July 25, 1901 



NA rURE 



easily and rapidly suppressed, is always introduced again year 

 after year from the neighbouring countries. 



Permit me to mention only one other disease, because it is 

 etiologically very closely akin to tuberculosis, and we can learn 

 not a little for the furtherance of our aims from its successful 

 combating. I mean leprosy. It is caused by a parasite which 

 greatly resembles the tubercle-bacillus. Just like tuberculosis, 

 it does not break out till long after infection, and its course is 

 almost slower. It is transmitted only from person to person, 

 but only when they come into close contact, as in small dwell- 

 ings and bedrooms. In this disease, accordingly, immediate 

 transmission plays the main part : transmission by animals, 

 water, or the like is out of the question. The combative 

 measures, accordingly, must be directed against this close inter- 

 course between the sick and the healthy. The only way to 

 prevent this intercourse is to isolate the patients. This was 

 most rigorously done in the Middle .-^ges by means of numerous 

 leper-houses, and the consequence was that leprosy, which had 

 spread to an alarming e-xtent, was completely stamped out in 

 Central Europe. The same method has been adopted quite 

 recently in Norway, where the segregation of lepers has been 

 ordered by a special law. But it is extremely interesting to see 

 how this law is carried out. It has been found that it is not at 

 all nece5s.iry to execute it strictly, for the segregation of only 

 the worst cases, and even of only a p.irt of these, sufficed to 

 produce a diminution of leprosy. Only so many infectious cases 

 had to be sent to the leper-houses that the number of fresh cases 

 kept regularly diminishing from year to year. Consequently the 

 stamping-out of the disease has lasted much longer than it 

 would have lasted if every leper had been inexorably consigned 

 to a leper-house, as in the Middle Ages ; but in this way, too, 

 the same purpo.se is gained, slowly, indeed, but without any 

 harshness. 



These examples may suffice to show what I am driving at, 

 which is to point out that, in combating pestilences, we must 

 strike at the root of the evil, and must not squander force in 

 subordinate ineffective measures. Now the question is whether 

 what has hitherto been done, and what is about to be done, 

 against tuberculosis really strikes at the root of tuberculosis, so 

 that it must sooner or later die. 



In order to answer this question it is necessary first and fore- 

 most to inquire how infection takes place in tuberculosis. Of 

 course, I presuppose that we understand by tuberculosis only 

 those morbid conditions which are causedjby the tubercle-bicillus. 



In by far the majority of cases of tuberculosis the disease has 

 its seat in the lungs, and has also begun there. From this fact 

 it is justly concluded that the germs of the disease, i.e. the 

 tubercle-bacilli, must have got into the lungs by inhalation. As 

 to the question where the inhaled lubercle-bacilli have come 

 from, there is also no doubt. On the contrary, we know with 

 certainty that they get into the air with the sputum of con- 

 sumptive patients. This sputum, especially in advanced stages 

 of the disease, almost always contains lubercle-bacilli, some- 

 times in incredible quantities. By coughing, and even speaking, 

 it is flung into the air in little drops, i.c in a moist condition, 

 and can at once infect persons who happen to be near the 

 coughers. But then it may also be pulverised when dried, m 

 the linen or on the floor for instance, and get into the air in the 

 form of dust. 



In this manner a complete circle, a so-called circnhts viliostis, 

 has been formed for the process of infection, from the diseased 

 lung, which produces phlegm and pus containing tubercle-b.acilli, 

 to the formation of moist and |dry particles . which, in virtue of 

 their smallness, can keep floating a good while in the air), and 

 finally to new infection, if particles penetrate with the air into 

 a he.ilthy lung and originate the disease anew. But the tubercle- 

 bacilli may get to other organs of the body in the same way, 

 and thus originate other forms of tuberculosis. This, however, 

 is a considerably rarer case. The sputum of consumptive people, 

 then, is to be regarded as the main source of the infection of 

 tuberculosis. On this poini, I suppose, all are agreed. The 

 question now arises whether there are not other sources too, 

 copious enough to demand consideration in the combating of 

 tuberculosis. 



Great importance used to be attached to the hereditary trans- 

 mission of tuberculosis. Now, however, it has been demon- 

 strated by thorough investigation that, though hereditary tuber- 

 culosis is not absolutely non-existent, it is nevertheless extremely 

 rare, and we are at liberty, in considering our practical measures, 

 to leave this form of origination entirely out of account. 



NO. 1656, VOL. 64] 



But another possihiiity of tubercular infection exists, as is 

 generally assumed, in the transmission of the germs of the 

 disease from tubercular animals to man. This manner of 

 infection is generally regarded nowadays as proved, and as so 

 frequent that it is even looked upon by not a few as the most 

 important, and the most rigorous me.asures are demanded 

 against it. In this Congress also the discussion of the danger 

 with which the tuberculosis of animals threatens man will play 

 an important part. Now, as my investigations have led me to 

 form an opinion deviating from that which is generally accepted, 

 I beg your permission, in consideration of the great importance 

 of ihis question, to discuss it a little more thoroughly. 



Genuine tuberculosis has hitherto been observed in almost 

 all domestic animals, and most frequently in poultry and cattle. 

 The tuberculosis of poultry, however, differs so much from 

 human tuberculosis that we may leave it out of account as a 

 possible source of infection for man. So, strictly speaking, 

 the only kind of animal tuberculosis remaining to be considerec' 

 is the tuberculosis of cattle, which, if really transferable lo man, 

 would indeed have frequent opportunities of infecting humir 

 beings through the drinking of the milk and the eating of the 

 flesh of diseased animals. 



Even in my first circumstantial publication on the etiology of 

 tuberculosis I expressed myself regarding the identity of 

 human tuberculosis and bovine tuberculosis with reserve. 

 Proved facts which would have enabled me sharply to distin- 

 guish these two forms of the disease were not then at my 

 disposal, but sure proofs of their absolute identity were equally 

 undiscoverable, and I therefore had to leave this question 

 undecided. In order to decide it, I have repeatedly resumed 

 the investigations relating to it, but so long as I experimented 

 on small animals, such as rabbits and guinea-pigs, I failed to 

 arrive at any satisfactory result, though indications which 

 rendered the difference of the two forms of tuberculosis probable 

 were not wanting. Not till the complaisance of the Ministry of 

 Agriculture enabled me to experiment on cattle, the only 

 animals really suitable for these investigations, did I arrive at 

 absolutely conclusive results. Of the experiments which I have 

 carried out during the last two years along with Prof. Schiiltz, of 

 the Veterinary College in Berlin, I will tell you briefly some of 

 the most important. 



A number of young cattle which had stood the tuberculin test, 

 and might therefore be regarded as free from tuberculosis, were 

 infected in various ways with pure cultures of tubercle-bacilli 

 taken from cases of human tuberculosis ; some of them got the 

 tubercular sputum of consumptive patients direct. In some cases 

 the tubercle bacilli or the sputum were injected under the skin, 

 in others into the peritoneal cavicy, in others into the jugular 

 vein. Six animals were fed with tubercular sputum almost 

 daily for seven or eight months ; four repeatedly inhaled great 

 quantities of bacilli, which were distributed in water and scrt- 

 tered with it in the form of spray. None of these cattle (there 

 were nineteen of them) showed any symptoms of disease, and 

 they gained considerably in weight. From six to eight months 

 after the beginning of the experiments they were killed. In 

 their internal organs not a trace of tuberculosis was found. 

 Only at the places where the injections had been made small 

 suppurative foci had formed, in which few tubercle-bacilli could 

 be found. This is exactly what one finds when one injects dead 

 tubercle-bacilli under the skin of animals liable to contagion. 

 So the animals we experimented on were aff'ected by the living 

 bacilli of human tuberculosis exactly as they would have baen by 

 dead ones : they were absolutely insusceptible to them. 



The result was utterly different, however, when the same 

 experiment was made on cattle free from tuberculosis with 

 tubercle-bacilli that came from the lungs of an animal suffering 

 from bovine tuberculosis, .\fter an incub.ation period of about 

 a week the severest tubercular disorders of the internal organs 

 broke out in all the afifected animals. It was all one whether the 

 infecting matter had been injected only under the skin or into 

 the peritoneal cavity or the vascular system. High fever set in, 

 and the animals became weak and lean ; some of them died 

 after a month and a half to two months, others were killed in a 

 miserably sick condition afcer three months. After death 

 extensive tubercular infiltrations were fourd at the place where 

 the injections had been made, and in the neighbouring 

 lymphatic glands, and also far advanced alterations of the 

 internal organs, especially the lungs and the spleen. In the 

 cases in which the injections had been made into the peritoneal 

 cavity the tubercular gro>vths which are so characteristic of 



