CHEMIC COMPOSITION OF THE HUMAN BODY. n 



transformation of the carbohydrates. In the animal body the fats are 

 found largely in the subcutaneous tissue, in the marrow of bones, in and 

 around various internal organs and in milk. In these situations fat is 

 contained in small, round or polygon-shaped vesicles, which are united by 

 areolar tissue and surrounded by blood-vessels. At the temperature of the 

 body the fat is liquid, but after death it soon solidifies from the loss of heat. 



The fats are compounds consisting of carbon, hydrogen, and oxygen. 

 The percentage composition of fat (stearin) is as follows: Carbon, 76.86; 

 hydrogen, 12.36; oxygen, 10.78. The fat found in animals is a mixture, in 

 varying proportions in different animals, of three neutral fats stearin, 

 palmitin, and olein. Each fat is a derivative of glycerin and the particular 

 acid indicated by its name e.g., stearic acid, in the case of stearin, etc. 

 The reaction which takes place in the combination of glycerin and the 

 acid is expressed in the following equation: 



C 3 H 5 (HO) 3 + 3C 18 H 3 60 2 = C 3 H 5 (C 18 H 35 O 2 ) 3 + 3 H 2 O. 

 Glycerin. Stearic Acid. Stearin. Water. 



Hence, strictly speaking, the fats are compound ethers, in which the 

 hydrogen of the organic acid is replaced by the trivalent radicle, tritenyl, 

 C 3 H 5 . 



Stearin, C 3 H 5 (C 18 H 35 O 2 ) 3 , is the chief constituent of the more solid 

 fats. It is solid at ordinary temperatures, melting at 55 C., then solidify- 

 ing again as the temperature rises, until at 71 C. it melts permanently. It 

 crystallizes in square tables. 



Palmitin, C 3 H 5 (C 16 H 31 O 2 ) 3 is a semifluid fat, solid at 45 C. and 

 melting at 62 C. It crystallizes in fine needles, and is soluble in ether. 



Olein, C 3 H 5 (C 18 H 33 O 2 ) 3 , is a colorless, transparent fluid, liquid at 

 ordinary temperatures, only solidifying at o C. It possesses marked 

 solvent powers, and holds stearin and palmitin in solution at the temperature 

 of the body. 



Saponification. When subjected to the action of superheated steam, 

 a neutral fat is saponified i.e., decomposed into glycerin and the particular 

 acid indicated by the name of the fat used: e.g., stearic, palmitic, or oleic. 

 The reaction is expressed as follows: 



C 3 H 5 (C 18 H 33 2 ) 3 +3H 2 = C 3 

 Olein. Water. Glycerin. Oleic Acid. 



The fat acids thus obtained are characterized by certain chemic fea- 

 tures, as follows: 



Stearic acid is a firm, white solid, fusible at 69 C. It is soluble in 

 ether and alcohol, but not in water. 



Palmitic acid occurs in the form of white, glistening scales or needles, 

 melting at 62 C. 



Oleic acid is a clear, colorless liquid, tasteless and odorless when pure. 

 It crystallizes in white needles at o C. 



If this saponification takes place in the presence of an alkali e.g., 

 potassium hydroxid or sodium hydroxid the acid produced combines 

 at once with the alkali to form a salt known as a soap, while the glycerin 

 remains in solution. The reaction is as follows: 



3 KHO + 3 C 18 H 34 2 = 3 KC 18 H 33 2 + 3 

 Potassium. Oleic Acid. Potassium Oleate. W; 



ater. 



