No. 6. DEPARTMENT OF AGRICULTURE. 467 



infection, if particles penetrate with the air into a healthy lung and 

 originate the disease anew. But the tubercle-bacilli may get to 

 other organs of the body in the same way, and thus origioate 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 point, I sup- 

 pose, 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 transmis- 

 sion of tuberculosis. Now, however, it has been demonstrated by 

 thorough investigation that, though hereditary tuberculosis 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. 



But another possibility of tubercular infection exists, as is gen- 

 erally 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 rigor- 

 ous measures 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 investiga- 

 tions 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 this question, to discuss it a little more thor- 

 oughly. 



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 tuber- 

 culosis 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 considered is the tuberculosis of cattle, 

 which, if really transferable to man, would indeed have frequent op- 

 portunities of infecting human 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 identiy of human tu- 

 berculosis and bovine tuberculosis with reserve. Proved facts which 

 would have enabled me sharply to distinguish 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 urdecided. In order to decide it, I have re- 

 peatedly resumed thp investigations relating to it, but so long as T 



