458 
CONGRESS ON TUBERCULOSIS. 
cepted opinion regarding the identity or non-identity of bacteria 
associated with disease in more than one species of animal. Since 
it thus appeared to be proved that the only difference between 
human and bovine tubercle bacilli lay in their accidentally dif¬ 
ferent 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 trans¬ 
mission 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. 
What are the grounds upon which we are asked to discard con¬ 
victions that appeared to rest on such a solid basis ? I 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 for 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 relied upon as a means of distinguishing the bacilli of bovine 
tuberculosis from those of the human 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 ba¬ 
cilli from the one species to the other, and cases of primary 
intestinal tuberculosis from the consumption of tuberculous milk 
ought to be of common occurrence. But post-mortem examina¬ 
tion of human beings proves that cases of primary intestinal 
tuberculosis are extremely 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 in 
this way. 
Now, with the utmost diffidence I venture to submit that at 
least one of the premises contained in this argument is not well 
founded, that the others have little or no bearing on the ques¬ 
tion, and that there still remain reasonable grounds for regard¬ 
ing tuberculous cows’ milk as distinctly dangerous to human 
beings. 
It cannot be denied that what may be called bovine tubercle 
