52 SECTIONAL ADDRESSES 



of living matter in which every dissymmetric component was present in 

 equal quantities of both its antimeric forms. 



This can perhaps be made clearer by consideration of some reaction 

 which we might regard as a simplified model of a biological process. Let 

 us consider the hydrolysis of dextro-sucrose by invertase, at not too great 

 concentrations, so that the velocity of hydrolysis is approximately pro- 

 portional to the concentrations both of substrate and of enzyme, and 

 compare the initial rate of inversion with what it would be if we employed 

 instead inactive materials at the same total concentrations — ^/-sucrose 

 and inactive invertase. From the known specificity of the action of 

 invertase we may safely assume that ordinary invertase would activate 

 dextro-sucrose only and that its mirror image would activate Ifevo-sucrose 

 only. 



Then it is clear that in the first experiment every sucrose molecule that 

 encountered invertase would be susceptible of activation by it, whereas 

 in the second only half the encounters would be potentially effective and 

 the reaction would proceed at only half the rate at which it takes place 

 in the optically active mixture. 



Great caution is obviously necessary in applying the law of mass action 

 to biological processes, since adsorptions on enzymes and on active 

 surfaces have to be taken into account ; if in our model we had sufficiently 

 increased the sugar concentrations, so that the enzyme was working at 

 its maximum capacity, there would have been little or no difference 

 between the rates of hydrolysis in the active and the inactive mixtures. 



If, however, we are justified in assuming that in living matter con- 

 centrations of this order are not approached, and that diminutions in 

 concentration of a molecular species would be accompanied by an approxi- 

 mately proportionate fall in the velocity of the reaction or reactions in 

 which it was concerned, then the inactivation of living matter by the 

 instantaneous replacement of half of each of its optically active components 

 by their enantiomorphs would suddenly diminish the rates of all the stereo- 

 specific reactions proceeding in it to rates approximating more or less, 

 in the case of reactions of bimolecular type, to one-half of their former 

 magnitudes. 



Thus, in a general way, it is clear that if we are right in assuming that 

 the reactions of living matter include reactions of a stereo-specific type, 

 then living matter must gain very greatly in efficiency through the optical 

 activity of its dissymmetric components. 



Let us now consider the optical activity of living matter in connection 

 with the phenomenon of growth. 



In the growth of, for example, a vegetable organism of a primitive 

 undifferentiated type we observe the existing tissue building up, with the 

 aid of absorbed radiant energy, tissue of the same nature as itself from 

 the materials of its inorganic environment. 



We have an association of chemical compounds which is capable of 

 synthesising from simple inorganic materials each of the organic materials 

 of which it is itself composed, and the rates of production of these are 

 controlled, so that each is produced at a rate which, on the average, is 

 proportional to the amount of it present in the tissue. 



