PROBLEM 4. How We Attc'?/jpt to Stop the Spread of Disease 



353 



Fig. 313 This old creek is beifig straightened and ?nade deeper. How will this affect 

 mosquito breedi?ig? 



pupae breathe through tubes which 

 come in contact with the air at the sur- 

 face of the water. See Figure :?i2. This 

 is their undoing. For by spreading the 

 thinnest film of kerosene or other oil 

 over the surface of the water we can cut 

 off their air supply and kill them before 

 they develop into adults. Sometimes it 

 is easier and more effective to fill in or 

 drain the stagnant pools. Sometimes it 

 is more convenient to stock the waters 

 with small fish that feed on the larvae 

 and pupae. 



How successful have we been? When 

 the life history of the mosquito became 

 known it seemed a relatively easy matter 

 to exterminate them. In the early years 

 of this century General Gorgas of the 

 United States Army began systemati- 

 cally to exterminate the yellow fever 

 mosquito in Havana, Cuba. There the 



mosquitoes laid eggs in water barrels or 

 other Mater containers. These were 

 cleaned up or kept covered. The prob- 

 lem, therefore, seemed not too difficult. 

 Other communities followed Havana's 

 example, and it was believed for a time 

 that yellow fever was being conquered. 

 These hopes, however, were soon de- 

 stroyed, for it was discovered that vari- 

 ous species of jungle mosquitoes are car- 

 riers of the virus and that many species 

 of monkeys can and do become infected. 

 Mosquitoes bite monkeys as well as man 

 and transfer the virus readily from mon- 

 key to monkey or from monkey to man. 

 The task of wiping out mosquitoes in all 

 the jungles of the tropics is more than 

 man can tackle; yellow fever is far from 

 being conquered. 



Malaria, too, for a time seemed to be 

 under control. Our success in building 



