Manchester Memoirs, Vol. xlii. (1898), No. 12. 9 



as has been especially shewn by the researches of Waller, 

 this current of action may be taken not only as the token, 

 but also as an exact measure of vital activity; the sweep 

 of the current rises or falls as the power of the nerve fibre 

 waxes or wanes. 



Taking this electric change as the sign and, indeed, as 

 the measure of the events in a nerve fibre which constitute 

 its phase of activity, and which we speak of as a " nervous 

 impulse," we are able to estimate the features of nervous 

 impulses, the rate at which they travel along a nerve fibre, 

 the length of nerve fibre occupied by a nervous impulse 

 as it sweeps like a wave along its course, and such rises 

 or falls of its amplitude as may from time to time occur. 



In this way we find no essential differences between a 

 nervous impulse of natural or of artificial origin. When a 

 nerve fibre is stimulated at any point of its course by an 

 electric current or other artificial stimulus, or when it is 

 thrown into action in a natural way, and is the instrument 

 of sensations or of voluntary or other movements, the 

 nervous impulse, as shewn by the electric change, possesses 

 the same essential features, such difference as occurs being 

 one of energy only. Further, we have reason, by the same 

 token, to think that when a nervous impulse sweeps along 

 even a great length of fibre, it does not materially change 

 otherwise than perhaps by somewhat diminishing as it 

 parses along. 



Further, while it is a prominent characteristic of the 

 tissues of the living body in general that activity, whether 

 natural or artificial, when carried beyond certain narrow 

 limits, leads to fatigue and ultimately to exhaustion, 

 careful observations shew that to the nerve fibre under 

 artificial stimulation exhaustion is unknown. Every com- 

 plete nervous mechanism, involving more than the mere 

 nerve fibre, is not only subject to fatigue, but is perhaps more 

 readily subject than are even other tissues, as is notably 



