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 cutis, and scrofuloderma; choroidal 
tuberculosis, idiopathic serous pleurisy and lymphatic 
enlargements simulating pseudoleukemia. 
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 
