tural flavors of well-prepared
foods aid in digestion. In the feeding of farm animals it has been found
that when foods are consumed with a relish better returns are secured
than when unpalatable foods are fed. To secure palatability the
excessive use of condiments is unnecessary. It is possible to a great
extent during preparation to develop and conserve the natural flavors.
Some foods contain bitter principles which are removed during the
cooking, while in others pleasant flavors are developed. Palatability is
an important factor in the digestibility of foods.

238. Physiological Properties of Food.--Some food materials,
particularly fruits and vegetables, contain compounds which have
definite physiological properties, as tannin which is an astringent,
special oils which exert a cathartic action, and the alkaloids which
serve as irritants to nerve centers. Wheat germ oil is laxative, and it
is probable that the physiological properties of graham and whole wheat
breads are due in some degree to the oil which they contain.[67] The
use of fruits, herbs, and vegetables for medicinal purposes is based
upon the presence of compounds possessing well-defined medicinal
properties. As a rule food plants do not contain appreciable amounts of
such substances, and the use of food for medicinal effect should be by
the advice of a physician. The physiological properties of some foods
are due to bacterial products. See Chapter XX.

239. Individuality.--Material difference in digestive power is
noticeable among individuals. Digestion experiments show that one person
may digest 5 per cent more of a nutrient than another. This difference
appears to be due to a number of factors, as activity of the organs, as
affected by exercise and kind of labor performed; abnormal composition
of the digestive fluids; or failure of the different parts of the
digestive tract to act in harmony. Individuality is one of the most
important factors in digestion. Persons become accustomed to certain
foods through long usage, and the digestive tract adapts itself to those
foods, rendering sudden and extreme changes in the dietary hazardous.
Common food articles may fail to properly digest in the case of some
individuals, while with others they are consumed with benefit. What is
food to one may prove to be a poison to another, and while general
statements can be made in regard to the digestibility of foods,
individual differences must be recognized.

240. Ps