226 



BIOLOGY FOR BEGINNERS 



blood of a well person. Not only has this been shown, but by means 

 of experiments in which several men sacrificed their lives, it is also 

 proven that this is the only way in which these, and probably 

 other diseases, are transmitted. Men tended yellow fever patients, 

 slept hi their beds, wore their clothes and though exposed hi every 

 way, did not contract the disease as long as screened from mos- 

 quitoes. Others who allowed themselves to be bitten by mos- 

 quitoes which had previously bitten yellow fever patients, in- 

 variably contracted the disease, which in some cases resulted in 

 their death. From these sacrifices, methods of control have 



FIG. 77. Mass of mosquito eggs. 



developed which have saved thousands of lives in all parts of the 

 world. 



Life History. As with the fly, a knowledge of its life history 

 enables man to contend with the mosquito, and these campaigns 

 are much more successful than those against the fly. The eggs 

 are laid in stagnant water; ponds, rain barrels, and even tin cans 

 furnish ideal breeding places. They are deposited in tiny rafts, 

 consisting of many eggs covered with a waterproof coating, and 

 when they hatch the larvae emerge downwards into the water, 

 and become the familiar " wigglers " seen in rain barrels. Though 

 living in water the mosquito larva breathes air, which it obtains 

 through a tube, projecting from the posterior of its abdomen. 

 It may often be seen with this tube at the surface and the body 



