106 



ELEMENTS OF GEKERAL SClEKCE 



two days. At that rate how many flies might be produced 

 from a single pair during four summer months ? 



121. How house flies carry bacteria. The mouth and feet 

 of the house fly are covered with small, roughish hairs which, 

 when magnified under a lens, show clearly that many bacteria 

 may lodge there as the fly walks upon the refuse which usu- 

 ally forms its food. The bacteria may be deposited from the 

 fly's feet upon any food or any person upon which the fly 

 may alight. Some of the bacteria are swallowed by the fly 



FIG. 53. Stages in the life of the house fly 

 A, egg; B, larva; C, pupa; D, mature fly 



and may later be excreted and deposited at its next lighting 

 place perhaps upon someone's food. The transmission of 

 bacteria by the feet of flies is shown in the illustration on 

 page 107. 



122. Disposal of house flies. House flies may be disposed 

 of if a little attention is given to the matter. If the refuse 

 in which they lay their eggs and in which the larvae live is 

 removed, no new crops of flies can be produced. Traps may 

 be so arranged as to catch adult flies, after which they may 

 easily be killed. Obviously cooperation is needed to eliminate 

 this insect, for so long as any person in a community supplies 

 the materials for the growth of flies, just so long will that 



