UPON INDUCED CONTRACTIONS. 
235 
as it indicates an intimate connection between nervous influence and the action of 
the electric current according to the direction of the latter. 
I have therefore exercised the greatest care in studying this phenomenon; and if I 
have not been able to show the connection in all its evidence, and to express it with 
that degree of simplicity which is the characteristic of physical laws, I venture to 
hope that this failure will in part be attributed to the obscurity in which the sub- 
ject is involved, and that some degree of favour may be accorded to the efforts which 
I have made in this direction. It is a very rare circumstance to find a frog that does 
not present the phenomenon which has been already described ; and in particular 
those frogs which pass several days in winter without nourishment, never fail to 
manifest it. In this case they appear more disposed to become tetanic ; and, in effect, 
they do almost all become so when they are prepared by dividing their spinal marrow, 
and remain so during some seconds. The phenomenon in general manifests itself 
after the current has been passed for twenty-five or thirty minutes. The tetanic 
contraction lasts a very long time, and it often happens that when this has ceased, 
there are twitchings in the limb from time to time. These phenomena equally occur 
on passing the current through the nerves without its traversing the muscles. In 
like manner they may be elicited in the living frog, only in this case the tetanic con- 
traction lasts a much shorter time. The phenomenon never occurs when the current 
acts only on the muscle, w T hich it may be made to do by disposing the frog in the 
ordinary manner, without having divided the pelvis. On the other hand, it presents 
itself after the spinal marrow has been destroyed. 
It is not essential to the manifestation of the phenomenon in question that the 
muscles should be thrown into contraction at the commencement of the passage of 
the current, which may easily be seen by closing the circuit by the aid of a bent 
metallic conductor ending in some paper which slowly imbibes a certain quantity of 
water. If, instead of arresting the current by removing one of the reophores of the 
pile, a metallic arc be introduced between the two glasses, the tetanic contraction 
occurs just the same. But if to the end of this curved rod be attached some paper, 
so as to occasion the passage of the current to cease more slowly as regards the frog, 
then instead of one tetanic convulsion we have a series of contractions succeeding 
each other at short intervals of time. 
In whatever manner the current through the nerve of the inverse limb is arrested, 
the tetanic contraction is excited. It suffices for this to moisten the nerve with a 
large drop of water, or to double it back upon itself for the contraction to take place; 
while this does not occur if the current is arrested for the muscle. This is easily 
effected by bringing the reophore of the pile, w T hile the circuit is still kept closed, in 
contact with the thigh at the point where the nerves iminerge. 
The following experiment proves still more clearly the part which the nerve plays 
in this phenomenon. If, while the circle remains closed, and it has been previously 
ascertained that the tetanic contraction will follow the opening of the circuit, the 
2 h 2 
