iv GENERAL PHYSIOLOGY OF NERVOUS SYSTEM 241 



The former were discovered in 1843 by Du Bois-Reymoud, who 

 gave the name of electrotonus to the special electrical state produced 

 by the passage of a galvanic current, in both the intrapolar and 

 the extrapolar parts of a nerve. The latter, which were accurately 

 described by Pfltiger in 1859, are more properly termed electro- 

 tonic alterations of the excitability and conductivity of nerve. 

 Both these effects are in reality manifestations of the chemical 

 phenomena of electrolysis and polarisation. 



We know that the passage of a galvanic current through a 

 moist conductor is accompanied by phenomena of electrolysis and 



' Fid. 154. Correction of the facial paralysis two and a half months after the crossing of the 

 external branch of the spinal accessory with the facial. (Purpura.) 



dissociation, which reach their maximal development at the 

 points of entry and exit of the current, i.e. at the electrodes. 

 When the current passes through a moist conductor, the presence 

 of electrolytes (i.e. the molecules of a neutral salt in solution) 

 renders the fluid acid at the anode and alkaline at the kathode 

 owing to the transport of the acid negative ions to the positive pole, 

 and of the basic positive ions to the negative pole of the current. 

 If after a prolonged passage of current through the fluid the 

 electrodes are disconnected with the cell and connected to a 

 galvanometer, a so-called " polarisation current " is seen in the 

 opposite direction to the polarising current ; this is due to the 

 accumulation of positive ions at the kathode and negative ions at 

 the anode of the polarising current. 



Since nerve is a moist conductor, the passage of a galvanic 



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