CHEMICAL BASIS OF THE ANIMAL BODY. 133 



It is quite insoluble in water and in cold alcohol, but soluble in solutions 

 of bile salts. 



Solutions of cholesterin possess a left-handed rotatory action on 

 polarised light, (a) D = 3 -5 in ethereal solution, =37 in chloroformic. 



Cholesterin occurs in small quantities in the blood and many tissues, 

 and is present in abundance in the white matter of the cerebro-spinal 

 axis and in nerves. It is a constant constituent of bile, and forms fre- 

 quently nearly the whole mass of some gall-stones. It is found in many 

 pathological fluids, hydrocele, the fluid of ovarial cysts, &c. also in faeces 

 and milk 1 . It also occurs in the substance of the crystalline lens, more 

 especially in ' cataract.' 



Preparation. Gall-stones supply the most convenient source of 

 cholesterin. These are pounded, extracted with boiling water and dis- 

 solved in boiling alcohol. The solution is filtered through a heated 

 filter, and .the cholesterin separates out in a fairly pure condition as 

 the filtrate cools. It is purified by resolution in boiling alcohol to 

 which some caustic soda has been added, from this it again separates 

 on cooling, and is finally washed with cold alcohol and water. 



Cholesterin is characterised, apart from its crystalline form, by 

 some striking reactions which may be obtained even with microscopic 

 quantities. 



(i) When the crystals are treated with concentrated sulphuric acid 

 they usually turn violet or red. On the addition of a little iodine the 

 play of colours is very marked, the crystals being variously coloured, 

 blue, red, green, violet 2 . 



(ii) When dissolved in chloroform, the solution turns blood-red on 

 the addition of an equal volume of concentrated sulphuric acid : this 

 turns to blue, green and finally yellow, the change of colour being very 

 rapid if the solution is freely exposed to the air in an open dish. The 

 sulphuric acid under the chloroform exhibits a green fluorescence 3 . 



(iii) When evaporated to dryness on porcelain with a few drops of 

 concentrated nitric acid, a yellow residue is obtained, which turns red 

 if treated, while still hot, with ammonia. 



1 Tolmatscheff, Hoppe-Seyler's Med. Chem. Untersuch. Hf. 2 (1867), S. 272. 

 Schmidt-Mulheim, Pfliiger's Arch. Bd. xxx. (1883), S. 384. 



* See figures in Funke, Atlas d. physiol. Chem. Leipzig, 1858, Taf. vi. Fig. 2, 3. 

 This work should be consulted for the crystalline forms of all physiologically im- 

 portant substances. See also Ultzmann u. Hofmann, Atlas d. Harnsedimente. Wien, 

 1872. 



3 Cf. Burchard, Inaug. Diss. Kostock 1889. Abs. in Ber. d. d. chem. Gesell. 

 Ref. Bd. 1890, S. 752. 



