

THE TISSUES 29 



The fats are esters usually of the triatomic alcohol glycerin 



(OH 

 C 3 HJ OH 



(OH 



by the replacement of the hydrogen of the hydroxyl molecules 

 by the radicles of the fatty acids. 



The most abundant fatty acids of the body are : 



Palmitic Acid, C 16 H 3] 0,OH 

 Stearic Acid, C 18 H 35 0,OH 

 Oleic Acid, C 18 H 33 0,OH 



and from these the three fats 



Palmitin, C 3 H 5 (0,C 16 H 31 0) 3 = C^O,, 

 Stearin, C 3 H 5 (0, C 18 H 35 0) 3 = C 57 H 110 6 

 Olein, C 3 H 5 (0,C 18 H 33 0) 3 = C 57 H 104 6 

 are produced. 



It will be observed that the molecules of these fats are 

 very rich in carbon and hydrogen, and very poor in oxygen 

 i.e. they contain a large amount of material capable of being 

 oxidised, and thus capable of affording energy in the process 

 of combustion. 



The fats resemble one another in being insoluble in water, 

 but soluble in ether and in hot alcohol. As the alcohol cools, 

 they separate out as crystals. They differ from one another in 

 their melting point, palmitin melting at the highest and olein 

 at the lowest temperature. Fat which is rich in palmitin 

 and stearin, as ox fat, is thus hard and solid at the ordinary 

 temperature of the air, while fats rich in olein, as dogs' fats, are 

 semi-fluid at the same temperature. The olein acts as a solvent 

 for the fats of a higher melting point. (For tests, see Chemical 

 Physiology.) 



The functions of adipose tissue are twofold : 



1st. Mechanical. The mass of adipose tissue under the skin is 

 of importance in protecting the deeper structures from injury. 

 It is a cushion on which external violence expends itself. 

 Further, this layer of subcutaneous fat prevents the loss of heat 

 from the body, being, in fact, an extra garment. 



2nd. Chemical. Fat, on account of its great quantity of 

 unoxidised carbon and hydrogen, is the great storehouse of 

 energy in the body (p. 393). 



