PHILOSOPHICAL SOCIETY OF WASHINGTON. 61 



by Du Bois-Reymond 27 to be equal to .022 Daniell in the sciatic 

 nerve of the frog. When a nervous impulse passes aloug the nerve 

 the natural current is diminished ; it experiences a negative varia- 

 tion, which, according to Bernstein, 28 when the impulse results from 

 a very potent stimulation, may more than neutralize the natural 

 current. The same physiologist has shown that this negative 

 variation moves along the nerves of the frog at the rate of 28 

 metres per second ; that is, at the same rate as the nervous impulse 

 itself, as determined without reference to the electrical phenomena. 



As in the case of the muscle-currents, these phenomena have been 

 differently interpreted by Hermann, 29 who denies the existence of 

 any natural nerve-current in uninjured nerves, and ascribes those 

 observed in the experiments to the circumstance that the parts of 

 the nerve dead or dying, in consequence of the section, become nega- 

 tive to the living nerve. The negative variation produced by the 

 stimulation of a nerve he explains by assuming that the stimulated 

 part of the nerve becomes, in consequence of the changes resulting 

 from the stimulation, negative to the unstimulated parts. I will 

 not attempt to enter to-night into the merits of the controversy still 

 in progress with regard to this question ; nor will I pause to discuss 

 the exceedingly curious and interesting phenomena of electrotonus, 30 

 concerning which, I will only say that the question has even been 

 raised by Radcliffe as to how far these phenomena are peculiar to 

 nerves, and how far they may be regarded as mere phenomena of 

 the electrical currents employed, which would be equally manifested 

 under similar circumstances if a wet string or other bad conductor 

 should be substituted for the nerve. 31 



However these disputes may be ultimately decided ; whatever 

 the actual facts with regard to the electrical manifestations in nerves 

 at rest or in action, may ultimately prove to be, there is a group of 

 easily repeated elementary experiments which seem to show pretty 

 distinctly that whatever the nervous impulse may be, it is not merely 

 an electrical current. 



It was known already when Haller wrote 32 that a string tied 

 tightly around a nerve, although it in no wise interferes with the 

 passage of electrical currents, puts a speedy end to the transmission 

 of nervous impulses. With this old experimental difficulty uncon- 

 tradicted, it seems strange that anyone should declare at the present 

 time that " the main objections raised to the electrical character of 

 nerve energy is based upon its slow propagation." 33 In fact this 



