Biomedical Engineering Reference
In-Depth Information
Franklin, the scientist, is most popularly known for his kite experiment during a
thunderstorm in June 1752 in Philadelphia. Although various European investigators had
surmised the identity of electricity and lightning, Franklin was the first to prove by an
experimental procedure and demonstration that lightning was a giant electrical spark.
Having previously noted the advantages of sharp metal points for drawing “electrical fire,”
Franklin put them to use as “lightning rods.” Mounted vertically on rooftops, they would
dissipate the thundercloud charge gradually and harmlessly to the ground. This was the
first practical application in electrostatics.
Franklin's work was well received by the Royal Society in London. The origin of such
noteworthy output from remote and colonial America made Franklin especially marked.
In his many trips to Europe as statesman and experimenter, Franklin was lionized in social
circles and eminently regarded by scientists.
12.2.3 Galvani's Experiments
Against such a background of knowledge of the “electric fluid” and the many powerful
demonstrations of its ability to activate muscles and nerves, it is readily understandable
that biologists began to suspect that the “nervous fluid” or the “animal spirit” postulated
by Galen to course in the hollow cavities of the nerves and mediate muscular contraction,
and indeed all the nervous functions, was of an electrical nature. Galvani, an obstetrician
and anatomist, was by no means the first to hold such a view, but his experimental search
for evidence of the identity of the electric and nervous fluids provided the critical
breakthrough.
Speculations that the muscular contractions in the body might be explained by some
form of animal electricity were common. By the eighteenth century, experimenters were
familiar with the muscular spasms of humans and animals that were subjected to the
discharge of electrostatic machines. As a result, electric shock was viewed as a muscular
stimulant. In searching for an explanation of the resulting muscular contractions, various
anatomical experiments were conducted to study the possible relationship of “metallic
contact” to the functioning of animal tissue. In 1750, Johann Sulzer (1720-1779), a profes-
sor of physiology at Zurich, described a chance discovery that an unpleasant acid taste
occurred when the tongue was put between two strips of different metals, such as zinc
and copper, whose ends were in contact. With the metallic ends separated, there was no
such sensation. Sulzer ascribed the taste phenomenon to a vibratory motion set up in
the metals that stimulated the tongue and used other metals with the same results. How-
ever, Sulzer's reports went unheeded for a half-century until new developments called
attention to his findings.
The next fortuitous and remarkable discovery was made by Luigi Galvani (1737-1798), a
descendant of a very large Bologna family, who at age 25 was made Professor of Anatomy
at the University of Bologna. Galvani had developed an ardent interest in electricity and its
possible relation to the activity of the muscles and nerves. Dissected frog legs were conve-
nient specimens for investigation, and in his laboratory Galvani used them for studies of
muscular and nerve activity. In these experiments, he and his associates were studying
the responses of the animal tissue to various stimulations. In this setting, Galvani observed
that while a freshly prepared frog leg was being probed by a scalpel, the leg jerked
