ements. The mouth supplies the saliva; in
the walls of the stomach are little glands which produce the gastric
juice; the pancreatic juice is made by the pancreas; the liver secretes
bile; while scattered along the small intestines are minute glands
which make the intestinal juice. Each of these fluids has a particular
work to do in transforming some part of the food into suitable material
for use in the body. The saliva acts upon the starch of the food,
changing it into sugar; the gastric juice digests albumin and other
nitrogenous elements; the bile digests fat, and aids in the absorption
of other food elements after they are digested; the pancreatic juice is
not confined in its action to a single element, but digests starch,
fats, and the albuminous elements after they have been acted upon by the
gastric juice; the intestinal juice is capable of acting upon all
digestible food elements.

[Illustration: The Alimentary Canal, _a._ Esophagus; _b._ Stomach; _c._
Cardiac Orifice; _d._ Pylorus; _e._ Small Intestine; _f._ Bile Duct;
_g._ Pancreatic Duct; _h._ Ascending Colon; _i._ Transverse Colon; _j._
Descending Colon; _k._ Rectum.]

THE DIGESTION OF A MOUTHFUL OF BREAD.--A mouthful of bread
represents all, or nearly all, the elements of nutrition. Taking a
mouthful of bread as a representative of food in general, it may be said
that its digestion begins the moment that it enters the mouth, and
continues the entire length of the alimentary canal, or until the
digestible portion of the food has been completely digested and
absorbed. We quote the following brief description of the digestive
process from Dr. J.H. Kellogg's Second Book in Physiology[A]:--

[Footnote A: Good Health Pub. Co., Battle Creek, Mich.]

"_Mastication._--The first act of the digestive process is mastication,
or chewing the food, the purpose of which is to crush the food and
divide it into small particles, so that the various digestive fluids may
easily and promptly come into contact with every part of it.

"_Salivary Digestion._--During the mastication of the food, the salivary
glands are actively pouring out the saliva, which mingles with the food,
and by softening it, aids in its division and prepares it for the action
of the other digestive fluids. It also acts upon the starch, converting
a portion of it into grape-sugar.

"_Stomach Digestion._--After receiving the food, the stomach soon begins
to pour out the gastric juices, which first make