CHEMICAL BASIS OF THE ANIMAL BODY. 135 



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 

 cholin, glycerinphosphoric acid, and barium stearate. This may be thus 



represented : 



Glycerinphosphoric 

 Lecithin. Stearic acid. acid. Cholin. 



CJH^PO, + 3H 2 = 2C 18 H 36 2 + C 3 H 9 P0 6 + C 5 H 15 N0 2 . 



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 however more probable 

 from the most recent researches that it is really an ethereal compound 

 of this acid with the cholin l . It appears also that there probably exist 

 other analogous compounds in which the radicles of oleic and palmitic 

 acids take part. 



In accordance with these views the constitution of lecithin may be 

 most adequately represented by the following formula 



/OH 

 O PO X 



X O.C 2 H 4 .(CH 3 ) 3 N.OH, 



where C n H 2n _ 1 O 8 represents the radicle of a fatty acid which in ordinary 

 lecithin appears to be that of stearic, viz. C 18 H 35 2 . 



Glycerinphosphoric acid. C 3 H 9 PO 6 . [C 3 H 5 .(OH) 2 .O.PO(OH) 2 ]. 



Occurs as a product of the decomposition of lecithin, and hence is 

 frequently found in those tissues and fluids in which the latter is present. 

 It may occur occasionally in urine 2 . 



The acid is dibasic and forms salts which are usually, so far as they 

 are known, soluble in cold water, but the lead salt is an exception to 

 this rule and may hence be used as a precipitant. The salts are insolu- 

 ble in alcohol. 



It may be prepared by the decomposition of lecithin when boiled 

 with caustic alkalis or baryta. It may also be synthetised by the 

 direct action of phosphoric anhydride or glacial phosphoric acid on 

 glycerin. The formation by this method may be regarded as resulting 

 from the union of one molecule of glycerin with one of phosphoric acid 

 and elimination of one molecule of water. 



1 Hundeshagen, Jn. /. prakt. Chem. Bd. xxvm. (1883), S. 219. Gilson, Zt. f. 

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



2 Sotnitschewsky, Zt. f. physiol. Chem. Bd. iv. (1880), S. 214. But see also 

 Bobin, Arch, de Pharm. T. n. p. 532, and Chem. Centralb. 1888, S. 186. 



