TUBERCULOSIS. 225 



consist in nodes, nodules, or collections of agminated 

 nodules, called tubercles, scattered irregularly through 

 the tissues, which are devitalized or disorganized by 

 their presence. When tubercle bacilli are introduced 

 beneath the skin of a guinea-pig, the animal shows no 

 sign of disease for a week or two ; it then begins to lose 

 appetite and gradually to diminish in flesh and weight. 

 Examination at this time will show a nodule at the point 

 of injection and enlargement of the neighboring lymphatic 

 glands. The atrophy increases, the animal shows a febrile 

 reaction, and at the end of a varying period of time, 

 averaging about twelve weeks, dies. Post-mortem ex- 

 amination shows a cluster of tubercles at the point of 

 inoculation, enlargement of lymphatic glands both near 

 and remote from the primary lesion (due to the presence 

 of tubercles), and a widespread invasion of the lungs, 

 liver, kidneys, peritoneum, and other organs and tissues, 

 with tuberculous tissue in a more or less advanced con- 

 dition of necrosis. Sometimes there are no tubercles 

 discoverable at the point of inoculation. There is no 

 regularity in the distribution of the disease. Tubercle 

 bacilli are demonstrable in immense numbers in all the 

 diseased tissues. The disease as seen in the guinea-pig is 

 more extended than in other animals because of its greater 

 susceptibility, and the death of the animal is more rapid 

 than in other species for the same reason. In rabbits the 

 lesion runs a longer course with similar lesions. In 

 bovines and sheep the infection is generally first seen 

 in, and is principally confined to, the alimentary appa- 

 ratus and the associated organs, though pulmonary dis- 

 ease also occurs. In man the disease is chiefly pulmonary, 

 though gastro-intestinal and general miliary forms are also 

 common. The development of the lesions in whatever 

 tissue or animal always depends upon the distribution of 

 the bacilli by the lymph or the blood, and is first inflam- 

 matory, then degenerative, in type. 



The experiments of Koch, Prudden and Hodenphyl, 

 and others have shown that when dead tubercle bacilli 



15 



