270 BACTERIOLOGICAL AND ENZYME CHEMISTRY 



already described, to separate these mixtures into their 

 optically active constituents, as well as to produce optically 

 active compounds in the first instance, if an optically active 

 substance is used as a starting point. Thus, e.g., cane 

 sugar can be synthesised by comparatively simple reactions 

 from glucose and fructose, but in aU cases where an opti- 

 cally active body is obtained, the agency of life steps in at 

 some point. 



This important fact was clearly realised by Pasteur, whose 

 words on the subject are worth quoting : ' To transform 

 an inactive compound into another inactive compound, which 

 has the power of resolving itself simultaneously into a right- 

 handed compound and its opposite, is in no way comparable 

 with the possibiHty of transforming an inactive compound into 

 a single active compound. This is what no one has ever done ; 

 it is, on the other hand, what hving nature is continually doing 

 before our eyes.' 



It is to the action of enzymes present in the living proto- 

 plasm, especially in chlorophyll, that we must look for this 

 selective synthetic power of the plant cell. We have learnt, 

 through the work of Croft Hill and others, that the action of 

 an enzyme may show itself in a building-up or anabohc process, 

 as well as in a breaking-down or catabohc process. We may 

 perhaps conceive of the enzyme as a kind of framework into 

 which the molecules must fit themselves, in order that a certain 

 substance may be produced, either on the up or down grade of 

 a chemical change. Thus, in the case of maltose, we can con- 

 ceive the various atomic groupings setting themselves to form 

 maltose, or, on the other hand, passing back through the same 

 framework to form glucose, the hexose which, it will be 

 remembered, is produced when maltase acts upon maltose. 

 Similarly invertase may act as the framework for the building 

 up or breaking down of cane sugar. 



It is evident that our knowledge of this subject is still of a 

 speculative character, but enough has been said to indicate the 



