KYNURENIC ACID. 229 



demonstrated the possible origin of aromatic oxyacids in tissue 

 metabolism, since they have found them in the urine of ani- 

 mals which were entirely free from all bacteria. It seems 

 desirable to emphasize the preceding facts because the experi- 

 ments of Haagen have repeatedly been misinterpreted and 

 quoted in evidence of the intestinal origin of kynurenic acid,* 

 although Haagen has carefully avoided such an interpretation 

 of his observations.! Finally, the experiments of Capaldi $ 

 have given additional evidence against the assumed intestinal 

 origin of kynurenic acid. 



In considering the immediate antecedents of kynurenic acid, 

 tyrosin is at once suggested. The behavior of this aromatic 

 compound with reference to its possible synthesis to oxyquin- 

 oline-carboxylic acid in the body has been investigated by 

 Hauser and Solomin,|| both of whom failed to obtain evi- 

 dence of any direct relationship between the two substances. 



Plan of present investigation. The present investigation is 

 an attempt to ascertain something more definite regarding the 

 conditions which determine and modify kynurenic acid pro- 

 duction and excretion. Unless otherwise stated, the data have 

 been obtained with dogs. The animals were kept in suitable 

 roomy cages which permit the separate collection of urine and 

 faeces, and stand in a light, well-ventilated space. It was not 

 found necessary to resort to catheterization, since the periods 

 of observation always extended over more than one day and 

 the animals soon became accustomed to discharge their urine 



* Cf. for example, Hauser, Arch. f. exper. Pathol. u. Pharmakol., 1895, 

 xxxvi, p. 3; also, Neumeister, Lehrbuch der physiol. Chemie, 2te Auflage, 

 1897, p. 721. " Eine altere, von Baumann stammende Angabe, dass die Quan- 

 titat der Kynurensaure von den Faulnissprocessen im Darm unabhangig sei, 

 scheint durch die neueren Untersuchungen widerlegt zu sein." 



t Cf . Haagen, loc. cit., p. 26, " . . . so ist es zweifelhaft, ob die nach anderen 

 Antisepticis, besonders nach Naphthalin, gef undene Verminderung der Kynu- 

 rensaure auf Beschrankung der Darmfaulniss, oder ob sie nicht vielmehr auf 

 anderen Umstanden beruht." 



J Capaldi, Zeitschr. f. physiol. Chemie, 1897, xxiii, p. 87. 



Hauser, Arch. f. exper. PathoL u. Pharmakol., 1895, xxxvi, p. 1. 



|| Solomin, Zeitschr. f. physiol. Chemie, 1897, xxiii, p. 497. 



