TUBERCULOSIS IN CATTLE. 37 
species of bacillus which has considerable resemblance to the 
tubercle bacillus, but which is not the tubercle bacillus. When 
studied microscopically, this bacterium cannot be distinguished 
from the true tubercle bacillus, and if found in milk would un- 
doubtedly be confused with it. Moreover, when inoculated 
into guinea pigs it produces a disease, and frequently death, 
with symptoms very similar to those of true tuberculosis. An 
examination of the body after the animal has died shows the 
presence of abnormal growths very similar to those produced 
in tuberculosis itself. Now, these bacilli are certainly quite 
common in milk and butter, and if butter or milk containing 
them is inoculated into guinea pigs the animals will die and 
show some symptoms of tuberculosis. The experiment 
would be undoubtedly set down as indicating the presence of 
the tubercle bacilli in the milk. But this bacillus is not harm- 
full to other animals, and probably not to man. It is cer- 
tainly not the cause of tuberculosis. Now, the studies of recent 
months have shown that many of the fatal results in the guinea 
pig experiments have been caused by these false tubercle 
bacilli, and not by the true bacillus tuberculosis. By further ex- 
perimentation it is possible to distinguish between these two 
types of organisms. They grow differently and have differ- 
ent pathogenic powers. Now, recognizing the common pres- 
ence of this false bacillus in milk and butter, it is plain that the 
previous experiments of inoculating guinea pigs are open to 
quite serious question. Some observers have gone so far as 
to claim that nearly all of the fatal results obtained from in- 
oculating butter into guinea pigs have been due to this false 
bacillus, and not to the true bacillus. Even those who have 
been foremost in the inoculation experiments, and in claiming 
the seriousness of the problem, have acknowledged that many 
of the positive results have been due to this false bacillus, al- 
though they still claim that the true tubercle bacillus produces 
a certain proportion of the positive results in their experiments. 
This claim cannot be doubted. . 
From all these facts it is clear that the method of testing the 
infectiousness of milk by the use of guinea pigs is open to 
serious question. ‘This is entirely too sensitive a method of 
testing, for the guinea pig will succumb to a disease, either 
tuberculosis or one of a similar nature, from the inoculation of 
products which would be entirely harmless to man, and in some 
cases from products which contain absolutely no true tubercle 
bacilli at all, While, therefore, the inoculation experiments 
S.—4 
