1 90 Biological Chemistry. 



tissues, and the group of substances containing phosphorus, 

 known as the phospholipins, of which lecithin and the 

 various brain lipoids, such as cerebrone, are examples. 



Cholesterol, C 27 H 46 0, a monohydroxy alcohol, melting 

 point 148-5-150'8, is the chief constituent of certain 

 forms of gall-stones. It and its hydroxy derivatives are 

 found in the majority of tissues. Its constitution is com- 

 plex, and is still unknown. It can best be prepared in 

 quantity from brains. The latter are dried by mixing 

 with plaster of Paris, and the powder thus formed is 

 ground up with sand. On extracting this mixture with 

 cold acetone, and evaporating the extract, almost pure 

 cholesterol separates. 



Lecithin was originally prepared from yolk of egg. It 

 yields on hydrolysis fatty acids, glycero-phosphoric acid, 

 and choline. The constitution which has been assigned to 

 it is the following : 



CH 2 -OCOC 17 H 35 



JH-0 CO C 17 H 35 (or some other fatty acid radicle) 



P(OH) OCH 2 CH 2 N(CH 3 ) 3 OH 



II 







Such a product on complete hydrolysis would yield glycerol, 

 fatty acids, phosphoric acid, and the basic substance choline, 

 OH-CH 2 -CH 2 -N(CH 3 ) 3 OH, which on heating in aqueous 

 solution decomposes into ethylene glycol (p. 76) and tri- 

 methylamine 



OH CH 2 CH 2 -N(CH 3 ) 3 OH = OH CH 2 -CH 2 -OH + N(CH 3 ) 3 



The chemistry of lecithin is still, however, very in- 

 definite, and it is doubtful whether a pure product has 

 as yet been obtained. It is generally prepared from the 

 alcoholic extract of egg-yolk by precipitation with an 



