132 



ELECTRO-PHYSIOLOGY 



CHAP. 



by less steepness of pitch and more extended time-distribution. 

 We may affirm without hesitation that nerve and muscle are 

 thrown into a much more protracted state of excitation by linear 

 variations of current of a finite pitch than by momentary stimuli. 

 The same may be true of physiological innervation. The 

 strikingly low rate of oscillations of the muscle-current, as noted 

 by Loven, both in strychnin-tetanus and in voluntary innervation, 

 on the capillary electrometer, makes it probable that a complete 

 tetanus may none the less occur in the frog's muscle, while 

 induction shocks must act at considerably greater frequency to 

 produce the same effect. 



II. INFLUENCE OF DIRECTION UPON THE EXCITING 

 EFFICIENCY OF CURRENTS 



In addition to pitch, density, and duration, as well as kind 

 of increase, of the exciting current, the effect of electrical excita- 



Fio. 184. Schema for the transverse excitation of nerve. (Hermann.) 



tion of the nerve depends, as in muscle, upon direction of current, 

 with reference both to arrangement of fibres and to peripheral organ 

 at the working end of the nerve. As regards the former, it was 

 known to Galvani that transverse passage of current through a 

 motor nerve at as nearly as possible right angles to the axis of 

 the fibres produced no effect. Galvani bridged the nerve across 

 a moist and not very thick thread (Fig. 184 a\ through which he 

 led a constant current. In consequence of the narrow path of 

 the current through the nerve, there are comparatively few 

 opportunities for the formation of longitudinal components, 

 though these are by no means entirely excluded. On the other 

 hand, it is doubtful whether any considerable fraction of the 

 current traverses the nerve, unless very strong currents are made 



