512 Royal Society : — 



memoir rests is performed as follows : — The sciatic nerve taken from 

 a frog, a fowl, or some other recently killed animal, is used for the 

 purpose. The operator first assures himself that no sign of current 

 is manifested on simultaneously touching with the galvanometer two 

 points of the nerve equidistant from its cut extremities. The dis- 

 turbing effect of the electric current naturally generated in nerves 

 may also be eliminated by placing two nerves, or two portions of 

 nerve, in such relative position that their natural currents shall be 

 opposed in direction and mutually neutralize their effects on the 

 galvanometer. To the nerve or piece of nerve thus tested are applied, 

 at some distance from its extremities, the electrodes of a pile of eight 

 or ten elements, and the exciting or pile-current is allowed for a 

 short time to pass along the included part of the nerve. When 

 the nerve is now put in communication with the galvanometer, the 

 needle deviates, and indicates that the nerve is traversed, in the por- 

 tion which had been included between the electrodes of the pile, by a 

 current the direction of which is opposite to that of the current of 

 the pile, and which lasts for a certain time. Signs of secondary 

 current are also obtained by applying the galvanometer to the parts 

 of the nerve which have not been traversed by the pile-current, that 

 is, the end-parts between the extremities of the nerve and the points 

 touched by the electrodes of the pile ; but the secondary currents in 

 these end-portions of the nerve are in the same direction as the 

 pile-current, and therefore opposed to that of the secondary current 

 developed in the part included between the electrodes and traversed 

 by the pile-current. It is further observed, that of the two end- 

 currents the one adjacent to the point of application of the negative 

 electrode is stronger than the other. 



It is to be noted that the secondary current endures for some time 

 after the cessation of the exciting current ; hence it is evidently not 

 caused by induction. The author thus explains its production : — At 

 the points of a nerve which have been acted on by the electrodes of a 

 pile the products of electrolysation are accumulated, and thence spread 

 through the tissue more or less, according to differences of its structure 

 and chemical disposition ; conditions, persistent for a time, are thus 

 established for generating a current when the circuit is completed 

 between two different points of the nerve. The same thing happens 

 when a strip of paper or flannel, moistened with a weak saline solu- 

 tion, is first subjected to the current of a pile and then tested with 

 the galvanometer, or if such a strip is so tested after having been 

 simply wetted at one part with acid and at another with alkaline 

 solution, to represent the effect of electrolysation by an exciting cur- 

 rent ; and in either case the direction of the secondary current in the 

 moistened strip, both in the part included between the points of 

 application of the electrodes and in the excluded parts at the ends, 

 corresponds with that in the nerve. 



The experiment succeeds perfectly in the entire nerve of a living ani- 

 mal, such as the sciatic of a rabbit or a fowl. But the result is inde- 

 pendent of the vital condition of the nerve, for the effect is found to be 

 . equally great four days after death as at the moment an animal is killed. 



