SPOIIOZOA 1105 



During the first part of the acute attack the predominant forms are 

 sehizonts, but later in the course of the disease, as a result of 

 increasing immunity or of treatment, the sporogenous cycle becomes 

 evident. The trophozoites, in increasing numbers, develop into 

 sporonts rather than schizonts. These forms do not develop a vacuole 

 but increase in size and remain round or oval bodies. When mature 

 they occupy most of the red cell but show no sign of nuclear change 

 or of segmentation and they are then called gametocytes. The sex 

 can be distinguished in well stained specimens by remembering that 

 the micro gametocyte, or male form, is rich in nuclear chromatin, 

 of which the flagella or spermatozoa will be formed after the game- 

 tocyte has been ingested by the proper mosquito. The macro game- 

 tocyte, or female form, is distinguished, on the other hand, by the 

 store of nutrient material in the cytoplasm, causing it to stain 

 deeply. 



After ingestion by a susceptible mosquito the red cells undergo 

 dissolution and the contained gametocytes are liberated. The micro- 

 gametocyte sends out several micro gametes (flagella) one of which 

 fertilizes a macrogamete by penetrating the cytoplasm and uniting 

 with its nuclear chromatin. The fertilized cells change its shape 

 from round to ovoid and becomes motile and is called a traveling 

 vermicule, or ookinette. It travels to the stomach wall which it 

 penetrates and comes to rest on its outer surface and is then called 

 an ob'cyst or zygate. The cyst or zygate increases in size with 

 each successive segmentation of its nucleus until it is ripe. It then 

 ruptures and discharges a mass of sporozoites into the body cavity. 

 These wander to all parts of the body of the mosquito but many 

 reach the salivary glands and later the saliva, and when next the 

 mosquito bites they are injected into the new host. 



In the state of Mississippi Bass has shown that the age distribution 

 is such that 23 per cent of the population under 20 years of age 

 showed parasites in the blood, whereas only 19 per cent of persons 

 over 20 years were infected, and that the five-year period from 5 to 

 9 years of age showed the greatest number of infections. 



Eace and color are important, and negroes showed 36 per cent 

 more infections than whites, and the high point is reached much 

 earlier in black than in white children. (South Med. Jour., 1919, 

 12, 456.) 



The parasites belong to the class of hemosporidia, and are closely 

 related to the coccidia, which are parasites of epithelial cells, while 



