314 PROTOPLASMIC ACTION AND NERVOUS ACTION 



particular living system under consideration thus 

 determine the duration and other special features of 

 its action-currents, and hence also the time-relations of 

 the dependent or correlated phenomena; e.g., velocity 

 of transmission, refractory period, summation, and 

 chronaxie. 



The passive iron model again affords a clear and 

 simple illustration of the manner in which rapid electro- 

 motor fluctuations can result from changes in the char- 

 acter of the boundary layer between the two chemically 

 interacting phases. When such a wire, immersed in a 

 solution of nitric acid and connected through a voltmeter 

 with an indifferent electrode (platinum wire) also 

 immersed in the acid, is activated, a sudden change of 

 potential (of about 0.7 volt) is observed. With strong 

 acid (60 vols, per cent 1.42 acid or stronger) this variation 

 is automatically and rapidly reversed and the metal 

 resumes its former potential within a second or two; 

 this reversal is a result of the re-deposition of the passivating 

 surface-film; the chemical reaction then ceases. Under 

 certain conditions the return of complete passivity may 

 be delayed, or rhythmical fluctuations of potential and 

 chemical activity may occur; the latter phenomenon is 

 frequent in a somewhat weaker acid (between 50 and 55 

 volumes per cent), and depends upon the alternating 

 formation and dissolution of the passivating film.^ 

 Many striking electrical phenomena, having features 

 which have been regarded as especially characteristic 

 of bioelectric processes, are in fact exhibited by this 

 model. These phenomena show that rapid variations of 



^ For a fuller description of these phenomena cf. my article in Jour. 

 Gen. Physiol. (1920), op. cit., pp. 1 13-15. 



