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AUBERCULOSIS IN’ CATTLE. 13 
poisonous and are probably identical with tuberculin. These 
poisons directly affect the tissues of the animals within which 
the bacillus is growing, causing various pathological growths 
which characterize the disease. The tubercules so character- 
istic of this disease are simply pathological growths in the ani- 
mal, stimulated by the poisons excreted by this little micro- 
organism. The tubercle bacillus 1s capable of living as a para- 
site in quite a large number of warm-blooded animals. Those 
with which we are the most interested are, of course, man and 
cattle, but in addition to these we find that the bacillus can live 
as a parasite in horses, birds, rats and mice, pigs, goats, sheep, 
cats, dogs, and, indeed, other animals. The last four take it 
rarely. The only ones with which the agriculturist is especially 
interested are cattle and swine. The presence of the bacillus 
in other animals is too rare to make it a factor of any import- 
ance in agriculture. 
The question whether the bacillus which produces the dis- 
ease in man is identical with that found in cattle has always 
been one of very great interest and manifestly of very great 
importance. Upon the affirmative settlement of this question 
rests the possibility of the transference of the disease from 
animals to man and from man to animals. It has been very 
generally believed by scientists from the very first that the 
species of bacillus found in man and cattle are the same. 
There appears to be no difference in the bacillus as found in 
these two animals, when it is studied with the best micro- 
scopical apparatus. It has been shown by demonstration that 
the tuberculous material from man may produce the tuber- 
culosis disease in cattle, and there have been many instances 
that point to the conclusion that the disease has been trans- 
mitted from cattle to man. If the disease can thus be carried 
from one to the other, there can be no question that the bacillus 
is the same in both animals. But there are still some facts 
which forbid us to give a positive answer to the question, and 
there is as yet no absolutely uniform opinion upon the subject. 
It has been learned as the result of recent experiments. that, 
although there may be but one species of tubercle bacilli, there 
are a number of varieties more or less distinct and of different 
virulence. Some of these varieties appear to have a very much 
more decided power of producing the disease than others. 
~ Some of them inoculated into an animal will produce a viru- 
lent case of the disease, while other varieties under similar cir- 
cumstances produce only a mild type. Recognizing, then, 
