the explanation of the electro-physiological phenomena which take 

 place on the opening of the circuit, on a fundamental physical fact. 



" If in a frog prepared in the usual way for electrical experiments 

 a continuous current is passed up one hind limb and down the other, 

 for 1 5, 20, or 30 seconds, according to the force of the current, it is 

 known that the opening of the circuit is accompanied by violent con- 

 tractions of the limb traversed by the inverse current. These con- 

 tractions depend, as I showed many years ago*, on a particular state 

 of the nerve ; and in fact the contractions are obtained and continue 

 when the circuit is interrupted by cutting the nerve near the spine, 

 but they are no longer produced if the nerve is cut near its insertion 

 in the muscles of the leg. 



" My object in this memoir has been to prove that the particular 

 state of the nerve above described consists in secondary electromotor 

 power, that is, in a well-known physical phenomenon. The course 

 of the secondary current, which is downward or direct in the nerve that 

 has been traversed by the upward or inverse pile-current, explains, 

 according to the well-known laws of electro-physiology, the effects 

 produced by it on that nerve on the opening of the circuit. 



" The differences of electromotor power found in various points 

 of the electrolysed nerve, the prevalence of this power in the part of 

 the nerve near the positive electrode, very probably also the different 

 degree of this secondary electromotor power in the various strata 

 which compose the interior and the envelope of the nerve, are cir- 

 cumstances which seem to explain the secondary current which takes 

 place in the nerve at the opening of the circuit, and which is direct 

 and most intense in the nerve which has already been traversed by 

 the inverse current, most intense also in the vicinity of the positive 

 electrode. 



" In order, therefore, to explain the phenomena which accompany 

 the opening of a circuit, we must henceforth have recourse to the 

 fact of the development of secondary electromotor power in nerves 

 and the laws according to which it manifests itself." 



* Phil. Trans. 1847, pp. 235, 236. 



