CH. VI.] CEREBROSIDES. 165 



The nature of the fatty acids is not yet determined. It 

 is possible that they differ with different specimens. They 

 seem to be unsaturated acids of the C 16 or Qg series. 



Choline or trimethyl-/3-hydroxy-ethyl-ammoniurn hy- 

 droxide is of considerable interest, since it is closely 

 related chemically to muscarine, a very poisonous base 

 obtained from certain fungi. In fact, pseudo-muscarine, 

 which somewhat resembles muscarine, has recently been 

 shewn to be the nitrous acid ester of choline. Our present 

 knowledge concerning choline and related substances will 

 be found in Barger's " The Simpler Natural Bases " 

 (Longmans, Green and Co., 1914). 



Kephalin differs from lecithin in being insoluble in 

 alcohol. Chemically, it differs in that the base united to 

 the phosphoric acid radicle is not choline, but oxyethyla- 

 mine, NH 2 .CH 2 .CH 2 OH. 



The preparation of lecithin is described by Maclean in 

 his monograph. 



The Galactolipins or Cerebrosides. 



These compounds do not contain phosphorus. Their 

 name is derived from the fact that they yield galactose on 

 hydrolysis, and are particularly abundant in the brain, 

 though they are found elsewhere in the body. Two mem- 

 bers of this class have been described, Phrenosin and 

 Kerasin. Their constitution can be represented as follows : 



Phrenosin 



Phrenosinic acid, C^ Hgo O 3 , an a-hydroxy 



fatty acid. 

 Galactose. 

 Sphingosine, C^Hgg NO 2 , a base. 



(Lignoceric acid, 

 Kerasin \ Galactose. 



{Sphingosine. 



