NERVOUS TISSUE. 249 



lar fatty acid radicals which are present in the molecule. The for- 

 mula of a typical lecithin would be the following : 



CH 2 0-C 17 H 35 CO 

 -CH 35 CO 



v><j~L 2 \_y ^^17 



CHO -C 17 



2 O-PO-0-C 2 H 4 

 \ 



OH HO 



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

 glycero-phosphoric acid. Upon decomposition the molecule splits 

 according to the following reaction : 



C 44 H 90 NP0 9 +3H 2 0=2(C 18 H., 2 )+C,H 9 P0 6 +C 5 H 15 N0 2 . 



Lecithin. Stearic acid. Glycero-phosphoric Choline 



acid. 



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

 in nearly all animal and vegetable tissues. Lecithin is a primary 

 constituent 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 

 crystallize in the form of small plates by cooling the alcoholic solu- 

 tion 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-oxy ethyl-ammonium hydroxide 

 and has the following formula : 



CH 2 -CH 2 (OH) 



\ 

 OH 



Recent 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 connection tests for choline (see p. 252) are of interest and 

 value. 



Protagon, another nitrogenous phosphorized substance is a body 



