HOW THE BODY USES FOOD
=Organs for making ready the Food.=--Before the food can get into the
blood and be carried over the body to feed the muscles and the brain,
it must be made into a fluid. This changing of the solid food into a
liquid by the stomach and other organs is called _digestion_. The
organs which do this work are known as _digestive organs_. They
consist of a _food tube_ and several bodies called _glands_.
=The Food Tube.=--The food canal is about thirty feet long. Its first
part, the _mouth_, opens back of the tongue into the throat, named the
_pharynx_. This leads into a tube, the gullet, passing down through
the back part of the chest into the _stomach_ below the diaphragm. The
stomach is a bent sac opening into a tube over twenty-five feet long
called the _bowels_ or _intestines_. This tube is folded into a bunch
which fills a large part of the cavity of the abdomen.
[Illustration: FIG. 23.--The plan of a gland. _a_ carries blood to the
gland and _v_ takes it away after the gland has taken out what it
needs. On the right side the top of the gland has been cut off.]
=The Glands or Juice Makers.=--A gland is a little tube closed at one
end, or a bunch of such tubes, which can take something out of the
blood and make it into a juice. A gland under each ear and four others
near the tongue make the juice called _saliva_ which flows into the
mouth through tubes.
A long, flat, pink gland back of the stomach is called the _sweetbread_
or _pancreas_. This and a large brown gland, the _liver_, empty their
juices into the intestines. The whole inner surface of the stomach and
intestines is lined with tiny tubes, the glands. The juice of these with
that of the other glands softens the food and makes it into a liquid.
=The Work of the Mouth.=--The mouth has three things to do: It should
break the lumps of food into fine bits so it can be well wet with the
slippery fluid called _saliva_ and also easily swallowed. It must roll
the food about so that it gets soaked with saliva. It must hold the
food long enough to get much taste from it because this starts the
juices to flowing into the stomach. Food gives out its taste only
after it is changed to a liquid. It should not be washed down with
water, as this weakens the juices in the stomach.
[Illustration: FIG. 24.--The three glands which make the saliva for
acting on the food in the mouth.]
No food should be swallowed until it is broken into bits nearly as small
as the head of a pin. Some foods, such as cheese, bananas, and nuts,
should be made even finer than this. There is nothing in the stomach to
crush to pieces large lumps of food. The juices of the stomach can do
their full work only when the food is well chewed in the mouth.
[Illustration: FIG. 25.--Photograph of a chestnut chewed a half minute
by a boy who had poor teeth because he had not taken care of them. The
lumps are so large that the juices of the stomach could not dissolve
them.]
=The Chewing of Food keeps away Sickness.=--Bread, meat, and potatoes
should be cut into pieces no larger than half the size of your thumb
and each piece put separately into your mouth with a fork. It should
then be chewed from twenty to thirty times before another piece is put
into the mouth. Food treated in this way will not cause headache or a
sickness in the stomach called _indigestion_ or _dyspepsia_. It is
said that there are so many persons with this kind of sickness that
more than $5,000,000 are spent every year for medicine to help them.
Too little chewing of the food while you are young may not cause many
aches or pains, but if you form the habit of rapid eating it is hard
to learn to eat slowly. No one who chews his food poorly can avoid
sickness long or grow well and strong.
[Illustration: FIG. 26.--Photograph of a chestnut chewed a half minute
by a boy with good teeth.]
=The Work of the Stomach.=--When the food is swallowed, it passes
through the gullet into the stomach. This is a sac holding more than
a quart (Fig. 27). It is made of an outer wall of muscle and an inner
skinlike coat full of tiny tubes called _gastric glands_. Millions of
these give out drop by drop a watery fluid named _gastric juice_. This
juice begins to flow as soon as we smell or taste food and continues
to drop out as long as there is any food in the stomach.
The use of the gastric juice is to help change part of the food into a
more watery fluid. To do this it must be well mixed with the food.
This mixing is done by the muscles in the outer wall of the stomach
(Fig. 29). They squeeze together and then loosen up in such a way as
to move the food about and turn it over until every particle is wet
again and again with the gastric juice.
=How long Food stays in the Stomach.=--A ring of muscle around the end
of the stomach keeps the food from escaping until it has become a thin
grayish liquid. The stomach can finish its work on some kinds of food
in one or two hours. With other foods it must work four or five hours.
The stomach can finish its work on soft boiled eggs, milk, roasted
potatoes, and broiled lamb within two hours. With pork, veal, cabbage,
and fried potatoes it must work four or five hours. When a person is
sick the stomach is weak, and he should have only the food which
causes the stomach the least work.
=The Work of the Intestines.=--The last part of the work in getting
the food ready for the blood is done in the long folded tube known as
the intestine (Fig. 27). Here juices coming from the pancreas and
liver mix with the food and change into a liquid those parts not acted
on in the stomach.
The intestine does quite as much work as the stomach. Sometimes when
the stomach is sick, too much work is put off on the intestines and
then they become sick and give much pain.
The pint of watery fluid from the pancreas and the quart of greenish
yellow fluid called _bile_ given out by the liver are carried through
two tubes into the intestine (Fig. 27). To mix these juices with the
food the intestine is being swung gently back and forth and the walls
squeezed together by muscles forming its outer coat. As soon as the
intestine has finished its work the food begins to enter the blood.
[Illustration: FIG. 27.--The organs which get the food ready to enter
the blood.]
[Illustration: FIG. 28.--Showing how the food in the dog is carried
from the intestine to the liver and heart. The white tubes carry the
fats up to the vein in the neck, and the dark tubes which are veins
carry the other part of the food to the liver.]
=How Food gets into the Blood.=--An hour or two after food has entered
the intestine it is almost as thin a fluid as milk. Millions of tiny
fingerlike growths stick out from the inner side of the intestines
and drink in the watery food. These little fingers for drinking up the
food are scarcely one fourth as large as the point of a pencil. They
are called _villi_.
The villi are filled with blood tubes having thin walls. The food passes
through these walls into the blood stream. Much of it then goes to the
liver, but the fatty parts flow up a tube along the backbone and empty
into a blood tube in the neck. From the neck and the liver the food goes
with the blood to the heart which sends it to all parts of the body.
=What the Liver does.=--The liver is a dark red body nearly as large
as the upper half of your head. It lies just below the diaphragm. It
works night and day helping to keep the inner parts of the body clean
and at the same time deal out food.
The liver takes some waste out of the blood and sends it out into the
intestine with the bile. When there is no food in the intestine, the
bile is stored up in the _gall bladder_ under the liver. The liver
changes certain waste matter in the blood into such form that other
organs can cast it out of the body. It also stores up certain parts of
the food coming from the intestines and gives it out to the body
little by little as it is needed.
=When and How much to Eat.=--When the food organs do not do their work
rightly, the whole body becomes sick. Eating too much overworks the
stomach. It becomes so full that the food cannot be moved about and
well mixed with the juices. Germs then work on the food and make it
sour. In fact the germs may change part of the food into a poison.
This poison will cause headache and a bad feeling.
Do not form a habit of taking powders to cure headache. They are likely
to hurt the heart. Take less food, eat it more slowly, and do not wash
it down with drink. Stop eating before your stomach feels full.
Each meal gives the stomach about four hours of work to do. It then
needs one hour of rest. This shows that the time from one meal to the
next should be about five hours. Very young children and sick persons
need food oftener. Boys and girls should not eat candies, cake, or
other food between meals. It spoils the appetite and is likely to get
the stomach out of working order.
=Danger Signals.=--A white or yellowish coat on the tongue, a bad
breath, pain in the bowels, or a headache is a danger signal. It tells
that the food organs are not doing their work as they should and unless
help is given sickness is likely to occur. Medicine may help, but using
foods easy to digest, eating less, chewing more, and getting plenty of
exercise in the fresh air are likely to be the greatest aids to health.
=The Chewing of Tobacco and Digestion.=--Some men chew tobacco as much
as ten hours every day. The taste of the tobacco makes the saliva flow
from the glands into the mouth. This dissolves the poison out of the
tobacco and it is then spit out. If the tobacco-soaked saliva were all
swallowed, the man would be poisoned.
The chewing of tobacco causes the loss of much saliva which is needed
to help digest the food. Anyone who tires his jaw by chewing tobacco
is not likely to chew his food well. Some of the poison in the tobacco
is taken into the body through the blood vessels in the lining of the
mouth. This is shown by the fact that a boy not used to tobacco
becomes very sick after he has chewed a mouthful for only ten minutes.
=Smoking and Digestion.=--Some persons think that the smoking of a
cigar after a meal helps digestion. It may do so in some cases. If a
lawyer is much excited about a case he is trying, or a business man is
in trouble about his losses, the thinking causes the blood to flow to
the head when it is needed in the stomach to give out digestive juices.
The taste of the tobacco smoke may cause some gastric juice to run out
into the stomach, but at the same time it is likely to hurt the nerves
of taste so that food cannot give so much enjoyment as when the nerves
are unharmed. Although smoking may at the time help digestion a
little, the poison in the tobacco may afterward injure the body. This
poison is especially harmful to growing bodies, and boys who are wise
will refuse to smoke on all occasions.
=Beer and Digestion.=--Some people drink beer with their meals because
they think it makes the food taste better. It really prevents them
from getting the full taste of the food because they wash it down
before it is well soaked with the saliva.
[Illustration: FIG. 29.--The stomach, showing the arrangement of the
muscular fibers which alcohol may hinder from doing good work. At the
right a piece is cut out of the top layer of muscle.]
The flavor of beer may sometimes cause an extra flow of gastric juice
into the stomach, but the alcohol in the beer is likely to make the
movements of the stomach slower. This prevents the food from being
well and quickly mixed with the juices. Several glasses of beer used
at one meal will make the stomach do its work very slowly, and it will
not do it well.
=Wine and Digestion.=--Wine is taken by some people to give more
appetite for food. It is likely, however, to do more harm than good
because the alcohol in it makes the muscles which mix the food in the
stomach act more slowly. Some of the food may sour before it gets wet
with the juice. Much wine used at a meal is always harmful.
=Natural Appetite.=--If one is in health, he should feel a desire for
his food at every meal. This desire for a reasonable amount of food is
a natural appetite. Fresh air and exercise will do much to give one
the right kind of an appetite. The eating of much sweets and the
breathing of bad air are likely to spoil the appetite.
The use of some things, such as opium, tobacco, beer, wine, and
whisky, creates an unnatural appetite. That is, after one has used
these articles a few months he cannot stop their use without great
suffering. The younger the person, the sooner the appetite becomes
fixed. For this reason _young persons should never use tobacco or
alcoholic drinks of any kind_.
PRACTICAL QUESTIONS
1. What is digestion?
2. Name the parts of the food tube.
3. Where does saliva come from?
4. Explain how the food is acted on in the mouth.
5. Why should food be well chewed?
6. What forms the gastric juice?
7. Of what use is the gastric juice?
8. How long does food stay in the stomach?
9. Name some foods easily digested.
10. What does the intestine do?
11. What are villi?
12. Tell how the food gets into the blood.
13. Of what use is the liver?
14. Why should we not eat too much?
15. Should we eat between meals?
16. Give three reasons why you should not use tobacco.