SPOROZOA 425 



The young parasites destined to become gametocytes ex- 

 hibit relatively less ameboid movement. Their pigment exists as 

 large granules, some of them even rod-shaped. The macrogame- 

 tocyte attains a diameter of 15 to 25/1 and usually destroys its 

 erythrocyte and escapes from it entirely. The cytoplasm stains 

 deeply with methylene blue. The microgametocyte is smaller 

 with paler cytoplasm. The development of the parasite in the 

 mosquito (Anopheles) is wholly analogous to that of PL falciparum, 

 although there are some slight morphological differences ob- 

 served. Development ceases at temperatures below 16 C. 



ABC D 



FIG. 201. Plasmodium vivax. Stages in growth of the sexual cells (gametocytes). 

 A and B, Young sexual cells distinguished from the agametes by the absence of 

 vacuoles and the more regular outline. C, Full-grown macrogametocyte. D, Full- 

 grown microgametocyte. X22oo. (After Doflein.} 



Plasmodium Malariae. The young quartan parasite is not 

 characteristic, but in its growth it soon stretches as a band across 

 the erythrocyte. Later it almost fills the cell and then segments, 

 producing 6 to 14, most often 8, merozoits. The infected erythro- 

 cyte is not enlarged or distorted nor does it become pale or show 

 granulation. The gametocytes, when stained, are not very 

 different in appearance from the asexual cells. In the living 

 preparation they show much more active protoplasmic move- 

 ment. The sexual cycle takes place in Anopheles and agrees very 

 well with that of the other two malarial parasites, as far as it has 

 been studied. 



Malaria is probably the most important as well as the most 

 well-known human disease due to protozoa. It is characterized 



