62 BULLETIN OF THE 



latter objection is altogether a subordinate difficulty which may 

 perhaps be entirely explained away ; the main experimental objec- 

 tion does not relate to the velocity, but to the conditions, of the 

 propagation of the nervous impulse. If, instead of tying a string 

 around it, the nerve be merely pinched or bruised well with a pair 

 of forceps so as to destroy its delicate organic texture ; if it be com- 

 pressed tightly by a tiny metallic clamp ; if it be divided by a sharp 

 knife, and the cut ends brought nicely into contact, or brought in 

 contact with the extremities of a piece of copper wire, it will still 

 conduct electrical currents as well as ever, but can no longer transmit 

 the nervous impulse. So, too, there are certain poisons, such as 

 the woorara, which completely destroy the capacity of the nerve 

 for transmitting nervous impulses, without in the least diminishing 

 its conductivity for electricity. 34 



In view of these and other practical difficulties, the best instructed 

 modern physiologists no longer attempt to identify the nervous 

 impulse with the electrical phenomena by which it is accompanied. 

 Du Bois-Reymond himself has suggested that the nervous agent " in 

 all probability is some internal motion, perhaps even some chemical 

 change, of the substance itself contained in the nerve-tubes, spread- 

 ing along the tubes." 35 Herbert Spencer came to the conclusion 

 that " nervous stimulations and discharges consist of waves of mo- 

 lecular change" 36 flowing through the nerve-fibres; and I suppose 

 that most physiologists at the present time think of the nervous 

 current in some such way as this. Even those who attach most 

 importance to the electrical phenomena will, I take it, agree with 

 Michael Foster, that these " are in reality tokens of molecular 

 changes in the tissue much more complex than those necessary for 

 the propagation of a mere electrical current." 3: 



We do not, however, as yet possess any sufficient foundation of 

 facts on which to build a reasonable hypothesis as to the nature of 

 the molecular disturbances that accompany a nervous impulse. 

 The labors of the physiological chemists have taught us nothing 

 with regard to the changes that go on, except that the axis-cylinder 

 which, in the inactive living nerve is alkaline, becomes acid after 

 long continued activity, or after death. 33 We can measure the 

 velocity with which the impulse travels ; we can stiffly the con- 

 ditions under which it arises ; we can believe, as I certainly do, that 

 it will ultimately receive a chemico-physical explanation, but its 

 real nature we do not yet know. 



