310 Biological Chemistry. 



It will be observed from the above table that the 

 higher acids undergo oxidation, whereas benzoic and I 

 phenylacetic acid do not. These acids, whether injected 

 directly or formed as oxidation products of higher acids, I 

 are not excreted as such in the urine. They form I 

 conjugation products with glycine in the organism, ben- 

 zoic acid being excreted in the form of hippuric acid, 

 C 6 H 5 -CO-NH-CH 2 -COOH,and phenylacetic acid as phenyl- 

 aceturic acid, C 6 H 5 -CH 2 -CO-NH-CH 2 -COOH. Similar cases i 

 of conjugation taking place in the animal organism have I 

 already been referred to, notably those of the glycuro- j 

 nates (p. 286), when conjugation takes place with an 

 oxidation product of sugars. In this case, conjugation 

 takes place with glycine, derived apparently from the 

 proteins by hydrolysis. 



The results obtained by Knoop have led him to pro- 

 pound his /3-oxidation theory. According to this, the 

 carbon atom in the /3-position in a fatty acid is selected 

 for oxidation. The degradation of phenylvaleric acid 

 would be represented, therefore, by the following stages : 



C 6 H 5 -CH 2 .CH 3 .JCH 2 COOH -* C 6 H 5 -CH 3 j.CH 2 .COOH->C 6 H 5 COOH 



Phenylvaleric Acid. Phenylpropionic Acid. Benzoic Acid. 



In the cases of benzoic and phenylacetic acid no 

 /5-carbon atom exists, and they are excreted unchanged. 

 This theory of /3-oxidation has not been universally 

 accepted ; but Dakin has shown that fatty acids can be 

 degraded by similar stages in vitro, when they are sub- 

 mitted to oxidation by hydrogen peroxide at 37. 

 It is also noteworthy that the fatty acids derived from 

 milk-fat and other animal fats always contain an even 

 number of carbon atoms. Whatever may be the ultimate 

 conclusions as to the mechanism of the destruction of acids 

 in the organism, Knoop's investigations form an interesting 



