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 ho