CHAPTER X 



CATALYSIS IN RELATION TO THE CHEMICWL 

 PROCESSES IN LIVING MAITER 



The chemical reactions in protoplasm are under the 

 control of structure, as we have seen, and their velocity 

 is decreased and, in the case of the most characteristically 

 vital reactions, the specific syntheses, is reduced to zero 

 when protoplasmic structure is destroyed. If we class 

 this influence of structure as catalysis, the case becomes 

 one of heterogeneous catalysis, in which the reacting 

 substances are predominantly substances in aqueous 

 solution. Organic solvents, however, are also present, 

 represented chiefly by the lipoids; and, as in all cases of 

 heterogeneous catalysis, the interfacial relations are 

 undoubtedly of primary importance. The permanent 

 structural elements are chiefly protein in composition, 

 probably associated with lipoid; and this fact favors the 

 inference that the interfaces between the soUd protein 

 structures of the cell and the adjoining more fluid ])hases 

 are the site of the biologically essential reactions, and 

 especially of the syntheses. The fact that surface- 

 active substances as a class interfere so strongly with 

 these reactions favors this interpretation. 



The distinctive syntheses of living matter are those 

 of proteins. These are the syntheses on which specific 

 growth depends, and growth is the fundamental vital 

 activity. It thus appears probable that growth is 

 chiefly a result or expression of synthetic reactions 

 occurring at such interfaces; and the general susccpti- 



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