00).=

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