62 PHYSIOLOGY 



tion of the sebaceous glands in man and the higher animals, which 

 furnishes the natural oil of hair, wool, and feathers, consists, with 

 small traces of glycerides, of cholesterol esters. Lanoline, which is 

 purified wool fat, consists almost entirely of cholesteryl stearate and 

 palmitate. These cholesterol fats are attacked with extreme difficulty 

 by ferments or micro-organisms. It is probably on this account that 

 they are manufactured in the body for protective purposes. So 

 far as we know, when once formed, they are incapable of further 

 transformation in the body. They are not appreciably altered by 

 the digestive ferments of the alimentary canal, and the cholesterol is 

 said to pass through the latter unaltered.* Cholesterol is also found 

 in combination with fatty acids in every living cell. Whenever 

 protoplasmic structures are extracted with boiling ether, a certain 

 amount of cholesterol is present with the fats which are so extracted. 

 In view of the great stability of this substance when exposed to the 

 ordinary mechanisms of chemical change in the body, it seems 

 probable that the part played by cholesterol is that of a framework 

 or skeleton, in the interstices of which the more labile constituents 

 of the protoplasm can undergo the constant cycle of changes which 

 make up the phenomena of life. 



PHOSPHOLIPINES OR PHOSPHATIDES 



The fats form the chief constituent of the deposited and reserve 

 fat throughout the animal kingdom and are also contained in the 

 protoplasm of the living cell. The chief fatty constituents of 

 protoplasm differ from the above fats in the following particulars : 

 they contain phosphoric acid and an amine. On this account they 

 have been called phosphorised fats Thudichum, who isolated various 

 compounds of this nature from brain, suggested the term phospha- 

 tides as a general name for them. The term lipoid has also been 

 used, but it includes all the substances composing a cell which 

 are soluble in ether, e.g. cholesterol, cetyl alcohol, and the fats. 

 Leathes has suggested the term phospholipine for those compounds, 

 for it denotes that the compound is partly fat (lip), that it contains 

 phosphorus, as well as a nitrogenous basic radical (ine). The 

 phospholipines comprise the substances lecithin, cephalin, cuorine, 

 sphingomyeline. In brain and other tissues similar compounds, which 

 contain no phosphorus, occur, and in the place of glycerol we may 

 find galactose. Leathes has proposed calling these compounds lipines 

 and galactolipines. 



Lecithin, the chief phospholipine, is an ester compounded of two 

 fatty acid radicals phosphoric acid, glycerol, and the amine, choline. 

 The various lecithins may be distinguished, according as they contain 



* According to Gardner, cholesterol may be absorbed from the intestine. 



