LECT. XII. XIII. ACTION OF CURRENT ON NERVES. 243 



it with the quantity of electricity which excites it. I have 

 lately proved, by employing Breguet's apparatus before 

 mentioned, that this contraction is proportionate to the 

 quantity of electricity which excites it. 



Theory of the Action of the Current on the Nerves. With 

 the knowledge of these facts, all of which I have recently 

 established by a great number of experiments, I hope to be 

 enabled to give a very simple theory of the action of the 

 electric current on the nerves, and of the phenomena which 

 it produces in animals. 



No experiment demonstrates that the electric current ex- 

 cites muscular contraction during its passage in the nerves. 

 This passage only modifies the excitability of the nerve. 

 Contraction is constantly produced by the effect of the 

 electric discharge, properly so called, namely, by the neu- 

 tralization of the two opposite electrical conditions accu- 

 mulated at the poles, and which give the spark. Every 

 one knows, that when we close the circuit of a pile, as well 

 as when we open it, there is a spark. Under precisely the 

 same circumstances the current always excites contractions 

 of a frog excited by touching its nerve with the armatures 

 of a Leyden bottle, which has already been discharged, 

 several times by a metallic arc, to be convinced how ex- 

 cessively feeble is the discharge capable of producing this 

 effect. A bottle which, as we have stated, has been already 

 discharged many times, can yet produce fifteen or twenty 

 contractions in a frog. 



On the discharge of the bottle, we likewise see that the 

 contraction of the limb, traversed by the inverse discharge, 

 first ceases, whilst that which is provoked by the direct 

 discharge continues. 



There is no difficulty, therefore, in understanding why, 

 when the excitability of the nerve is lessened, the spark 

 produced by the interruption of the- direct current should 



