10 BULLETIN" NO. 200, U. S. DEPARTMENT OF AGRICULTURE. 
can not be overcome. In the first place, some trouble resulted from 
smaller particles of manure sifting through between the cross strips 
and accumulating in the water below. This was especially the case 
when sawdust and shavings were used for bedding instead of straw. 
If this material were allowed to accumulate there would finally be 
enough of it to provide a breeding place on the concrete floor, where 
the maggots should be killed by drowning. Much of this sifting 
could be prevented by placing the cross strips closer together, so that 
only |-inch or even |-inch spaces were afforded. It is not at all 
likely that J-inch spaces would interfere with migration: but in spite 
of such improvement there would be, even with the most careful 
handling, a certain amount of straw or small particles of manure 
which would fall from the sides of the heap or from the fork at the 
time it was put on the platform. It will always be necessary to clean 
out the concrete floor more or less regularly, and for this purpose a 
long-handled stable broom will be satisfactory when the water sup- 
ply does not permit the use of a strong stream from a hose. To facili- 
tate the cleaning of the floor the platform should not be less than 
1 foot high nor more than 10 or 12 feet wide. The solid matter which 
happens to be washed into the cistern will decompose in time and be 
pumped back with the liquid onto the manure heap. 
In dry weather evaporation of the water on the concrete floor will 
leave large areas of floor surface dry. Larvae falling from the manure 
above onto the dry floor will crawl away and can crawl up the vertical 
sides of the surrounding rim; in fact, they could crawl up this surface 
even if it were as smooth as glass. To insure that all larvae are 
drowned it is necessary to keep this in mind, and every day, when the 
manure is added to the heap, more water can be supplied if necessary. 
This operation will consume very little time. 
The most serious defect was found in the fact that mosquitoes 
bred very freely in the water standing in the concrete basin and in 
the cistern. In order not to have one pest multiplying at the expense 
of another, it is necessary to run all water out of the concrete floor at 
least once a week and to clean the floor at this time; if then a little 
oil is poured over the surface of the liquid in the cistern, mosquito 
breeding will be prevented entirely. This method was used during 
the last weeks of the experiment with satisfactory results. If the cis- 
tern were carefully and tightly covered, perhaps the use of oil would 
not be necessary. 
No counts or estimates were made of the larvae destroyed during 
October and November. It is known, however, that larvae continued 
to appear in the water on the floor during the most of October and 
during the warmer parts of November. On December 10 the manure 
was examined without removing it from the platform, and therefore 
