EXPERIMENTAL INOCULATION. 241 



as was first shown by Koch ; but in this case their dis- 

 covery is usually of little importance, as the intestinal 

 lesions, as a rule, occur only in advanced stages when 

 diagnosis is no longer a matter of doubt. 



Experimental Inoculation. Tuberculosis can be arti- 

 ficially produced in animals by infection in a great many 

 different ways by injection of the bacilli into the sub- 

 cutaneous tissue, into the peritoneum, into the anterior 

 chamber of the eye, into the veins ; by feeding the animals 

 with the bacilli ; and, lastly, by making them inhale the 

 bacilli suspended in the air. 



The exact result, of course, varies in different animals 

 and according to the method of inoculation, but we may 

 state generally that when introduced locally into the tissues 

 of a susceptible animal, the bacilli usually produce the lesions 

 above described, terminating finally in a local caseation ; 

 that there then occurs a tubercular affection of the neigh- 

 bouring lymphatic glands, and that lastly there may be a 

 rapid extension of the bacilli to other organs by the blood 

 stream and the production of general tuberculosis. Of 

 the animals used for the purpose, the guinea-pig is most 

 susceptible. 



When a guinea-pig is inoculated subcutaneously with 

 tubercle bacilli from a culture, or with material containing 

 them, such as phthisical sputum, a local swelling gradually 

 forms which is usually well marked about the tenth day. 

 This swelling becomes softened and caseous, and breaks 

 down, leading to the formation of an irregularly ulcerated 

 area with caseous lining. The lymphatic glands in relation 

 to the parts can generally be found to be enlarged, and of 

 somewhat firm consistence, about the end of the second or 

 third week. Later, in them also caseous change occurs, 

 and a similar condition may spread to other groups of glands 

 in turn, passing also to those on the other side of the body. 

 During the occurrence of these changes, the animal loses 

 weight, shows general disturbance of nutrition, gradually 

 becomes cachectic, and dies, death occurring sometimes 

 within six weeks, sometimes not for two or three months. 

 16 



