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? 



Problem 129 : To determine the harm done by the fly and 

 the way it does this harm. 



Material. Sterile Petri dish containing culture medium. 



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? 



JAN. FEB MCH. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. 



INFANT MORTALITY CURVE. 



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

 d, mean temperature. 



