100 THE FATS. 



occurs in bodies which have been interred in moist soils, or have 

 been in water for a considerable time after death. 



Source of Fat in the Human Body. Human fat is de- 

 rived from the fats, the carbohydrates, and the proteids of the food. 

 In fatty meats, nuts, eggs, milk, and other foods more or less fat 

 exists as a constituent, and undoubtedly contributes to the forma- 

 tion of the fat of the body. That the fat of the food can be 

 deposited as such in the tissues was for a time denied, but it has 

 been shown by feeding starved dogs upon such fatty foods as rape- 

 seed oil, linseed oil, or mutton tallow, that they will not only take 

 on fat, but that some of the kind of fat which enters into their 

 food is deposited as such in their tissues. Food containing starch 

 and sugar is also fattening in its nature, and persons who have an 

 excess of fat are placed upon a diet containing a minimum of these 

 ingredients. Herbivorous animals the cow, for instance rely 

 entirely upon vegetable food for their support, and it is the carbo- 

 hydrates which this contains that are converted into the fat of 

 their milk and that which covers their muscles. It is doubtless 

 from the carbohydrates that most of the fat is produced. That 

 proteid food will also produce fat is shown by the amount of the 

 latter which carnivorous animals put on. 



Offices of Fat. The offices which fat subserves in the human 

 body are manifold : (1) It protects the underlying parts from in- 

 jury, as in the palrn of the hand and the sole of the foot; (2) it 

 serves as a lubricator, as in the sebaceous matter poured out upon 

 the skin, which it keeps soft and pliable ; (3) it acts as a non- 

 conductor of heat, aiding in the retention within the body of the 

 vital heat which would otherwise be lost so rapidly as to produce 

 injurious results ; (4) it serves as a reservoir when the supply of 

 food is cut off or diminished ; thus in wasting diseases the fat 

 deposited in various parts of the body is absorbed and contributes 

 to its nutrition ; (5) it is a source of energy and of heat through 

 its oxidation, the final products of which are CO 2 and H 2 O. 



Important properties of fats, besides those already men- 

 tioned, which deserve special consideration, are two that of form- 

 ing a soap and that of forming an emulsion. 



Saponification. Fats are saponifiable i. e., capable of being 

 converted into a soap. Thus when heated with a caustic alkali 

 the fat is split up as already described, into glycerin and a fatty 

 acid, and the latter unites with the base, the compound resulting 

 being a soap. Thus if palmitin and potassium hydrate are the 

 fat and alkali used, the product is a soap whose chemical composi- 

 tion is potassium palmitate. This is expressed in the following 

 formula : 



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. Potassium hydrate. Glycerin. Potassium palmitate. 



