PEOFESSOE MATTEUCCI’S ELECTEO-PHYSIOLOaiCAL EESEAECHES. 
143 
found, it was of some interest to determine the quantity of electricity necessary, in 
acting on the nerves or muscles of a frog, to produce that contraction; the results 
obtained in this last research led me to the experiments on muscular respiration which 
form the subject of the second part of this memoir. After having measured the quantity 
of zinc oxidized in a given time in a pile, the current of which is employed to excite 
contractions in a gastrocnemius, we have still to find the duration of the passage of that 
current necessary for obtaining a contraction. For this purpose a current of a couple, 
amalgamated zinc and platinum, in water slightly salt, is sent for upwards of twenty-four 
hours into a neutral solution of nitrate of silver. The silver collected on the negative 
electrode, exactly weighed, gives the quantity of zinc oxidized in the pile. In order to 
determine the time of the passage of the current in a gastrocnemius required to produce 
normal contraction, ^. e. the work already determined, I employed a method differing 
little from that imagined by M. Pouillet for measuring very short intervals of time. I 
fix on the radius of a wheel, six or seven metres in circumference, a strip of amalgamated 
copper 1 millimetre wide. The wheel being set in motion with a uniform velocity of 
about four tmais in a second, the time employed by the circumference of the wheel in 
passing an arc of 1 millimetre is necessarily very short, but can nevertheless be measured 
accurately. ^Virile the wheel is in movement, two amalgamated brass springs are 
brought in contact with its periphery : these springs form part of the circuit of the pile, 
in which are comprised a gastrocnemius recently prepared and fixed in the dynamo- 
meter and a galvanometer. I have thus obtained normal contraction by the passage of 
a current, which produced no sensible deflection of the needle of the galvanometer, and 
of which the duration was about 10 , 00 0 ^^. of a second. If we admit, which we may 
do without error, that the conducting power of the gastrocnemius does not exceed that 
of the solution of nitrate of silver, the quantity of zinc oxidated in the pile during that 
time is measured by the 7 billionth of a milligramme of zinc*. 
Taking the mechanical equivalent of heat determined by the experiments of Joule, 
and reasoning according to the principles of the dynamical theory of heat, and finally 
supposing that all the zinc oxidated in the above experiments is converted into electrical 
current, and hence into muscular energy, one arrives at a conclusion which is far from 
being in conformity with the theory : the quantity of vis viva of a muscle corresponding 
to the above-mentioned quantity of zinc, would be enormously greater than that deduced 
from the principles of that theory. This discordance will cease, when it shall be proved 
that nervous irritation excites new chemical actions in the muscle, and that these are 
associated with its state of contraction : in this way the electrical current acting on a 
nerve should be considered in its mechanical effects as the spark which ignites gunpowder 
or a mixtm’e of hydrogen and oxygen. 
* These numbers represent only a limit ; but if one reflects that the contraction of a frog is excited by 
the discharge of a Leyden jar of the smallest possible dimensions and which has been previously discharged 
by a metallic arc, it becomes evident that this limit greatly exceeds the reality. 
