It is important that the housekeeper not only understand the nature and
composition of foods, but she should also know something of their
digestive properties, since food, to be serviceable, must be not only
nutritious, but easily digested. Digestion is the process by which food
rendered soluble, and capable of being absorbed for use in carrying on
the various vital processes.

The digestive apparatus consists of a long and tortuous tube called the
alimentary canal, varying in length from twenty-five to thirty feet,
along which are arranged the various digestive organs,--the mouth, the
stomach, the liver, and the pancreas,--each of which, together with the
intestines, has an important function to perform. In these various
organs nature manufactures five wonderful fluids for changing and
dissolving the several food elements. 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._