ommon fats and oils, may
be found in any reference book on oil analysis.

PHYSIOLOGICAL USE OF FATS AND OILS

In animal organisms, fats are the one important form of energy storage.
They also form one of the most important supplies of energy reserve
material in plants. Carbohydrates commonly serve this purpose in those
plants whose storage reservoirs are in the stems, tubers, etc.; but in most
small seeds the reserve supply of energy is largely in the form of oil, and
even in those seeds which have large endosperm storage of starch, the
embryo is always supplied with oil which seems to furnish the energy
necessary for the first germinative processes.

Fats are the most concentrated form of potential energy of all the
different types of organic compounds which are elaborated by plants. This
is because they contain more carbon and hydrogen and less oxygen in the
molecule than any other group of substances of vegetable (or animal)
origin. It has been pointed out that a quantity of fat capable of yielding
100 large calories of heat will occupy only about 12 cc. of space, whereas
from 125 to 225 cc. of space in the same tissue would be required for the
amount of starch of glycogen necessary to yield the same amount of heat, or
energy, when oxidized.

The fats undoubtedly catabolize first by hydrolysis into glycerol and fatty
acids, and then by oxidation possibly first into carbohydrates and then
finally into the end-products of oxidation, namely, carbon dioxide and
water. The following hypothetical equation to represent the oxidation of
oleic acid into starch, suggested by Detmer, is interesting as a suggestion
of how much oxygen is required and how much heat would be liberated by such
a transformation:

C_{18}H_{34}O_{2} + 27O = 2(C_{6}H_{10}O_{5}) + 6CO_{2} + 7H_{2}O

Complete oxidation of oleic acid to the final end-products, carbon dioxide
and water, would require much more oxygen, thus:

C_{18}H_{34}O_{2} + 51O = 18CO_{2} + 17H_{2}O.

Hence, Detmer's reaction would yield only approximately one-half the total
energy available in the acid; but it does indicate the possibility of
redevelopment of fatty acids or fats from the unoxidized carbohydrate
material which remains in the equation. Moreover, there is abundant
evidence to show that, in both animal and plant tissues, energy changes are
brought about chiefly by the transformation of fats into carbohydrates and
_vice vers