When Frogs Danced: The Revolution of Electricity with Galvani and Volta

By Mirella Melo

Abstract

Here, I will explore the advancements and historical context of electricity study from the 18th to the 19th century, highlighting the foundational contributions of Luigi Galvani. It delves into the initial exploration of electrical phenomena by Stephen Gray and Charles du Fay and the subsequent influence of Benjamin Franklin’s experiments and theories. After a period of stagnation following Galvani's research, the report details a renewed interest in animal electricity during the 19th century. Key figures such as Carlo Matteucci, Luigi Rolando, Pierre Flourens, Emil du Bois-Reymond, and Julius Bernstein significantly advanced the field, leading to a more profound understanding of electrophysiology.

1. Introduction

The 18th century, often called the Age of Enlightenment or the Age of Reason, was a pivotal period in history characterized by a profound shift in thought and philosophy, especially in Europe and America. This era is marked by a fervent pursuit of knowledge, emphasizing reason, scientific inquiry, and questioning doctrines and traditions [1].

During this era, electricity was a major focus of scientific study. In England, Stephen Gray (1666-1736) demonstrated that electricity could be transmitted over distances through conductors, distinguishing them from insulators. In Paris, Charles du Fay (1698-1739) identified "vitreous" and "resinous" types of static electricity, noting their ability to attract or repel. He theorized the existence of two opposing electrical forces. In the same context, Benjamin Franklin (1706-1790), working primarily in the American colonies, contributed to the field with his experiments and theories, particularly his proposal of the single fluid theory of electricity and the groundbreaking kite experiment. His work was instrumental in evolving the concept of electrical charge [2]. These foundational studies were ultimately unified by J.J. Thomson's discovery of the electron in 1897, connecting the early macroscopic observations of electricity with the emerging particle theory.

Within this historical context and the then-current research landscape, still in the process of formalization in the field of electricity, Luigi Galvani (1737-1798) and Alessandro Volta (1745-1827) brought forth their contributions. They were two pioneering figures, and their work laid the crucial groundwork for the development of electrical science. They did not work together; instead, their relationship is best described as a scientific rivalry.

2. Discussion

Galvani was an Italian physician, physicist, and philosopher who spent most of his career at the University of Bologna. Although his research was influenced by researchers such as Stephen Gray and Charles du Fay, his major reference came from the researcher Benjamin Franklin (1706-1790) [2].

Galvani's work, particularly his experiments on “animal electricity,” extends Franklin's research on lightning and the single fluid theory. Franklin's lightning experiments, which involved flying a kite during a thunderstorm to prove that lightning is electrical in nature, showcased that electrical principles could explain and manipulate atmospheric phenomena. This demonstration likely inspired Galvani to explore the effects of electricity on biological systems, hypothesizing that similar electrical principles could be active within living organisms, as illustrated in Figure 1.a. Additionally, Franklin’s methodical approach, using simple but clever experimental setups to test specific theories, likely influenced Galvani's experimental designs to stimulate nerve and muscle tissues with electricity, as shown in Figure 1.b [2][3].

Another important contribution from Franklin is his single fluid theory, which stated that electricity involved a single fluid where an excess resulted in a positive charge (previously thought of as vitreous electricity) and a deficit resulted in a negative charge (previously thought of as resinous electricity), simplified the conceptual framework of electrical forces. Galvani's hypothesis of “animal electricity” as a distinct form of natural force inherent within living tissues can be seen as a direct application of Franklin's electrical theory to the domain of physiology [2].

Figure 1. Experiments illustrating  (a) the atmospheric electricity captured using a metal rod during a storm, with the charge directed to a dissected frog's leg to observe muscular twitching, and (b) Galvani’s different setups [4].

Galvani's interest in the effects of electricity on frog legs began around 1780. While dissecting frogs at the University of Bologna, he observed that the legs twitched when struck by a spark from an electrostatic machine. This observation led him to speculate about the nature of the force causing this movement. He proposed that living tissue contained an innate, vital force that he characterized as electrical in nature, a hypothesis known as “animal electricity.” [3-6]

One of Galvani's most famous experiments involved forming an arc made of two different metals (e.g., brass and iron) touching a frog's nerve and muscle. When the circuit was completed, the frog's leg would twitch. This setup, known as the "Galvanic circuit," suggested that electricity could be generated and conducted within the body, refuting the idea that it was solely an external force. Galvani also found that muscle contractions could be induced without any external electrical source simply by using metallic instruments to connect nerves and muscles, further supporting his theory of animal electricity [3-6].

Volta was an Italian physicist, chemist, and pioneer in the study of electricity. He was a professor at the Royal School in Como and later at the University of Pavia. In response to Galvani's findings, Volta began experiments that led him to propose a different interpretation. Volta demonstrated that the electrical activity observed by Galvani could be replicated by creating a circuit out of two different metals without the need for frog tissues, proving that the source of electricity was chemical reactions between the metals. In 1800, this led Volta to invent the voltaic pile, the first chemical battery, which produced a steady electric current. Volta's invention was revolutionary, providing a reliable source of electrical current and proving that electricity could be generated chemically. This laid the foundations for the field of electrochemistry [2].

After Volta provided a well-accepted alternative explanation for the frog’s leg movement, Galvani's reputation suffered significantly, leading to a decline in support and funding for his research. Galvani died in 1798, poor and discredited, shortly after being dismissed from his academic position in Bologna [5]. Despite these personal and professional declines, Galvani's pioneering experiments laid the groundwork for the birth of electrophysiology, the study of the electrical properties of biological cells and tissues. It marked the first systematic study of how electricity functions in living organisms. In addition, the experiments were crucial in the development of neuroscience, particularly in understanding how nerve cells communicate with muscles, suggesting that electrical impulses travel along nerve fibers [6].

Only in the 19th century the field of electrophysiology was continued by scientists such as Luigi Rolando (1773-1831) and Pierre Flourens (1794-1867), who investigated the brain's electrical excitability and its relation to function; Carlo Matteucci (1811-1868), who demonstrated that injured tissue generates an electric current; and Emil du Bois-Reymond (1818–1896), who discovered action potentials in nerve and muscle cells [3].

A significant advance in bioelectricity was brought by Julius Bernstein (1839-1917), who elucidated the process of nerve signal transmission and the membrane theory of the action potential. Figure 2.a shows a complex diagram referred to as a "differential rheotome," which was a device used by Bernstein to measure the velocity of nerve conduction. The rheotome was used to apply electrical stimuli to a nerve at precise intervals and to open the circuit at specific moments, allowing the recording of the nerve's response to the stimuli. Figure 2.b illustrates the actual device. Figure 2.c presents the first published recording of the time course of the action current. The downward deflection indicates the action potential, an electrical impulse that travels along the nerve fiber that occurs when a neuron is activated [3].

Figure 2. (a) The "differential rheotome," a device that delivers electrical stimuli to nerves and allows timed recordings of the response at various intervals following the stimulus [7]. (b) Photograph of the actual device with a width of 20 cm [8]. (c) The first published recording shows the timing of the action current, also known as "negative variation," within a nerve [7].

3. Outlook and relevance of work

In the Age of Enlightenment, areas such as governance, science, religion, and human rights were being widely debated. The field of electricity was among the foremost focuses regarding scientific study. Experiments and discoveries brought forth by scholars such as Stephen Gray, Charles du Fay, Benjamin Franklin, Luigi Galvani, and Alessandro Volta were not isolated incidents but part of a broader, dynamic movement towards understanding the forces of nature [1].

From Volta's breakthroughs, the physical study of electricity made substantial progress, with the invention of the voltaic pile leading to innovations in energy storage and the burgeoning field of electrochemistry. Yet, the exploration of animal electricity did not achieve any significant new breakthroughs for about thirty years following Galvani's research. Although he died without receiving due recognition, Galvani's initiative to apply then-known electrical concepts to biological systems earned him the title of a pioneer in electrophysiology and neuroscience. After Galvani's studies, figures such as Luigi Rolando, Pierre Flourens, Carlo Matteucci, Emil du Bois-Reymond, and Julius Bernstein could significantly develop areas of brain mapping, injury response, cellular bioelectricity, and signal transmission [2][3].

References

[1] Robertson, John. The Enlightenment: A very short introduction. OUP Oxford, 2015.

[2] Heilbron, John L. Electricity in the 17th and 18th centuries: A study of early modern physics. Univ of California Press, 2022.

[3] Turkel, William J. Spark from the deep: How shocking experiments with strongly electric fish powered scientific discovery. JHU Press, 2013.

[4] Galvani, Luigi. De viribus electricitatis in motu musculari commentarius. Soc. Typogr., 1792.

[5] Blondel, Christine. "Animal electricity in Paris: From initial support, to its discredit and eventual rehabilitation." Luigi Galvani International Workshop. Proceedings. Universita di Bologna, 1999.

[6] Piccolino, Marco. "Animal electricity and the birth of electrophysiology: the legacy of Luigi Galvani." Brain Research Bulletin 46.5 (1998): 381-407.

[7] Bernstein, J. U. L. I. U. S. "Ueber den zeitlichen Verlauf der negativen Schwankung des Nervenstroms." Archiv für die gesamte Physiologie des Menschen und der Tiere 1.1 (1868): 173-207.

[8] Nilius, Bernd. "Pflügers Archiv and the advent of modern electrophysiology: From the first action potential to patch clamp." Pflügers Archiv 447 (2003): 267-271.