THE PHYSIOLOGICAL ACTION OF THE ELECTRIC CURRENT. 
493 
the inverse current for two seconds, 4°; after five seconds, 6°; after thirty seconds, 
10°; after 120 seconds, 10°. With another frog-, which had been very long under the 
influence of the direct current, the contractions, after passing the inverse current for 
two seconds, 0° ; after passing the current ten seconds, 0°; sixty seconds, 1°; 120 
seconds, 2°. In another experiment, at the expiration of two seconds of the passage 
of the inverse current, contraction 0° ; after a passage of five seconds, 3°; twenty 
seconds, 8°; fifteen seconds, 10°; thirty seconds, 10°. In a fourth experiment, the 
duration of the inverse current and the degrees of contraction were as follows : — two 
seconds, 0° ; three seconds, 3° ; ten seconds, 6° ; fifteen seconds, 8° ; thirty seconds, 
10°; sixty seconds, 10°. In all these experiments I left as short an interval of time 
as possible between each such successive current. 
It has been already seen what takes place when the inverse current is passed, and 
the nerve is endowed with a very high degree of excitability: the passage of the in- 
verse current for only one second suffices, in such a case, to restore to the nerve all 
the excitability it is capable of acquiring-. To distinguish the phenomenon we are 
now considering upon a nerve in the state of excitability alluded to above, the in- 
verse current should be made to act for very small fractions of seconds. 
Next in the order of our investigations, we are led to examine whether this aug- 
mented excitability of the nerve, produced by the passage of the inverse current, can 
persist, even after the cessation of this current, or whether, on the contrary, it can 
have no existence beyond the period that the nerve is under the immediate influence 
of the current. It has already been mentioned, that when the direct current has been 
made to act for twenty-five or thirty minutes, so as no longer to produce any con- 
traction, on passing the inverse current there is scarcely ever any contraction on 
closing the circuit. This contraction, which is always the first to disappear, may still 
be reproduced, but to effect this it would be necessary that the passage of the inverse 
current should be prolonged considerably, and that the circuit should remain open 
as short a time as possible. In effect, every time that the frog presents the pheno- 
menon of persistent and tetanic contraction, that is to say, after the inverse current 
has been passed for a considerable time, a contraction takes place on closing the 
circuit, and the tetanic convulsion ceases on the instant. It is therefore proved that 
this increase of excitability, produced by the passage of the inverse current, persists 
for a very short time when the nerve is very excitable, while this persistence increases 
with the diminution of the excitability, and with the duration of the inverse current. 
The same law is therefore always verified according to the different degree of excita- 
bility of the nerve. 
A few experiments, conducted in a different manner, lead to the same conclusion. 
I pass an inverse current for some time through the nerve of a frog disposed in my 
apparatus ; I then break the circuit, and leave it so for a time varying for each expe- 
riment. I close the circle, and always again break it immediately, and note down 
the contraction which follows. The circumstance which varies in all these experi- 
