16 



dations are the result of practical experience), house flies will have 

 almost no chance to breed, and their numbers will be so greatly re- 

 duced that they will hardly be noticeable. Many experiments have 

 been made in the treatment of manure piles in order to kill the mag- 

 gots of the house fl}^, and the chloride-of-lime treatment has been 

 found to be the cheapest and most efficacious. 



It has been stated above that the closet for the reception of manure 

 should be made tight to prevent the entrance or exit of flies. A win- 

 dow fitted with a wire screen is not desirable, since the corroding 

 chloride fumes will ruin a wire screen in a few days. 



Fruit flies. — While extended investigations have shown that the 

 common house fly is the fly most to be feared in guarding against 

 typhoid, on account of the fact that over 99 per cent of the flies found 



Fig. 10. — Drosophila nmpelopMla: a, Adult ; h, antenna of same : c, base of tibia and first 

 tarsal joint of same ; d, puparium, side view ; e, puparium from above ; /, full-grown 

 larva; g, anal spiracles of same. Enlarged (author's illustration). 



in kitchens and dining rooms and attracted to food supplies are house 

 ■flies, there are a few others which are attracted to and which may 

 breed in human excrement that also have to be guarded against, and 

 as these do not breed in horse manure the treatment just described 

 will not be effective against them. The care of human excrement, 

 however, will prevent the carriage of typhoid germs even by these 

 species. The little fruit flies of the genus Drosophila (fig. 10), which 

 breed in overripe or decaying fruit, are the principal species in this 

 category. Therefore, fruit storehouses or fruit receptacles should be 

 screened, and overripe fruit should not be allowed to remain in dining 

 rooms or kitchens for any length of time. 



OTHER DISEASES CARRIED BY INSECTS. 



While in malaria and typhoid we have the two principal diseases 

 common to the United States which may be conveyed by insects, the 



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