134 LECITHIN. 



COMPLEX NITROGENOUS FATS AND THEIR DERIVATIVES'. 

 Lecithin. C^ H^ NP0 9 . 



Occurs widely spread throughout the body. Blood (red-corpuscles) 2 , 

 bile, and serous fluids contain it in small quantities, while it is a con- 

 spicuous component of the brain, nerves, yolk of egg, semen, pus, white 

 blood-corpuscles, and the electrical organs of the ray. It occurs also in 

 yeast 3 and other vegetable cells, and in small amount in milk 4 . 



The presence of lecithin in the red blood-corpuscles may prove to be of no 

 inconsiderable importance in connection with the possible fixation by them of 

 carbonic anhydride 5 . Setschenow has shown that lecithin acts like a base towards 

 carbonic anhydride, each molecule of the substance being able to combine loosely 

 with approximately one molecule of the anhydride ('092 gr. lecithin fixes 2'7 cc. of 

 C0 2 ) at a partial pressure of 56 mm. 6 . Further, it is stated that red blood-corpuscles 

 contain about '75 p.c. of lecithin 7 , hence 100 grm. red corpuscles 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 therefore in living blood incapable of playing the part above ascribed to it. 

 Still the possibility that it may do so is distinctly worth some consideration, 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' 8 . 



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 9 . 



Lecithin is easily decomposed ; not only does this decomposition set in 



1 For a fuller account of the several substances comprised in this group see 

 Gamgee, Physiol. Chemistry, Vol. i. 1880, p. 425 et seq. 



2 Cf. Hoppe-Seyler, Physiol. Chem. 1877, S. 402. 



3 Hoppe-Seyler, Zt. f. physiol. Chem. Bd. n. (1878), S. 427; Bd. in. S. 374. 



4 Tolmatscheff, also Schmidt-Miilheim, loc. cit. (sub. Cholesterin). 



5 Al. Schmidt, Ber. d. sdchs. Gesell. d. Wiss. Bd. xix. (1867), S. 30. Zuntz, 

 Centralb. f. d. med. Wiss. 1867, S. 529. Setschenow, Ibid. 1877, S. 625; 1879, S. 

 369 ; Pfliiger's Arch. Bd. vm. 1874, S. 20. Fredericq, Compt. Eend'.^. LXXXIV. 1877, 

 p. 661. Mathieu et Urbain, Ibid. p. 1305. 



6 Setschenow, Hem. de VAcad. Imp. St Petersb. T. xxvi. (1879), %. 13, p. 19. 



7 Hohlbeck, Kef. in Hoppe-Seyler, Physiol. Chem. 1877, S. 402. 4 



8 See M'Kendrick, General Physiology, 1888, p. 19. jf 



9 Hdbch. d. vhvs.-vath. chem. Anal.. 1883. S. 166. 



