70 CONTRIBUTION TO THE 



injured nerves maintained by the enquirers named with reference to 

 the break-contraction cannot therefore be regarded as established 

 by faultless experiments. 



In the numerous experiments relative to the law of contraction 

 which I have made on nerves still connected with the spinal cord, 

 I have never observed the break -contraction absent when its 

 presence was to be expected, and when the experiment was rightly 

 made. 



My theory is as little capable of explaining opening tetanus as 

 the laws of du Bois-Reymond and Pfliiger are able to account for 

 closing tetanus without a further assumption. The two phenomena 

 are attributable to the same cause. The most likely theory, in my 

 opinion, is that of Engelmann J , according to which both closing 

 and opening tetanus are dependent on a latent state of stimulation 

 of the nerve from the influence of temperature, evaporation, or other 

 causes. Of course this stimulation by itself is not sufficient to elicit 

 tetanus, but it becomes so in parts of the nerve in which the ex- 

 citability is increased ; that is, in the neighbourhood of the negative 

 pole after closure, and in that of the positive pole (the negative 

 pole of the polarisation-current) after opening. This explanation 

 may or may not be sufficiently complete ; the chief point, in any 

 case, is, that the opening tetanus is to be regarded as the equivalent 

 of the closing tetanus ; and I shall content myself in this paper 

 with establishing a parallel between the phenomena occurring when 

 a current is opened and those which present themselves when it is 

 closed. In the breaking tetanus the excitation starts from the 

 negative pole of the polarisation-current, which is what my theory 

 requires. 



The phenomenon of the c voltaic alternatives ' can be very simply 

 explained by my theory. We know that, if a weak current is 

 passed in the same direction with another current already traversing 

 the nerve, its action is very considerably increased, since the exciting 

 point now falls on a part of the nerve of which the excitability is 

 increased. On the other hand, the excitation-effect by the closure 

 of a weak current in the opposite direction is diminished, since the 

 exciting point then falls on a part of the nerve where the excita- 

 bility is lowered 2 . We shall see how the voltaic alternatives may 

 be explained from this point of view. 



We will suppose that the polarising current is ascending, because 



1 Engelmann, Archiv fur die ges. Physiologic, iii. p. 411, 1870. 



3 Compare Griitzner, Archiv fiir die ges. Physiologic, vol. 28, p. 143, 1882. 



