348 



ELECTRO-PHYSIOLOGY 



CHAP. 



It is evident that not merely the muscle-fibres corresponding 

 with the plate, but those surrounding it also, would be similarly 

 excited ; under normal conditions, however, this is experimentally 

 found not to be the case. Moreover, the lines of current traverse 

 the adjacent fibres at right angles to the long axis, i.e. in the 

 ineffective direction. There are certain artificial, and therefore 

 a priori improbable, conditions under which such a distribution of 

 potential might come about in the plate, " that the resulting current 

 through the corresponding fibres should be perceptibly denser 

 than in the adjacent fibres," but these commend themselves the 

 less in that they at once destroy analogy with the electrical plate. 

 It is, e.g., conceivable that a P.D. should arise at the under-surface 

 only of the end-plate, on excitation (Fig. 228); this would then 



t 



at the moment of discharge form " a mosaic of positive and nega- 

 tive points, between which only molecular currents circle, and 

 these, at a distance equal to the least diameter of the plate, would 

 be of imperceptible density." Considering further that the facts 

 of comparative histology of the motor nerve-endings are in direct 

 contradiction with the theory of discharge, since the presence of 

 true typical end-plates appears to be confined to the muscles of 

 the higher vertebrates, a few fishes, and insects, the theory in its 

 original form is hardly tenable. Du Bois-Eeymond accordingly 

 proposed a " modified theory of discharge " ; but this is scarcely 

 more acceptable than the first, since its postulates are equally 

 inadequate. 



" Definite anatomical relations are required to account for 

 the inefficacy of the process towards adjacent muscle-fibres, and 

 should consist in a slight, hook-shaped curvature of the extreme 

 end of each hypolemmal nerve-fibre on to the surface of the con- 



