Did you ever see a fly wipe his feet before he came into the house? No, indeed; and he goes anywhere he pleases, over the bread and into the cream. Yet he was born in dirt and bred in dirt, and he lives in dirty places all the time he is not crawling over your clean things and spoiling them. Flies are hatched from eggs; and these eggs can hatch only in piles of dirt, such as heaps of manure, or places where garbage and scraps from the house are dumped or thrown. We call the common fly the "domestic" or "house" fly, because he lives only in the neighborhood of houses and barnyards where heaps of manure and piles of dirt are allowed to gather. When the fly first hatches from the egg, it is a little white, wriggling worm called a _maggot_, like those that some of you may have seen in decaying meat or fish or cheese. The maggots must have decaying substances to eat and live upon while they are growing, and this is why the eggs are laid in manure heaps and garbage piles. [Illustration: A MAGGOT HATCHING FROM THE EGG (Greatly magnified.)] It takes the maggot about five days to grow to its full size, and then it turns into a _chrysalis_. That is, it is shut up in a kind of case that it has spun for itself, like the cocoon of the silkworm or the caterpillar. In about five days more it breaks out of this cocoon and appears as a fly with wings. So, you see, the eggs must stay in that manure heap about two weeks if they are to hatch. If, within that time, the manure is carted away and thrown out somewhere where it will dry, the little unhatched flies will be killed, or prevented from hatching. All we have to do, then, to be entirely rid of flies about our houses is to see that the heaps of manure and all piles of cans and garbage are taken away at least once a week. [Illustration: FLY MAGGOTS ON OLD NEWSPAPER Note the size of the maggot compared with the newspaper type.] If manure heaps or piles of dirt cannot, for any reason, be carried away as often as this, then they can be sprinkled with something that is poisonous to flies, such as arsenic or kerosene. This will kill the maggots. If we keep every kind of waste and scraps from the house, and all the manure from the barn and the pig-pen and the hen-house carefully cleaned up, or sprinkled with some poison, we shall get rid of flies entirely and never need to use screens at the doors and windows. Until we do this, it is best to put screens at the doors and windows in the summer time, and particularly to screen carefully any place where food is kept or cooked; for we know that a great many cases of typhoid and of other diseases of the stomach and bowels, such as _summer sickness_, or summer _diarrhea_, and _cholera morbus_, are carried to our food by the dirty feet of flies.