ychological Factors.--Previously conceived ideas concerning
foods influence digestibility. Foods must be consumed with a relish in
order to secure the best results, as flow of the digestive fluids and
activity of the organs are to a certain extent dependent upon the nerve
centers. If it is believed that a food is poisonous or injurious, even
when the food is wholesome, normal digestion fails to take place. In
experiments by the author, in which the comparative digestibility of
butter and oleomargarine was being studied, it was found that when the
subjects were told they were eating oleomargarine, its digestibility was
depressed 5 per cent, and when they were not told the nature of the
material, but assumed that butter was oleomargarine, the digestibility
of the butter was lowered about 6 per cent.[13] Preconceived notions in
regard to foods, not founded upon well-established facts, but due to
prejudice resulting from ignorance, cause many valuable foods to be
excluded from the dietary. Many persons, like the foreign lady who,
visiting this country, said she ate only acquaintances, prefer foods
that have a familiar taste and appearance, and any unusual taste or
appearance detracts from the value because of the psychological
influence upon digestion.

CHAPTER XVI

COMPARATIVE COST AND VALUE OF FOODS

241. Cost and Nutrient Content of Foods.--The market price and the
nutritive value of foods are often at variance, as those which cost the
most frequently contain the least nutrients.[75] It is difficult to make
absolute comparisons as to the nutritive value of foods at different
prices, because they differ not only in the amounts, but also in the
kinds of nutrients. While it is not possible to express definitely the
value of one food in terms of another, approximate comparisons may be
made as to the amounts of nutrients that can be secured for a given sum
of money when foods are at different prices, and tables have been
prepared making such comparisons.

[Illustration: FIG. 56.--COMPOSITION OF FOODS.

(From Office of Experiment Stations Bulletin.)]

242. Nutrients Procurable for a Given Sum.[7]--To ascertain the
nutrients procurable for a given sum first determine the amount in
pounds that can be obtained, say, for ten cents, and then multiply by
the percentages of fat, protein, carbohydrates, and calories in the
food. The results are the amounts, in pounds, of nutrients procurable
for that sum of money. For e