278 TUBERCULOSIS 



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 irregular 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 

 long delayed, calcification may have occurred in some of the 

 nodules. Tubercle nodules, though rather less numerous, are 

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

 latter organs being usually of smaller size though occasionally in 

 large numbers. The extent of the general infection varies; 

 sometimes 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. 280). 



Varieties of Tuberculosis. — 1. Human and Bovine Tubercu- 

 losis. — Up till recent years it was generally accepted that all 

 mammalian tuberculosis was due to the same organism, and, 

 in particular, that tuberculosis could be transmitted from the 

 ox to the human subject. The matter became one of special 

 interest owing to Koch's address at the Tuberculosis Congress 

 in 1901, in which he stated his conclusion that human and 

 bovine tuberculosis are practically distinct, and that if a 

 susceptibility of the human subject to the latter really exists, 

 infection is of very rare occurrence, — so rare that it is not 

 necessary to take any measures against it. Previously to this, 

 Theobald Smith had pointed out differences between mammalian 

 and bovine tubercle bacilli, the most striking being that the 



