Malarial Parasites 501 



time that varies — twenty-four to forty-eight hours (Plasmodium 

 falciparum), forty-eight hours (Plasmodium vivax), seventy-two 

 hours (Plasmodium malarise) — the schizonts mature, becoming nearly 

 as large or quite as large as the corpuscles. The pigment granules 

 now collect at the center and the substance of the parasite divides 

 into a group of equal-sized merozoits, commonly known as spores. 

 Of these there are usually eight in the meroblasts of Plasmodium 

 malariae, from fifteen to twenty-five in those of Plasmodium vivax, 

 and from eight to twenty-five in Plasmodium falciparum. As the 

 spores become fully formed and ready to separate, the paroxysm of 

 the disease begins. It ends as the spores are freed and enter new 

 corpuscles to begin the cycle over again. After a good many parox- 

 ysms have occurred it may be observed that not all of the schizonts 

 change to meroblasts and form spores. Some remain large spheroidal 

 bodies or, as in Plasmodium falciparum, assume a peculiar crescentic 

 form and remain unchanged in the blood. These are the sexual 

 |)arasites. The female is usually the larger and is known as the 

 macrogametocyte, the male, the smaller, the microgametocyte. These 

 are the bodies which, when removed by the mosquito, lay the foun- 

 dation of its infection. When they are withdrawn for microscopic 

 exarnination or exposed to the intestinal juices of the mosquito, the 

 microgametocyte becomes tumultuous, its granules are observed to 

 be in a state of active cytoplasmic streaming, and suddenly there 

 burst forth long slender filaments, the microgametes or spermatozoits. 

 These correspond with the flagella of Laveran and others, and are the 

 same bodies that Manson thought might be the form in which the 

 parasite leaves the insect's body. The microgametes lash vigorously 

 for a time, then, breaking loose, swim away, and, as MacCallum 

 observed, conjugate with macrogamefes, sexually perfect cells formed 

 from the macrogametocytes by "reduction division" and polar body 

 formation, thus fertilizing them. As the result of this fertilization a 

 zygote or ookinete is formed. It assumes a somewhat elongate pointed 

 form and attaches itself to the wall of the mosquito's stomach. In 

 the course of time it penetrates and appears upon the outside, project- 

 ing into the body cavity. It grows larger and rounder, divides into 

 several segments, and eventually forms an oocyst with many small 

 cells, which break up into myriads of tiny elongate fusiform bodies, 

 the sporozoits. These, in the course of time, seem to find their way 

 to the salivary glands, entering into the epithelial cells and taking 

 radial positions about the nuclei, where they remain for a time. Later, 



18, ookinete on the wall of the mosquito's stomach; ig, penetration of the gastric 

 epithehum by the ookinetes; 20 to 25, stages of sporogenesis on the outer wall 

 of the mosquito's stomach; 26, migration of the sporozoits to the salivary glands 

 of the mosquito; 27, salivary gland with sporozoits in the epithelial cells, and 

 escape of the sporozoits from the salivary glands through the insect's proboscis 

 at the time a human host is bitten; i, free sporozoit from the mosquito's saliva 

 in the human blood; 2, penetration of the sporozoit into a red blood-corpuscle, 

 beginning the human cycle again CLuhe). 



