CHEMICAL BASIS OF THE ANIMAL BODY. 209 



is perhaps the better, since it indicates the method by which the bile-acids 

 are decomposed during its preparation, viz. by treatment with alkalis. The name 

 'cholic' was first applied by Gmelin 1 and subsequently by Strecker 2 to the acid 

 which is now always known as glycocholic. The acid now known as taurocholic 

 was originally called ' choleic ' by Demarcay, and the same name has been quite 

 recently used to denote an acid (C 25 H 42 4 ) closely related to cholalic acid (see 

 below). 



This acid occurs in traces as a product of the decomposition 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 

 glycin or taurin, for the acids which, as sodium salts, exist character- 

 istically in bile (see below). 



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 tempe- 

 rature. It is not however necessary to employ the purified acids for 

 this purpose since the raw bile suffices. The bile is boiled for twenty- 

 four hours with as much caustic baryta as it will hold in solution, 

 concentration during this operation being avoided by means of a con- 

 denser attached to the mouth of the flask. When the decomposition 

 is complete the fluid is filtered while still hot, and the filtrate concen- 

 trated until crystals, consisting of the barium salt of the acid, are 

 copiously formed. These are then purified by recrystallisation from 

 boiling water and decomposed by the addition of hydrochloric acid. 

 The free cholalic acid is finally obtained in a pure form by solution in 

 a small volume of boiling alcohol from which it separates out in the 

 crystalline form on cooling. 



As thus prepared 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 J molecules of 

 water of crystallisation which may be driven off by heating to 100 C. 

 The crystals are but slightly soluble (1 in 750) either in water, even 



1 Die Verdauung nach Versuchen, 1826. 



2 Liebig's Ann. Bd. LXV. (1848), S. 1. 



