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, CsH5.03.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, Ci2H2402, myristic acid, Ci4H2g02, 

 and arachidic acid, C2oH4o02- Of the unsaturated fatty acids, besides 

 oleic acid, we probably also have in small quantities glycerides of acids 

 of the linolic acid series C B H 2o -402 and of the linolenic acid series, 

 C B H2n-6-O2. In this case the question can be raised whether or not 

 these 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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