PRODUCED BY A CONSTANT CURRENT. 21 



In the description of the experiments these abbreviations are 

 used. 



+ P = the distance of the positive pole from the muscle. 

 P = the distance of the negative pole from the muscle. 

 E = the distance of the spot stimulated from the muscle. 

 Kli = the number of rheochord units in the derivation circuit 1 . 

 7 = the position of the sliding-weight on the lever. 



Partly to represent the results more clearly, partly to give 

 sufficient proof of the superiority of the mechanical method of 

 stimulation for investigations relating to the general physiology 

 of nerves, I have appended to the description of the experiments 

 reproductions of my curves in fairly large number 2 . 



1. The extrapolar changes of excitability at the negative 

 pole of an ascending current. 



With weak and moderate currents the excitability is considerably 

 increased. This increase attains its full strength directly after 

 the current is closed. An intensity of the stimulus which shortly 

 before called forth quite feeble muscular contractions or none at 

 all, now evokes very strong ones. The increased excitability 

 is observed during the whole time the current is closed. Never- 

 theless the contractions diminish in course of time, though to a 

 very slight extent, sometimes indeed scarcely appreciably, and in 

 many cases not at all. If the current is opened the contractions 

 resume their previous magnitude. No inhibition showed itself with 

 the conditions under which my experiments were conducted ; on 

 the contrary a slight augmentation of excitability set in after the 

 current was opened. This increase, however, as already pointed 

 out, is trifling and is not always distinctly apparent. It lasts a 

 longer or shorter time and gradually disappears. 



During the closure of the current the increase is greatest at 

 the negative pole, and from thence stretches upwards. The greater 

 the strength of the polarising current, the greater also is the 

 change of excitability, and the more distinctly do its attendant 

 phenomena appear. At the same time it extends over larger 

 tracts of the nerve. 



If the experiment is repeated in such a way that the polarising 

 current is opened and closed in regular succession, while its 



1 Cf. Hermann, Archiv fur die ges. Physiologic, vii, 1873, p. 333. 

 a These have been omitted, as it appeared that the experimental results could 

 be understood without them. 



