INSECTS AS SPREADERS OF DISEASE 



399 



The habits of the fly are such that we cannot afford to be 

 associated* with this animal in any way whatever. The female 

 lays her eggs in horse manure ; but where there is no horse 



FIG. 205. Flies and intestinal diseases 



In New York City a careful study was made (1907-1908) to find the relation between the 

 prevalence of flies and the amount of typhoid fever. The height of the dotted line cor- 

 responds to the number of flies caught in traps, week by week, from the beginning of 

 June to the end of October. The solid line corresponds to the number of people who 

 died from intestinal diseases during the same period in the same districts of the city. 

 Typhoid is most frequent where and when flies are most abundant, and there is a direct 

 connection between the insects and the distribution of the disease 



manure, she will use cow, sheep, pig, or chicken manure, or 

 decaying fruit, fish, meat, or vegetables, ordinary garbage, for 

 example, or any mass of decaying organic matter. The adult 

 fly will visit, for feeding, not only such materials as have been 

 mentioned, but all kinds of perfectly good food that may be 



