490 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 



there may be over ten generations of flies. This accounts for the 

 great number of flies in July and August. Fortunately, rela- 

 tively few flies survive the winter. 



The foot of the fly shows a wonderful adaptation for clinging to 

 smooth surfaces. Two or three pads, each of which bears tubelike 



hairs that secrete a 

 sticky fluid, are found 

 on its under surface. 

 It is by this means that 

 the fly is able to walk 

 upside down, and carry 

 filth and bacteria on its 

 feet. 



claw mom TIP OF FOOT 



Foot of a house fly. 



Amer. Mus. of Nat. Hist. 

 Why is the fly a carrier of diseases? 



Project. To determine 

 the breeding places of 

 flies in your neighbor- 

 hood. 



The house fly a dis- 

 ease carrier. The com- 

 mon fly is recognized 

 everywhere as a pest. 

 Flies have long been known to spoil food through their filthy 

 habits, and they are blamed for spreading several diseases caused 

 by bacteria. It has been found that a single fly might carry on 

 its feet anywhere from 500 to 6,600,000 bacteria, the average 

 number being over 1,200,000. Not all of these germs are harm- 

 ful, but they might easily include those of typhoid fever, tuber- 

 culosis, " summer complaint," and possibly other diseases. A 

 pamphlet published by the Merchants' Association in the city of 

 New York shows that the rapid increase of flies during the summer 

 months has a definite correlation with the increase in the number 

 of cases of ' ' summer complaint. ' ' Observations in other cities seem 

 to show that the increase in the number of typhoid cases in the 

 early fall is due, in part at least, to the same cause. 



Project. If vital statistics of your community are available, work 

 out a correlation between the increase of flies and the increase of 

 certain diseases. 



