EXPERIMENTAL INOCULATION. 249 



be detected, though sometimes their number may be very small ; 

 here, especially, repeated examiriations may be necessary. The 

 bacilli often occur in little clumps, as shown in Fig. 92. In 

 tubercular ulceration of the intestine their presence in the 

 faeces may be demonstrated, as was first shown by Koch ; but 

 in this case their discovery 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 artificially 

 produced in animals by infection in a great many different ways 

 — by injection of the bacilli into the subcutaneous 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 gen- 

 erally that when introduced into the tissues of a susceptible 

 animal, the bacilli produce locally the lesions above described, 

 terminating in caseation ; that there occurs a tubercular affec- 

 tion of the neighbouring 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 may break down, leading 

 to the formation of an irregularly ulcerated area with caseous 

 lining. The lymphatic glands in relation to the parts can gen- 

 erally be found to be enlarged and of somewhat firm consist- 

 ence, 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, gradually becomes cachectic, 

 and ultimately dies, sometimes within six weeks, sometimes not 

 for two or three months. Post mortem, in addition to the local 

 and glandular changes, an acute tuberculosis is usually present, 



