MALARIA 291 



which swim rapidly and penetrate into the female 

 forms. A female, thus fertilized, bores its way 

 through the stomach wall and grows to a consider- 

 able size in the surrounding tissues. Then the 

 substance of the female divides up into a great 

 number of minute, spindle-shaped bodies, many of 

 which find their way into the salivary glands of the 

 mosquito. When the infected mosquito feeds on 

 a human subject these spindle-shaped bodies pass 

 with the saliva into the blood, and start the 

 asexual cycle previously described. 



In this disease it is man, and not the mosquito, 

 who forms the chief reservoir of infection. A man 

 once infected, even though no longer exposed to 

 re-infection, may harbour the parasite for years. 



Much has been done to diminish the prevalence 

 of this disease by studying the life-histories of mos- 

 quitoes and applying suitable preventive measures 

 to their breeding places, and by the use of nets 

 and screens in preventing both the healthy and the 

 infected from being bitten. Before measures can 

 be applied with success it is almost always neces- 

 sary to study very thoroughly the conditions 

 prevailing in the locality, and to survey the 

 whole area accurately. Quinine has a marked in- 

 fluence on the parasites in the body, and the use 

 of this drug as a preventative and as a curative 

 agent has had a very beneficial influence in the 

 prevention of malaria. 



The diseases hitherto discussed are transmitted 



19-2 



