s are left from the used food, and other waste
matter is formed by the dead and worn-out parts of the body. This
waste is gathered up by the richly branching blood tubes and carried
to the lungs. Here some of it passes out at every breath. Part of the
waste goes out through the skin with the sweat and part passes out
through the kidneys. In this way the dead matter is kept from
collecting in the body and clogging its parts.

=How the Parts of the Body are made to work Together.=--The mass of
red flesh covering the bones is made up of many pieces called muscles.
Whenever we catch a ball or run or even speak, more than a dozen
muscles must be made to act together just in the right way. When food
goes into the stomach, something must tell the juice to flow out of
the walls to act on the food. The boss or manager of all the work
carried on by the thousands of parts of the body is known as the
_brain_ and _spinal cord_ with their tiny threads, the _nerves_,
spreading everywhere through bones and muscles. The brain and spinal
cord give the orders and the nerves carry them (Fig. 5).

=The Servants of the Body.=--The parts of the body are much like the
servants in a large house or the clerks in a store. One servant or
clerk does one kind of work while another does something entirely
different. Each portion of the body does a different kind of work.
Each one of these parts doing a particular work is called an _organ_.
The stomach is an organ to prepare food and the heart is an organ for
sending the blood through the body.

[Illustration: FIG. 5.--On the left are shown the branching tubes
which carry blood to all parts of the body; on the right are the
brain, spinal cord, and nerves which direct the work of the organs.]

The entire body is composed of several hundred organs. Each of them is
formed of several kinds of materials named _tissue_. A skinlike tissue
makes up the lining of the stomach, while its outside is made of
muscular tissue. The smallest parts of a tissue are little bodies
named _cells_, and very fine threads called _fibers_.

=Growth of the Body.=--The body grows rapidly in childhood and more
slowly after the sixteenth year, but it continues to get larger until
about the twenty-fifth year of age. Some children always grow slowly,
have weak bones, and frail bodies. This is generally so because they
have poor food or do not chew it well, and get too little fresh air,
sunshine, and sleep.

The use of beer, wi