AMCEBA AND SOME ALLIES 297 



and from the blood corpuscles, a quantity of poisonous ma- 

 terial is released and mingles with the liquid of the blood. 

 This poisonous material induces the fever which always fol- 

 lows the chill. The released spores may enter red corpuscles 

 again and, in forty-eight hours in one type of malaria and 

 seventy-two hours in another, form spores once more. 



Some of the amoebulse (amceba-like stages) of the parasite 

 have a different history. While most of them in the red cor- 

 puscles of a person go on reproducing nonsexually, as just 

 described, some develop into a form which, by comparison 

 with higher animals, we call the female cell (Fig. 155, h 2 ) r 

 and others into male cells (Fig. 155, i). If now the person 

 be exposed to the bite of a mosquito of the genus Anopheles,, 

 the male and female cells of Plasmodium reach their full 

 development in the human red blood corpuscles, as these 

 rest in the stomach of the mosquito. Leaving the corpuscles, 

 the two cells unite to form a worm-like cell (Fig. 155, k), 

 which penetrates to the outer wall of the stomach of the 

 mosquito, where it increases in size to form a large sphere 

 (Fig. 155, p). In a short time the sphere subdivides into 

 countless extremely minute blasts (Fig. 155, m). These 

 make their way through the body cavity of the mosquito to 

 the salivary glands (Fig. 155, n). Penetrating to the interior 

 of those glands, the blasts enter the ducts, and are carried 

 outward and down the insect's proboscis by the saliva when 

 the mosquito bites another person. Then in the human 

 blood the blasts enter the red corpuscles and become amoe- 

 bulse, thus completing a cycle. 



Prominent among the scientific men who since 1896 have 

 discovered the facts of the life history of the malarial para- 

 site are Dr. Ross, of India, and Professor Grassi, of Italy. 

 Upon their discoveries, and those of others, are based the 

 numerous operations against the mosquito in the vicinity 

 of large cities. 



