354 PHYSIOLOGICAL CHEMISTRY 



choline. Each lecithin molecule contains two fatty acid radicals 

 which may be those of the same or different fatty acids. Thus we have 

 different lecithins depending upon the particular fatty acids radicals 

 which are present in the molecule. The formula of a typical lecithin 

 would be the following. 



CH 2 OOC.C 17 H 35 



I 

 CH OOC.Ci 7 H 35 



I 

 CH 2 O PO O.C 2 H 4 



\ 

 (CH 3 ) 3 -N 



OH HO 



This lecithin would be called distearyl-lecithin or choline-distearyl- 

 glycero-phosphoric acid. Upon decomposition the molecule splits ac- 

 cording to the following reaction: 



3H 2 -> 2Ci 8 H 36 2 + C 8 H 9 POe + C 5 H 15 NO 2 . 



Lecithin. Stearic acid. Glycero-phosphoric acid. Choline. 



The lecithins are not confined to the nervous tissues but are found in 

 nearly all animal and vegetable tissues. Lecithin is a primary con- 

 stituent of the cell. It is soluble in chloroform, ether, alcohol, benzene, 

 and carbon disulphide. The chloroform or alcohol-ether solution 

 may be precipitated by acetone. Lecithin may be caused to crystal- 

 lize in the form of small plates by cooling the alcoholic solution to a 

 low temperature. It has the power of combining with acids and bases, 

 and the hydrochloric acid combination has the power of forming a 

 double salt with platinic chloride. 



Choline, as was indicated above, is one of the decomposition 

 products of lecithin. It is trimethyl-hydroxy ethyl-ammonium hydroxide 

 and has the following formula: 



CH 2 .CH 2 (OH) 



OH 



Researches have shown that great importance is to be attached to the 

 detection of choline in the cerebro-spinal fluid and the blood in certain 

 cases of degenerative disease of the nervous system. In this connec- 

 tion tests for choline (see page 357) are of interest and value. 



Protagon, another nitrogenous phosphorized substance, is a body 

 over which there has been much discussion. Upon decomposition it 



