148 ON NERVE-EXCITATION BY THE NERVE-CURRENT. 



The great excitability exhibited by the nerves of cooled frog's in 

 the vicinity of a freshly-made transverse section, led me to choose 

 the central end of such a nerve as the point of excitation of the 

 secondary preparation. I laid bare the two sciatic nerves from the 

 spinal column to near the knee, and used one of these nerves, 

 divided at both ends, as the primary, the other still connected with 

 the leg as the secondary preparation. The peripheral end of the 

 primary nerve was placed upon the central end of the secondary, 

 so that both nerves lay close tog-ether for a space of five or six 

 millimeters, and with their transverse sections in one plane. With 

 this arrangement, the current of one nerve, so to speak, compensates 

 that of the other. Granting now that in consequence of a momen- 

 tary excitation of the primary nerve, the current suddenly vanishes 

 in its peripheral end (negative variation down to zero), then the 

 compensation of the current of the overlying secondary nerve is 

 thereby suddenly removed ; at this moment the end of the primary 

 nerve being suddenly deprived of current acts merely as an external 

 closure to the current of the secondary nerve, and the latter, by this 

 sudden derivation of its proper current, must suffer a weak excita- 

 tion. But if, as Bernstein once supposed 1 , the current of the 

 excited nerve actually alters its direction, this current will, after 

 its reversal, act upon the secondary nerve as a weak descending 

 current, which is added to the proper current in that nerve at the 

 moment that this is closed externally. 



Before tetanising the central end of the primary nerve by means 

 of weak induction currents, I provided its peripheral end, and at 

 the same time the central end of the adjacent secondary nerve, with 

 a new transverse section common to both, by a single stroke of the 

 scissors. / thus actually succeeded in provoking weak tetanic agita- 

 tion of the secondary preparation at each tetanisation of the primary 

 nerve. Of escape of current or of unipolar action there could be no 

 question, seeing that the exciting currents acting upon the central 

 end of the primary nerve were so weak as to be only just efficacious 

 when the electrodes were placed near the transverse section, and 

 that all secondary action was absent when I moved the electrodes 

 to a part of the primary nerve nearer to the secondary preparation. 



In so far as one may regard as excluded any excitation of the 

 secondary nerve by electrotonic currents the distance from the point 

 of excitation to that of contact with the secondary nerve being 



1 Untersuchungen iiber den Erregungsvorgang im Nerven und Muskelsystem, 9, 

 1871. 



