284 THE PROTOZOA 





It has been thought proper by some to consider the malarial para- 

 sites as belonging to two genera, the genus Plasmodium, characterized 

 by round sexual forms and including P. vivax and P. malaria and the 

 genus Laverania, characterized by crescent-shaped sexual forms and 

 including but one species L. malaria, that of aestivo-autumnal malaria. 



In addition to man, infections with parasites of a similar nature are found in mon- 

 keys (Plasmodium kochi; the sexual forms alone seem to be present), in birds 

 (Hcsmamaeba relicta; this organism is usually designated Proteosoma). An infection 

 of crows and pigeons of like nature is Halteridium. Numerous haemosporidia have 

 been reported for bats, various other mammals, tortoises, lizards, etc. 



The life history of the malarial parasite is one of the most interesting chapters in 

 medicine. Laveran discovered the parasite in 1880. In 1885, Golgi noted that 

 sporulation occurred simultaneously at time of malarial paroxysm. Koch, Golgi, 

 and Celli demonstrated existence of different species for different types of fever. 

 King and Laveran (1884) considered possibility of mosquito transmission. Manson 

 (1894) formulated hypothesis that gametes were destined to undergo development in 

 the mosquito from observing that flagellated bodies only appeared some time after 

 the blood was withdrawn. 



Ross (1895) demonstrated that flagellation takes place in the stomach of the mos- 

 quito. McCallum (1897) saw fertilization of macrogametes by microgametes of 

 Halteridium. Opie recognized differences in sexual characteristics. 



Ross (1898) demonstrated life cycle of bird malaria (Proteosoma}, showing for- 

 mation of zygotes and presence of sporozoites in salivary glands. Grassi and Big- 

 nami proved the cycle for Anophelinas for human malaria. In 1900 (Sambon and 

 Low), infected mosquitoes from Italy were sent to London, where, by biting, they 

 infected two persons. 



Life History. Malaria can be transmitted by subcutaneous or 

 intravenous injection of the blood of a patient with the disease into a 

 well person, the same type being reproduced. 



Such a method of transmission is only of scientific interest and the 

 regular method is as follows: An infected anopheline at the time of 

 feeding on the human blood introduces through a minute channel in the 

 hypopharynx the infecting sporozoite of the sexual cycle. 



When man is first infected by sporozoites we have starting up a nonsexual cycle, 

 which is completed in from forty-eight to seventy-two hours, according to the species 

 of the parasite. The falciform sporozite bores into a red cell, assumes a round shape 

 and continues to enlarge (schizont). Approaching maturity, it shows division into a 

 varying number of spore-like bodies. At this stage the parasite is termed a mero- 

 cyte. When the merocyte ruptures, these spore-like bodies or merozoites enter a 

 fresh cell and develop as before. 



Malarial Toxin. At the time that the merocyte ruptures it is 

 supposed that a toxin is given off which causes the malarial paroxysm. 



