210 DYSLYSIK GLYCOCHOLIC ACID. 



2. Dyslysin. C^H^O,. 



When cholalic acid is heated to 200 C. or boiled for some time 

 in solution with hydrochloric or sulphuric acid it loses two mole- 

 cules of water and yields a resinous anhydride called dyslysin, 

 from its insolubility in water, alcohol, and alkalis. As resulting 

 from the dehydration of cholalic acid it is found sometimes in 

 small amount in the faeces. It is a non-crystalline substance 

 which is soluble in an excess of ether, also in solutions of cholalic 

 acid or of its salts. By treatment with boiling alkalis it may be 

 reconverted by hydration into cholalic acid. 



The various forms of cholalic acid which may be prepared from 

 the bile of different animals each yield a corresponding form of 

 dyslysin. 



3. Glycocholic acid. C^H^NO,,. 



This substance was first described by Gmelin (1826), by whom 

 it was then named ' cholic acid.' It is found not in the free state 

 but as a sodium salt, chiefly in ox-bile but also in that of man, 

 mixed in both cases with a much smaller and variable amount of 

 taurocholic acid, also present as a sodium salt. In carnivora it 

 occurs, if at all, in such minute traces only, that it may be said 

 to be absent from the bile of these animals ; hence their bile-acid 

 consists entirely of taurocholic acid. 1 In icterus the urine may 

 contain small quantities of glycocholic acid. 



Preparation. This may be affected in several ways, using ox- 

 bile as the source ; of these the following is as convenient as any 

 (Drechsel). 2 The bile is mixed with washed sand and evaporated 

 on a water-bath until it presents a pulverisable mass. This is 

 then extracted in a flask with strong boiling alcohol and yields a 

 green solution, which is filtered, decolourised with animal char- 

 coal, and concentrated to a sirup. The latter is then dissolved 

 in a minimal quantity of absolute alcohol and precipitated by an 

 excess of ether. The precipitate which consists of glycocholate 

 of soda together with the corresponding salt of any taurocholic 

 acid which is present in the bile, is collected, dissolved in a little 

 water, and acidulated with sulphuric acid in presence of some 

 ether as long as any precipitate is formed. By this means the 

 acids are separated from their sodium salts, and on standing a 

 crystalline mass of glycocholic acid is obtained, practically free 

 from taurocholic acid, which, since it is, unlike the glycocholic, 

 extremely soluble in cold water, remains in solution in the mother 

 liquor. The crystals may be purified by recrystallisation from 



1 For earlier references to the bile-acids of various animals see Bayer, Zt. f. 

 physiol. Chem. Bd. in. (1879), S. 293. 



2 Anleit. z. Darstell. physiol. -chem. Praparate, 1889, S. 33. 



