64 CONTRIBUTION TO THE 



These experiments may suffice to show the agreement between 

 Griitzner's results and the polarisability of different tracts of the 

 nerve. On what this difference of polarisahility depends does not, 

 as I have already pointed out, concern the question with which we 

 are now occupied. It is probably due, mainly at least, to the 

 greater conductivity of the thicker parts of the nerve. I have not 

 attempted to determine whether other circumstances also exert an 

 important influence. 



We have found, therefore, a most remarkable parallelism between 

 the break-contraction and polarisation, not merely in the funda- 

 mental phenomena, but also in those of secondary importance. I 

 may therefore venture to regard polarisation as the cause of the 

 break -con traction, which, accordingly, is neither less nor more than 

 a make-contraction dependent on the existence of a polarisation current. 



It is self-evident that the absolute magnitude of the polarisation- 

 current cannot be regarded as an objection to this theory. The 

 exciting action of a current is conditional, not on its strength alone, 

 but also on the abruptness of its commencement. It is for this 

 reason, for example, that the effect of an induction-shock on the 

 nerve is so much greater than that of the constant current. The 

 current of polarisation, already in existence during the passage of 

 the polarising current, must come into action when the latter is 

 opened, with an abruptness almost equal to that of an induction- 

 shock, and so produce an excitation in spite of the smallness of its 

 absolute strength. From this quarter, therefore, so far as I can 

 see, no objection can be made to my theory. When the circuit of 

 the polarising current is broken, that of the polarisation current is 

 closed through the physiologically inactive nerve-sheaths, indepen- 

 dently of any external derivation. In order to test still further 

 this theoretical view, as well as its working capabilities, I shall 

 now enquire whether we can obtain a simple and unstrained ex- 

 planation of all the well-established phenomena presenting themselves 

 on interruption of the polarising current. 



III. 



The fundamental conception in my theory of the break-contraction 

 is the reference of all the phenomena appearing on interruption of 

 a current to those which are exhibited on its closure. This once 

 made good, it then only remains to explain scientifically the make- 

 contraction and its attendant phenomena, to enable us to construct 

 a satisfactory theory of the action of the electric current on nerve. 



