108 CHEMISTRY OF THE PROTEIDS CHAP. 



Phenylacetic acid was converted into phenaceturic acid 



(no hippuric acid), 



Ethyl-benzeAe ^ hippuric acid 



(no phenaceturic acid), 



Mandelic acid remained unchanged. 



There is thus a marked difference between the oxidation of an 

 alcohol (ethyl-benzene and its corresponding acid (phenylacetic acid). 



Phenyl-butyric, phenyl-a-lactic, phenyl-pyro-uvic (and other five 

 acids examined by Knoop) containing more than 2C in the side-chain 

 did not give rise to benzoic acid. 



It has already been pointed out that phenyl-propionic acid can 

 only become oxidised in the ^-position, and this rule seems to hold 

 good for all saturated, normal, terminally phenyl- substituted fatty 

 acids ; analogous changes seem to take place in diabetes when oxy- 

 butyric and acet -acetic acid appear in the urine. In the case of 

 phenyl-alanin and other a-substituted phenyl-propionic acids, and in 

 phenyl-a-amino-cinnamic acid, the a-substi tut/ion seems to make /3- 

 oxidation impossible, and it must be assumed that the substances last 

 mentioned undergo some other change before they become oxidised. 



Nencki and Schultzens l were the first to show that leucin and 

 glycocoll administered in the food give rise to urea. Salkowski 2 con- 

 firmed this observation, and obtained similar results with sarcosin 

 and alanin, while Knieriem 3 and Salkowski 4 found aspartic acid also 

 to increase the urea output. 



The extent to which the administration of various amino-acids 

 will allow animals to maintain their nitrogen equilibrium was first 

 studied by Loewi, 5 who showed that such end products of digestion, 

 which no longer give the biuret-reaction, are still able to replace the 

 albumins destroyed during the metabolism. 



That amino-acids, when given in moderate amounts [glycocoll up 

 to 5 grins., z-alanin (3 grms.), leucin (8 grms.), phenylalanin (3 grms.)], 

 are completely broken up, has been shown by Abderhalden and 

 Bergell. 6 Given in excess (25 grms. to a dog), glycocoll appears 

 partly unchanged in the urine (Salkowski), and tyrosin given to 

 rabbits gives rise to tyrosin-hydantoin, according to Blendermanns. 7 



Nencki and Schultzens, Zeitschr.f. JSiol. 8. 124 (1872). 

 Salkowski, Zeitschr.f. physiol. Chem. 4. 100 (1880). 

 Knieriem, Zeitschr. /. Bid. 1O. 263 (1874). 

 Salkowski, Zeitschr. f. physiol. Chem. 42. 213 (1904). 

 0. Loewi, Arch.f. experim. Pathol. u. Pharm. 48. 303 (1902). 

 Abderhalden and Bergell, ibid. 39. 9 (1903). 

 7 Blendermanns, ibid. 6 234 (1882). 



