x ELECTROMOTIVE ACTION IN NERVE 323 



suffices for the extent of displacement involved by the strength of 

 stimulus, viz. a larger proportion in the region of anelectrotonus, 

 where displacement is less easy ; a smaller amount in that of 

 katelectrotonus, where it is facile. Pntiger illustrates this 

 hypothesis by the figure of a wheel turning on a horizontal 

 axis, its revolutions being aided or hindered by the greater or 

 less pressure of a sliding spring. This wheel carries, at the 

 peripheral end of a horizontal spoke, a laterally -projecting, 

 horizontal paddle. A thin stream of water falls on this from 

 above, and thus presses down the wheel, until the paddle is pushed 

 out of reach of the stream of water. The proportion of the falling 

 stream of water, i.e. of the dynamic energy available, required by 

 this constant revolution of the wheel, is greater in proportion as 

 the spring presses more heavily upon the wheel, and the latter 

 therefore revolves less easily. The reason that the anelectro- 

 tonised parts lose their conductivity in pronounced electrotonus 

 would accordingly be that, in consequence of the excessive rise of 

 inhibitory energy, the total sum of active energy discharged by the 

 stimulus is no longer adequate to bring about the corresponding 

 displacement of molecular inhibition, just as, with undue pressure 

 of a spring against the wheel, the whole column of water is 

 inadequate to move the paddle, with the wheel, beyond its reach. 

 The fundamental law of electrical excitation at the poles, as laid 

 down by Pfliiger, whereby the commencement of katelectrotonus 

 produces the closure twitch, the disappearance of anelectrotonus 

 the opening twitch, is explained by himself as follows, upon this 

 theory. The commencing anelectrotonus reinforces the inhibitory 

 energy, and therefore displaces the piston D of the schema in the 

 direction of the arrow ab, driving it away from the opening of the 

 sluice ; obviously no fluid can then escape from the opening g. On 

 the contrary, the streaming out, i.e. the conversion of potential into 

 active energy, is now even less possible than in the previous rest- 

 ing state of inhibition ; it is therefore impossible that excitation 

 should ensue from the entry of anelectrotonus. The opposite occurs 

 at the region of the kathode. The commencing katelectrotonus 

 diminishes inhibitory energy, weakens the elastic force of the 

 piston spring, the piston is pushed by the overwhelming hydro- 

 static pressure in the direction of the arrow cd, the mouth by 

 which the fluid escapes is freed, in other words, there is a dis- 

 charge of potential energy. If the energy lost in the discharge 



