70 PHYSIOLOGICAL CHEMISTRY 



Lecithin is soluble in absolute alcohol, and in ether, but may 

 be precipitated from the latter solution by adding acetone. On 

 hydrolysis lecithin yields higher fatty acids, glycerine, phos- 

 phoric acid and an organic base choline. It is believed to have 

 the following formula, where R indicates a fatty acid residue. 







II 

 CH 2 C R 







II 

 CH C R 



CH 2 0. 



O CH 2 CH 2 N (CH 3 ) 3 OH 



P 



/ \ 

 OH 



Cholesterol. Cholesterol is a substance which resembles the 

 fats in some of its physical properties, but has little relation 

 to them chemically. It is widely distributed in nature, and is 

 found in large amounts in the brain and nerve tissue. It oc- 

 curs also in small amounts in the blood, and in the bile, from 

 which it is occasionally deposited in gall stones, whence it is 

 most easily obtained. Cholesterol is insoluble in water, acids, 

 or alkalies. It is readily soluble in hot alcohol, in ether, chloro- 

 form, benzol, etc. Cholesterol crystallizes from hot alcohol or 

 other solvents, forming large colorless plates. It gives many 

 color reactions. If a chloroform solution of cholesterol is care- 

 fully treated with concentrated sulphuric acid so as to form a 

 layer of acid at the bottom of the test tube, the chloroform solu- 

 tion becomes a brilliant red, and the acid layer dark red with a 

 green fluorescence. This test is known as Salkowski's test. 

 The Lieberman-Burchard test is one of the best of the choles- 

 terol tests. To 2 c.c. of a chloroform solution of cholesterol, 



