CHEMICAL BASIS OF THE ANIMAL BODY. 211 



2. Dy sly sin. 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 molecules of 

 water and yields a resinous anhydride called dyslysin, from its insolu- 

 bility 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 l . In icterus the urine may contain small quantities of glycocholic 

 acid. 



Preparation. This may be effected 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 charcoal 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 



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

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



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



02 



