irably. Cities use steam sterilizers
because of the greater convenience in furnishing steam to a large tank
as compared with filling and emptying a tank with water and then
providing sufficient heat to boil that water. The exposure to steam
should last from half an hour to an hour, depending on whether the
objects to be disinfected are small, open, and loose, or large, compact,
and dense. Some articles, like bales of rugs, rolls of wool, and large
bundles of cloth, cannot be sterilized at the center by ordinary steam,
and while it is not likely that infection at the centers of such tightly
rolled bundles has occurred if exposure took place while rolled up, yet
it is certain that the disinfection does not reach these centers. In the
case of such bundles as rugs from infected countries, where any single
rug may become the medium of infection, it is requisite to thoroughly
sterilize all parts of the bundle. For this purpose, it is necessary not
merely to expose the articles to live steam, but to have the live steam
under pressure so that it is forced into the inside of the packages by
an excess of external pressure. This is probably not available in an
ordinary house, where boiling must continue to be the method of
disinfection.

_Drying, light, and soil._

Before leaving this chapter, three agencies for disinfection may be
pointed out, not perhaps to be depended on, but in order that the kindly
provisions of nature may be appreciated. All germs removed from the
body, which is their natural home, and exposed to the air are subject to
drying and thus are killed. Unfortunately, this does not become true
except after long periods of time, nor is it equally true with all
germs, but it is certainly one of the methods by which the evil effects
of disease germs may be lessened. The germ of consumption lasts as long
as any germ, and yet this, when dried in the street, loses its vitality
after about a week. Similarly, the typhoid fever germs, unless kept in a
moist condition, dry up and die in a few days. With the drying, however,
comes the danger that in the process they may be lifted by the wind and
carried in the air to the mouths or nostrils of well persons, so that it
is not wise to depend solely on this method of disinfection.

Sunlight is more positive than the wind, and the exposure to direct
sunlight of a bottle filled with disease germs will kill them all in two
or three hours. The surface layers of a pond never have as