408 ELEMENTARY BIOLOGY 



died with the disease. They shook out these contaminated articles and 

 slept in the soiled garments and in the soiled bedclothes for twenty 

 days. None became infected. This experiment was repeated two 

 times more, with no results that would indicate the slightest con- 

 nection between the vomits and excretions of the patients and the 

 infection of new cases. 



In the other building a volunteer allowed himself to be stung by 

 a mosquito that had drawn blood from a patient some two weeks 

 earlier. The bedding and other utensils were thoroughly sterilized, 

 and the volunteer had been in quarantine for two weeks, to make 

 sure that he was not infected when he came into the building. On 

 the fourth day he developed the symptoms of the disease. Other 

 volunteers, on the other side of the screen, were not affected. Ten 

 or more individuals contracted yellow fever as a result of stings from 

 mosquitoes that had previously bitten sick persons, and not one of 

 those who stayed on the other side of the screen. In the course of 

 the experiments Dr. Carroll and Dr. Lazear also became sick, the 

 latter dying as a result (Fig. 211). 



442. Fighting mosquitoes. With a realization of the impor- 

 tance of the mosquito in the transmission of these serious dis- 

 eases arose the question of how to combat the pests. Of 

 course each one of us can keep on killing mosquitoes on sight 

 and feel that he is doing his duty. But the mosquitoes do not 

 recognize city limits or state lines, and gayly fly from one 

 man's land to another's. So far the only effective campaign 

 against mosquitoes has been waged on a comprehensive scale 

 by a whole community at a time. It seems that the best way to 

 prevent malaria and yellow fever is by means of ditches to drain 

 off marshy land, by means of cartloads of dirt to fill in low- 

 lying spots, by means of oil on such puddles as cannot be filled 

 or drained, and by means of lids or screens to cover up such 

 cisterns, tanks, or buckets as have to be kept with water stand- 

 ing in them, while all old cans and broken crockery and other 

 possible containers for water are scrupulously placed where the 

 female mosquitoes cannot reach them. For the life history of 

 the mosquito requires quiet water for the laying of the eggs and 



