1238 LECITHIN. 



(iii) When evaporated to dryness on porcelain with a few 

 drops of concentrated nitric acid, a yellow residue is obtained, 

 which turns red if treated, while still hot, with ammonia. 



Complex Nitrogenous Fats and their Derivatives. 

 Lecithin. C 44 H 90 NPO 9 . 



Occurs widely spread throughout the body. Blood (red- 

 corpuscles), bile, and serous fluids contain it in small quanti- 

 ties, while it is a conspicuous component of the brain, nerves, 

 yolk of eggs, semen, pus, white blood-corpuscles, and the 

 electrical organs of the ray. It occurs also in yeast and other 

 vegetable cells and in small amount in milk. 



When pure, it is a colourless, slightly crystalline substance, 

 which can be kneaded, but often crumbles during the process. 

 It is readily soluble in cold, exceedingly so in hot alcohol; 

 ether dissolves it freely though in less quantities, as also do 

 chloroform, fats, benzene, carbon disulphide, etc. It is often ob- 

 tained from its alcoholic solution, by evaporation, in the form 

 of oily drops. It swells up in water, and during the action, 

 as observed under the microscope, extremely curious curling 

 filamentous processes can be seen to protrude from the edge of 

 the solid. These are the so-called 'myelin forms.' 



Preparation. Usually from the yolk of egg, where it occurs in 

 union with vitellin. Its isolation is too complicated to admit of any 

 brief description. 



Lecithin is easily decomposed; not only does this decompo- 

 sition set in at 70° C, but the solutions, if merely allowed to 

 stand at the ordinary temperature, acquire an acid reaction, the 

 substance being decomposed. Acids and alkalis, of course, 

 effect this much more rapidly. If heated with baryta-water it 

 is completely decomposed, the products being choline, glycerin- 

 phosphoric acid, and barium stearate. This may be thus 

 represented: — 



Glycerinphosphoric 

 Lecithin. Stearic acid. acid. Choline. 



C 44 H 90 NPO 9 + 3H 2 = 2C 18 H 36 2 + C 3 H 9 P0 6 + C 5 H 15 N0 2 . 



When heated in an ethereal solution with dilute sulphuric 

 acid, it is merely split up into choline and distearyl-glycerin- 

 phosphoric acid. Hence it has frequently been regarded as a 

 sort of salt of choline with distearyl-glycerinphosphoric acid. 

 It appears however more probable from the most recent re- 

 searches that it is really an ethereal compound of this acid 

 with the choline. It appears also that there probably exist other 

 analogous compounds in which the radicles of oleic and palmitic 

 acids take part. 



