B.— CHEMISTRY 53 



We have particularly to note that, though the new tissue is built up 

 from symmetrical inorganic materials, each of its dissymmetric com- 

 ponents is produced in one only of its two optically active forms, and this 

 form is the same as that present in the tissue by which it has been 

 produced . 



We must therefore conclude that the chemical reactions concerned in 

 growth, or at any rate those concerned in the production of the primary 

 dissymmetric tissue components, are completely stereo-specific. The 

 mechanism concerned in the synthesis of, for example, glucose from 

 carbon dioxide and water produces dextro-giucose only without , apparently, 

 a trace of its enantiomorph. 



Let us now endeavour to imagine what the effect on the process of 

 growth would be if all the dissymmetric components of the growing tissue 

 were instantaneously racemised. On account of the stereo-specific 

 character of the mechanisms of growth we should then have two practically 

 independent mechanisms working side by side. We should have the 

 original mechanism producing dissymmetric compounds of the con- 

 figurations which occur in nature, <^-glucose, ^/-cellulose, J-tartaric acid, 

 /-leucine, and so on. We may arbitrarily call this the (/-system. The 

 concentrations of all its dissymmetric components would be reduced by 

 this racemisation to half their original values. Working alongside this, 

 and in practical independence, we should have the enantiomorphous 

 /-system producing antimers of the dissymmetric compounds found in 

 nature. 



The velocities of the different synthethic processes would be variously 

 affected by this change. The velocity of the fundamental process of 

 carbohydrate photosynthesis, the formation of the symmetrical compound 

 formaldehyde from symmetrical carbon dioxide and water, would remain 

 unchanged. This process is independent of mirror-image isomerism ; 

 there is thus no need for assimilation pigments to be optically active, and 

 chlorophyll is in fact described as being optically inactive. Again the 

 condensation of formaldehyde to glucose, in which a dissymmetric 

 polymerisation-catalyst must necessarily be involved, since normally the 

 d-iorm of glucose is alone produced, would take place initially with 

 unaltered velocity on account of the symmetry of formaldehyde. 

 Immediately after the change the inactive tissue would go on producing 

 JZ-glucose at the same rate at which the optically active tissue had been 

 producing ^/-glucose. 



As soon, however, as we come to consider the further transformation 

 of the first formed optically active products, the relative inefiiciency of 

 the optically inactive tissue becomes apparent. 



If, for example, the glucose in the tissue undergoes a transformation 

 involving interaction with another dissymmetric substance, such as a 

 polymerisation under the influence of a dissymmetric catalyst, then, as 

 we have already seen with our model, the inversion of sucrose, the process 

 should proceed less rapidly in the inactive than in the active tissue to a 

 degree dependent on the order of the reaction involved, provided always 

 that the concentrations are below those at which the catalyst becomes 

 saturated. 



