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PROFESSOR MATTEUCCI’S ELECTRO-PHYSIOLOGICAL RESEARCHES. 
broken and closed again, and there will be but that one contraction visible : there 
never will be any contraction either in the direct or in the inverse limb on closing 
the circuit. If the current be then passed for a certain time longer, on opening the 
circuit we shall have the persisting contraction already alluded to. On re-establish- 
ing the circuit during this tetanic condition, the inverse limb is convulsed for an 
instant, and then regains its natural state. This is the circumstance to which I 
wished to call attention : the contraction in the inverse limb on closing the circuit 
(which had previously ceased), reappeared when the phenomenon of the persisting 
contraction manifested itself. 
It is now time to speak of what happens if the nerves, after having been acted 
upon by an inverse current, circulating through them for some time, be then sub- 
jected to the influence of a direct current, or one taking an opposite direction. This 
case, which belongs naturally to the voltaic alternatives, is easy to foresee. The 
contraction subsists, but only at the moment of closing the circuit. As regards the 
limb which has been traversed by the direct current, on subjecting it to the inverse 
current, two things may occur equally easy to foresee. If the passage of the direct 
current through the nerve has been of long continuance, so that there is no contrac- 
tion when the circle is closed, nothing takes place on passing the inverse current ; 
there is no contraction on breaking the circuit. If, on the other hand, the passage 
of the direct current has not been too protracted, so as not to entirely destroy the ex- 
citability of the nerve, on passing the inverse current the contractions reappear on 
breaking the circuit. It will be seen in the course of this memoir, that it is clearly 
proved by experiments the most exact, that the contractions exhibited in this case 
increase within certain limits proportionally with the time of the passage of the 
inverse current. I shall reconsider these phenomena in the course of this paper, and 
at present limit myself to the conclusion that the inverse current is not endowed with 
the property of destroying the excitability of the nerve ; that in some cases it is clearly 
shown by experiment that this excitability is reproduced by the passage of that current , 
and that, on the contrary, the direct current easily destroys the excitability of the 
nerve. 
Lastly, I directed my experiments in the view of ascertaining the difference of ex- 
citability of the nerve due to the electric current according to its direction, by sub- 
stituting the ordinary stimulating agents for provoking it, in the place of electricity. 
The following experiments admit of being easily verified. The frog is prepared in the 
usual manner, and is disposed for the experiment in the way so frequently described. 
The passage of the current is continued until there is no contraction except in the 
inverse limb on breaking the circuit. Arrived at this point, the passage of the current 
is to be interrupted, and each nerve is to be touched separately with caustic potassa, 
or better still with a heated iron ; the result is so constantly the same that the direc- 
tion of the current passed through the two nerves may even be told by it. The effect 
of the caustic potassa, or heated iron, upon the inverse nerves is merely that of pro- 
