CHEMICAL BASIS OF THE ANIMAL BODY. 1287 



of the bile-acids in the small intestine, in larger quantities in 

 the contents of the large intestine, and in the faeces of man and 

 many^ animals. In icterus the urine is also stated to frequently 

 contain traces of this acid. Its principal interest lies in its 

 being the starting-point, by its union with glycine or taurine, 

 for the acids which, as sodium salts, exist characteristically in 

 bile. 



Owing to the readiness with which ox-bile can be obtained 

 in large quantities, this has been most frequently used for the 

 preparation of cholalic acid, whose properties as usually given 

 hence refer to the acid as obtained from this source. More 

 recent researches have however demonstrated comparatively 

 unimportant but still distinct differences in the composition 

 and properties of the acid as it occurs in the bile-acids of 

 different animals. The description of the acid which here 

 follows refers to that form which is obtained from ox-bile. 



Preparation. This depends upon the decomposition of the 

 bile-acids (glycocholic and taurocholic) by means of alkalis at 

 boiling temperature. 



The acid possesses the following properties. The crystals 

 obtained from hot alcoholic solutions are usually in the form 

 of large rhombic tetrahedra or octahedra, containing 2|- mole- 

 cules of water of crystallization which may be driven off by 

 heating to 100 C. The crystals are but slightly soluble (1 in 

 750) either in water, even when boiling, or in ether, but readily 

 soluble in alcohol. This acid may also be obtained in an amor- 

 phous form by concentrating its solutions to dryness and is now 

 less insoluble than Avhen crystallized. The alkali and barium 

 salts of cholalic acid are soluble in water and in alcohol espe- 

 cially when warm, and yield, like the free acid, dextrorotatory 

 solutions. For solutions of the anhydrous acid (a) D =H-50. 

 When crystallized with 2JH 2 O, (a) D =+35. In alcoholic 

 solutions of the sodium salt (a) D = +31*4. 



The constitution of cholalic acid is scarcely as yet definitely 



known but may be represented by C 20 H 31 < (CH 2 OH) 2 . It 



yields with iodine a compound which like that resulting from 

 the interaction of iodine and starch possesses a brilliantly 

 blue colour and is specifically distinctive, since it cannot be 

 obtained either from the bile-acids or choleic acid (see below) 

 or the products of the decomposition of cholalic acid. 



When cholalic acid is prepared from human bile it exhibits 

 certain differences, more especially as regards the lesser solu- 

 bilities of its alkali and barium salts, which led to its being 

 regarded as distinct from that obtained from ox -bile and hence 

 it was called anthropocholalic acid. It appears however that 

 the bulk of the acid is identical with that from ox-bile, the 



