PUBLIC HEALTH L3 



the water through which the larvae can not extrude their 

 breathing tubes and they are thus suffocated. The apphca- 

 tion of niiscible oils is efficacious, but attended with some 

 danger, since it destroys fish and predator}^ insects which are 

 themselves some of the most im])ortant natural enemies of 

 mosquitoes. Very frequently even oiling is not necessary, 

 as much swamp land may be permanently freed from mos- 

 quitoes by very simple systems of drainage ditches which 

 prevent the accumulation of the stagnant water in whicli the 

 larvae occur. 



As pointed out, the reduction of malaria in communities is 

 permanently accomplished most readily by the application 

 of anti-mosquito measures, aimed nuiinly at the breeding- 

 places of Anopheles mosquitoes. Such work is being exten- 

 sively carried on by the V. S. Public Health Service, by other 

 federal bureaus, by many state boards and commissions, and 

 by certain private or semi-private institutions in widely 

 scattered parts of the country. Through their individual 

 and collective efforts an enormous amount has been accom- 

 plished, although painfully little in comparison with what 

 could well be spent upon the problem, which is without 

 question one of the great public health problems in the 

 United States at the present time. 



Another mosquito-borne disease which has aroused more 

 interest in America on account of its spectacular appearance 

 and higher mortality is yellow fever. This is due to a filter- 

 able virus, concerning the nature of which we can only specu- 

 ulate at the present time, although enough has been ascer- 

 tained through experimental work to demonstrate that the 

 virus is a living organism which undergoes a development of 

 definite periodicity in mosquitoes of a single species known as 

 Stegomyia fasciata. This mosquito enjoys a very wide distri- 

 bution in many parts of the world, mainly in the tropics, but 

 also extends into the warmer temperate regions. Yellow fever 

 is not so extensively distributed, being absent in many places 

 where Stegomyia occurs, but it is nevertheless present in 

 many parts of the tropics in both hemispheres and all that is 



