8s 



2d. Those parasites were injected into his blood by the bite 

 of a mosquito infected with this parasite. The man receives in- 

 fection no other way. 



3d. The mosquito herself received this infection by having 

 previously fed on a man whose blood contained these parasites. 

 The mosquito acquires infection in no other way. 



4th. The only mosquitoes which are infected with malaria are 

 those of the genus Anopheles, and not all species of Anopheles. 



This change from man tO' mosquito and back again is neces- 

 sary for the continual existence of the parasites, just as neces- 

 sary as that the germ of wheat must be alternately in the ground 

 and in the air. It cannot live indefinitely in the mosquito. It 

 cannot live indefinitely — although miuch longer — in man. With- 

 out this continued change between the two hosts, as they are 

 called, the parasite dies. 



This is our clue for malaria control : 



1st. To keep infected mosquitoes away from men; or 



2d. To keep mosquitoes away from infected men. 



Control of either host — the man or the mosquito^ — will elimi- 

 nate malaria. 



METHODS O^ MALARIA CONTROL. 



Briefly, we aim to 



1st. Get rid of Anopheles mosquitoes — no other kind make 

 any difference. 



2d. Prevent the access of Anopheles mosquitoes to men. 

 3d. Free all men in the community fromi malaria parasites. 

 4th. Immunize men against infection by means of quinine. 

 Let me explain — 



(1) That getting rid of Anopheles mosquitoes would elimi- 

 nate malaria does not require explanation. 



(2) The same is necessarily true if no such mosquitoes have 

 access to men. 



(3) If all men were free of malaria parasites there would 

 be no way of infecting mosquitoes, and unless infected they 

 cannot give malaria. 



