314 Royal Society : — 



parts of the nerve, being much stronger in the portion of the nerve 

 near the positive electrode, than in that near the negative electrode ; 

 and this difference is greater in a nerve which has been traversed by 

 the current in the direction contrary to that of its ramification, than 

 in a nerve traversed by a current in the same direction as its rami' 

 fication" 



The unequal intensity of the secondary current and its maximum 

 near the position of the positive electrode, is shown by catting an elec- 

 trolysed nerve into two or more equal lengths, which are then severally 

 opposed to each other in connexion with the galvanometer, and the 

 greatest differential current is found to be produced by the part near 

 the situation of the positive electrode. Again, the greater effect of 

 a pile- current passed inversely to the direction of the ramification of 

 the nerve, is shown by opposing two nerves which have been tra- 

 versed in different directions by the same current ; or by dividing a 

 nerve and opposing its two equal halves after they have been tra- 

 versed in opposite directions by the same current. 



The application of these facts respecting the secondary current in 

 nerves to the explanation of the phenomena which take place in 

 nerves on the opening of a circuit, is treated of in the concluding 

 part of the paper, which we give with slight abridgement in the 

 author's own words : — 



" The object of these researches," he observes, " was not to study 

 the production of secondary electromotor pow r er in nerves rather than 

 in other porous and humid bodies of various structure and chemical 

 composition. Under this point of view it is evident that the phe- 

 nomenon is complex and its analysis difficult. In the present state 

 of science, therefore, we are unable to account for the differences 

 presented by a nerve in its different points, according to their prox- 

 imity to one pole or the other, and the direction in which the nerve 

 is traversed by the current. It is possible that similar differences 

 will present themselves in other bodies not organized nor taken from 

 living animals. It is sufficient for my present object to have proved 

 that the secondary electromotor power of a nerve requires for its 

 development the integrity of structure of the nerve itself, not, how- 

 ever, the excitability of the living animal ; and to have determined 

 rigorously the differences of this power which have led me to ground 

 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 15, 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. 



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



* Phil. Trans. 1847, pp. 235, 23G. 



