Biomedical Engineering Reference
In-Depth Information
Volta expressed immediate interest on learning of Galvani's 1791 report to the Bologna
Academy on the “Forces of Electricity in Their Relation to Muscular Motion.” Volta set
out quickly to repeat Galvani's experiments and initially confirmed Galvani's conclusions
on “animal electricity” as the cause of the muscular reactions. Along with Galvani, he
ascribed the activity to an imbalance between electricity of the muscle and that of the nerve,
which was restored to equilibrium when a metallic connection was made. On continuing
his investigations, however, Volta began to have doubts about the correctness of that view.
He found inconsistencies in the balance theory. In his experiments, muscles would convulse
only when the nerve was in the electrical circuit made by metallic contact.
In an effort to find the true cause of the observed muscle activity, Volta went back to an
experiment previously performed by Sulzer. When Volta placed a piece of tinfoil on the tip
and a silver coin at the rear of his tongue and connected the two with a copper wire, he got
a sour taste. When he substituted a silver spoon for the coin and omitted the copper wire,
he got the same result as when he let the handle of the spoon touch the foil. When using
dissimilar metals to make contact between the tongue and the forehead, he got a sensation
of light. From these results, Volta came to the conclusion that the sensations he experienced
could not originate from the metals as conductors but must come from the ability of the
dissimilar metals themselves to generate electricity.
After two years of experimenting, Volta published his conclusions in 1792. While credit-
ing Galvani with a surprising original discovery, he disagreed with him on what produced
the effects. By 1794, Volta had made a complete break with Galvani. He became an outspo-
ken opponent of the theory of animal electricity and proposed the theory of “metallic
electricity.” Galvani, by nature a modest individual, avoided any direct confrontation with
Volta on the issue and simply retired to his experiments on animals.
Volta's conclusive demonstration that Galvani had not discovered animal electricity was
a blow from which the latter never recovered. Nevertheless, he persisted in his belief in
animal electricity and conducted his third experiment, which definitely proved the
existence of bioelectricity. In this experiment, he held one foot of the frog nerve-muscle
preparation and swung it so the vertebral column and the sciatic nerve touched the muscles
of the other leg. When this occurred or when the vertebral column was made to fall on the
thigh, the muscles contracted vigorously. According to most historians, it was his nephew
Giovanni Aldini (1762-1834) who championed Galvani's cause by describing this important
experiment in which he probably collaborated. The experiment conclusively showed that
muscular contractions could be evoked without metallic conductors. According to Fulton
and Cushing, Aldini wrote:
Some philosophers, indeed, had conceived the idea of producing contractions in a frog without metals;
and ingenious methods, proposed by my uncle Galvani, induced me to pay attention to the subject, in order
that I might attain to greater simplicity. He made me sensible of the importance of the experiment and there-
fore I was long ago inspired with a desire of discovering that interesting process. It will be seen in the Opus-
coli of Milan (No. 21) that I showed publicly, to the Institute of Bologna, contractions in a frog without the
aid of metals so far back as the year 1794. The experiment, as described in a memoir addressed to
M. Amorotti [
] is as follows: I immersed a prepared frog in a strong solution of muriate of soda. I then
took it from the solution, and, holding one extremity of it in my hand, I suffered the other to hang freely
down. While in this position, I raised up the nerves with a small glass rod, in such a manner that they
did not touch the muscles. I then suddenly removed the glass rod, and every time that the spinal marrow
sic
