THE FATS 63 



different fatty acid radicals, as oleyl-lecithin, stearyl-lecithin. The 

 following formula represents distearyl-lecithin : 

 CH 2 -0-OC.(CH 2 ) 16 CH 3 



CH 0-OC.(CH 2 ) 16 CH 3 



CH 2 



HO/ \).CH 2 .CH 2 .N(CH 3 ) 3 



OH 



On warming with baryta water lecithin is broken down into fatty 

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



trimethyl-oxethyl-ammonium hydrate, N - (CH 3 ) 3 must be distin- 



OH 



guished from neurine, N -j (CH 3 ) 3 which is trimethyl- vinyl- ammonium 



[OH 



hydrate, and is 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 processes of the 

 cell. There is no doubt that it may serve, inter alia, as a source 

 of the phosphorus required for building up the complex nucleo- 

 proteins of cell nuclei. It seems to represent an intermediate stage in 

 the utilisation of neutral fats by protoplasm, and its occurrence in the 

 brain as a constituent of more complex molecules, which contain also 

 a carbohydrate nucleus (galactosides, such as cerebrin), might be inter? 

 preted as indicating some share also in the metabolism of carbohydrates. 

 Lecithin may be extracted from tissues by boiling with absolute 

 alcohol. On cooling the alcoholic extract in a freezing mixture, the 

 lecithin separates out as granules or semi- crystalline masses. When 

 dried in vacuo, it forms a waxy mass, which melts at 40 to 50 C. In 

 water it swells up to form a paste, which, under the microscope, is seen 

 to consist of oily drops or threads, the so-called myelin droplets. In 

 a large excess of water it forms an emulsion or a colloidal solution. 

 Its power of taking up water on the one hand, and its solubility in 

 alcohol and similar media on the other, give it an intermediate position 

 between the water-soluble crystalloids and the insoluble fats, and 

 enable it to play an important part both as a vehicle of nutritive 

 substances and as a constituent of the lipoid membrane, which bounds 

 and determines the osmotic relationships of all living cells. 



