UPON INDUCED CONTRACTIONS. 
237 
manner. The direct current acts by exciting-, when it commences, a contraction which 
we know to be stronger than that produced in the same case by the inverse current. 
A limb traversed by the direct current may be compared to a limb fatigued by re- 
peated efforts. The inverse current may be supposed to act in an opposite manner, 
and during its passage the nervous force might accumulate in the nerve. 
I prefer, however, suppressing considerations of this nature on account of the vague 
and uncertain impression which they are calculated to leave in a reflecting mind. 
It may not, however, be without some utility to close my electro-physiological 
researches with an attempt at embracing, under some general views, the phenomena 
of muscular contraction, of the production of electricity in fish, and of the relation 
between the electric current and nervous influence. 
I would here recall the facts discovered by M. Longet and myself, on treating the 
motor nerves with the electric current. Monsieur Longet and myself discovered that 
the action of the electric current upon these nerves was precisely the opposite of its 
action upon the mixed nerves. 
The direct current acting upon the motor nerves, determines the contraction in the 
second period of the excitability of these nerves when it ceases to pass, and the in- 
verse current produces it when it begins to pass. It is natural to think that the 
phenomenon of tetanic contraction would be produced by the cessation of the direct 
current when the motor nerves are acted upon. In connexion with this subject, I 
will here relate a phenomenon which I have lately discovered, and which appears to 
me to be worthy of remark. With the aid of a wheel armed with insulating metallic 
teeth, similar to that of Mons. Masson, I passed a current in a frog prepared in the 
manner described above, that is to say, like that placed astride between two glasses. 
In this manner I pass the current 500 or 600 times in the frog. After this, on 
attempting to interrupt, and then again establish the circuit, the following phenome- 
non strikes the experimenter. The inverse limb contracts on closing the circle, and 
the direct limb on opening the circle. On leaving the circle closed for some minutes, 
the ordinary phenomena — the opposite of the preceding — appear ; that is to say, the 
direct limb contracts on closing, and the inverse limb on breaking the circle. It is 
very difficult to reproduce these phenomena in the same frogs, on account of the 
extreme feebleness produced by the numerous contractions. 
The above fact establishes a fresh connection between nervous influence and the 
passage of the electric current according to the direction of the latter. I will return 
to this subject in the general views which I announced above. 
Pisa, December 1 846. 
