Lon Wilkens, a retired professor of neuroscience who lives on St. George Island, explores the history of a fascinating aspect of nature
Many of us are aware of the lesser electric ray, Narcine brasiliensis, some perhaps too familiar considering the nearly 35-volt jolt it can deliver if touched. Less common locally is the related Atlantic torpedo, Torpedo nobiliana.
We intuitively understand the physical basis of an electric shock, with our lives dependent on an electrical infrastructure. Nevertheless, it is fascinating to reflect back in history, imagine how an electrical shock from a fish was viewed when all of nature was interpreted on the basis of four elements, air, earth, fire, and water. In contrast, electricity is a phenomenon of relatively recent history, popularized beginning in the 18th century by Benjamin Franklin flying his kite in a thunderstorm.
First, it is instructive to review the diversity of “electric” fish. Mostly, we think of electrogenic fish that produce an electric organ discharge (EOD). Then there are fish that are electrosensory, a sense we do not possess. Many fish are both electrosensory and generate EODs.
Fish can be strongly or weakly electrogenic. The former includes skates and rays, (the genus Torpedo contains 10 species, some generating EODs up to 220 volts), stargazers (to 50 volts), and the electric Nile catfish Malapterus electricus (to 350 volts). Most familiar is the South American electric eel, Electrophorus electricus, with EODs of up to 700 volts, jolts known to stun and disable a horse.
In contrast, weakly electric fish generate EODs around 1 volt, several hundred species in all including many common in the aquarium trade such as elephantnose and knifefishes. These fish are also electrosensory and communicate with each other electrically. Moreover, by monitoring objects that distort their own electric fields they can electrolocate, analogous to sonic location used by bats and porpoises, “active” mechanisms especially useful in the dark.
Other electrosensory fish are “passive” (no EODs), detecting the electrical fields of both animate and inanimate objects as weak as 1 nanovolt (10-9 V) per centimeter. To illustrate this extraordinary sensitivity consider that a shark can detect a flounder buried in the sand, and can navigate, monitoring its own electric field as it swims, its body acting as a conductor moving through the earth’s magnetic field, the biological equivalent of an electricity generator. The passive electrosense is a primitive feature found in lampreys, all elasmobranchs (sharks, skates and rays), sturgeon and paddlefish. Essentially an aquatic sensory mechanism, the duckbill platypus, a mammal, has developed a parallel electrosense used to detect prey..
Origins are with Mediterranean torpedoes
The shocking history origins deal primarily with torpedoes abundant in Mediterranean waters and brought to the attention of scholars, physicians and philosophers during the classical Greco-Roman era. The earliest reference to torpedoes was in Hippocratic writings in the 5th century B.C. Plato and Socrates (4th century B.C.) alluded to their powers as magic, “benumbing the mind,” whereby the flat sea torpedo torpifies those who come into contact. The Greeks referred to the effect as nįrkė, from which narcotic, narcosis, narcotize were derived based on the fish’s ability to cause numbness, torpor, and involuntary muscle twitches.
Aristotle (374-322 B.C.), writing in his Historia Animalium, noted its specialized numbing as a “purposeful intelligence” that it used to capture prey. He was supplied specimens by local fishermen and by Alexander the Great. These fishermen reported that the mysterious force of the torpedo could be felt even at a distance when touched holding a metal rod (trident) or the salty lines of a fishing net.
Pliny the Elder (1st century A.D.), the great Roman naturalist, wrote in his 37 volume Naturalis Historia that “if only touched with the end of a spear or staff, this fish has the property of benumbing even the most vigorous arm and of riveting the feet of the runner.” He interpreted the shock as “an odor of emanation from the fish, a poison that could run up a spear and kill a man, even a horse,” a mixture of science and fable.
Greco-Roman medical literature included many therapeutic uses for the torpedo discharge, of course without any idea of the force electricity. Among some 271 remedies ascribed to Scribonius (3 B.C.-54 A.D.) were treatments using torpedoes for headaches to gout. The latter, foot pain or podagra, was common among Roman aristocrats given their rich diets and lead poisoning from wine containers. The foot placed on a live torpedo on the moist shore relieved gout pain up to the knee. Headache relief involved placing a live torpedo on the spot of the pain but required subsequent removal “lest ability to feel be taken away.” This numbing effect is not so far-fetched knowing now that electrical stimulation is used clinically to relieve pain and thought to release endorphins.
In addition to relief of headache pain, Discorides (1st century A.D.) used torpedoes to treat a condition of “the seat,” now interpreted to mean application to the prolapsed seat (prolapsus ani in Latin), that is, hemorrhoids. This form of electrotherapy is potentially valid given that electrical stimulation can cause constriction of blood vessels and hemorrhoidal shrinkage.
Galen (129-200 A.D.), the most accomplished physician and philosopher in Roman antiquity, also tested the shock of the torpedo, finding it useful in treating headaches. In describing its analgesic remedy, he likened the effect to a “cold venom,” some form of “corpuscular matter.” He equated hand numbness transmitted through the trident to the lodestone (a magnet) effect in which a body can acquire the power of a separate object.
The immobilizing actions of the torpedo also captured the imagination of ancient poets who suggested that catching a torpedo can make an angler remorseful. Oppian (2nd century A.D.), writes poetically that “the Cramp-fish (torpedo) paint their magick wands, where icy torch the strongest fin commands… one touch of her’s dams up the vital Flood, Contracts the Nerves, and clots the stagnate Blood.” Torpedoes also appeared prominently in Mediterranean paintings and pottery.
Authors from classical antiquity significantly influenced how torpedoes, along with the Nile catfish, were perceived well into the Middle Ages, a period during which Christianity and Islam emerged along with a decline in the spirit of scientific investigation, the Dark Ages. Physicians still used torpedoes for head pain and podagra as specified in medical texts. Byzantine writings concerning nįrkė were essentially compilations from the previous classical era and associated the “magical powers” with various occult practices.
Well into the Renaissance, despite advances in architecture, medicine, and science, there was no further insight into the nature of the discharge. By the 16th century, European exploration and conquest had generated considerable interest in the “torporific” (electric) eel that horrified natives along the Orinoco River in South America. Still, the only explanation available was that the torpedo discharge was mechanical, associated with violent contractions in the fish.
The discharge itself was interpreted at the time according to atomistic theories of sensation attributed largely to Galileo, whereby microscopic pores, canals and glands produced minute corpuscles (atoms) used to explain multiple physiological processes including perspiration. This was incorporated in Stefano Lorenzini’s (1678) “corpuscular” theory attributing numbness to corpuscles (molti corpuscoli) that entered the hand to block nerves as a result of touching the fish. The mechanical theory was later discredited since contractions by the torpedo proved to be “invisible,” unrepeatable, and any movements were no doubt affected by the tremor induced in the experimenter’s hand in response to the shock.
Electricity as a physical entity became established in mid-17th century Europe, confirmed scientifically by the 18th using instruments such as the Leyden jar, a capacitor that was introduced into the public’s imagination by Abbe Jean-Antoine Nollet (1700-1770), in a demonstration before royal onlookers in Versailles that 180 hand-holding grenadiers who completed the circuit leaped in unison at its discharge.
These instruments were capable of producing sparks, akin to static electricity we can generate by stroking fur or amber, and were seemingly related to the demonstration of atmospheric electricity by Benjamin Franklin. Self-educated, Franklin abandoned his lucrative printing business in 1748 to study electricity and later moved to England in 1757 to join the Royal Society of London, where he contributed prominently to developments in fish electricity. He also is credited with the concept of polarity, based on his theory that lightning is charged differently between clouds (negative) and land (positive), and concluding that natural and man-made electricity are the same.
As interest in electricity grew in the 18th century, it led to numerous attempts, including by Franklin, to use electrotherapy to treat palsies, hysteria, and other paralyzing illnesses. Still, despite the ancient history of torpedo therapeutics, no scientific understanding of animal electricity was yet available. Although nerves were envisioned as conduits to the brain as early as the 4th century B.C., conveyance (conduction) along the nerve was still attributed variously to ethereal spirits, fluids, or mechanical vibrations.
Benjamin Franklin helps with experiments
As interest in animal electricity continued to grow, electric fish contributed significantly to the eventual electrical basis of physiological function in both nerve and muscle. A major contribution from the Dutch, with settlements in Guiana, S.A., came from awareness of the more powerful electric eel whose discharge was equated with that of the Leyden jar, both capable of knocking a person to the ground. The only difference was that neither spark (eq., lightning) nor weak crackling sound (eq., thunder) could be elicited from the eel, facts that contributed to remaining resistance to the idea of fish electricity.
An American physician who worked briefly in Guiana (Edward Bancroft, 1744-1821) presented evidence that shocks from the torporific eel traveled up the fishing line and could be felt by several people holding hands (in series). John Walsh (1726-1795), a wealthy English colonel with an interest in natural history provided singular evidence for the electrical nature of Torpedo.
Armed with a series of experiments outlined by his collaborator, Benjamin Franklin, Walsh traveled to La Rochelle and nearby l’Isle de Ré on the French Atlantic coast where the rays were abundant. Using public demonstrations he showed that the discharge could be felt 40 feet away when connected to the fish by a wire, that up to eight persons holding hands in series were affected, and that two persons, one touching the upper surface of the fish, the other the lower surface, only felt the shock when they completed the circuit by holding hands. In letters back to Franklin, Walsh concluded that the effect “is certainly torpedinal electricity.”
His work was forwarded to Henry Cavendish (1731-1810), the brilliant chemist (discoverer of oxygen), physicist and member of the Royal Society (along with Walsh, Franklin, Bancroft and other notables), who provided quantitative explanations supporting fish electricity. Franklin returned to the United States in 1775 in fear of arrest as a spy as progression toward the American Revolution became obvious. Ironically, it was August 1, 1776, when Walsh finally succeeded in demonstrating the convincing “spark” from a fish discharge, made possible by the arrival of a live electric eel from Guiana whose discharge was 10 times greater than the torpedo.
The torpedo and electric eel were important in the realization that animals function electrically. As such they had great influence on two Italian physician scientists, Luigi Galvani (1773-1798) and Alessandro Volta (1745-1827). Galvani’s experiments led him to propose that electricity was inherent in the tissues of the nerve by demonstrating that frog leg muscles twitched when the [motor] nerve was stimulated with a weak electrical current. One such experiment used long wires connected to an electrical device in the room. This is known to have inspired Mary Shelley to create Frankenstein in her 1817 saga by attracting the electrical activity from a lightning storm.
Volta claimed that the electricity was not intrinsic to the nerve but rather originated in the metals Galvani used to touch the nerve. His own experiments with the frog used a pile or battery that he is credited with inventing. This first battery, dissimilar metals sandwiched around moistened cardboard, was inspired in turn by the electric organ of the torpedo. From these signature experiments, preceded by work through the ages, it is clear that torporific fishes have played a major role in shaping civilization through the life sciences and medicine.
Lon Wilkens, an emeritus professor of neuroscience at the University of Missouri-St. Louis, lives on St. George Island.