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CHAPTER IV.
ANIMAL FATS AND PHOSPHATIDES.
1. Neutral Fats and Fatty Acids.
The fats form the third chief group of the organic food of man and
animals. They occur very widely distributed in the animal and plant
kingdoms. Fat occurs in all organs and tissues of the animal organism,
though the quantity may be so variable that a tabular exhibit of the
amount of fat in different organs is of little interest. The marrow con-
tains the largest quantity, having over 96 per cent. The three most
important deposits of fat in the animal organism are the intermuscular
connective tissue, the fatty tissue in the abdominal cavity, and the
subcutaneous connective tissues. In plants, the seeds and fruit and in
certain instances also the roots, are rich in fat. Fat also occurs deposited,
during the winter’s rest, in the trunks of trees.
The fats consist almost entirely of so-called neutral fats, with only
very small quantities of fatty acids. The neutral fats are esters of the
triatomic alcohol, glycerin, with monobasic fatty acids. These esters
are triglycerides; that is, the hydrogen atoms of the three hydroxyl
groups of the glycerin are replaced by the fatty-acid radicals, and their
general formula is therefore, C3H5.O3.R3- The animal fats consist
chiefly ’of esters of the three fatty acids, stearic, palmitic, and oleic acids.
In certain fats, especially in milk-fat, glycerides of fatty acids such as
butyric, caproic, caprylic, and capric acids also occur in considerable
amounts. Besides the above-mentioned ordinary fatty acids, stearic,
palmitic, and oleic acids, we also find in human and animal fat, exclusive
of certain fatty acids only little studied, the following non-volatile fatty
acids, as glycerides, namely, lauric acid, C12H24O2, myristic acid, C14H28O2,
and arachidic acid, C20H40O2. Of the unsaturated fatty acids, besides
oleic acid, we probably also have in small quantities glycerides of acids
of the linolic acid series C„H2a -402 and of the linolenic acid series,
C„H2O -G-02. In this case the question can be raised whether or not
tin -c acids are not derived from the phosphatides mixed with the fats,
in the plant kingdom triglycerides of other fatty acids, such as lauric
acid, myristic acid, linoleic acid, erucic acid, etc., sometimes occur
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