E GERMS

=197. Catching diseases.=--Our body may get out of order like a
machine. Some parts of it may be cut, or broken, or worn out, or hurt
in other ways. Then we are sick until it is made whole again. Sickness
always means that a part of the body is out of order.

Some kinds of sickness are like a fire. A small bit of something from
a sick person may start a sickness in us, just as a spark may set a
house on fire. Then we may give the sickness to others, just as a fire
may spread to other houses. If a person has measles, we may catch the
measles if we go near him; but if a person has a toothache, we cannot
catch the toothache from him. So we may catch some kinds of diseases,
but we cannot catch other kinds.

=198. Bacteria and germs.=--Every kind of catching sickness is caused
by tiny living things growing in our flesh and blood. Some of them are
tiny animals. Most of them are plants, and are called _bacteria_ or
_microbes_. A common name for all of them is _germs_.

The word germ means nearly the same as the word seed. Bacteria are so
small that we cannot see them unless we look at them through a strong
microscope. Then they look like little dots and lines (p. 54). A
million of them could lie on a pin point; but if they have a chance,
they may grow in numbers, so that in two days they would fill a pint
measure.

Very many kinds of bacteria and other germs are found nearly
everywhere. They are in the soil and in water, and some float in the
air as dust. When they fall on dead things, they cause _decay_ or
_rotting_. When we can fruit, we kill the germs by boiling the fruit
and the cans. Then we close the cans tightly so that no new germs can
get into them. The fruit will then keep fresh for years.

Decay is nearly always a good thing, for by it dead bodies and waste
substances are destroyed and given back to the ground, where plants
feed upon them. Many plants would not grow if they could not feed upon
decaying things. So most bacteria and other germs are useful to us.
But some kinds of germs will grow only in our bodies, and these kinds
are the cause of most of our sickness.

=199. Germs of sickness.=--We catch a sickness by taking a few of the
germs of the sickness into our flesh. There they grow quickly, like
weed seeds in the ground, and form crops of new germs within a few
hours. After a few days the germs become millions in number, and crowd
the cells of our flesh, just as weeds may crowd a potato pl