PROFESSOR MATTEUCCI’S ELECTRO-PHYSIOLOGICAL RESEARCHES. 
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should be constant, a Wheatstone’s pile is the best adapted for the experiment. As the 
nervous filament by which the current is transmitted must be perfectly free from all 
trace of blood or other animal substance, it must be carefully cleaned, using a pair of 
forceps and lightly wiped with a piece of blotting-paper. It is also requisite that the 
gilded steel needle, which is introduced into the muscle of the thigh as nearly as pos- 
sible to the insertion of the nerve, and which serves to complete the circuit, should, 
so far as is practicable, be always inserted in the same position in all the experiments. 
Lastly, care must be taken in choosing suitably the weight attached to the limb of 
the frog : if the weight be too small, the limb is not brought back to its position 
after contraction ; on the other hand, if the weight be too great, the nerve is stretched, 
and the indications given by the apparatus are too small. 1 found that a weight of 
0'600 gr. is the best adapted for the purpose. 
I here give one of a series of experiments, undertaken with the view of resolving 
the question which I had proposed to myself. 
I fasten a living frog to the clamp of the apparatus by passing a thread of silk round 
the thorax under the front claws : I then remove all the viscera of the abdomen, one 
of the limbs, and the muscles, as well as the bones of the pelvis : the frog, thus pre- 
pared, retains its natural liveliness for at least twenty or thirty minutes. I proceed 
to pass the direct current through the lumbar nerve, and I obtain contractions mea- 
sured by the apparatus at 14°, 12°, 10°, 9°, 8°. I continue the passage of the current 
as short a time as possible, and close the circuits instantly after having opened 
them. The contractions first of all diminish rapidly, and then for a certain time 
they remain the same, if we are careful to leave the circuits closed as short a time 
as possible. When the deviation of the needle points constantly at 8°, I cut the spinal 
marrow of the frog, and pass the current again immediately : I have again the con- 
traction 8° as before. I have frequently repeated this same experiment, and invariably 
with the same result. I also found that the duration of the contractions which persist 
the longest does not vary, in consequence of the section of the spinal marrow. It is 
therefore certain that the excitability of the nerve undergoes no immediate change 
after its separation from the nervous centre. 
I then continued my investigations of this subject, conducting my experiments 
in a different manner from that already described, that is, by comparing the con- 
traction of the muscular fibre excited by the passage of the electric current in a 
nerve which had been separated for several hours from the nervous centre, to that of 
another similar muscle the nerve of which had not undergone this operation. 
It is hardly necessary to repeat, that, in order to the success of these experiments, 
Breguet’s apparatus must be used, employing the precautions already mentioned ; 
the most indispensable of which is the careful removal of all traces of blood, &c. from 
the lumbar nerves of frogs submitted to these comparative experiments ; they should 
also, as far as possible, be prepared in the same manner, so that their conditions 
should be similar. 
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