I 6 ANIMAL ELECTRICITY. LECTURE I. 



That has been an electrical effect of a non- 

 electrical excitation, and I mieht with a little care 

 and a rather more sensitive oalvanometer demon- 

 strate a similar effect on the isolated nerve ; finally, 

 I might proceed a step further, and show that an 

 electrical effect accompanies a natural discharge of 

 nerve-impulses, as well as the impulses aroused by 

 all artificial stimuli, whether these be or be not of 

 electrical origin. But to do this would be super- 

 fluous to my present purpose, which is simply to 

 show^ that an electrical stimulus Is not indispensable 

 to an electrical effect. Electrical stimulation is 

 however so conveniently applied, can be so nicely 

 timed and graduated, that except in a few rare 

 cases w^e shall systematically make use of it, and 

 it was therefore essential that you should realise 

 at the outset that the electrical nature of the effect 

 is not determined by the electrical nature of the 

 stimulus. Later, when we shall examine the elec- 

 trical effects manifested by the heart and by the 

 retina, we shall see cause to be still more fully 

 convinced of this. 



In recollection of the fact that as regards muscle 

 the mechanical and electrical response to stimukition 

 run a nearly parallel course, and utilising the fact 

 first ascertained by du Bois-Reymond that an im- 

 pulse aroused at any part of a nerve Is conducted 

 in both directions from the stimulated point, we 

 may establish a comparison between the changes 



