244 ON THE EXCRETION OF 



Discussion of the preceding analytical data. So far as has 

 been observed, all aromatic compounds found in the organism 

 of the higher animals are derived either from benzene deriva- 

 tives introduced into the system, or from the proteids, which 

 must accordingly contain aromatic radicals. A synthesis of 

 the latter in the animal body from carbohydrates or fats 

 scarcely seems probable in view of the accumulated experi- 

 mental data bearing on the problem.* The present study of 

 kynurenic acid excretion lends additional force to this view 

 as applied to quinoline derivatives. Thus kynurenic acid is 

 almost always found in the urine during starvation, a condi- 

 tion in which body proteids form the source of the nitrogen- 

 ous compounds excreted. This observation, repeatedly made 

 (. </., Dogs G, H, J, K), leaves little doubt that kynurenic 

 acid is a true product of proteid katabolism, and for the most 

 part, at least, is not dependent for its origin on the putre- 

 factive processes in the intestine, a possibility which has 

 already been mentioned. 



Quantitatively considered, kynurenic acid production bears 

 a more or less direct relation to the variations in the decom- 

 position of proteid material, whether the latter be the " tissue 

 proteid " of a starving animal, or introduced as food and the 

 kynurenic acid formed incidental to its metamorphosis. More- 

 over, our experiments furnish repeated evidence that kynu- 

 renic acid is a concomitant or direct product of accelerated 

 proteid metabolism. There is no lack of evidence that the 

 proteid molecule may break down in the body into a nitro- 

 genous and non-nitrogenous portion. The former part is 

 doubtless rapidly further broken down, oxidized and synthe- 

 sized perhaps into various nitrogenous constituents of the 

 urine. The non-nitrogenous moiety is less speedily elimi- 

 nated. It may be converted into glycogen, or dextrose, or 

 fat ; and forming, as it does, the major part of the original 

 molecule, it may be distributed to the tissues more slowly in 

 proportion as they demand it.f The experiments of Feder f 



Cf. Raumann, Zeitschr. f. physiol. Chemie, 1886, x, p. 123. 



t Cf. Reilly, Nolan and Lusk, Amer. Jour. Physiol., 1898, i, p. 404. 



} Feder, Zeitachrift fur Biologie, 1881, xvii, p. 641. 



