6 METABOLISM OF ORGANIC AND INORGANIC PHOSPHORUS. 



LECITHIN-. 



The lecithins are ester compounds which may be regarded as having 

 been formed by the union of one molecule of glycerol with two mole- 

 cules of a fatty acid (stearic acid, palmitic acid, or oleic acid), one 

 molecule of phosphoric acid, and one molecule of cholin, with the 

 loss of four molecules of water. The formula for lecithin is 

 C^H^NPOj,. The lecithin radical contains one atom of nitrogen 

 for every atom of phosphorus. 



Cholin is an ammonium base, the composition of which is accu- 

 rately known. When heated it splits into glycol (ethylene alcohol), 

 and trimethylamin. Its synthesis corresponds with this decomposi- 

 tion. Wurtz a produced it by the action of ethylene oxid and 

 \\ater on trimethylamin. In the animal kingdom cholin has, up to 

 the present time, been found only in lecithin. It was first obtained 

 by Strecker 6 from the bile, which contains lecithin, and hence was 

 called cholin. Liebreich c found it among the products of the decom- 

 position of phosphorus compounds from brain tissue. Diaconow d 

 showed that it was a product of the decomposition of lecithin. In 

 the new tissues of plants cholin is found in other combinations as 

 well as in lecithin. At present Jbut little is known about the part 

 which the lecithins play in the vital functions. 



An important question is whether the lecithins of the body tissues 

 are produced from the lecithins of the food or by synthesis from 

 other materials such as fat, protein, and phosphoric acid. It has 

 been ascertained from experiments on artificial pancreatic digestion 

 that the lecithins take up water and readily split up into glycero- 

 phosphoric acid, fatty acids, and cholin. It is not yet known whether 

 this decomposition . is complete in normal digestion, or a portion is 

 absorbed unchanged, and if so, how large a portion; whether only 

 the undecomposed part, when absorbed, can be utilized in the build- 

 ing up of the tissues, or the products of decomposition which are 

 absorbed again become united; or finally whether lecithin may also 

 be formed from other material. The absorption of lecithin or of its 

 products of decomposition is complete, according to Bunge, as he 

 states that neither lecithin nor glycero-phosphoric acid can be found 

 in the feces. More recent work, however, by Long e seems to show 

 that the feces sometimes contain lecithin in considerable quantities. 

 The presence of lecithin in milk, eggs, and many other foods indi- 

 cates that this substance is essential in nutrition. 



Centrbl. med. Wissensch., 1868, 6 : 69, 431. 



& Ann. Chem. Pharm., 1862, 123 : 353; 1868, US : 77. 



clbid., 1865, 134: 29. 



d Centrbl. med. Wissensch., 1868, 6:97, 434. 



J. Amer. Chem. Soc., 1906, 28 : 704; Long and Johnson, ibid., 1499. 



