Abstract
At the meeting of the American Society of Biological Chemists in December, 1919, the matter of a classification of the fats and related substances was brought before the members for discussion. It was decided that the available knowledge on the subject was insufficient to justify a classification at that time. While admitting the truth of the conclusion it has seemed to me since, that something might be gained by an attempt at classification,—in clarifying our ideas and in bringing the newer developments in the field into connection with the old—even though the scheme might later have to be radically changed or even abandoned. It is becoming more and more apparent, for example, that the fats and the substances ordinarily grouped under the name of lipoids are so intimately related both chemically and in metabolism—all being directly connected with the metabolism of the fatty acids—that they should be considered together, and when so considered they form a group which is believed to be as distinct and well defined as that of the carbohydrates and proteins. The following is an outline of proposed classification:
THE LIPOIDS.
The higher fatty acids, their naturally occurring compounds and certain substances found naturally in chemical association with them.
The group is characterized in general by insolubility in water and solubility in‘ fat solvents‘-ether, chloroform, benzol, etc.
Simple Lipoids.
Esters of the fatty acids with various alcohols.
Fats.-Esters of the fatty acids with glycerol. (fats which are liquid at ordinary temperatures are called oils.)
Waxes.-Esters of the fatty acids with alcohols other than glycerol. Beeswax, lanolin, cholesterol oleate.
Compound Lipoids.
Compounds of the fatty acids with alcohols but containing other groups in addition to the alcohol.
Phospholipoids.-Substituted Fats containing phosphoric acid and nitrogen-lecithin, cephalin, etc.
GlycoZipoids.-Compounds of the Fatty acids with a carbohydrate and nitrogen but containing no phosphoric acid.-Cerebron, etc.
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