228 BIOLOGY FOR BEGINNERS 



1. Drainage of swamps, covering or removal of rain barrels, 



cisterns, cans, or any hollows where water may accumulate. 



2. Spraying swamps and ponds with petroleum which covers 



the water with a film of oil so that neither larva or pupa can 

 breathe, and also kills any adults which it strikes, though 

 this oil treatment is injurious to plants and fishes in the 

 water thus treated. 



FIG. 79. Mosquito larvae and pupae, T. incidens, with their breath- 

 ing-tube at the surface of the water. From Doane. 



3. Fish and dragon flies are natural enemies of mosquitoes and 



should be encouraged. 



4. Careful screening of houses and wearing of protective clothing 



especially in infected regions is a helpful precaution. 



5. Persons suffering from malaria should avoid being bitten 



lest they thus infect others. Yellow fever cases are now 

 quarantined in screened rooms for the same reason. 



