ACTION OF ELECTRICITY ON THE NERVES 485 



When a galvanic current is passed through a liquid or a moist 

 animal tissue, decomposition occurs, by what is known as electrolysis, 

 or internal polarization. The products of this decomposition, called 

 ions, are of course different in different liquids or moist tissues. These 

 accumulate at the poles and after a time disturb the currents and the 

 phenomena produced, the electrolytic process acting in the same way 

 as an exciting electric current. In animal tissues, acids accumulate at 

 the anode, and alkalies, at the cathode. The ions which pass to the 

 anode are called anions, and those which accumulate at the cathode are 

 called cations. In physiological experiments, it often is desirable to 

 eliminate electrolysis, or internal polarization, and this is done by using 

 the non-polarizable electrodes devised by Du Bois-Reymond. These 

 may be described as follows : " The researches of Regnault, Matteucci 

 and Du Bois-Reymond have proved that such electrodes can be made by 

 taking two pieces of carefully amalgamated pure zinc wire, and dipping 

 these in a saturated solution of zinc sulphate contained in tubes, their 

 lower ends being closed by means of modeller's clay moistened with a 

 0.6 per cent normal saline solution. 1 The contact of these electrodes 

 with the tissues does not give rise to polarity " (Landois and Stirling). 



It is evident that the galvanic current may be applied to a nerve 

 so that the direction may in the one case follow the course of the nerve, 

 that is, from the centre to the periphery, and in the other, be opposite 

 to the course of the nerve. These are called respectively descending 

 and ascending currents. When the positive pole (copper) is placed 

 nearer the origin of the nerve, and the negative pole (zinc) below this 

 point in the course of the nerve, the galvanic current follows the nor- 

 mal direction of the motor conduction, and this is called the descending 

 current. When the poles are reversed and the direction is from the 

 periphery toward the centre, it is called the ascending current. It will 

 be convenient to speak of these two currents respectively as descend- 

 ing and ascending, in detailing experiments on the action of electricity 

 on the nerves. 



I The main points to be noted in regard to the effects of the appli- 

 I cation of electricity to an exposed nerve are the action of constant cur- 

 ( rents, the phenomena observed on closing and on opening the circuit 

 I and the effects of an interrupted current. 



\ During the passage of a feeble constant current through a nerve, 

 whatever be its direction, there are no convulsive movements and no 

 evidences of pain. This fact has long been recognized by physiologists, 



1 Using ordinary electrodes, when brought in contact with an animal tissue, they become 

 surrounded with positive and negative ions, which form miniature batteries giving off an electric 

 stimulus when the circuit is closed or opened. 



