244 PROTOPLASMIC ACTION AND NERVOUS ACTION 



Facts like these (the so-called '^ preferential catalysis") 

 may be regarded as e\idence of conditions which in 

 their higher developments in Hving organisms appear 

 as the highly selective specificity of many enzymes. 



The recent work of Langmuir and Harkins^ has 

 shown that molecules assume definite orientations at the 

 surfaces at which they are adsorbed. This orientation is 

 undoubtedly a factor in the chemical effect produced; 

 reactive groups may thus be brought into a position in 

 which they more readily come into contact with other 

 molecules (or the reactive groups of other molecules), 

 and in this manner reaction is furthered. Cases of 

 preferential catalysis may thus be explained. The 

 catalytic effectiveness of phase-boundaries exhibits itself 

 in many remarkable ways. Taylor and Langmuir^ 

 cite Faraday's observation that a perfect crystal of 

 sodium sulphate does not efiioresce until its surface is 

 scratched or broken, when the effiorescence spreads from 

 the injured part over the rest of the crystal. Other 

 similar examples are well known; apparently the 

 reactivity of molecules is altered by the adjacent 

 molecules of reaction-product: the use of ''catalyst- 

 promoters" in chemical processes illustrates the same 

 phenomenon. Enhanced reactivity at interfaces is in 

 fact a very general phenomenon; and in Hving matter, 

 with its polyphasic constitution, the conditions are 

 exceptionally favorable for this type of influence. 



' Langmuir, loc. cit.; Harkins, loc. cit. 



2 H. S. Taylor, " Catalysis and Catalytic Agents in Chemical Pro- 

 cesses," Jour. Franklin Inst., CXCIV (1922), i; Langmuir, "Chemical 

 Reactions at Surfaces," Trans. Faraday Soc, XVII (192 1), Part III 

 (September); reprinted in Gen. Elec. Rev., XXV (1922), 445. 



