CHAP. X.] THE NERVOUS TISSUES. 443 



through a heated funnel and the filtrate is cooled. The deposit, 

 which consists of cerebrin, protagon, other complex phosphorized 

 bodies, and cholesterin, is collected on a filter, washed with cold alcohol, 

 and then, after being pressed between filter paper, is shaken in a 

 stoppered bottle with ether; the ethereal solution is filtered, the ether 

 is distilled off, and the residue, consisting of impure cholesterin mixed 

 with some lecithin, is heated in a water bath for an hour with an 

 alcoholic solution of caustic potash. The contents of the flask are 

 then evaporated to dryness on the water bath, and the dry residue 

 is washed with water and dissolved in a mixture of ether and 

 alcohol, from which it is allowed to crystallize by the spontaneous 

 evaporations of the solvents. 



Properties Pure cholesterin separates from its solutions in 



anhydrous ether or chloroform in the form of needles 

 containing no water of crystallization; but from alcohol it separates in 

 the form of rhombic tables. 



FIG. 60. CRYSTALS OF CHOLESTEBIN AS IT SEPARATES FROM ALCOHOL OR ETHER 

 CONTAINING WATER. (Frey.) 



Cholesterin is insoluble in water, alkalies and dilute acids; it is 

 very slightly soluble in cold, but soluble in 9 parts of boiling, alcohol. 

 It is highly soluble in ether cold and boiling, in chloroform, benzol, 

 and in solutions of salts of the bile acids. 



Dry cholesterin melts at 145, and distils in vacuo at 360. Its 

 solutions exert a left-handed rotation on the plane of polarization. The 

 specific rotatory power of solutions of cholesterin (a) jD = 31'6. Amongst 

 the most useful reactions for detecting cholesterin are the following : 



1. When treated with concentrated sulphuric acid, and after- 

 wards a little iodine, a play of colours, of which blue, green, and 

 red are the most prominent, is produced. This reaction may be 

 employed as a more stringent proof than that offered by the 

 microscopic characters of the crystals, and it may be well observed 

 under the microscope. 



2. When cholesterin is gently heated with five volumes of 

 sulphuric acid and one volume of water, the edges of the crystals 

 are seen to become of a carmine colour; this reaction admits of 



