184 ELECTRO-PHYSIOLOGY . n.vr. 



already seen that the same effect appears in striated muscle. 

 There we had direct proof of " false " break twitches caused 

 by internal short-circuiting of the demarcation current, compen- 

 sated during closure of the battery current in the leading-off 

 circuit. It is natural to apply the same explanation to the 

 primary break twitch from the transverse section, in nerve- 

 excitation. This was actually done by Griitzner (41) and 

 Tigerstedt (41), who only go too far, inasmuch as they deny 

 any real break excitation due to fall of the current, and assume 

 that every so-called opening excitation is constitutionally an 

 effect of closure, deriving from an interference between exciting 

 current and nerve current, which last may be either a demarca- 

 tion or a polarisation current. 



As against this view it must be maintained that in nerve, as 

 in muscle, there is a true opening excitation, viz. a reaction of the 

 excitable substance towards the changes produced by current 

 (at the anode). The interference effects between exciting current, 

 and pre-existing differences of potential, which underlie the 

 " false " opening twitches, can only be dealt with later, in 

 discussing the electromotive action of nerve. 



Since (as appears directly from the above) the effects of 

 exciting motor nerves with the constant current depend essen- 

 tially upon the relations of excitability in the nerve, we should 

 anticipate a fairly complicated reaction from a nerve -muscle 

 preparation, inasmuch as it presents a multiplicity of functional 

 elements, differing in excitability as was shown, e.g., for the 

 rheoscopic frog's leg with flexors and extensors supplied by a 

 common nerve-trunk, and in a far higher degree in the crayfish 

 claw. As regards the first case, it may be remarked that, accord- 

 ing to Griitzner (42), the excitation of the frog's sciatic with 

 currents of increasing intensity excites quite different muscles 

 at closure, and at a later period. If there is eventually an 

 adequate break excitation, those muscles alone twitch which first 

 became active at closure. The opening stimulus thus acts here 

 (with stronger currents) like a weak closing excitation. The 

 same may be observed on man when the electrodes of a sufficiently 

 strong battery are applied to the sulcus bicipitalis interims. At 

 a certain strength of current, the muscles that twitch at make 

 and at break are different (flexion of lumd at make, pronation at 

 break). 



