118 THE NATUKE OF THE 



normal excitability; but neither of these two events alone acts as 

 a stimulus. 



Further on Hermann refers, quoting- experiments by Hering and 

 Biedermann, to a series of phenomena from which he attempts to 

 show that my theory is arbitrary, inasmuch as certain excitations 

 can be regarded either as make- or break-excitations. This I 

 fully admit, but would remark that no conclusion can be drawn 

 from such experiments, either for or against any theory. I shall 

 therefore not consider these experiments further. 



But I must refer more particularly to one point, which is 

 essentially of great significance for my theory, and has been 

 brought forward in objection both by myself and by Hermann. It 

 is well known that an opening excitation occurs, not only when 

 the whole exciting current is opened, but also on disappearance of 

 a portion of it. In the first case the stimulus was caused by 

 the appearance of the polarisation-current ; but can the same 

 explanation be offered if part of the original exciting current re- 

 mains ? The accompanying diagrams will express the alterations 

 in the current which occur in this case. 



Let us suppose that a current of strength S passed along a 

 nerve falls to zero at any moment t. According to the ordinary 

 theory it is this fall which produces the excitation, but according 

 to our theory it is the sudden appearance of the polarisation- 

 current in the opposite direction which at its first appearance 

 may have the same strength as the original current. If now 

 instead of letting this current fall to zero (or, which is the 

 essential point for us, instead of causing a polarisation-current 

 equal to the original current but opposite in direction to appear) 

 we let it fall to half its original strength, it is easy to see that 

 according to the above assumption the polarisation-current will 

 have, not the strength S, but only half the strength. [In other 

 words, if the polarisation-current produced by the passage of an 

 extraneous current S through a nerve is of such strength that they 

 mutually mask each other, the effect of opening the extraneous 

 current is to unmask a counter-current of which the initial inten- 

 sity is equal to S. If S is not opened but merely diminished, the 

 counter current will be similarly unmasked, but will have an 

 initial intensity equal to the amount by which S has been dimin- 

 ished. In the original this is illustrated by a figure which we 

 omit. EDITOR.] 



The first question, accordingly, which presents itself is as to the 



