1108 



PATHOGENIC PROTOZOA 



and assumes the shape of a signet ring, the red chromatin dot being 

 the stone. This small tertian ring grows rapidly as the fever sub- 

 sides, and at the same time the infected cell increases in size. 

 Twenty-four hours after the chill the ring has grown so much that 

 it is referred to as the large tertian ring, and its tendency to 

 irregularities of shape and ameboid form becomes apparent, and 

 fine granules of pigment, called melanin or hemozoin, begin to be 

 visible. After thirty-six hours the rings will all have grown into 

 large ameboid forms. After about forty hours the parasite occupies 

 almost the entire cell and the pigment begins to collect in masses 



FIG. 153. PLASMODIUM VIVAX. (Army Med. School Collection, Washington, D. C.) 



toward the center. Soon after the first signs of segmentation appear, 

 which becomes more and more distinct until fifteen to twenty 

 separate segments or merozoites are seen, each composed of nucleus and 

 cytoplasm. The pigment of the adult parasite and the unused 

 portion of the cytoplasm are cast off after segmentation as a rest- 

 korper, which is promptly phagocyted and such masses accumulate 

 in the spleen, bone marrow and viscera. With rupture of the 

 erythrocyte, at the time of the chill, the merozoites are set free, 

 and if not phagocyted, immediately attack new erythrocytes and 

 the asexual or schizogenous cycle is repeated, until treatment or 

 Jncreasing immunity halts or alters the cycle. 



