THE PHYSIOLOGICAL ACTION OF THE ELECTRIC CURRENT. 
485 
more or less approximated. One of these pivots is the centre of a circle RS, which 
bears a division. A long- ivory needle TV is attached to this pivot; it is very light, 
and turns with the slightest possible touch. The use of this ivory index is obvious. 
In effect, when this index is brought in contact with the semicircular one PQ, which 
is attached to the axis of the pulley, and the pulley is put in motion, the movement 
is communicated tho te 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 de- 
scribed, 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, sufficient to allow of the 
limb returning 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 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 AB 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 everybody 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 suppress here a great number of 
small details which are essential to complete success in the experiments, but which 
naturally present themselves to any person repeating them with some degree of care. 
One thing is very certain, which is, that it will ever be impossible to make any ad- 
vance in the study of the physiological action of the electric current, without having 
recourse to processes which give the measure of that action. 
The phenomenon which first engaged my attention is that which I had already 
observed, and which is referred to at the commencement of the present memoir. I 
have frequently repeated the experiment, varying the force of the current and the 
duration of its passage, and have found the results invariably the same. At the 
outset of the experiment, the two limbs, direct and inverse, are seen to contract 
both at the commencement and on the cessation of the current. After some minutes, 
varying from fifteen to twenty, according to the vigour of the animal, and especially 
according to the force of the current, the difference in the contraction of the two 
limbs manifests itself, that is to say, the leg traversed by the inverse current con- 
