nd chemical changes cannot take place if the
food is not in proper mechanical condition. In general, the finer the
food particles, the more completely the nutrients are acted upon by the
digestive fluids and absorbed by the body. Nevertheless, the diet should
not consist entirely of finely granulated foods. Some foods are valuable
mainly because of the favorable action they exert mechanically upon
digestion, rather than for the nutrients they contain.[62] Coarsely
granulated breakfast foods, whole wheat flour, and many vegetables
contain sufficient cellular tissue to give special value from a
mechanical rather than a chemical point of view. The extent to which
coarsely and finely granulated foods should enter into the ration is a
question largely for the individual to determine. Experiments with pigs
show that if large amounts of coarse, granular foods are consumed, the
tendency is for the digestive tract to become inflamed and less able to
exercise its normal functions. Coarsely granulated foods have a tendency
to pass through the digestive tract in less time than those that are
finely granulated, due largely to increased peristaltic action, and the
result is the food is not retained a sufficient length of time to allow
normal absorption to take place. In the feeding of farm animals, it has
been found that the mechanical condition of the food has a great
influence upon its economic use. Rations that are either too bulky or
too concentrated fail to give the best results. In the human ration, the
mechanical condition of the food is equally as important as its chemical
composition.

236. Mastication is an important part of digestion, and when foods are
not thoroughly masticated, additional work is required of the stomach,
which is usually an overworked organ because of doing the work of the
mouth as well. Although much of the mechanical preparation and mixing of
foods is of necessity done in the stomach, some of it may advantageously
be done in the mouth. The stomach should not be required to perform the
function of the gizzard of a fowl.

237. Palatability of Foods.--Many foods naturally contain essential
oils and other substances which impart palatability. These have but
little in the way of nutritive value, but they assist in rendering the
nutrients with which they are associated more digestible. Palatability
of a food favorably influences the secretion of the gastric and other
digestive fluids, and in this way the na