156 COMPARATIVE ELECTRO-PHYSIOLOGY 



as between the equatorial point A and the two terminal 

 sections a and a' ; that symmetrical points c c\ b b\ a a\ are 

 equipotential ; and that a point relatively nearer the terminal 

 section is galvanometrically negative, in reference to one 

 further away from it. It will also be seen that this electrical 

 distribution is exactly the same as that seen in a muscle- 

 cylinder, with terminal sections, as given in fig. 104. 



Thus, without the postulation of any electro-motive mole- 

 cules so-called, these experimental results afford a simple 

 and direct explanation of the so-called current of injury, as 

 the excitatory after-effect of strong stimulation. 



FIG. no. Electrical Distribution in Plant-cylinder with Opposite 

 Ends Sectioned 



The Current of Injury is simply therefore an excitatory 

 after-effect, due to incomplete recovery from over-strain. 

 But even after strong stimulation a slow recovery may occur, 

 and the Current of Injury will thus undergo a progressive 

 diminution. This will probably account for Engelmann's 

 observation that in medullated nerves the E.M.F. of the 

 artificial cross-section fell, by as much as from 25 to 60 

 per cent, in the first two hours after section, and disappeared 

 altogether within twenty-four. The renewal of the cross- 

 section he found to renew the original difference. This is 

 an obvious case of renewal of the effect by re-stimulation. 



The disappearance of negativity, owing to recovery, only 



