106 THE NATURE OF THE 



action of a current occurs only on closure and at the cathode ; the 

 excitatory effect of opening a current begins, no doubt, at its 

 anode, but only because this is the cathode of the polarisation- 

 current at closure. 



In the region of the anode there is diminished excitability, and 

 with strong currents excitations cannot be transmitted from the 

 anode ; hence the diminution and disappearance of the make- 

 contraction with an ascending current, and, we now add, the 

 diminution and disappearance of the break-contraction with a 

 descending current ; for just as in the previous case there was 

 an obstruction at the anode to the transmission of an excitation 

 to the muscle, so now there is an obstruction at the anode of the 

 polarisation-current. 



On opening a polarising current there is, as is well known, 

 diminished excitability immediately afterwards in the region of 

 the cathode, increased excitability in the region of the anode. 

 The relation has apparently been reversed, but on our hypothesis 

 remains just the same ; for in the one case the cathode of the 

 primary current, while in the other the anode of the primary 

 current, is cathode to the polarisation-current. 



The above, as the reader will admit, is a series of very remarkable 

 agreements between what our hypothesis demands and the actual 

 facts. This agreement, however, holds still further. The well- 

 known 'Voltaic alternatives' consist in the fact that a nerve or 

 muscle through which a current has been passed for some time 

 becomes very sensitive to closure of a current of opposite direction, 

 while its sensibility to a current of the same direction is diminished. 

 The explanation is simple that the second current is, in the one 

 case in the same direction as the polarisation-current, in the other 

 case in the opposite direction. 



If our hypothesis as to the nature of the break- excitation is 

 correct, the stronger the secondary polarisation-current, and the 

 less the resistance it encounters, the earlier will a break-contraction 

 occur, provided always that its anode does not block the way from 

 the point of excitation to the muscle. Now my investigations 

 and Tigerstedt's have proved that within the periods taken for 

 stimulation-experiments the strength of the polarisation-current 

 increases with the duration of closure of the polarising current. 

 Nothing is easier to show than that with equal strengths of 

 current break-contractions occur much more readily if the current 

 is kept closed a little longer. Small fractions of a second make 



