HYDROCARBONACEOUS SUBSTANCES. 



65 



its original character, and its elements appear under new forms of com- 

 bination. When an oily or fatty matter is kept for some hours at a high 

 temperature in emulsion with water and an alkali, it is decomposed 

 with the assimilation of the elements of water, producing a fatty acid 

 and glycerine. The change which takes place is as follows : 

 STEARINE. WATER. STEARIC ACID. GLYCERINE. 

 C 5 7H 110 6 + 8H a O = C 54 H 108 O e + C 3 H 8 3 . 

 The acid product is stearic, palmitic, or oleic acid, according to the 

 variety of fat used ; and, when set free, it unites with the alkali, form- 

 ing a neutral stearate, palniitate, or oleate. In such a combination the 

 oil is said to be saponified, and in this form becomes more or less sol- 

 uble in watery and serous liquids. Oil may be also decomposed by 

 means of superheated steam, with the production of glycerine and free 

 fatty acid, the latter of which is then easily saponified by either a caus- 

 tic alkali or an alkaline carbonate. 



There is some doubt whether the saponification of fat takes place in 

 the animal body. Saponified fats are enumerated by some observers as 

 constant ingredients of the blood-plasma, while their presence is denied 

 by others. All agree that if present they are in extremely minute 

 proportion, by far the larger quantity of fat retaining its chemical char- 

 acters so long as it can be traced in the circulation. 



Condition of Fatty Matters in the Living Body. None of the fatty 

 substances occur naturally in an isolated form, but they are mingled in 

 varying proportions in all the ordinary animal and vegetable fats and 

 oils. The consistency of the mixture varies with the relative quantity 

 of its ingredients. The more solid fats, such as suet and tallow, consist 

 largely of stearine ; the softer 



fats, as lard, butter, and those FlG - 5 - 



of human adipose tissue, contain 

 a greater abundance of palmi- 

 tine ; while the liquid fats, like 

 fish oils, olive oil, and nut oil, 

 are composed mainly of oleine. 

 As a general rule, in the warm- 

 blooded animals, these mixtures 

 are fluid, or nearly so; for, 

 although both stearine and pal- 

 niitine, when pure, are solid at 

 the temperature of the body, 

 they are held in solution during 

 life by the oleine with which 

 they are associated. 



As the body cools after death, 

 the stearine and palmitine some- 

 times separate in a crystalline 

 form, since the oleine can no longer hold the whole of them in solution. 

 (Fig. 5.) 



E 



OLKAGINOUS SUBSTANCES OF HUMAN FAT. Stearine 

 and Palmitine crystallized ; Oleine fluid. 



