THE PHYSIOLOGICAL ACTION OF THE ELECTRIC CURRENT. 
497 
point there is no sign given by the electrometer with a dry pile. I then place the 
prepared frog astride between the balls of the universal discharger, and establishing 
a communication between the coating of the jar and these two balls, very strong con- 
tractions of the frog follow. Continuing this operation in precisely the same manner, 
and producing successive discharges of the same bottle through the frog, I never 
obtain less than twelve contractions, and in some cases I have even had as many as 
twenty. The first fact which strikes our attention in these experiments is that which 
Volta himself did not fail to observe. The most feeble discharge, said Volta, directed 
from the nerve to the muscle, and which provokes contraction, is but the one-fourth 
or even the one-sixth of that which is necessary to produce contraction when directed 
from the muscle to the nerve. This difference we are enabled to measure more 
exactly by acting with the electric current. In order to repeat this experiment 
of Volta with greater facility, and at the same time in a more conclusive manner, I 
confined myself to making the discharge act upon the nerve alone in the following 
manner. The frog is prepared in the ordinary manner, the pelvis divided, and it is 
stretched upon an isolating plane ; the two extremities of the universal discharger 
are so disposed as only to admit of the discharge circulating through the nerves and 
the portions of spinal marrow. Thus one nerve is traversed by the direct discharge 
and the other nerve by the inverse. I have always used the same bottle after having 
discharged it with the metallic arc. After the first contractions, which are excited 
equally in both limbs, that limb only continues to contract which is traversed by the 
direct discharge. These results occur equally when nerves, which have not pre- 
viously been subjected to any discharge, are acted upon. This is easily put to the 
proof by merely discharging the bottle several times through other frogs before be- 
ginning to act upon those which had been purposely put aside without the shock 
being passed through them. It is soon seen, after a few touches, that that limb 
alone contracts the nerve of which was exposed to the action of the direct dis 
charge. 
We may therefore conclude that the action of electricity upon the mixed nerves of 
an animal living or recently killed, is reduced to the two following facts : — 
1. The electric discharge traversing a nerve awakens muscular contraction ; but 
this contraction is much stronger when produced by the direct discharge than when 
it is excited by the inverse discharge. 
2. The electric current circulating through a nerve of a living animal, or an animal 
newly killed, produces a variation in the excitability of the nerve: if the current is 
direct, the excitability is diminished and destroyed ; while, on the contrary, the exci- 
tability is preserved and increased by the passage of the inverse current. 
It is needless to observe that these latter phsenomena can be verified in the dead 
animal only within such limits as are necessarily fixed by the cessation of the vital 
conditions essential to the preservation of the properties of the nerve. It will be ob- 
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MDCCCXLVI. 
