320 



BIOLOGY AND HUMAN LIFE 



and stable manure at least once a week,^ and to keep streets, 

 back yards, markets, and kitchens perfectly clean (Fig. 149). 



Lime, crude oil, copper sulfate, formaldehyde, and other poisonous 

 substances have been used in treating garbage and manure to prevent 

 the breeding of flies; but such treatment is generally undesirable be- 

 cause it makes the manure and garbage worthless for use as fertilizer. 

 Borax and hellebore can be used so as not to injure the manure. 



Fig. 149. A breeding place for house flies 



The community that saves itself money or trouble by permitting back yards of 

 this kind usually pays for its economy and indifference with disease and death. With 

 the economies of motor cars and traction engines must be reckoned the reduction in 

 typhoid fever and other fly-borne diseases 



Until a community succeeds in eliminating the flies it is well 

 for every household to protect its own food supply by suitable 

 screening of the house and by special care in regard to the ex- 

 posure of food. Every purchaser of food can help by system- 

 atically refusing to patronize dealers whose premises harbor 

 flies, and we can all help by keeping our own premises clean 

 and free from these insects (Figs. 150, 151). 



^ The life histor>- of the fly covers a period of ten days. 



