INSECTS.--Flies, cockroaches, and other scavenging insects may carry disease germs on their feet and thus infect food on which they walk. Typhoid, cholera, dysentery, and other diseases have been carried by flies. Flies are always a menace, and should not be tolerated; moreover, the thought of their coming to food directly from manure piles and privy vaults is disgusting. Houses should be thoroughly screened in the fly season, but it is better to destroy the nuisance at its source. The chief breeding places of flies are garbage cans and manure piles. If the garbage can is water tight, closely covered, frequently emptied, and thoroughly cleaned, flies will not develop in it; about ten days must elapse from the time when the egg is laid until the insect is ready to fly. Fly traps to fit on the garbage can are useful. Manure should be screened and removed frequently, or it can be treated chemically. Methods for treating it are given in "Preventive Medicine and Hygiene."--Rosenau, p. 255, and in Bulletin No. 118, of the U. S. Dept. of Agriculture, July 14, 1914. [Illustration: FIG. 8.--A FLY WITH GERMS (GREATLY MAGNIFIED) ON ITS LEGS. (_U. S. Dept. Agri._)] Other diseases carried by insects are malaria and yellow fever, each by a special species of mosquito; typhus fever, by lice; and bubonic plague, by rat fleas. Various diseases less common in this country are carried by other insects. Even when mosquitoes are not carrying disease germs their bites may be harmful since they are often rubbed, especially by children, until the skin is broken, and various infections may enter through the wounds. Insects of every kind, rats, mice, and vermin should be excluded from houses. SEWAGE.--Discharges from the bowels and bladder contain various germs, and constitute one of the most important routes by which germs of typhoid fever, cholera and certain other diseases travel from person to person. Keeping sewage out of the water supply is consequently of great importance. Where a system of sewage disposal exists, the responsibility of making the system adequate and thus safeguarding public health rests upon the community as a whole. Communities ordinarily get just as much, or just as little typhoid fever as they are willing to endure. [Illustration: FIG. 9.--HOW A WELL MAY BE POLLUTED. (_From "The Human Mechanism."_ Copyright by Theodore Hough and William T. Sedgwick. Ginn and Company, publishers. Used by permission.)]