ELECTEICAL BKEAK-EXCITATION. 113 



currents are conducted much better through the closed derivation- 

 circuit than through the nerve itself. This experiment, which has 

 been already described by du Bois-Reymond, shows how great an 

 influence the polarisation-current (in this case chiefly external) 

 exerts on the appearance of break-contractions 1 . But even with 

 unpolarisable electrodes, and therefore with an internal polarisation- 

 current only, the same thing occurs, though not to the same extent. 

 Thus the less the resistance to the polarisation-current the more 

 readily do break-contractions occur. These I shall call ' polarisation 

 break-contractions,' in contrast to the ' additive' break-contractions 

 previously referred to. 



In conclusion, I shall shortly refer to a break-contraction which, 

 differs from that already mentioned in that its appearance is retarded. 

 In my preliminary communication I regarded this phenomenon, 

 which had been observed by Pfliiger and was recently studied more 

 thoroughly by Biedermann, as due to the fact that the anode of the 

 polarisation after-current lay between the point of stimulation and 

 the muscle, and hindered for a shorter or longer time (for the 

 strength of the polarisation-current rapidly diminishes) the excitation 

 from reaching the muscle. This explanation applies of course only 

 to the case of opening descending currents, with which Pfliiger had 

 also exclusively observed this phenomenon. My experiments on this 

 subject are however as yet incomplete, therefore I shall not give an 

 account of them at present. 



Apart from this retarded break-contraction, we have met with 

 three distinct kinds of break-contraction in this investigation : 

 (i) additive in the same direction ; (2) additive in the opposite direc- 

 tion, due to the appearance of the nerve-current ; and (3) polari- 

 sation break-contractions, due to the appearance of the current of 

 internal polarisation. All these break-contractions can, as we have 

 seen, be shown to be caused by, or, to speak more cautiously, to be 

 coincident with the appearance of a new current rather than the 

 disappearance of the original one. They may all therefore be 

 in reality make-contractions. At any rate, we know with absolute 

 certainty that closure of a current passing through a muscle or 

 nerve excites these organs : when we see, on the other hand, that 

 on opening a current a new current comes into existence, we are 

 justified in inferring that it is the coming into existence of the 



1 This meets the objection in Hermann's paper, p. 105. He inferred from my 

 preliminary communication that I had only used polarisable electrodes in my experi- 

 ments. 



