HAEMOSPORIDIA 607 



temperature, etc. Boyd and co-workers showed that when the ano- 

 phelines which fed on patients infected by P. vivax were allowed to 

 feed on other persons, their infectivity was as follows: 1-10 days 

 after infective feeding, 87.2%; 11-20 days, 93.8%; 21-30 days, 78%; 

 31-40 days, 66%; 41-50 days, 20%; and over 50 days, none. In a 

 similar experiment with P. falciparum, during the first 10 days the 

 infection rate was 84%, but thereafter the infectivity rapidly dim- 

 inished until there was no infection after 40 days. It is generally 

 known that the development of the parasites in mosquitoes depends 

 a great deal on temperature. Although the organisms may survive 

 freezing temperature in mosquitoes (Coggeshall), sporozoite-for- 

 mation is said not to take place at temperatures below 16° C. or 

 above 35° C. (James). According to Stratman-Thomas (1940), the 

 development of Plasmodium vivax in Anopheles quadrimaculatus is 

 completed within the temperature range of 15-17° to 30° C. It 

 varies from 8 to 38 days after infective feeding. The optimum tem- 

 perature is said to be 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 very 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 

 oocysts may survive the winter and complete their development in 

 the following spring. Duration of infection in Anopheles (Boyd and 

 St.-Thomas, 1943a; Boyd, St.-Thomas and Kitchen, 1936). 



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. 

 (Boyd, 1934, 1940, 1940a; Boyd and Kitchen, 1948). 



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. But since 1945, cases of malaria have rapidly declined and 

 there is prospect of the disappearance of endemic malaria from the 

 United States (Andrews, Quinby and Langmuir, 1950; Andrews, 

 1951). In malarious countries, the disease is a serious economic and 

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

 about a large number of persistent sickness, the loss of man power 

 and retardation of both mental and physical development among 



