FATS AND LIPOIDS 57 



Lecithins differ from fats in containing nitrogen and phosphorus. 

 Two of the hydroxyl groups of the glycerine radical are combined 

 with fatty acids, the remaining one being linked to phosphoric acid in 

 conjunction with an ammonium base, cholin. The structural formula 

 of lecithin is, therefore 



fCH. 2 OC 17 H 35 CO 



} Stearic acid 



101 



1 



Glycerine { CHOC 17 H 35 CO 



/OH 



OK, P 



0-N=(CH 3 ) 3 



Phosphoric \ 



Acid CH 2 CILjOH 



Cholin 



Pure lecithin has a waxy appearance; it is soluble in alcohol and 

 chloroform, less soluble in ether. When mixed with water and viewed 

 under the microscope, it gives out peculiar processes which remind 

 one of the pseudopodia of an amoeba. There are various lecithins, 

 which differ according to the fatty acid combined with the molecule. 



Like the fats, the lecithins can be hydrolyzed. When saponified 

 they yield fatty acid, glycerophosphoric acid, and cholin : 



C 41 H 90 NP0 9 + 311,0 - 2(C 18 H 36 2 ) + C 3 H 9 P0 6 + C 5 H 15 N0 2 



Lecithin Stearic Glycero- Cholin 



acid phosphoric 



acid 



Lecithin is split up by cell ferments, and phosphatides may be 

 rebuilt in the laboratory of the cell. 



Cholin trimethyloxyethylammonium hydrate 



OH 



is closely related to the alkaloid muscarin. Methylamines are among 

 the products of bacterial decomposition of lecithins. Neurln, which 

 contains one molecule of water less than cholin, is a very poisonous 

 product, and may be the cause of " ptomain" poisoning. Cholin pro- 

 duces a marked fall of blood-pressure when injected into the blood. It 

 is said that cholin occurs in the blood and spinal fluid when nervous tissue 

 is undergoing degeneration, and can be isolated as yellow octahedral 

 crystals by adding platinum chloride to an alcoholic extract of the 

 fluids. These crystals differ from similar ones obtained by the inter- 

 action of potassium chloride (also present in blood) with platinum 

 chloride, in that they become changed when treated with a strong solu- 

 tion of potassium iodide to dark brown plates. The claim that cholin 

 can be demonstrated in these fluids has not met with general acceptance. 



II. THE GALACTOSIDES. These bodies occur largely in the body 

 known as protagon, obtained from the brain tissue. They are so 



