8 THE HOUSE FLY— DISEASE CARRIER 



species reared from this substance has been piibHshed 

 by the writer (1901). 



The typhoid fly is, possibly next to horse manure, 

 attracted to human excreta, and not only visits it wher- 

 ever possible for food, but lays its eggs upon it and 

 lives during its larval life within it. It will not only 

 do this in the latrines of army camps, in the open box 

 privies of rural districts and small villages, but also 

 upon chance droppings in the field or in the back alley- 

 ways of cities, as has been repeatedly shown experi- 

 mentally in Washington. 



It may very readily happen that the flies of any given 

 neighborhood have come from a single source, and 

 that the substances in which they breed differ accord- 

 ing to locality and according to the supply of breed- 

 ing substance.' Under ordinary city conditions, un- 

 doubtedly the most frequent nidus is in the horse 

 manure of stables, but when the conditions in a com- 

 munity of a radically different nature are studied the 

 result is sometimes surprising. In the course of his 

 investigations of conditions in small towns with espe- 

 cial reference to the hookworm disease, Stiles has found 

 that in cotton-mill towns, for example, the privies may 

 be a much more important breeding place of flies than 

 the manure piles, not only more important since flies 

 breeding in this substance are more likely to carry 

 disease germs, but also numerically more important; 

 for you may have 250 uncared-for privies and perhaps 

 only one or even no manure pile. And there are com- 

 munities also where horses are scarce and pigs are 



