486 PROTOZOOLOGY 



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. 499) 



Without pigment granules; minute parasites of erythrocytes 



Family 3 Babesiidae (p. 502) 



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. 



Until recent years it had been generally believed that the sporo- 

 zoites upon entering the blood vessel, penetrate and enter immedi- 

 ately the erythrocyte and begin intracorpuscular development, 

 which process Schaudinn (1902-1903) reported to have seen in life. 

 Although some authors still follow this view, thei'e are increasing 

 numbers of others who doubt Schaudinn's observation, since no one 

 has up to the present time been able to duplicate the observation. 

 James (1931) noticed the ineffectiveness of quinine as a causal pro- 

 phylactic in malaria infection, and suggested the possibility that 

 the sporozoites are carried away immediately from peripheral to 

 visceral circulation and develop in the cells of reticulo-endothelial 

 system. 



Boyd and Stratman-Thomas (1934) found that the peripheral 

 blood of a person who had been subjected to the bites of 15 anophe- 

 line mosquitoes infected by Plasmodium vivax, did not become in- 

 fectious to other per.sons by subinoculation until the 9th day and that 

 the parasites were not observed before the 11th day in the stained 

 films of the peripheral blood. Warren and Coggeshall (1937) observed 

 that when suspensions of the sporozoites of P. cathemerium ob- 

 tained from infected Culex pipiens, were inoculated into canaries, 

 the blood was not infectious for 72 hours, but emulsions made from 

 the spleen, liver and bone marrow contained infectious parasites 

 which brought about infection by subinoculations in other birds. 

 These and many similar observations cannot be satisfactorily ex- 

 plained if one follows Schaudinn's view. The fact that P. elongatum 

 is capable of undergoing schizogony in the leucocytes and reticulo- 



