30 PHYSIOLOGY. 



draw out from this source a supply for nutrition. This fatty tissue 

 is found between the muscles,, bones, vessels, etc., and, by its accumu- 

 lation under the skin, gives to the surface of the body its full and 

 regular outline. 



By reason of its bad conducting power, it helps to keep the 

 various structures of the body warm by a coating of it lying under 

 the skin. This fact is best illustrated in warm-blooded aquatic ani- 

 mals, such as the seal, porpoise, or whale. 



The normal fats found in the body and used for food are divided 

 into three compounds: stearin, palmitin, and olein. 



Stearin is the most solid of the three. It is typically illustrated 

 in mutton suet, and is the element which makes this fat so hard and 

 firm, and characterizes it at once. Its melting-point is 145 F., so 

 that at ordinary temperatures it is solid. 



Falmitin occupies a position midway between stearin and olein 

 as regards consistency. It is the principal constituent of most animal 

 fats, and occurs largely in vegetable fats also. 



Olein is always found in a fluid state unless the temperature be 

 very low. When the olein ingredients predominate in a body it is 

 then in a liquid state, as in the case of the oils. Olein is found in 

 both animal and vegetable fats, but the vegetable fats are richer in it 

 than the animal. The oils used in food olive-oil, oil of sweet 

 almonds, etc. are derived from the vegetable kingdom. 



Human fat contains about 75 per cent, of olein plus a small 

 quantity of fatty acids in a free state. All are soluble in hot alcohol, 

 ether, and chloroform, but insoluble in water. 



Saponification. 



When fat is boiled with alcoholic soda or potash, the particles of 

 fat are broken up into a small quantity of glycerin and a large quan- 

 tity of fatty acid. The fatty acid unites with the soda or potash, 

 forming, as a result, soap. This process of soap-forming is known as 

 saponification. 



Emulsification. 



If oil and water are well shaken together the fatty particles do 

 not form a part of the water, but are held in suspension and come 

 to the surface in the form of small globules. A mixture of an oil, 

 a soap, and water is spoken of as an emulsion. No emulsion is per- 

 manent, for even in milk, the most perfect of emulsions, the fatty 

 particles in the form of cream rise to the surface in a few hours. 



