86 GUIDE TO THE STUDY 



corpuscle, is deposited in it. This pigment makes it possible 

 to detect the presence of malarial parasites even in freshly 

 drawn and unstained preparations. It is characteristic of infec- 

 tions with Plasmodium vivax that the infected corpuscles become 

 enlarged as the parasite develops. Not infrequently they become 

 stippled with deep-staining granules, the Schiiffner's dots. In 

 the older parasites the dark pigment becomes more concentrated 

 and the red-staining chromatin divides into small masses near the 

 periphery. These with a small amount of protoplasm become 

 the asexual spores or merozoites. In P. vivax they number 15 to 

 25, or thereabouts. The corpuscle ruptures and the merozoites, 

 along with the pigment and a little residual protoplasm, escape 

 into the blood stream. Such of the merozoites as are not 

 destroyed by phagocytes re-enter red corpuscles and thus continue 

 the asexual phase, or schizogony. The entire cycle from sporula- 

 tion to the next escape of merozoites is undergone in 48 hours. 



The sexual cycle, or sporogony, is completed in mosquitoes of 

 the genus Anopheles, but the gametocytes are to be found in the 

 human blood after the disease has progressed for some days. 

 They can be distinguished from the schizonts by the fact that 

 in the full-grown stage the chromatin forms one mass instead of 

 being broken up preparatory to formation of merozoites. In the 

 macrogametocyte this mass is compact and excentrically placed 

 and the pigment consists of long rods. In the microgametocyte 

 the chromatin is centrally placed and more diffuse, and the 

 pigment is in small rods. 



Plasmodium falciparum. — Preparations from a case of malig- 

 nant malaria, caused by Plasmodium falciparum, should be 

 compared with the above. As a rule only the ring stages and the 

 mature gametocytes are found in the peripheral blood, the 

 schizogony occurring in the internal organs of the host. There 

 will be demonstrated sections of the brain from a fatal case of 

 malignant malaria showing the schizonts in the capillaries. 

 The gametocytes are very characteristic crescent or sausage- 

 shaped forms. The macrogametocyte has its chromatin in a 

 single mass in the center and the pigment clumped, while the 

 microgametocyte stains less deeply, has more diffuse chromatin, 

 and has its pigment scattered. 



Plasmodium malariae. — A third species of malarial parasite, 

 Plasmodium malaria;, is the cause of quartan malaria of man. 

 The schizogony is completed in 72 hours. The infected corpus- 



