8 THE HOUSE FLY—DISEASE CARRIER 
species reared from this substance has been published 
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 
