240 ELECTRIC CURRENT. LECT. XII. XIII. 



the pulley, and the pulley is put in motion, the movement is 

 communicated to the ivory^index, and this latter will stop 

 at the point at which it arrives in its gyration, even when 

 the pulley is brought back to its former position by the little 

 weight. It must be allowed, that without such an index 

 as the one described, it would have been impossible to have 

 judged of the extent of the movement of the pulley produced 

 by the contraction, on account of its short duration. The 

 weight I have been in the habit of using is 0-600 gramme 

 [= 9-266 grs. troy,] sufficient to allow of the limb return- 

 ing to its position after the contractions have ceased ; a 

 heavier weight than this would stretch the nerve too much. 



The following is a description of the manner in which I 

 pass the current. In every case it is always a half frog, 

 deprived of the muscles and bones of the pelvis, which is 

 used for this experiment. The half frog is thus reduced to 

 a portion of spinal marrow, which is held in the vice, the 

 nervous filament, the thigh and the leg, minus the claw, 

 which is cut off'. The little hook of the wire, G, is inserted 

 between the bone and the tendo-achillis. Lastly, a gilded 

 steel needle is thrust into the muscles of the thigh, as near 

 as possible to the insertion of the nerve ; and to this needle 

 is soldered a very fine copper wire, K, covered over with 

 silk, which is fixed to the piece of ivory, E. It is quite 

 clear that in order to pass the current through the nerve, 

 nothing more is wanting than to touch the support, A B> 

 with one pole of the pile, in any point whatever, and the 

 wire which is soldered to the steel needle with the other 

 pole. In all my experiments I made use of a Wheatstone 

 pile, the elements of which, as every one knows, are formed 

 of an amalgam of zinc, contained in a cylinder of wood 

 immersed in a solution of sulphate of copper, in which the 

 copper of the pile dips. 



I cannot here give you all the details of the numerous ex- 



