[Sidenote: Cellulose--its purpose, source, and importance]
Cellulose, from the standpoint of human nutrition, is not a food
product, being insoluble by the digestive juices, but it is very
important in the digestion and the alimentation of other foods. Its
chief purpose is to excite stomach and intestinal peristalsis. All
plant products in their natural form contain some cellulose, though the
percentage is very small in such grains as rice and barley. The bran of
wheat or of corn is chiefly cellulose. Wood is almost pure cellulose.
Cellulose can be digested by strong acids into simple carbohydrates, in
the same way that starch may be. Sugar can be manufactured from wood or
rags, but the process is yet too expensive to be applied commercially.
Some of us may live to see the time when the chief food of mankind
will be manufactured from scrap lumber and waste paper. Bacteria have
the power of digesting cellulose. The bacterial action or fermentation
in the human intestines may cause a small amount of cellulose to be
digested, but the quantity is of no consequence from a nutritive point
of view.