322 ELECTRO-PHYSIOLOGY CHAP. 



tory force is therefore the indirect cause of a positive increment of 

 potential, and, conversely, a negative increment of the one tends 

 to negative increase of the other. On this assumption the de- 

 pression of excitability in the anelectrotonised parts, and its rise 

 in such as are katelectrotonised, is quite intelligible : the greater 

 elastic force of the inhibitory spring in the anelectrotonic region 

 involves a greater expenditure of force in order to push back the 

 piston to the opening of the cylinder-sections, than in the normal 

 state ; the diminished energy of inhibition in the region of kat- 

 electrotonus involves less force. It is harder to explain, first, 

 how with low intensity of polarising current an excitation 

 generated at any transverse section can be transmitted through 

 katelectrotonised as well as anelectrotonised tracts in the 

 same way as through the nerve in the natural state (and, strictly 

 speaking, this is not the case), so that the stronger excita- 

 tion discharged above an ascending current produces a more 

 vigorous twitch than in the natural state, although it must be 

 transmitted through the anelectrotonised parts, which, with direct 

 excitation, give less response : secondly, how it is that at a consider- 

 able strength of polarising current the anelectrotonised parts lose 

 their conductivity also. These difficulties were, however, surmounted 

 by Ptiiiger. The conduction of excitation set up at any transverse 

 section is effected by the expenditure of the dynamic energy 

 discharged at the seat of stimulation upon the displacement of 

 molecular inhibition in the next section, the energy thereby 

 released in the second section displaces the molecular inhibition 

 in the next, and so on. The molecular inhibitions are less easily 

 displaced in the anelectrotonised parts in consequence of the 

 increased elasticity of the spring, more easily displaced in the 

 katelectrotonised parts, than under natural conditions. The fact 

 of unaltered conductivity in weak electrotonus therefore indicates 

 that in all conducting sections of the nerve, the magnitude of dis- 

 placement of the molecular inhibitions depends entirely upon the 

 amount of dynamic energy set free at the directly-excited trans- 

 verse section, and is proportional with the same in every section, 

 irrespective of whether the displacement of inhibitions is facilitated 

 or hindered. This is only possible if, when excitation is trans- 

 mitted from one section to the next, the total sum of dynamic 

 energy released is not consumed in the displacement of molecular 

 inhibition : such a proportional aliquot part only being required as 



