132 PHYSIOLOGICAL CHEMISTRY. 



CH 2 -OR 



CH -OR' 

 CH 9 -OR". 



Second, by the replacement of the H's of the carboxyl groups of 

 the three fatty acid molecules by the glycerol radical, thus yielding 

 the following type of formula in which R represents the glycerol 

 radical, 



OOCH 31 C 15 



/ 



R-OOCH 31 C 15 

 \ 

 OOCH 31 C 15 . 



Of these two processes the second is the more logical procedure 

 from the standpoint of the ionic theory. The three fatty acid 

 radicals entering into the structure of a neutral fat may be the 

 radicals of the same fatty acid or they may consist of the radicals 

 of three different fatty acids. 



By hydrolysis of a neutral fat, i. e., by the addition to the mole- 

 cule of those elements which are eliminated in the formation of 

 the fat from glycerol and fatty acid, it may be resolved into its 

 component parts, i. e., glycerol and fatty acid. In the case of tri- 

 palmitin the following would be the reaction : 



Tri-palmitin. Glycerol. Palmitic acid. 



This process is called saponification and may be produced by boil- 

 ing with alkalis; by the action of steam under pressure; by long- 

 continued contact with air and light; by the action of certain bac- 

 teria and by fat-splitting ezymes or lipases, c. g., pancreatic lipase 

 (see page 143). The cells forming the walls of the intestines evi- 

 dently possess the peculiar property of synthesizing the glycerol and 

 fatty acid thus formed so that after absorption these bodies appear 

 in the blood not in their individual form but as neutral fats. This 

 synthesis is similar to that enacted in the absorption of protein 

 material where the peptones are synthesized into albumin in the 

 act of absorption. 



The principal animal fats with which we have to deal are stearin, 

 palmitin, olein and butyrin. Such less important forms as laurin 



