ventive 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.)]

In places having no system of drainage privies must be used. They can be
made harmless, as army camps prove, but they require scrupulous care.
Fecal matter must be prevented from draining into wells and other water
supplies, and must be screened from flies. The privy should be located
at a distance from the well. The minimum distance that is safe depends
in each case upon the nature of the soil and the direction of the
natural drainage. Even when the privy is situated below the well on
sloping ground, drainage may still occur from the privy to the well;
however, a well-made, properly located pit privy is safe unless it is
near a limestone formation. The dry earth system is satisfactory in
places having an efficient public scavenger system; in this system pails
or cans are used to receive the discharges, which are then covered with
sand, ashes, earth or, preferably, chloride of lime. The buckets are
frequently emptied and the contents buried at l