ines by which the food is moved along, and aids absorption. It
is remarkable and interesting that a fluid so useful as the bile should
be at the same time composed of waste matters which are being removed
from the body. This is an illustration of the wonderful economy shown by
nature in her operations.

"The food is moved along the alimentary canal, from the stomach
downward, by successive contractions of the muscular walls of the
intestines, known as peristaltic movements, which occur with great
regularity during digestion.

"_Absorption_.--The absorption of the food begins as soon as any portion
has been digested. Even in the mouth and the esophagus a small amount is
absorbed. The entire mucous membrane lining the digestive canal is
furnished with a rich supply of blood-vessels, by which the greater part
of the digestive food is absorbed.

"_Liver Digestion._--The liver as well as the stomach is a digestive
organ, and in a double sense. It not only secretes a digestive fluid,
the bile, but it acts upon the food brought to it by the portal vein,
and regulates the supply of digested food to the general system. It
converts a large share of the grape-sugar and partially digested starch
brought to it into a kind of liver starch, termed glycogen, which it
stores up in its tissues. During the interval between the meals, the
liver gradually redigests the glycogen, reconverting it into sugar, and
thus supplying it to the blood in small quantities, instead of allowing
the entire amount formed in digestion to enter the circulation at once.
If too large an amount of sugar entered the system at once, it would be
unable to use it all, and would be compelled to get rid of a
considerable portion through the kidneys. The liver also completes the
digestion of albumen and other food elements."

TIME REQUIRED FOR DIGESTION.--The length of time required for
stomach digestion varies with different food substances. The following
table shows the time necessary for the stomach digestion of some of the
more commonly used foods:--

min
Rice 1 00
Sago 1 45
Tapioca 2 00
Barley 2 00
Beans, pod, boiled 2 30
Bread, wheaten 3 30
Bread, corn 3 15
Apples, sour and raw 2 00
Apples, sweet and raw 1 30
Parsnips, boiled 2 30