912 APPENDIX. 



Preparation. By the dry distillation of salicylic acid, also from the acid pro- 

 ducts of the distillation of coal. It is obtained in the last portions of the distillate 

 when preparing indol, and is separated by forming a compound with bromine, 



3 . 



[KYNURENIC ACID. This acid is obtained from the urine of dogs. It crystal- 

 lizes in long needles or four-sided prisms [Fig. 256], and with barium forms peculiar 

 triangular crystals [Fig. 257]. 



THE BILE SERIES. 



Cholalic (or Cholic) Acid. H.CH 24 H 39 5 + H 2 0. 



Occurs in traces in the small intestine, in large quantities in the contents of the 

 large intestine, and the feces of men, cows, and dogs. 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 crystallizing from hot alcoholic solutions in tetrahedra. 

 These crystals are insoluble in water and ether. In the amorphous form it is some- 

 what soluble in water and ether. Heated to 200 C. , it is converted into water and 

 dyslysin (C 24 H 43 3 ). 



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

 +50 for the yellow light; when it crystallizes with H 2 0, the rotation is +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 +31.4. 



Preparation. By the decomposition of bile acids by means of acids, alkalies, or 

 fermentative changes. 



Bayer * has examined the bile acids obtained from human bile, and has prepared from them 

 cholalic acid. To this he assigns the formula Ci 8 H 28 O4. 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 analyzed by 

 Strecker. Bayer's results, however, require further confirmation. 



Pettenkofer' s test* 



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 on the red side of F. 



The reaction is much impeded by the presence of coloring matters ; moreover, 

 proteids and other bodies easily decomposed by sulphuric acid, such as amyl-alcohol 

 and oleic, give a similar result ; the coloring matter produced from these bodies 

 does not, however, give the absorption bands described above. 3 



Glycocholic Acid. C 26 H 43 N0 6 . 



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

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



To avoid confusion it is now best to use the term " cholic " as a synonym for " cholalic," 

 Demarcay, who first (1838) described the cholalic acid as a product of th'e decomposition of bile 

 acids, having given it the name of cholic acid. The name cholalic acid is perhaps the best, since 

 it indicates the method by which the bile acids are split up, viz., by treatment with alkali. 



This is the principal bile acid of ox-gall : it is also present in the bile of man, but 

 has so far not been observed in that of carnivora. In icterus the urine may contain 

 traces of this acid. 



It crystallizes in fine, glistening needles. These are slightly soluble in cold water, 

 readily so in hot water and alcohol, but insoluble in ether. They possess a bitter 

 and yet sweet taste, and a strong acid reaction. 



The salts of this acid are readily soluble in water and crystallize well. The salts, 

 as well as the free acid, exert right-handed polarization amounting to +29.0 for 

 the acid, and + 25.7 for the sodium salt, both measured for yellow light. 



1 Zeitschr. f. physiol. Chem., Bd. ii. H878-79), S. 358. 



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



8 For further information on this subject see : Bischoff, Zeitschr. f. rat. Med., Ser. 3, Bd. xxi., S. 

 126. Schulze, Ann. d. Chem. u. Pharm., Bd. Ixxi. (1849), S. 266. Pchenk, Anatom. -physiol. Unter- 

 such., Wien, 1872, S. 47. Adamkiewicz, Pfliiger's Arch., Bd. ix. (1874), S. 156. 



