HAEMOSPORIDIA 491 



])eratiire is said to l^e 28° C. at which the development is com- 

 pleted in the shortest time. A period of 24 hours at 37.5° C. will 

 sterilize all but a ver\^ small per cent of Anopheles quadrimaculatus 

 of their Plasmodium vivax infection. This has a bearing on the trans- 

 mission of Plasmodium vivax in summer months. In certain localities 

 (;ocysts may survive the winter and complete their development in 

 the following spring. 



There are three long-recognized species of human Plasmodium. 

 They are P. vivax, P. falciparum and P. malariae. To these P. ovale 

 is here added. Each species appears to be represented by numerous 

 strains or races as judged by the differences in virulence, immuno- 

 logical responses, incubation period, susceptibility to quinine, etc. 



Malaria has been, and still is, perhaps the most important proto- 

 zoan disease of man. In India alone, malaria fever is held to be the 

 direct cause of over a million deaths annually among nearly 100 

 million persons who suffer from it (Sinton, 1936). In the United 

 States, the disease had been prevalent in places in south-eastern 

 States. In malarious countries, the disease is a serious economic and 

 social problem, since it affects the majority of population and brings 

 about an immense number of persistent sickness, the loss of man 

 ])0wer, and retardation of both mental and ])hysical develo])ments 

 among children. 



It must be added here that human ingenuity has been of late util- 

 izing the malarial organism in combatting another disease; namely, 

 naturally induced malaria (P. vivax) therapy has been successfully 

 used in the treatment of patients suffering from general paresis and 

 other forms of neuro-syphilis (Boyd and Stratman-Thomas, 1933). 



P. vivax (Grassi and Feletti) (Fig. 228). The benign tertian malaria 

 parasite; schizogony completed in 48 hours and paroxysm every 

 third day. Ring forms: About 1/4-1/3 the diameter of erythrocytes; 

 unevenly narrow cytoplasmic ring is stained light blue (in Giemsa) 

 and encloses a vacuole; nucleus stained dark-red, conspicuous. 

 Growth period: Irregular amoeboid forms; host cell slightly' enlarged; 

 Schiiffner's dots begin to appear. Grown schizonts : In about 26 hours 

 after paroxysm; occupy- about 2/3 of the enlarged erythrocytes, up 

 to 12/z in diameter, which are distinctly paler than uninfected ones; 

 Schiiffner's dots more numerous; brownish haemozoin granules; a 

 large nucleus. Schizogonic stages: Repeated nuclear division produces 

 12-24 or more merozoites; multinucleate schizonts about 8-9m in 

 diameter; haemozoin granules in loose masses; merozoites about 1.5,u 

 long. Gamctocytes: Time recjuired for development of ringform into a 



