PHYSIOLOGY OF NERVE 261 



successively electrically negative (zincative) to the rest. This has 

 been termed the current of action, and the negative variation is 

 evidently only a particular case of this, namely, when the response 

 from one spot is altered by the presence of an injury there ( 4 ), 

 neglecting for the present certain possibilities to be considered 

 later. 



These remarks can therefore be summarised thus : 



(1) Any injured spot is electrically negative (zincative) to any 

 uninjured. 



(2) Any active spot is as a rule electrically negative (zincative) 

 to any inactive spot. 



Injury and excitation give, therefore, as a rule, an electrical 

 response of the same sign. Whether this is the result of the same 

 process or not is a matter that is not quite as simple as at first 



Rg.HLr 



'' Electro tonufi. 



sight might be supposed, though there is undoubtedly a close 

 connection between the two responses. 



There is still another phenomenon to be noted in excised 

 medullated nerve. If a constant current be passed through one 

 part of the nerve, the extra-polar parts of the same nerve also give 

 a current, the electronic current (Fig. 3). 



These various electric effects have been subjected to elaborate 

 investigation and experiment, because they are the only direct 

 unequivocal signs of nerve activity. The actual metabolism of 

 nerve is at best very slight in amount. It is true that deprivation 

 of oxygen for some hours paralyses a nerve ( 5 ' 6 ' 7 ), that the result 

 of excitation gives an effect similar to that of C0 2 ( 8 ), and that 

 experiments to be noted later give some indication of fatigue, 

 but there is no detectable change in the reaction of nerves as a 

 result of activity (unless certain experiments referred to later are 

 to be interpreted in this sense), and there is no other effect such as 

 that of heat produced or of mechanical shortening l that shows 



1 If a nerve is excited at one end by maximal induction shocks, and the 

 other end examined with suitable precautions under a microscope magnifying 200 

 diameters, no shortening or movement of any kind can be detected. But 'Waller 



