Under the names of oil, butter, fat, lard, suet, and grease, a substance
is used largely as an article of food, which differs from starch and
sugar in the absence of oxygen gas. The composition of these oleaginous
substances may be represented as follows:—Carbon 11 parts; hydrogen 10
parts; oxygen 1 part.
Oil differs from the other carbonaceous substances in food in not only
supplying materials for maintaining animal heat, but in forming a part of
the tissues of the body called fat. The quantity consumed in animal food
is very large, constituting frequently more than half of the bulk of the
food consumed. It is also found very generally present in the vegetable
substances used as food. Although essential as an article of diet in
certain quantities, oil is less digestible than other kinds of food, and
those foods which contain it in large quantities are generally
indigestible. The principal source of oil used as food from the
vegetable kingdom is the Olive. This plant is cultivated in the south of
Europe. The part of the plant which contains the oil is the fruit. The
seeds of most plants contain oil in addition to starch and other
principles. Many seeds are used for obtaining oil for various purposes
in the arts, as the poppy, rape, mustard, hemp, and flax seeds. In Case
20 is a collection of nuts and seeds containing oil commonly eaten as
food. Case 21 contains the analysis of the coco-nut; and in the same
Case that of an African bread called “Dika bread,” both of which
illustrate food products containing an abundance of oil. The cocoa, or
chocolate plant, is one of the most remarkable vegetable productions
yielding oil, the seeds giving nearly 50 per cent. of a hard oil, or
butter. See Case 53.