I 



THE FATS 57 



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 PFOSPHATIDES 



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. Thudi- 

 chum, who isolated various compounds of this nature from brain, suggested 

 the term phosphatides 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 com- 

 pound 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 com- 

 pounds, 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 different 

 fatty acid radicals, as oleyl-lecithin, steaTyl-lecithin. The following formula 

 represents distearyl-lecithin : 



CH 2 OC.(CH 2 ) 16 CH 3 



I 

 CH OC.(CH 2 ) 16 CH 3 



I 

 CH 2 -0 V .0 



O.CH 2 .CH 2 .N(CH 3 ) 3 



I 

 OH 



On warming with baryta water lecithin is broken down into fatty acid, 

 glycerophosphoric acid, and choline. The. latter base, which is trimethyl- 



(C 2 H 4 OH 

 oxethyl-ammonium hydrate, N \ (CH 3 ) 3 must be distinguished from 



(OH 



(C 2 H 3 

 neurine, N UCH 3 ) 3 which is trimethyl- vinyl-ammonium hydrate, and is 



(OH 



much more poisonous than choline. Choline forms a salt with hydrochloric 

 acid which, with platinum chloride, yields a double salt of characteristic 

 crystalline form, insoluble in absolute alcohol. The universal distribution of 

 lecithin seems to indicate that it plays an important part in the metabolic 



