ON NERVE-EXCITATION BY THE NERVE-CURRENT. 135 



As a matter of fact, beginning with tJie weakest currents entering the 

 nerve by its transverse section, one first obtains the maJce -contraction at 

 closure of the nerve-circuit, and only with stronger currents at closure 

 of the battery-circuit as well. And similarly in the case of the break- 

 contraction. 



Biedermann 1 has recently examined the relative inefficiency of 

 currents which pass out of a nerve at its transverse section; a 

 phenomenon which he has found especially striking in the case 

 of the nerves of warm-blooded animals. Concerning this matter 

 one must be careful to distinguish, in a current that flows through 

 the nerve, between such branches as have their course in the ex- 

 citable substance of the nerve fibres from those which traverse 

 constituents of the nerve which simply do duty as physical con- 

 ductors, in other words, the physiologically important from the 

 physiologically unessential. The points where any such physio- 

 logically important current enters or leaves the excitable substance 

 of a nerve fibre are to be regarded as its physiological anode or 

 kathode. If now a certain part of the proper nervous substance of a 

 fibre is electromotive, as we may, according to Hermann, assume 

 the part adjoining an artificial transverse section to be, and if the 

 current arising at this spot is opposed in direction to any branch 

 current from the battery, then it is clear that a passage of the 

 latter through the electromotive portion of the fibre can only 

 occur when the nerve-current which already exists at that spot is 

 overcompensated by the current which is led in, this requiring, of 

 course, a relatively strong battery-current. Supposing further that 

 the electrical current excites the nerve only at its' point of exit 

 from the excitable substance, then an excitation by a current leaving 

 the nerve by a transverse section would not be possible unless this current 

 were sufficient to overcompensate the nerve-current at its source. 



As to how far the current, once it has exceeded the local strength 

 or density requisite to this internal compensation of the nerve- 

 current, can act as an excitant to the electromotive portion of the 

 nervous substance by means of its residue, so to speak, must for the 

 present remain unanswered on account of the alteration of the 

 nerve-substance which obtains here. Beyond this point the current 

 no longer finds any excitable substance. 



Similar considerations may be urged concerning the relative 



1 Beitrage zur allg. Nerven- und Muskelphysiologie, Sitzungsberichte, Vienna, vol. 

 Ixxxiii, Part iii, p. 289, 1881. 



