THE ART OF PARASITISM 



227 



lorozoitsi 



ifeetecL 

 sctUvory 

 glcmcd 



gametoejtc 



migrate to the blood stream and so reach various parts of the body, 

 there producing cysticerci. As in the case of Trichinella, human 

 infection really becomes a blind alley for the parasite. 



Malaria. One of the most economically important parasites is 

 the causative organism of malaria, a minute spore-forming protozoan 

 of the genus Plasmodium. 

 The infective stage, or spo- 

 rozoite, reaches the blood 

 stream of man in the saliva 

 of the mosquito, which is 

 poured into the wound im- 

 mediately after the victim 

 is punctured. This minute 

 parasite promptly pen- 

 etrates a red corpuscle and 

 starts to de\'elop asexually, 

 growing until it fills about 

 one half of the corpuscle. 

 It is now ready to undergo 

 the asexual reproductive 

 cycle. The chromatin mate- 

 rial is gradually separated 

 into a number of tiny 

 masses, each one of which 

 finally becomes surrounded 

 by a bit of cytoplasm. 

 Growth continues until the 

 red corpuscle is filled with e eye e o 



a number of new indi\-iduals called merozoites. Soon the corpuscle 

 bursts, liberating these merozoites, each one of which seeks out a 

 new corpuscle and begins the asexual cycle all over again. 



This asexual cycle recurs regularly, the intervals depending upon 

 the species of parasite infecting the blood stream. Thus in the case 

 of tertian malaria, schizogony is completed every twenty-four hours, 

 while in the quartan type it takes forty-eight hours to complete it. 

 The periodic chills and fever so characteristic of malaria occur at 

 the time of the bursting of the red corpuscles with the subsequent 

 release of the asexually formed merozoites and the accompanying 

 waste matter. Quinine is the most widely used drug to combat the 

 infection as it destroys the newly "hatched" merozoites. 



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