764 PATHOGENIC PROTOZOA 



sporozoites. These possess the power of ameboid motion, and rapidly 

 penetrate into an erythrocyte, in which they grow quickly ; they con- 

 stantly move about inside the cell until nearly full grown, and are 

 during this stage called trophozoites. The substance of the erythrocyte 

 is rapidly consumed by the parasite and a dark pigment, melanin or 



FIG. 182. MIDGUT OF CULEX MOSQUITO, COVERED WITH OOCYSTS OF PROTEOSOMA 

 PR^ECOX. V, Vasa malpighii. (After Doflein and Ross. MacNeal, "Pathogenic 

 Microorganisms," published by P. Blakiston's Sons & Co.) 



hemozoin, is formed from the destroyed hemaglobin. The mature 

 parasite divides into many small forms called merozoites, and these, 

 when freed by the rupture of the degenerated erythrocyte, escape into 

 the blood plasma, and if not phagocyted, penetrate other erythrocytes 

 and repeat the asexual or schizogenous cycle. The pigment and undi- 

 vided portion (restkorper) of the cytoplasm of the mother cell 

 accumulate in the bone marrow, spleen and other viscera. 



MALARIA 



This is one of the most common and widespread of preventable 

 human diseases, and in some localities is the cause of a greater mor- 

 tality and morbidity than tuberculosis. It is caused by one or more 

 of the three forms of the malarial plasmodium. As a rule the infec- 

 tions are simple, yet in the tropics it is not uncommon to find two 

 species of plasmodia in the same patient, and this condition is called 

 a mixed infection. 



History. The disease under various names, as chills and fever, 

 Roman fever, Chagres fever, has been known since the greatest an- 

 tiquity. The cause was not discovered until 1880, when Laveran, a 

 French military surgeon stationed in Algeria, first saw the organism 

 and described it as the cause of malaria. He saw and described not 

 only the pigmented trophozoite, but also the crescentic gametes and 

 flagellating microgametocytes, and, because of the activity of the 

 flagella, called the parasite Oscillaria malaricBj a name afterwards 



