THE TUBERCLE. 589 



dothelial cells to a certain degree. Under some 

 circumstances, especially in the parenchymatous 

 organs and lymph glands, this injury may be so 

 great as to cause the death of the adjacent cells 

 (focal necrosis). When it is of a lower order the 

 connective tissue and endothelial cells respond to 

 the stimulus by dividing mitotically and eventu- 

 ally accumulate in large numbers within a limited 

 area surrounding the micro-organisms. Not only 

 the endothelial cells of the lymph spaces, but also 

 those of the adjacent blood vessels, take part in 

 the proliferation, many of the vessels being obliter- 

 ated in consequence. Not infrequently bacilli arc 

 ingested by the new cells, although the ability of 

 the latter to destroy the organisms is not clearly 

 established. Metchnikoff says that tubercle bacilli 

 may remain intracellular for many months and, 

 although not killed, the pathogenicity is decreased 

 or destroyed. The new cells are of polygonal shape, 

 are fairly rich in cytoplasm, contain large vesicular 

 nuclei and are termed "epithelioid" cells. 



Certain of the epithelioid cells, usually those in Giant ceils. 

 the center of the tubercle, where the bacilli are 

 most numerous, undergo atypical proliferation in 

 that repeated nuclear division takes place without 

 corresponding division of the cytoplasm. This 

 process results in the formation of the multinu- 

 clear giant cell which is so characteristic of the 

 well-developed tubercle, although not distinctive of 

 the disease. According to Weigert, the failure of 

 complete cell division is due to injury to the cyto- 

 plasm (partial necrosis) by the bacteria which the 

 cell contains. Metchnikoff and others take a dif- 

 ferent view of the formation of giant cells, con- 

 sidering that they represent individual epithelioid 



