ORIGIN OF ENZYMES 363 



a very important part, but it does not seem to be the sole 

 determinant, it simply constitutes a part of the general 

 organisation of the living system. 



As has been pointed out above, nucleic acid itself also 

 arises in the living organism in accordance with the same 

 rules as the other components of the protoplasm, that is to 

 say, on the basis of strictly co-ordinated, constantly repeated, 

 catalytically induced exchange reactions. ^^ 



It is clear that no substance which forms a major com- 

 ponent of protoplasm can be reproduced by a chance or 

 easily attained relationship between the rates of reactions. It 

 requires the absolutely constant, continually repeated chains 

 and cycles of reactions which together comprise the network 

 of the self-reproducing, living, open system. As we have seen 

 above, the origin of such a system may be regarded, theoreti- 

 cally, as a result of the directed evolution of our original, 

 dynamically stable, colloidal formations. 



The living systems which were first formed already had 

 all the features needed for their selection to be of the nature 

 of purposeful ' natural selection ' in the biological sense of 

 the expression. Further improvements in their internal 

 organisation, rationalisation of their metabolism, therefore, 

 went forward at a faster pace. As a direct result of this, all 

 intermediate forms of organisation were destroyed, swept 

 from the face of the Earth by natural selection. This is why 

 we have now no possibility of studying these forms directly 

 and filling in, with factual material, the abyss which exists 

 between the organisation of the original systems and the 

 organisation of even the simplest of present-day organisms. 



The evolution of metabolism : the origin 

 of enzymes. 



Experiments with models which reproduce the phenomena 

 in dynamically stable colloidal formations may, perhaps, play 

 an important part in this connection. Studies of this sort 

 are, however, still only beginning to be made* and the 



* In particular in the form of attempts to incorporate active preparations 

 of enzymes in the coacervate drops with a view to conferring some 

 dynamic character on the drops. — Author. 



