35 2 AGRICULTURAL BACTERIOLOGY. 



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 ex- 

 tremely 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 

 disease 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 

 commonly regarded as a different type of the organism. 

 They are, however, closely related and there is considerable 

 evidence that the one type may be converted into the other 

 under proper conditions. 



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 lungs, in the bones, in the joints, in 

 the kidneys, in the skin and, in short, almost anywhere. 

 When occurring in the different organs it receives different 

 names, consumption^ scrofula, lupus, liip disease, nephritis, be- 

 ing some of its common names. Knowing the wide ravages 

 of the disease it is something of a surprise to find that it is not 

 especially virulent and, indeed, when the individual is in good 

 health, it will commonly produce either no trouble or only a 

 local infection which is quickly healed. If a lymphatic gland 

 is infected, for example, there may be simply a small tubercle 

 which, after running a definite course, has a tendency to be- 

 come hardened and dormant without producing further trouble. 



