THEOKY OF THE BBEAK-CONTE ACTION. 71 



this direction favours the occurrence of a break-contraction, which, 

 again finds its explanation in this, that the polarisation-current is 

 descending-, and the excitation therefore encounters no obstacle in 

 its progress to the muscle. If, now, the circumstances indicated by 

 Engelmann are in operation, a tetanus occurs in place of a simple 

 muscular contraction, when the current is broken. Supposing the 

 polarising current is again passed in the same direction before the 

 tetanus has ceased, the polarisation-current is arrested by the 

 polarising current ; the tetanus vanishes while the current is now 

 passing the second time, it generates a new polarisation-current, 

 which on interruption again produces tetanus. If now the direction 

 of the current is reversed, and the current again closed, there is 

 added to the polarisation-current another flowing in the same 

 direction, so that their negative poles coincide ; the tetanus must 

 increase. The voltaic alternatives are thus necessary consequences 

 of my theory. 



I have thus proved the agreement between all the most important 

 phenomena occurring when a polarising current is opened and the 

 corresponding phenomena arising when it is closed. In order 

 ' to subject the theory to a final test it still remains to examine 

 whether it is in accordance witji the recent researches of Biedermann 

 and Griitzner. 



In a very thorough investigation Griitzner x has shown the great 

 importance of the nerve-current proper in relation to the result of 

 electrical stimulation of nerves. All the phenomena with which 

 Budge, Pfliiger, Fleischl, and Hermann have made us acquainted 

 relative to the excitability of different parts of a nerve, he explains 

 by the action of the nerve-current, having proved that the current 

 of an ordinary nerve-preparation takes a different direction at dif- 

 ferent spots, and that therefore the exciting action of a current is 

 either strengthened or weakened, according as its direction is 

 opposed to or coincides with that of the nerve-current. 



In connection with these investigations Griitzner also succeeded 

 in showing the very great importance of the nerve-current as deter- 

 mining the opening contraction under certain circumstances. Let 

 us suppose that by means of an ascending current we stimulate a 

 divided nerve near its cut surface. The stimulating current is now 

 flowing in the opposite direction to the nerve-current, and three 

 things are possible ; the stimulation-current may be weaker than 

 the nerve-current, of the same strength, or stronger. If it is weaker 



1 Gnitzner, loc. cit. pp. 130-178. 



