266 PATHOLOGY OF THE BLOOD AND CIRCULATION. 



him. Such an arrangement of epithelioid and lymphoid 

 cells, with often a large multi nucleated giant-cell in their 

 centre, constitutes the typical histological tubercle (see Fig. 

 106). 



The structure of these tubercles, however, varies consider- 

 ably ; in some instances the leukocytic migration is so great 

 as almost to hide the epithelioid cells. If properly stained, the 

 tubercle bacillus may be found between the epithelioid cells 

 first formed ; later they are more numerous, many being 

 within the cells, especially- within the giant-cells. 



The giant-cell was at one time supposed to be typical of 

 tuberculosis, but it is now known to be frequently found in 

 other chronic inflammatory processes, and in some tumor- 

 formations, though neither so abundant nor so conspicuous. 

 They often have as many as fifteen to twenty nuclei arranged' 

 around the periphery of the cell or at either of its poles. By 

 some observers the giant-cells are supposed to result from 

 the rapid multiplication of the nuclei of the epithelioid cells 

 without division of the cell-protoplasm ; according to Metsch- 

 nikoif and others, they result from the running together of 

 the phagocytic leukocytes and epithelioid cells, combining, as 

 it were, for a common weal. 



Caseation is a most characteristic change affecting the tuber- 

 cle. It consists in the transformation of its centre, often, in 

 fact, of the whole tubercle depending on the abundance and 

 virulence of the bacteria into a structureless, opaque, and 

 granular material, macroscopically resembling cheese. In 

 part this is due to toxins resulting from the growth of the 

 tubercle bacilli ; and in part is due to the entire absence of 

 blood-supply, which can be demonstrated in properly injected 

 specimens, the capillaries being traceable to the margin of the 

 tubercle only. 



Fibroid transformation : When the inflammatory process is 

 very chronic, and the bacilli few in number, in place of a 

 necrotic and destructive process caseation the tissues seem 

 to gain the upper hand, and by the active proliferation and 

 development of the connective-tissue cells a new fibrous tissue 

 is formed and thus the disease is limited ; the tubercle is said 

 to have undergone a fibroid change, and is replaced by scar- 

 tissue. 



