x ELECTROMOTIVE ACTION IN NERVE 325 



excitability (positive modification) appears, and slowly subsides, in 

 the previously anelectrotonic portion of the nerve, on opening the 

 current. Pfliiger takes this to mean that the action of the 

 constant current weakens the energy of molecular inhibition, 

 which is highly probable, seeing that, according to his theory, 

 the current acts during its passage upon the inhibitory forces, but 

 not directly upon potential energy. The weakened inhibitory 

 force left over at break must obviously present less resistance to 

 the transformation of potential into active energy than it would 

 on resuming the proportions normal to it before closure of the 

 current ; and this explains how the nerve that is depressed by 

 current comes to be more excitable, i.e. apparently invigorated. 

 The restitution of the normal inhibitory forces, as gradually 

 brought about by metabolism, explains the subsidence of the positive 

 modification. The brief negative modification that appears in the 

 region of katelectrotonus after opening the current is explained by 

 Pfliiger as a momentary deficit of potential energy, and this again 

 by the fact that katelectrotonus (sv^ra) keeps the sluice permanently 

 open, i.e. causes a continuous outflow of potential energy. 



Lastly, with regard to the after-effects of the polarising current, 

 manifested in a more or less prolonged discharge of potential 

 energy, Pfliiger has shown that the opening tetanus starts from 

 the region of anelectrotonus; this indicates that there is, on opening 

 the more sustained currents within the previously anelectrotonised 

 tract, a persistent discharge of potential energy. If we represent 

 this as the displacement of the piston by the reinforced spring, and 

 assume that the column rises so much under the action of the water 

 in A, that the piston is pushed back again to the spiral opening, 

 there will be then a considerable accumulation of water at A. 

 If the elasticity of the spring is suddenly depressed, the column of 

 water will push the piston far back, and a greater quantity of 

 water will flow for a longer time, until equilibrium is restored 

 again. This process corresponds with the opening tetanus. 



Pfliiger's theory thus succeeds in presenting the main phenomena 

 of electrical excitation of nerve under the figure of a complicated 

 mechanical schema : it gives no real explanation of them. It 

 seemed, however, advisable to give the theory in detail, seeing 

 that it found wide acceptance. While Pfliiger himself developed 

 his hypothesis independently of du Bois-Keymond's molecular 

 theory, Bernstein attempted later to establish a direct relation 



