When flies are very abundant in a room they can be most readily gotten rid of by fumigation with sulphur, or by the use of pure pyrethrum powder either burned or puffed into the air. Herrick (1913) recommends the following method: "At night all the doors and windows of the kitchen should be closed; fresh powder should be sprinkled over the stove, on the window ledges, tables, and in the air. In the morning flies will be found lying around dead or stupified. They may then be swept up and burned." This method has proved very efficaceous in some of the large dining halls in Ithaca. The writers have had little success in fumigating with the vapors of carbolic acid, or carbolic acid and gum camphor, although these methods will aid in driving flies from a darkened room. All of these methods are but makeshifts. As Howard has so well put it, "the truest and simplest way of attacking the fly problem is to prevent them from breeding, by the treatment or abolition of all places in which they can breed. To permit them to breed undisturbed and in countless numbers, and to devote all our energy to the problem of keeping them out of our dwellings, or to destroy them after they have once entered in spite of all obstacles, seems the wrong way to go about it." We have already seen that _Musca domestica_ breeds in almost any fermenting organic material. While it prefers horse manure, it breeds also in human feces, cow dung and that of other animals, and in refuse of many kinds. To efficiently combat the insect, these breeding places must be removed or must be treated in some such way as to render them unsuitable for the development of the larvæ. Under some conditions individual work may prove effective, but to be truly efficient there must be extensive and thorough coöperative efforts. Manure, garbage, and the like should be stored in tight receptacles and carted away at least once a week. The manure may be carted to the fields and spread. Even in spread manure the larvæ may continue their development. Howard points out that "it often happens that after a lawn has been heavily manured in early summer the occupants of the house will be pestered with flies for a time, but finding no available breeding place these disappear sooner or later. Another generation will not breed in the spread manure." Hutchinson (1914) has emphasized that the larvæ of houseflies have deeply engrained the habit of migrating in the prepupal stage and has shown that this offers an important point of attack in attempts to control the pest. He has suggested that maggot traps might be developed into an efficient weapon in the warfare against the house-fly. Certain it is that the habit greatly simplifies the problem of treating the manure for the purpose of killing the larvæ.