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 larvce 

 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 unpublished observations on this point are interesting.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 



