272 ELECTRO-PHYSIOLOGY 



CHAP. 



in the second nerve ; in other words, at the strength of current 

 employed, the second nerve is directly excited as far as c', as soon 

 as the current is applied at b : thus the experiment only shows 

 that the electrotonus spreads in both nerves with equal rapidity, 

 and gives no conclusions as to the rate of this transmission. 



Another series of experiments refers to the time-development 

 of the electrotonic changes of excitability, which as was pointed 

 out by Pfliiger are in close relation with the galvanic effects, 

 and, as it were, merely represent another symptom, or another side 

 of the same underlying process in the nerve. It is therefore 

 legitimate to draw conclusions from the temporal distributions of 

 the one alteration to that of the other. Pfltiger (32) has, more- 

 over, demonstrated by direct experiment, at least for anelectrotonus, 



FIG. 208. 



that the alterations of excitability appear simultaneously with 

 the galvanic alterations. 



If (Fig. 208) a strong ascending current (ab) is passed steadily 

 through the central end of the nerve of an ordinary nerve-muscle 

 preparation, the myopolar portion of the nerve falls into anelectro- 

 tonus ; the corresponding incremental current can be led off by 

 a second pair of electrodes (cd) situated within the same region, 

 to the nerve B of a second preparation, so that this is traversed 

 at the same distance from the muscle, but in the opposite, i.e. 

 (in the respective position of both preparations) ascending direc- 

 tion. As soon as the primary nerve (cd) becomes electromotive, 

 under the presumption of a transmission of electrotonic alteration 

 at given rapidity from the polarised region db y a branch current 

 passes at the same moment through ef, and produces secondary 

 excitation in this nerve. From the fact that it is invariably the 

 muscle (B), and never that of the primary preparation (A), that 

 twitches, Pfliiger concludes that at the time when the electro- 

 tonic incremental current traverses the tract (cd) of the first 

 nerve - muscle preparation, and excites the second muscle to 

 secondary (paradoxical) contraction, the same incremental current 

 which excites the second muscle leaves the first at rest ; i.e. in 



