762 THE BILE SERIES. [App. 



In icterus, the urine often contains traces of this acid. But its principal 

 interest lies in its being the starting point for the various bile acids 

 (see below). The pure acid may be amorphous, or crystalline, in 

 the latter case crystallising from hot alcoholic solutions in tetrahedra. 

 These crystals are insoluble in water and tether. In the amorphous 

 form, it is somewhat soluble in water and aether. Heated to 200 C., it 

 is converted into water and dyslysin (C 24 H 43 Oo). 



This acid possesses, in the anhydrous condition, a specific rotatory 

 power of + 50 for the yellow light : when it crystallises with H 2 O, the 

 rotation is 4- 35. The rotatory power of the alkali salts is always less 

 than the above, and when in solution in alcohol, the rotation is 

 independent of the concentration. For the alcoholic solution of the 

 sodium salt, the rotation is + 314. 



Preparation. By the decompositions of bile acids by means of acids, 

 alkalis, or fermentative changes. 



Bayer 1 has examined the bile-acids obtained from human bile, and has pre- 

 pared from them cholalic acid. To this he assigns the formula C 18 H 08 4 . If 

 this be so, then cholalic acid of human bile would seem to be a body entirely 

 different from that obtained from ox bile, and analysed by Strecker. Bayer's 

 results however require further confirmation. 



Pettenkofer's test 2 . 



This well-known, test for bile acids depends on the reaction of 

 cholalic acid in presence of sugar and sulphuric acid. If to a solution of 

 the acid a little sugar be added, and then sulphuric acid, keeping the 

 temperature below but not much below 70 C., a beautiful reddish purple 

 is obtained. If diluted with alcohol this solution gives a characteristic 

 spectrum with two absorption bands, one between D and E, nearest to E, 

 the other close to F 011 the red side of F. 



The reaction is much impeded by the presence of colouring matters; 

 moreover proteids, and other bodies easily decomposed by sulphuric 

 acid such as amyl-alcohol and oleic acid, give a similar result, the 

 colouring matter produced from these bodies does not however give the 

 absoiption bands described above 3 . 



Glycocholic acid. C 26 H 43 NO 6 . 



This body was first obtained in the crystalline form and described by 

 Gmelin (1826), who gave it the name of 'cholic' acid. 



1 Zeitschr. f. physiol Cliem. Bd. n. (1878-79), S. 358. 



2 Pettenkofer, Annalen. d. Chem. u. Pharm. Bd. LII. (1844), S. 90. 



3 For further information on this subject see: Bischoff, Zeitsch.f. rat. Med. Ser. 

 3, Bd. 21, S. 126. Schulze, Ann. d. Chem. u. Pharm. LXXI. (1849), S. 266. Schenk, 

 Anatom. physiol. Untersuch. Wien, 1872, S. 47. Adamkiewicz, Pfliiger's Arch. Bd. 

 is. (1874), S. 156. 



