Microbic Diseases Individually Considered. 248 



tlieir nuclei divide, and this is quickly followed by 

 the division of the cell body. Simultaneously, the 

 elements take a polyhedral form (epithelioid cells). 

 This division continues and gives birth to a mass of 

 new cells which constitutes the first stage of the 

 tubercle. In the course of this initiatory period a 

 certain number of elements may break up and dis- 

 appear, but, as a rule, those which are directly in 

 contact with the bacillar focus, around the center of 

 irritation, acquire considerabledimensions, their nuclei 

 continuing to multiply whilst the cell body remains 

 single (giant cells) ; these giant cells, however, are 

 also formed, at least under certain circumstances, by 

 the fusion of several epithelioid cells. When the 

 process begins in the interior of the blood vessels the 

 leucocytes participate in it from the first, but in the 

 opposite case they only intervene at a later stage by 

 emigrating toward the invaded parts in order to en- 

 ter into the struggle against the intruding germs; 

 they then conduct themselves like the elements men- 

 tioned above. During this time there is formed at 

 the periphery of the epithelioid zone a layer com- 

 posed of leucocytes and fixed cells in way of mul- 

 tiplication, which in some degree limits or temporarily 

 arrests the extension of the process. 



The giant cells especially act as phagocytes ; they 

 contend against the bacilli, impair their vitality and 

 tend to bring about their degeneration. Metschni- 

 koii' has described a series of involution forms of 

 bacilli in the giant cells of the spermophile. The 

 epithelioid and lymphoid cells have the same prop- 

 erty. Both giant cells and epithelioid cells may be 

 absent when the bacilli are extremely virulent or 



