22 CHEMICAL CONSTITUENTS OF BODY AND FOOD. 



oxide (C 2 H 4 0), trimethylamine N(CH 3 ) 3 , and water. It was at one time 

 thought to be identical with the base neurine, which Liebreich separated 

 from nervous tissues, and the two are closely related; empirically 

 choline (C 6 H 15 lSr0 2 ) is neurine (C 5 H 13 lSrO), plus water. In constitution 

 neurine is trimethylvinylammonium hydroxide. 



Glycero-plwsplwric acid is glycerin, in which one of the hydroxyl 

 hydrogens is replaced by phosphoric acid, less hydroxyl ; thus 



HO OH 



C 3 H 5 HO (H 2 P0 3 )HO C 3 H 5 OH 



HO P0 3 H 2 



(glycerin) (phosphoric acid) (glycero-phosphoric acid) 



If the other two hydroxyl hydrogens are replaced by the radicle of 

 stearic acid, we obtain 



OH 9 .0 C r H 35 CO 



CH".O c 17 H 35 co 



which is distearyl-glycero-phosphoric acid. This is then united to 

 choline (less hydroxyl), and we obtain lecithin, or distearyl lecithin, as 

 it should be more properly termed ; for other lecithins exist in which 

 palmityl, oleyl, or other fatty acid radicles take the place of stearyl. 



The exact manner of the union of the acid with choline is a matter of 

 controversy, for up to the present lecithin has not been prepared synthetically. 

 Hundeshagen l prepared artificially a choline salt of distearyl-glycero-phosphoric 

 acid, which is isorneric with lecithin, but which possesses none of its 

 characteristic properties. 



The constitution of lecithin is not therefore that of a salt in which choline 

 plays a part of the base, as Diaconow 2 first suggested, but more probably it 

 is an ether-like combination, the choline radicle being united to the acid by 

 means of the oxygen of the hydroxyl; the formula for distearyl-lecithin 

 would therefore be (Strecker) 3 



CH 2 .0 C 17 IL 5 CO 



/"ITT S~\ /"^ TT f~^t \ 



OH . U Uj^llorV^^ 



CIIo.O PO O.C 2 H 4 ) 



| (CHo)A N 

 OH HO U ) 



The following equation represents the decomposition of lecithin, such 

 as occurs on boiling it with alkaline solutions : 



44 H 90 NP0 9 +3H 2 - 2C 1? H 3fl p 2 H-C 3 H fl PO fl +C 6 H 16 N0 2 



(lecithin) (stearic acid) (glycero- (choline) 



phosphoric acid) 



Lecith-albumins. See p. 69. 



Cholesterin. Cholesterin is contained in small quantities in all proto- 

 plasmic structures ; it is also found in blood corpuscles and in bile. It is a 

 large constituent of sebum and similar oily secretions of the skin. In 

 nervous tissues it is an especially abundant constituent of the white sub- 

 stance of the medullary sheath. It may be prepared by making a hot 



1 Journ.f. praJct. Chem., Leipzig, 1883, Bd. xxviii. S. 219 ; see also E. Gilson, Ztschr. /. 

 physiol. Chem., Strassburg, Bd. xii. S. 585. 



2 Ccntralbl.f. d. med. Wissensch., Berlin, 1868. 



3 Ann. d, Chem., Leip/ig, 1868, Bd. cxlviii. S. 77. 



