220 THE ORIGIN OF LIFE 



artificial cells in gelatin media. But as the 

 element is more unstable, the analogy to living 

 forms becomes more marked. So that by the 

 method of extrapolation we may reasonably hope 

 to reach ultimately those substances which in a 

 similar manner produce cells which might very 

 appropriately be said to be alive. 



We have seen that by the presence of such 

 substance or substances in the nucleus the process 

 of metabolism can be maintained. In such in- 

 stances as have been mentioned the metabolism 

 is purely artificial, and it does not seem as if it 

 were much more than a secondary efiect. But 

 this is not so, since the assimilation would depend 

 upon the separate molecular aggregations formed, 

 which would influence the catalytic interactions 

 in the cell itself. Living proteid is protoplasm 

 under the influence of these disturbances, which 

 keep the molecular and atomic interactions, that 

 constitute metabolism, going. 



The question then arises, and very naturally so, 

 as to whether these metabolisms are of the same 

 nature as the metabolisms which living proteid 

 actually undergoes. The answer is that the cells 

 in one case, namely the artificial ones, can be 

 regarded as nothing more than models of the 

 original in nature. The labile constitution of 

 living proteid, as distinct from the state of stable 

 equilibrium of dead proteid, may be accounted for 

 in some such way, but whether the actual chemical 

 changes are the same it cannot, of course, be said ; 



