6 BULLETIN" NO. 200, U. S. DEPARTMENT OF AGRICULTURE. 
some emphasis entirely aside from its bearing on the practical use 
of the maggot trap. The explanation is probably to be found in 
the changes which take place in the manure heap during storage. As 
the pile stands it settles considerably, with a consequent decrease of 
ah spaces, and, especially if watered, air does not penetrate far below 
the surface. Deherain and Dupont (1900) have shown tha£ in manure 
well heaped so that air can not penetrate readily, the confined gases 
consist largely of carbon dioxid and methane, and that oxygen is 
not found except near the surface. It may well be that the lack of 
oxygen and the abundance of carbon dioxid render old manure 
unfavorable for the breeding of flies. It may also be that the com- 
position of the gases in the manure is one of the factors which in- 
fluence migration and the choice of a place for pupation. 
LARVAE DESTROYED Br TNE MAGGOT TRAP 
L 
(^ \ \ NUMBER WH/CH PUPATED ,'N THE MANURE. 
\ E/SOO 
(\ AVERAGE OP /O COUNTS AT K/TCHF/v BEro&E- AUGUST /O- 
AfTEf? AUGUST /O. 
AVERAGE OPS COUNTS AT STABLE BEFORE AUGUST /O- 
AVERAGE OP S COUNTS AT STABLE AETER AUGUST /O. 
Fig. 2. — Graphical representation of the work of the maggot trap and its effect on the prevalence 
of flies. (Original.) 
EFFECT ON THE FLY PREVALENCE AT THE STABLE AND KITCHEN. 
Turning now to the second line of observation, it will be of interest 
to determine to what extent the maggot trap influenced the number 
of flies at the stable and kitchen. An answer to this is to be found in 
the series of fly counts made during the season, both before and after 
the trap was started. In taking these counts "tanglefoot" sticky 
fly paper was used. The papers were exposed for 24-hour intervals 
and counted immediately at the end of that period. Figure 3 is a 
graphic representation of these series of counts at the stable and 
kitchen. In each case the number given is the total caught on two 
papers exposed at the same time. At the kitchen the two papers 
were always exposed in the same way on top of the garbage pails, 
and at the stable one paper was put on the floor just outside the 
