284 TUBERCULOSIS 
that the bacillus may frequently be found alive outside the bodies 
of animals. It occurs in sputum, in milk, in water, in dust, etc., 
but in these media it does not multiply, at least under any con- 
ditions to which they are normally subjected, and we must there- 
fore conclude that its multiplication is confined to the bodies of 
animals. While it can flourish in the artificial media of the labo- 
ratory, when kept at special temperatures, it does not flourish in 
nature, outside the bodies of animals upon which it lives as a 
parasite. 
Animals Subject to the Disease.—Besides living in man the 
organism can flourish in the bodies of cattle, hogs, dogs, cats, mon- 
keys, rabbits, guinea-pigs, and some other animals. In all these it 
produces very similar symptoms, differing slightly, of course, in 
the different animals. The characteristic feature of the disease is 
the production of tubercles—swollen masses of tissue—which 
eventually break down into a cheesy mass. These tubercles may 
appear at almost any part of the body. Of all the animals the 
guinea-pig is the most delicately susceptible to the bacillus. An 
extremely small infection will produce the disease in the guinea- 
pig, and for this reason these animals are used in experiments 
to test the presence of the bacillus. A little suspected milk 
inoculated under the skin of the guinea-pig will produce the dis- 
ease inevitably, if only the smallest number of virulent germs are 
present. Besides these mammals a number of birds show a similar 
disease, with a similar bacillus present in the infected organs. The 
bacillus in birds is, however, in some respects, slightly different 
from that in men and cattle, and is frequently regarded as a dif- 
ferent type of the organism. 
Most parasitic bacteria are able to grow only on certain parts 
of the body, diphtheria commonly in the throat, cholera in the 
intestine, etc. But the tubercle bacillus can live in almost any 
part. It is found in the intestinal organs, in the lymphatic glands, 
in the /ungs, in the bones, in the joints, in the kidneys, in the skin, 
and, in short, almost anywhere. When occurring in the different 
