682 MICROBIOLOGY OF THE DISEASES OF MAN AND ANIMALS. 



diarrhoea in chicks is due to an infection by a coccidium (Coccidium 

 avium). (Bacillary White Diarrhoea of Chicks, p. 604). 



ELEMOSPORIDIA. 



The most important parasites of this order are those, belonging to the 

 Genus Plasmodium, which cause malaria in man. Organisms similar to these 

 are parasitic in the red blood cells of monkeys and bats. In birds, Proteosoma 

 and Hamoproteus are two genera of parasites of the red blood cells; it was 

 the study of these avian parasites which led to the discovery of the way in which 

 malaria is transmitted by the bites of a mosquito. 



PLASMODIUM. 



Three species of this genus are parasitic in man: Plasmodium vivax, the 

 cause of tertian malaria, Plasmodium malaria causing quartan malaria, and 

 Plasma dium falciparum, which causes quotidian malarial fever. 



MALARIA. 

 Plasmodium. 



Malaria is a disease caused by a Plasmodium and transmitted by the 

 bite of an anopheline mosquito. 



Malaria exists in all parts of the tropical and subtropical world 

 (Fig. 126). 



A young malarial parasite enters a red cell and supports itself by feeding upon the 

 cell's substance. The parasite grows, and if it is to multiply asexually, divides into a 

 number of merozoites which it frees by bursting. Those of the merozoites which 

 escape ingestion by the white cells of the blood enter red cells where they may 

 again multiply asexually, or they may develop into sexual forms. When blood, 

 containing malarial parasites, is ingested by a suitable mosquito, all the parasites, 

 except the adult sexual ones, are digested and die. Soon after they are ingested, 

 both microgametocyte and macrogametocyte extrude polar bodies and the micro- 

 gametocyte produces several microgametes, one of which enters and fertilizes 

 the macrogamete. The macrogamete then becomes a motile ookinet, which makes 

 its way until it comes to lie just beneath the outer surface of the mosquito'? 

 stomach. There it develops, as an oocyst, until it reaches several times its 

 original size. Its ectoplasm divides into a number of areas, or sporoblasts, each of which 

 subdivides to form many very small, hair-like sporozoites. When the oocyst bursts, 

 some of the sporozoites find their way into the salivary glands of the mosquito, and, 

 when it bites, they are extruded, with the saliva, into the body of the person from whom 



