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 



