306 



Prof. F. Gotch and Mr. G. J. Burch. Electrical 



w^ 



M 



X indicates the seat of excitation on the sciatic plexus ; M the muscles below the 

 knee; P indicates the circuit traversed by the polarising current; E the 

 electrometer circuit. The unbroken arrow indicates the direction of the 

 persistent polarising current in the nerve, the dotted one that of the persisjbent 

 extrapolar effect thus produced. The anode and cathode of the polarising 

 current are indicated by the letters a and c respectively. The signs ( + ) and 

 ( ) refer to the persistent difference of the electrometer contacts during 

 polarisation. 



differences in their electrical state. The proximal electrometer 

 contact is that nearest the seat of excitation, and is represented in 

 the figure by the broad dark line. In arrangement A it lies in the 

 anodic extrapolar region, and owing to polarisation effects, is 

 rendered positive to the distal one during the polarising flow ; in B 

 it is in the cathodic extrapolar region, and is negative to the distal 

 one during such flow ; in C it is in the cathodic region, but, as in A, 

 is positive to the distal one, whilst in D it is in the anodic region, 

 but is negative to the distal one as in the case of B. 



The results as regards the character of the excitatory change 

 differ in accordance with the particular arrangement employed, but 

 it will be seen that with arrangements fA and C, the records of the 

 response to a single stimulus resemble one another inasmuch as the 

 prolonged tail, previously referred to as characteristic of the nerve 

 with a fresh cross-section, now becomes strikingly evident. On the 

 other hand with B and D the records resemble that of the uninjured 

 nerve, the spike alone being present. 



It will be convenient to describe the results under two headings 

 in accordance with this general subdivision ; and, as experiments 

 have been made on the preparations of all the types previously 

 referred to, the results under each heading comprise those observed 

 in fresh nerves uninjured and with cross-section, and in kept nerves. 



