192 THE HOUSE FLY—DISEASE CARRIER 
dry so quickly from top to bottom that, although flies 
may and do lay their eggs on it, the larvae are for the 
most part destroyed by the drying. When the weather 
is at all moist, however, these individual horse drop¬ 
pings will give out their supply of flies. Again, if the 
drying of the manure is delayed only until the larvae 
have reached a certain size, they will still be able to 
transform. An experiment made by Hine in this direc¬ 
tion is of interest as showing the vitality of larvae 
under adverse conditions. Several glass jars were 
partly filled with thoroughly air-dried horse manure; 
then from a manure pile larvae of different sizes were 
procured, sorted, and put into the jars; flies issued in 
every case, but those from the larvae that were small¬ 
est when sorted out were not more than half normal 
size. This suggests that larvae do not have to be very 
large before they are in position to contend with ad¬ 
verse conditions and produce adults even when the 
food supply is shut off, since it seems reasonably cer¬ 
tain that larvae will not feed upon perfectly dry sub¬ 
stances. 
As to human excreta, observations have shown that 
single droppings in the field or elsewhere will support 
a generation of flies perfectly. In Washington in the 
summer of 1900 this was proved on numerous occa¬ 
sions during June and July. 
The possibility of fly breeding from spread manure 
is another important and very practical point. Hine’s 
unpublished observations on this point are interesting. 
Cages covering twenty-five square feet of surface were 
