602 PROTOZOOLOGY 



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 persons 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- 

 endothelial cells in addition to erythrocytes of host birds had been 

 observed by Raffaele (1934) and Huff and Bloom (1935). 



As to the nature of development of Plasmodium during the pre- 

 patent period, James and Tate (1938) showed that there occur schiz- 

 onts and schizogonic stages in the endothelial cells of the spleen, 

 heart, liver, lung, and brain of the birds infected by P. gallinaceum 

 (Fig. 257). They suggested the term exo erythrocytic to this schizog- 

 ony in contrast to the well known erythrocytic schizogony. Huff and 

 his co-workers made a series of detailed studies of pre-erythrocytic 

 stages of this avian species. According to Huff and Coulston (1944). 

 the sporozoites that are inoculated into the skin of chickens, are en- 

 gulfed by phagocytes in 0.5-6 hours. In heterophile leucocytes, the 

 sporozoites are apparently killed, but in the cells of lymphoid- 

 macrophage system they develop into cryptozoites (Huff, Coulston 

 and Cantrell, 1943) by assuming a spheroid shape and increasing in 

 size for the first 36 hours, during which time there is a rapid re- 

 peated division of the nucleus. The schizogony is completed in 36 to 

 48 hours, each giving rise to 75-150 merozoites. These merozoites 

 enter new lymphoid-macrophage and endothelial cells and become 

 metacryptozbites which undergo schizogony similar to that of the 

 cryptozoite. After three or four generations, the merozoites enter 

 erythrocytes, and thus the erythrocytic stages appear in five to 10 

 days. Porter (1942) distinguishes two types of exoerythrocytic de- 

 velopment in avian Plasmodium; namely, gallinaceum-type just 

 quoted and elongatum-type 



Exoerythrocytic or E.-E. stages were further discovered in saurian 

 Plasmodium (Thompson and Huff, 1944; Garnham, 1950) and in 

 mammalian malaria organisms (Shortt and Garnham, 1948). In P. 



