244 
PROFESSOR MATTEUCCl’S ELECTRO-PHYSIOLOGICAL RESEARCHES. 
in what this difficulty consists, it being- sufficiently apparent in itself. I have there- 
fore confined my efforts to the discovery of the relation between the electro-physio- 
logical effects, and the quantities of electricity which produce them, finding it almost 
impossible to arrive at approximative measures of these absolute effects. 
On passing an electric current from different piles along the nerve of a frog dis- 
posed in the apparatus described in my Fourth Series, fig. 1, and noting the movements 
of the index in the different cases, it will be perceived that the limb is raised to the 
same height for very different currents. Thus I have found that a current from a 
Grove’s pile of six couples of plates, and one from six of a Faraday’s pile with and 
without a powerful magnet in the circuit, and finally a current from only one couple 
of Wheatstone’s plates, give the same number of degrees for the movement of the 
index of my apparatus. It is clear from the above that all these currents are too 
strong for the effects to be compared together ; it would be precisely the same case 
if we were to pretend to measure different currents with a galvanometer the needle 
of which is propelled to 90° by the most feeble of these currents. The real object, 
therefore, to be ascertained was the feeblest current which produced the greatest pos- 
sible medium contraction. I succeeded in the following manner in discovering this. 
I employed a small Wheatstone’s pair of plates, of constant force, introducing within 
the circuit a cylinder of distilled water. This water is contained in a glass tube a 
centimetre in diameter, and bent in the form of the letter U. By plunging the 
metallic conducting wires more or less deeply in this tube, I vary at will the resist- 
ance of the circuit. The following are all the details of the experiment. The Wheat- 
stone pair of plates was exactly like that described in the memoir of that skilful 
experimenter ; the circuit is composed of a copper wire covered with silk, and half a 
millimetre in diameter, which serves to close the circuit interrupted by the cylinder 
of distilled water. The extremities of the wire which dips in the cylinder were of 
platinum ; the length of the copper wire in all about three metres. The circuit was 
closed and broken by rapidly plunging one end of the wire, held in the hand, into a 
capsule of mercury. Both the pile and my apparatus were perfectly insulated, and 
the copper wire which served to close and break the circuit was varnished at that 
part which was held in the hand. The depth to which the current, which I call limited, 
penetrated within the column of water was about eighty-eight centimetres (in the 
case of very vivacious frogs rapidly prepared) during the first fifteen or twenty con- 
tractions. In order to render these experiments as comparable one with another as 
is possible in this kind of research, it is necessary that the circuit be broken always 
at equal intervals of time. I leave the circuit closed as short a time as possible, and 
invariably allow from fifteen to twenty seconds between one experiment and the 
other. I always employ the direct current for reasons well-known. 
The difference occasioned by the column of eighty-eight centimetres of water, and 
which showed that I had arrived at the limited current, was very manifest in my 
apparatus ; thus at a depth of a few centimetres less I had the highest indication, the 
