There have been many attempts to find some cheap chemical which would destroy fly larvæ in horse manure without injuring the bacteria or reducing the fertilizing values of the manure. The literature abounds in recommendations of kerosene, lime, chloride of lime, iron sulphate, and other substances, but none of them has met the situation. The whole question has been gone into thoroughly by Cook, Hutchinson and Scales (1914), who tested practically all of the substances which have been recommended. They find that by far the most effective, economical, and practical of the substances is borax in the commercial form in which it is available throughout the country. "Borax increases the water-soluble nitrogen, ammonia and alkalinity of manure and apparently does not permanently injure the bacterial flora. The application of manure treated with borax at the rate of 0.62 pound per eight bushels (10 cubic feet) to soil does not injure the plants thus far tested, although its cumulative effect, if any, has not been determined." As their results clearly show that the substances so often recommended are inferior to borax, we shall quote in detail their directions for treating manure so as to kill fly eggs and maggots. "Apply 0.62 pound borax or 0.75 pound calcined colemanite to every 10 cubic feet (8 bushels) of manure immediately on its removal from the barn. Apply the borax particularly around the outer edges of the pile with a flour sifter or any fine sieve, and sprinkle two or three gallons of water over the borax-treated manure. "The reason for applying the borax to the fresh manure immediately after its removal from the stable is that the flies lay their eggs on the fresh manure, and borax, when it comes in contact with the eggs, prevents their hatching. As the maggots congregate at the outer edge of the pile, most of the borax should be applied there. The treatment should be repeated with each addition of fresh manure, but when the manure is kept in closed boxes, less frequent applications will be sufficient. When the calcined colemanite is available, it may be used at the rate of 0.75 pound per 10 cubic feet of manure, and is a cheaper means of killing the maggots. In addition to the application of borax to horse manure to kill fly larvæ, it may be applied in the same proportion to other manures, as well as to refuse and garbage. Borax may also be applied to the floors and crevices in barns, stables, markets, etc., as well as to street sweepings, and water should be added as in the treatment of horse manure. After estimating the amount of material to be treated and weighing the necessary amount of borax, a measure may be used which will hold the proper amount, thus avoiding the subsequent weighings.