402 FAMILY: TRYPANOSOMIDyE 



(Fig. 187). In whatever part of the body parasites are found — and they 

 may occur in any organ or tissue — they are practically always within 

 the cytoplasm of large cells of the endothelial type. It was Christophers 

 (1904) who first showed that, pathologically, kala azar was essentially an 

 infection of the endothelial cells of the blood-vessels. It must be remem- 

 bered that in smears of organs or in blood-films, the parasites are often 

 seen extracellularly, but, though such forms must occur in the passage 

 of parasites from cell to cell, the extracellular position as usually seen 

 is due to the breaking-up of the large cells in preparation of the films. 







si's . 4'«'<^««'vv ?' 



Fig. 186. — Section of Human Spleen (x 750): Leishmania donovani within 

 Macrophages. (After Nattan-Larrier, 1913.) 



Not infrequently, portions of the cytoplasm, fragmentation bodies, of 

 these large cells are broken off in the process of film-making, and if found 

 to harbour parasites, they may produce an appearance of multiple seg- 

 mentation, especially when the outlines of the organisms are imperfectly 

 stained. In sections of tissues where artificial rupture of the cells has 

 not taken place, the parasites are practically always found to be intra- 

 cellular. Furthermore, in films, parasites are sometimes seen lying over 

 red blood corpuscles, and have been described as actually within these 

 cells, like the malaria parasite and piroplasmata. This is merely an 



