82 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



is found to be the most stable arrangement, while rings of more 

 than seven atoms are difficult if not impossible to prepare. 



Further it has been found that differences in the constitu- 

 tion of certain nitrogen compounds find their best explanation 

 on the assumption of a varying arrangement in three-dimen- 

 sional space of the groups attached to the nitrogen. 



Recent researches by Pope and by Kipping have extended 

 the idea of space-isomerism to the derivatives of silicon, tin 

 and other elements. Pope has also recently developed a 

 theory according to which the crystalline form of every sub- 

 stance is minutely dependent upon its molecular structure, thus 

 confirming Pasteur's original suggestion, while approaching 

 the subject from the side of the molecule rather than from the 

 side of the crystal. 



These references to recent developments in space- 

 isomerism, or stereo-isomerism, have been made because 

 remarkable relationships have been found to exist between 

 the actions of enzymes and the stereo-chemical configura- 

 tion of the molecules of the substances upon which they 

 act ; in fact, a very common method for obtaining an 

 active substance from the inactive mixture, which results 

 from ordinary methods of preparation, consists in submitting 

 such an inactive mixture to the action of certain organisms 

 or the enzymes secreted by them, when one modification is 

 generally attacked at a different rate from the other. Further 

 references to this subject, and also to the theory of the natural 

 production of optically active substances, will be made later. 

 We have now to consider a class of substances which perhaps 

 more than any other serve as the basis for extremely important 

 fermentation processes, viz., the sugars. 



INTRODUCTION TO THE CHEMISTRY OP THE SUGARS 



The term ' sugar ' as popularly understood generally refers 

 to cane sugar or preparations made from it. Chemically 

 speaking, however, the word has a much wider application, 



