122 NEUTRAL FATS. 



Stearin (Tri-stearin). C 3 H 5 (C 17 H 35 .CO.O) 3 . 



This is the hardest and least fusible of the ordinary fats of the 

 body ; is also the least soluble, and hence is the first to crystallise out 

 from solutions of the mixed fats. Readily soluble in ether and in 

 boiling alcohol. It crystallises usually in square tables or glittering 

 plates. It presents peculiarities in its fusing points, melting first at 55 

 then solidifying as the temperature is further raised and melting finally 

 and permanently at 71. 



Preparation. From mutton suet, its separation from palmitin and 

 olein being effected by repeated crystallisation from ether, stearin being 

 the least soluble. It is however very difficult to obtain it pure by this 

 process. 



Olein (Tri-olein). C 3 H 5 (C 17 H 3 3. CO. O),. 



Is obtained with difficulty in the pure state, and is then fluid at 

 ordinary temperatures. It is somewhat soluble in alcohol, very soluble 

 in ether. It readily undergoes oxidation when exposed to the air, and 

 is converted by mere traces of nitrous acid into a solid isomeric fat 

 tri-elaidin. Olein is saponified with much greater difficulty than are 

 palmitin and stearin. 



Preparation. From olive oil, either by cooling to C. and pressing 

 out the olein that remains fluid, or by dissolving in hot alcohol and 

 cooling, when the olein remains in solution while the other fats crystal- 

 lise out. 



The fats which occur in the animal body are mixtures of the 

 above three substances in varying proportions. The normal fat of 

 each animal or class of animals is however characterised by the 

 constant preponderance of one of the three; thus in the fat of man 

 and carnivora palmitin is in excess over the other two. In the fat of 

 herbivora stearin predominates and in that of fishes olein. Butter 

 contains in addition to the above, several fats formed by the union of 

 glycerin with the radicles of the lower acids of the acetic series. 



There is no doubt that a large part of the fat laid on in the animal 

 body during fattening cannot be accounted for by the fat given in the 

 food and must hence arise from a conversion of proteids or carbo- 

 hydrates into fat. (See 506, 507.) The question as to how the 

 storage arises from these food-stuffs is one which has given rise to a 

 prolonged controversy. On the one hand Voit and his followers urged 

 that although carbohydrates do lead to a rapid storing of fat in the 

 body, they do so not directly by being themselves converted into fat, 



