EON THE INTERNAL POLARISATION OP NERVES. 79 



mtinues for several minutes with constantly diminishing 

 strength, and almost never entirely disappears, so that for a new 

 experiment with the same tract of nerve, compensation must 

 usually be employed to bring- the needle to zero 1 . Hermann's con- 

 clusions relative to the electrotonic after-effect occurring- outside 

 the electrodes we need not consider in the following investiga- 

 tion. 



Since then, no enquirer, so far as I know, has given a thorough 

 study to the subject of internal polarisation in nerves. Yet a property 

 which is so markedly conspicuous in nerve and muscle, as compared 

 with other moist conductors, would seem to deserve investigation. 

 Perhaps one might arrive at new and important points of view 

 with regard to the way in which these tissues react to the electric 

 current. 



The investigations here communicated concern only nerves, partly 

 because these appear to offer greater preliminary interest, partly 

 because in muscle the contraction and the change of position which 

 it entails exert a disturbing action on the investigation. In all 

 probability the same laws hold good for the internal polarisation 

 of muscle as for that of nerve. A future investigation will throw 

 further light on this question. 



In my experiments the polarising current was conducted to the 

 nerves by the same electrodes as were used to lead the polarisation- 

 current to the galvanometer. By this proceeding I hoped to be 

 able to apply directly the results obtained to the phenomena which 

 occur in excitation experiments with a constant current. 



The experiments were arranged as follows. From the battery S^ 

 (fig. 3), the polarising current passes through a rheochord 1th. 

 introduced as a derivation-circuit, to a Pohl's reverser J? 15 and 

 from there through a mercury key K and a Morse key T to the 

 nerve NN 9 from which it returns to the reverser, and so on. 

 Through the opposite arm of the Morse the current is taken to 

 the galvanometer G. The ' rest-current ' of the nerve is compen- 

 sated in the usual manner by means of a du Bois' compensator CC 

 (represented in the diagram as a straight line). 



A spring s keeps one arm ^ of the Morse pressed against the 

 plate a, so that the contact t 2 -b leading to the galvanometer is 

 open. If contact is made at this point by pressing on the other 



1 Hermann, "Untersuchungen zur Physiologic der Muskeln und Nerven, iii. pp. 71-74 ; 

 Berlin, 1868. 



