Issued i -i J|:= U. S. DEPARTMENT OF AGRICULTURE, 1 I BUREAU OF ANIMAL INDUSTRY. BULLETIN No. 93. - A. D. MELV1N, CHIEF OF BUREAU. 8 1 3 = iHE RELATION OF TUBERCULOUS LESIONS TO THE MODE OF INFECTION. E. C. SCHROEDER, M. D. V., Superintendent of l^.\pfrinient Station, ^ Bureau of Animal lndustr\ , 5 r0 2. AND W. E. COTTON, p 5[ Expert Assistant at Experiment Station, J~jj -i ^ection, is densely and evenly sprinkled with minute yellow areas about one-thirtieth of an inch in diameter, which are made up of aggregations of very minute necrotic points. All the surface lesions are beneath the capsule, and the number of lesions is so great that more lung tissue is involved than is left unaffected. .Microscopic examination of the little yellow areas shows the presence of innumerable tubercle bacilli. f ' Tin' liver, spleen, kidneys, stomachs, and. intestine are in apparently normal condition. The case is a perfect picture of fatal miliary tuberculosis of the lung of recent origin, with a rapidly developing infection of the lymphatic EXPERIMENTS WITH HOGS. 9 glands generally. The affection of the lung was so extensive that death was probably due directly to suffocation. The rapid character of the disease and the early fatal termination are attributable to the extreme susceptibility of this particular calf to tuberculosis. THE EXPERIMENTS WITH HOGS. The records of the three hogs are as follows: Hogs Nos. 1383, 1384, and 1385 were tested with tuberculin without reaction on April 4, 1906, and each received on April 6, 1906, an inoculation of tubercle culture, Bovine III, under the skin covering the dorsal surface of the tail just anterior to its end. The hogs were killed a little more than two months later and examined post-mortem. The autopsy records follow : Hog No. 1383. June 12, 1906, killed and examined post-mortem. At the time of death the animal seemed very much distrest and gave the impression that it would die within a few hours. General condition very good, fat, weight about 200 pounds. The seat of the inoculation in the tail, about20cm. (Sinches) from its point of attach- ment to the body, shows considerable connective tissue thickening. The superficial inguinal glands contain several small tuberculous areas. The lung is adherent to the chest wall and diaphragm, and the various lobes to each other. Sprinkled evenly over and thruout its entire substance are innumer- able tuberculous masses from 1 mm. to 1 cm. in diameter; fully one-half of the lung tissue is destroyed. The pulmonary and costal pleune and the thoracic surface of the diaphragm are thickly studded with innumerable tubercles from 1 mm. to 1 cm. in diameter. The convex surface of the liver is sprinkled with minute tubercles; a similar but less marked condition is found on the concave surface. No tubercles were found in the parenchyma of the organ. No lymph-gland disease was found in any part of the body excepting that recorded in the superficial inguinal glands. Hog No. 1384- June 13, 1906, killed and examined post-mortem. General condi- tion very good, fat, weight about 200 pounds. The tail, about 25cm. QO inches) from its point of attachment to the body, at the seat of inoculation, is somewhat thickened. On section the increased connective tissue is found to be sprinkled with a dozen or more minute necrotic foci, less than one-half mm. in diameter. One of the superficial inguinal glands contains a few tuberculous foci. The lung is adherent to the chest wall and to the diaphragm. The costal and pul- monary pleune and the thoracic surface of the diaphragm are closely sprinkled with small tubercles which vary in size from points to 3 mm. in diameter. The cephalic lobes on both sides, the entire left median lobe, the anterior and dependent portions of the right median lobe, and the anterior portions of both principal lobes are com- pletely solidified and tuberculous thruout; the balance of the lung is sprinkled evenly with innumerable tuberculous areas from 1 mm. to 1 cm. in diameter. The bronchial glands on both sides are greatly enlarged and sprinkled with a small number of very minute necrotic foci. The liver is evenly sprinkled with innumerable foci of tuberculosis, 2 mm. and less in diameter. The gastro-hepatic chain of lymph glands are enlarged and sprinkled with minute foci of tuberculosis. The spleen contains a sprinkling of tuberculous foci. Hog No. 1385. June 13, 1906, killed and examined post-mortem. General condi- tion very good, fat, weight about 200 pounds. The tail, about 20 cm. (8 inches) 13619 No. 93062 10 TUBERCULOUS LESIONS AND MODE OF INFECTION. from its point of attachment to the body, at the seat of inoculation, is somewhat thickened, and has on its lower surface a flat sore about 2 cm. in diameter. On sec- tion the thickening is found to be due to an increase in the amount of connective tissue. One of the right superficial inguinal glands is enormously enlarged, fully ten times its normal diameter, and completely tuberculous. The corresponding gland on the left side is slightly enlarged and contains a few tuberculous foci. The lung is adherent to the chest wall by a number of fine connective tissue threads. The entire organ is densely and evenly sprinkled with innumerable tuberculous masses from 1 to 5 mm. in diameter. The tubercles are so numerous that fully one- third of the entire lung tissue has been displaced by them. The liver contains about a dozen minute tubercles 1 mm. and less in diameter. Spleen contains about a dozen tubercles less than 1 mm. in diameter. No lesions of the lymph glands were found excepting those recorded for the super- ficial inguinals. THE COURSE OF THE INFECTION FROM TAIL TO LUNG. The post-mortem examinations of the three hogs and the one calf that became affected with tuberculosis show the most extensive lesions in the lung in every case. When we bear in mind that this resulted from tubercle bacilli introduced into the bodies of the animals by sub- cutaneous inoculations at the ends of their tails, we are justified in con- cluding that one of two courses was taken by the bacilli to reach the lung: (1) They were taken up b}^ the eapillaiy blood vessels and carried to the lung directly with the venous blood stream; or (2) they were taken up by the lymph radicals, past along the lymph channels by or thru the lymph glands, entered the great thoracic duct, and thru it were poured into the venous circulation. Once tubercle bacilli have entered the venous blood stream there is nothing in the way of the direct infection of the lung except, first, smooth-walled vessels of constantly increasing caliber, second, the smooth- walled chambers of the heart, and third, the smooth- walled pulmonary arteries that end in the exceedingly fine, thin-walled, com- plex capillary system of the lung, the anastomosis of which is so com- plete and the close and intricate intercommunication so frequent that it is not difficult to conceive of individual vessels in which perfect stasis may occur. The destruction of tubercle bacilli by leucocytes or phagocytes after they have entered the blood dors not require consideration in this con- nection, nor the attenuation of the bacilli by the germicidal action of the blood for various other species of bacteria. If these were factors of importance against tin- infection of an organ with tuberculosis it would have been impossible, as has been done in some of our earlier work." to demonstrate the persistence of live tubercle bacilli of an original virulence too low to cause a progressive affection in the tissues of cattle for period^ of time varying from three month- to two years. Bureau of Animal Industry Mullctin NH. A:.', 1'art III. COURSE OF INFECTION FROM TAIL TO LUNG. 11 In this connection it may be interesting 1 to give an observation made at the Experiment Station on two cows, each of which received an injection of tubercle bacilli into a quarter of her udder thru her teat in a manner special!}- devised to prevent the occurrence of a trauma. The one cow received live tubercle bacilli of low virulence and the other dead tubercle bacilli of the same strain. As a result of the injections the udders of both cows were considerably affected and secreted a cream}", slightly viscid, fluid, which contained innumerable leucocytes. The cow that received the dead bacilli recovered com- pletely in about two months, and the cow that received the live bacilli, while she made an apparent recovery in about eighteen months, con- tinues to secrete tubercle bacilli, virulent for guinea pigs at this date, four years and ten months after injection. The microscopic examinations of the secretions from the injected quarters of the udders of the two cows showed that the dead tubercle bacilli were almost invariably located within leucocytes, and that the live tubercle bacilli were rarely located in the leucocytes and almost invariably floated free in the fluid in which the leucocytes were sus- pended. Additional experiments are now in progress to determine whether this is always the case with tubercle bacilli in the udders of cattle. Relative to the course followed by the infectious material in the four tail-injected animals we have the following facts: (1) The excessive disease in the lung in all cases; (2) the presence of superficial inguinal disease in all cases; (3) the infection of the liver in the three hogs, but not in the calf; (4) the infection of the spleen in two hogs; (5) the infection of the bronchial glands in one hog and in the calf, and, (6) in addition to the infection of the lung, superficial inguinal and bronchial glands, the infection in the calf of the coccygeal, mesenteric, and mediastinal glands; and, in addition to the infection of the lung, super- ficial inguinal glands, liver, spleen, and bronchial glands in one hog, an infection also of the gastro-hepatic glands. From this we may conclude that the infectious material, after it h.al been taken up by the lymph radicals in the tail, past more or In- directly to the superficial inguinal glands, which filtered out and retained some of the bacilli. The two glands at the root of the tail in the calf evidently have a position in the lymphatic chain between the tail and the superficial inguinal glands. Whether the disease in the mesenteric glands of the calf was due to direct transmission of infec- tion to them from the seat of inoculation, or was due to bacilli coughed up from the lung and swallowed and past thru the intestinal wall, could not be definitely determined. The infection of the liver and spleen is probably secondary and followed after the infection of the lung. The less amount of disease in the livers of the hogs and its entire absence in the calf bears out this assumption. The same is 12 TUBERCULOUS LESIONS AND MODE OF INFECTION. true of the disease in the spleen, which was slightly affected in two hogs and normal in one hog and in the calf. As with our previously published experiments in which hogs received injections of virulent tubercle bacilli subcutaneously in the abdominal region," and the experiment in which hogs contracted tuberculosis thru eating artificially infected milk, 6 it is shown with these injections that tubercle bacilli may pass from portions of the body remote to the lung fairly directly to it and cause pulmonary tuberculosis. And this passage ma} 7 occur without the formation or development of a well-marked chain of lesions along the path followed by the bacilli from the point of entrance in the body to their localiza- tion in the lung. SOME CORROBORATIVE EVIDENCE OF OTHER INVESTIGATORS. That tubercle bacilli can pass thru lymph glands, along lymph chan- nels into the great thoracic duct, and thru it into the venous circulation, from which the infection of the lung occurs, is receiving, in addition to the evidence drawn from our own experiments, the strongest sup- port from the work of other investigators. According to a resume of their work in a recent number of the Medical Record, Schlossman and St. Engle have exprest practically the same conclusion. The} 7 drew it from the occurrence of tubercle bacilli in the lungs of guinea pigs into the stomachs of which an emulsion of tubercle bacilli was introduced by means of a laparotomy especially made to exclude the direct infection of the air passages or lung. Calmette is quoted in the British Medical Journal ll to have observed that pigment ingested by adult animals found its way at once to the lungs, while that ingested by young animals was first stopt by the mes- enteric glands, and that he had produced a case of pulmonary tuber- culosis without lesions of the gastro-intestinal mucosa or the mesenteric glands by introducing suspensions of tubercle bacilli into tho rumens of goats. THE INHALATION AND INGESTION METHODS OF INFECTION CONTRASTED. The practical conclusion to be drawn from tho results obtained is that ingestion is a greater danger than the respiration of tubercle bacilli, especially as the tubercle bacilli may be ingested in the fresh state in which they are expelled from tuberculous lesions and can not be respired until they have been subjected to various attenuating a Bureau of Animal Industry, Bulletin No. 86. & Bureau of Animal Industry, Bulletin No. 88. cVol. 70, No. 5, p. 191. 'X... L':!Ti, March 17, 11)06, p. 623. INHALATION AND INGESTION CONTRASTED. 13 processes. The substance in which tubercle bacilli are enveloped or embedded when they leave the infected organs under ordinary and usual conditions requires considerable time before it can be sufficiently dried and pulverized to float in the air. Bacilli do not rise from moist surfaces and float in the air. The complete desiccation that must occur in advance of pulverization is either a comparatively slow process or is hastened by agencies, like the heat from the direct rays of the sun, that have a potent influence against the vitality of pathogenic bacteria. Sputum, for example,, dries on the surface in a way that coats it with a protective membrane thru which evaporation progresses slowly; it is a very adhesive substance and becomes more so during the first stages of drying, and it must be exposed when thoroly dried to actual attrition before it can be detached from the surface on which it has dried and reach a sufficient disintegration to be blown about as dust. THE THEORY OF INFECTION BY INHALING DRIED SPUTUM. Dried, pulverized sputum has long been regarded as the most pro- lific and important agent for the dissemination of tuberculous infec- tion. Koch, in his Nobel lecture delivered at Stockholm on December 12, 1905, a declared that only those tuberculous patients who suffer from laryngeal and pulmonary tuberculosis and whose sputa contain bacilli are dangerous to those around them in a noteworthy degree. On the other hand we learn from the investigations of Cadeac ? ' that the hypothesis of the transmission of tuberculosis by inhalation of the dust from dried sputa has not been proved. He found that expecto- rated matter dried slowly and was neither simple nor easy to convert into dust; that sputa spread thickly on a glass plate and exposed to natural light adhered as a bright varnish and was not easily powdered into dust until the tenth or twelfth day, and that even on the sixth day a considerable quantity of powdered sputum was required to cause a discrete tuberculosis on peritoneal injection of guinea pigs. Sputum spread on a marble plate and kept above a stove for fourteen days was found to have lost its virulence for guinea pigs, and spread on a porous plate and exposed to sunlight it was not. effective for inoculation after forty-eight hours. Dried in the dark, some virulence was retained. THE MORE SERIOUS DANGER FROM FRESH AND MOIST TUBERCULOUS MATERIAL. We gather from these various facts that too much importance has been given to dried and pulverized, and not enough to fresh and moist tuberculous material. The respirator}' theory to account for the rela- tively great frequency with which tuberculosis is localized in the lung The Lancet, May 26, 1906. &Lyon Medical, December 10, 1905; British Medical Journal, March 10, 1906. 14 TUBERCULOUS LESIONS AND MODE OF INFECTION. really requires dried and pulverized sputum to give it a reasonable footing', and if pulverized sputum is shown to be inert the theory has nothing left to stand on. With the respiratory and inhalation theory shown to be unnecessar}' to account for the infection of the lung, and the outline we have given of the manner in which the lung becomes infected, fresh and moist tuberculous material must be given a place of primary importance, and exposure to it must be persistently avoided and regarded as the exceptionally great danger. This can not be too much emphasized. Exposure to fresh and moist material that contains tubercle bacilli occurs probably with great frequency, thru the ingestion of food that has been handled and prepared by persons affected with tuberculosis. To quote again from Koch's Nobel lecture, previously referred to, we have the following: Attention must be paid to the fact that it is not only the secretion of the lungs called sputum that is dangerous as containing bacilli, but that according to the inves- tigations of Flugge the smallest droplets of phlegm that are thrown into the air by tuberculous persons when they cough, clear their throats, and even when they speak, also contain bacilli and can cause infection. What more fruitful source of food infection with tubercle bacilli can exist than that implied in the foregoing quotation, when the culinaiy operations of a household are intrusted to a tuberculous person, whether servant or member of the family, or when the food in an eating-house or hotel is prepared by a tuberculous cook or a cook with a tuberculous assistant, or when food is exposed to no further means of contamination than a tuberculous waiter, who breathes over cold and hot dishes alike, commonly with perfect ignorance and disregard of the insidious but fatal poison that may escape from his mouth with every word he speaks and everj T accelerated expiration that passes his lips? THE FACILITY WITH WHICH BACILLI FROM TUBERCULOUS COWS MAY ENTER HUMAN FOOD. Altho authorities are not in accord on the intertransmissibility of human and bovine tuberculosis, we feel that it is necessary to call attention to one way in which tubercle bacilli, scattered by tuberculous cattle, are undoubtedly often introduced into human food. Tuberculosis of men and cattle was universally regarded as etiolog- ically the same affection until Dr. Theobald Smith, of America, pointed out a morphological difference between tubOrde bacilli isolated from human and bovine lesions, and Dr. Robert Koch, of Germany, later on, characterized bovine tuberculosis as a disease that coirid be almost, if not entirely, ignored :is a source of infection dangerous to man. ()])])i-d to the view of Doctor Smith is the frequent isolation of bacilli from human tuberculous lesion ^ that arc morphologically of the bovine type. This circumstance may l>e interpreted to mean one of HUMAN AND BOVINE TUBERCULOSIS. 15 two things either that persons who succumb to tuberculosis due to bacilli of the so-called bovine type were infected from cattle, or that the difference between the so-called human and bovine types has a sig- nificance similar to that of the morphological variation common with most bacteria. Doctor Koch's assertion that cattle tuberculosis is a negligible quan- tity in the measures that must be taken for the preservation of human health is based largely, if not wholly, on negative evidence, or, strictly speaking, no evidence at all. He, as well as many other investigators, found that it was difficult to induce tuberculosis in cattle by exposing them to or injecting them with tubercle bacilli obtained from human sources, and concluded from this that man was equally resistant to tubercle bacilli obtained from bovine sources. The premise does not justify the conclusion, and the mass of circumstantial evidence that is contrary to its acceptance is extremely voluminous and convincing. Many tubercle bacilli have been isolated from human lesions that are more infectious for cattle than many, tubercle bacilli isolated from lw vine lesions, and it is now pretty generally admitted that tubercle bacilli from bovine sources as a rule have a higher virulence than tubercle bacilli from human sources for all animals with which they have been tested. The animals tested include several species of the quadrumania, which are certainly much nearer to man, anatomically and physiologically, than to cattle. It would be curious indeed if man were an exception to a rule that has been found by conclusive tests to be applicable to the animal nature of all the species of the mammalian kingdom to which man belongs. To establish definitely that one species is an exception to a condition that is true of all the tried species of a great kingdom should require preponderating evidence, and can not be settled with negative evidence or a simple process of reasoning from analogy. In fact, it is not a process of reasoning at all with which we are dealing; it is a simple assumption to say that a being which is ordinarily affected with a weaker virus of a special kind is immune against the stronger virus usually found in connection with another being, simply because the being with the stronger is to some extent immune against the weaker virus. The commonly lower virulence of tubercle bacilli from human lesions may be due in part to the comparative!} 1 greater care bestowed on sick persons, and the general treatment, medical and other kind, that they receive, which prolongs their lives and the duration of the affection, and consequently exposes the virus to possible modifying influences of a biologic order. This seems more probable, since it has been shown that the disease has the elements of a self -limited affection, by the fact that it is possible to induce an immunity against tuberculosis by the injection of tubercle bacilli of a virulence too low to cause a progressive tuberculosis. 16 TUBERCULOUS LESIONS AND MODE OF INFECTION. But we do not wish to enter into a long argument on this question, and must return to the subject of tubercle bacilli from cattle that may enter human food. We believe that we have said enough to show that it is desirable in every sense of the word to protect our health against tuberculous infection from cattle and to know thru what channel it may reach us. We are compelled to maintain this view, tho it is opposed to the opinion of Doctor Koch, of the inestimable value of whose general work on tuberculosis we have the highest appreci- ation and sincerely feel and believe that it gives him the rank of a public benefactor of the first order. It has been shown by our work at the Experiment Station during the past year, an account of which will be published in a separate article, that the main channel thru which tubercle bacilli leave the bodies of tuberculous cattle is the rectum, and that feces may be regarded as a parallel substance with cattle to sputa with man in the dissemination of tubercle bacilli. This was demonstrated thru micro- scopic examinations and inoculation tests with small animals. The feces not only of cattle'afi'ected with advanced tuberculosis, but also of a large percentage of those so slightly affected that their tuber- culous condition was not suspected until they had been tested with tuberculin, were found to contain a sufficient number of microscopically discoverable tubercle bacilli to equal many millions in the total mass of feces past by a single cow each day. The bacilli were found to be evenly distributed in the feces, which is fairly good evidence that they had past thru the greater portion, probably the entire length, of the digestive tract. This even distribution was similar to that of the bacilli in the feces of healthy cattle that were given water to drink to which 'tubercle bacilli had been intentionally added. That the bacilli were virulent was proved by causing tuberculosis to develop in guinea pigs l>y inoculating them with feces and with milk soiled with feces from naturally tuberculous cows, as well as from the healthy cows that drank water to which tubercle cultures had been added. Now. if many millions of tubercle bacilli are commonly past by tuberculous cows, evenly distributed in their feces, which we have definitely convinced ourselves to be the case, it is not difficult to see that, because of the intensely infected environment of tuberculous cattle, it is no easy matter to obtain milk at all times free from tubercle bacilli. How easily feces, and with them tubercle bacilli, may be introduced into the milk pail no one who has witnessed the milking of cows need be told. CONCLUSIONS. (1) We believe that we have shown that systematic investigation is gradually retiring the inhalation theory that has long been used to explain the frequency with which tuberculosis is a pulmonary disease CONCLUSIONS. 17 and that the ingestion of tubercle bacilli is being proved to be the real method thru which tuberculous infection reaches the lung, as well as other organs of the body. When substances of dissimilar specific gravity move at the same rate of speed under similar conditions', it is a physical fact that the force required to change their direction is proportionately greater as the specific gravity increases. If the substances of dissimilar specific gravity are air and dust and the change of direction is due to move- ment thru the far-from-straight, moist-walled passages from the nasal openings, or even the mouth, to the lung, the dust will be thrown at every turn, because of its greater specific gravity, against the walls of the air passages, to which it will adhere because they are moist, and the ciliated epithelium with which the respiratory passages are lined will tend to move the adherent particles outward and not inward. It is, hence (excepting, possibly, with extremely forcible inspiratory movement in a dust-saturated atmosphere), almost a physical impossi- bility for dust particles to penetrate with the air into the lung. If no other argument than this could be brought to bear against the inhala- tion theory of pulmonary tuberculosis and it applies with equal force against inhalation of other infectious material, including the micro- organisms of pneumonia it would be sufficient to condemn it. (2) Not only is the inhalation theory dying and making room for the fact that ingestion is the true mode of infection with tuberculosis, but the theory that dust from pulverized sputa is the most important factor in the transmission of tuberculosis from subject to subject is gradually losing ground also and giving wa^v to the conviction that fresh tuberculous material must be lookt to as the true agent thru which infection occurs. (3) While many cases of tuberculosis undoubtedly have their origin thru food directly or indirect!}" infected with fresh tuberculous mate- rial by tuberculous persons, there is no means to-da} 7 by which per- sons are brought into closer contact with fresh tuberculous material than milk and daily products obtained from, and in the environment of, tuberculous cows. The wide use of milk, its rapid distribution because of its perishable character, the ease with which it may be con- taminated by having tubercle-bacilli-laden feces splashed, spraj^ed, switched, or otherwise introduced into it in a fresh state, all speak for one conclusion, namely, that we have no more active agent than the tuberculous cow for the increase of tuberculosis among animals and its persistence among men. SUMMARY OF THE CONCLUSIONS. The main facts are as follows: (a) Tuberculosis is a disease contracted thru the ingestion of tubercle bacilli. 18 TUBEKCULOUS LESIONS AND MODE OF INFECTION. (b) The lung is the most frequent organ affected, independently of the point at which the infectious material enters the body. (c) Tuberculous infection may pass from one part of the body to another remote to it without leaving a chain of lesions to mark its path. (d) Fresh tuberculous material has the highest, and dried and pulverized material a doubtful significance. (e) Tuberculous material from cattle has the highest virulence for all tested species of the mammalian kingdom, to which man anatom- ically and physiologically belongs, and tuberculous material from man has a lower virulence. (f) Man is constantly exposed to fresh tuberculous material in a helpless way thru his use of dairy products from tuberculous cows and cows associated with tuberculous cattle. It seems from this array of facts, every one of which is based on positive experimental evidence, that we should feel no doubt regarding our plain duty, which is, no matter what other measures we adopt in our iight against tuberculosis, not to neglect one of the chief, if not the most important, source of infection the tuberculous dairy cow. ADDENDUM. RECENT WORK BY A FRENCH INVESTIGATOR. Since concluding this article a recent paper by Cadeac has appeared in Le Bulletin Medical of September 5, 1906, of which the following resume* was given in the New York Medical Record of October 6, 1906, and it seems desirable to quote it here, because of its important bearing on the relative danger to health represented on the one hand by exposure to dried and pulverized, and on the other by exposure to moist and fresh tuberculous material : Cadeac declares that the dust ground from dried tuberculous sputum is harmless both to the digestive and respiratory passages. Not a single experiment has shown the transmission of tuberculosis by the inhalation of dust gathered from localities inhabited by tuberculous patients. The writer has demonstrated that it is almost impossible to cause the development of this disease by the inhalation of this infected dust. The desiccation and rapid conversion of sputum into flying dust are the natural means of preservation against tuberculous infection. Mere we have a double argument, equally potent against the inhala- tion theory of pulmonary tuberculosis and in favor of the greater danger from exposure to fresh and moist tuberculous material. A- \\<- have already said, without dried and pulverized infectious material the inhalation theory has absolutely no foundation on which it can reasonably stand; and, if dried and pulverized material is as inert as the investigations of Cadeac represent it to be, fresh and moist material for men and animals alike must be lookt to as the true cause for the ADPENDUM. 19 transmission and persistence of tuberculosis. The inhalation theory, and the great importance attached to dust as an agent for the transmission of tuberculosis, are beginning to have the appearance of two errors that have long hampered the fight that is being made against tuber- culosis. A clear comprehension of the many ways in which fresh tuberculous material, the infectious potency of which is unquestionable, can be introduced into articles of food used by man and animals, shows conclusively that this is sufficient to account for the frequency with which infection occurs and the widespread character of the disease. 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