INSECTS AND DISEASE 



379 



the whitish maggots feed and grow in the filth for three or four 

 days before changing to the quiescent pupal stage which lasts 

 four or five days longer. Then the adult fly issues. Some of 

 the filth through which the fly has to crawl as it issues from the 

 pupa inevitably clings to the little brush-like feet and the hairy 

 body. If the flies bred only in stable manure and flew directly 

 from the stable to the house there would be comparatively 



FIG. 167. Head of house-fly, showing eyes, antennae and mouth-parts. 



(Much enlarged.) 



little reason to complain, at least from a sanitary standpoint, 

 for the amount of filth they carry from the barnyard to our food 

 would be of little consequence. Too often, however, they visit 

 other places before calling on us, and, unfortunately, these other 

 places are often most unclean. Experiments have shown 

 that when the fly walks over germ-infected material many of 



