PARASITES AND DISEASE (VEGETABLE PARASITES) 169 



the mononuclear variety, which do not undergo the 

 rapid degeneration of the polynuclears. 



(4) A reticulum of fibers is formed by the fibrillation 

 and rarefaction of the connective-tissue matrix. This 

 is most apparent, as a rule, at the margin of the growth. 



(5) In some tubercles giant cells are formed by in- 

 crease in the protoplasm and in the nuclei of the indi- 

 vidual cells, or possibly by the fusion of several cells. 



Once formed the tubercle may undergo 



Caseation. At the center of the tubercle the cells 

 under the action of the bacilli and their toxins undergo 

 coagulation necrosis and are converted into a structure- 

 less mass. The process extends until the entire tubercle 

 is converted into a cheesy, homogeneous mass, in which 

 the bacilli are still active, after which it may undergo 

 softening, encapsulation, or calcification. 



Instead of caseation, which must be looked upon as 

 degenerative and dangerous, the tubercle may undergo 



Sclerosis. With the destruction of the cells at the 

 center of the tubercle there may occur fibroid transform- 

 ation at the periphery, the tubercle being converted into 

 a firm resistant mass. It is in this manner that healing 

 occurs. 



By the fusion of softened caseous tubercles, cavities 

 are formed which are sometimes termed cold abscesses, 

 because of the absence of true pus in their contents. 



Morbid Physiology. In addition to the disturbances 

 of function which the tuberculous infection causes at 



