PARTS OF THE BODY
=Regions of the Body.=--In order to talk about any part of the body it
must have a name. The main portion of the body is called the _trunk_.
At the top of the trunk is the _head_. The arms and legs are known as
_limbs_ or _extremities_. The part of the arm between the elbow and
wrist is the _forearm_. The _thigh_ is the part of the leg between the
knee and hip.
The upper part of the trunk is called the _chest_ and is encircled by
the ribs. The lower part of the trunk is named the _abdomen_. A large
cavity within the chest contains the lungs and heart. The cavity of
the abdomen is filled with the liver, stomach, food tube, and other
working parts.
=The Plan of the Body.=--All parts of the body are not the same. One
part has one kind of work to do while another performs quite a
different duty. The covering of the body is the _skin_. Beneath is the
red meat called _muscle_. It looks just like the beef bought at the
butcher shop which is the muscle of a cow or ox. Nearly one half of
the weight of the body is made of muscle.
[Illustration: FIG. 4.--General plan of the organs of the body.]
The muscle is fastened to the _bones_ which support the body and give
it stiffness. The muscle by pulling on the bones helps the body to do
all kinds of work. The muscles and bones cannot work day after day
without being fed. For this reason a food tube leads from the mouth
down into the trunk to prepare milk, meat, bread, or other food, for
the use of the body.
=Feeding the Body.=--The mouth receives the food and chews it so that it
may be easily swallowed. It then goes into a sac called the _stomach_.
Here the hard parts are broken up into tiny bits and float about in a
watery fluid. This goes out of the stomach into a long crooked tube, the
_intestine_. Here the particles are made still finer, and the whole mass
is then ready to be carried to every part of the muscles, bones, and
brain to build up what is being worn out in work and play.
=Carrying Food through the Body.=--In all parts of the body are little
branching tubes. These unite into larger tubes leading to the heart.
Through these tubes flows _blood_. Hundreds of tiny tubes in the walls
of the intestine drink in the watery food, and it flows with the blood
to the heart. The heart then pushes this blood with its food out
through another set of tubes which divide into fine branches as they
lead to every part of the body (Fig. 5).
=Getting rid of Ashes and Worn-out Parts.=--The body works like a
machine. Food is used somewhat as a locomotive uses coal to give it
power to work. Some ashes 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, wine, or tobacco may hinder the body from using food
for growth, or they may poison the body so that it will never be large
and strong. The body should grow about a hundred pounds in weight
during the first thirteen years of life. Whether children grow little
or much generally depends on the food they give their bodies.
PRACTICAL QUESTIONS
1. Point out and name four parts of the body.
2. Name the two parts of the trunk.
3. What does the chest contain?
4. What is muscle?
5. How is the body fed?
6. Give three parts taking waste out of the body.
7. Of what use are the brain and nerves?
8. Name two organs.
9. How long does the body continue to grow?
10. Why are some children weak and of slow growth?