STEREO-CHEMISTRY AND PHYSIOLOGY 459 



thirds of the excreted substance being in the active form, show- 

 ing that the racemic compound had been broken down into its 

 components, one of which had been destroyed. It is therefore 

 obvious that the formation of racemic arabinose due to disease 

 must take place in an organ so situated that after being 

 liberated from it the arabinose is not submitted to any process 

 of decomposition. 



Since a difference in configuration such as exists between 

 dextro and laevo forms has such a pronounced effect on the 

 nutritive values of the arabinoses, it is not astonishing that 

 Nagano 1 found a similar difference between laevo xylose and 

 laevo arabinose, the former being more easily absorbed by the 

 system. The configuration formulae of the two substances are 

 shown below. 



Analogous results were obtained by Neuberg and Meyer 2 

 in the case of the mannoses, CH 2 OH . CHOH . CHOH . CHOH . 

 CHOH.CHO. The dextro form appeared best suited for 

 nutrition. The chief point of interest for stereochemical workers 

 lies in the fact that during the passage of the dextro, laevo 

 and racemic compounds through the system derivatives of 

 another sugar, glucose, were produced. The formulae of 

 df-mannose and af-glucose are given below. 



As can be seen from an inspection of the formulae, the 

 change from mannose to glucose necessitates the rearrangement 

 of the groups attached to the lowest carbon atom in the formula. 

 Such a rearrangement implies no great strain on the molecular 



1 Nagano, Pfluger's Arc/u'v., 90, 389 (1902). 



2 Neuberg and Meyer, Zeit. physiol. C/ie/n., 37, 530 (1903). 



