406 



SCIENCE OF HOME AND COMMUNITY 



FIG. 160. Foot of fly, 

 a germ carrier. 



sucked up through its proboscis and taken into its digestive 



system. The fly may then enter our homes or places where 



food is sold ; and as it alights on the food 



or falls into the milk, it leaves some of 



these bacteria, either in the particles of 



filth that fall from its body, or in the fly 



specks deposited. When the food is eaten, 



these germs are taken into the human 



system and produce disease. Or, again, 



the fly may alight directly upon the face and fingers of human 



beings and leave bacteria, which may then be taken into the 



mouth. The evidence which is being gathered indicates that 



diseases are frequently spread by flies. 



Evidence against the fly. Following is some of the evi- 

 dence that flies are carriers of diseases. 



1. It is the habit of 

 flies to feed on filth of all 

 kinds in which bacteria 

 are abundant. 



2. Bacteria are present 

 in great numbers on flies. 

 This has been shown by 

 allowing a fly to walk on 

 a medium in which bac- 

 teria will grow. After 

 this had stood a few days, 

 large numbers of colonies 

 of bacteria developed in 

 the culture. 



The bacteriologist at 



the Connecticut Experiment Station devised a method for 

 estimating the number of bacteria found on a single fly. 

 Four hundred and fourteen flies were examined, and on each 

 fly was found an average of a million and a quarter bacteria. 

 Very few of these were the kind that produce disease, but 



FIG. 161. Fly tracks on a culture. 



