DISEASES CAUSED BY PROTOZOA. 



119 



infected blood the malarial parasites are taken into 

 the stomach and undergo reproduction. After seven 

 to ten days they find their way to the salivary glands. 

 When the mosquito bites man the parasites are ex- 

 creted with the saliva into- the wound. In the blood 

 the parasites enter and develop within the red blood- 

 cells. As they grow they fill more and more of the 

 corpuscle and finally become segmented into smaller 



Fig. 17. Plasmodium vivax, parasite of tertian fever. In the 

 upper row and on left of lower row, various stages of intra- 

 corpuscular development ; the two last figures in lower row are 

 free sexual individulas, microgametocytes (sperm cells), which 

 are about to set free the microgametes, or males. (After 

 Reinhardt.) 



bodies that are to become parasites. When this de- 

 velopment is complete, requiring forty-eight or seventy- 

 two hours, depending upon the type of parasite, the 

 red blood-corpuscle is ruptured and the segments set 

 free in the circulating blood, causing the chill and 

 fever that are so characteristic of the disease. In this 

 way more and more blood-cells are attacked and 

 destroyed, which explains the anemia. 



