444 



SPECIFIC MICRO-ORGANISMS 



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 PI. falci- 

 parum, although there are some slight morphological differences 

 observed. Development ceases at temperatures below i6° C. 

 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- 



FiG. 209. — Plasmodium vivax. Stages in growth of the sexual cells (gameto- 

 cytes). A and B, Young sexual cells distinguished from the agametes by the ab- 

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

 D, Full-grown microgametocyte. X2200. {After Doflein.) 



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 th";y show much more active protoplasnjic 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 

 by recurrent paroxysms of fever with afebrile intervals, progress- 

 ive anemia and weakness, with the accumulation of a dark brown 

 or black pigment in the spleen and liver. This pigment is pro- 

 duced by the parasites and set free into the blood when they 



