386 



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 electrolysatiou 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 hi 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. 



The author next gives the results of experiments made to deter- 

 mine the influence of various physical and chemical conditions on the 

 secondary electromotor power of nerves. The method he generally 

 followed was by comparing the secondary currents caused by the same 

 pile-current in a natural and in an altered nerve. He had previously 

 ascertained that when the same pile-current is passed through two 

 nerves at once they are equally affected, and give when placed in 

 opposition no differential deflection of the galvanometer, although 

 singly each might give a secondary current of 40 or 50. Now by 

 sending the same pile-current simultaneously through two nerves or 

 portions of nerve, either before or after the one of them has been sub- 

 jected to the particular conditions to be tried, and finally placing the 

 two in opposition in connexion with the galvanometer, the occurrence 



