THE PHYSIOLOGICAL ACTION OF THE ELECTRIC CURRENT. 
495 
circuit is opened. The experiment may be prolonged for several hours with the same 
results. 
The following experiments were performed for the purpose of comparing together 
the contractions caused by the direct and inverse currents at the instant of closing 
the circuit in both cases. The frog in these experiments was prepared in the manner 
described, then cut in half, and a nerve of one half was acted upon by the direct 
current, and a nerve of the other half by the inverse current. The experiments were 
repeated several times, first passing the direct current, at one time, through one half 
of the frog, and afterwards the inverse through the other half, or reversing this order. 
The following are the numbers obtained :■ — 
Contraction on the introduction Contraction on the introduction 
Number of experiments. of the direct current. of the inverse current. 
O O 
1 
16 
8 
2 
16 
4 
3 
14 
6 
4 
18 
12 
5 
16 
12 
6 
24 
8 
7 
20 
16 
8 
8 
4 
Although the correspondence between the numbers in the two columns is far from 
being constant, it is nevertheless proved in a very evident manner, that the contrac- 
tion caused by the introduction of a direct current upon a mixed nerve, which has 
not been previously stimulated by the current, is always stronger than that which 
follows the introduction of the inverse current. The result is the same if a discharge 
of the Leyden jar is used to provoke the contraction ; that is to say, a very slight 
shock from the Leyden jar, if direct, will cause contraction, and which would be in- 
sufficient to effect this if inverse. 
While repeating the experiments referred to in the above table, I took occasion to 
note down the contractions which took place on opening the circuit of the inverse 
current. The contraction so produced is never stronger than that which occurs the 
first time that the direct current is passed. Both contractions are in general similar 
if the nerve is very excitable, and the inverse circuit left closed for a very short time. 
When the excitability of the nerve is considerably diminished, the inverse current 
must be made to circulate for a much longer time, to produce, on opening the cir- 
cuit, the same contraction as that caused by the introduction of the direct current. 
I will now sum up, with a few general conclusions, the results of all the experi- 
ments hitherto cited. 
1. The passage of the electric current through a mixed nerve produces a variation 
in the excitability of the nerve, differing essentially in degree, according to the direc- 
tion of the current through the nerve. This excitability is weakened and destroyed. 
