246 
PROFESSOR MATTEUCCl’S ELECTRO-PHYSIOLOGICAL RESEARCHES. 
its limit, we invariably observe that the contraction remains the same, or nearly so, 
as when there was no other nerve than that of the frog contained in the apparatus. 
On the contrary, if these experiments were not performed until the current was less 
than the limited current, then, after the second nerve had been added, there was no 
longer any contraction that could he measured. 
It is, I repeat, by taking our departure from the limited current that we must de- 
termine in every case, performing the experiments with all the precautions described, 
and always being careful to wait until the natural contractions of the frog have 
ceased; and in this manner we may attain to numerical results which will admit of 
being compared together. 
Before stating these numbers I must speak of a research which it was necessary to 
make in order to render these results as exact as possible. I allude to the duration 
of these contractions, both great and slight. I have measured these with the appa- 
ratus (figs. 2, 3, 4), which appears to me analogous in principle to that upon which 
the instruments invented by Messrs. Wheatstone and Breguet for measuring the 
velocity of projectiles are founded. 
This is a magnet (a, fig. 4), the anchor ( b ) of which is moveable, and at each move- 
ment. strikes against the knob of a chronometer (c). The small weight (o, figs. 2, 3) 
which the frog raises in contracting is constructed in such a manner as to complete 
or break the circuit of the magnet. When the contraction takes place the circuit is 
broken, and it is re-established an instant afterwards when the contraction ceases. 
It then is broken again, and so continues to alternate. It will be seen from this 
that the interval of time elapsed between two successive contractions executed with- 
out any time being lost between them, will be marked by the chronometer. 
I have found that in this manner the interval is constant for the first ten or fifteen 
seconds, during which it is 0''*25 ; after which it becomes longer, and remains 0' L 33 
for ten or fifteen seconds longer, and afterwards it becomes 0 7 ‘41, O' o8, &c. 
By varying the length of the stratum of water in three different experiments and 
with the frog still vivacious, my apparatus showed contractions differing from 6° to 
10° up to 28° or 32°. The duration of the interval was perceptibly the same in all 
(0"*30 to 0"-33). 
Finally, it remained to measure the duration of the two different acts which are 
produced in the frog’s limb in the interval between one contraction and the next, that 
is to say the limb is raised and contracts, then ceases to contract and falls. 
I employed to ascertain this the same method which, I believe, the celebrated 
Watt adopted in the first instance for determining the velocity of the pistons in his 
machines. A fine point was attached to the little shank fastened to the leg of the 
frog, which point scraped, during the contraction, against a rapidly revolving smoked 
disc, of which the rotations were perfectly uniform. 
The trace which the point leaves on the disc during its elevation may serve to in- 
dicate the duration of this elevation when it is known how long it takes to perform 
one revolution of the disc. The disc I used performed forty-eight revolutions in 1”. 
