CHAP. VII.] THE CONNECTIVE TISSUES. 261 



two methods are employed in the commercial separation of fats from 

 certain animal products. 



Chemical ^ke ^ s wn ^ cn are contained within the fat cells of 



constitution man and the higher animals are mixtures of the so- 

 of the neutral called neutral fats termed stearin, palmitin, and olein, 

 of which the two former are solid bodies at ordinary 

 temperatures, and are, at the temperature of the body, held in solution 

 by the third. 



The neutral fats are the most abundant of the non-nitrogenous 

 organic proximate principles of the body and contain the elements 

 carbon, hydrogen and oxygen. These fats consist of ethers derived 

 from the triatomic alcohol glycerin C 3 H 6 (OH) 3 . 



We may form a true conception of the relations of a neutral fat 

 to glycerin by examining the relations of an artificial neutral 

 fat, or glycerin ether, triacetin, to glycerin, and these wilLbe easily 

 illustrated by the aid of the two graphic formulae here appended. The 

 three carbon atoms of glycerin are seen to be linked to the atoms of 

 three OH groups ; the H in any one or in all of these may be re- 

 placed by the oxidized radical of a fatty acid, e.g. by acetyl C 2 H 3 O ; 

 when all three of the hydrogens are thus replaced the neutral fat 

 called triacetin is formed, thus : 



H H H 



H H H | 



| | | H-C C C-H 



H C C C H | 



III 000 



O O O I 



I i i o-c o=c c=o 



H H H ill 



H C~H H C~H H-C-H 



Glycerin. H H H 



Triacetyl-glycerin ether, or triacetin. 



The neutral fats of adipose tissue are constituted on the same 

 type as triacetin, except that, instead of acetyl, other acid radicals 

 take the place of the H in the OH groups. 



In the two more solid fats, stearin and palmitin, the oxidized 

 radicals of stearic and palmitic acids occupy the position of the acetyl of 

 triacetin; in the more liquid constituent of the fats, viz. olein, the 

 oxygenized radicals of oleic acid occupy the same position. 



Sometimes, instead of the terms stearin, palmitin, and olein, the 

 more precise designations of tristearin, tripalmitin and triolein are 

 employed. 



The formulae of the three principal fats are appended and their 

 relationship shewn to glycerin and the acids. 



Palmitin C 3 H 5 (OC 16 H 31 0) 3 Palmitic acid C 16 H 31 0,OH 



Glycerin C 3 H 5 (OH) 3 Stearin C 8 H 5 (OC 18 Ha50) 8 Stearic acid dgHwOjOH 



Olein C 3 H 5 (OC 18 H 33 0) 3 Oleic acid C 18 H330,OH 



General The neutral fats are all solid at a certain tempera- 



properties of ture, above which they are fluid ; this temperature is 

 the neutral called their melting-point. They are all soluble in 

 boiling alcohol, in ether, benzol, carbon disulphide 



