600 PROTOZOOLOGY 



produces numerous sporozoites (p). When fully mature, the oocyst 

 ruptures and the sporozoites are set free in the haemolymph through 

 which they migrate to the salivary glands (g, r). The sporozoites 

 make their way through the gland epithelium and finally to the duct 

 of hypopharynx. They are ready to infect a human victim when the 

 mosquito pierces with its proboscis the skin for another blood meal. 

 Thus the sexual reproduction occurs in the mosquito (primary host) 

 and the asexual reproduction, in man (secondary host). 

 The Haemosporidia are divided into three families: 



With pigment granules 



Schizogony in peripheral blood of vertebrates . . Family 1 Plasmodiidae 



Gametocytes in peripheral blood; schizogony elsewhere 



Family 2 Haemoproteidae (p. 618) 



Without pigment granules; minute parasites of erythrocytes 



Family 3 Babesiidae (p. 622) 



Family 1 Plasmodiidae Mesnil 



Genus Plasmodium Marchiafava and Celli. Schizogony in erythro- 

 cytes and also probably in endothelial cells of man, mammals, birds, 

 and reptiles; sexual reproduction in blood-sucking insects; widely 

 distributed. Numerous species. 



In all species, the infection in a vertebrate host begins under natu- 

 ral condition with the inoculation of the sporozoites by a vector 

 mosquito. The form, size and structure of the sporozoites vary widely 

 within a species so that identification of the species in this stage ap- 

 pears to be impossible (Boyd, 1935). Until some 20 years ago, it had 

 been generally believed that the sporozoites upon entering the blood, 

 penetrate and enter immediately the erythrocyte and begin intra- 

 corpuscular development, which process Schaudinn (1902) reported 

 to have seen in life. In this the eminent pioneer protozoologist was in 

 error, since no one has up to the present time been able to confirm 

 his observation. Et. and Edm. Sergent (1922) were the first to find 

 that quinine given in large doses to the canaries on the day the birds 

 were bitten by Culex mosquitoes infected with Plasmodium relictum, 

 did not prevent infection in the birds. During the course of studies on 

 P. vivax in cases of general paresis, Yorke and MacFie (1924) dis- 

 covered that if quinine was given before the inoculation of infected 

 blood, no infection resulted, but if the sporozoites were inoculated, 

 quinine did not prevent infection. Similar observations were made 

 on other species of malarial organisms. James (1931) suggested the 

 possibility that the sporozoites are carried away from peripheral to 

 visceral circulation and develop in the cells of the reticuloendo- 

 thelial system. 



