Tuberculosis. 



301 



others believe, as the name endotheHoid would suggest (epithehoid 

 synonymous and used rather to indicate the general epithelial-like 

 appearance than referring to the source of these elements), 

 that they are derived from the endothelial cells, mainlv those of the 

 lymph spaces in which the bacilli are lodged. The true lympho- 

 cytic nature and origin of the peripheral zone of small mono- 

 nuclear cells is commonly accepted. There is considerable uncer- 

 tainty as to the mode of formation of the giant cells. According to 

 some they are the result of the fusion of cells undergoing hyaline 

 or coagulative change ; and are therefore looked upon by these per- 

 sons as evidence of beginning or advancing degeneration in the 

 focus. From this standpoint a miliary tubercle when exhibiting one 

 or more giant cells in its structure is essentially a degenerating 

 tubercle. Others believe that they are the result of inefficient proto- 

 plasmic division of growing cells, in other words are of a prolif- 

 erative type of development and not of the significance just indi- 

 cated. Tubercles of fresh and undegenerated structure are com- 

 monly called gray tubercles ; older and degenerated ones, yellow 

 tubercles. | 



The site of formation of the tubercle is in the connective tissue 

 framework of the affected part or in the walls of the blood vessels 

 and in the lymphatic foci of die tissue. This gives the cellular pro- 

 liferation a connective tissue frame work or reticulum as a skeleton, 

 which may, however, be in part, too, a product of the fibroblasts 

 and giant cells, which of course also supply an intercellular sub- 

 stance. Although endothelial cells also take part in the formation 

 of the cellular nodule these do not develop into vascular buds, and 

 the miliary tubercle is avascular. The endothelial cells in their pro- 

 liferation may occlude the lumen of the capillary vessels ; and more- 

 over by the growth of the cellular mass the vessels may be com- 

 pressed. In contrast to these factors the tuberculous reaction may 

 also present itself as a dift'use proliferation, without production of 

 sharply defined nodules and with the formation of new blood ves- 

 sels. In this case there is found a soft, gray or grayish red layer, 

 especially seen in serous surfaces (bovine heart), which is not likely 

 to undergo more than a slight caseation, or. if it does, only after 

 considerable time. This, too, always has a distinct granular appear- 

 ance looking as if caused by fusion of closely set miliary tubercles. 

 This diffuse growth is due to the fact that separate groups of tuber- 

 cle bacilli do not here occur as the centres of nodular circumscribed 

 cellular collections, but that large numbers of the organisms are 

 scattered all through the tissue. 



