Marine Hospital Report for 1893. 1 Numerous references are given of the alleged transmission of various diseases by means of rags. Among the diseases mentioned are smallpox (126 outbreaks), influenza, scarlet fever, erysipelas, typhoid fever, septicemia, cholera, and a disease peculiar to rag dust, called " flock cough." Rags and Smallpox. It has been believed that small- pox is frequently introduced among the workers in paper mills by the rags which they handle. Numerous instances have been reported from Maine, Massachusetts and Wiscon- sin, as well as from foreign countries. Most of the evidence is very inconclusive, as no effort is made to exclude other sources of infection, and the disease is usually prevailing generally at the time. The most suggestive outbreaks are a series reported by the Massachusetts State Board of Health. 2 Here from one to three cases occurred in six mills in different localities at a time when there was no smallpox in the town. Dr. Abbott, who personally studied these outbreaks, was con- vinced that they were due to handling rags. Yet it is curious that almost nothing has been heard of this sort of infection 1 Rep. Surg. Gen. U. S. Mar. Hosp. Serv., 1893, II, 330. 8 Rep. St. Bd. Mass., 1888, xvi. INFECTION BY FOMITES 223 during the last twenty years, and this at a time when small- pox was of a remarkably mild type and great quantities of clothing worn by patients must have escaped disinfection. Abbott was also convinced that, owing to the length of time between the collection of the rags and the opening of the bales, no danger was to be apprehended from foreign rags. Doty 1 says " that the most careful investigation has failed to present satisfactory evidence that either foreign or domes- tic rags act as a medium of infection." He has personally carefully studied the question in Egypt, where many rags are collected for the American market, and he says that there is no evidence of the infection of the handlers of even the fresh rags. Rugs and Plague. Remlinger 2 has recently called atten- tion to the supposed danger to be apprehended from draper- ies, and particularly also rugs, from the Orient. He rightly says that many of the rugs are very filthy, and must have been infected during their use or manufacture. Yet during all the prevalence of cholera and bubonic plague in Asia dur- ing recent years not a single case of these diseases has been brought into Europe or America in this way, though great quantities of rugs, draperies and rags have been imported without disinfection or with very imperfect disinfection. Money and Disease. Money is popularly believed to be a common means of spreading disease. Indeed there are few things which at first sight seem more likely to do so than paper money. Germs readily become attached to its surface, it passes rapidly from one person to another, it is kept in inti- mate contact with the person, held closely in the hand and often put to the lips. Nevertheless there is no good evidence that money has ever actually been the means of spreading contagious disease. If money is frequently a carrier of infec- tion, persons who handle a great deal of money ought to be particularly subject to infectious disease. This does not seem 1 Doty, Med. Rec., N. Y., 1900, LVIII, 681. 2 Remlinger, Hyg. ge"n. et appliq., Par., 1907, II, 257. 224 THE SOURCES AND MODES OF INFECTION to be the case, though there are unfortunately no good pub- lished statistics bearing on the subject. However, it is the business of the supporters rather than the opponents of the theory to produce the figures. I have been on the lookout for contagious disease among bank clerks, but the very few cases that have come to my knowledge during the past twenty-five years have evidently been contracted in other ways. According to Hilditch, 1 the " United States treasurer, who has given the subject long and careful consideration, is emphatic in his statement that ' there is not the slightest evi- dence to show that the employees in his department contract infectious diseases any oftener than others who are not in this line of work.' ' It may be argued, and there is some truth in this, that tellers are accustomed to take considerable precaution, such as keeping the fingers away from the lips and washing the hands before eating. Tram-car conductors are, however, I know from observation, particularly prone to hold bills and coins between the lips, and are in other ways extremely careless, yet they certainly show no excess of scarlet fever, diphtheria or smallpox. A bacteriological study of paper money has been made by Hilditch above referred to. He examined twenty-four bills and found the number of bac- teria varied from 14,000 to 586,000 per bill. Pus bacteria were found, as was to have been expected, but no other patho- genic forms. Hilditch could find accounts of only four other similar investigations, none of which, however, were as thorough as his. Bacteria are not found in any large num- bers on coins, chiefly because of the germicidal action of the metal, as shown by the researches of Park, 2 Vincent 3 and Bolton. Much Evidence Unsatisfactory. It would be easy to find hundreds of alleged instances of fomites infection, in some of which the infection was supposed to have persisted for 1 Hilditch, Pop. Sc. Month, N. Y., 1908, LXXIII, 157. 2 Cited by Hilditch. 3 Vincent, Abst. Med. News, N. Y., 1892, LXXX, 275 INFECTION BY FOMITES 225 years. Those mentioned in the preceding pages are only a few which I happened to have at hand. In most of them there is no real evidence that the disease was produced in the manner claimed. The error made in claiming so much for fomites infection in yellow fever shows how great is the lia- bility of error for other diseases. Persons, not Things, are Dangerous. It must also be borne in mind that in very many of the reported cases the supposed infected articles were carried by some person. That the person may be the " carrier" of living germs on his own mucous surfaces, though showing no symptoms, we now know full well. Until recently this was not known, hence it was universal to consider things, not persons, as the bearers of infection. We can now see that persons in whom the germs are growing are much more likely to be the agents of infec- tion than are things on which the germs are dying. Some of the instances of alleged fomites infection, such as the room infection in scarlet fever referred to, are doubtless really instances of carrier infection. Fomites and Tetanus. It is not for a moment to be assumed that there are no instances of fomites infection. It is not impossible, or at all improbable, that occasionally typhoid fever, smallpox, diphtheria and other diseases are caused by material things holding the living bacteria for some weeks or even for months. In some instances the clinical evidence of fomites infection is very strong, though perhaps it can rarely if ever be in any individual instance entirely conclusive. If it can be substantiated by bacteriological evi- dence, it becomes so much the stronger. The strongest evi- dence we have of fomites infection is concerning anthrax and tetanus. This is not surprising when it is recalled that the bacilli of both of these diseases are spore-forming and capable in that state of resisting unfavorable conditions of life for years. Thus Smith 1 finds that tetanus bacilli will survive boiling for sixty minutes at a time, or twenty minutes on 1 Smith, Theobold, J. Am. M. Ass., Chicago, 1908, L, 929. 226 THE SOURCES AND MODES OF INFECTION each of three successive days. This explains why they have been found alive and virulent in commercial gelatine and in that situation have been known to give rise to the disease in human beings. 1 Of six samples of cotton lamp wick pur- chased in various shops in Havana, five were shown by the inoculation of white mice to be infected with tetanus. This material was used by midwives for tying the umbilical cord, and after sterile material was furnished them by the depart- ment of health it is said that almost no deaths from infantile tetanus occurred in Havana. 2 The number of deaths from tetanus in children under one year of age in Havana decreased from 128 in 1901 to 18 in 1908. Some of the Fourth of July tetanus is believed to be due to the presence of the spores in the wads of blank cartridges, and they were demonstrated in them by Dolley, 3 and are said to have been found in car- tridges in Germany byMusehold of Strassburgand others, but several other American observers failed to find tetanus germs in a total of 759 cartridges examined. Fomites and Anthrax. The spores of anthrax are so resistant that they have been kept for ten or twelve years, but the bacilli themselves do not survive any longer than typhoid bacilli. Anthrax, though rather rare in the United States and England, is very common in some parts of the world, particularly in Asia, and the spores are frequently imported in dry animal products from Asiatic countries. Legge 4 cites from several observers who recovered the spores from hair and hides imported from China and Siberia. More recently Eurich 5 has examined nearly 750 specimens of wool, hair and dust from these materials. In over 600 specimens 1 Tuck, Jour. Path. & Bacteriol., Edinb. & Lond., 1904, IX, 38. 2 Junta Sup. de San. de la Isla de Cuba, Supplement*) y Note Adi- cional, 1902-03, 4. 3 Dolley, J. Am. M. Ass., Chicago, 1905, XLIV, 466. 4 Legge, Lancet, Lond., 1905, 1, 694, and Rep. Insp. of Fact., Lancet, Lond., 1904, I, 1206. 6 Rep. Anthrax Investigation Bd., Bradford, Eng., No. 3, 1908, 8. INFECTION BY FOMITES 227 free from blood he found no anthrax germs, but he did find them in 20, or 14.4, per cent, of 139 bloodstained specimens. These findings are substantiated in his last report (1909), and he speaks of a case of anthrax in a man who handled wool in which anthrax spores were actually found. In 64 samples of dust, anthrax germs were demonstrated only once. 1 Page 2 also gives references to other similar findings. But such observations are not necessary to show that the disease is transported in this way, for there is ample clinical evidence that such goods are the direct cause of anthrax in men and animals. In fact, most industrial anthrax in Western Europe and North America is caused by handling wool, hair and hides imported from anthrax-infested countries. Fomites and Typhoid Fever. One of the most remarkable of the authenticated instances of fomites infection is the transmission of typhoid fever by means of army blankets from South Africa. 3 These blankets came from Africa in October, 1902, and were then sold. They went to 290 different parties. One lot used on the transport Cornwall apparently gave rise to the disease in May, 1903; the use of another lot in England was also followed by typhoid fever. Some of the blankets were considerably soiled, and living bacilli were found on several that were examined in London. Fomites and Diphtheria. A young man working in a laboratory in an American city spilled some bouillon culture of diphtheria bacilli on his coat. This coat, without disin- fection, he wore when calling on the young woman to whom he was engaged, and she developed diphtheria two days later. The culture which was spilled contained only the branching forms of the diphtheria bacillus, and the culture from the patient's throat showed the same forms. But very few instances other than the above are on record 1 Rep. of Chief Inspector of Factories and Workshops, 1907, 57. 2 Page, J. Hyg., Cambridge, 1909, IX, 357. 3 Parkes, Practitioner, Lond., 1903, LXXI, 297. 228 THE SOURCES AND MODES OF INFECTION where pathogenic bacteria have actually been found on mate- rials which presumably have carried infection. According to Simpson, 1 plague bacilli were found by Kitasato on cotton goods imported into Japan, and this was thought by Kitasato to be the way in which the disease was introduced into that country, but from what is now known about the mode of extension of the disease this seems highly improbable. Few Instances of Fomites Infection. But while we may admit that occasionally the virus of even many of the com- moner diseases may be retained on fomites for a considerable length of time, and ultimately give rise to new cases, there is no clinical evidence to show that such instances are at all common. Even when carefully sought for, fomites infection is not very often found. In my early work as health officer I firmly believed in the importance of this factor, and dili- gently sought for evidence. The fact that I found very little was one thing which led to a more careful consideration of the subject. Of 13,970 cases of scarlet fever reported in Michi- gan, 2 only 335 were attributed to fomites infection. To an even less degree are diphtheria and measles attributed in this report to fomites infection. Of 221 cases of bubonic plague in Natal, 3 only 8 were by Hill attributed to fomites infection, and Mitchell in Port Elizabeth attributed only 6 of 337 cases to the same source. When we consider that most of the evidence is extremely flimsy, and that much of the alleged fomites infection is probably carrier infection, and remembering also how the history of yellow fever has taught us to be wary of such proofs, we are forced to the conclu- sion that there is little in the history of the more prevalent infectious diseases to indicate that fomites infection is at all common. Reasons for Belief in Fomites. One reason why fomites infection looms so large in the minds of health officers, as 1 Simpson, Treatise on Plague, Cambridge, 1905, 204. ' * Rep. St. Bd. Health, Mich., 1906, 134. J. Hyg., Cambridge, 1907, VII, 712. INFECTION BY FOMITES 229 well as of the laity, is that the striking character and air of mystery about the alleged incidents are so impressive. " Death in a Toy," or " A Child Succumbs to the Dread Disease from Infection Lurking in its Mother's Shawl," appeal to the imagination. That the invisible emanations of disease should cling to a garment for years is too near akin to the stories of the Arabian Nights not to impress the average mind. Hence it is that the comparatively few instances of real fomites infection have far more than their due weight in our estimation of the relative importance of different modes of infection. Even if all the alleged instances of fomites infection were true, the amount of disease apparently caused in this way is relatively very small. The frequency with which conta- gious disease can be traced to fomites is not the reason for the general belief in the importance of this mode of infection. The real reason, I have no doubt, is, that until very recently there seemed to be no other way of explaining isolated cases of disease. As a rule it is impossible, even with modern aids to the diagnosis of obscure cases, to trace the source of infec- tion of most cases of contagious disease, particularly in cities. The theory of long persistent fomites infection seemed to offer a reasonable solution, and hence met with universal acceptance. The theory was almost a necessity to explain the facts as they were formerly understood. Now we have no need- for such a theory, and a much more satisfactory explanation is at hand. Evidence against Theory. It is only within a very few years that the frequency with which mild atypical cases of disease occur has been recognized, and the existence of numerous entirely healthy carriers is a modern discovery, which is even now denied by some. The more carefully individual cases and outbreaks of disease are studied, the more often are they traced to missed cases and carriers. It is not probable that we shall ever be able to discover the origin of all our contagious disease. We can only infer its 230 THE SOURCES AND MODES OF INFECTION source from the data we have. As was shown in the first chapter, there is every reason for thinking that disease germs rarely grow outside of a living body. Two other theories are open to us. Disease may be due to the persistence of infection on things, or it may be due to exposure to mild cases or carriers. There should be no hesitancy in choosing between the danger from rapidly dying germs on books, money, furniture or clothes, and rapidly growing germs in the mouth, nose and intestines of persons. Moreover things must be carried, people move freely at will. If the danger from fomites infection were as great as is generally believed, the contagious diseases would be much more common than they are. The advocates of this theory are constantly telling us how easily everything near the sick becomes infected and how long the infection lasts. Every one knows that at the best disinfection is imperfect, and that much that passes for disinfection is no disinfection at all. Then the missed cases, which all admit occur in considerable numbers, to say nothing of the carriers, are constantly infect- ing large numbers of things which are not subjected to any disinfection. Yet our scarlet fever and diphtheria are not increasing, which means that one case of the disease gives rise to no more than another case. If fomites infection occurred as easily as is alleged, each case would ramify through fomites into a dozen more cases. One reason for doubt about the prevailing ideas of fomites infection is this: if fomites infection were as common and as easy as is alleged, few could escape it, and the infectious diseases would be much more prevalent than they are. As was shown in Chapter IV, the chances for the transfer of fresh infective material are so extremely numerous that there is no necessity for assuming the far more difficult and uncertain modes of aerial convection and transmission by fomites, and indeed there seems to be little opportunity for their action. Bacteriological Evidence. Having considered some of the clinical evidence of the part played by fomites in the INFECTION BY FOMITES 231 transmission of infection, it is desirable to inquire what light the laboratory study of disease has thrown on the problem. One of the first labors of the discoverer of a pathogenic organ- ism is to determine its resistance to various hostile influences, such as heat, cold, drying, light and disinfectants. The Effect of Drying upon Bacteria. Drying, exposure to light and lack of nourishment are the principal factors which determine the life of micro-organisms on fomites. Besides the study of the germs of special disease by those particularly interested, Germano, whose work is mentioned in the chapter on aerial infection, Ficker, 1 Zonchello, 2 Heim, 3 and Buckley, 4 among others, have given careful and system- atic attention to the effect of drying on the vitality of bac- teria. Exceedingly divergent results have been reported by these different observers. This, however, is not surprising if the number of factors involved is taken into consideration. Among the most important of these factors is the amount of light. Germs that are killed in a few minutes in direct sunlight may live for weeks in a dark place or even in diffused light. The thicker the layer of infectious material, the longer is its virulence likely to be maintained. This thickness depends largely upon the nature of the medium. In a dried watery medium, bacteria may die quickly, while they may survive long in sputum or feces. The more complete the drying, the shorter the life, and alternate drying and damp- ening is unfavorable. The higher the temperature, the sooner the germs perish. Their vitality also varies with the rapidity of the drying process and the material on which they happen to be. Old cultures die sooner than fresh ones, and different strains have different powers of resistance. The chemical composition of the medium and 1 Ficker, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1908, LIX, 367. 3 Zonchello, Giornale della Real Soc. Ital. d' Igiene, 1905, XXVII, 489, 537. 1 Heim, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1905, L, 122. 4 Buckley, Pub. Health, Lond., 1906-07, XIX, 290. 232 THE SOURCES AND MODES OF INFECTION the presence or absence of other organisms may have an influence. The spores of bacteria are so resistant that we should natu- rally expect the diseases caused by the spore-forming kinds to be readily carried on fomites. As has been shown, this is true of anthrax and tetanus, diseases which belong to this class. Typhoid Bacilli. Among the more hardy non-spore- forming bacteria is the bacillus of typhoid fever. In the first chapter it was shown that in the presence of moisture, as in privy vaults, the soil, milk, water, etc., this bacillus some- times lives for some months, though it often dies out in a much shorter time. It remains to consider the duration of its life when in a more or less dry condition. Firth and Horrocks 1 found that typhoid bacilli would live on khaki for 78 days, in feces dried on serge for 9 to 17 days, on serge for 10 days after it had been exposed to direct sun- light for 50 hours. Pfuhl 2 says that dried on linen they lived 97 days. Germano 3 cites Gaffky as reporting that the typhoid bacillus would live for 3 months when in a dry con- dition, and that Uffelmann recovered it from various dry materials after a period of from 21 to 80 days. But Germano suspects that the substances were not perfectly dry. Ger- mano himself was able to preserve typhoid bacilli dried on wood or linen for 90 days, but when he inoculated sterile dust with a bouillon culture, the bacilli did not survive over 4 days and sometimes perished in 1 day. Most of them died off very rapidly. Buckley 4 found they would live for from 5 days when dried on paper in a room to 119 days when kept on wood in a moist chamber. The consensus of opinion seems to be that while under unfavorable conditions, 1 Firth and Horrocks, Brit. M. J., Lond., 1902, II, 936, 1094. 2 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. * Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXIV, 403. 4 Buckley, Pub. Health, Lond., 1906-07, XIX, 290. INFECTION BY FOMITES 233 as when quite dry and exposed to light, the typhoid bacillus may die in a few days, yet under conditions which must fre- quently prevail it may remain alive on such things as cloth- ing and bedding for some months. Mediterranean Fever. The micrococcus of Mediterra- nean fever has about the same resistance as that of typhoid fever. Like the typhoid bacillus, it is killed in an hour or two in direct sunlight. Dried on glass it survives 16 days, in moist soil 72 days and on a blanket 80 days. 1 Diphtheria. Loeffler kept dry diphtheria bacilli alive for from 9 to 16 weeks, Roux and Yersin for 5 months, D'Espine and Morignac for between 3 and 4 months, and Park for 4 months. 2 Germano 3 found that they would retain their virulence after remaining in dry earth or dust for 20 to 40 days, and Reyes 4 found them virulent in sand and on cloth after 14 days. Buckley 5 recovered living bacilli, when dried in the air on paper, after 6 days, on wood after 8 days, on cotton and on glass after 24 days, and on plaster after 37 days. Hill 6 exposed to ordinary room conditions, glass rods which had been rubbed on a culture of diphtheria bacilli. Of these 28 per cent survived 14 days and 9 per cent 20 days. Houston 7 found that they died very quickly in earth. Leighton 8 recovered them from warm moist modeling clay up to 18 days. Williams 9 could not recover the germs after 24 hours from pencils moistened by the lips of patients who had the bacilli in the throat, 1 Horrocks, Rep. Commission Roy. Soc., Pt. I, 1901. 2 Cited by Germano. 3 Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXV, 439. 4 Reyes, Jahrb. u. d. Fortschr. . . . d. path, mik., Baumgarten, 1895, XI, 203. 6 Buckley, Pub. Health, Lond., 1906-07, 290. 6 Hill, Am. Pub. Health Ass. Rep., 1902, XXVIII, 209. 7 Houston, Rep. Med. Off. Loc. Gov. Bd., Lond., 1898-99, XXXIII, 413. 8 Leighton, Pediatrics, 1901, XII, 360. 9 Williams, N. Y. Health Dept., Sci. Bull. 2, 1895, 16. 234 THE SOURCES AND MODES OF INFECTION Dysentery Bacilli. According to Pf uhl 1 the bacillus of dysentery may remain alive for 17 days when dried on cloth, or 10 days when in dry sand. In direct sunlight it dies in 30 minutes. 2 Kruse 3 claims that when dry it will retain its vital- ity for months. Tubercle Bacilli. More attention has been paid to the vitality of the tubercle bacillus than to that of other bacteria. It is generally believed to be one of the most resistant, but Hill 4 has shown that under the same natural conditions of dryness, light, etc., the diphtheria bacillus will outlive it. Many of the earlier writers claimed a very considerable lon- gevity for the tubercle bacilli in dried sputum. Villemin, Schill, Fischer, Koch, De Thoma, Sormani, Maffuci and Cadeac and Malet claimed a life of from 1 to 9 months. 5 Ransome and Delepine 6 found that the bacilli if exposed to air and light would not survive 45 days, but if kept in dim light they did survive. Twichell 7 placed sputum in a folded hand- kerchief, in a folded carpet, and spread on wood, and ex- posed it to the air at ordinary temperatures and in diffused light. The bacilli survived for 39 to 70 days. In sunlight they died in a few hours. Migneco 8 found that when dried on cloth in the sun they lived from 20 to 30 hours. Not so Resistant as Believed. Many recent observers do not find this bacillus so resistant as has been supposed. That it perishes in direct sunlight in less than an hour seems certain. Weinzirl, 9 using improved methods, finds that it will not survive 10 minutes, and frequently dies in 2 minutes. 1 Pfuhl, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1902, XL, 555. 2 Shiga, Deutsche med. Wchnschr., 1901, XXVII, 765, 783. Kruse, Deutsche med. Wchnschr., 1901, XXVII, 370, 386. Hill, Am. Pub. Health Ass. Rep., 1902, XXVII, 209. Kolle and Wasserman's Handbuch [etc.], Jena, 1903, II, 108. Ransome and Dele*pine, Proceedings Royal Society, No. 336. Twichell, Med. News, N. Y., 1905, LXXXVII, 642. 8 Migneco, Arch, of Hyg., Miinchen u. Leipz., 1895, XXV, 361. 9 Weinzirl, J. Infect. Dis., Chicago, 1907 [Suppl. No. 3], 128. INFECTION BY FOMITES 235 Cade*ac * spread sputum on marble and could find no living germs after the fourteenth day. On a porous plaster plate they died within 2 days. Hill 2 dried sputum on glass rods in the air under ordinary room conditions, and found no liv- ing bacilli at the time of his first test, which was made after 16 days. Rickards, Slack and Arms 3 have made very careful tests by exposing sputum on wood and cloth in the rooms of ordinary tenements. They find that when dry and kept in diffused light the bacilli will live about 1 month, in dark and dry rooms up to 85 days; another strain survived only 45 days under the latter conditions. Rosenau 4 says that further work upon the viability of the dried tubercle bacillus may change our views as to its hardiness, and failure to recognize lesions produced by the dead bacillus is responsible for some of the false conclusions reached by certain experimenters. Plague Bacilli. Simpson 5 states that the German Plague Commission found that in a large number of experiments with sputum, blood, etc., dried on all sorts of materials, under natural conditions, the bacilli of bubonic plague do not sur- vive over 8 days. Of many specimens of the organism dried on cover glasses and sent to England, none survived the journey. Kitasato 8 found that plague pus dried on cover glasses lost its virulence, when exposed to the sun, in from 3 to 4 hours, and this has been substantiated by others. As was referred to in the first chapter, the work of the last Eng- lish Plague Commission shows that virulent plague bacilli cannot be found in the dirt floors of native houses after 48 hours. According to the careful experiments of Buckley, 7 1 CadSac, Lyon meU, 1905, CV, 865, Abst. Brit. M. J., Lond., 1906, I. Hill, Am. Pub. Health Ass. Rep., 1902, XXVIII, 209. Rickards, Slack and Arms, Am. J. Pub. Hyg., Bost., 1909, V, 586. Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No 57, 1909. Simpson, Treatise on Plague, Cambridge, 1905, 96. Kitasato, Lancet, Lond., 1894, II, 428. Buckley, Pub. Health, Lond., 1906-07, XIX, 290. 236 THE SOURCES AND MODES OF INFECTION plague bacilli remain alive after drying in the air, for 11 hours when dried on cotton, 2 hours on wood, 5 hours on plaster, 2 hours on glass, and 3 hours on paper. When kept in a desiccator they survived on cotton for 22 hours, and in a moist chamber for only 36 hours. Gotschlich, 1 by folding material containing the germs in cloth, could preserve them alive for from 3 to 4 weeks. Simpson 2 reports that infected cloth may retain its virulence for 80 days. According to Verjbitski, 3 the crushed viscera of experimental animals and the crushed bodies of fleas when smeared on cloth and dried will preserve the bacilli alive for 130 days at a temperature of 4-5 C., and for 35 days at room temperature. Bandi and Stagnitta-Balistreri state that these bacilli may survive in the bodies of dead rats for 2 months. The vitality of the plague bacillus has been carefully investigated by Rosenau, 4 who does not consider it a frail organism. Temperature is the most important factor in its life. It may lose its virulence before it loses its vegetability. It dies in a few days on the dry surface of hard objects and on paper. Rosenau says that bedding may harbor the infection for a long time. Tidswell, 5 experimenting with a large number of materials, found that plague bacilli dried under natural conditions lived only from 3 to 4 days, but when dried slowly on muslin they might live for 21 days. The colder the climate the greater is the chance of the persistence of infection. In this all are agreed. Pus-forming Bacteria. The pus-forming bacteria are quite resistant to drying. According to Germano, 8 streptococcus 1 Gotschlich, cited by Kolle and Wasserman's Handbuch [etc.], Jena, 1903, II, 496. 2 Simpson, Treatise on Plague, Cambridge, 1905, 93. 3 Verjbitski, J. Hyg., Cambridge, 1908, 203. 4 Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 4, 1901. 6 Tidswell, Report on Plague in Sydney, J. A. Thompson, 1902, 67. 8 Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXVI, 66. INFECTION BY FOMITES 237 withstands drying for a month, but different strains have varying degrees of resistance. See also Heim 1 and Neisser, 2 who found that these organisms would withstand drying for a long time. Buckley 3 could keep staphylococcus alive for only 7 days when on paper in the air, and on other sub- stances and under different conditions for varying times, up to 130 days on cotton kept in a desiccator. Cholera Spirilla. Germano 4 in a number of experiments found that the cholera spirillum in dried feces lived only 3 days and in other experiments only 1 day. He also cites Zon- chello as reporting that it is among the least resistant bac- teria. Kitasato 5 states that it may retain its virulence up to 8 days, but that it may die sooner, especially when dried on glass. Usually it lives from a few hours up to 4 days. Koch and Gaffky 6 state that when dried on glass it survives only a few hours, but when dried on fabrics it may retain its viru- lence up to 4 days. Buckley 3 found that cholera germs would survive when dried in the air, 9 hours on cotton, 8 hours on wood, 1} hours on glass, and 5 hours on paper. They did not survive nearly so long when dried in a desiccator. This is contrary to the experience of others, for as a rule bacteria live much longer when dried in a desiccator than when dried in the open air under natural conditions. Gotschlich 7 says that cholera germs will live in dejecta dried in the air on clothing for 36 days, and when damp, according to Karl- niski's observations, for 7 months. He considers that such a long life is exceptional, and that generally the spirillum dies in a few days. A duration of only a few days, or even hours, Heim, Ztsch. f. Hyg. u. Infectionskrankh., Leipz., 1905, L, 122. Neisser, Ueber Luftstaub-Infection, Inaug. Dis., Breslau, 1898. Buckley, Pub. Health, Lond., 1896-97, XIX, 290. Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXIV, 403. Kitasato, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1885, V, 134. Koch, Arb. a. d. k. Gesundsamte, Berl., 1886, I, 199. Gotschlich, Kolle and Wasserman's Handbuch [etc.], Jena, 1902, I, 211. 238 THE SOURCES AND MODES OF INFECTION was also found by Gamaleia, 1 Hesse 2 and Koch and Gaffky. Pneumococci. The pneumqcoccus is widely distributed in healthy human mouths, and the opportunities for the direct transference of fresh secretion are so numerous that it probably is of no importance whether this organism lives long or not. Wood 3 found that while pulverized sputum lost its virulence in a few hours when dried in mass, it might, under favorable conditions, retain it 35 days. Buerger 4 recov- ered the pneumococci from a handkerchief 7 days after it had been in use. Germano 5 and some others claim a consider- ably greater resistance. Germano kept it alive in dust for 140 days, but the tendency of later observers is to consider it a much feebler organism. Influenza Bacilli. According to Pfeiffer, 8 the influenza bacillus retains its vitality when dried in sputum for 36 to 40 hours. When dried on a cover glass and kept at 37 C., it survives for only 2 hours, and when kept at room temperature for from 8 to 20 hours. Meningococci. The evidence in regard to the germ of cerebro-spinal meningitis appears to be somewhat conflicting. Germano and Neisser claim considerable resistance for it, as also does Jaeger. 7 Germano said it would live for 80 to 90 days, but it is said that he did not work with the true menin- gococcus. 8 More careful and recent observers do not find it so resistant. Councilman 9 found that it would live when dry Gamaleia, Deutsche med. Wchnschr., 1893, XIX, 1350. Hesse, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1893, XIV, 30. Wood, J. Exper. M., N. Y., 1905, VII, 592. Buerger, J. Exper. M., N. Y., 1905, VII, 518. Germano, Ztschr. f. IJyg. u. Infectionskrankh., Leipz., 1897, XXVI, 66. Pfeiffer, Nothnagel's Encycl. Pract. Med., Phila. and Lond., Influ- enza, 1895, 584. Jaeger, Med. Klin., Berl., 1905, I, 990, 1011. Arkwright, J. Hyg., Cambridge, 1907, VII, 193. Special Report on Cerebro-spinal Meningitis, Mass. St. Bd. Health, 1898, 78. INFECTION BY FOMITES 239 in a dark room less than 72 hours. Albrecht and Ghon 1 could keep it only 24 hours in the dark, and Bettencourt and Franca 2 less than 9 hours. Kache, 3 Kutscher 4 and Fliigge 5 had similar results, and Arkwright 6 succeeded in keeping the organism alive only from 20 to 48 hours. Lingelsheim 7 says that in culture media it dies in a few hours, but in sputum it may be kept alive for 5 days. Gonococci. According to Schaffer and Steinschneider, 8 and Ullmann 9 the gonococcus lives only a few hours on textiles, at most 36 hours, and often dies as soon as thor- oughly dry. Hertmanni 10 from his own observations and those of others, whom he cites, concludes that the Tryponema pal- lida of syphilis may retain its motility for some months if left moist and in the dark. Drying quickly kills it. Bacteria on Fomites. Pathogenic bacteria have fre- quently been sought for on various articles believed to be likely to be the means of transporting disease, but with the exception of the spores of anthrax and tetanus they have rarely been found. The finding of anthrax and tetanus spores has already been referred to. Besides the places mentioned, tetanus germs have been found in the soil in various places, in the dirt filling between the floors of houses u and in one Albrecht and Ghon, Wien. klin. Wchnschr., 1901, XIV, 984. Bettencourt and Franca, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1904, XLVI, 463. Cited by Fliigge. Kutscher, Deutsche med. Wchnschr., 1906, XXXII, 1071. Fliigge, Klin. Jahrb., Jena, 1905, XV, 373. Arkwright, J. Hyg., Cambridge, 1907, VII, 193. Lingelsheim, Klin. Jahrb., Jena, 1905, XV, 373; Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1908, LIX,. 457. 8 Verhandl. d. IV Kong. d. deutsch. dermatol. Gesellsch., Breslau, 1904. 9 Ullmann, Wien. med. Blatter, 1897, XX, 703 et seq. 10 Hertmanni Dermat. Ztschr., Berl., 1909, XVI, 633. 11 Heinzelmann, Munchen med. Wchnschr., 1891, XXXVIII, 185, 200. 240 THE SOURCES AND MODES OF INFECTION instance in a house where there had been a death from tetanus. 1 Distribution of Germs of Suppuration. The pus organ- isms are quite resistant to drying, and if they were not, they are so widely distributed, being found constantly on the skin and mucous surfaces of human beings, that their presence might be expected wherever human beings are found. They have as a matter of fact been found almost wherever sought, as on clothing, books, money, instruments, floors and wood- work, and indeed on anything that is touched by the hand of man. Diphtheria Bacilli on Fomites. Diphtheria bacilli have been frequently searched for on all kinds of objects and fre- quently found. Abel 2 and Wesbrook 3 found them on toys, and in Abel's case it was 86 days after infection. Trevelyan 4 recovered them from a handkerchief 11 weeks after it had been used by a diphtheria patient. Park 5 took cultures which proved positive in almost every instance, from dried stains on bedclothing soiled by children sick with diphtheria. He also found the bacilli alive in a piece of membrane after 4 months. Wright and Emerson 6 made 20 cultures from various articles in the Boston City Hospital, and found 5 positive. Of these 3 were from the shoes, 1 from the hair of an attendant, and 1 from a floor brush. Schumburg 7 in 40 cultures from a room occupied by a diphtheria patient recovered virulent bacilli from a drinking glass and the handle of a mirror. In 2 of the 5 cultures the virulence of the organism was low. 1 Gotschlich, Kolle u. Wasserman's Handbuch [etc.], Jena, 1902, 1, 210. 2 Abel, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1892, XIV, 756. 3 Wesbrook, Wilson and McDaniel, Am. Pub. Health Ass. Rep., 1899, XXV, 546. 4 Trevelyan, Lancet, Lond., 1900, I, 1443. 6 Park, Med. Rec., N. Y., 1892, XLII, 116. 6 Wright and Emerson, Centralbl. f. Bakteriol. [etc.], I Abt. Orig., Jena, 1894, XVI, 412. 7 Schumburg, Ztschr. f. arztl. Fortbild., Jena, 1905, II, 567. INFECTION BY FOMITES 241 Welch ardt 1 took 300 swabbings from various things in a sick-room and 250 from other parts of the house, and found diphtheria germs 3 times on objects which had been in contact with the patient's mouth. Hill 2 took 532 swabbings from a room occupied by a diphtheria patient, and obtained 4 posi- tive results, all of which were from objects handled by the patient. In Providence about 200 swabbings taken under similar circumstances showed no diphtheria bacilli. These last three observations indicate that diphtheria bacilli are not very numerous, even on objects brought into close con- tact with the patient. Kober 3 could find no bacilli on the floor, bed linen, etc., of 10 houses in which there had been diphtheria, and he states that Heymann did not find them in the Hygienic Institute at Breslau. Klein could not find them on telephones in London, 4 and Hill in Boston 5 could not find them on 24 mouthpieces of lung-testing machines. Tubercle Bacilli on Fomites. While the tubercle bacillus is not so resistant to drying as was formerly thought, it is discharged in such numbers in the sputum that it has been found outside of the body more often than have any other organisms except the pus-forming bacteria. Reference to finding it in dust will be given in the next chapter. When in considerable masses of sputum, and kept damp, the bacillus will survive longer than when mixed with dust. Besides on the floors and various articles in rooms, the bacillus has been found in books which were in use for some years in a circu- lating library. 6 Petersson 7 examined the history charts kept by the bedside of tuberculous patients and put away for 1 Weichardt, Jahresb. u. d. Fortschr. . . . d. path. Mik., Baum- garten, 1900, XVI, 197. Hill, Am Pub. Health Ass. Rep., 1902, XXVIII, 209. Kober, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXXI, 449. Klein, Abst. J. Am. M. Ass., Chicago, 1905, XLIV, 1866. Hill, Rep. Bd. Health, Boston, 1906, 91. Mitulescu, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1903, XLIV, 397. 7 Petersson, Ztschr. f. klin. Med., Berl., 1907, LXIII, 346. 242 THE SOURCES AND MODES OF INFECTION periods varying from months to years. He found by micro- scopic examination tubercle bacilli on two books that were kept for six years. Bissell 1 washed the pockets of some uni- forms that had been used by soldiers sick with consumption, and obtained two positive results by guinea-pig inoculation. Friberger 2 used a vacuum cleaner to remove the dirt from clothing fresh from use by tuberculous patients, and found virulent bacilli in 3 of 12 tests. Cholera Spirilla. Although the life of the cholera spiril- lum outside of the body appears to be short, usually only a few days and often less, some early observers, as Babes, 3 claim to have found it on the personal effects of cholera patients. Resistance of Protozoa. There is no theoretical reason why the protozoan blood parasites might not, in a spore-like, resistant stage, withstand drying and remain alive for some time outside of the body. But there is no experimental evi- dence to show that in any of the well-known protozoan dis- eases such spores are formed. There is certainly no clinical evidence to show that such diseases are ever carried on fomites, and for malaria, yellow fever, sleeping sickness and Texas cattle fever there is convincing evidence that they are not so carried. Resistance of Vaccine Virus. With two exceptions, prac- tically no experimental work has been done with the virus of any of the infectious diseases, a specific organism for which has not been determined. Vaccine virus has an extensive use, and it is desirable to store it and transport it long dis- tances, so that its keeping qualities have received considerable attention. When the infectious material dries naturally in the crust which forms from the vesicle, it retains its virulence for a considerable time. These crusts were largely used in 1 Bissell, Med. News, N. Y., 1899, LXXIV, 156. 2 Friberger, Ztschr. f . Tuberk. u. Heilstaltenw., Leipz., 1908-09, XIII, 37. 8 Shakespeare, Report on Cholera in Europe and India, U. S. Gov. Print. Off., 1890, 606, INFECTION BY FOMITES 243 Providence for maintaining the Jennerian strain of vaccine, which was used in the health department for nearly fifty years. The crusts, when taken from the arm and kept wrapped in paper in a dark place, could be relied upon to retain their virulence for a month, and often did retain it longer. When kept in a tightly corked bottle in a refrigerator, they will generally remain virulent over 6 months. If exposed to light and air and varying temperature, the virulence may be lost in less than a month. A thin layer of the same lymph on a quill does not remain active when exposed to the air for more than a week or ten days. The ivory points covered with vaccine matter, which were so much used a few years ago, were usually guaranteed to keep 3 weeks, and often did remain virulent a month or more. But there was usually more than one layer, and the thickness of the material was further increased by the presence of blood and leucocytes. According to Seaton, 1 dried vaccine matter on points may keep for from 6 or 9 months or more, and he quotes Husband as securing successful vaccinations from 7 of 93 dried points kept for periods varying from 6 to 30 months. Vaccine matter in powder also has been kept by Warlomont and others for several months. 2 Recently Green 3 has kept dried pulverized vaccine matter in sealed tubes for periods varying from 20 days at 37 C. to 252 days at 10-15 C. and 301 days at 4 C. Although under exceptional circumstances dried vac- cine matter may be kept a considerable time, it requires great care and often results in failure. Hence early in the nine- teenth century, in order to introduce vaccination into her American possessions, the Spanish Government 4 sent out a ship with a number of children on board, so that by successive arm-to-arm vaccinations fresh lymph might be carried across the seas. At the end of the nineteenth century, when Porto 1 Seaton, Handbook of Vaccination, 1868, 172. 1 Warlomont, Manual of Animal Vaccination, Phila., 1886, 139. Green, J. Hyg., Cambridge, 1908, VIII, 528. 4 Life of Jenner, Baron, I, 606; II, 78. 244 THE SOURCES AND MODES OF INFECTION Rico came under the control of the United States, the diffi- culty of transporting vaccine virus to the island became so great, so little active virus surviving even this short voyage, that it was necessary to establish a vaccine farm on the island. In the Philippine Islands it was found to be necessary to transport the virus packed in ice to inland villages. 1 Resistance of -Smallpox Virus. It is a common belief that the crusts in variola are infectious, and they are supposed to have been used at times in the practice of inoculation. I do not remember to have seen any evidence of this till I came across the work of Brinckerhoff. 2 He refers to a rather limited literature, and details his own experiments, which determined a persistence of virulence in the crusts for periods of from 22 to 52 days, and in one instance to 88 days. Comparative Resistance. Experiment shows that some pathogenic organisms, like those of gonorrhea and cerebro- spinal meningitis, are of such feeble resistance that infection by fomites, as ordinarily understood, is in these diseases highly improbable. It is also shown that certain other bacteria, as those of diphtheria, typhoid fever and tuberculosis, are resist- ant enough to make infection by fomites very possible. But it appears that all known pathogens, except those having spores, tend to die off quite rapidly outside of the body, and that under natural conditions it is rather the exception for them to persist for any great length of time. It is worth noting that the typhoid bacillus is more resistant than any other pathogenic organism referred to. Yet we hear almost nothing about fomites infection in that disease. Is it not because attention has been directed to other sources which have been believed to be sufficient, so that there has been little temptation to assume infection by fomites ? Infection by fomites has, on the other hand, been considered of much importance in cholera, the spirillum of which is far less resist- ant than is the bacillus of typhoid fever, probably because 1 Rep. Bd. Health, Philippine Isl., 1904-05, 23. 2 Brinckerhoff, J. Med, Research, Bost., 1904, XI, 284. INFECTION BY FOMITES 245 in the absence of the knowledge of carriers which we now possess the world-wide diffusion of this disease seemed inex- plicable except by means of fomites. Experiments with Yellow Fever. With a few notable exceptions, little experimental work has been done to deter- mine the part played by fomites in the spread of disease. When Reed, Carroll Lazear and Agramonte proved that yel- low fever is transmitted by the mosquito, it still remained uncertain whether it might not also be carried in other ways, and sanitary officials were generally so convinced of the over- whelming evidence of the great part played by fomites, that definite proof or disproof of the fact was earnestly desired. The complete failure of the commission to produce the disease in human beings by fomites is well known, and their experi- mental work has now been corroborated by abundant clinical evidence from all the great endemic foci of this disease. In these experiments, non-immunes were confined in a small room for a number of days in close contact with bedding and clothing fresh from yellow-fever cases, most of which was soiled with excreta and vomitus. 1 The experiments were repeated a number of times, but in no instance did the disease develop. When not long after I stood in one of those dirty little rooms in company with Dr. Finlay and Dr. Gorgas, and saw some of the old bedding lying in the corner, I realized as never before how very much greater are the difficulties in observation than in experiment, and it seemed that the time had come when the prevailing views as to the importance of fomites infection in other diseases than yellow fever should be seriously reviewed. Observations on Plague. In another disease, bubonic plague, exceptionally brilliant work, from the purely epidemi- ological standpoint, has been done by Thompson in Australia. It is true enough that conditions are much more favorable for observation when a disease first invades a country than when it has become as widespread as plague is in India, but in no 1 Phila. M. J., 1900, VI, 790. 246 THE SOURCES AND MODES OF INFECTION place have they been taken advantage of as they were in Sydney. Thompson 1 showed conclusively that rat plague preceded human plague, that the flea was the intermediary between rat and man, and that in New South Wales, at least, fomites had no part in the diffusion of the disease. These observations have been confirmed in other parts of Australia. 2 Experiments with Plague. The present English Plague Commission have, by their ingenious and painstaking ex- periments and observations in India, confirmed Thompson's work. Reference will be made in another chapter to the experiments on the transmission of the disease by the air, in which they definitely proved that aerial infection does not take place. They also studied experimentally the conditions of house infection, and their work is among the best planned and executed and the most convincing of any that has ever been attempted for any disease. Besides much other work, they placed guinea pigs in the houses of an Indian village just vacated by the inhabitants because of plague, thus sub- stituting an experimental population under control for the normal human population. 3 The results were in every way in accord with the view that plague is primarily a rat disease, and is transmitted from rats to man, or to other animals, by means of fleas. In these and in similar less extensive experi- ments 4 there was evidence to show that the animals could not contract the disease from the dwellings themselves. To test more definitely the possibility of transmission by fomites other experiments were made. The floors of houses were soaked with cultures of the bacilli, and guinea pigs placed upon them. Of 24 exposed during the first hour after in- fection 4 died; of 12 exposed up to six hours 4 died; but during all this interval pools of the culture were upon the floor. Of 24 animals exposed after twelve hours only 1 1 Thompson, J. Hyg., Cambridge, 1906, VI, 537. 2 Ham, Rep. on Plague in Queensland, 1900-07, Brisbane, 1907. J. Hyg., Cambridge, 1907, VII, 799-875. 4 J. Hyg., Cambridge, 1906, VI, 450-482. INFECTION BY FOMITES 247 succumbed. Guinea pigs were also allowed to run freely about hospital wards in which cases of bubonic plague were being treated, and 15 were confined in a room with freshly soiled bedding, which was renewed every day for six weeks. In none of the animals did the disease develop. Again (p. 887), clothing from infected houses, removed without pre- cautions to prevent the transport of fleas, was placed in cages containing 26 guinea pigs, 1 of which died of the plague. A few fleas which had been brought in the clothing were found in the cages. It seems to be quite clear from these experiments that while infection by fomites is pos- sible, it is probable only when the infection is exceedingly gross and the contact is intimate, as in the case of the in- fected floors referred to above; or it may also be possible when infected fleas are transported in the goods. How common this is has not yet been determined. Tuberculosis. I know of no other diseases in which seri- ous experimental work has been done to determine the part played by fomites in their diffusion. It is particularly re- markable that tuberculosis has not been thus critically studied. Every one has been calling for room disinfec- tion as a powerful means of combating this disease, yet it does not seem to have occurred to anyone to place suscep- tible animals in a series of supposedly infected rooms (as was done in the case of plague in India) to determine if pos- sible how great the danger from room infection really is. Disinfection Unnecessary after Diphtheria. By a study of the facts presented in this chapter the writer was con- vinced some time since that the danger from fomites in- fection is for most diseases very much less than is generally believed. In diphtheria particularly it appeared that little if any sickness could be due to infection remaining about the house or its contents after the termination of isolation. As isolation is almost invariably terminated without any reference to the presence of carriers in the family, it ap- peared to be absurd to disinfect the material things in the 248 THE SOURCES AND MODES OF INFECTION house when in all probability some carrier was still growing the bacilli. Hence in March, 1905, terminal disinfection was abandoned in Providence, except in those very few instances in which the family was willing to wait for two successive negative throat and nose cultures from each of its members. The attempt was thus made to test the im- portance of fomites infection by abandoning disinfection and noting any change that might occur in the prevalence or distribution of the disease. One obvious way of testing the influence of disinfection is to compare the recurrence of the disease after disinfection with the amount which occurred after the warning placard was removed without disinfection. The following shows the number of recurrences within 60 days after disinfection, the number of infected families and the ratio between the two, during the years 1902 and 1905. YEAR. Infected Families. Recurrences. Ratio. 1902.. 1903. 358 453 6 7 1.67 1 54 1904 559 10 1 78 1905 87 2 2.30 Total '1457 25 1.71 The following shows the same facts where there was no disinfection. YEAR. Infected. Families. Recurrences. Ratio. 1905.. 258 4 1 55 1906 259 4 1 55 1907 343 7 2 04 1908 687 17 2 34 1909 472 10 2 12 1910 431 4 93 1911 550 8 1 49 Total.... 3000 54 1 80 INFECTION BY FOMITES 249 The period from 1902 only is taken, because previous to that time the duration of isolation was somewhatjpnger, but there has been no change since. Very few health officers keep any record of the recurrences in diphtheria and other infectious diseases, but such records are kept in Baltimore, where terminal disinfection is practiced in an unusually thorough manner, and is. in a large majority of cases tested for its efficiency. In order to make the Providence figures comparable to those of Baltimore, it was necessary to in- clude recurrences in other families in the house as well as in the family first invaded, and to calculate the percentage on total cases, rather than on invaded households. The following are the figures and there is nothing in them to indicate that terminal disinfection is of any value in pre- venting recurrences. BALTIMORE. DISINFECTION. YBAKS. Cases. Recurrences. Ratio. 1903-1909 6931 122 1.76 PROVIDENCE. NO DISINFECTION. YEARS. Cases. Recurrences. Ratio. 1905-1911 4189 69 1.64 Again, it may be objected that recurrence in the family is no criterion of the infection of the house, for it may be that the family is largely immune. This would certainly be much less true of those members of the family who went away during the sickness. Of 634 minors who thus re- turned to the non-disinfected house only 2 were taken sick. So, too, if terminal disinfection is such an important matter, 250 THE SOURCES AND MODES OF INFECTION its neglect should be followed by an increase in the disease. As a matter of fact, after disinfection was abolished diphthe- ria diminished, until at one time in the following August there was not a single reported case in the city. Again in August, 1908, the disease was reduced to a single recog- nized case. There has been a marked increase since, common to many parts of New England, and the excess in Boston, where disinfection is practiced, has been greater than in Providence. Still another test of the danger from the omission of disinfection is the extension of the disease to other families in the same house. Of 2592 such families with susceptible children only 19 or 0.73 per cent were in- vaded by the disease within two months after the termi- nation of isolation in the non-disinfected apartment. It may be suggested that, though no official disinfection was practiced, the houses were perhaps thoroughly cleansed by the occupants. I must confess that I hoped that the aban- donment of official disinfection would cause people to do more cleansing for themselves, but there has thus far been little improvement, and as a large part of our diphtheria occurs among poor and ignorant people, many of whom are recent immigrants, house cleaning by the family can scarcely be expected to be very efficient at present. It appears, then, that this experiment shows that house infection in diphtheria is in Providence a negligible factor in the dis- semination of the disease. Disinfection Unnecessary after Scarlet Fever. So sim- ilar, from an epidemiological standpoint, are scarlet fever and diphtheria that I have been gradually abandoning disinfection after the former disease also. The following shows the recurrences where there was and where there was not official disinfection. The first table shows the number of recurrences within 60 days after disinfection for scarlet fever, the number of infected families, and the rate of recurrence during the years 1904-09. INFECTION BY FOMITES 251 YBAB. Infected Families. Recurrences. Ratio. 1904.. 1905 868 298 12 2 1.38 67 1906 398 9 2 26 1907 540 8 1 48 1908 273 3 1 09 1909 52 3 5 77 Total 2429 37 1 52 During the last four years the recurrences where there was no disinfection were as follows: YEAR. Infected Families. Recurrences. Ratio. 1908.. 40 1 2 50 1909 377 10 2 65 1910 389 5 1 29 1911 434 4 92 Totals . 1240 20 1 61 As in diphtheria so in scarlet fever the infection of well persons who return to the house after the termination of isolation may perhaps be a measure of the value of terminal disinfection. In Providence, during the years 1887-89, of 1816 persons, mostly under 14 years of age, who had never had scarlet fever, and who returned home after disinfection, 33, or 1.8 per cent, developed the disease. Of 207 persons who, since 1908, have returned to non-disinfected houses, 3, or 1.4 per cent have contracted scarlet fever. During the years 1908-10, of 138 persons so returning none were attacked. The only apparent recurrences were in 1911. Again one may examine the recurrences in other families in the same house. Of 1329 such additional families in 1904- 08 there was recurrence within two months after disinfection 252 THE SOURCES AND MODES OF INFECTION in 21, or 1.6 per cent. Of 1005 families in 1909-11, living in houses where there had been no disinfection, there were recurrences in 15, or 1.5 per cent. A further comparison showing the results with and with- out disinfection can be made with the data from Baltimore. To make these comparable to the Providence figures there have been included, in the latter, recurrences in other fam- ilies in the same dwelling. The ratio is calculated on the number of cases instead of on the number of families as in the table next preceding. BALTIMORE. DISINFECTION. YEABS. Cases. Recurrences. Ratio. 1903-09 5792 84 1 44 PROVIDENCE. No DISINFECTION. YEABS. Cases. Recurrences. Ratio. 1908-11 1801 31 1 72 The health commissioner of Buffalo * reports, as illustrat- ing the efficacy of disinfection, that after 3029 cases of scarlet fever where terminal disinfection was practiced and tested, there were 117 recurrences, or 3.8 per cent. Disinfection Unnecessary in Other Diseases. In any disease which is widely distributed, and in which there is ample opportunity for extension from mild cases, from car- riers, from cases in the early stages, and from convalescents, the absolute disinfection of all possible fomites at the as- sumed termination of the sickness will probably have no influence in checking the disease. Thus I can see no use in disinfecting after measles, whooping cough, influenza, pneu- monia or cerebro-spinal meningitis, and I think that this 1 Rep. Dept. of Health, 1909, 20, 44. INFECTION BY FOMITES 253 view is held by the majority of our health officers and epi- demiologists. In fact it is the expressed opinion of most health officers that disinfection after measles is unneces- sary, as there is no evidence that fomites are a factor in the spread of the disease. Disinfection after measles, which was practiced in Aberdeen for twenty years, had no influ- ence on the prevalence of the disease. When official dis- infection after measles was temporarily suspended in New York from January 10, 1908, to March 1, neither the sus- pension nor the resumption of the practice appeared to have any effect on the epidemic curve. Disinfection after cerebro-spinal meningitis is also absurd, as the meningo- coccus lives only a few hours, and carriers are almost the sole means by which this disease is spread. This is coming to be the accepted view and in a recent publication of the U. S. Public Health Service 1 Frost makes no mention of terminal disinfection among prophylactic measures. Much disinfection after tuberculosis is also without reason. If a patient has been living with his family and taking no pre- cautions, certainly no amount of terminal disinfection will atone for long-continued sanitary sin. If precautions are taken, the phthisiologists tell us that there is no danger in living with the patient, and if so, certainly there can be no possible danger in living in his house after he is dead. The only occasion for disinfection after consumption, then, is when the apartments of a careless patient are to be occu- pied by another family, and, after all, we have no evidence to show how much danger there is even then. Yet many health officers make disinfection after every death from consumption' the first and often the only measure taken to restrict tuberculosis. Dr. William C. Woodward of Washington in the discus- sion of a paper read before the American Public Health Association presented some figures which he believes indi- 1 U. S. Pub. Health and Mar. Hosp. Serv., Pub. Health' Rep., 1912, XXVII, 97. 254 THE SOURCES AND MODES OF INFECTION cate that terminal disinfection after tuberculosis is a valu- able prophylactic measure. He says that during a period of about two years ending in May, 1910, 1650 houses in Washington were disinfected because of tuberculosis. Sub- sequent to the disinfection there were reported from the disinfected houses cases of tuberculosis sufficient to give an annual attack rate of 223 while the attack rate through- out the remainder of the population was 414. Even in smallpox there are bits of evidence to show that fomites play an unimportant part. Jordan l refers to two unvaccinated men who fumigated and handled infected smallpox clothing for two months without contracting the disease but who succumbed to it as soon as they came in contact with patients. School Disinfection. When a number of cases of scar- let fever or diphtheria develop in a school, the public is in- clined to consider room infection the source and to demand " disinfection." This subject has lately, perhaps owing in part to the efforts of sellers of disinfectants, been much dis- cussed in England, but fortunately the leading officials refuse to be influenced by public clamor. Among others, Kerr 2 has clearly set forth the reasons why the room can rarely be at fault in school outbreaks of the contagious diseases. In another place Kerr 3 reports 26 instances in which scarlet fever patients in the desquamating stage were found in school. In 2 instances the room was disinfected after their removal and in 1 of these a secondary case de- veloped 9 days later. In the other 24 instances there were 2 secondary cases. Hope 4 says, "All evidence points strongly to the fact that when children contract infectious disease in school the channel of infection is not by means of school desk or floor but by the personal infection of another child." 1 Jordan, Am. J. Pub. Hyg., 1910, VI, 755. 2 Kerr, Pub. Health, Lond., 1909, XXIII, 49. * Kerr, Rep. Med. Off. Education, Lond., 1909, 59. 4 Hope, Rep. to Education Authority, Liverpool, 1909, 9. INFECTION BY FOMITES 255 French Views on Disinfection. Recently, 1 at a discus- sion in Paris, Comby, Courmont and Lemoine took the ground that the active disinfection which has been insisted on in that city in recent years has not reduced the mortality from scarlet fever, diphtheria or measles, for which dis- eases it is required. Comby 2 is emphatic in his contention that it is persons, not things, that are the bearers of con- tagion. The same position was taken by Semaine medicate for February 14, 1906. Lemoine 3 has found disinfection not so essential as has been claimed. At the hospital at Val de Grace certain rooms were used for isolating single cases of contagious disease. There was often such demand for their use that cases of different diseases quickly suc- ceeded one another, sometimes without any disinfection and often with slight disinfection by washing the walls as high as could be reached. Sixty-five cases of scarlet fever, .41 of measles, 25 of mumps, 31 of diphtheria, 4 of smallpox, 1 of chicken pox and 136 of other diseases are reported as rapidly succeeding one another in these rooms. One case of measles and 4 of scarlet fever developed in the rooms. Often it was necessary to shift entire wards of twenty to thirty beds, with only a slight attempt at disinfection. This was done a good many times during nine years with- out bad results. We have had a similar experience at the Providence City Hospital where no attempt is made to disinfect the walls and ceilings of the cubicles in which different diseases rapidly succeed one another, and there has never been an instance in which infection could pos- sibly be attributed to neglect of this rite. English Views. There is a growing tendency on the part of many English health officials to attach less impor- tance to the part played by fomites in the spread of disease and consequently less value to terminal disinfection as 1 Bull, et m&n. Soc. meU d. h6p. de Par., 1909, n. s., XXVII, 585. 2 Comby, Presse med., Paris, 1909, XXVII, 249. 3 Lemoine, Rev. d'hyg., 1907, XXIX, 1057. 256 THE SOURCES AND MODES OF INFECTION ordinarily practiced. Richards l does not consider disin- fection of the room necessary, provided the floors are washed and things which came in contact with the patient are cleansed and disinfected. Butler, Barlow, Hogarth and others have expressed a growing belief that fomites play a comparatively unimportant part in the spread of disease. The views of Hope and Kerr are referred to above. The writer has received a number of letters from English and Colonial medical officers of health indicating agreement with the main proposition of this chapter. American Views. It is not, of course, to be expected that the majority of health officers would be willing to abandon terminal disinfection as now practiced. There are, however, very many of the most thoughtful, and at the same time most conservative, who agree that the present methods of disinfection should either be made really effi- cient or else given up. They are ready to admit that fomites are a far less important factor in the spread of dis- ease than was formerly thought, but they think that even minor factors should if possible be efficiently controlled. A few health officers are willing to test the matter for themselves and have given up or are gradually omitting gaseous disinfection after scarlet fever and especially after diphtheria. The health officer of one important American city was trying gradually to abandon terminal disinfection until his progressive attitude was frowned upon by the state health officials. In Newton disinfection is not com- pulsory. When Terminal Disinfection is Desirable. When a new or rare disease invades a locality, it may at times be desir- able to take extraordinary precautions to prevent its exten- sion, which would be entirely useless if the disease were established. This, it is true, is not the popular or legal way of regarding preventive measures, but it is the scientific one. If a case of smallpox should occur in Providence, 1 Richards, Pub. Health, Lond., 1909, XXIII, 42. INFECTION BY FOMITES 257 which has been free from it for several years, it would be worth while, perhaps, to expend considerable time and money in disinfection, even though the chance of infection from the room or goods might not be one in a thousand. But if there were hundreds of cases of measles in the city, it would be folly to go to the same trouble and expense for each case, even if the chance of infection were ten times as great. A spark in the dry grass should be stamped out at any cost, but it is useless to waste time in extinguishing the smoldering flames left here and there as the line of fire is sweeping across the prairie. Objections to Disinfection. There are several objec- tions to the present practice of terminal disinfection. One is that it only partially disinfects. If disinfection is to be honestly and efficiently applied, methods must be changed. But even as now practiced, disinfection is expensive. Many cities employ disinfectors, with horses and apparatus, while their laboratory languishes, their medical inspection is poor and their diphtheria patients must secure antitoxin as best they can. Another serious objection to routine terminal disinfection is that it misleads the public. They are given a false sense of security, and they are encouraged in the old belief that it is things, not persons, which are dangerous. We can never successfully preach the truth about carriers, or teach the necessity for stricter personal cleanliness, so long as we continue to make so much of a fetish of the practice of disinfection. Cleanliness versus Disinfection. I am here referring to terminal disinfection, which is often only a fumigation, or smell-producing process. The continued practice of clean- liness all through the sickness, and indeed at all times, by which the transference of fresh infective material may be prevented, is another matter, the value of which was con- sidered in the preceding chapter. Conclusions. It seems to me, in view of the considera- tions here presented, that we are justified in concluding that, 258 THE SOURCES AND MODES OF INFECTION 1. There is no good epidemiological evidence that any diseases except those due to spore-forming bacteria are to any great extent transmitted by fomites. 2. Judging from our experience with yellow fever most of the alleged evidence of infection by fomites is no t to be relied upon. 3. Even if all the alleged fomites infection is real, only a very small part of contagious disease is traceable to this source. 4. The theory of fomites infection was an a priori not an a posteriori theory, and is no longer demanded. 5. Other modes of transmission so much more satisfac- torily account for the spread of disease, that there seems to be really little opportunity for infection by fomites. 6. Laboratory investigation shows that fomites infection with spore-forming bacteria is common; that such infection in typhoid fever, tuberculosis, diphtheria and with other resistant organisms doubtless sometimes takes place; that it is possible in cholera and plague, while such infection in gonorrhea, influenza, cerebro-spinal meningitis and pneu- monia must be practically impossible. 7. Experiment and epidemiological observation have demonstrated that fomites infection is practically unknown in yellow fever and is probably so in the other diseases car- ried by flying insects. 8. Experiment and observation show that fomites are of little moment in the diffusion of bubonic plague, and of no moment in the extension of Mediterranean fever, both formerly believed to be spread in this way. 9. Observations made in Providence indicate that fo- mites infection is of no practical importance in the diffusion of diphtheria. 10. Observations in Providence indicate that fomites are of no practical importance in the diffusion of scarlet fever. Finally, it may be affirmed that the evidence has been rapidly accumulating that fomites infection is of very much less importance than was formerly believed. CHAPTER VI. INFECTION BY AIR. Reasons for Former Belief. From time immemorial the air has been considered the chief vehicle of infection. This was but natural, for until recently the virus of the infectious diseases was believed to be gaseous, or at least readily dif- fusible, and readily borne by air currents. The infective material was supposed to be given off in the expired breath, and to emanate from the surface of the body and from moist soil and decomposing matter of all kinds. Contagious dis- eases were known to arise without any apparent connection with other cases, and what could be more natural than to assume that the invisible, imponderable materies morbi is mixed with and carried by the air? Moreover one of the most widespread and best known diseases, malaria, was shown by a great mass of clinical evidence to be an air-borne disease, and yellow fever, another infectious disease of great importance, was also on good grounds believed to be trans- mitted in the same manner. What seemed to be well estab- lished for these two diseases was assumed on much more slender evidence to be true of most, if not all, the infectious diseases. It is true in a certain sense that the two diseases just mentioned are air-borne, that is, they are transmitted by small insects, which " diffuse," as it were, from their breeding places and are readily wafted by air currents. It is not in this sense that the term air-borne is used in this chapter, but the inquiry here made is whether the virus of the infectious diseases is borne by the air, either free or attached to small particles of inanimate matter. Then, again, the first symptoms of measles, and often of influenza, are connected with the nose> diphtheria appears to be a throat disease, while consumption and pneumonia infect 259 260 THE SOURCES AND MODES OF INFECTION the lungs. What is more natural than to assume that the air which bathes these parts is the vehicle of infection ? But since it has been shown that the pneumococcus is constantly found in the blood in pneumonia, and has been demonstrated before the initial chill, and since tubercle bacilli readily reach the lungs through the circulation, the force of this argument is lost. Omitting the insect-borne diseases, let us see first what epidemiological evidence there is that the contagious diseases are air-borne. Smallpox Air-borne from Hospitals. Smallpox is be- lieved to be more widely air-borne than is any other disease. The modern doctrine of the aerial transmission of smallpox received its greatest support from the investigations of Power 1 in 1881 concerning the conditions about the Fulham Hospital in London. That smallpox could be carried by the air long distances had been claimed by many before that time, for Dr. Waterhouse of Cambridge, more than one hundred years ago, believed the disease had been wafted across from Boston to Charlestown, though later he was inclined to deny this mode of transmission. Power showed that smallpox had not prevailed to any extent in the vicinity of the Fulham Hospital before the hospital was opened, and that on a number of occa- sions soon after it was occupied by a considerable number of patients the disease began to develop in the neighborhood. Furthermore he showed that there was a progressive decrease in the amount of smallpox as the distance from the hospital increased, the alleged influence of the hospital extending to at least one mile. It was furthermore shown by the doctor that this distribution of the disease was uniform in every direction from the hospital, that is, in every quadrant of the circle surrounding it. Later investigations at this hospital yielded similar data. 2 Smallpox almost always developed in the vicinity whenever the hospital was occupied by from 1 Rep. Med. Off. Loc. Gov. Bd., Lond., 1880-81, X, Supl. 302. * Rep. Med. Off. Loc. Gov. Bd., Lond., 1884-85, XIV, 55, 1885-86, XV, 111. INFECTION BY AIR 261 eighty to one hundred acute cases. But on one occasion, at least, there was no outbreak even when the hospital was fully occupied. The conclusion was that when a considerable number, eighty to one hundred, acute cases of smallpox are gathered in a hospital, there is great danger that the virus of the disease will be carried by the air a mile or more from the hospital in quantity sufficient to infect persons at that distance. Power considered that the hospital was thus the focus of infection on one occasion when there were only twenty patients, and at another time when there were only nine, of which five were acute. It was thought, from a study of the conditions at the time of the outbreak, that the dis- semination was favored by still, damp weather. A somewhat similar though not generally so well defined or nicely graded distribution of smallpox around hospitals was believed by many to have been demonstrated in the cases of theHomerton, Deptford, and Hempstead hospitals. It was natural that twenty-five years ago, when knowledge of modes of infection was far more vague than at the present time, and with such evidence at hand, the officers of the Local Government Board should have been firmly convinced of the importance of aerial transmission in the spread of smallpox, and that this opinion should have been shared by many medical officers of health. Subsequent to the investigations referred to above, outbreaks due to the spread of this disease from hospitals are said to have occurred, among other places, at West Ham, 1884-85, 1 Nottingham, 1887-88, 2 Oldham, 1888 and 1892, 3 Warrington, 1892-93, 4 Bradford, 1893, 5 Liverpool, 1902-03, 6 and in Gates- 1 Rep. Med. Off. Loc. Gov. Bd., Lond., 1886-87, XVI, 97. 2 Whitelegge, Practitioner, Lond., 1888, XLI, 65. 1 Report on the Health of Oldham, 1892, by Niven; also Niven,Pub. Health, 1892-93, V, 324, 366. 4 Gornall, Rep. on the Epidemic of Smallpox in the years 1892-93 In Warrington, 1885, 111. 6 Evans, Brit. M. J., Lond., 1894, II, 356. 6 Reece, Special Rep. Loc. Gov. Bd., Lond., No. 208, 1905, Smallpox in Liverpool. 262 THE SOURCES AND MODES OF INFECTION head and Felling, 1903-04. 1 In Glasgow 2 Chalmers states that smallpox seemed to develop around the hospital when it contained many patients, but that this did not invariably occur. When the hospital was removed to another location, it again appeared to be a focus of disease. Much has been made of the alleged aerial transmission of smallpox from the ships lying in the Thames below London and used for the reception of cases of that disease from the metropolis. Bu- chanan 3 and Thresh 4 attempt to show that after the ships were brought into use the disease was carried by the air to the Essex shore at Purfleet and West Thurrocks in the Orsett Union. It is true enough that the incidence of the disease was very great in these districts, but it is difficult to under- stand why it is not as well explained by contact infection, as were hundreds of similar outbreaks in England and the United States. The chief evidence on which the theory of aerial infection is based is the existence around the hospital, in every quadrant, of a graduated incidence of the disease. No such evidence is presented in this instance, and the area of infection attributed to the ships lies only in one direction from them. Smallpox appeared on the shore nearest the ships, and then gradually extended to a distance of two or three miles. This sort of extension is just what would be expected in contact outbreaks. If air-borne, the near and distant communities should have been affected at the same time. It was claimed by Dr. Thresh that the influence of the ships could be noted at a distance of four or five miles. It was also claimed that several vessels anchored near the hospital ships developed smallpox twelve days later. That ships leaving London during the period of the extensive out- 1 Buchanan, Special Rep. Loc. Gov. Bd., Lond., Smallpox in Gates- head and Felling, 1904. 8 J. Royal San. Inst., 1905, XXVI, 212, and Tr. Epidemiol. Soc., Lond., 1904-05, n. s., XXIV, 151, 244. 3 Rep. Med. Off. Loc. Gov. Bd., Lond., 1902-03, XXXII, 81. 4 Thresh, Tr. Epidemiol. Soc., Lond., 1902, n. a., XXI, 101. INFECTION BY AIR 263 break in that city should occasionally carry smallpox with them is not remarkable. Finally it was admitted that surrepti- tious communication with the ships occasionally occurred. Aerial Convection Denied by Some. Many sanitary offi- cials did not, and do not, accept these conclusions, and nu- merous instances are given where the disease has not extended from hospitals. Thus Renney 1 says that in 1883-84 he saw 300 cases of smallpox treated in wards which were situated between twenty and two hundred and twenty-four feet of other hospital wards, schools and houses, without any exten- sion, though only the school was protected by vaccination. At another time he saw a considerable number of cases cared for without harm in a ward from forty to one hundred and thirty-eight feet from other occupied buildings. So Wilson at Rugby 2 had a hospital within a few yards of a much fre- quented road with no untoward results. At many other times he has seen smallpox hospitals maintained in close proximity to other occupied buildings without aerial trans- mission resulting. Boobbyer 3 treated 20 cases near a high- way where a thousand workmen passed daily, and not a case was contracted from them. Ker 4 at Edinburgh had a small- pox hospital in connection with a general hospital, and close to other institutions, and with a population of 3000 persons liv- ing within a mile circle. There were only 4 cases within this circle, of which 2 were known to be contracted elsewhere. Dr. Thorne Thorne 5 stated that in two instances only had he seen evidence of the aerial extension of smallpox from a hospital, namely, at Maidstone and at Stockton, while he had seen numerous instances where there was no extension, notably at Leeds and Nottingham. Renney, Jour. Roy. San. Inst., 1905, XXVI, 210. Wilson, Brit. M. J., Lond., 1905, II, 630. Boobbyer, Tr. Epidemiol. Soc., Lond., 1905, n. s., XXIV, 219. Ker, Tr. Epidemiol, Soc., Lond., 1905, n. s., XXIV, 174. Thorne Thorne, Rep Med. Off. Loc. Gov. Bd., Lond., 1880-81, X, Supl. 40. 264 THE SOURCES AND MODES OF INFECTION At Manchester Niven 1 reported only 13 smallpox cases out of a population of over 40,000 living within a half mile to a mile area around the hospital and none among the 606 persons living within the half-mile circle. Other instances can be given where smallpox hospitals have not infected their neighborhood, and these facts should have some weight, though according to the advocates of the theory aerial trans- mission is to be expected only under certain conditions of the atmosphere. There is not much evidence bearing upon this subject to be obtained in the United States, partly because smallpox hospitals have been much more rarely situated in thickly populated districts and partly because less attention has been given to the subject here than in England. American Evidence against Theory. In Philadelphia it is claimed 2 that the hospital has been the source of smallpox in its neighborhood. Thus in one outbreak in the municipal ward in which the hospital was situated the case rate was 61 per 10,000, nearly twice that of any other ward, and it decreased as the distances from the hospital increased. The same conditions were noted in another outbreak. In Boston in 1902-03 there was some discussion as to whether the disease spread from the hospital, which was on a busy street and near many occupied buildings. The evidence was that there was not much smallpox in the neighborhood, and also that contact infection from the hos- pital could not be excluded. In New Orleans 3 a large number of cases of smallpox were in 1900 treated in a hospital in close proximity to a dense population, but without evidence of extension. Dr. Theard writes me that his observations, extending over nine years since that time, have only strengthened his views then ex- pressed, namely, that smallpox virus is not carried from hos- 1 Niven, Tr. Epidemiol. Soc., Lond., 1905, n. s., XXIV, 157. 8 Rep. Bu. of Health, Phila., 1903, 29. 1 Rep. Bd. Health of the City of New- Orleans, 1900-01, 33. INFECTION BY AIR 265 pitals by the air. In Brooklyn smallpox is cared for at the contagious-disease hospital, in pavilions about twenty feet from those occupied by measles and scarlet-fever patients. There has been no extension of the disease, though this may be largely due to the effort to keep the other patients well protected by vaccination. But there is also a considerable population within a mile of the hospital which has never been injuriously affected by it. In Providence the smallpox hos- pital is distant only four hundred or five hundred feet from a number of cottages and an excursion ground frequented by hundreds of persons daily. It is true that only about a dozen patients have ever been there at one time, but it is hard to understand why ten patients should not be more dangerous at five hundred feet than one hundred patients a mile dis- tant. In Detroit, Dr. Kiefer writes me, there has been no extension from the hospital, and in Chicago * there was less smallpox around the hospital than in other parts of the city. Theoretical Objections. I have been led to question this theory of the aerial transmission of smallpox for various reasons. From what is known of the nature of the virus of so many other diseases it seems highly improbable that they are carried any great distance by the air, and in fact it is only for smallpox that this mode of transmission is claimed. But smallpox virus is certainly solid matter, and it certainly after a time loses its vitality, and in all respects other than the one under consideration it behaves not unlike the mate- ries morbi that we are better acquainted with. Again, it would be most remarkable, if the disease extends from, say, one hundred cases to the distance of a mile with sufficient intensity to infect many persons, that it should not extend one hundred feet from ten cases or even from one case. Why should we not expect aerial infection frequently to operate at short distances from single cases ? Yet such transmission does not occur unless it be with great rarity. How rare it ia for any claim to be made that this disease has been carried 1 Rep. Health Dept., Chicago, 1907-10, 60. 266 THE SOURCES AND MODES OF INFECTION across the street from house to house, and how unique a rigid demonstration of such an occurrence would be! How often a single case in a crowded lodging house, ship's steerage, or hospital ward, fails to infect others! Yet we are asked to believe that one hundred cases can give rise to a whole circle of cases a half mile away. Either the amount of virus must depend upon the number of patients, or it must under hospi- tal conditions develop in some marvelous way outside of the body. Contradictions in Claims. If the evidence adduced in favor of this theory is examined, several suspicious circum- stances are noticed. It is very curious that a material sub- stance should be borne by the air without reference to air currents ; yet in the earlier reports by Powers all evidence of such currents was lacking. It is true that in later reports the wind has been claimed as a factor, as at Gateshead and Felling, but the evidence in this case has been made valueless by more detailed search for the origin of the cases. At Liver- pool the disease was distributed in different directions around the three hospitals, so that if air-borne it must have been independent of air currents. Savill at Warrington even claimed that the virus diffused against the wind. The reports of the Fulham Hospital give one the impression that the virus of smallpox must diffuse like a gas, which certainly is not thinkable. If air-borne at all, it must be carried as is dust or as are liquid particles. If the virus does diffuse in all direc- tions like a gas, the intensity of the infection should diminish according to the square of the distance, which it did not do at Fulham and Liverpool. Whether it diffuses or is carried like solid particles, the houses nearest the hospital should be by far the most intensely infected. Solid particles are speed- ily, under ordinary conditions, precipitated to the ground, as one may easily note by observing a cloud of dust of any kind. The particles of smallpox virus ought, then, to work their chief havoc close to the hospital. Yet this incidence was not always the case, even at Fulham, and similar absence of near-by INFECTION BY AIR 267 infection was noted at Stockwell 1 and Liverpool. 2 Again, quite a number of instances are given where large institu- tions, like schools, workhouses and general hospitals, have been located within the area alleged to have been severely infected from the hospital, and yet have nearly or entirely escaped. It is curious, too, that in the only instance I have noticed in which the sex of the patients in the infected area was given, namely Fulham, 3 twenty-four were male and seventeen female. As so many more men are away from their homes at work, a much larger female population must be exposed to the hospital influence, and the female patients ought to be more numerous than the male. In most out- breaks of smallpox the male patients are more numerous, because the men move about more, and are thus more likely to be exposed to cases of disease. Again, it is remarkable that extension should be more likely to take place from acute than from chronic cases. In the former it is probable that the moist mucous membrane is the only source of infec- tion, while in the latter the dried crusts are known to be infectious. Distribution of Cases Opposed to Theory. It is thus seen that there are a number of facts and a number of theoretical considerations opposed to the theory of aerial transmis- sion. That smallpox is distributed with decreasing inten- sity around smallpox hospitals is not a demonstration that the hospital is the cause, for as even the advocates of the theory admit, sucti circles of infection can be drawn around other points in a city during epidemic times, as was indeed shown by Hope in Liverpool in 1902-03 and Clayton at Gates- head in 1903-04. In fact most outbreaks, not only of small- pox but also of scarlet fever and diphtheria, are in a general way arranged around a center, with more cases toward the center 1 Rep. Roy. Com., Smallpox and Fever Hospitals, Lond., 1882, 92. 2 Hope, Observations by the Med. Off. Health on the Report of Dr. Reece on Smallpox at Liverpool. C. Tinling & Co., 1905, 11. Rep. Med. Off. Loc. Gov. Bd., Lond., 1880-81, X, Supl. 268 THE SOURCES AND MODES OF INFECTION and fewer toward the periphery. It is not remarkable that occasionally a smallpox hospital is found near the center of such a localization of disease. As favoring this chance, it must be remembered that the population near a smallpox hospital is likely to be of the poorer classes, upon whom the weight of this disease most often falls. That surrounding outbreaks occur chiefly after the hospital has been occupied, is only to be expected, as the hospital is occupied by a number of cases only in epidemic times. Much stronger evidence would be offered by the advocates of this theory if they could show that no other explanation of the origin of the cases could be found than hospital infection. This they are not able to do, and in the absence of such evidence, and in the face of the evidence against the theory, the theory must be considered not demonstrated. Cases often traced to Other Sources. A good deal of evidence in regard to the influence of hospitals in the spread of smallpox was collected in England at a time when there was no registration of the disease, when the frequency and importance of mild cases were not recognized as at present, and when its administrative control was not so complete. Thus it was stated that many cases of smallpox walked to the Homerton Hospital to apply for admission, ambulance drivers stopped at public houses, children of the neigh- borhood rode on the steps of the ambulance and the patient's friends inside. It would not be surprising if, under such con- ditions, smallpox spread by contact and indeed it was admit- ted that this was a factor. It is interesting to note that even Power found personal exposure the cause of nine out of thirty- two cases near Fulham. In many outbreaks, where there is no question at all of hospital infection, to trace the source of such a proportion of cases is all that can be expected. Again, in the block of houses nearest the same Fulham Hospital Dudfield l showed that twenty of forty-one cases were due to 1 Dudfield, Rep. Roy. Com., Smallpox and Fever Hospitals, Lond., 1882, 101. INFECTION BY AIR 269 contact infection. According to Clayton, 1 the medical officer of health of Gateshead, of the fifty-six cases of smallpox within one-half mile of the hospital, on which Buchanan bases his conclusion that the disease was carried by the air, fifty- two were traced to contact infection. Clayton in his report on this outbreak very clearly shows the fallacy of most of the arguments presented by Buchanan. In Liverpool it was shown by the advocates of aerial transmission that within one-quarter of a mile of the Parkhill Hospital the rate of incidence of smallpox was five hundred and twenty-six per ten thousand houses, while in the city outside of hospital areas it was only eighty-five. A detailed study shows that this apparent high rate depended on only nine patients in one hundred and seventy-one houses, and Hope shows that of these nine, four were known to be due to direct exposure to other cases. A careful study of the report by Reece 2 of this Liver- pool outbreak is well worth while by all interested in this subject. A most ingenious use has been made of the facts, but an impartial critic must see that the conclusions arrived at are entirely unwarranted. If one is still in doubt, he should read the report of Hope, 3 the medical officer of health of Liverpool, which clearly and briefly refutes all the arguments of the government inspector. Conclusions concerning Smallpox. It appears that the evidence for the aerial transmission of smallpox from hospi- tals consists solely of the alleged distribution of the disease, at a gradually decreasing rate, around the hospital, the exist- ence of the cases being assumed to be otherwise unexplained. It will be noted: 1. That there are comparatively few instances of such dis- tribution recorded. 1 Clayton, J. Roy. San. Ins., 1905, XXVI, 199. 2 Reece, Rep. Local Gov. Bd., Lond., No. 208, Smallpox in Liverpool, 1905. 3 Hope, Observations by the Med. Off. Health on the Report of Dr. Reece on Smallpox at Liverpool. C. Tinling & Co., Liverpool, 1905 270 THE SOURCES AND MODES OF INFECTION 2. That many instances are noted where there was no such diffusion. 3. That in some of the alleged instances, as at Fulham, Gateshead and Liverpool, a large number of the surrounding cases have been shown to be due to contact infection. 4. That in the long run the amount of infection around the hospital should diminish according to the square of the distance. This it does not do, but it diminishes irregularly, just as it does in most outbreaks of this and other diseases due to contact infection. 5. There may sometimes be contact infection from the hos- pital. The surrounding population is often of the poorer sort, and is consequently particularly subject to the 'disease. Contact infection and chance may be sufficient to account for those instances where a smallpox hospital is the center of a local outbreak. The evidence in favor of the aerial transmission of small- pox from hospitals is so slight that it should never influence a municipality in its selection of a hospital site. Chicken Pox. Caiger, 1 while able successfully to isolate scarlet fever, diphtheria and whooping cough in his hospital wards by the cubicle system, had several transfers of chicken pox, and concludes from his experience that this disease is frequently air-borne. Others in England and in the United States have had difficulties in isolating chicken pox. Good- all, 2 however, has isolated this disease in cubicles with only 1 cross infection which he does not think was air-borne. Scarlet Fever believed to be Air-borne. Scarlet fever also is generally believed to be an air-borne disease. One reason for this is doubtless because until recently the desquamating epidermis was considered to be the chief vehicle of infection. t As the epidermis comes off to a large extent as very fine light particles, it was but natural to assume that these would be 1 Rep. Metropol. Asylums Bd., 1907, 1908. 2 Pub. Health, Lond., 1911-12, XXV, 17. INFECTION BY AIR 271 readily carried by the air. Recently much clinical evidence has accumulated which indicates that the epidermal scales are not infectious, and this has in turn developed doubts as to the disease being commonly air-borne. Whether or not the epidermis is infectious, there seems to be no really good evidence that the disease is caused by air-borne infection. On the contrary, there is considerable evidence that it is not air- borne. Scarlet Fever in Hospitals. The writer, like every health officer, has frequently noted that a case of this disease may remain in school or hospital ward for days, or sometimes for weeks, without another case developing, or at most only one or two cases. Such facts indicate that the disease is not easily air-borne. Visitors to fever hospitals do not contract scarlet fever. Thus, of three hundred to four hundred non- immune students who visited the scarlet-fever wards of the Philadelphia hospital, remaining in the ward from twenty minutes to an hour, not one contracted the disease. 1 Often- times scarlet fever does attack other patients in hospitals, but it is in a manner to indicate contact rather than air-borne infection. When contact infection is rigidly guarded against, as in the Pasteur Hospital in Paris and in many English hospitals, scarlet fever may be, and is, treated in the same ward with other diseases without cross infection. The failure of contagious disease to spread in hospitals when cpntact infection is guarded against was referred to in some detail in the chapter on contact infection, and is a striking demon- stration of the small part played by aerial infection in the transmission of the common contagious diseases. Scarlet Fever in Dwellings. I have been much impressed by the fact that scarlet fever and likewise diphtheria do not extend from one family to another in the same house. Most people in Providence live in houses of two or three stories, rarely more, with one or two families on each floor. Of 4306 1 Welch and Schamberg, Acute Infectious Diseases, Phila., 1905, 346. 272 THE SOURCES AND MODES OF INFECTION " other families " living in the same house with scarlet-fever families, only 6.8 per cent were invaded. Investigation has shown that with very few exceptions the infection takes place through close intercourse before the disease is recognized or, more rarely, after the isolation has been terminated. Most of the disease in the "other families " develops within a few days after the report of the primary case, and is doubtless due to contact infection before the disease is recognized. Between the end of the second week and the termination of isolation, the disease extends to other families in the house in only 0.6 per cent of the cases, and in most of these it is known that isolation is not carried out, and that there is free intercourse between the families. If the disease were air- borne, it would certainly pass from one family to another in the house, which it does not do. Scarlet Fever and Outdoor Air. If scarlet fever is not air-borne from family to family in the house, one would not expect it to be borne from house to house by the air. Yet such a claim is sometimes made, and even that the virus of the disease may thus be transmitted a considerable distance. A number of the reports of the health department of Phila- delphia contain shaded maps purporting to show an excess of this disease, as well as of smallpox, in those parts of the city near the hospital. I do not think that much value at- taches to such maps, for there are too many factors involved, and very rarely is the intensity of the disease as great close to the hospital as the theory demands. Moreover, around very many hospitals no such distribution of the disease can be shown. Thus Tarnissier, 1 in Paris, found that the En- fants Malades and Trousseau hospitals could not be con- sidered foci of infection. The same is true of the scarlet-fever wards in Providence, in Detroit and in Boston. -In the latter city, 2 for the period studied, there were no cases of the disease within one-eighth of a mile of the hospital, while in the next 1 Tarnissier, Semaine med., 1903, 267. 2 Med. and Surg. Rep., Bost. City Hosp., 1897. INFECTION BY AIR 273 eighth of a mile circle there were sixty-eight cases, in the next seventy-one, in the next seventy-five and in the next seventy- two. Where various contagious diseases are treated in different wards of the same hospital there is sometimes cross infection. But this occurs so irregularly as to time and place, and is so limited in amount, that it can scarcely be attributed to any- thing but contact infection. As most of the physicians and nurses in our contagious hospitals have no appreciation of what true medical asepsis really means, it is surprising that we see as little cross infection as we do. If scarlet fever does not spread within the walls of the Pasteur Hospital, it would indeed be marvelous if it should extend to the neighboring houses. If it does not pass from family to family in the same house, it would be most surprising if it could be wafted by the air over large areas around the Philadelphia Hospital. Diphtheria and Sewer Air. Diphtheria was formerly be- lieved to be a filth disease, and it was also believed that air, especially sewer air, was frequently the vehicle of infection. Graham-Smith refers to this, 1 and shows that there is no foundation for this belief, and that diphtheria bacilli have never been found in sewer air. He says that Shattock culti- vated bacilli of low virulence in sewer air for two months, but could not thereby increase their virulence. As I was, years ago, prejudiced in favor of the filth origin of this disease, I gave the matter careful consideration in my investigation of cases, but was never able to find any evidence that sewer gas was an etiological factor. Indeed my observation of diph- theria and typhoid fever had as much to do with my dis- carding the filth and sewer-gas theories as had the slowly accumulating mass of bacteriological evidence. Diphtheria in Hospitals and Dwellings. From an epi- demiological standpoint diphtheria and scarlet fever are much alike. As the latter disease has been supposed to be air- 1 Nuttall and Graham-Smith, The Bacteriology of Diphtheria, Cambridge, 1908, 321. 274 THE SOURCES AND MODES OF INFECTION borne from person to person, so has the former, and there is the same lack of positive evidence for both diseases ; and the evidence against the theory is much the same for diphtheria as for scarlet fever. As is stated by Graham-Smith, bacterio- logical evidence is all against diphtheria being an air-borne disease except in rare instances, yet probably most medical men and most health officers consider that the disease is commonly spread in this way. But visiting students in hos- pital wards do not contract it, and it does not spread when cases of this disease are treated in pavilions together with other diseases. In Providence I am certain, from a careful study of about eleven thousand cases, that it practically never extends from one family to another in a house except by per- sonal contact ; and it does not extend from one hospital ward to another through the air. At North Brother Island in New York there is a diphtheria ward only a few feet from a tuber- culosis ward; and Dr. S. A. Knopf tells me that there is no cross infection. Similar conditions are noted in many other hospitals. Yet Coutts 1 recently suggested, without any evi- dence, that certain cases of diphtheria were due to street dust, and Cornell 2 attempted to show that the development of the disease in a certain locality in Philadelphia was due to air- borne infection. At best there was in the instances reported by the latter only a possibility of aerial infection, with the probabilities very much against it, while the facts as stated did point very strongly to the existence of unrecognized cases probably spreading the disease by contact. Typhoid Fever and Sewer Air. During the heyday of the sewer-gas theory of disease, numerous outbreaks of typhoid fever were supposed to have been traced to infection by means of air from sewers and drains. A number of typical reports are given by Roechling, 3 and others may be found scattered through medical literature. In none of these is real 1 Coutts, Pub. Health, Lond., 1906-07, XIX, 297. 2 Cornell, N. York M. J. [etc.], 1905, LXXXII, 1318. Roechling, Sewer Gas and Health, Lond. & N.Y., 1898, 30. INFECTION BY AIR 275 proof given that the disease was thus caused; it was merely a plausible hypothesis. Now in the light of present-day knowledge of bacteria and sewer air it is no longer a plausible hypothesis. For years past we have been able to trace most of our outbreaks of this disease to water, milk, oysters or other food, or to contact infection. In most instances they could not be due to sewer air. Usually investigation shows that house or institution outbreaks cannot possibly be due to sewer air, and where such an hypothesis is permissible, it usually appears highly improbable. I see almost every year small house outbreaks of typhoid fever. There is rarely any evidence of the escape of drain air into the house, and in almost all instances such escape is impossible. Most of these house outbreaks indicate contact infection, and in none can contact infection be excluded. I have never seen the slightest evidence that typhoid fever is ever due to sewer air, though I began my public-health work with a fairly strong belief in the danger from this source and sought diligently for evi- dence of it. Typhoid Fever and Dust. It is also claimed that infected dust may be the cause of outbreaks of this disease. This mode of infection was considered to be of some moment in the Spanish- American and Boer 1 wars, and certainly bacterio- logical evidence points to its possibility. Many outbreaks sup- posed to be due to dust infection have been reported. Some of these are referred to by Germano 2 and Visbecq 3 and in the Report on Typhoid Fever in the war with Spain, 4 but if the original reports of these outbreaks are examined it will be seen that the evidence is very weak indeed. Because the houses 1 Tooth, Brit. M. J., Lond., 1900, II, 1368; Tr. Clin. Soc., XXXIV, 1213. 2 Germano, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXIV, 403. 3 Visbecq, Arch, de med. et pharm. milit., Par., 1903, XLI, 536. 4 Abst. of Rep. on the Origin and Spread of Typhoid Fever in U. S. Military Camps during the Spanish War of 1898, Wash., 1900, 215. 276 THE SOURCES AND MODES OF INFECTION or apartments or barracks where an excess of typhoid fever appears are situated not far from a place where possibly infected feces are deposited, it is argued that the disease is caused by the wind blowing over the spot alleged to be in- fected. Quill 1 reports that typhoid fever was brought to a certain garrison in India by a company of five thousand Boer prisoners, many of whom were infected. The disease con- tinued to spread among the prisoners for three months, until there were from six to eight hundred cases. Then it slowly appeared among the garrison, until there were twenty-four cases. It was supposed to be caused by dust blown from the latrines, though the possibility of fly-borne infection is men- tioned; but an extraneous source, or unsuspected contact infection, is highly probable, though neither is excluded or even mentioned. Mewius 2 gives an excellent report of what he considers an air-borne outbreak, but it appears rather to have been due to contact infection, a typical outbreak of what Winslow calls prosedemic infection. The fact that typhoid fever, dysentery and cholera 3 can be treated in a well-managed hospital without spreading to other patients is good evidence that these diseases are not air-borne under such circumstances. Infantile Diarrhea and Dust. Newsholme, 4 judging largely from the fact that the summer diarrhea of infants occurs with greater frequency during dry seasons, and in towns with poor scavenging, infers that it is due, to some extent at least, to the infection of milk and other foods by dust. This also is the view of Hope, 5 who states that in Liverpool in six Septembers with an average rainfall of 13.8 inches there were 373 deaths from diarrhea, while in four- Quill, Brit. M. J., Lond., 1902, I, 383. Mewius, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1896, XXIII, 497. Woodruff, J. Am. M. Ass., Chicago, 1905, XLV, 1160. Newsholme, Pub. Health, Lond., 1899-1900, XII, 139. Hope, Pub. Health, Lond., 1898-99, XI, 435. INFECTION BY AIR 277 teen Septembers with 10.9 inches of rain the deaths num- bered 573. Influenza. During the present pandemic of influenza, especially at its commencement, it was frequently stated that the disease was chiefly air-borne, and air-borne to great dis- tances, even across the Atlantic. This view prevailed be- cause the disease spread with such great rapidity, appearing on this side of the Atlantic at about the same time that it did in England, and developing almost simultaneously in a large number of localities. The subject has been thoroughly studied by Leichtenstern, 1 Parsons 2 and Schmid. The lat- ter's observations were in Switzerland chiefly, where he had ample opportunity to study the outbreak in small isolated communities. His work is reviewed by Leichtenstern, who states that the disease never developed except after the ad- vent of some stranger. Parsons studied the incidence of the disease on several thpusand deep-sea fishermen and on four hundred offshore lighthouse keepers, and in no instance did the disease develop except as the result of contact with the sick or within two or three days after leaving shore. He says there is no evidence whatever that the disease is air- borne. Leichtenstern studied the extension of the disease to distant countries, and found that all the evidence pointed to personal contact as the only factor in its spread. Thus care- ful epidemiological investigation is entirely in accord with the findings of bacteriology, for the weak resistance of the bacillus makes it difficult to understand how the disease can be carried by the air as readily as is often alleged. This feebleness of the germ renders it unlikely that influenza is a dust-borne disease. Of course it may spread by droplet infection, but the increased volume of the secretions, the per- sistence of the bacillus after recovery and the great number of carriers give such opportunities for contact infection that 1 Leichtenstern, Nothnagel's Encycl. Pract. Med., Influenza, Phila. and Lond., 1905, 523. ^ * Parsons, Brit. M. J., Lond., 1891, II, 303. 278 THE SOURCES AND MODES OF INFECTION it is hardly necessary to attribute much importance to aerial infection, as the term is generally used, or to fomites infection. Poliomyelitis. Hill, 1 from a careful study of this disease in Minnesota, was led to suggest the theory that this might be a dust-borne disease. He finds that usually outbreaks occur in hot, dry weather, and many cases had long exposure to dust infected with animal feces, especially those of the horse. Hill says that at Winona and some other places the disease ceased soon after the watering of the roads was begun. The fact that poliomyelitis occurs chiefly in the driest season of the year has led some others to accept Hill's proposition, and some have made similar observations as to the checking of outbreaks. Hillier 2 reports an outbreak at Stowmarket, Eng., brought to a sudden stop by the watering of streets. Experiments indicate that the virus has considerable resistance and may possibly be transported by dust. Landsteiner, Levaditi and Pastia 3 found that it was virulent after being dried thoroughly for 24 days. Neustadter and Thro 4 in at least one instance succeeded in causing the disease in a monkey by inoculating dust from a room occupied by a case of the disease. Fifty grams of dust were shaken up with 30 c.c. of water and 5 c.c. of the filtrate were used for the experiment. Measles. Measles is considered a typical air-borne disease, at least within doors, but the experience of the Parisian hospitals 5 shows that the danger of infection within wards decreases as the opportunity for contact infection is 1 Hill, Northwestern Lancet, Sept. 1, 1909 [reprint]. 2 Hillier, Med. Off., 1912, VII, 78. 3 Landsteiner, Levaditi and Pastia, Ann. de 1'Inst. Pasteur, Par., 1911, XXV, 805. 4 Neustadter and Thro, N. York M. J., 1911, XCIV, 614. 5 Grancher, Cong. Internat. de me"d., 1900, XIII, C.-r., Par., Sect, de med. de Tenfance, 478. Moizard, Bull, et mem. Soc. med. d. hop. ' de Par., 1900, 3 s., XVII, 683. Martin, Rev. d'hyg., Par., 1903, XXV, 256; Bull, et mem Soc. med. d. hop. de Par., 1904, 3 s., XXI, 297. INFECTION BY AIR 279 lessened. Grancher was the first to avowedly disregard infection by air and to attempt to control the spread of disease by strict attention to medical asepsis. At Tho- pital des Enfants-Malades he did not at first use cubicles but merely wire screens or low partitions between the beds. During the 10 years when this experiment was going on measles was introduced 139 times and from these cases 115 cross infections resulted, less than one-third as many as occurred when attention was not focused on the prevention of contact infection. A suggestive instance is reported of a child with measles who remained for 24 hours in an open ward with many susceptibles, and it is stated that in the 3 cases which later developed there had been contact with the first patient, either direct, or by freshly infected fomi- tes. At the Pasteur Hospital 126 cases of measles were cared for without a single cross infection. At the Provi- dence City Hospital which was opened in March, 1910, many different diseases are cared for in rooms open most of the time into a common corridor as in the Pasteur Hos- pital, while other mixed cases are " barriered " in other wards, as described on pages 200 to 202. Up to September, 1911, 56 cases of measles had been admitted, with extension in only one instance to one child. 1 Since then there have been two small outbreaks which Richardson thinks were most likely not due to aerial infection but to some failure in technique. One of these outbreaks arose from a single case, though at other times several cases had been cared for at one time without extension. In this outbreak one of the cases was on a different floor from the infecting case. Rohmer 2 from his hospital experience at Cologne is satisfied that measles is not air-borne further than between adjoin- ing beds. English Hospital Experience. Most English hospital superintendents who have tried cubicles and barriers do 1 Richardson, Internat. Hosp. Rec., 1911, XV, 18. 2 Rohmer, Jahrb. f. Kinderheilkunde, 1912, LXXV, 7& 280 THE SOURCES AND MODES OF INFECTION not think that measles can be safely treated in this way because they consider it likely to be air-borne, or that is the explanation offered by some at least. Caiger, 1 Thom- son, 2 Goodall, 3 Gordon 4 and Biernacki 5 may be mentioned as holding this view in regard to measles and chicken pox. All these and Crookshank 6 do not find that diphtheria is air-borne under the hospital conditions mentioned and uncomplicated scarlet fever usually is not. Caiger does not think that rubella and whooping cough are readily air-borne, while Thomson is inclined to think that they are. Biernacki agrees with Caiger as to rubella and also as re- gards whooping cough, if the beds are at least 12 feet apart so as to prevent droplet infection in coughing. Even then he usually employs a canopy as an additional precaution. Biernacki thinks that ring-worm is readily air-borne. This also is the view held by Gates from a study of this disease in schools. 7 Just as this is going to press an article by Rundle and Burton 8 has appeared reporting two years* experience with a hospital ward at Liverpool in which a variety of infectious and non-infectious cases were cared for without any at- tempt at air isolation. In all, 668 persons passed through the ward, of whom 69 had scarlet fever, 40 diphtheria, 37 measles, 38 varicella, 9 whooping cough and 215 erysipelas. There were only 2 cross infections, 1 of diphtheria and 1 of scarlet fever. These authors believe that in hospital wards the " danger of aerial infection is to be disregarded for practical purposes. " 1 Caiger, Rep. Metropol. Asylums Bd., 1907, 1908, 258; Med. Officer, 1910, V., 76. 2 Thomson, Rep. Metropol. Asylums Bd., 1908, 261; Med. Officer, 1910, V, 197. Goodall, Rep. Metropol. Asylums Bd., 1910, 257. 4 Gordon, Rep. on Health of Manchester, 1908, 154. 6 Biernacki, The Nursing Times, 1908. 6 Crookshank, Essays and Clinical Studies, Lond., 1911, 134. 7 Gates, Pub. Health, Lond., 1910-11, 226. 8 Rundle and Burton, Lancet, Lond., 1912, I, 720. INFECTION BY AIR 281 Typhus Fever not Air-Borne. As will be shown in Chapter VIII, it is quite probable that typhus fever is transmitted by insects exclusively. But whether this is so or not, the successful management of this disease in the same wards with other patients in Edinburgh, in Liverpool and in Mexico City indicates that it is not an air-borne disease. Pneumonic Plague. The extensive outbreak of plague in Manchuria in 1910 attracted much attention, since rodents, while perhaps furnishing the original infection, played little part in the extension, as it seemed to be spread almost exclusively from person to person. Kitasato, 1 if reported correctly, concluded that the disease could not be air-borne but is caused " by coming in close contact with plague victims and by sputa." That droplet infection is of great importance in this type of the disease cannot be doubted and was amply demonstrated by Strong. 2 In a preliminary note he reports experiments in which 15 of 39 plates held in front of coughing patients were infected with virulent bacilli. He says that the air throughout the ward was infected, though the experiments, as reported, do not seem to furnish proof of this. Respirators are said to have been used successfully in avoiding infection by physicians and others in close contact with the patients. No real evidence, however, seems to have been advanced to show that the disease was air-borne other than by droplets. Infection by Air not Impossible. Since the development of bacteriology, evidence has been accumulating to show that the air as a vehicle of infection is of less importance than was formerly believed. Very little evidence has been found in support of the theory and much against it. It has been definitely proved that some diseases are not air-borne and the evidence against certain others is very strong. While the tendency is thus away from air infection we must 1 Kitasato, U. S. Pub. Health and Mar. Hosp. Serv., Pub. Health Rep., 1911, XXVI, 567. * Strong, J. Am. M. Ass., Chicago, 1911, LVII, 1270. 282 THE SOURCES AND MODES OF INFECTION be on our guard lest our generalization carry us too far. It may be a fact that most diseases are not air-borne, and yet further investigation may show that certain other diseases concerning which we are still in doubt may be usually transmitted in this way. Winslow has recently been making some interesting ex- periments in New York concerning the presence of living streptococci in dust. He finds that certain types of strep- tococci characteristic of human secretions are found in a viable condition in enormous numbers in both house and street dust, notwithstanding the fact, which also has been demonstrated, that these bacteria tend to die off with great rapidity when thrown off from the body. Several observers in different parts of the country have recently noted the presence of streptococci in outbreaks of severe sore throat, and Winslow asks whether it may not be possible that street dust as well as indoor dust may be a factor in the spread of this affection. Infection by Air at Short Range. Most of the discussion thus far has related in large part to alleged extension of dis- ease through the air from apartment to apartment, or from house to house, or from hospital to adjoining districts. Transmission over such considerable distances might be rare or even impossible, and yet nevertheless the air might be the chief vehicle in ordinary institution or family infec- tion. That it is believed to be so is indicated by the com- mon regulation that a wet sheet shall be hung before the door of the sick-room to prevent the escape of germs, by the wearing of caps by visitors and the disinfection of inacces- sible portions of the room. If we ask the reason for this universal belief in the importance of air-borne infection, we shall find that it is based entirely on theory, and that there is no clinical evidence at all to indicate that such a mode of infection is of any great importance. What evidence we have indicates rather that infection by means of the air is of comparatively little importance. INFECTION BY AIR 283 Reasons for Belief. The real reasons why people gener- ally attach so much importance to this mode of infection are, first, the hearty belief in the general theory of aerial infection which has prevailed from remote antiquity, and, secondly, because infection so often takes place when there has not been any known contact. Contact is the most certain and obvious mode of infection, and other modes should not be assumed without good reason. The burden of proof rests on those who make the assumption. Air and Aseptic Surgery. The history of aseptic surgery is very suggestive in connection with the theory of air-borne infection. Lister at first unquestionably considered the air to be the chief source of wound infection, and this view for awhile dominated surgical practice. Then gradually more and more attention was given to contact infection, contact with instruments, contact with the patient's own skin, con- tact with the operator's hands. As danger from these sources was more and more perfectly guarded against, surgery became more and more successful and aerial infection was less and less dreaded. A successful surgeon of my acquaintance tells me that he can operate with as little wound infection in a tenement house as in the best operating room. Ochsner 1 says, "Air infection is not impossible, but practically no wound infection is to be considered except from contact." Most surgeons at the present time consider aerial infection of very little importance. Nevertheless it has been shown, as we shall see, that the air, even of well-constructed operating rooms, contains considerable numbers of living pus-forming bacteria. Yet they are usually not numerous enough nor virulent enough to infect, and unless there is some other source of infection the wound heals aseptically. Pus-forming bacteria are quite resistant, and are by far the most numerous and ubiquitous of all disease germs and more likely to be found in the air, and the fact that they generally fail to infect should give pause to any claim that the much less numer- 1 Ochsner, Clinical Surgery, Chicago, 1902, 26. 284 THE SOURCES AND MODES OF INFECTION ous air-borne germs of other diseases are the chief source of infection. Sewer Air and Bacteria. In this connection the relation of sewer air to the transport of bacteria should be referred to. Winslow 1 in a very valuable paper gives a brief history of the theories on this subject, and shows how the former ideas as to the great danger to be apprehended from sewer air gradually gave way before increasing knowledge of bacteria, and particularly after it was determined' that these organisms are not readily detached from moist surfaces. From that time it was generally believed that sewer air had little or nothing to do with the extension of the infectious diseases. The subject, however, was reopened by Andrewes 2 and Hor- rocks. 3 The latter showed that under natural conditions B. prodigiosus and also the bacillus of typhoid fever might be carried by the sewer air long distances and escape at man- hole and soil-pipe openings. Lewis 4 also showed that sewage bacteria could be found in the air passing over a sewage farm, and also in that blowing at low tide over a beach where sewage was discharged. Winslow by a series of careful experi- ments confirmed the work of Horrocks, but went further and determined the number of bacteria that are transported in this way. He found, as have others, that mechanical splash- ing may produce a slight local infection of the air in immediate contact with the spray, but such infection extends for only a very short distance and persists for not more than a minute or two. A careful quantitative study of the air of nineteen different plumbing systems in various parts of Boston showed that very few sewage bacteria are found in such air. These bacteria were found only four times in 200 liters of air, 1 Winslow, Rep. to San. Com. Nat. Ass. Master Plumbers, 1907-09; Abst. Am. J. Pub. Hyg., Bost., 1909, V, 640. 2 Andrewes, Rep. Med. Off. Local Gov. Bd., Lond., 1906-07, XXXVI, 183, and 1907-08, XXXVII, 266. 8 Horrocks, Pub. Health, Lond., 1907, XIX, 495. 4 Lewis, Scot. M. & S. J., Edin., 1907, XX, 487. INFECTION BY AIR 285 and then in the presence of mechanical spraying of sewage at the point of collection. To illustrate the paucity of dan- gerous bacteria in sewer air he says: " In a surface water of good quality, like that of New York City, the colon bacillus can almost invariably be iso- lated from ten cubic centimeters. This means a slight degree of intestinal pollution, but experience has shown that the chance of infection from such a water is but slight; and we drink it without serious alarm. If one were to breathe for 24 hours the undiluted air of a house-drainage system, at any point not immediately infected by mechanical splashing, it appears that less than fifty intestinal bacteria would be taken in; for the daily consumption of air is about 10,000 liters, and in 200 liters I obtained negative results from air of this sort. In drinking New York water twice as many colon bacilli are ingested every day, for 1000 cubic centi- meters is a small amount for daily consumption. So there would be less danger of contracting disease from continually breathing the air of a vent pipe, or of a soil pipe, except where liquid is actually splashing, than from drinking New York water." Anthrax. Some time since, while considering this subject, it occurred to me that anthrax ought to be air-borne more often than any other disease. The spores are extremely resist- ant, and are found in great numbers in hair, wool, etc., and the manipulation of these materials is quite likely to raise a considerable amount of dust. If this be so, and if floating germs are carried to the alveoli of the lungs, as is alleged, the pulmonary type of this disease ought to be very common. Formerly this seems to have been the case. According to the report of the Local Government Board, 1 of thirty-two cases occurring in the woolen industry of Bradford during nine months, twenty-three were of the internal type. Since then great effort has been made to eliminate dust as much as possible from the woolen and other industries in which dry 1 Rep. Med. Off. Local Gov. Bd., Lond., 1882-83, XII, 98 286 THE SOURCES AND MODES OF INFECTION infected material is handled. As a consequence, as stated in the last report of the factory inspector which I have at hand, 1 of four hundred forty-four cases of industrial anthrax in Eng- land from 1899 to 1907 only twenty-one were of the pul- monary type, and all of these twenty-one were in the dusty woolen industry. The disease is not nearly so common in the United States, owing to the fact that less infected material is imported, but of fifteen cases in Philadelphia two only were internal. Even now, under the best conditions, there must be considerable infected dust caused by opening and separat- ing the bales, and the comparative rarity of the pulmonary type of the disease indicates that it is not very easily air- borne, though it appears almost certain that some cases develop in this manner. Furthermore, it appears that this disease may be transmitted by the air even out of doors. Legge states that he has seen two horses infected by feeding where the dust from the blower of a wool-sorting room was discharged, and Silberschmidt 2 reported a similar infection of eight out of twenty-two horses near a hair factory at Zurich. Slight Evidence that Disease is Air-borne. It is thus seen that clinical and epidemiological evidence of the spread of contagious diseases through the medium of the air is scanty. No proof of extension through the external air is presented for any important disease except smallpox, and this is far from conclusive. I have never seen any good clin- ical evidence that diseases are air-borne, even indoors. On the contrary, there is much evidence that this mode of infec- tion is not a common one. The reasons for 'the widespread belief in the transmission of disease through the air seem to be entirely theoretical, and to have been developed simply because no other satisfactory explanation was at hand. Let us now consider laboratory and experimental evidence. 1 Report Chief Inspector of Factories and Workshops, 1904, 49; 1905, 49; 1906, 38; 1907, 56; also Legge, Lancet, Lond., 1905, 1, 841. 2 Silberschmidt, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1896, XXI, 455. INFECTION BY AIR , 287 Bacteria not given off from Moist Surfaces. Among the many new conceptions which resulted from the study of bacteriology, one of the most novel was that, contrary to all previous ideas, bacteria are not given off from and are not readily detached from moist surfaces or liquids in a state of rest. This was first shown by Tyndall and has been con- firmed by Nageli, 1 Buchner, 2 Wernich, 3 Huhs 4 and others. When this became known, numerous experiments were undertaken to determine whether the expired air was free from germs, as in accordance with the newly discovered facts it should be. Tyndall was the first to show that bacteria are not found in expired air, and Gotschlich 5 cites a dozen or so workers, all of whom obtained only negative results from an examination of the expired air. According to Fliigge, 6 Cadeac and Malet, Grancher and Gennes, and Miiller were unable to find tubercle bacilli in the ordinary expiration of phthisical patients, and these early observations have been amply confirmed by others. It has been shown not only that air currents are incapable of removing bacteria from liquids but also that such currents do not remove them from the surfaces of solids. Most mate- rials which contain pathogenic bacteria, such as culture media, saliva, mucus, pus, excreta, etc., present, when dry, a some- what hard and often glazed surface, so that it is not sur- prising that exceedingly strong air currents, even of sixty meters per second, do not remove the contained germs. This, 1 Nageli, Die niederen Pilze, Miinchen, 1877, 107, Untersuchugen in die niederen Pilze, 1882. 2 Nageli u. Buchner, Sitzungsber. d. Bay. Akad. d. Wiss., Miinchen, 7 June, 1879. 3 Wernich, Virchow's Arch, f . path. Anat. [etc.], Berl., 1880, LXXIX, 424. 4 Huhs, Ztschr. f. Tuberk. u. Heilstattenw., Leipz., 1906, IX, 396. 5 Gotschlich, Kolle u. Wassermann, Handbuch [etc.], Jena, 1902, I, 171. 6 Fliigge, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1899, XXX, 107. 288 THE SOURCES AND MODES OF INFECTION according to Gotschlich, 1 has been demonstrated by Nageli, Buchner, Wernich, Hamburger and Stern, and Flugge. Got- schlich says that Honssell found it impossible to detach bacteria from infected clothing. Infection in Dust. So firmly was the theory of aerial infection intrenched in the minds of men, that search was made for some other means than the expired breath by which bacteria might get into the air. It was very early found that many bacteria could withstand drying for con- siderable periods of time, and it was at once suggested that material containing disease germs might become dry and pul- verized, and that the resulting infective dust might readily be transported by currents of air. Indeed Koch 2 was one of the earliest, as well as one of the strongest, supporters of this view. Resistance of Bacteria to Drying. If dust is a vehicle for the transport of the germs of disease, and bacteria are air-borne on or in bits of dust, or float as separate particles, they must withstand a considerable amount of drying. That some species do retain their vitality and virulence after becoming quite thoroughly dry, has been demonstrated. Sys- tematic studies of the effects of drying and of light on dif- ferent disease-producing bacteria have been made, and almost every germ has been examined from this standpoint by men particularly interested in working out its biological characters. In some instances, as, for example, the tubercle bacillus, the experiments and observations are very numerous. In the chapter on fomites infection, the resistance of the different pathogenic organisms to dry ness and to light was considered. While some species were shown to have very little resisting power, the germs surviving for a few hours or a few minutes only, others, like the bacilli of typhoid fever, diphtheria and 1 Gotschlich, Kolle u. Wassermann, Handbuch [etc.], Jena, 1902, I, 170. J Koch, Mit. a. d. k. Gesundheitsamte, 1884, II, Trans. Sydenham Soc. Pub., CXX. INFECTION BY AIR 289 tuberculosis, may, when dry, retain their vitality for months. In addition to the general knowledge of the resisting power of bacteria, which has been accumulating, special and systematic attempts have been made to determine directly the chances of infection by air-borne dust. Studies on the Drying of Germs. Among the earliest work of this kind was that by Germane. 1 He employed room dust and different kinds of earth, which after sterilization were inoculated with cultures of bacteria grown in various media. He found that generally the bacteria perished sooner in room dust than in other materials, and that bacteria which, like the typhoid bacillus, might survive for months even when dried on clothing or solid material, would speedily die in a very short time in dust. After a large number of experiments he concluded that cholera, plague, typhoid fever, influenza and gonorrhea could not be dust-borne; that under certain circumstances, with strong air currents, streptococcus and the germs of pneumonia and of diphtheria might be air- borne, and that, besides the spores of anthrax and tetanus, many of the pus organisms, meningococcus and the tubercle bacillus, might be transported in dust. It is suspected that he did not employ the true coccus of cerebro-spinal meningi- tis, for recent workers are agreed that this bacterium has very weak powers of resistance. His results with the pneumo- coccus also are surprising, as this too is rather feeble. Neisser 2 in 1898 made a careful study of the strength of air currents necessary to move dust infected with various pathogenic bacteria. He showed that currents of from 1 to 4 mm. per second are sufficient, to transport room dust, and it was chiefly with such currents that he worked. He used from twenty to thirty drops of an agar culture mixed with 30 c.c. of sterile dust. He drew dust through narrow tubes in a rather complicated apparatus, and it appears that 1 Germane, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1897, XXIV, 403; 1897, XXV, 439; 1897, XXVI, 66, 273. 1 Neisser, Ueber Lauftstaub-Infection, Inaug. Dis., Breslau, 1898. 290 THE SOURCES AND MODES OF INFECTION the conditions were too far removed from the natural to render the results of much value. Neisser's conclusions were that diphtheria, typhoid fever, plague, cholera, pneumonia, are not dust-borne diseases, but that spores, most of the pus organisms, tubercle bacilli, and the germs of cerebro-spinal meningitis may be so carried. It will be seen that to a large extent he agrees with Germano, but it is to be noted, however, that his tests, like those of Germano, were all culture tests, except those for tuberculosis, in which alone animal inocula- tions were made. Besides such systematic work as that of Germano and Neisser, much has been done in the study of special diseases by men particularly interested therein. Drying of Typhoid Bacilli. Firth and Horrocks 1 found that the typhoid bacillus would live for 23 days in sand dry- enough to be blown by the wind. Harrison and Harrison,* working in India, recovered the organism after 118 hours when kept in diffused light in very dry dust. Aldridge 3 moistened sand with urine containing typhoid bacilli on three successive days, and dried it on the fourth day, and blew it with a bellows over sterile bouillon. He recovered the bacillus on the 1st, 4th and 9th day thereafter. Horrocks 4 showed that the micrococcus of Mediterranean fever would survive in dry soil for about 3 weeks. Drying of Diphtheria Bacilli. Fliigge 5 says .that diph- theria bacilli perish when dry enough to be blown about in dust. This is confirmed by Pernice and Scagliosi and Reyes. 8 Reyes found they would live for 14 days in dry sand. Drying of Plague Bacilli. Tidswell, 7 experimenting with dust of various kinds, could not recover the bacillus of bu- 1 Firth and Horrocks, Brit. M. J., Lond., 1902, II, 936, 1094. 2 Harrison and Harrison, J. Roy. Army Med. Corps, Lond., 1904, II, 721. Aldridge, Indian M. Gaz., Calcutta, 1903, XXXVIII, 249. Horrocks, J. Roy. Army Med. Corps, Lond., 1905, V, 78. Fliigge, Ztschr. f . Hyg. u. Infectionskrankh., Leipz., 1895, XVII, 401. Cited by Germano. Tidswell, Rep, on Plague in Queensland, 1902, 67, INFECTION BY AIR 291 bonic plague after 11 days when the dust was dried under natural conditions, and it usually died within 3 or 4 days. When dried very slowly it lived about twice as long. Rose- nau 1 found that this bacillus did not live in dried bone dust over 6 days, and he did not recover it from dry and sterile garden soil after 1 day. Drying of Tubercle Bacilli. More attention has been given to the tubercle bacillus than to any other pathogenic organism. Besides other experiments referred to elsewhere in these pages it may be mentioned that Kirstein 2 experi- mented with various kinds of dust, and could not find living tubercle bacilli after 8 days. The dust was artificially infected and exposed to diffused light. He thinks droplet in- fection far more important than dust infection. Cadeac 3 was unable to reduce sputum to dust until it had been dried 10 to 12 days, while the tubercle bacilli had nearly died out on the 6th day. Even when pulverized sputum is injected into animals, tuberculosis rarely develops, and it must be still rarer as the result of inhalation. Sticher 4 also and Beninde 5 found it difficult to demonstrate living bacilli in dried and pulverized sputum under natural conditions. Nevertheless most observers do find living tubercle bacilli in dust, though usually with weakened virulence. Drying of Cholera Spirilla. According to Germano, chol- era spirilla may sometimes survive in dust for 3 days, but oftentimes they die in 1 day. He says that Honssell was never able to obtain living spirilla from infected dust, though Uffelmann was able to do so for a short period. 1 Rosenau, U. S. Pub. Health and Mar. Hosp. Serv. Hyg. Lab. Bull. No. 4, 1901. 2 Kirstein, Ztschr. f. Hyg. u. Infectionskrankh., Leipz., 1905, L, 186. 3 Cadeac, Lyon M*ias been the seat of bacterial growth, has been known tci cause sharp outbreaks characterized by acute gastrointestirjal symptoms. If living bacteria of this group are present, infection with them may result, causing a slow after development of symptoms somewhat akin to those of typhoid fever. The cooking of meat cannot be relied upon wholly to prevent sickness arising from this sort of food infection. Government inspection is suggested as the only method by which these diseases can be prevented. If, how- ever, bacilli are found in healthy animals, it is questionable whether any amount of inspection would entirely eliminate the danger. How great the danger is it is difficult to deter- mine. A good many outbreaks have been reported in Ger- many, aggregating thousands of cases, and reports come not rarely from England. No data are available for the United States. For several years I have been on the lookout for the reports of such cases in the medical press and in the " Index Medicus," and one year I employed a press-clipping bureau to secure cuttings from the lay press, but I have notes of scarcely more than a dozen outbreaks. Doubtless others occurred, but they cannot have been very numerous. A good many reports of instances of " ptomaine poisoning " find their way into the newspapers, which prove on investi- gation to have no basis in fact. Meat and Tuberculosis. In the public mind the fear of contracting tuberculosis by eating meat is very considerable, and public sentiment is sufficient to support very stringent regulation of the sale of meat from diseased animals. Yet it does not appear that there is a single recorded instance of the transmission of disease in this way. And we should expect that if such were possible it would be exceedingly rare. Tubercle bacilli have their habitat in lungs, liver, intestines, glands and other viscera, and not usually in the muscle or fat. The tubercle bacillus is easily killed by heat, and very little of this class of food is eaten without cooking. Smoked INFECTION BY FOOD AND DRINK 373 beef and ham are occasionally eaten without cooking, but even then considerable time is consumed in the process of corning and smoking, and in the rare cases in which a few bacilli are contained in the meat they are likely to have lost most of their virulence. As for the viscera, if they are used at all for food they are generally pretty well cooked. Cornet states that Schottelius studied the use of meat from tuberculous animals in Wiirzburg, and could not find a case of the disease, although the meat was eaten in every form. It has been said that while tuberculosis has been decreasing the consump- tion of meat has been increasing; and this is certainly an indication that the use of meat cannot be a factor of any great moment in the causation of the disease. At the most it is scarcely possible for the disease to be derived from this source except in rare instances. Conclusions. The diseases which it is alleged may be transmitted by flesh foods are those caused by animal para- sites, of which trichinosis is the most important, diseased conditions produced by the colon group of bacilli, and tuber- culosis. The latter is a negligible quantity, the second group probably causes very few deaths in this country, while trichi- nosis is doubtless the most important disease transmitted in this manner. Federal Control. The federal government has instituted an expensive meat-inspection service, ostensibly to guard the health of the public, but as trichinosis, the most common and serious of the animal diseases, though it is very rare in man, is ignored, it is suspected that the system was insti- tuted by Congress as the result of an ill-informed though popular demand. Filthy conditions in the slaughterhouses, and the killing of diseased animals, though their flesh may not be injurious to health, are shocking to the esthetic sense and the public demands reform. Including the expense of inspection and the value of the meats condemned, the cost to the country is $5,000,000 or $6,000,000 per annum. It is true that the conditions of labor in the great packinghouses 374 THE ^SOURCES AND MODES OF INFECTION have been improved, and that cleanlier methods of handling meat have been enforced, but it is doubtful whether any sick- ness among consumers has been prevented. I cannot help thinking how much ultimate good might have accrued if a tenth of the sum spent in meat inspection had been devoted to the systematic study of the many unsolved problems of sanitation, such as, for instance, the danger from fomites, the part played by air in the spread of disease, the causes of the decline of tuberculosis and the mode of extension of the disease, the relation of food to health, the causes of infantile diarrhea, the relation of water supplies to the general health, or the meaning of bad air and its effect on health. Infection by Shellfish. Oysters. Since oysters and other shellfish are often eaten raw, and often live in sewage-polluted waters, they might be suspected, and indeed were suspected by Sir Charles Cameron as long ago as 1880, of being the cause of typhoid fever, and in 1893 Thorne suggested that the sporadic cases of cholera which appeared here and there in England were due to the eating of raw shellfish infected at the mouth of the Humber. The first demonstration of the relation of shell- fish to disease was by Conn. 1 He showed that 23 of 100 students who went to a certain banquet developed typhoid fever, probably as a result of eating oysters. Of those who did not eat raw oysters none were sick, and one man who did not go to the banquet ate oysters at the dealers' and also was sick. The oysters had been kept about 300 feet from a drain leading from a house where there was typhoid fever. Similar out- breaks have been reported by Chantemesse, 2 Mosny, 3 Chatin, 4 1 Conn, Rep. St. Bd. Health, Connect., 1895, 253; Med. Rec., N. Y., 1894, XLVI, 743. 2 Chantemesse, Bull. Acad. de med., Par., 1896, 3 a. XXXV, 588, 724. 3 Mosny, Rev. d'hyg., 1900. 4 Chatin, Semaine med, 1897, XVII, 91. INFECTION BY FOOD AND DRINK 375 Thresh and Wood, 1 a committee which studied the subject at Atlantic City, 2 Fraser, 3 Soper 4 and Morse. 5 Clams, Mussels. Clams as well as oysters have been believed to be the cause of outbreaks, 8 and where mussels and cockles are consumed raw in considerable quanti- ties they are equally liable to carry the infecting organ- isms. Three outbreaks in Norwich, England, in 1908 were traced to mussels. 7 Mussels also were believed to be the cause of an outbreak of typhoid fever in North Ormsby, 8 and have been an important factor in the causation of typhoid fever in Belfast. Shellfish in English Cities. Not only have shellfish been shown to be the cause of marked outbreaks of illness, as just shown, but they are strongly believed by many, espe- cially by English health officials, to be an important source of the ordinary " residual " typhoid fever occurring in cities. Newsholme 9 is especially insistent on this. A careful study of the matter in Brighton, where he was then health officer, showed that in 1894-96, of 189 reported cases of typhoid fever, 41 were imported, and of the 148 remaining, 51, or nearly 30 per cent, had eaten raw oysters or mussels within the incuba- tion period of the disease. These shellfish all came from grounds which were contaminated with sewage. From 1894 to 1902, of 643 reported cases of typhoid fever, 158 were due to eating oysters and 80 to other shellfish, making in all about 37 per cent due to this cause. Similar observations and con- clusions may be found in the reports of the health officers of Birmingham, Leicester, Southend, Manchester, London, Thresh and Wood, Lancet, Lond., 1902, II, 1567. Phila. M. J., 1902, X, 634. Fraser, Lancet, Lond., 1903, I, 183. Soper, Med. News, N. Y., 1905, LXXXVI, 241. Morse, Rep. St. Bd. Health, Mass., 1900, 836. Plowright, Brit. M. J., Lond., 1900, II, 681. Rep. on Sanitary Condition of Norwich, 1908, 14. The Medical Officer, 1909, II, 431. Newsholme, J, San, Inst,, Lond., XVII. 376 THE SOURCES AND MODES OF INFECTION Portsmouth and other places. The typhoid death rate in English cities is low and health officials find it difficult to account for the origin of the cases. The pollution of shellfish with sewage is not uncommon around the English and Irish coasts. 1 A considerable percentage of the cases of typhoid fever are known to have eaten shellfish, often from polluted sources, within two to four weeks of the date of attack. Perhaps the assumption is justifiable that some of these cases at least are due to the shellfish. Typhoid fever has for some time been rather prevalent in Belfast, and a special commis- sion was appointed for its investigation. This commission believes that the chief source of the disease is mussels and cockles, picked up by the poorer people along the sewage- polluted flats. 2 Mair 3 states that in Belfast it was impossible to make a satisfactory canvass of the number of mussel users, either among the general population or among the typhoid patients. He bases his conclusions as to the part played by mussels on a careful statistical study, and shows that the disease in Belfast has varied according to changes in the amount of mussels consumed. He also shows that Jews and the wealthier classes, who use no mussels, had little typhoid fever. Nash 4 states that at Southend 54 per cent of the typhoid-fever cases confessed to the eating of shellfish, while only 0.4 per cent of 501 sick with other diseases confessed to such eating. Since the consumption of raw shellfish has decreased, typhoid fever has decreased also. In Leicester, 5 50 per cent of the typhoid cases ate mussels, but they were used in only 15 per cent of a small number of non infected houses. Johnston 6 found that 25.8 per cent of 62 persons 1 Rep. Med. Off. Loc. Gov. Bd., 1894-95, XXIV; Loc. Gov. Bd. for Ireland, Rep. on Shellfish Layings, 1904. 2 U. S. Pub. Health & Mar. Hosp. Serv., Pub. Health Rep., Wash., 1908, XXIII, 995. 3 Proc. Roy. Soc. Med., Lond., 1909, II, Epidem. Sect., 187. 4 Nash, Pub. Health, Lond., 1903-05, XVI, 80. 5 Rep. Med. Off. Health, Leicester, 1908, 31. 6 Johnston, The Medical Officer, II, 1909, 431, INFECTION BY FOOD AND DRINK 377 with typhoid fever had eaten shellfish, mussels and peri- winkles within a short time of their illness, while of 827 other persons only 7.3 per cent had eaten them during the whole summer. In the United States, also, non-epidemic or " residual " typhoid has been attributed to the use of raw oysters, as in New York. 1 The chief reason for this seems to be that there is known to be a considerable consumption of sewage-infected oysters. 2 Most of the beds on which oysters are grown are free from dangerous pollution, but it is quite common to " fatten," i.e., freshen and swell them, in estuaries near sewer openings. Danger Variable. It seems reasonable to conclude that the danger from eating sewage-infected shellfish is a real one. Exactly how great it is, is difficult to determine. In England anywhere from 15 to 50 per cent of the disease in cities is attributed to eating raw mussels or oysters, but this is on the supposition that every typhoid patient who has recently eaten raw shellfish derived the disease from that source. In Provi- dence raw oysters are very popular; they are consumed in restaurants in large numbers, and form a course in a large proportion of banquets and dinners. Many oysters are grown in the upper part of the bay, in water grossly contami- nated with sewage, and in the water and in the oysters colon bacilli are found. Until within two or three years, numbers of oysters from clean water have been "fattened" near sewer openings, yet Providence has a typhoid death rate less than half that of the average American city. Oys- ters are not eaten to any extent in August, when typhoid fever begins to increase, and they are largely consumed in the winter and spring, when there is little of the disease. During the years 1902-05, of 263 typhoid-fever patients who 1 Med. News, N. Y., 1904, LXXXIV, 325; 1905, LXXXV, 571. 2 Report of U. S. Commissioner of Fisheries for year ending Jan. 30, 19C4, Appendix, 189; Rep. Dept. Health, City of N. Y., 1904, I, 313; Rep. St. Bd. Health, New Jersey, 1904, 226; Rep. Dept. Health, Balti- more, 1907, 124. 378 THE SOURCES AND MODES OF INFECTION replied definitely as to whether they had eaten oysters, only 26, or about 10 per cent, said that they had. Very few raw oysters are eaten by laboring people, but at present laboring people furnish fully their share of typhoid fever. While the amount of typhoid fever due to the use of raw shellfish is not very great, this danger ought to be eliminated entirely, and state boards of health should have the authority to forbid the sale of shellfish from polluted waters. Crawfish and Typhoid Fever. Dr. Bissell of Buffalo wrote to me about an interesting local outbreak of typhoid fever which was at first suspected to be due to milk. But further investigation showed that it was confined chiefly to boys, and that these boys were in the habit of catching craw- fish from a lake grossly polluted with sewage. After par- tially cooking the crawfish before an open fire in the field, the boys would eat them. Infection by Fried Fish. In 1900, Earner 1 of London reported outbreaks of typhoid fever in Southwark, Lambert and Kensal-town which seemed to be confined in each case to the customers of certain fried- fish shops. While the sickness was believed to be due to the eating of fish, no conclusion was reached as to how the fish became infected. It is scarcely possible that infection of the fish before cooking should not be destroyed by the pro- cess, and yet it seems unlikely ihat handling by carriers after infection could cause such an outbreak. Infection by Watercress. In the summer of 1903 there was a very considerable out- break of typhoid fever in Hackney, London. 2 This was very carefully investigated by Warry, and he eliminated all articles of food and drink as sources of the infection, except water- cress. Of the 110 cases 55.3 per cent ate watercress which 1 Earner, Special Rep. to Med. Off. Health, Lond., 1900. 8 Warry, Rep. Med. Off. Health, Lond., 1903, 35. INFECTION BY FOOD AND DRINK 379 grew in sewage-polluted water. An inquiry showed that the incidence of the disease on watercress eaters was three times as great as upon those who did not eat it. Infection by Celery. Morse 1 reports an outbreak of typhoid fever due to the use of celery. There were 49 cases in an insane asylum. Nearly all of these belonged to the class of pay patients, to whom alone celery was served. Several other persons, how- ever, had access to the celery and contracted the disease. There were no cases except four contact cases among non- users of celery. There had been typhoid fever in the insti- tution some months before and the celery bed had received the hospital sewage. The disease developed soon after the celery came into use. 1 Morse, Rep. St. Bd, Health, Mass., 1899, 761, CHAPTER VIII. INFECTION BY INSECTS. Importance of Subject. The subject-matter of this chap- ter is of the utmost importance in the practical work of pre- ventive medicine, and it is of equal interest to the student of scientific epidemiology. Our actual knowledge of the insect carriers of disease has all been acquired during the last fif- teen or twenty years, and marks as brilliant and successful an epoch in the history of medicine as did the phenome- nal development of bacteriology in the years immediately preceding. I hesitate very much to discuss the subject at all, as most of the diseases considered are essentially tropical, and of tropical diseases I have had no personal knowledge. But even we who dwell in temperate regions are likely to meet with isolated cases of tropical diseases, or to suffer from occasional invasions of yellow fever, bubonic plague and relapsing fever. In any event, it is important that both the student of preventive medicine and the health officer keep informed as to current progress in this line of research, and ever bear in mind the possibility that insects may play a part, at least, in the spread of those diseases with which he is more familiar. Modes of Transmission. There are various ways in which disease may be transmitted by insects. The most interesting and to us novel manner in which this happens is that the discovery of which we owe to Theobold Smith, in which the insect, as well as the higher animal, serves as the true host of the pathogenic organism which causes the Sedgwick, Rep. Bd. Health [etc.], Mass., 1892, 736. 436 THE SOURCES AND MODES OF INFECTION berg had issued orders to guard against flies, but they had little effect. Veeder * clearly set forth the possibility of the transfer of fecal matter to food by means of flies, and he declared that flies were the principal cause of the prevalence of the disease in the camps. The report of the commission to investigate the cause of the fever, although laying chief stress on contact infection, forcibly emphasized the part played by flies in the spread of the disease. 2 Vaughan, a member of the commission, personally urged the importance of flies in the spread of this disease. 3 Ever since, great popular and scientific attention has been bestowed upon the fly in the United States and also in other countries. Other Reports of Typhoid Fever due to Flies. Nuttall cites Quill, Tooth and Calverly, Smith, Austen, Straton and Jones as attributing much of the army typhoid in South Africa and India to the presence of flies. Numerous writers on typhoid fever in civil life have referred to the fly as a most active agent in the transmission of this disease. In " The House Fly at the Bar," published by the Merchants' Association of New York in 1909, are printed opinions of seventy or more health officials and others, all but nine or ten of whom are emphatic in their statements that flies are very important carriers of disease germs. Some few, how- ever, consider that the case against the fly has not been proved, though some circumstances are suspicious. Several give instances of fly infection that have come to their notice. Hurty writes of an outbreak in an asylum following the brief use of the privy by a walking case of typhoid fever. Flies abounded and there was no chance for contact. Taylor, of Denver, reported typhoid fever at a dairy. The milk be- came infected, he thinks by flies, for the privy was near the milk house, and gelatine cultures exposed near the privy 1 Veeder, Med. Rec., N. Y., 1898, LIV, 429. 2 Abst. of Rep. on the Origin and Spread of Typhoid Fever in U. S. Military Camps during the Spanish War, 1898, 183. 3 Vaughan, J. Am. M. Ass., Chicago, 1900, XXXIV, 1451, 1496. INFECTION BY INSECTS 437 and in the milk house showed colonies of typhoid bacilli, presumably deposited by flies! Dr. H. W. Hill, the exceed- ingly cautious epidemiologist of the Minnesota State Board of Health, writes me that from his observations in that state he "firmly believes that flies are an important factor in the spread of typhoid in such places as mining and lumber camps, and that the small country village with its exposed outdoor closets parallels the camp conditions exactly." He further states that Wald noted that in a certain camp the Italians did not contract the disease because, as he thought, they did not eat between meals, while the Finns suffered severely because they kept their food laid out on the table all the time, where it was exposed to innumerable flies, and helped themselves during the day at random. Pease 1 refers to an outbreak of 50 cases at Castleton from June to September all in the vicinity of a yard where typhoid excreta were thrown and where flies abounded. Button 2 accused bluebottle flies of carrying infection from the feces of a carrier to 4 other members of the family. In 1906 an outbreak of typhoid fever near London was thought by Ransome and Young to be due to swarms of flies which bred in a manure dump near by. 3 In none of these alleged instances of fly-borne infection are other modes excluded, and often it is quite as probable that the cases were due to contact, and in scarcely any of them is there more than a possibility that the disease was caused in the manner alleged. Numerous bulletins and circulars have been issued by state and municipal health officials, some of which depict, in exaggerated language and with extravagant illustration, the danger to be feared from this household pest, and a dis- tinguished entomologist has urged that the familiar name of M . domestica be changed from house fly to typhoid fly. 1 Long Island M. J., Brooklyn, 1910, IV. 2 Button, J. Am. M. Ass., Chicago, 1909, LIII, 1561. 3 Rep. Med. OS. to Lond. Co., Council, 1907, Append. III. 438 THE SOURCES AND MODES OF INFECTION Flies suspected from their Habits. The chief reason why the fly is believed to be the carrier of diarrhea, cholera and typhoid fever are that flies are seen to pass from feces to food; that they have been shown to carry fecal bacteria, and in several instances the specific bacteria of cholera and typhoid fever; and that they often swarm in unusual num- bers at times and in places where there is an exceptional prevalence of disease. The very definite observations of Hamilton, Fricker, Klein, Simmonds, Bartarelli Faichnie, Mann and Tsuzuki as to the finding of infected flies in in- fected houses, and the accounts given by Veeder, Vaughan, Tooth, Smith, Hill and others, of the contamination of food by flies in camps, military and civil, certainly render it probable that these insects do at times cause sickness, and may under certain conditions, such as prevail in camps, be an important factor in outbreaks. But these observations are far from a demonstration of what is now generally claimed, that flies are the chief factor in the spread of typhoid fever, and perhaps of summer diarrhea, in well- ordered civil communities. Dr. Howard's Views. Howard in his admirable work on the house fly, before cited, devotes 174 pages to the " Carriage of Disease," a large part of which is taken up by a consideration of typhoid fever; he quotes many of the writers referred to in the last few pages of this book and also some others as Wanhill in Bermuda, and Washburn in Minnesota, who, noting the filthy habits of flies and their seasonal distribution in relation to typhoid fever, are con- vinced that flies are an important factor in the causation of this disease. Very little convincing epidemiological evi- dence is offered. Howard apparently bases his own view on this matter upon the habits of the fly, for he says that " the correlation or non-correlation of the curve of house fly abundance and the abundance of typhoid has prac- tically no effect upon our conclusions as regards the pos- sible transfer of the disease by flies." Howard cites as INFECTION BY INSECTS 439 significant the experience of Palmer in Georgia who offered to care for, without charge, any typhoid patient living in a fly-proof house, but none applied. He also found no secondary cases in families which controlled flies as directed. This does not appear to throw much light on the subject, for, if there were no secondary cases, his families must have been wonderfully well trained in avoiding contact infection; and this is doubtless the complete explanation. Seasonal Distribution of Flies and Typhoid Fever. As the seasonal distribution of flies has been studied with reference to diarrhea, so has it been studied with reference to typhoid fever. Jackson, in his report to the Merchants' Association in New York before referred to, gives a chart showing the seasonal distribution of flies in New York and of deaths from typhoid fever, the latter being set back two months to allow for the assumed time between the date of infection and the date of death. Hamer thinks two months is too long a time. He thinks that it is nearer five weeks. The apex of the typhoid curve corresponds fairly well with the apex of the fly curve, but there is a rise in the typhoid curve in February, two-thirds as high as that of August, which certainly cannot be attributed to flies. Ainsworth in India 1 states that at Poona the maximum admissions of typhoid, fever to the hospital occur about one month after the maximum fly catch. Judging from Ainsworth 's paper, there appears to be great seasonal variation in the number of flies in Poona, correlated closely with the temperature, as with us. In Jacksonville 2 it is said that the fly curve and the typhoid-fever curve correspond closely, though Dr. Terry gives no figures or diagrams. According to Howard a similar correlation has been worked out by Purdy in New Zealand (1910) and Osmond in Cincinnati (1909). 1 Ainsworth, J. Roy. Army Med. Corps, Lond., 1909, XII, 485. * Am. J. Pub. Health, 1912, II, 14. 440 THE SOURCES AND MODES OF INFECTION Evidence against Theory. Niven 1 found that, while in Manchester in 1903 the maximum number of flies was caught about August 29, the maximum number of cases of typhoid was not reached until November, during the whole of which month the morbidity remained high. In 1906 2 there was, as usual, a well-marked maximum of flies about September 1, and while the typhoid morbidity was high in September, being 65, it was somewhat higher in October, and there were 46 cases in November and 50 in January and only 21 in July and 23 in August. In Washington, 3 in 1908, the maximum fly catch was for the week ending June 24, after which it steadily and rapidly decreased. The maximum of typhoid cases, according to date of at- tack, was in the week ending July 22, but instead of falling rapidly, as did the fly catch, it continued high until the middle of September. There certainly is little parallelism between the two curves. The commissioners appointed to study the disease, and who make the report, say that the evidence is quite strong that flies play a relatively small part in the spread of typhoid fever in Washington. In Providence the seasonal distribution of typhoid fever cases, according to date of first symptoms, for the six years 1904-1909, was as follows. All cases due to milk and all certainly contracted out of the city are excluded. Jan. Feb. Mar. Apr. May June 45 36 26 48 49 56 July Aug. Sept. Oct. Nov. Dec. 80 161 133 117 96 59 According to observations of Sykes, the maximum fly catch out of doors was about the last of July, when it began to fall 1 Niven, Rep. on Health of Manchester, 1903, 123. s Rep. on Health of Manchester, 1906, 63, 84. 8 U. S. Pub. Health & Mar. Hos. Serv., Hyg. Lab. Bull., No. 52, 30. INFECTION BY INSECTS 441 off quite rapidly. The observations as to the indoor catch were not very numerous, but it seems probable that the flies go indoors in greater numbers as the weather grows cooler in September. There is certainly not a very close agreement between the number of flies and the prevalence of typhoid fever. It is scarcely possible that the typhoid fever develop- ing in November is due to flies, and yet there were 96 cases in November, and the November rate is higher than that of any other month except August, September and October. If we cannot attribute the excess in November to flies, why should it be thought necessary to attribute the excess of the preceding three months to flies? I can see nothing in the seasonal distribution of typhoid fever in Providence to warrant the assumption that flies are an important factor in its causation. In London, 1 while the typhoid curve and the fly curve corresponded fairly well in 1907, in 1908 the greatest preva- lence of flies was in the second week in August, while the maximum of typhoid fever notifications was in the second week in November. In 1909 there was only a slight autum- nal rise of typhoid fever, the maximum being in January, while the maximum fly prevalence was in August. Correlation of Typhoid Fever and High Temperature. I have been able to find only the very few observations noted above as to the correlation of fly distribution and typhoid fever, and these few do not indicate that there is any reason to assume that the flies stand in causative relation to the fever. The very careful work of Sedgwick and Winslow 2 shows that throughout the world, and in both hemispheres, there is a distinct relation between this disease and the sea- sonal rise in temperature. These authors, though they recognized a certain amount of infection by flies, explained the autumnal increase in typhoid fever as due to the direct 1 Rep. Med. Off. Health, Co. of Lond., 1907, 1908, 1909. 2 Sedgwick and Winslow, Mem. Am. Acad. Arts & So., 1902, XII, No. 5. 442 THE SOURCES AND MODES OF INFECTION and favorable action of high temperature on the life of the bacillus outside the body. This view hardly seems tenable from what has since been learned of the life habits of the bacillus, and I think is now no longer held by the authors. It is the custom now for most writers to attribute to flies the chief role in the autumnal excess of typhoid fever, but from the evidence at hand it seems wiser, while admitting the fact of seasonal distribution, as determined by Sedg- wick and Winslow, to await further study before attributing this definitely to any one cause or group of causes. Epidemiological Evidence, Minnesota. More direct evidence of fly carriage is offered by Hill. 1 He reports three large insane hospitals, with 1400 to 1800 patients each, having outbreaks of typhoid fever at about the same time in the summer. In one, the wards of the institution, though screened, were full of flies, which followed the food from the kitchen, which was unscreened and swarming with the in- sects. In a second hospital the disease was confined almost exclusively to the men, whose dining rooms, and wards too, were swarming with flies, while the women's side was com- paratively free. In both these institutions the outbreak continued until cold weather. In another hospital the flies were so numerous that when they settled on the slender wire supporting the electric lamps they gave it the appear- ance of an inch rod! The management determined to exterminate the flies, which they did, and though it was two months before cold weather, no more cases developed after the period of incubation had passed. Such a bit of evidence is not conclusive, but, if observed often enough, would be cumulative and would indicate a real causative relation between typhoid fever and flies as can no amount of watching the habits of flies or comparing fly curves and typhoid curves. Evidence from Jacksonville, Richmond and Asheville. The health officers of the two cities first named have very 1 Hill, Rep. State Bd. Health, Minn., 1911, 206. INFECTION BY INSECTS 443 forcibly called attention to the much greater liability of infection by flies in the comparatively more " unsanitary " cities of the south and have criticized the present writer for an apparent disregard of this, and it is true it must be ad- mitted that a large part of what is here written about the comparative unimportance of nuisances in general and the fly nuisance in particular is based upon conditions studied in the cities in the northern states and in England. Ac- cording to Terry, 1 Jacksonville, with its large numbers of poorly made privies and enormous swarms of flies, has in the past been no better than an old-time army camp as regards conditions favoring the spread of typhoid fever. Late in 1910 a most energetic campaign was begun against the fly and for the construction of fly-proof privies. In 1911 there were reported only 142 cases of typhoid fever as against 321 for the same period of 1910. Formerly 60 per cent of the cases had been in the privy section and 40 per cent in the sewered section, though the distribution of the population was the reverse of these figures. After the fly campaign there was little difference in the incidence of the disease in the sewered and unsewered portions. The high typhoid rate of several Georgia cities showed no falling off in 1911. It would have been well if Terry had given the typhoid fever figures for a number of years and had also shown the seasonal distribution so that it might be seen whether the decrease was confined chiefly to the fly season. Still the figures as they stand are striking and call for con- tinued effort along the same lines. Just as this is going to press the Report of the Board of Health of Jacksonville for 1911 has come to hand and on page 16 is a diagram which shows that reduction in typhoid fever incidence in 1911 was confined to the May- August period, the time of fly prevalence. In Richmond, Levy 2 has been carrying on an energetic and well-directed campaign against typhoid fever since * Terry, Am. J. Pub. Health, 1912, II, 14. 1 Levy, Rep. Health Dept., Richmond, 1910. 444 THE SOURCES AND MODES OF INFECTION 1907, with the result that the death rate per 100,000 fell from nearly 50 in the preceding five years to 24.1 in 1909, 21.9 in 1910 and 17.8 in 1911. In 1910 strong effort was made to prevent fly infection by screening privies and patients, and by reducing the number of flies. In a letter Dr. Levy states that the number of flies is still large but that the screening has been very effective. I judge that he attributes a good deal of the typhoid reduction to this, but it is difficult to disentangle this factor from supervision of cases, instruction of attendants, disinfection of excreta and better notification. It is worth noting that the decrease does not seem to be greater for the summer months than for the winter when flies can scarcely be a factor. In Asheville, N. C., so Dr. McBrayer writes me, there was a reduction in typhoid fever cases from 119 in 1910 to 60 in 1911, due chiefly, he believes, to strict control of privies which are now required to be made fly-proof. Privies, Flies and Typhoid Fever. That an excess of typhoid fever is found in cities or sections of cities where there are many open privies has often been noted. Of late some have attributed this to the transference of infected matter by flies. There is little warrant for this assumption, though Terry says that in Jacksonville after the screening of the privies there was no excess of typhoid fever in the unsewered parts of the city. But meanwhile an active campaign against typhoid fever was being waged, and more cleanly privies and better care of cases would do much to prevent contact infection. That the excess of typhoid fever in privy districts is doubtless largely due to contact is shown by the fact that, as has recently been noted in Providence, localized outbreaks among careless people using privies have occurred out of fly time. In Washington 1 investigation has shown that in the fly season the users of privies furnish a higher percentage of typhoid fever as com- 1 U. S. Pub. Health and Mar. Hosp. SerV. Lab., Bull. 78, 1911, 66, 160. INFECTION BY INSECTS 445 pared with the users of water-closets than they do in the winter time. The percentage of cases furnished by the users of privies in fly time was 13.3, in the winter 7.7, but the figures were not large. It was also found in Washington that during 1908 and 1909 the 32 per cent of the population living in unscreened houses furnished about 59 per cent of the cases occurring in the summer and fall. But, as the report suggests, people living in unscreened houses are more likely to have other unsanitary surroundings and to be of careless habits. Sykes' investigations in Providence showed that flies are 25 to 30 times more numerous in the uncleanly parts of the city than they are in the clean parts, and the differences in the indoor catch is even greater. Though, as shown above, there appears to be some excess of typhoid fever in the fly- infected and privy-using parts of cities, the difference bears no comparison to the difference in fly distribution. Unwise to Claim Too Much. While the fly is a nuisance and it is highly desirable to get rid of it, and while it seems likely that it is to some extent a means of spreading disease, it is extremely unwise to make definite statements that it is the chief source of diarrhea, of cholera or of typhoid fever, unless we have very exact proof, and it is unwise, unless such proof is at hand, to urge large expenditures to get rid of flies, promising thereby the eradication of typhoid fever and other diseases. If it should chance that a mistake has been made, and that the fly is not the chief disseminator of typhoid fever, and the disease still persists after the fly has disappeared, we need not be surprised if the public fail to take us seriously when we advise, on knowledge that is well established, that mosquitoes are the sole carriers of malaria and yellow fever; that escape from the tsetse fly means escape from sleeping sickness; and that a rat-proof city will be a plague-proof city. Control of Flies. As flies are a great nuisance and a possible source of danger it is very desirable that they 446 THE SOURCES AND MODES OF INFECTION should be eliminated as far as possible, but too much money should not be expended in the experiment and too large results should not be promised. Each individual family can very effectually control these pests by good screening and the use of fly paper. It is desirable that people should be educated to dislike flies. Chantemesse says that the housewife should think it as much of a discredit to have flies in her house as bugs in her bed. Circulars of informa- tion may be distributed, but care should be taken to avoid exaggeration and not to promise too much either as to the effectiveness of remedies or the resulting decrease in disease. We know even now far too little about the habits of flies and the best ways of attacking them. Packard and How- ard gave us our first definite knowledge, but this has been much extended by Newstead, 1 who showed that the fly is far less exclusive in its choice of breeding places than was supposed. Howard in his " The House Fly Disease Carrier " gives a summary of our present knowledge which contains much information. The recent papers by Terry and by Dodd previously cited recite interesting and suggestive experi- ences. It appears that effective scavenging is the most important means of getting rid of flies. If yards, streets and vacant lots were kept clean, market refuse removed promptly, and all garbage kept covered, there would be an enormous reduction in the number of flies about dwellings. The most practicable way to prevent the breeding of flies in stable manure is to compel its removal once a week. Wher- ever it is possible the privy vault should be abolished. When this is impossible, the fly-proof privy has been urged and the Federal Government has issued a detailed account of how one may be economically constructed. 2 This 1 Newstead, Rep. on the Habits, etc., of the House Fly, to the Health Committee, Liverpool, 1907. 1 Stiles and Lumsden, U. S. Dept. Agriculture, Farmers Bull. 463, 1911. INFECTION BY INSECTS 447 has seemed somewhat visionary, but the energetic work done by the health officers of Richmond, Jacksonville and Asheville show that by means of constant supervision it is possible to make such privies effective. The question of covering food in markets and shops to protect it from flies as well as from dust has been much discussed. Slack l in an excellent paper concludes that the danger from this source in a well-ordered city is not very great, but that for aesthetic reasons the public might well demand, through ordinances or otherwise, that food be so protected. In this opinion the writer heartily concurs. Summary. After this brief examination of the evidence in regard to the role of insects in the transmission of disease we are justified in the following conclusions: First. It is certain that yellow fever and malaria are transmitted solely by certain mosquitoes, and that by con- trolling the mosquitoes it is possible, even under very un- favorable conditions, to eradicate or reduce to a minimum these two diseases. Second. It is highly probable that the relapsing fevers are transmitted solely by certain ticks, sleeping sickness by the tsetse fly, filariasis by the mosquito, pappataci fever by a fly and typhus fever by lice. Third. The bubonic type of plague in human beings is usually transmitted from rat to man by the flea. Fourth. It is probable that under certain conditions, as in military and civil camps and in filthy communities with- out sewerage, insects, especially flies, may be an important factor in the spread of the fecal-borne diseases, but there is no evidence that in a well-sewered city with few privies the house fly is a factor of great moment in the dissemination of disease. 1 Slack, Am. J. Pub. Hyg., 1909, V, 159. INDEX Actinomycosis 366 African cattle fever 122 Air, see Sewer air. bacillus influenzae not carried by 99-100 tuberculosis in 298-299 bacteria found in 282, 298-301 danger of infection by 300 expired, free from germs 287 infection by, thought important 137 conclusions 313-315 experiments with anthrax 312 Mediterranean fever 311-312 plague 281, 312-313 not impossible 281 of wounds by 300-301 pneumococcus in 300 pus-forming bacteria in 299-300 swine plague bacilli in 300 Air-borne anthrax 285-286 chicken pox 270, 280 disease in hospitals 270-271, 279-280 slight evidence of . . '. 286 infection indoors 282 in surgery 283-284 reasons for belief in 259-260, 283 influenza is not 277 malaria is not 384 measles 272-280 rubella 280 scarlet fever 270-273, 280 out of doors 272-273 small-pox, cases traced to other sources 268-269 conclusions 269-270 evidence against 266-269 of, in United States 264-265 from hospitals 260-270 infection of, denied 263-270 objections to theory 265-266 tuberculosis 194, 202-203 typhus fever 281 whooping cough 280 Amebae dysenteriae, carriers of 118 grown on culture media 24 in soil 24 in well persons 118 on vegetables 24 449 450 INDEX Amebae, intestinal parasites 112 species of 24 Amebic dysentery 24, 118 American hospitals 142-145, 279 Anchylostoma, see Uncinaria, Hookworms. duodenalis 186 Anchylostomiasis, due chiefly to contact 186-187 Animals, diseases of, affecting man 371-373 spread tuberculosis by licking one another 204 Anopheles mosquitoes carry malaria 382-383 species and habits 385-386 Anthracosis 306-307 Anthrax, a dust-borne disease 285-286 an air-borne disease 285-286 and fomites 226-227 insects 416-417, 423 bacillus, see Bacillus anthracis. due to food infection 2, 365 experiments in infection by air 312 from hair, hides 227 morocco factories 3 wool 227 wool refuse perpetuated by direct contact soil in relation to 2 spores in dust, hair, hides, wool 226-227 spread by unrecognized or concealed cases Antisepsie medicale in French hospitals 198, 278-279 Antitoxin may favor spread of disease 386-387 Ants carry bacillus murium typhi 419 plague bacilli 419, 424 Aspergillus destroys mosquitoes 390 Asylums, bacillary dysentery in 183-184, 430-431 percentage of bacillus diphtherias carriers in 90 typhoid fever in 51-52, 442 Atoxyl to prevent sleeping sickness 402 Atypical cases, laboratory evidence of 123 not easily distinguished from carriers 130-131 Babies' Hospital, gonorrhea in 165-166 Bacillary dysentery, carriers of 67-69 caused by contact 183-184 culture of bacillus in eye 183-184 in camps 183 in institutions 183-184 mild cases of 68-69 Bacillus anthracis, see Anthrax spores. carried by flies 419, 423 growth in ponds relation to the soil 2, 4 saprophytic existence of Bacillus coli communis cause of diarrhea 367 in dust of schoolrooms 294 on the hands 179, 192 on roller towel 192 INDEX 451 PAGE Bacillus diphtherias carried by flies . 423 carriers in family 89-90 insane asylum 90 schools 90-94 investigation of, in Massachusetts. . . 83 of 82-99 found intermittently 98 in bread 26 carriers, varieties of 83 virulence of .82, 84-86, 91-92 clay 233 convalescents 82, 84-85, 98-99 dust 290,294 holy water, on cups, pencils, drinking glass . 192 membrane 240 milk 25,26 otitis 94-95 pupils cause disease in teacher 98 rhinitis 94-95 rooms 233, 241 scarlet fever 86-88, 91, 96 school children 82-86, 88, 90-94 soil 26 sore throat 93-^94, 98-99 well persons 82-83 life of, in butter 251 may be air-borne 289 not in normal throats 84-85 on coat 227 drinking glass 192 fomites 192-193, 227, 240-241 virulence of 240 pencils 193, 233 resistance to drying 233, 290 saprophytic existence of 25 Bacillus dysenteriae, carried by flies 423 cause of diarrhea 367 in carriers 67-69 f eces 24 milk 15 soil 23 resistance to drying 234 saprophytic existence of 23 Bacillus enteritidis, cause of diarrhea 367 (Gaertner) in ice cream 250 in food poisoning 58, 371 sporogenes, cause of diarrhea 367 Bacillus influenzae in droplets 298 not carried by air 99-100 saprophytic 26 persistence of 100 resistance to drying 238 widely distributed 100-101 Bacillus leprae in droplets 297 452 INDEX PAGE Bacillus morbificans in food poisoning 371 Bacillus paratyphi, cause of diarrhea 367 in feces 16 food poisoning 371 not found in healthy persons 59-61 Bacillus paratyphi A in carriers 58 Bacillus paratyphi B in carriers 59 Bacillus pestis carried by ants 419-424 in bodies of fleas. 236 convalescent animals 69-70 convalescents 70 cow dung 23 dust 290-291 sputum 71 infection of soil by. 22 not found on floors 235 on cotton goods 228 resistance to drying 235-236, 290-291 saprophytic existence of 22 Bacillus prodigiosus on flies 425 in droplets 295-297 sewer air 284 Bacillus pullorum, carriers of 71 Bacillus tetani in blank cartridges 6, 226 dirt of floors 239 gelatine 6, 284 intestines of animals 5 soil ' 6,239 latency of 106 on lamp wick 6, 226 resistance of 6, 225-226 saprophytic existence of 6 Bacillus tuberculosis, carriers of 103-105 in air 298-299 butter. 364-365 communion cups 195 droplets 295-296 dust 292-293 flies, and fly specks 422^23 lymphatic glands 203 milk 355-356 nose and mouth 103-104, 193, 203 railway carriages 292 room 235, 292 tonsils 203-204 tramcars 292 latency of 104-105 may be dust-borne 289-290 pass from stomach to lungs 305-308 not found in street dust 292 in expired air 287 on spirometer 195 saprophytic 26 so resistant as believed 234-235 INDEX 453 Bacillus tuberculosis, on a glass 195 dishes 195 fomites 194-195, 241-242, 292, 293 hands 193-194 napkin rings 195 sidewalks 194 telephones 195 tongue 203 perishes in light 234-235 proportion of human and bovine types. . . 360-361 resistance to drying 234-235, 241-242, 291 swept from sidewalk by dresses 194 Bacillus typhi carried on fingers 169-170 flies and 420-422 in blood 34-35 bones 35 butter 16 cerebro-spinal fluid 35 dead animals 8 dust 290 feces 9, 34-36 gall bladder 35, 42 ice 13, 319, 340-341 kidneys 35 milk 15 ovaries 35 oysters '. 13 privy vaults 9-10 - prostatic fluid 37 seltzer water 13 seminal vesicles 37 septic tank effluent 10 sewer air 284 soft drinks 13 soil 7, 10 epidemiological evidence of growth 16 spleen 35 sputum 37-38 tidal mud 8 tonsils 34 urine 37 persistence of 10 water 10-13 epidemiological evidence of growth 17 modes of contamination 320 recovered from 319 increase in milk 17 intermittent excretion of 46-47 moisture necessary to growth of 16 on blankets 227 vegetables 8 path of entrance 34, 178 resistance to drying 232-233, 290 saprophytic existence of 7, 16 454 INDEX PAGE Bacteria and sewer air 284-285, 288-289 cultured less resistant than uncultured 11 effect of drying upon 231-232 found in air 298-301 inhalation of 304r-305 not found in expired air 287 given off from moist surfaces 287, 288 of suppuration, see Pus bacteria. on cups 192-193 f omites 239-242 hands 192-194 money 223-224 pencils 192-193 Bagging, yellow fever from 213 Balantidium 112 Ballast, yellow fever from 213 Bathing, typhoid fever from 324-325 Baths, public, encourage cleanliness 211 Bed clothing, bacillus diphtherias on 240 Bed, smallpox from 214 Bedbugs and anthrax 417 kala-azar 402 plague 414 relapsing fever 411-412 typhoid fever 418 Bedpan carries dysentery amebae . . . . 183 Betel nut, cholera spread by 185 Biological carriers distinguished from mechanical carriers 413 Black-leg 4 Blank cartridges, bacillus tetani in 6 Blankets, bacillus typhi on 227 Blood, bacillus typhi in 34r-35 infection of, cause of typhoid fever 34-35 meningococcus in 73 yellow fever virus in 393-394 Boer War, typhoid fever from dust in 275-276 flies in 436 Books, bacillus tuberculosis on 241 scarlet fever from 215 Boophilus annulatus and cattle fever 112 Botryomycosis 366 Bovine tuberculosis bacillus may infect man 353-354 Bread, bacillus diphtherias in 26 Brill's disease 409 Broad Street well 316-317, 325 Brush, bacillus diphtherias on 240 Bubonic plague, see Plague. Butter, a source of diphtheria 350 bacillus tuberculosis in 364-365 typhi in 16 life of bacillus diphtherias in 251 Calliphora erythrocephala 428 Camps, bacillary dysentery in . . . . 183 INDEX 455 Camps, filthy condition of 180 typhoid fever in 170-171, 435-437 Caps and gowns to prevent infection 218 Carbolic acid in well water 324 Carriers a recent discovery 33, 38 source of protozoan disease 126 and mild cases, number of 124-125, 133-135 cause cattle fever 112 cerebro-spinal meningitis 74-81 cholera .65-67, 185 diphtheria 94-99 glanders 99 malaria 114-115 nagana 113 typhoid fever 47-54 definition of and classification of 38-39 during incubation 39 evidence against 55 of infectivity 127-131 explain spread of cerebro-spinal meningitis 78-81 in bacterial diseases 127 in institutions 50-52, 65, 67 infect food 47-51, 60, 65 milk 52-54 intermittent excretion in 46, 62 laboratory evidence of 123 less infective than the sick 155 more dangerous than things 225 not always dangerous 129 of amebic dysentery 118, 183 bacillary dysentery 67-69 bacillus pullorum 71 cattle fever 112 cerebro-spinal meningitis 72-81 cholera 61-67 diphtheria, importance of 149-152 dourine 113 glanders 99 gonorrhea 102 influenza 99 lepra bacilli 105 malaria 114-115 measles Ill Mediterranean fever 72 nagana 113 paratyphoid fever 58-61 plague 69-71 pneumococcus 101-102 poliomyelitis ', 118-121 pus organisms 105-106 scarlet fever 109 sleeping sickness 115-116 smallpox 109-110 tetanus bacilli 106 456 INDEX PAGE Carriers of tubercle bacilli 103-105 typhoid fever : 38-55 among different classes 39-44 cannot be isolated 152 duration of infection 45 Vincent's angina 117 relation to inactivity 125 shade into missed cases and atypical cases 130-131 virulence of germs in 126 Cartridges, bacillus tetani in 226 Cattle fever 112, 122 Celery, typhoid fever caused by 379 Cerebro-spinal meningitis an accident of infection 81 carriers of 73-81 explain spread of 78-81 contagiousness of 79-80 due to pneumococcus 81 infection by carriers 74-81 isolation a failure in 81, 146 path of infection 73 prompt isolation in, a success 146 secondary cases 79-80 Charbon symptomatique 4 Charts, bacillus tuberculosis on 241-242 Chicken pox air-borne 270, 280 Chicks, white diarrhea of 71 Children not cleanly 190 Cholera and contact 184-185 flies 420, 430 fomites 215 atypical cases 65 caused by washing soiled linen in running streams 325 from betel nut 185 carriers 65-67, 185 clothing 215 handling food 185 rags 222 shellfish 374 soil 2& unrecognized cases 20, 65 water 325-326 wells 325-326 infection of nurses 185 not dust-borne 289-290 on shipboard due to infected water 326 outbreaks in various places 20 spirillum, see Spirillum cholerae. Christmas presents, diphtheria from 215 Cimex lectularius, see Bedbug. Citellus beecheyi 413 Clams, typhoid fever from 375 Clay, bacillus diphtherias in 233 Cleanliness, education in, needed 208-209 municipality should encourage 210-211 INDEX 457 PAGE Cleanliness, neglected 206-208 rare 178-180 in children 190 teaching of, in school 209-210 versus disinfection 257 Cloth, yellow fever from 213 Clothing as fomites 216 bacillus tuberculosis on 242 cholera from 215 infection by, rare 217-219 leprosy in 216 scarlet fever not from 217 typhoid fever from 219 typhus fever not from 216-217 Coat, bacillus diphtheriae on 227 scarlet fever from 215 Cockles, typhoid fever from 375-376 Cockroaches and disease 418 Colon bacillus, see Bacillus coli communis. Communion cups, bacillus tuberculosis in 195 individual, adopted 210 Conductors not infected by money 224 Connorrhinus 403, 404 Contact by drinking cups 189-190, 192-193 chief mode of infection 195-206 indirect, vehicles for 188-190 infection and fingers 188-189 disregard of 207-208 importance of 206 in amebic dysentery 183 bacillary dysentery 183-184 cerebro-spinal meningitis 73-74, 76-77, 80 cholera 184-185 diarrhea 185 diphtheria 196-202 gonorrhea 165-167 influenza 277 measles 199 Mediterranean fever 312 scarlet fever 196-202 syphilis 164, 167-169 tuberculosis 204-205 typhoid fever 17, 47-50, 169-183 amount of 177-178 evidences of . 177 in civil life . 171-173 in hospitals 198-202 opportunities for 179-180 role of privies 180-182 Spanish war 170 why disregarded 179-181 uncinariasis 186 less easy in some diseases than in others .... 187-188 most obvious 164 458 INDEX PAGE Contact infection, opportunities for 190-192 mode of infection between families 196-198 with missed cases, importance of 190-192 well carriers, importance of 191 Contacts, diphtheria carriers among 89 typhoid carriers among 43 Contagiousness, factors involved 153-155 less outside family 154-155 than believed 153-155 of carriers less than that of sick 155 Convalescents, cholera spirilla in 61-65 diphtheria bacilli in 84, 85 dysentery amebse in 118 bacilli in 68-69 malarial parasites in 114-115 meningococci in 74-77 plague bacilli in 70-71 pneumococci in 101 typhoid bacilli in 40-41 Cornet, diphtheria from 215 Cotton goods, bacillus pestis on 228 smallpox from 214 Cow dung, bacillus pestis in 23 Cows, diphtheria in 347 scarlet fever said to occur in 346-347 Crawfish and typhoid fever ' 378 Cream, typhoid fever from 349 Cubicles for isolation in French hospitals 198-200 Culex, experiments with 383 f asciatus and yellow fever 392 fatigans and dengue 410 filariasis 399 Culicides 388-389 mosquito destruction by 390, 397 Culture method of diagnosis, introduction of 137-138 Cups, bacteria on 192-193 Danysz rat virus carried by flies 424 Dead animals, bacillus typhi in 8 bodies, spirillum cholerae in 19 Dengue transmitted by mosquitoes 409 Dermacenter andersoni 412 Diarrhea, bacteria which cause 367 due to condensed milk 368-369 contact 185, 367 dust 276-277 flies 431-435 milk 366-369 not always 185 water 327-329, 331, 334 explosive outbreaks 369 nature of 366-367 prevention of 369-370 INDEX 459 PAGE Diarrhea, relation of feeding to 367-369 white, of chicks 71 Diphtheria, atypical 92-94, 133 bacillus, see Bacillus diphtherise. carried to homes by discharged scarlet fever cases ... 98 carriers, importance of 149-152 isolation of, often impossible 150-152 chronic , 99 cultures introduced 137-138 value of findings 84r-85 disinfection unnecessary after 247-250 extension in dwellings 197-198 family infection 89-90 from butter 350 carriers 95-99 Christmas presents 215 comet 215 drinking glass 192-193 fomites 215-227 milk 96-97, 346-347 pitcher. 97 sewer air 273 teacher 97 tools 215 in cows 347 Owatonna, Minn 144 Providence 136, 138 Willard State Hospital 144 isolation, duration in Providence 143 in institutions, failure of 143-145 principles of 149-152 mild cases found by cultures 138 not air-borne in hospitals 273-274 dust-borne 290 from soil 28 of extra-corporal origin 29 similarity to scarlet fever. 106-107 warning sign in 151 with recurrent ear discharge causes infection 98 Disease rarely carried by physicians 217 Dishes, bacillus tuberculosis from 195 Disinfection, American views on 256 desirable at times 256-257 English views on 255-256 French views on 255 in Providence 137 abandoned 247-252 schools 254 objections to 257 of little value 247-256 unnecessary after diphtheria 247-250 in other diseases 252-254 scarlet fever 250-252 versus cleanliness 257 460 INDEX PAQB Dog drinks from the drinking glass on train 190 Dourine, carriers of , 113 Drainage, mosquito destruction by 390 Dresses, bacillus tuberculosis on 194 Drinking cups, contact infection by 189-190 glass, bacillus diphtheriae on 192 common, abolished 210 Droplet infection 295-298 Droplets, bacillus influenzas in 298 leprse in 297 prodigiosus in 295-297 tuberculosis in 295-296 pneumococcus in 298 streptococcus salivarius in 297 versus dust 303-305 Drying, effect upon bacteria. 231-232, 288-289 resistance of bacillus diphtherias to 233, 290 dysenteriae to 234 influenzae to 238 pestis to 235-236, 290-291 tuberculosis to .... 234-235, 241-242, 291 typhi to .- 232-233, 290 gonqcoccus to 239 meningococcus to 238-239 micrococcus of Mediterranean fever to 233 pneumococcus to 238 protozoa to 242 pus-forming bacteria to 236-237 smallpox virus to 244 spirillum choleras to 237-238, 242, 291-292 spirochete of syphilis to 239 spores to 232 vaccine virus to 242-244 Dust, anthrax spores in 227 bacillus coli communis in 294 diphtheriae in 290, 294 pestis in 290-293 tuberculosis in 292-293 typhi in 290 danger from slight 294-295 infection 288 meningococcus in 289-290, 293 micrococcus melitensis in 21, 300 pneumococcus in 293-294 pus organisms in 294 streptococcus in 282 versus droplets 303-305 Dust-borne disease 288-290 anthrax 285-286 diarrhea 276-277 influenza -. 277 Mediterranean fever 312 poliomyelitis 278 tuberculosis 288, 291-293, 301-311 INDEX 461 PAGE Dust-borne disease, typhoid fever 275-276 Dwellings, extension of diphtheria in 197-198 scarlet fever extension in 196-197 Dysentery, see Bacillary dysentery. amebic 118, 183 due to chronic carriers 183 infection from bedpan 183 produced in men by amebae grown in culture . 24 monkeys by amebse 24 transmitted by contact 183 bacillus, see Bacillus dysenteriae. due to flies 430-431 infection by water 326-329, 331 Ear discharge causes diphtheria 98 Elephantiasis 399 Endemic diseases 29-30 English hospitals 139-142 isolation in 200-202 Entameba coli and entameba histolytica, distinction between. . .24, 118 Erysipelas from rags 222 Family, carriers in, cerebro-spinal meningitis 75 diphtheria 89 infection of, in house 28, 196-198 isolation in 160-161 typhoid fever by contact in 176 Feces, bacillus dysenteriae in 24 paratyphi in 16 typhi in. 9, 35-36 persistence of 10 intermittency of 46-47 hookworms in 187 spirillum choleras in 19 Filaria bancrofti 398 Filariasis and mosquitoes 398-399 Filth theory of disease 27 Filtration of water 338 reduces typhoid fever 321 Fingers and contact infection 188-189 Fish, infection by fried 278 Fishermen, influenza among 277 Fleas and anthrax 417 plague 23, 312-313, 413^16 bacillus pestis in 236, 414-415 Flies a nuisance 445-446 and anthrax 419 cholera 430 diarrhea 431-435 dysentery 430 Egyptian ophthalmia 419 murrina 429 plague 419, 424 tuberculosis . . 429 462 INDEX Flies and typhoid fever 169-171, 182-183, 435-445 epidemiological evidence 442-445 evidence against theory . . . . 440-441 reports of outbreaks 435-439 statistical evidence 439-445 bacillus tuberculosis in 422-423 carry bacillus anthracis 419, 423 diphtherise 423 dysenterise 423 prodigiosus 425 typhi 420-422 Danysz rat virus 424 fecal bacteria 425-427 germs 419-437 gonococci 424 lime from privies 425 poliomyelitis 427 spirillum cholerse 420 control of 445-447 difficult to infect by 425 habits bring them in contact with excrement 438 infected, in typhoid houses 421-422 local variation in distribution 435, 445 mechanism of infection 424 range of flight 427 reduction of and decrease of typhoid fever 442-444 seasonal and local distribution 427 species in houses 428 tuberculosis due to 429 Flock cough from rags 222 Floors, bacillus pestis not on 235 tetani in dirt of 239 Fly specks, bacillus tuberculosis in 422-423 Fomites: Bagging 213 Ballast 213 Barbers' utensils 168 Barracks 76, 216 Bedding 168, 214 Blankets 227 Books 215, 241 Brush 240 Cartridges 6, 226 Charts 241, 242 Christmas presents 215 Clay 233 Cloth 213 Clothing 169, 215-216, 219, 242 Coat 215, 227 Communion cups 195 Cornet 215 Cotton 214 Cotton goods 228 Cups 192-193 Dentists' tools 168 INDEX 463 Fomites: Drinking glass 168, 189-190, 192-193, 195, 240 Floors 235, 239 Furniture 241 Gelatine 6, 226 Glass blowers' tubes 168 Grain 213 Hair 215, 226, 227 Handkerchief 168, 234, 240, 293 Hides 226,227 House, see Room. Lamp wick 6, 226 Letters 215 Linen, soiled 175, 214, 240 Lumber 214 Mattress 213 Merchandise . 213 Mirror 240 Money 168, 223, 224 Napkin rings 195 Nursing bottles 168 Oyster buckets 213 Pencils 168, 193, 233 Pins 168 Pitcher 97 Rags 169, 222 Railway carriages 292 Roller towel 210 Room 214, 216, 219-222, 233, 235, 241, 292, 294 Rugs 223 Shawl 409 Shoes 218, 240 Spirometer 241 Spoons> etc 168 String 168 Surgeons' instruments 168 Telephones 195, 241 Thermometer 174 Tools 215 Toys 240 Tramcars 292 Wind instruments 168 Wool 226, 227 Fomites and anthrax 226-227 cholera 215 diphtheria 215, 227 plague, experiments in India 246-247 observations in Sydney 245-246 scarlet fever 214-215 smallpox 214 tetanus. 225-226 tuberculosis, lack of experiments 247 typhoid fever 227 typhus fever 216-217, 409 yellow fever 213-214, 394 464 INDEX PAGE Fomites and yellow fever experiments in Havana 245 bacillus diphtheria? on 240-241 tuberculosis on 241-242 bacteria of suppuration on 25 on 239-240 clothing as 216 conclusions concerning 258 definition of term 212-213 evidence of infection by, unsatisfactory 224-225 infection, bacteriological evidence 230-231 evidence against 229-230 few instances of 228 reasons for belief in 228-229 thought important 137 Food, carriers infect 47-51, 60, 65 handling by contacts 162-163 infection and cholera 185 tuberculosis 364, 372-373 typhoid fever 169-170, 364, 374-379 poisonings 38, 60, 371-372 spirillum cholerae in 20 Foot-and-mouth disease and milk 366 French hospitals 198-200 "Antisepsie medicale" in 198 cubicles for isolation in 198-200 screens for isolation in 198-200 Furniture, bacillus diphtherias on 241 Gall stones and typhoid fever 36, 42 Gelatine, bacillus tetani in 6, 226 Glanders, carriers of 99 Glands, bacteria of suppuration in . . 25 cervical and mesenteric, bacillus tuberculosis in 203 Glass, bacillus diphtherias on 192, 240 tuberculosis on 195 contact infection by drinking from 189-190 Glossina morsitans 113 palpalis 115, 399-401 Goats and Mediterranean fever 21, 72, 365 Gonococci carried by flies 424 Gonococcus, not saprophytic 26 resistance to drying 239 Gonorrhea, air-borne infection not possible 166-167 believed to be spread by contact 164-167 carried by nurses 166-167 in Babies' Hospital. 165-166 infection by f omites impossible 166-167 latency of 102-103 not dust-borne 289 persistence of 102-103 Gown and cap for physicians and nurses in contagious cases. ... 218 Grain, yellow fever from 213 Ground squirrels and plague 413 Guinea pigs, bacillus pestis in 69-70 INDEX 465 PAGE Hair, anthrax spores in 226-227 scarlet fever from 215 Handkerchief, bacillus diphtherias on 240 tuberculosis on 234, 293 Hands, bacillus coli communis on 179, 192 tuberculosis on 193-194 pus bacteria on 192-194 should be washed 179-180 Hazens theorem 329 Hides, anthrax spores in 226-227 Holy water, bacillus diphtherias in 192 Homalomyia canicularis 428 Home isolation effective 160 Hookworms, see Uncinaria, Anchylostoma 186-187 enter through skin 187 grow in soil 186 in feces. 187 Hospital isolation, failure of 139-142 in 161 Hospitals, air-borne disease in 270-271, 279-280 bacillary dysentery in 183-184 contact infection in ' 198-202 diphtheria not air-borne in 273-274 in America 142-145 England 139-142 France 198-200 scarlet fever, not air-borne from 272-273 smallpox, air-borne infection from 260-270 typhoid fever by contact in 173-174 value of 160 House, infection from family to family 28 of, cause of scarlet fever 214-215 tuberculosis infection in 205, 220-222 Houses, species of flies in 428 Ice, bacillus typhi in 13, 319, 341-342 infection by 339-342 Ice cream, a source of disease 349-350 control of 350 Incubation stage infective 39-40 Infection, former theories of 1 not so easy as believed 84, 153, 191-192 Influenza among fishermen 277 lighthouse keepers 277 atypical cases 99 bacillus, see Bacillus influenzae. from rags 222 not air-borne .; 277 carried across Atlantic 277 dust-borne 277, 289 spread only by contact 277 Inhalation of bacteria 304-305 Insect-borne disease usually due to protozoa 380-381 Insects as biological and mechanical carriers 380-382 466 INDEX PAGE Insects carry germs on bodies 418 first proof of transmission of disease by 381-382 infection by, importance of subject 380 Texas cattle fever first disease proved to be carried by. . 381-382 Institutions, carriers in 50-52, 65, 67 Intermittent excretion in carriers 46, 62, 68, 76, 98 Isolation a failure in cerebro-spinal meningitis 146 measles 145-146 smallpox 147 causes of failure 147-149 duration of 160-162 effective if prompt 146, 157-158 in Michigan 156-158 rare diseases 158-159 hospitals, failure of 139-142 in American cities 142-145 English hospitals 200-202 family 160-161 effective 160 hospital 161 Monsall Hospital 200-202 Providence 136, 160 villages. . .155-158 not effective in extensive outbreaks 158 to be too strict 151-152 of cerebro-spinal meningitis 146 diphtheria 136, 137-139, 143, 149, 156 duration in Providence 143 malaria 388 measles 145, 156 plague 415 rare diseases 158 scarlet fever 136, 139, 156 school children 162 sleeping sickness 401 smallpox 139, 147, 156 typhoid fever 152, 156 wage earners 152, 162-163 yellow fever 393 should vary 155 too rigorous 152-153 useless if many carriers 159 value of 151-152 Jews do not eat shellfish 376 Kala-azar and insects 402 Kissing means of spread of tuberculosis 202-203 spreading syphilis 168 Laboratory infection, bacillary dysentery 183-184 typhoid fever 175 tuberculosis infection in 308-309 Laniblia.. 112 INDEX 467 Lampwick, bacillus tetani on 6, 226 Latency of infection common 106, 122 Laundress contracts smallpox 214 typhoid fever 175 Laundries and disease 218-219 tuberculosis 219 Leishmania donovani 402 tropica. . . 404 Leprosy, bacilli remain latent 105 in clothing 216 isolation of 156 Letters, scarlet fever from 215 Lettuce, bacillus typhi on 8 Lice and relapsing fever 412 typhus fever and 405-409 Light, bacillus tuberculosis perishes in 234-235 Lighthouse keepers, influenza among 277 Linen, soiled, smallpox from 214 typhoid fever from 175, 219 Lockjaw, see Tetanus. Lucilia csesar or "blue-bottles" 428, 437 Lumber, smallpox from 214 "Lung Blocks" in New York 220-222 Lupus due to inoculation with saliva 203 Malaria, an endemic disease 29-30 and insects 382-392 water 384 anointing the skin in 389 clearing of space about dwellings 389 discovery of insect transmission 382-383 experiments on infection of human beings 383 isolation sometimes necessary 388 killing of mosquitoes in houses 388 latency of 1L3-115 explanation 114-115 in children 114-115 percentage of 114-115 mosquito sole carrier of 383-385 not air-borne 384 due to soil infection 30 from water 335-336 on ship Argo 335 screening of patients 388 success of mosquito destruction 390-391 ways of prevention 386-390 Malta, Mediterranean fever exterminated at 72 Malta fever, see Mediterranean fever. Mattress, yellow fever from 213 Measles an air-borne disease 278-280 carriers of Ill disinfection after 253 isolation in, a failure 145-146 not from soil. . 28 468 INDEX PAGH Measles, number attacked Ill per cent of children attacked 145 Meat and tuberculosis- 372-373 infection by 371-374 inspection, federal control of 373-374 Mechanical carriers distinguished from biological carriers. ...... 413 Mediterranean fever an endemic disease 21 and contact infection 312 dust 312 goats 21,72,365 caused by milk from infected goats 21, 365 experiments in infection by air 311-312 exterminated at Malta 72 goats carriers of 72 human carriers of 72 in United States 365 micrococcus of, resistance to drying 233 on a steamship 72 spread by urine 22 Membrane, bacillus diphtherias in 240 Meningitis, cerebro-spmal, see Cerebro-spinal meningitis. Meningococcus causes rhinitis 73 found intermittently 76 only near sick 77 in ah* 77 contacts 73-74, 76-77, 80 dust 289-290,293 families 75-80 normal nose 73 nose in sickness 72 infection in barracks . . . 76 not saprophytic 26 persistence of infection 7475 resistance to drying 238-239 Merchandise, yellow fever from 213 Michigan, isolation effective in -. 156-158 Micrococcus albus 24 aureus 24 citreus 24 melitensis, discovery and study of 21 in dust 21, 300 resistance to drying 233 saprophytic existence of 21 meningitidis, see Memingococcus. pneumoniae, see Pneumococcus. Mild cases of infectious disease not recognized 134135 Milk and disease 342-370 bacillus diphtherias in 25-26 dysenteries in tuberculosis in 355^356 typhi in 15-17 carriers infect 52-54 classification of 363 condensed and diarrhea 368-369 INDEX 469 PAGE Milk, diarrhea from 366-369 diphtheria from 96-97, 345-346 foot-and-mouth disease from 366 handling by contacts 162-163 increase of bacillus typhi in 17 infection by water 323 from human sources 347-348 Mediterranean fever from 365 mode of infection of 347-348 outbreaks, characteristics 342-343 few in large cities 344-345 frequency of 343-344 source of infection 346-347 pasteurization of 348-349 protection against tuberculosis from 362-363 of 348-349 rabies from 366 scarlet fever from. ; 346-349 spirillum cholerae in 19 sterilization of vessels 348 streptococcus in 352 tonsillitis from 351-352 tuberculosis from 354-362 amount of 356-362 epidemiological evidence 361-362 instances of 360 tuberculous, consumed by children 357-360 typhoid fever from 51-54, 343-345 Mills-Reincke phenomenon 329-335 Miners, typhoid fever among 182 Minnesota, smallpox isolation abandoned in 147 Mirror, bacillus otiphtheriae on 240 Missed cases a recent discovery 33 Moist surfaces, bacteria not given off from 287-288 Money and disease 223-224 i bacteria on 223-224 Monkeys, dysentery in 24 Monsall Hospital, isolation in 200-202 Montana, smallpox isolation abandoned in 147 Mosquito destruction by culicides 390, 397 drainage 390 oiling 390 prevention 389-391 Mosquitoes and dengue 409-410 filariasis 398-399 malaria * 382-383 conditions for carrying 385-386 yellow fever 392-398 destruction of 397 habits 395 destruction of, in malarious houses 388 habits of 385 species which carry malaria 382-383, 385 success of measures for extermination 390-391 470 INDEX Mosquitoes, transportation of 395 Mouth, bacillus tuberculosis in 103-104, 193 pneumococcus in 101-102 Mucous surfaces, bacteria of suppuration on 24 Mud dumped near intake cause of typhoid fever 320 Municipal versus personal prevention 208 Murium typhi, bacilli of, carried by ants. 419 Murrina, flies and 429 Musca domestica (see Flies) 418, 428, 437 Muscina stabulans 428 Mussels, infection by 375-377 Myzomyia ludlowii 385 Nagana 113 Night soil as a fertilizer 9 North Boston well 317 Nose, bacillus tuberculosis in 103-104, 193, 299 meningococcus in, in sickness 72-73 in normal 73 tuberculosis of 204 Nurses, gown and cap for, in contagious cases 218 infect patients with typhoid fever 174 typhoid fever among 173-174 Oiling, mosquito destruction by 390 Ophthalmia, Egyptian, carried by flies 419 Opilacao due to connorrhinus 403 Opsonic index in typhoid carriers 42 Oriental sore and insects 404 Ornithodorus moubata 411 Otitis, bacillus diphtherias in 94-95 Owatonna, Minn., diphtheria in 144 Oyster buckets, yellow fever from 213 Oysters, bacillus typhi in 14 "fattening" of 377 infection by 374-378 Pail-closets cause typhoid fever 181-182 Pappataci fever and insects 404 Paratyphoid bacilli, see Bacillus paratyphi. fever 58-61 Pediculis vestamenti and typhus fever 405-409 Pellagra and insects 403 Pencils, bacillus diphtherias on 193, 233 bacteria on 192-193 Personal versus municipal prevention 208 Persons, not things, are dangerous 225 Phlebotamus. 404, 405 Physicians, gown and cap for, in contagious cases 218 rarely carry disease 217 Pigment to lungs from stomach 306 Piroplasma bigeminum 112, 381-382 Placards for contagious diseases 151 INDEX 471 PAGE Plague, air-borne 281 and bedbugs 414 fleas 23, 312-313, 413-416 epidemiological evidence 414-415 experimental work 414-415 flies 419,425 fomites, experiments in India 246-247 observations in Sydney 245-246 ground squirrels 413 other rodents 413-416 rats 23, 6^-70, 413-416 rugs 223 atypical and chronic in animals 69-70 human 70 bacillus, see Bacillus pestis. experiments in infection by air 312-313 isolation of 415-416 not dust-borne 289-290 Plasmodium 113, 384-385 Pneumococcus cause of meningitis 81 in air 300 convalescents 101 droplets 298 dust.. 293-294 normal mouths 101-102 may be air-borne 289 not dust-borne 290 saprophytic 26 persistence of 101 resistance to drying 238 virulence of, in carriers 101-102 Pneumonia and water 333 Poisoning by food 371-372 Poliomyelitis a dust-borne disease 278 atypical cases 121-122 carried by flies 427 carriers of . . : 118-121 Privies and water-closets usually filthy 179-180 encourage uncleanliness 182, 211 infect water supplies 320 removal of, causes decrease of typhoid fever 181-183 typhoid fever from . 169-170, 179-183 Privy vaults, bacillus typhi in 9-10 Prosodemic infection, typhoid fever by 172 Prostatic fluid, bacillus typhi in 37 Proteosoma in birds 383 Protozoa, difficult to cultivate 27 not saprophytic 26 resistance to drying 242 Protozoan disease, carriers a source of 126 latency in 111-112 Psocidse and disease 418 Pulex irritans 414 Purification of water 338-339 472 INDEX PAGE Pus bacteria 24 distribution of 240 in air 299-300 dust 294 glands 25 schoolrooms 294 skin and mucous surfaces 24 tonsils 24 water 25 may be dust-borne 289-290 on fomites 25 resistance to drying 236-237 saprophytic existence of 24-25 Quarantine and sleeping sickness 401 yellow fever 396 Quinia prevents malaria , 386-388 Rabies from milk 366 Radishes, bacillus typhi on 8 Rags and disease 222-223 cholera from 222 erysipelas from 222 flock cough from 222 influenza from 222 scarlet fever from 222 septicemia from 222 smallpox from 222-223 typhoid fever from 222 Railway carriages, bacillus tuberculosis in 292 Rat-proofing of buildings 416 Rats and plague 23, 69-70, 413-416 carriers of plague 70 chronic plague in 69 destruction of 416 Relapsing fever and bedbugs 411-412 lice 412 ticks 410-411 infectious during afebrile period 116 types and parasites 116 Resistance of bacteria less in cultures 11 Rhinitis, bacillus diphtheriae in 94-95 caused by meningococcus 73 Rhode Island, death rate from typhoid fever 18 Rice, spirillum choleras in 20 Rocky Mountain fever and ticks 412 Rodents, plague derived from 413-416 Roller towel, bacillus coli communis on 192 should be abolished 210 use of, forbidden 211 Room, bacillus diphtherias in 233, 241 tuberculosis in 235 infection cause of typhoid fever in barracks 216 Rooms, infection of 205, 214-215, 219-222 INDEX 473 Rubella, air-borne 280 Rugs and plague 223 Saliva, inoculation with, cause of lupus 203 transfer of 189 vehicle of infection 188-190 Sarcophaga 428 Scarlet fever, air-borne 270-273 out of doors 272-273 and books 215 clothing 217 coat 215 fomites 214-215 house infection 214-215 letters 215 milk 346-347 rags 222 atypical. 107-109 disinfection unnecessary after 250-252 due to ice cream 350 extension in dwellings 196-197 hospital temporarily closed in Leicester 141 hospitals in England 139-142 in cows. 346-347 in Providence 136 like diphtheria 106-107 not air-borne from hospitals 272-273 from soil 28 virulence varies hi 140 Scenopinus fenestralis 428 Schizotrypanum cruzi 404 School children, isolation of 162 disinfection 254 teaching cleanliness in 209-210 Schoolrooms, bacillus coli communis hi 294 pus organisms in 294 Screening for protection against malaria 388 of cases of malaria 388 yellow fever 396-397 Screens for isolation in French hospitals 198-200 Sedgwick, typhoid fever outbreak in Bondville, Mass 169 Seltzer water, bacillus typhi in 13 Seminal vesicles, bacillus typhi in 37 Septic infection and insects 417418 tank effluent, bacillus typhi in 10 Septicemia from rags 222 Sewer air and bacteria 284-285 diphtheria 273 typhoid fever. 274-275 bacillus prodigiosus in 284 typhi in 284 infection by 297, 299 Sex of smallpox cases 267 Sheet hung before door to prevent infection 282 474 INDEX Shellfish, infection by 374-378 Shipboard, influenza on 277 malaria on 335 typhoid fever by contact on 176 Ships for smallpox hospitals 262-263 Shoes as carriers of infection 218 bacillus diphtherise on 240 Shuttle, infection from 192 Sidewalks, virulent bacilli tuberculosis on 194 Simulium 403 Skin, bacteria of suppuration in 24 hookworms enter through 187 Sleeping sickness, an endemic disease 30 and tsetse flies , 399-^01 atoxyl to prevent 402 discovery of trypanosome 399400 in lower animals 400 is it carried mechanically? 400-401 modes of transmission 399-401 not due to soil infection 30 per cent of carriers 115-116 persistence of infection 115-116 prevention of 401-402 quarantine '. 401 Smallpox, air-borne, conclusions . 269-270 evidence against 266-269 infection of, denied 263-270 in United States 264-265 objections to theory 265-266 sex of cases 267 and fomites 214 rags 222-223 atypical cases . 109-110, 133 carriers 109-110 hospital ships 262-263 isolation in, often a failure 147 mild cases of 109-110 not from soil 28 virus, resistance to drying 244 Soft drinks, bacillus typhi in 13 Soil, amebse dysenteriae in 24 bacillus cliphtherise in 26, 28 dysenteriae in 23 pestis in 22 tetani in 239 typhi in 7, 10 hookworms grow in 186 infection, cholera from 29 in common diseases 28 typhoid fever from 29 melitensis micrococcus in 21 not infected with cattle fever 30 malaria 30 measles 28 INDEX 475 Soil, not infected with scarlet fever 28 sleeping sickness 30 smallpox 28 Texas cattle fever 30 yellow fever 30 spirillum cholerae in 19-20 Sore throat and milk 351-352 Spanish- American War, typhoid fever in 17, 56, 435 from dust in 275-276 flies 435-436 Spirillum cholerae carried by flies 420 found in water 326 grow only in human body 20 in convalescents 61-62 cooked food 20 dead bodies 19 feces 19 gall bladder 62 healthy persons 62-65 milk 19 soil 19,20 water 19 intermittent excretion 62 resistance to drying 237-238, 242, 291-292 saprophytic existence of 19 Spirocheta carteri 116, 412 duttoni 116, 411 Spirochete of syphilis, latency of 116 not saprophytic 26 resistance to drying 239 Spirometer, bacillus diphtheriae not on 241 tuberculosis not on 195 Spitting should be forbidden 211 Spores may be dust-borne 290 resistance to drying 232 Springs as sources of infection 324 Sputum, bacillus pestis in 71 typhi in. . 37-38 Squirrels, see Ground squirrels (Citellus beecheyi). Stamp out disease, failure to 135-136 Stegomyia calopus .392, 395, 405 Sterilization of municipal water supplies . 339 Stomach, bacillus tuberculosis may pass to lungs from 305-308 Stomoxys calcitrans 428 Storage of water 338 Street dust, bacilli tuberculosis not found in 292 Streptococcus enteritidis, cause of diarrhea 367 in dust 282 milk 352 may be air-borne 289 py9genes 24 salivarius in droplets 297 Suppuration, bacteria of, in healthy organs '. 105-106 latency of bacteria of 105-106 476 INDEX Suppuration, result of infection by bacteria 24 Surgery, air-borne infection in 283-284 Swine infected by bacillus tuberculosis through the tonsils .... 203-204 plague bacilli in air 300 Syphilis, air-borne infection not possible 167 articles infected with 168-169 believed to be spread by contact 164-169 droplet infection in 167 fomites infection in, not important 169 infection by kissing 168 non-sexual contact 168-169 latency of 116 not persistent 168-169 sexual act chief mode of infection 168 spirochete of, see Spirochete of syphilis. spread solely -by contact 167-168 Tabanus lineola 3 Teacher caused diphtheria 97 contracts diphtheria from pupil 98 Telephones, bacillus diphtherias not on 241 tuberculosis on 195 Tetanus and fomites 225-226 bacillus, see Bacillus tetani. decrease of, in Havana 226 from lamp wick used for tying umbilical cord 5, 226 in Red Bank, N. J 5 on Long Island 5 Texas cattle fever, an endemic disease 30 carried by tick 112 first disease proved to be carried by insects . 381-382 riot due to soil infection 30 persistence in blood 112 Thermometer transfers bacillus typhi 174 Things not so dangerous as persons 225 Ticks and relapsing fever 410-411 Rocky Mountain fever 412 Texas cattle fever 112, 122, 381-382 Tidal mud, bacillus typhi in 8 Tongue, bacillus tuberculosis on 203 Tonsillitis and milk 351-352 Tonsils, bacillus tuberculosis in 203-204 typhi in. 34 bacteria of suppuration in 24 tuberculosis infection through 306 of 204 Tools, diphtheria from 215 Towel, see Roller towel. Toys, bacillus diphtheria on 240 Tramcars, bacillus tuberculosis in 292 Treasurer of United States, investigation of money as carrier of disease by 224 Treponema pallida in gummata 116 life of, short 167, 169 INDEX 477 PAGE Trier, typhoid fever in 17, 57 Trypanosoma bruccei 113 equiperdum 113 gambiense 115, 399-401 Tsetse flies and sleeping sickness 115, 399-401 nagana 113 Tuberculosis and flies 429 fomites, lack of experiments 247 laundries 219 meat .272-273 bacillus, see Bacillus tuberculosis. bovine, eradication of 364 contact infection in 204-205 experiments concerning air-borne infection 301-311 feeding experiments 354-355 from flies 429 house infection 220-222 milk 354-368 amount of 356-362 epidemiological evidence 361-362 instances of 360 protection against 362-363 shuttle 192 water. ;: 332-333 human and bovine reciprocally infective 353 infection by air 194, 202-203 dust questioned 302-303 in the home 205 stomach 305-308 experiments under natural conditions. . .309-311 in alimentary tract 203-204 animals through mouth and pharynx 204, 306 laboratory 308-309 unnatural conditions of experiment 308 mode of infection, evidence from pathology 205 of the nose 204 t9nsils 204 proportion of human and bovine types of bacillus 360-361 spread by animals licking one another 204 kissing 202-203 through tonsils 204, 306 Tuberculous milk consumed by children 357-360 Typhoid bacillus, see Bacillus typhi. carriers 18, 38-55, 180 cannot be isolated 152 cause disease. 47-54 inf ective during incubation stage 39-40 number of 180 opsonic index in 42 percentage of 40-44 feces in yard 170, 173, 182 fever among nurses 173-174 an infection of the blood 34-35 and gall stones 36, 42 478 INDEX Typhoid fever and high temperature 374-375 tonsillitis 34 atypical 56-59 believed to be an intestinal disease 178 by bathing. 324-325 contact 17, 47-51, 169-183 in an almshouse 175 civil life 171-173 hospitals .' 173-174, 436 South Africa 171, 436 Spanish War 170-171, 435-436 the family 176 on shipboard 176 food infection 169-170 prosedemic infection 172 carriers of, among different classes 39-44 duration of infection 45 causes of excess in cities 321 contact outbreaks in cities 172-173 contracted by laundress from soiled linen 175 death rate in Rhode Island 18 decreases with removal of privies 181-183 filthy habits cause of 170, 173, 182 from bedbugs 418 celery 379 clothing 219 crawfish 378 cream 349 dust 275-276 flies 169-171, 182-183, 435-447 correlated decrease 442-444 seasonal distribution 439-442 statistical evidence 439-445 fomites 227 handling typhoid cultures 175 ice cream 349-350 infected bedding 175 milk : 51-54, 345-346 mud dumped near intake 320 pail closets 181-182 privies 169-170, 179-183 rags 222 sewer ah- 274-275 shellfish 374-378 soil infection 29 soiled linen 219 springs 324 thermometer 1?4 unrecognized cases 133 water 317-325 watercress 378-379 wind blowing sewage to water works 320 houses, infected flies in 421-422 in barracks due to room infection 216 INDEX 479 Typhoid fever in mines 182 soldiers' home due to contact infection from physician 175 Spanish War 17, 56, 435 Trier 17 waitress due to contact infection 175 infection stopped by strict cleanliness 174 less with water closets 181-182, 144 mild cases in Panama 57 Spanish War 56 Trier 57 not an intestinal disease 34 dust-borne 289-290 outbreaks continued by contact infection 172-173 in Providence, R. 1 18 prevalent in country 173 spread among patients by nurses 174 by kitchen help 175 waitress 175 "Typhoid Mary" 47 Typhus fever and flies 408 lice 405^09 carried in shawl 409 considered air-borne 408 from clothing 216-217 identity of strains 409 not air-borne 281 of extra-corporal origin 29 Uncinaria, see Hookworms, Anchylostoma. americana 186 due chiefly to contact 186-187 Urine, bacillus typhi in 37 persistence of 10 cause of Mediterranean fever 22 Vaccine, resistance to drying 243-244 transport across ocean 242-244 Vaginitis in Babies' Hospital 165-166 Vegetables, amebse dysenteriae on 24 bacillus typhi on 8 Venereal diseases, see Gonorrhea; Syphilis. Vincent's angina 117 Wage earners, isolation of 152, 162-163 Waitress, typhoid fever spread by 175 Warning sign in diphtheria 151 Washing soiled linen in running streams cause of cholera ^ 325 Water and cholera V325-326 diarrhea 327-329, 331 dysentery 326-329, 331 malaria. 335, 384 pneumonia , 333 480 INDEX PAGE Water and the general death rate 331 tuberculosis 332-333 typhoid fever 317-325 worms 336 yellow fever 336 bacillus typhi in 10-13, 319 recovered from 319 bacteria of suppuration in 25 closets, typhoid fever less with 181-182 filtration of 338 infection by 316-339 of 18 milk by 323 micrococcus, melitensis in 21 mode of infection with typhoid bacilli 320 municipal supplies infected 320, 326 outbreaks, characteristics 317-319 protection of 337-338 purification of 338-339 spirillum cholerae in 19 sterilization of municipal 339 storage of 338 Watercress, typhoid fever caused by 378-379 Wells, amount of typhoid fever due to 322-324 cholera infection from 325-326 conditions of safety 324 infection from 316-317, 321-325 protection of 337 White diarrhea of chicks 71 Whooping cough, air-borne 280 not of extra-corporal origin 29 Willard State Hospital, diphtheria in 144 Wind blowing sewage to water works cause of typhoid fever 320 Wool, anthrax from 227 spores in 226-227 Worms derived from water 336 Wounds, infection of , by air 300-301 Yellow fever an endemic disease 30 and bagging 213 ballast 213 cloth 213 fomites 213-214, 394 experiments in Havana 245 grain 213 mattress 213 merchandise 213 mosquitoes 293-298 oyster buckets 213 quarantine 396 discovery of causation 392-394 latent period in outbreaks 393-394 mild and atypical cases 117 mosquito destruction 397 INDEX 481 PAGE Yellow fever mosquito, habits of ^ 395 not due to soil infection 30 from water 336 preventive measures 396-397 screening of cases and houses 396-397 success of mosquito destruction 391, 395, 397-398 virus filterable . . . , 393-394 in blood.. ..393-394 7^> 570076 Engineering Library TY OF CALIFORNIA QEFARTJv.ENT OF CIVIL. ENGINEERING LEY, CALIFORNIA 1 UNIVERSITY OF CALIFORNIA LIBRARY