No. 6. DEPARTMENT OK AGRICULTURE. 477 



conflict with the conclusion that huimin and bovine tuberculosis were 

 identical diseases, but they brouj^iil to light what appeared to be 

 additional evidence of this identity, such as the discovery that tuber- 

 culin produced a specific reaction in tuberculous cattle, whether 

 human or bovine bacilli had been employed in its preparation. In 

 short, the ideutity of the bacilli from the two sources appeared to be 

 as firmly established as any other generally accepted opinion regard- 

 ing the identity or non-identity of bacteria associated with disease 

 in more than one species of animal. vSiuce it thus appeared to be 

 proved that the only difference between human and bovine tubercle 

 bacilli lay in their accidentally ditlerent position — one being parasitic 

 in man and the other in cattle — it was natural to conclude that, when 

 circumstances were favorable for the transference of bacilli from 

 one species to the other, human tuberculosis might have an animal 

 origin, and vice versa. 



Opinions varied as to the frequency with which this transmissiou 

 of tuberculosis from one species to the other occurred, but practically 

 never within the last eighteen years regarding the possibility and 

 probability of such reciprocal infection. ^Vhat are the grounds 

 upon which we are asked to discard convictions that appeared to 

 rest on such a solid basis? 1 shall endeavor to state them briefly, 

 as I understand Dr. Koch's train of reasoning. 



(1) The bacilli found in cases of bovine tuberculosis are much more 

 virulent lor cattle and other domestic quadrupeds than the bacilli 

 found in cases of human tuberculosis. 



(2) This difference is so marked and so constant that it may be re- 

 lied upon as a means of distinguishing the bacilli of bovine tubercu- 

 losis from those of the humao disease, even assuming that the former 

 may occasionally be found as a cause of disease in man. 



(3) If bovine bacilli are capable of causing disease in man, there 

 are abundant opportunities for the transference of the bacilli from 

 the one species to the other, and cases of primary- intestinal tuber- 

 culosis from the consumption of tuberculous milk ought to be of 

 common occurrence. But post-mortem examination of human be- 

 ings proves that cases of primary intestinal tuberculosis are ex- 

 tremely rare in man, and therefore it must be concluded that the 

 human subject is immune against infection with the bovine bacilli, 

 or is so slightly susceptible that it is not necessary to take any 

 steps to counteract the risk of infection m this svaj. 



Now, with the utmost diffidence I venture to submit that at least 

 oneofthepremisescontainedinthisargumentis not well founded, that 

 the others have little or no bearing on the question, and that there 

 still remain reasonable grounds for regarding tuberculous cows' 

 milk as distinctly dangerous to human beings. 

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