32O PHYSIOLOGICAL CHEMISTRY. 



cholic acid, but in ox bile the relation is variable. The 

 amounts of the pigments are small and not accurately known. 

 Glycocholic Acid. This is a complex substance made up 

 of a combination of glycocoll or glycine with cholalic acid. 

 The constitution of the acid is not known, but the empirical 

 formula C 26 H 43 NO 6 has been given to it. In the bile it exists 

 in the form of a sodium or potassium salt, which is readily 

 soluble in water or alcohol. The free acid is but slightly solu- 

 ble; hence the addition of mineral acids to bile produces a 

 precipitate. On boiling a solution of glycocholic acid with 

 weak acids or alkalies a cleavage follows, and glycocoll and 

 the nitrogen-free cholalic acid separate. Water is taken up 

 at the same time. This is a reaction analogous to the separa- 

 tion of glycocoll and benzoic acid from hippuric acid by the 

 same manner of treatment. There appear to be several 

 cholalic acids, but with the common one the reaction would 

 be represented, probably, in this way : 



C 26 H 43 N06 + H 2 = C 2 H 3 2 NH 2 + C 2 4HO 5 . 



Cholalic Acid. Although many investigations have been 

 carried out with this substance its constitution is not clear. 

 The above empirical formula, C 24 H 40 O 5 , is that of a mono- 

 basic acid to which Mylius has given this possible structure, 



rCHOH 

 r CH 2 OH 

 C2oH H CH 2 OH 



[COOH 



The free acid is very slightly soluble in water, but the alkali 

 salts are readily soluble. The free acid is somewhat soluble 

 in ether; hence it is found as a decomposition product of the 

 bile acids in the crude fat extracted from feces. By oxidation 

 cholalic acid yields several new acids which have been much 

 studied with the hope of gaining an insight into the struc- 

 ture of the original acid. Among the various derived acids 

 these may be mentioned : Cholcic acid, C 25 H 42 O 4 , dehydro- 

 cholcic acid, C 24 H 34 O 4 , cholanic acid, C 24 H 34 O 8 . Fellic acid, 



