224 ELECTRO-PHYSIOLOGY CHAP. 



and that the opposed, direction of current to the closure excita- 

 tion, no external changes being perceptible. It can scarcely 

 be doubted that this state also must be interpreted by local 

 fatigue confined to the point at which current leaves the con- 

 tractile substance, since there is no reason for assuming alterations 

 of excitability in the intrapolar tracts, either positive or negative ; 

 while, 011 the other hand, it is indubitable that the excitatory 

 process at the (" physiological ") kathode occurs not merely at 

 the moment of closure, but is also continuous, although as a 

 diminishing quantity, during the entire passage of the current. It 

 must therefore be taken as proven, that at least those tracts 

 of the muscle, over which the persistent closure excitation extends, 

 are more fatigued than the rest of the muscle, in which no 

 manifestations of excitation can be detected during longer passage 

 of not excessively strong currents. 



The difference between local and general fatigue of a muscle 

 is very pronounced when the response of a muscle fatigued by 

 tetanus is compared with that of one that has been polarised by 

 the constant current. Uniform stimuli (single induction shocks 

 are best), whose efficacy for the normal muscle has been tested, 

 are sent into different points, and the difference in height of 

 twitch before and after fatigue determined. In the first case the 

 excitability of the entire muscle will be much diminished, and 

 entirely abolished for weaker stimuli (that had previously been 

 effective), while a polarised muscle reacts to stimuli acting 

 upon its continuity, as well as before the passage of the current, 

 although the closure of a current, in the same direction as 

 the " polarising " current, produces no sign of contraction, 

 when it happens to coincide in its point of exit. From 

 this we may conclude that the cause of failure of excitation 

 in this case is to be sought in alterations localised at the 

 point at which the current leaves the muscle-substance, or in 

 close proximity to the same. This also appears from the effects 

 of closing a current opposed in direction to the polarising current, 

 when the excitation will be discharged at the point which 

 was formerly the seat of the anode. The closure twitch 

 observed under these conditions in the polarised muscle is con- 

 siderably greater than before the passage of current (voltaic alterna- 

 tive). If this is correct, the effects of excitation by an induction 

 current must vary according as it is sent longitudinally through 



