610 PROTOZOOLOGY 



cies predominates in the spring and early summer over the other 

 species. 



P. falciparum (Welch) {Laverania malariae Grassi and Feletti; P. 

 tenue Stepens) (Fig. 260). The subtertian, malignant tertian or aesti- 

 vo-autumnal fever parasite; schizogonic cycle is somewhat irregular, 

 though generally about 48 hours. Ring forms: Much smaller than 

 those of P. vivax; about In in diameter; marginal forms and multiple 

 (2-6) infection common ; nucleus often rod-form or divided into two 

 granules; in about 12 hours after paroxysm, all schizonts disappear 

 from the peripheral blood. Growth and schizogonic stages: These are 

 almost exclusively found in the capillaries of internal organs; as 

 schizonts mature, Maurer's dots appear in the infected erythrocytes; 

 when about 5/x in diameter, nucleus divides repeatedly and 8-24 or 

 more small merozoites are produced; haemozoin granules dark brown 

 or black and usually in a compact mass; infected erythrocytes are not 

 enlarged. Gametocytes: Mature forms sausage-shaped ("crescent"), 

 about 10-12ju by 2-3ju; appear in the peripheral blood. Macrogameto- 

 cytes stain blue and contain a compact nucleus and coarser granules, 

 grouped around nucleus; micro gametocytes stain less deeply blue or 

 reddish, and contain a large lightly staining nucleus and scattered 

 smaller haemozoin granules. The organism invades both mature and 

 immature erythrocytes (Kitchen, 1939). Cytological study of micro- 

 gametocytes and microgametes (MacDougall, 1947) ; different strains 

 (Kitchen and Putnam, 1943); induced infection (Boyd and Kitchen, 

 1937); incubation period (Boyd and Kitchen, 1937b; Boyd and 

 Matthews, 1939); immunity (Boyd and Kitchen, 1945). 



The subtertian fever parasite is widely distributed in the tropics. 

 In the subtropical region, it is more prevalent in late summer or early 

 autumn. It is relatively uncommon in the temperate zone. The 

 malignancy of the fever brought about by this parasite is attributed 

 in part to decreased elasticity of the infected erythrocytes which be- 

 come clumped together into masses and which adhere to the walls of 

 the capillaries of internal organs especially brain, thus preventing the 

 circulation of blood through these capillaries. 



P. malariae (Laveran) (Fig. 261). The quartan malaria parasite; 

 schizogony in 72 hours and paroxysm every fourth day. Ring forms: 

 Similar to those of P. vivax. Growth period: Less amoeboid, rounded; 

 in about 6-10 hours haemozoin granules begin to appear; granules 

 are dark brown; in 24 hours, schizonts are about 1/2 the diameter 

 of erythrocytes which remain normal in size; schizonts often 

 stretched into "band-form" across the erythrocytes; no dots com- 

 parable with Schiiffner's or Maurer's dots. Mature and segmenting 



