EXPERIMENTAL INOCULATION 273 



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 

 generally 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 affection 

 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 generally 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 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, 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, the spleen 

 being specially affected. This organ is swollen, and is studded 

 throughout by numerous tubercle nodules, which may be minute 

 and grey, or larger and of a yellowish tint. If death has been 

 lono; delayed, calcification may have occurred in some of the 

 ii Mlules. Tubercle nodules, though rather less numerous, are 

 also present in the liver and in the lungs, the nodules in the 

 latti-r organs being usually of smaller size though occasionally in 

 large numbers. The extent of the general infection varies; 

 -"inetimes the chronic glandular changes constitute the out- 

 standing feature. Statements as to differences in the pathogenic 

 effects of bacilli from human and bovine sources will be found 

 below (p. 274). 

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