ELECTROMOTIVE ACTION IN NERVE 



321 



FIG. 2-20. 



there is an opening g in the horizontal arm of the cylinder, 

 which Pfliiger conceives to be spiriform, its highest point lying next 

 the piston. If the elasticity of 

 the spring is increased, it presses 

 more strongly upon the piston, 

 pushes it farther from the opening 

 g, and displaces the fluid in front 

 of it, which then rises higher in 

 the vertical limb, and there is in- 

 creased hydrostatic pressure. If, 

 on the other hand, the elasticity 

 of the spring is diminished, the 

 fluid displaces the piston in the 

 opposite direction cd, and pushes 

 it more or less away from the 

 opening g, which is then reached 

 by the fluid, which, on streaming out, acquires vital energy deriving 

 from the height of fall. With this streaming out, the hydrostatic 

 pressure diminishes, so that the force of the spring gradually 

 pushes the piston back again over the opening and ends the 

 discharge. 



We have next to see how this schematic mechanism explains 

 the reaction of the living transverse section of the nerve with 

 respect to excitation, conductivity, and excitability, and, in the first 

 place, the phenomena and laws of electrotonus. This explanation 

 follows simply from the following hypothetical premiss as set out 

 by Pfliiger. The electrical current flowing through a portion of 

 the nerve alters the force of molecular inhibition, and this alone, in 

 a direct sense, with no immediate modification of potential energy. 

 The effect of current on the inhibitory force is to increase it in 

 the region of anelectrotonus, and diminish it in that of katelectro- 

 tonus, i.e. the elastic force of the piston-spring increases in all 

 sections of the cylinder, which represent anelectrotonised sections 

 of the nerve, and decreases in those that are katelectro- 

 tonised. Further, in the anelectrotonic region the inhibitory force, 

 i.e. the piston D, is displaced in the direction of the arrow ab, 

 whereby the potential energy, i.e. the height of the column of fluid 

 at BO, increases, while in the katelectrotonic region, on the con- 

 trary, the piston is displaced in the direction cd, so that potential 

 energy is indirectly diminished. A positive increment of inhibi- 

 VOL. n Y 



