Biomedical Engineering Reference
In-Depth Information
convulsively whenever a nearby frictional electrical machine gave off sparks. Galvani said
the following of his experiments:
I had dissected and prepared a frog, and laid it on a table, on which there was an electrical machine. It so
happened by chance that one of my assistants touched the point of his scalpel to the inner crural nerve of the
frog; the muscles of the limb were suddenly and violently convulsed. Another of those who were helping to
make the experiments in electricity thought that he noticed this happening only at the instant a spark came
from the electrical machine. He was struck with the novelty of the action. I was occupied with other things at
the time, but when he drew my attention to it, I immediately repeated the experiment. I touched the other
end of the crural nerve with the point of my scalpel, while my assistant drew sparks from the electrical
machine. At each moment when sparks occurred, the muscle was seized with convulsions.
With an alert and trained mind, Galvani designed an extended series of experiments to
resolve the cause of the mystifying muscle behavior. On repeating the experiments, he
found that touching the muscle with a metallic object while the specimen lay on a metal
plate provided the condition that resulted in the contractions.
Having heard of Franklin's experimental proof that a flash of lightning was of the same
nature as the electricity generated by electric machines, Galvani set out to determine
whether atmospheric electricity might produce the same results observed with his electrical
machine. By attaching the nerves of frog legs to aerial wires and the feet to another electrical
reference point known as an electrical ground, he noted the same muscular response during
a thunderstorm that he observed with the electrical machine. It was another chance obser-
vation during this experiment that lead to further inquiry, discovery, and controversy.
Galvani also noticed that the prepared frogs, which were suspended by brass hooks
through the marrow and rested against an iron trellis, showed occasional convulsions
regardless of the weather. In adjusting the specimens, he pressed the brass hook against
the trellis and saw the familiar muscle jerk occurring each time he completed the metallic
contact. To check whether this jerking might still be from some atmospheric effect, he
repeated the experiment inside the laboratory. He found that the specimen, laid on an iron
plate, convulsed each time the brass hook in the spinal marrow touched the iron plate.
Recognizing that some new principle was involved, he varied his experiments to find the
true cause. In the process, he found that by substituting glass for the iron plate, the muscle
response was not observed, but using a silver plate restored the muscle reaction. He then
joined equal lengths of two different metals and bent them into an arc. When the tips of
this bimetallic arc touched the frog specimens, the familiar muscular convulsions were
obtained. As a result, he concluded not only that metal contact was a contributing factor
but also that the intensity of the convulsion varied according to the kinds of metals joined
in the arc pair.
Galvani was now faced with trying to explain the phenomena he was observing. He had
encountered two electrical effects for which his specimens served as indicator: one from
the sparks of the electrical machine and the other from the contact of dissimilar metals.
Either the electricity responsible for the action resided in the anatomy of the specimens with
the metals serving to release it or the effect was produced by the bimetallic contact, with the
specimen serving only as an indicator.
Galvani was primarily an anatomist and seized on the first explanation. He ascribed the
results to “animal electricity” that resided in the muscles and nerves of the organism itself.
