54 PHYSIOLOGY 



of the diglycerid.es and the triglycerides mixed esters, in which the fatty acid 

 radical varies, are possible : 



(6) (7) 



CH 2 OC.CH 3 CH 2 OH 



CHOH CH OC.CH 3 



CH 2 OC.CH 2 :CH 3 CH 2 OC.CH 2 CH 3 



(8) 

 CH 2 OC.CH 3 



CH OC.CH 2 .CH 3 

 CH 2 OC.CH 2 .CH 2 .CH 3 



The glyceryl esters which compose the fatty material of living matter 

 whether animal or plant are mainly triglycerides, the monoglycerides and 

 diglycerides being seldom found in nature. The natural fat is usually 

 found to consist of a mixture of triglycerides ; these triglycerides, instead 

 of being mixed esters as in formula (8), are generally simple esters as in 

 formula (5). The differences in the composition of the natural fats depend 

 therefore on the variety of the fatty acid radical combined with the glycerol. 



The fatty acids which enter into the composition of the triglycerides 

 belong to two main homologous series : 



A. The saturated fatty acids, namely : 



Formic acid, H.COOH 

 Acetic acid, CH 3 .COOH 

 Propionic acid, CH 3 .CH 2 .COOH 

 Butyric acid, CH 3 .CH 2 ,CH 2 .COOH 

 Valerianic acid, CH 3 .(CH 2 ) 3 .COOH 

 Caproic acid, CH 3 .(CH 2 ) 4 .COOH 

 Caprylic acid, CH 3 .(CH 2 ) 6 .COOH 

 Capric acid, CH 3 (CH 2 ) 8 .COOH 

 Laurie acid, CH 3 (CH 2 ) 10 .COOH 

 Myristic acid, CH 3 (CH 2 ) 12 .COOH 

 Palmitic acid, CH 3 (CH 2 ) 14 .COOH 

 Stearic acid, CH 3 (CH 2 ) 16 .COOH 

 Arachidic acid, CH 3 (CH 2 )18.COOH 

 Behenic acid, CH 3 (CH 2 ) 20 .COOH 

 Lignoceric acid, CH 3 (CH 2 ) 22 .COOH 



B. The unsaturated fatty acids, namely : 



(1) Acrylic series, e.g. oleic acid (C n H 2n _ 2 2 ) 



(2) Linoleic series, e.g. linoleic acid (C n H 2n _ 4 2 ) 



(3) Linolenic series, e.g. linolenic acid (C n H 2n _ 6 2 ) 



