SPOROZOA 1123 



Gorgas, in Havana, that stegomyia could be practically exterminated 

 by doing away with water in artificial containers in the neighbor- 

 hood of dwellings; this so reduced their numbers that when a case 

 of yellow fever was introduced into a community the disease would 

 not spread. In the same way malaria-carrying mosquitoes may be 

 fought, without regard to the presence of non-disease carriers. An 

 accurate mosquito survey is first made, both by examination of the 

 catch of adults and by a hunt for larvae in collections of water 

 throughout the district. A puddle or stream is examined by dipping 

 with a white saucer or a long-handled dipper, along the margins; 

 after a little practice it is possible to obtain any larvae which may 

 be present, and to decide by their appearance and behavoir whether 

 they are anophelines. It is, of course, unnecessary to waste time 

 and money destroying collections of water free from anophelines. 

 When the breeding places have been located, they may be destroyed 

 by the use of oil or larvacide, by draining or by filling. 



The use of oil and larvacides, while usually a temporary measure, 

 is, nevertheless, of great importance ; any light fuel oil may be used 

 by spraying, by mopping the sides of ditches or margins of ponds, 

 or by a drip barrel at the head of a water course. Since in the 

 malarial season the mosquito develops rapidly the oil must be applied 

 regularly once a week. It is better in the long run to begin in the 

 center of the settlement, with permanent improvements, working 

 outwards as money becomes available, and not to depend on oiling 

 except as a temporary measure. 



Wherever possible, the swampy areas and pools must be drained, 

 and for this purpose both agricultural tile and open ditches may be 

 used; in the tropics it is necessary to line the latter with concrete 

 to prevent overgrowth by rank vegetation and to protect the banks 

 against caving. Where, because of the lay of the land, drainage is 

 impracticable the area may be filled, or sometimes flooded, or 

 irrigated with sea water, in which most anophelines do not survive. 



3. The infection is kept alive in a community by human carriers, 

 and these are especially common among natives and the poor and 

 ignorant, and especially among the native children. Newcomers 

 should not live within five hundred yards of the dwellings of these 

 classes, as infected anophelines can easily travel shorter distances. 

 Only when it is possible to protect the natives also by these measures 

 is it safe to live among them; and that this is possible has been 

 shown many times, particularly in Panama. 



