ANIMAL ELECTkI(IT\. LK<:TUkK V. TO7 



in last resort physical, and, as we shall see, of electro- 

 lytic origin, are, nevertheless, entitled to the rather 

 indefinite qualification "physiological." 



Interrupt the physiological continuity of the nerve 

 between the leading-in and leading-out electrodes, by 

 crushing it in the interpolar region e' p (fig. 44), or 

 better by touching it with a drop of strong acid. The 

 physiological conductivity is abolished, the physical 

 conductivity is intact (or enhanced if acid has been 

 used), but the extrapolar effects A. and K. are com- 

 pletely abolished. 



Raise the temperature of the nerve above 40°, or 

 lower it to sav — S°, and al though — in the first case at 

 least — the physical conductivity has been enhanced, 

 the extrapolar currents, A. and K. are abolished, either 

 temporarily or permanently. 



There is no time to-day for me to show you a 

 properly made temperature observation, as given in 

 fig. 6^) (and it is only as I am speaking that it occurs 

 to me that we might have made a rough and expedi- 

 tious trial by merely dropping the nerve into some 

 hot salt solution), but I can at once show proof that 

 the A. and K. effects you have just witnessed did not 

 depend upon current-escape. Pinching the nerve 

 with forceps, and then testing as before, we find 

 that they are completely abolished. There is no 

 deflection whatever, i.c ., no current-escape. 



These currents depend therefore upon the physio- 

 logical state of the nerve —upon its "vitality" — and I 



