286 TUBERCULOSIS 
tion was raised as to their identity. Both diseases are produced 
by bacteria that appear identical, and that they were the same 
was taken for granted. In 1900, however, Prof. Koch raised the 
question whether they were not distinct, and gave experiments to 
show that the human bacillus does not produce the severe bovine 
tuberculosis when inoculated into cattle. The question caused 
intense interest and much discussion, and in spite of many experi- 
ments designed to settle the matter, there is still some dispute. 
A fair summary of the facts as they appear to the majority of 
bacteriologists to-day is as follows: 
Both bovine and human tuberculosis are caused by a bacterium 
that has great similarity in the two animals. But there are slight 
differences between them, both in microscopic appearance and in 
methods of growth, sufficient to make it necessary to recognize 
them as somewhat different types. When inoculated into animals, 
the organism from the bovine source proves to be more virulent 
than the one from the human source. The human bacillus, when 
inoculated into cattle, generally produces only a slight trouble, 
while the bovine bacillus is apt to bring about a progressive case of 
the disease of very serious character. What effect the bovine 
bacillus has when inoculated into man cannot yet be told from 
direct experiment, but there appear to be a number of tolerably 
sure cases of accidental inoculation of human beings with the 
bovine bacillus that have been followed by a development of the 
disease. The general conclusion is that, although the two are 
slightly different, each may produce the disease in the other ani- 
mal, and that the disease is, therefore, transmissible from animals 
to man. While the conclusion is still doubted by some, it is 
accepted by most bacteriologists. Whether the bovine bacillus is 
more virulent for man than is the human bacillus, as it is for 
other animals, is by no means settled. Furthermore, it is pretty 
generally agreed that human tuberculosis comes more often 
from human sources than from cattle. 
