THE FATS. 19 



Under the influence of superheated steam, mineral acids, and in the 

 body by means of certain ferments (for instance, the fat-splitting 

 ferment of the pancreatic juice), a fat combines with water and splits 

 into glycerin and the fatty acid. The following equation represents 

 what occurs in a fat, taking tripalmitin as an example : 



C 3 H 5 (O.C 1 .,H 31 CO) 3 H-3H 2 = C 3 H 5 (OH) 3 +3C 15 H 31 CO.OH 



(palmitin a fat) (glycerin) (palmitic acid a 



fatty acid) 



Saponification. In the process of saponification much the same sort 

 of reaction occurs, the final products being glycerin and a compound of 

 the base with the fatty acid, which is called a soap. 



Suppose, for instance, that potassium hydrate is used, we get 



C 3 H 5 (O.C 15 H 31 CO) 3 +3KHO - C 3 H 5 (OH) 3 +3C 15 H 31 CO.OK 



(palmitin a fat) (glycerin) (potassium palm itate 



a soap) 



To separate the neutral fats from one another, they have always to be 

 saponified; this can be accomplished by potassium hydrate, or still 

 better by sodium alcoholate (Kossel, Obermuller, and Kriiger). 1 On 

 evaporation of the alcohol, the soaps are dissolved in water, and pre- 

 cipitated by sugar of lead ; the lead compound of oleic acid is soluble in 

 ether ; the remaining soaps are treated with soda on the water bath, 

 dried, dissolved in alcohol, and separated by fractional precipitation with 

 barium acetate or barium chloride. 



In the decomposition of fat, propionic, acetic, and formic acids may 

 be found, which are absent from the fat in the fresh condition. This 

 occurs when the fat becomes rancid, and is also produced by putre- 

 factive organisms in the alimentary canal. The process is one of 

 oxidation, and the way in which low r er terms of the series are produced 

 may be illustrated by the following equations : 



C 3 H o q a +0 3 = C 2 H 4 2 +C0 2 +H 2 0. 



(propionic acid) (acetic acid) 



C 2 HA+0 3 =:CH 2 2 +C0 2 +H 2 0. 



(acetic acid) (formic acid) 



2CH 2 2 +0 2 :=2C0 2 +2H 2 0. 



(formic acid) 



Emulsification. Another change that fats undergo in the body is very 

 different from saponification. It is a physical rather than a chemical 

 change ; the fat is broken up into very small globules, such as is seen in 

 the natural emulsion milk. 



The fats of milk resemble in a general way those of adipose tissue, 

 but there is a considerable admixture of glycerides lower in the series 

 (see "Milk"). 



The fats of marrow are also like those of adipose tissue. As will be 

 noticed in the table on p. 17, bone marrow is the tissue which is richest 

 of all in fat. 



Eylert 2 described a new fatty acid in the marrow of ox-bone which he 

 called medullic acid, but this was shown by Mohr 3 to be only stearic acid. 



1 Numerous papers in vols. xiv., xv., and xvi. of Ztschr. f. pliysiol. Chem., Strassburg. 



2 Frtljschr.f. prdkt. PharmakoL, Bd. ix. S. 330. 



3 Ztschr. /. physiol. Chcm., Strassburg, 1890, Bd. xiv. S. 390. 



