46o SCIENCE PROGRESS 



arrangement, however, as it may be supposed to take place by a 

 wandering of a hydrogen atom, thus : 



The form (II) is unstable. If a model be built up to represent 

 these formulae, it will be found that when the hydrogen atom 

 marked with an asterisk wanders back from the position (II) 

 it may give rise to (I) or (III). The action of the living tissues 

 in this case is evidently exerted to bring about the change 

 of (II) into (III) rather than of (II) into (I). 



Rosenfeld ^ has found that sugars are excreted in urine in 

 the following order : galactose, mannose, glucose ; while the 

 alcohols follow the analogous order : dulcite, mannite, sorbite. 



These differences are probably caused by some reaction 

 similar to that which takes place in the selective fermentation of 

 certain sugars, which was described above. 



Having dealt with the influence of the configuration of 

 optical antipodes upon their nutritive value, we must turn 

 to another side of the question, and consider the relations 

 between the configurations and toxic qualities of various com- 

 pounds. No general rule can be laid down in this case ; for, 

 as in the case of nutrition, the experimental data are here 

 far too meagre to allow of generalisation. 



In the first place, it is advisable to point out that in 

 some cases influences intervene which are only indirectly 



^ Rosenfeld, Centralblatt f, innere Medicin, 21, 177 (1900), 



