THE AROMATIC OXY-ACIDS. 277 



The so-called damalic acid and damalurie acid, which are obtained 

 from the urine of the horse and the cow, probably represent a mixt- 

 ure of benzoic acid and volatile fatty acids. 



Kynurenic Acid. Kynurenic acid is said to be a constant con- 

 stituent of the urine of dogs. Its mother-substance is manifestly 

 an albuminous derivative, as the amount which appears in the urine 

 is largely dependent upon the quantity of albuminous food ingested. 

 Its elimination, moreover, continues during starvation, although the 

 amount is then reduced to a minimum. Its formation is apparently 

 not influenced by the degree of intestinal putrefaction, as the same 

 amounts are excreted when putrefactive processes have been reduced 

 to the lowest level by the administration of calomel or iodoform. 



Recent investigations have shown that the direct antecedent is 

 tryptophan (Ellinger). When this is fed to dogs a large increase 

 of kynurenic acid occurs. The same is seen in rabbits, even though 

 kynurenic acid does not normally occur in the urine of these animals. 

 In man, on the other hand, no kynurenic acid production occurs. 

 Of the manner in which the transformation is effected nothing is 

 known. 



Kynurenic acid is now regarded as f-oxy-/5-quinolm-carbonic acid : 



CH C(OH) 



HC X X C C.COOH 



I II I 

 HC C CH 



X CH N 



It is decomposed by heat, with the formation of carbon dioxide 

 and a basic substance, kynurin, viz. f-oxyquinolin. On reduction 

 the latter is transformed into quinolin. The changes are repre- 

 sented by the equations : 



(1) C 9 H 5 N(OH).COOH = C 9 H 6 N(OH) + CO 2 



Kynurenic acid. Kynurin. 



(2) C 9 H 6 N(OH) + 2H = C 9 H 7 N -f H 2 O 



Kynurin. Quinolin. 



On oxidation both kynurenic acid and kynurin yield kynuric or 

 oxalyl-anthranilic acid : 



,COOH 



X NH.CO.COOH 



The synthesis of kynurenic acid has been accomplished by R. 

 Camps. 



Isolation. To isolate kynurenic acid from the urine, 500 c.c. are 

 treated with hydrochloric acid in the proportion of 4 c.c. for every 

 100 c.c. of the urine. On standing for forty-eight hours the sub- 

 stance in question crystallizes out together with uric acid. To sepa- 

 rate it from the latter, dilute ammonia is added to the crystalline 



