ELECTRICAL AND OTHER FACTORS 257 



the rhythm of an automatic pulsation may be altered. 

 During the flow of the current the catalytic effect at 

 the cathode is heightened, while at the anode it is 

 decreased or the rhythm may be abolished.' The i)aral- 

 leHsm between these effects and those produced by the 

 constant current on the action of rhythmical tissues 

 hke the heart is evident. 



A more detailed account of the phenomena in film- 

 covered metallic systems of this kind is not possible 

 within the limits of space, but attention should be called 

 to another interesting feature of the electrical initiation 

 of these reactions. A pecuharity of the electrical 

 activation of passive iron is that it is not readily produced 

 by currents which rise slowly from a minimal strength to 

 a strength sufficient to activate with sudden closure.^ In 

 other words, the rate of change of the activating current 

 is an essential factor in the effect produced. This is a 

 well-known and highly characteristic feature in the 

 response of living tissues to electrical activation. Each 

 tissue has its characteristic time-factor of electrical excita- 

 tion or so-called ''chronaxie," and this is closely related 

 to the rate of change required of a stimulating current 

 (cf. p. 288). The time-relations of the activating current 

 in the metalKc system resemble those in livinp: tissues 

 in the further respect that in the case of alternating 

 currents the relation between the intensity required 

 for activation and the rate of alternation follows the 

 same law, as shown by Bredig and Kerb for the mercury 

 H2O2 system ;3 that is, there is an inverse relation bc- 



^ Bredig and Wilke, Biochcm. Zeitschrift, XI (1908), 67. 

 'Science, XLVIII (1918), 57- 



3 Bredig and Kerb, Verh. naturhisiorisch-mcd. Verrins zu llfidfl- 

 berg, X (1909), N.F., 23. 



