CATALYSIS AND BIOCHEMICAL PROCESSES 221 



Zn ions to enter the solution more rapidly and hence 

 accelerates the formation of the structure-forming pre- 

 cipitate of zinc ferricyanide.^ 



There is reason for believing that the remarkable 

 chemical activity of living matter, as well as its sus- 

 ceptibility to electrical influence and to stimulation, 

 is largely dependent on physical conditions which are 

 fundamentally of the kind just described. For example, 

 during stimulation the excited and the unexcited areas 

 of the reactive protoplasmic surface — the surface of the 

 irritable cell, neurofibril, or other structure concerned — 

 are at different electrical potentials; apparently the 

 current flowing between these two areas produces chem- 

 ical effects which secondarily determine the propagation 

 of the state of excitation and hence the distinctively 

 physiological effect or response. There is a close analogy 

 here to the case of local circuits in metals immersed in 

 electrolyte solutions; these circuits also form the con- 

 dition for the transmission of chemical effects. This 

 general condition will be considered more fully under 

 the subject of stimulation; at present it is sufficient to 

 call special attention to it as probably forming a highly 

 important factor in the catalytic or quasi-catalytic 

 action of Hving protoplasm. Here we use the term 

 "catalytic" simply as a designation for the remarkable 

 property shown by living protoplasm of enabhng reac- 

 tions to occur, at a relatively high velocity, which are 

 absent or inappreciable in dead protoplasm. 



The most familiar form of catalysis observed in 

 living organisms, and the one showing the closest parallels 



^ Cf. my two papers on precipitation growths from metals, Biological 

 Bulletin, XXXIII (191 7), 135, and (with E. N. Johnston) XXXVI (1919), 

 225. 



