198 THE HOUSE FLY—DISEASE CARRIER 
dissolved in a gallon of water and poured upon fifteen 
pounds of horse manure showed that 941 out of every 
1,000 larvae, or ninety-four and one-tenth per cent., 
were killed, while the same amount poured upon twelve 
pounds of horse manure killed ninety-five and seven- 
tenths per cent, of the larvae. Other experiments with 
the same substance indicated in one case that two and 
one-half pounds of the iron sulphate to the gallon of 
water poured on twelve pounds of manure killed but 
seventy-one per cent, of the larvae; in still another, two 
pounds of the sulphate and two gallons of water poured 
upon fifteen pounds of manure killed eighty-three and 
five-tenths per cent., while one gallon .of the same solu¬ 
tion to eleven pounds of manure killed none. Experi¬ 
menting with dry powdered iron sulphate mixed with 
horse manure at the rate of two and one-half pounds 
to the fifteen, he found eighty-seven and two-tenths 
per cent, of the larvae destroyed. At the rate of two 
and three-eighths pounds to twelve, eighty-six per cent, 
were killed. At two pounds to fifteen, forty-four and 
three-tenths per cent, were destroyed. At the rate of 
one and one-half pounds to twelve, sixty-nine and 
seven-tenths per cent, were killed. 
The conclusions drawn from these experiments were 
that the breeding of the house fly in manure can be 
controlled by the application of a solution of iron sul¬ 
phate—two pounds in a gallon of water for each horse 
per day—or by the use of two and one-half pounds of 
dry sulphate per horse per day. It was calculated that 
the average city horse produces about fifteen pounds 
