290 FLIES AND DISEASE 



When introduced into the blood by the bite of an 

 infected mosquito the parasite is a very minute 

 sickle-shaped body, which bores its way into a red 

 blood corpuscle. As the parasite grows it feeds on 

 the substance of the red blood corpuscle and grad- 

 ually destroys it. When it has reached a certain 

 size about three-quarters the diameter of the red 

 corpuscle the parasite divides into a number of 

 smaller bodies. Then the corpuscle bursts and the 

 small parasites escape into the blood and attack 

 other red blood corpuscles. By this means infection 

 is carried from one corpuscle to another, and very 

 rapidly millions of the blood corpuscles become 

 infected. This is the so-called asexual form of 

 multiplication. Together with the forms of the 

 parasite just mentioned certain large forms, which 

 are regarded as males and females, are produced in 

 some of the blood corpuscles. These sexual forms 

 cannot develop further in the blood, and if they 

 remain there most of them soon die off. The sexual 

 cycle is completed in the internal organs of those 

 species of mosquito, Anophelines, which can transmit 

 the infection. When such a mosquito feeds on the 

 blood of a patient it swallows both asexual and 

 sexual forms of the malaria parasite. The former 

 are digested and destroyed by the stomach juices 

 of the mosquito, but the latter develop and escape 

 from the blood corpuscles in which they were 

 previously confined. The male form divides up 

 into several thin, very minute, eel-like fragments, 



