MALARIA. 187 



Ross (1895) demonstrated that flagellation takes place in the 

 stomach of the mosquito. McCallum (1897) saw fertilization of 

 macrogametes by microgametes of Halteridium. Opie recognized 

 differences in sexual charactersistics. 



Ross (1898) demonstrated life cycle of bird malaria (Proteosoma), 

 showing formation of zygotes and presence of sporozoites in salivary 

 glands. Grassi and Bignami proved the cycle for Anophelinae 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. When man is at first infected by sporozoites we have 

 starting up a non-sexual cycle which is completed in from forty-eight 

 to seventy-two hours, according to the species of parasite. The falciform 

 sporozoite 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 merocyte. When the merocyte ruptures, these spore-like 

 bodies or merozoites enter a fresh red cell and develop as before. 



At the time that the merocyte ruptures it is supposed that a toxin is 

 given off which causes the malarial paroxysm. The cycle goes on by 

 geometric progression from the first introduction of the sporozoite, but 

 it is usually about two weeks before a sufficient number of merocytes 

 rupture simultaneously to produce sufficient toxin for symptoms 

 (period of incubation). This cycle is termed schizogony. 



After a varying time, whether by reason of necessity for renewal of 

 vigor of the parasite by a respite from sporulation, or whether from 

 a stand-point of survival of the species, sexual forms (gametes) develop. 

 Some think that sporozoites of sexual and nonsexual characteristics are 

 injected at the same time. It is usually considered, however, that sexual 

 forms develop from preexisting nonsexual parasites. 



These gametes show two types: the one which contains more pig- 

 ment, has less chromatin and stains more deeply blue is the female a 

 macrogamete; the other with more chromatin, less pigment and stain- 

 ing grayish-green rather than blue is the male a microgametocyte. 

 When the gametes are taken into the stomach of the Anophelinae, the 

 male cell throws off spermatozoa -like projections, which have an active 



