ELECTROTONUS. 221 



negative than they %uere. These changes are not, how- 

 ever, the same in degree at all points ; the change is 

 greatest in the immediate neighbourhood of the elec- 

 trode, and decreases proportionately with the distance 

 from- this. If the degree of positive increase from a 

 to n is indicated by Hnes, the height of which expresses 

 the increase, and if the tops of these lines are con- 

 nected, the result is the curve n p, the form of which 

 shows the changes in tension occurring at each point. 

 The changes on the kathode side may be represented 

 in the same way, but that in this case, in order to 

 show that the tension on that side becomes more nega- 

 tive, the lines may be drawn downward from the nerve. 

 The curved line q n', is the result. The two portions 

 of the curve n p and q n' then show the condition of 

 the extrapolar parts of the nerve. Nothing is really 

 known of the condition of the intrapolar portion of the 

 nerve, for, for external technical reasons, it is im- 

 possible to examine this.^ We can only suppose that 

 changes in tension such as those indicated by the 

 dotted curve p q occur there. 



If the curve in fig. 60 is compared with the dia- 

 gram of the changes in excitability during electro- 

 tonus (as given in fig. 31, page 130), the analogy 

 between the two phenomena is very striking. The 

 two really represent but different aspects of the same 

 process — of the changes, that is, which are induced in 

 the nerve by a constant electric current. Comparison 

 of the two curves shows, however, that when the 

 tension becomes more positive the excitability is de- 

 creased, and that when the tension becomes more 

 negative the excitability is increased. The change 

 ^ See Notes and Additions, No. 13. 



