BACILLUS OF TUBERCULOSIS. 277 



parrots, are not subject to tuberculosis, and cold-blooded 

 animals are altogether immune. 



Beside the affections already referred to in man the 

 following diseases have been traced to tubercular origin: 

 Among skin diseases, so-called inoculation-lupus, tuber- 

 culosis- verrucosa cntis, and scrofuloderma; choroidal 

 tuberculosis, idiopathic serous pleurisy and lymphatic 

 enlargements simulating pseudoleuksemia. 



The Action upon the Tissues of the Poisons Produced 

 by the Tubercle Bacillus. Soon after the introduction 

 into the tissues of tubercle bacilli, either living or dead, 

 the cells surrounding them begin to show that some 

 irritant is acting upon them. The connective-tissue 

 cells become swollen and undergo mitotic division, the 

 resultant cells being distinguished by their large size 

 and pale nuclei. A small focus of proliferated epithe- 

 lioid cells is thus formed about the bacilli, and accord- 

 ing to the intensity of the inflammation these cells are 

 surrounded by a larger or smaller number of the lym- 

 phoid cells. When living bacilli are present and multi- 

 plying, the lesions progress, the central cells degenerate 

 and die, and a cheesy mass results, which later may lead 

 to the formation of cavities. Dead bacilli, on the other 

 hand, give off sufficient poison to cause the less marked 

 changes only, and never produce cavities (Prudden and 

 Hodenpyl). Of the gross pathological lesions produced 

 in man by the tubercle bacilli the most characteristic 

 are small nodules, called miliary tubercles. When 

 young, and before they have undergone degeneration, 

 these tubercles are gray and translucent in color, some- 

 what smaller than a millet-seed in size, and hard in 

 consistence. 



But miliary tubercles are not the sole tuberculous 



