264 PATHOLOGY OF THE BLOOD AND CIRCULATION. 



evidences of advancing senile degeneration manifest them- 

 selves with equal rapidity, the numerous new bloodvessels 

 undergoing atrophy in a similar manner, and thus is formed 

 the cicatrix. 



The formation of new fibrous tissue and regeneration of 

 other connective tissues occur in much the same manner, 

 their differentiation occurring secondarily. 



THE INFECTIVE GRANULOMATA. 



Under this head are usually described a number of infec- 

 tious diseases all characterized by the formation of tumor-like 

 nodular masses, microscopically somewhat resembling granu- 

 lation-tissue in the number and character of their cells, which 

 have, however, but little tendency to develop into a perma- 

 nent tissue, and are very liable to undergo degenerative 

 changes. They are forms of subacute inflammation. 



Tuberculosis. 



The term tubercle was at one time applied to any nodular 

 growth. By Laennec it was employed mainly in connection 

 with the large caseous yellow nodules observed in phthisical 

 lungs. Baillie (1794) was the first to call attention to the 

 small, gray, millet-seed-sized tubercles found in the lungs, and 

 which are now regarded as the anatomical basis of the larger 

 yellow nodules. But even the smallest " miliary tubercle " 

 is found microscopically to be made up of still smaller cellular 

 tubercles. 



Though the histology of these cellular tubercles is quite 

 distinctive, since the discovery of the specific microbic cause 

 by Koch in 1882, the presence of this bacillus must be re- 

 garded as the essential characteristic of the disease : this then 

 is the criterion, whatever the macroscopic or microscopic 

 character of the lesion (see Figs. 104, 105). 



Histological tubercle : The first effect of the presence of the 

 tubercle bacillus in a tissue is the multiplication of its fixed 

 connective-tissue cells, resulting in the formation of cells 

 termed epithelioid on account of the resemblance to epithelial 

 cells in their abundance of protoplasm. There is also 



