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PROFESSOR MATTEUCCl’S ELECTRO-PHYSIOLOGICAL RESEARCHES. 
tracts only on breaking the circle, whilst the leg traversed by the direct current 
contracts only on closing it. The duration of the passage of the current, which is 
necessary for the production of these phenomena, is less in proportion as the current 
is stronger. If the passage of the current be continued through the same frog, it ends 
in the production of but one contraction, which is that which takes place on breaking 
the circuit, in the limb traversed by the inverse current. It is essential to the pro- 
duction of this latter phenomenon, to prolong the passage of the current more or 
less, from twenty to forty minutes, according to the strength of the current. I have 
frequently seen the contractions of the inverse limb prolonged, under the influence 
of a feeble current, and subsisting after four hours that the circuit had been kept 
closed. 
I was anxious to ascertain whether these phenomena could be produced equally 
well by limiting the passage of the current to the lumbar nerves alone. In this view 
I wrapped very thin laminae of tin round two nerves of the frog prepared in the 
manner above described, taking care to roll the laminae round the nerves as close 
as possible to their points of entrance into the thighs. On passing the current, 
precisely the same phenomena as those already described are observable. The 
only difference that can be distinguished is in the duration of the passage of the 
current which is necessary for producing contraction only in the inverse limb, on 
breaking the circuit. This duration is less in this case than in the preceding expe- 
riments. This difference is easily accounted for, by taking into consideration the 
diminished resistance of the circuit in such a disposition, and comparing it with that 
of the circuit formed by the entire frog. Of this fact I have been enabled to satisfy 
myself completely, by introducing a galvanometer in the two circuits. The difference 
between the two currents, the same pile being used, is so great that it is impossible 
to entertain any doubt upon the subject. Since, then, the current is strongest when 
the nerve only is traversed, the phenomena corresponding to the different periods of 
excitability of the nerve ought to be obtained in a shorter time. I hardly need say 
that the manner of obtaining these phenomena, described at the commencement of 
this memoir, is identical with that which I have mentioned. In effect, the current in 
the frog may just as easily be checked or renewed by taking out and replacing the 
poles of the pile in the liquid in which the frog’s paws dip, as by joining the two 
liquids by means of a metallic arc, and by removing the communication. Never- 
theless it may not be useless to mention an experiment having reference to this, 
which it is as well to be acquainted with. I assume that the frog is prepared in the 
manner described, and subjected for a sufficient time to the passage of the current, 
so that contraction takes place only in the inverse limb, and on breaking the circuit. 
This being the case, while the circuit is closed, let a drop of pure water, or salt water, 
serum, blood, or any other conducting liquid, be dropped upon each of the two nerves 
separately. The drop produces no effect upon the nerve traversed by the direct cur- 
rent, while the contraction of the limb whose nerve is traversed by the inverse current 
