RELATION OF ELECTRO-PHYSIOLOGICAL EFFECT TO INTENSITY OF CURRENT. 245 
same as that given when the stratum of water was not included in the circuit. With 
the column of water eighty-eight centimetres in depth, the indication was lessened 
by from 2° to 4°, and with a column of from ninety to ninety-five centimetres the 
diminution was very sensible. 
In the very numerous experiments which I have instituted on this subject, I have 
always, in each in particular, sought for the length of the stratum of water which gave 
the limited current. I repeat that it was very easy to effect this by approximating 
the wires more or less in the water. It remains now to be considered by what means 
the half, a third, a fourth of the quantity of electricity was made to pass into the 
same nerve. After several trials I returned to my first plan as being the least in- 
exact possible. When I wish to pass half the quantity of electricity through the 
nerve, I interpose a second nerve between the forceps and the thigh ; to pass a third 
of the current I add two nerves, and so on. Theoretically, and with regard to the 
great resistance of the circuit, it may be admitted as true that the half of the current 
passes into each of the two nerves, and a third into each of the three nerves, the same 
ratio being observable according as the subdivision of the current proceeds ; but 
having respect also to the bad conductibility of the nerve, which is certainly, from its 
nature* and dimensions, at least as great as that of the stratum of water, it might be 
imagined that in increasing the number of nerves the total current would be also 
augmented, and by that means rather more than the half of the current which passed 
into one nerve would pass in the case of the two nerves ; in the case of the three 
nerves, somewhat more than a third of the current for each nerve ; and so on. By 
introducing a galvanometer within the circuit, we are able to ascertain the very slight 
augmentation produced by the nerves successively added -f-. 
In order that these nerves might be similar in all points, as nearly as possible, they 
were always taken from frogs prepared at the same time as the frog which served for 
the experiment. Care must be taken in placing them side by side not to allow them 
to touch one another. I have invariably observed that when this happened, and that 
the nerve of the frog within the apparatus was enveloped by the nerves added sub- 
sequently, there were no longer any signs of contraction on passing the current, 
though these were immediately manifest when the same number of nerves were pre- 
vented from contact with one another. I look upon this result as a further proof 
that the cause of contraction from the passage of the electric current, is the discharge 
which takes place at the commencement and at the termination of the circuit. 
The following is the march of the phenomena in these experiments. If we begin 
to add the second and third, &c. nerve while the current is still tolerably far from 
* A hempen thread soaked in water, and a nervous filament as nearly as possible of the same dimensions, 
offer degrees of resistance which are in the following ratio, twelve for the moist thread, and fifteen for the 
nerve. The nerve must be very fresh to afford this resistance : it naturally increases in proportion as it be- 
comes dry. 
t In performing these experiments, I have found that if the stratum of water was more resisting than the 
nerve, there was no perceptible increase in the current from adding two, three, or four nerves to the circuit 
instead of one. In my experiment the resistance of the column of water is greater than of the nerve. 
