Physiology and electricity share a common historical journey. In the mid 1700’s, the Austrian writer/philosopher J. Sulzer noted that when two metal discs were placed on his tongue—one copper and one zinc—the combined metals yielded an odd sensation and taste. He expansively described the copper-zinc taste as “green vitriol.” Although Sulzer did not comprehend the forces behind his observation, he was experiencing was the literal “taste” of electricity generated by the interaction of these dissimilar metals.
Electrical activity generated by the combination of dissimilar metals was further explored by the Italian physician and botanist Luigi Galvani (1737-1798). While poking the leg muscles of a freshly dissected frog with two probes of copper and steel, Galvani was startled when the frog’s leg suddenly twitched. What had happened? The frog was clearly dead. After subsequent frog experiments, some ambitiously involving the use of a metal wire exposed to lightning, Galvani began to refer to this ephemeral twitching activity as “animal electricity.” In 1781, he published his widely-read “Commentarius,” which laid the foundations for modern electrophysiology and neuroscience. In the decades following Galvani’s initial discoveries, this notion of animal electricity as the “spark of life” became the subject of spirited debate, and even found its way into Mary Shelley’s 1818 novel “Frankenstein” as the reanimating force for the title character’s undead creation.
In 1799, Italian physicist and chemist Count Alessandro Volta (1745-1827), advanced Galvani’s discoveries into the first practical method of generating electricity. Volta rejected Galvani’s “spark of life” notion, and theorized that the “twitching” frog leg activity was not “animal electricity” but the result of an interaction between the frog’s leg and the metals. Volta further realized that the frog’s leg served as both a conductor of electricity (what we would now call an electrolyte) and as a detector of electricity. Using an electric eel as an natural example, he constructed alternating discs of zinc and copper with brine-soaked pieces of cardboard between the metals, which produced an electrical current. This became known as “Volta’s pile” and was the first “wet cell battery” that yielded a reliable, steady current of electricity.
Volta’s doctrine prevailed over Galvani’s until the 1820s, when Leopoldo Nobili used the newly invented “galvanometer” (a compass-like device for detecting electrical activity) to measure the current flowing through a frog’s leg muscle. This gave rise to a host of ghoulish experiments involving half-dismembered animals and severed human cadaver parts. It wasn’t until the 1840’s that researchers Carlo Mateucci and Emil du Bois-Reymond discovered that galvanic measurements of living muscle tissues could be steadily and reliably measured. Du Bois-Reymond pioneered research indicating that living tissue, such as muscle, was composed of “electric molecules,” and the measured electrical activity was the result of this native “electric molecule” behavior.
We now know that these are sodium, potassium, and other ions responsible for maintaining the “membrane potentials” in excitable cells, whether it’s a flexing muscle or a beating heart. Furthermore, these various measurements have unique electrical signatures that can be displayed as waveforms for muscle activity (EMG), heart activity (ECG) or a wide array of other body “signals.” Ultimately, electricity is a fundamental property of living organisms, the understanding of which was arrived at over a century of trial and error.
BIOPAC offers a variety of industry-leading hardware and software solutions for conducting Electrophysiology* studies. For more information about recording and analyzing body signals using the MP160 and other platforms, please visit the individual application pages on the BIOPAC website.
*Electrophysiology: the science and branch of physiology that pertains to the flow of ions (ion current) in biological tissues