272 spoRozoA. 



(flattened marginal forms) or disc-shaped bodies with a large 

 central vacuole and with an arched appearance (bridge forms). 

 In living blood, in the warm stage, the trophozoite may be 

 seen actively throwing out and withdrawing pseudopodia 

 within the corpuscle : this special activity earned the name 

 P. vivax for the species. After further growth the trophozoite 

 has a more irregular shape (amoeboid form) or the ring 

 form continues, the vacuole becomes larger, and a few yellow 

 or hght brown pigment granules are deposited in the cyto- 

 plasm. Growth is accompanied by three distinct changes 

 in the red blood- corpuscle ; it becomes larger, shghtly paler, 

 and shows on its surface a number of fine granules, which 

 stain bright pink by Romanowsky stains. These granules 

 are known as Schiiffner's dots : they are not visible in poorly 

 stained films. The schizont has the form of a circular plate 

 of cytoplasm, which almost completely fills the enlarged red 

 blood- corpuscle . Nuclear multipHcation takes place, producing 

 twelve to twenty-four nuclei. The cytoplasm gradually 

 segments into as many portions as the nuclei, and the merozoites 

 separate, leaving the pigment in the residual cytoplasm. 

 The merozoites are liberated into the plasma by the bursting 

 of the corpuscle and enter other corpuscles. The majority 

 of parasites complete schizogony at or near the critical period 

 of forty-eight hours, though some may do so before or after. 

 Sometimes double infections take place, sporozoites having 

 been introduced on two successive nights. The schizonts 

 of one batch will attain maturity one day and those of the 

 other twenty-four hours later. Thus there will be daily attacks 

 of fever instead of every other day. The initial attack of 

 fever takes place about ten to twelve days after the intro- 

 duction of the sporozoites by a mosquito. 



After schizogony has taken place a number of times some 

 of the merozoites develop into gametocytes. This phase 

 takes place mostly in the blood-vessels of the spleen or bone- 

 marrow, as the red blood-corpuscles containing the developing 

 gametoc3^es are held up in these organs. The gametocytes 

 attain maturity in about ninety-six hours, and the effect 

 produced on the red blood-corpuscles is the same as in the 

 case of the schizonts. The gametocytes are circular in outhne, 

 more regularly circular than the schizont ; each contains 

 a larger number of pigment granules, more or less uniformly 

 distributed in the cytoplasm, and a single nucleus. The 

 male gametocyte has hyaline cytoplasm which stains a pale 

 blue, and the nucleus is larger and contains fine chromatin 

 granules. The female gametocjrte has denser cytoplasm, 

 which stains more deeply blue, has a smaller nucleus, with 

 a single karyosome or a group of granules. Both contain 

 yellowish -brown pigment granules distributed in the cytoplasm. 



