PROTOZOA 185 



life history of the organism in general, pointing out the differ- 

 ences shown by the varieties later. 



i. The Asexual Cycle in Man. An infected mosquito con- 

 veys the parasites into the blood as minute hyaline bodies 

 which enter the blood-cells. At first they are small, round, 

 colorless bodies, exhibiting more or less active ameboid motion 

 in the fresh blood. Sometimes, particularly in the estivo- 

 autumnal form, a ring shape is assumed. Their size gradually 

 increases and pigment-granules appear, while in stained speci- 

 mens a nucleus containing chromatin granules is visible. As 



Fig. 114. Pure culture of trypanosomes of mosquitoes Crithidia fas- 

 ciculata. Elongated crithidia from same preparation as preceding (Novy, 

 MacNeal, and Torrey). 



the parasite approaches maturity, the chromatin becomes 

 scattered, and finally the protoplasm or mother-cell, known as 

 sporocyte, divides into six to twenty spores, daughter-cells or 

 merozoites, each containing a portion of the chromatin. The 

 number of spores formed and their arrangement before seg- 

 mentation takes place differ in the three varieties and will be 

 noted below. The spores burst through the envelop of the red 

 corpuscle and become free in the blood, but speedily enter 

 fresh corpuscles and pass through the same series of changes. 

 The febrile stage is synchronous with sporulation and liberation 

 of the young forms. 



