It takes him about two weeks to hatch and get away from these breeding places; so that if everything of this sort is cleaned up carefully once a week, or if, where manure heaps and garbage dumps have to remain for longer periods, they are sprinkled with arsenic, kerosene, corrosive sublimate, chloride of lime, or carbolic acid, he will perish and disappear as surely as grass will if you wash away the soil in which it grows. The presence of a fly means a dirty house or a dirty yard somewhere, and to discover a fly in your house should be considered a disgrace. Until people are aroused to the need of such cleanliness as will make flies disappear entirely, in most places it will be necessary, as warm weather approaches, to screen all doors and windows, and particularly all boxes, pantries, or refrigerators in which food is kept. If you cannot afford screens, use fly paper. These are all, however, only half-way measures and will give only partial relief. The best prevention of flies is absolute cleanliness. No dirt, no flies. Dust, a Source of Danger. Dust is an easily recognized form of dirt. It is dangerous in itself and nearly always contains germs of one sort or another mixed in with it. Shops and factories whose processes make much dust are usually very unhealthy for the workers, who are likely to show a high death-rate from consumption. Dust should be fought and avoided in every possible way. City streets should have good modern pavements,--preferably asphalt or some crude petroleum, or sawmill-waste, "crust," or coating,--which will not make any dust, and which can be washed down every night with a hose. In smaller towns where there is no pavement, dust may be prevented by regular sprinklings during the summer, preferably with some form of crude oil. Two or three full sprinklings of this will keep down the dust for the greater part of the summer. If these measures are properly carried out, they will prevent most of the dust that accumulates in houses, as nearly all of this blows in through the windows or is carried in on shoes or skirts. When this has once floated in and settled down upon the walls, furniture, or carpets, be very careful how you disturb it; for, as long as it lies there, it will do you no harm, however untidy it may look. The broom and the feather duster and the dry cloth do almost as much harm as they do good; for while they may remove two-thirds of the dust from a room, they drive the other third right into your nose and throat, where the germs it contains can do the most possible harm. Dusting should always be done with a damp cloth; sweeping, with a damp cloth tied over a broom; and, wherever possible, a carpet sweeper, or, better still, a vacuum cleaner, should be used instead of a broom.