316 ELECTEO-PHYSIOLOGY. 



of an ing;enious observation made by the French physiologists, Rousseau and 

 Martin-Magrou. In the experiments made by Longet and myself, the spinal 

 radicle was not separated from the spine, but was simply raised to the handle 

 (ansa) with a silk thread or by an isolating surface placed beneath it,. In this 

 mode of oj)erating, as has been already shown, the greater portion of the cur- 

 rt-nt does not pass in the nerve directly from one electrode to the other by the 

 shortest interval, but flows beyond the poles, being discharged into the neigh- 

 boring conductor, whence it is that in the portion of the nerve next to the mus- 

 cle the (hrived current has a direction opposite to that of the portion of the cur- 

 rent which passes from pole to pole by the shortest interval. I recur to the 

 experiment, before exhibited, of the wet string or cord bent in the form j^, and 

 which descends upon a stratum which is a good conductor. If I cause the 

 current to pass in the upper portion of the string we shall see a contraction in 

 the galvanoscopic frog whose nerve is extended on the string or on the con- 

 ducting surface beyond the poles ; this contraction is certainly the effect of the 

 so-called derived current. Therefore, to explain the effects of the current on 

 the spinal radicles, it.is necessary to decide which of these two portions of cur- 

 rent is that whose physiological action is in the ascendency. I will first state 

 that if, instead of operating on the spinal radicles still united to the medulla 

 and lifted to the handle with a silk thread, we cut these radicles at their de- 

 parture from the spine and keep their ends free, it will then be found that the 

 electric current acts as on the mixed nerves. 



In this arrangement the derived current beyond the poles can no longer 

 exist; it was this current, therefore, which interfered in the case of the anoma- 

 lies observed by Longet and myself. And, in fact, it is easy to prove, in regard 

 to any mixed nerve, that in proportion as its excitability is extinguished, this 

 excitability continues to retreat towards the muscles if the current is so em- 

 ployed as to excite contraction, and, on the other hand, that it retires towards 

 the nervous centres when the effects of sensation are contemplated. No wonder, 

 then, if in our experiments on the spinal radicles it was the derived current 

 acting in the portion of the nerve nearest to the muscle whose action was the 

 prevalent one. Of this an experimental proof can be given. Take, in order 

 to form one of the electrodes, a small fork of two branches and apply this fork 

 to the nerve of a galvanoscopic frog, while the other electrode is placed midway 

 between the points of the fork. If now the middle electrode be, for example, 

 the positive one, the current is divided into two branches, one descending and 

 the other ascending ; and although these two portions of cuiTent be equal, it 

 will be found that the prevailing effects are those due to the descending portion 

 which is nearest to the muscle. 



The same explanation applies to the experiments recently made by.Dr, Rad- 

 cliffe, by causing the current to pass through one of the lumbar nerves of a frog 

 prepared in Galvani's manner. If this nerve is raised to the handle and the 

 current be made to pass in the portion thus raised, contractions are excited in 

 the member whose nerve is not traversed by the current and which evidently 

 depend on the portion of the current which circulates beyond the poles, and 

 which, hence, invades the other lumbar nerve. 



The investigation has been extended to the action of the current on different 

 parts of the brain of an animal alive or recently killed, and it was simply found 

 that the current acted there like mechanical stimulants applied to those parts. 

 By operating with electricity on the ear or eye, the effects occasioned are sensa- 

 tions characteristic of the excitation of the nerves of those organs. As regards 

 the ear it is known that the passage of the current excites a continuous sound ; 

 in the eye a luminous sensation is produced at the beginning and at the termina- 

 tion of the passage of the current, as if the effect depended on a mechanical 

 action undergone by the eye and due to the contractions of the muscles of the 

 eye itself. These studies are deserving of greater development. 



