STEREOISOMERIC SUBSTANCES 479 



metabolism supposedly unite with urea rests. For example, 

 taurin, CA^ ' , according to Salkowski appears as tauro- 



\HSOi 



/NH(CO.NH 3 ) 



carbaminic acid, CA/ . Analogous statements are 



NHSO, 



made of sulphanilic acid, ethylamine, sarcosin, tyrosin and 

 phenylalanin. However, from the observations of Dakin 

 upon tyrosinhydantoin (Vol. I of this series, pp. 16 and 47, 

 Chemistry of the Tissues) and those of Weiland 66 it appears 

 that not only on boiling a urine after the addition of an 

 aminoacid, but on merely steaming it over a water bath, or 

 even on concentrating a neutral aqueous solution containing 

 urea and an aminoacid at a temperature of the water bath 

 not above 45 C. uraminoacids are formed. We are not at 

 present in position to make any assertions as to the physio- 

 logical significance of these acids. It is quite possible that 

 they are altogether artificial products of extracorporeal de- 

 velopment (vide supra, p. 98). 



Combinations of glycuronic acid will not be dealt with 

 here, as they have been considered previously. 



Behavior of Stereoisomeric Substances in the Body. 

 These considerations of the behavior of body-foreign sub- 

 stances in intermediate metabolism may be concluded by 

 directing attention to the importance of the stereochemic 

 configuration of such substances from this point of view. 



The recognition of this significance goes back to the 

 classical studies of Pasteur upon the influence of moulds 

 upon paratartaric acid and those of Emil Fischer upon the 

 variations in the behavior of stereoisomeric methylglu- 

 cosides toward invertin and emulsin. Since then a number 

 of other comparable observations have been collected. For 

 example, studies upon asymmetric cleavage of racemic man- 

 delic acid methylester, and brominated stearic acid glyceride 



M W. Weiland (G. Embden's Lab., Frankfurt a. M.), Biochem. ^Zeitschr., 

 38, 385, 1912. 



