ELECTROTONUS. 165 



experimental evidence is given as to whether any part 

 of the " mild galvanic current " accounted for the work 

 done, and its action was most likely that of an addi- 

 tional stimulus both to nerve action and the removal 

 of fatigue stuffs. Therefore, in the meantime, we may 

 take electricity into account solely in its capacity of a 

 stimulus. 



When a galvanic stream is sent along a nerve the latter is 

 thrown into the state called " electrotonus," which, however, is 

 a merely physical state, and may be represented by any moist 

 cord except for the changes caused on the protoplasm of the 

 living nerve by the action as a stimulus. Thus, in the state of 

 electrotonus, if moderate, the irritability may be increased 

 just as under moderate heat, while by excessive electric action 

 it is paralyzed, or destroyed altogether. The most powerful 

 action as a stimulus is produced by changes of intensity of the 

 current. Besides these actions as a vital stimulus, it appears 

 that as a physical force an opposing current may neutralize and 

 stop the nerve current (which, whatever its nature, is also pro- 

 bably a physical force), but whether physically or as a paralyzing 

 agent seems not determined.* In addition to these there are 

 an immense number of facts known which have probably little 



* From the recent experiments of Mr. Dew Smith, of Cambridge, 

 the influence would appear to be physical ("Journal of Anat. and 

 Phys.," Nov., 1873). Mr. S. stimulated the sciatic of a frog by elec- 

 tricity simultaneously at two points, one farther from the muscle than 

 the other. The force, he observes, of the muscular " contraction result- 

 ing is the same as when the near point only is stimulated: but when a 

 small interval of time is allowed to elapse between the two stimulations 

 the contraction increases, rising to a maximum as the interval is 

 lengthened, and afterwards dividing into two independent curves." 

 This is not merely a variation of the phenomena of summation of con- 

 tractions as observed by Helmholtz, for these apply to maximum shocks 

 only. The experimenter thinks it implies "a block of nervous im- 

 pulses," for a current proceeds in both directions from the two points 

 stimulated, and the two impulses moving in opposite directions mu- 

 tually antagonize each other. This, I think, points more to the neu- 

 tralization of movements of a physical force rather than to a paralytic 

 vital influence, and it may throw light on the nature of inhibitory 

 nerve action. 



