292 ELECTRO-PHYSIOLOGY CHAP. 



Series I. and II., a diminution of excitability at the kathode, 

 not merely while the current is passing but also after the polaris- 

 ing current has been opened. This lasts longer in proportion with 

 the intensity and duration of the current. Such a muscle, after 

 prolonged rest, possibly not for several minutes, will recover 

 itself so far that an induction current homodromous with that 

 which exhibited twitches previous to polarisation will again 

 produce excitation. Normal kathodic excitability is, however, 

 much more quickly restored, even when spontaneous recovery is 

 abolished on account of widespread local fatigue, if the polarising 

 current is reversed for a short time. Closely allied with this, 

 also, is the fact that anodic excitability is usually considerably 

 augmented after a not too brief polarisation of a curarised muscle, 

 provided the battery current is of adequate intensity. 



Although these manifestations of the so-called ''voltaic 

 alternative " have long been known, it has not been sufficiently 

 taken into consideration that this is just as much a polar, i.e. 

 purely local, effect of current as in the excitatory process at the 

 kathode. Heidenhain (43) discovered that muscles, the excita- 

 bility of which had been depressed by any injurious influences 

 (tetanising, protracted passage of current, heat, etc.) to such a 

 degree that they did not react perceptibly even to the closure of 

 very powerful currents, recovered their excitability partially, at 

 least, after they had been exposed for some time to the action of a 

 strong ascending or descending current, excitation occurring again 

 on opening the polarising, or closing a heterodrouious current, to 

 a greater or less degree : Rosen thai (44) pointed out the connection 

 between these facts and the phenomena of the voltaic alternative 

 in fresh, non-fatigued muscle, which he was the first to investigate. 



According to these observations, which are easy to confirm, 

 the response of every muscle sinks, with prolonged passage of 

 current in one direction, towards the closure of such a current, 

 being, on the contrary, considerably augmented for the opening as 

 well as closure of a current in the opposite direction. The first 

 effect, as was shown above, is dependent upon a state of fatigue 

 confined exclusively to the kathodic points. 



The experiments which led to this conclusion show, moreover, 

 that the increase in response to closure of a homodromous current, 

 demonstrable after break of an adequate polarising current, is 

 characteristic of the anodic points of fibres. 



