154 THE ECONOMIC IMPORTANCE OF ANIMALS 



pupae differ from the larvae? Watch to see the adults emerge 

 from the pupal case. How long does a complete life history take ? 

 Conclusion. — How many generations of flies might develop 

 during a hot summer ? 



Frohlein 129 : To determine the harm done hy the fly and 

 the luay it does this harm. 



Material. — Sterile Petri dish containing culture rnedium. 



Method. — ^ Allow a fly to walk over the surface of a sterile 

 Petri dish with culture medium within it. Cover the dish. After 

 three or four days examine the surface of the culture medium. 



Observations, — What do you see ? 



Note. — Flies breed in manure, filth of all kinds, and human excrement as well. 



Study a diagram showing the relation of typhoid fever to open 

 toilets and flies in Jacksonville, Fla, (page 224, Civic Biology). 

 Why were there fewer cases when the toilets were screened ? 



Study the diagram below. What relation exists between 

 diarrheal diseases and flies? Explain. 



Examine the foot of a fly under the compound microscope or 

 study upper figure, page 223, Civic Biology. What adaptations 

 for carrying germs do. you find ? 



Infant Mortality Curve. 



a, prevalence of flies ; 6, diarrheal under five years ; c, deaths under one year ; 

 d, mean temperature. 



