84 THE BENZOIC ACID GROUP. 



never contained hippuric acid, but only benzoic acid. Hence, too, 

 it is that we so often meet with only benzoic acid in human urine, 

 which, as it contains a far smaller proportion of hippuric acid, 

 must be employed in larger quantities ; and if some portions of it 

 have been long exposed to the air, which can hardly be avoided, 

 they produce such a change that only benzoic acid is found in the 

 whole urine. Hence it appears to be the fact, as Liebig assumed, 

 that a ferment is formed in the urine through which the nitro- 

 genous hippuric acid is converted into benzoic acid; for if we mix 

 a specimen of urine containing benzoic acid, whether from man or 

 from the horse, with another specimen containing hippuric acid, on 

 separating the acids from the mixture we almost constantly obtain 

 benzoic acid alone, the ferment of the urine containing benzoic acid 

 probably acting on the hippuric acid of the fresh urine even during the 

 evaporation of the mixture. Moreover, the conversion of benzoic 

 acid conveyed into the organism, into hippuric acid, which was 

 invariably observed by Wohler and Keller*, Ure,f and sub- 

 sequent experimenters, is in accordance with the idea that the 

 former, when it occurs in the urine, is only a product of decom- 

 position of the latter. 



Action. We shall return to the behaviour of benzoic acid in 

 the living animal body when we treat of hippuric acid. We will 

 here only remark that the ingestion of this acid causes an extremely 

 disagreeable irritation in the throat, and subsequently a very profuse 

 diaphoresis ; and, finally, that it is one of the very few acids which 

 produce a marked augmentation of the acidity of the urine. 



NON-NITROGENOUS ACIDS. 



We make a special group of these acids, although their sole 

 representative is lactic acid. Although this acid deserves a special 

 chapter in every work on physiological chemistry, we see good 

 reason for classing it in a special group of acid bodies. We have 

 already remarked (see p. 56) that in its composition lactic acid 

 presents a close analogy to metacetonic acid ; it is more than pro- 

 bable that many other acids exist which stand in the same relation 

 to the individual members of the first-described group of acids, as 



* Ann. d. Ch. u. Pharm. Bd. 43, S. 108. 



t Medico-Chirurgical Transactions. Vol. 24, p. 30 . 



