Chap. 21 THE PROTOZOANS 447 



other red blood cells and the cycle of growth and asexual multiplication just 

 described begins over again. Sexual development starts with a stage that dif- 

 fers scarcely at all from the sporozoite from which the asexual generations 

 develop. It also grows in. the red blood cell but instead of dividing into 

 merozoites it gives rise to either a male organism (microgametocyte) or 

 female (macrogametocyte). If left in the human body, these male and female 

 organisms usually die. 



Description of the parasite's life in the female mosquito. If the gameto- 

 cytes are taken into the stomach of a female anopheline mosquito they develop 

 into easily recognized male and female individuals (Fig. 21.15). The nucleus 

 of the male gametocyte (microgametocyte) divides and within a few minutes 

 6 to 8 microgametes, each with a flagellum, are formed. The female gameto- 

 cyte (macrogametocyte) does not divide and is the macrogamete. Into it one 

 of the microgametes enters. The union of these two cells makes a zygote (cor- 

 responding to the fertilized egg in higher animals). It becomes wormlike and 

 is called an ookinete. The ookinete bores into the stomach wall of the mosquito 

 and there, surrounded by a kind of cellular capsule (oocyst), it divides into 

 many sporozoites. There may be more than 10,000. These grow until they 

 burst the capsule and are freed in the body cavity of the mosquito, usually 

 within 10 days to three weeks depending on the temperature. In their migra- 

 tion in the body cavity, many of them reach the salivary glands and bore into 

 them, finally lodging in the tubes which carry saliva into the mouth. As many 

 as 200,000 sporozoites may be packed in one mosquito's salivary glands. 

 When an infected female mosquito bites (only the females suck blood), she 

 always injects her saliva into the blood capillary which she has pierced, at the 

 same time injecting parasites into the blood. 



Benign and Malignant Malarias. Benign malaria is characterized by periods 

 of fever, the malarial paroxysms, broken by periods of normal or below normal 

 temperatures. The period of fever consists of a seemingly cold stage of chills 

 during which there is actually a rise in temperature, a hot stage of high tem- 

 perature and a sweating stage, all of these occurring within about 10 to 12 

 hours. 



The nonsexual cycle of the life of the parasite occurs in the period between 

 the paroxysms. For Plasmodium vivax of benign tertian malaria, this period 

 lasts 48 hours and the paroxysm occurs on the third day. Plasmodium malariae 

 of benign quartan malaria has a nonsexual period of 72 hours and there is a 

 paroxysm on the fourth day. In malignant malaria the temperature changes are 

 likely to be less regular than in benign types and the paroxysms last longer. 



Malignant tertian malaria is caused by Plasmodium falciparum. This para- 

 site multiplies in very great numbers. Corpuscles containing their asexual 

 stages tend to clump in the capillaries. When such a clogging of capillaries 

 occurs in the brain ("cerebral malaria"), the patient becomes unconscious. In 



