134 LECITHIN. 



corpuscles contain about -75 p.c. of lecithin, 1 hence 100 grm. red cor- 

 puscles might therefore hold in loose combination rather more than 

 22 cc. of carbonic anhydride. It is of course possible that the lecithin 

 does not exist in a free state in the unaltered corpuscles, and is there- 

 fore in living blood incapable of playing the part above ascribed to it. 

 Still the possibility that it may do so is distinctly worth some con- 

 sideration, bearing in mind how scanty is our knowledge of the real 

 conditions which determine the fixation of carbonic anhydride by the 

 blood. 



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, benzol, carbon, disulphide, &c. It is often obtained 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.' 2 



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

 union with vitellin. Its isolation is complicated, and the reader 

 is referred to Hoppe-Seyler. 3 



Lecithin is easily decomposed ; not only does this decomposi- 

 tion set in at 70 C., but the solutions, if merely allowed to stand 

 at the ordinary temperature, acquire an acid reaction, the sub- 

 stance being decomposed. Acids and alkalis, of course, effect this 

 much more rapidly. If heated with baryta water it is completely 

 decomposed, the products being cholin, glycerinphosphoric acid, 

 and barium stearate. This may be thus represented : 



Glycerinphosphoric 

 Lecithin. Stearic acid. acid. Cholin. 



C 44 H 90 NP0 9 + 3H 2 = 2C 18 H 36 2 + C 3 H 9 P0 6 + C 5 H 15 NO., 



When treated in an ethereal solution with dilute sulphuric acid, 

 it is merely split up into cholin and distearyl-glycerinphosphoric 

 acid. Hence it has frequently been regarded as a sort of salt of 

 cholin with distearyl-glycerinphosphoric acid. It appears how- 

 ever more probable from the most recent researches that it is 

 really an ethereal compound of this acid with the cholin. 4 It 

 appears also that there probably exist other analogous compounds 

 in which the radicles of oleic and palmitic acids take part. 



1 Hohlbeck, Ref. in Hoppe-Sevler, Physiol. Chem. 1877, S. 402. 



2 See M'Kendrick, General Physiology, 1888, p. 19. 



3 Hdbch. d. phys.-path. chem. AnaL, 1883, S. 166. 



4 Hundeshagen, Jn. f. prakt. Chem. Bd. xxvin. (1883), S. 219. Gilson, Zt. f. 

 physiol. Chem. Bd. xn. (1888), S. 585. 



