B.— CHEMISTRY 51 



under the favourable conditions of the laboratory, it is impossible not to 

 feel a certain scepticism of an explanation based on the action of circularly 

 polarised light thus produced. 



It is true that circularly polarised light of greater intensity might be 

 produced by naturally occurring doubly-refracting minerals ; but its 

 production in this manner would be necessarily so highly localised and so 

 evenly distributed between the dextro- and laevo-forms that it is difficult 

 to believe that initially optically inactive living matter could be rendered 

 optically active through the agency of circularly polarised light produced 

 in this way. 



It would, therefore, seem not out of place to seek for other possible 

 causes of the dissymmetry of living matter, and it may be profitable to 

 inquire whether the property of growth which is characteristic of living 

 matter may not necessarily lead to its dissymmetry. 



We know that many components of living matter are substances of 

 great molecular complexity, and the more complex the substance the more 

 likely it is to be molecularly dissymmetric, and, as a matter of fact, a 

 large proportion of the compounds which occur in living organisms are 

 optically active. 



Again, many of the reactions which go on in living matter, and on 

 which vital activity depends, are thus reactions between molecularly 

 dissymmetric compounds. 



Now when a reaction takes place between two molecularly dissym- 

 metric compounds, there is always more or less difference between the 

 velocities of reaction of a given antimer of the one compound with the 

 two antimeric forms of the other. Thus, as was shown by Marckwald 

 and McKenzie, Isvo-menthol reacts more rapidly with dextro-mandelic 

 acid than it does with laevo-mandelic acid. 



It is easy to see why this should be. Chemical interaction between 

 organic compounds necessitates the apposition of the two reacting groups 

 in a particular manner, and when each of the reacting groups possesses 

 a complex environment it is evident that there must be a difference in the 

 readiness with which a dissymmetric molecule can be thus apposed to the 

 dextro- and Isevo-forms of a co-reactant molecule. 



We can express this by saying that reactions between molecularly 

 dissymmetric compounds are stereo-specific , and it is fairly obvious that, 

 in general, the more complex the compounds the more highly stereo- 

 specific reactions between them are likely to be. 



It is therefore probable that many of the reactions on which vital 

 processes depend are highly stereo-specific. Of isolated reactions that 

 can be studied in vitro, it would seem that those most nearly related 

 to the reactions of living matter are reactions involving enzymes, and it 

 is well known how highly stereo-specific these may be. 



Now in living matter, every dissymmetric component is present in one 

 only of its two antimeric configurations, and it appears that the configura- 

 tions of these components are so correlated that each dissymmetric 

 molecule encounters only that antimer of its dissymmetric co-reactants 

 with which it interacts the more rapidly. It is evident that living matter 

 thus constituted must be greatly more efficient than a hypothetical form 



