DIGESTION IN THE STOMACH
=17. The stomach.=--When food is swallowed it goes to the stomach. The
stomach is a thin bag. In a man it holds about three pints. Like the
mouth, it does three things to the food.
[Illustration: =Gastric glands in the stomach (x200).=
The cells _a_ and _b_, form the juice. The fibers _c_, bind the tubes
in place.]
_First_, the stomach gently stirs and mixes the food.
_Second_, it pours a fluid over the food. This fluid is called the
_gastric juice_. The gastric juice is sour and bitter.
_Third_, the gastric juice changes some of the albumin of food to a
liquid form.
If the mouth has done its work well, the stomach does its work easily
and we do not know it. But if the mouth has eaten food too fast and
has not chewed it well, then the stomach must do the work of the mouth
too. In that case it gets tired and aches.
=18. The intestine.=--The food stays in the stomach only a little
while. All the time a little keeps trickling into a long coil of tube.
This tube is called the _intestine_ or the _bowels_. Three or four
hours after a hearty meal the stomach is empty. Some of the food has
been changed to a liquid, but most of it has only been ground to
smaller pieces, and mixed with a great deal of water. Now it all must
be changed to a liquid.
=19. What the intestine does.=--Like the mouth and stomach, the
intestine does three things.
_First_, it mixes the food and makes it pass down the tube.
_Second_, two sets of cells behind the stomach make two liquids and
pour them into the intestine. One set of cells is the _sweetbread_, or
_pancreas_, and its liquid is the _pancreatic juice_. The other is the
_liver_ and its fluid is the _bile_.
_Third_, the pancreatic juice makes three changes in food. _First_,
like the mouth, it changes starch to sugar. _Second_, like the
stomach, it makes albumin a liquid. _Third_, it divides fat into fine
drops. These drops then mix with water and do not float on its top.
=20. Bile.=--The bile is yellow and bitter. It helps the pancreatic
juice do its work. It also helps to keep the inside of the intestine
clean.
=21. Digestion of water and minerals.=--Water and the mineral parts of
food do not need to be changed at all, but can become part of the
blood just as they are. Seeds and husks and tough strings of flesh all
pass the length of the intestine and are not changed.
=22. How food gets into the blood.=--By the time food is half way down
the intestine it is mostly liquid and ready to become part of the
blood. This liquid soaks through the sides of the intestine and into
the blood tubes. At last the food reaches the end of the intestine.
Most of its liquid has then soaked into the blood tubes and only some
solid waste is left.
=23. Work of the liver.=--The food is now in the blood, but has not
become a part of it. It is carried to the liver. There the liver changes
the food to good blood, and then the blood hurries on and feeds the
cells of the body. Spoiled food may be swallowed and taken into the
blood with the good food. The liver takes out the poisons and sends them
back again with the bile. The liver keeps us from getting poisoned.
=24. Bad food.=--Sometimes the stomach and intestine cannot digest the
food. They cannot digest green apples, but they try hard to do so.
They stir the apples faster and faster until there is a great pain.
Sometimes the stomach throws up the food and then the pain and
sickness stop. Spoiled food makes us sick in the same way.
=25. Too fast eating.=--When the food stays too long in the stomach or
intestine it sours, or decays, just as it does outside of the body.
This makes us very sick. When we eat too much, or when we do not chew
the food to small pieces, the stomach may be a long time in digesting
the food. Then it may become sour and make us sick.
=26. Biliousness.=--When the food is poor or becomes sour, it is
poorly digested. Then the liver has more work to do, and does not
change the food to blood as it should. It also lets some of the sour
poisons pass by it. These poison the whole body and make the head
ache. We call this _biliousness_. The tongue is then covered with a
white or yellow coat and the mouth tastes bad. These are signs of
sickness. The stomach and liver are out of order.
=27. Rules for eating.=--If we eat as we should, our stomach will
digest its food. We must follow three rules.
_First_, we must chew the food in the mouth until all the lumps are
fine. Then the food will be ready for the stomach.
_Second_, we must eat slowly. If we eat fast we cannot chew the food
well. The stomach cannot take care of food if it comes too fast. We
must swallow all of one mouthful before we put another into the mouth.
_Third_, we must eat only at meal times. The stomach needs a rest.
Even a little candy, or apples, or nuts will keep the stomach at work,
and tire it out. A child needs to eat more often than his father. So,
besides his meals, he should have something to eat in the middle of
the morning and some more in the afternoon. But he should not be
eating at all hours. He ought not to eat little bits just before
dinner, for that spoils his meal.
WHAT WE HAVE LEARNED
1. The stomach and intestine stir and rub the food, and mix it
with juices.
2. The juices change albumin to a liquid, and starch to sugar.
They also change fat to the form of tiny drops.
3. The digested food soaks through the sides of the intestine
into the blood tubes.
4. The blood carries the food to the liver.
5. The liver changes food to blood.
6. Blood goes to all parts of the body and feeds the cells.
7. The liver keeps poisons from getting into the blood.
8. Water and minerals become a part of the blood without being
digested.
9. When food is not well digested, the liver cannot make it into
good blood. This makes us bilious.
10. If food is not soon digested it sours and decays. This makes
us sick.
11. We can make food digest quickly by chewing it well and eating
slowly.