st friends are certain germs which help make the
ground rich, so that the crops will grow.

=Mold.=--The dust raised in sweeping contains tiny living seedlike
bodies. If these fall on bread, cheese, or fruit, and this food is
afterward kept moist in a warm room for a day or two, they will grow
into grayish fluffy spots. These spots are mold. The greenish white
growth on the top of some canned fruit and on berries left in the
warm kitchen over night is also mold.

Mold is a plant which grows from tiny round bodies acting like seeds
(Fig. 17). These seed bodies of mold are common in all dust and often
fly through the air. On this account food should be kept covered when
possible and especially when one is sweeping. Some mold gives bread,
cheese, and other food a bad taste, but it will not make one sick.

=How Germs Grow.=--Germs will not grow where it is very cold, but
freezing the germs does not kill them. Boiling one minute kills most
germs. Drying will stop the germs from growing, but will not kill all
of them. Sunlight kills many of them.

Moisture and warmth make germs grow rapidly. A germ in growing
lengthens out a little and then divides in the middle. It does this so
quickly that one germ may become two in fifteen minutes. Each of these
will then divide. In this way one germ can make many million germs in
a single day (Fig. 18).

=The Spoiling of Meat.=--Fresh meat will not remain good even one day
if left in a warm place. A large greenish blue fly seen buzzing about
in warm weather will sometimes lay its eggs on meat. These will hatch
the next day into little worms, called maggots. They grow rapidly and
a few days later change into flies.

[Illustration: FIG. 18.--Drawing of the germ at the top every ten
minutes, showing how it grew into two germs in a half hour. Much
enlarged.]

Germs will also spoil meat not kept cold. They feed on the meat and
give off a poison, making it unfit to eat. The bad odor tells when the
germs are at work. Every home should have a cold cellar or an ice box
to keep food from spoiling.

=Saving Food from Souring.=--The souring of milk and of cooked food of
any kind is due to the germs always present in the air and clinging by
the thousands to unwashed dishes and hands. If meat or fruit is cooked
and kept tightly covered, it will remain good for years. Many persons
save fruit and vegetables for use in winter by putting them in jars,
which are heated to kill the germs, and seale