CHOLESTERIN. 23 



alcoholic extract of the brain or spinal cord; on cooling, the cholesterin, to- 

 gether with protagon and cerebrin, separates out. From this mixture the 

 cholesterin is dissolved out with ether, and the ether distilled off'. To 

 get rid of traces of lecithin it is heated for an hour with alcoholic potash ; 

 this decomposes the lecithin, and the residue obtained by evaporating to 

 dryness is dissolved in a mixture of alcohol and ether ; from this solution, 

 cholesterin crystallises out as its solvents evaporate off. 



Cholesterin is readily obtained from gall stones by simply extracting 

 them with boiling alcohol, and treating with alcoholic potash to free it 

 from extraneous matter. 



Like the fats, cholesterin is insoluble in water, but freely soluble 

 in hot or cold ether, glycerine, benzol, hot alcohol, and chloro- 

 form. From anhydrous ether or chloro- 

 form it separates in the form of needles, 

 containing no water of crystallisation ; 

 from alcohol, or ether containing water, 

 it separates in the form of rhombic, 

 bright tables, which contain a mole- 

 cule of water of crystallisation, and 

 are easily identified by the microscope 

 (Fig. 6). 



Dry cholesterin melts at 145, distils in 

 vacuo at 360 C. ; its specific rotatory power 

 is (a) D = - 31'6. It may be recognised by FIG. 

 the following colour tests : 



). Cholesterin crystals. 

 After Frey. 



1. With iodine and concentrated sulphuric acid the crystals give a 

 play of red, green, and blue. 



2. Salkowski's reaction. 1 The cholesterin is dissolved in chloroform 

 and an equal volume of concentrated sulphuric acid added ; the solution 

 becomes first red and then purplish, while the sulphuric acid is dark red 

 with a green fluorescence. On pouring off the chloroformic solution, it 

 becomes green and finally yellow. 



3. Licbermann- Bur chard' s reaction. 2 This is a very delicate test, and 

 is stated to be capable of detecting one part of cholesterin in 20,000 of 

 solvent. The cholesterin is dissolved in 2 c.c. of chloroform, and ten 

 drops of acetic anhydride are added, and then concentrated sulphuric 

 acid drop by drop. The mixture becomes first red, then blue, and 

 finally green. 



Cholesterin is a monatomic alcohol, the formula of which has been 

 given as C 26 H 43 OH and C 27 H 45 OH. The second formula was first 

 ascribed to the substance by Eeinitzer, 3 and it is probably the correct 

 one, as it has been confirmed by the careful work of Obermiiller. 4 These 

 observers have prepared a large number of compounds and derivatives 

 of cholesterin, but its constitution still remains unknown. 



The subject is complicated by the circumstance that there are several 

 isomeric cholesterins. 



1 Arch. f. d. ges. PhysioL, Bonn. Bd. vi. 



2 Liebermann, Ber. d. deutsch. chem. Gescllsch., Berlin, Bd. xviii. S. 1804; Burchard, 

 " Beitrage zur Kenntniss der Cholesterine," Rostock, 1889. 



3 Reinitzer, Monatsh. f. Chem., Wien, 1888, Bd. ix. s. 421. 



4 Arch. f. PhysioL, Leipzig, 1889; Ztschr. f. pJnjsiol. Chem., Strasstmrg, 1889, Bde. 

 xv. S. 37 ; xvi. S* 143, 152. 



