282 ORGANIC AGRICULTURAL CHEMISTRY 



this is so the importance of phytosterol in plants as a source 

 of cholesterol in animals is connected with the antitoxic action 

 of cholesterol of which we shall soon speak. 



Lecithin. — This substance is definitely related to fats in its 

 constitution, as it is an ester of glycerol. Fats, it will be recalled, 

 are neutral or tri-acid esters of glycerol, i.e. all three of the 

 glycerol hydroxyl hydrogens are replaced by fatty acid radicals 

 Lecithin is like the fats in being a neutral or tri-acid ester but. 

 while in fats all of the hydroxyl hydrogens are replaced hy fatty 

 acid radicals J in lecithin only two of the three are thus replaced 

 hy fatty acid radicals. The third is replaced by the phosphoric 

 acid radical. In addition to this the phosphoric acid radical 

 has one of its remaining acid hydrogens replaced by a basic 

 radical of a compound known as choline. This choline is not a 

 simple alcohol but is a tri-methyl-hydroxy-ethyl ammonium 

 hydroxide compound. Thus in lecithin there are four distinct 

 parts, viz. (a) glycerol; (b) fatty acid, usually stearic, palmitic 

 or oleic; (c) phosphoric acid; (d) choline, a nitrogen (amine) 

 base. On hydrolysis lecithin yields all four of these parts and 

 this hydrolysis is produced enzymatically by the fat-splitting 

 enzyme lipase. Lecithin belongs to a group of compounds 

 known as phospho-lipines, which signifies fat-like bodies con- 

 taining phosphorus and also nitrogen (amine). 



The chief source of lecithin is the yolk of eggs, from which fact 

 the name lecithin is derived. It is also, like cholesterol, a normal 

 constituent of the living cell and is found in hlood, lymph and 

 muscle tissue. It is also often associated with fats, especially 

 in brain, nerve tissue and eggs. In plants it is found in the seeds 

 especially of legumes and cereals. 



The amounts of lecithin in some of these substances are as 

 follows : 



Egg yolk 9.4 per cent 



Liver 2.1 per cent 



Blood 1.8 per cent 



Legume seeds 0.8-1.6 per cent 



Cereal grains 0.25-0.53 per cent 



