14 THE HOUSE FLY—DISEASE CARRIER 
manure, he found that there were only two such ac¬ 
cumulations on the hospital grounds. The one at the 
stable was in a large masonry pit drained below and 
covered so that while not fly-proof it was dark and dry. 
No larvae or puparia were found in the pit. The ma¬ 
nure was molding and heating rapidly. Two other 
piles where the manure was kept dry and in the dark 
showed the same condition of rapid heating and mold¬ 
ing and no larvae were found. At the farm barn the 
manure was dropped through four traps where a pile 
accumulated, and was then taken to the part of the 
barn where the cow manure is collected and the two 
were mixed together. Here a considerable number 
of larvae and puparia were found, but not in sufficiently 
great numbers to account for the swarms around the 
buildings. They were more abundant in the part of 
the pile which consisted of pure horse manure and 
grew noticeably less until the cow manure was reached, 
when they were very few. Examination of the pig 
pen showed piles of pig manure mixed with the straw 
bedding exposed to air and rain. This was badly in¬ 
fested ; one ounce of material taken from a point a few 
inches below the surface displayed 868 puparia. An¬ 
other prolific source was found in piles of spent hops 
and barley malt—brewery waste which had been hauled 
in as a fertilizer. The hops showed a tendency to mold 
rapidly, and the flies did not breed in it as abundantly 
as in the looser barley malt. In parts of the malt where 
there was plenty of moisture the maggots were ex¬ 
tremely numerous; one ounce contained 1,018 mag- 
