The frog galvanoscope was a sensitive electrical instrument used to detect
voltage
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...
in the late 18th and 19th centuries. It consists of a skinned frog's leg with electrical connections to a nerve. The instrument was invented by
Luigi Galvani
Luigi Galvani ( , , ; ; 9 September 1737 – 4 December 1798) was an Italian physician, physicist, biologist and philosopher who studied animal electricity. In 1780, using a frog, he discovered that the muscles of dead frogs' legs twitched when ...
and improved by
Carlo Matteucci
Carlo Matteucci (20 June 1811 – 24 June 1868) was an Italian physicist and neurophysiologist who was a pioneer in the study of bioelectricity.
Biography
Carlo Matteucci was born at Forlì, in the province of Romagna, to Vincenzo Matteucci ...
.
The frog galvanoscope, and other experiments with frogs, played a part in the dispute between Galvani and
Alessandro Volta
Alessandro Giuseppe Antonio Anastasio Volta (, ; ; 18 February 1745 – 5 March 1827) was an Italian chemist and physicist who was a pioneer of electricity and Power (physics), power, and is credited as the inventor of the electric battery a ...
over the nature of electricity. The instrument is extremely sensitive and continued to be used well into the nineteenth century, even after
electromechanical
Electromechanics combine processes and procedures drawn from electrical engineering and mechanical engineering. Electromechanics focus on the interaction of electrical and mechanical systems as a whole and how the two systems interact with each ...
meters came into use.
Terminology
Synonyms for this device include galvanoscopic frog, frog's leg galvanoscope, frog galvanometer, rheoscopic frog, and frog electroscope. The device is properly called a ''galvanoscope'' rather than ''galvanometer'' since the latter implies accurate measurement whereas a galvanoscope only gives an indication.
[Hackmann, p. 257] In modern usage a
galvanometer
A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely. Galvanomet ...
is a sensitive laboratory instrument for measuring current, not voltage. Everyday current meters for use in the field are called
ammeter
An ammeter (abbreviation of ''ampere meter'') is an measuring instrument, instrument used to measure the electric current, current in a Electrical circuit, circuit. Electric currents are measured in amperes (A), hence the name. For direct measure ...
s. A similar distinction can be made between
electroscope
The electroscope is an early scientific instrument used to detect the presence of electric charge on a body. It detects this by the movement of a test charge due to the Coulomb's law, Coulomb electrostatic force on it. The amount of charge on ...
s,
electrometer
An electrometer is an electrical instrument for measuring electric charge or electrical potential difference. There are many different types, ranging from historical handmade mechanical instruments to high-precision electronic devices. Modern ...
s, and
voltmeter
A voltmeter is an instrument used for measuring electric potential difference between two points in an electric circuit. It is connected in parallel. It usually has a high resistance so that it takes negligible current from the circuit.
A ...
s for voltage measurements.
History
Frogs were a popular subject of experiment in the laboratories of early scientists. They were small, easily handled, and there was a ready supply.
Marcello Malpighi
Marcello Malpighi (10 March 1628 – 30 November 1694) was an Italians, Italian biologist and physician, who is referred to as the "founder of microscopical anatomy, histology and father of physiology and embryology". Malpighi's name is borne by ...
, for instance, used frogs in his study of lungs in the seventeenth century. Frogs were particularly suitable for the study of muscle activity. Especially in the legs, the muscle contractions are readily observed and the nerves are easily dissected out. Another desirable feature for scientists was that these contractions continued after death for a considerable time. Also in the eighteenth century,
Leopoldo Caldani and
Felice Fontana
Abbé Gasparo Ferdinando Felice Fontana (15 April 1730 – 9 March 1805) was an Italian polymath who contributed to experimental studies in physiology, toxicology, and physics. As a physicist he discovered the water gas shift reaction in 1780. He ...
subjected frogs to electric shocks to test
Albrecht von Haller
Albrecht von Haller (also known as Albertus de Haller; 16 October 170812 December 1777) was a Swiss anatomist, physiologist, naturalist, encyclopedist, bibliographer and poet. A pupil of Herman Boerhaave and Jacob Winslow, he is sometimes r ...
's
irritability theory.
Luigi Galvani
Luigi Galvani ( , , ; ; 9 September 1737 – 4 December 1798) was an Italian physician, physicist, biologist and philosopher who studied animal electricity. In 1780, using a frog, he discovered that the muscles of dead frogs' legs twitched when ...
, a lecturer at the
University of Bologna
The University of Bologna (, abbreviated Unibo) is a Public university, public research university in Bologna, Italy. Teaching began around 1088, with the university becoming organised as guilds of students () by the late 12th century. It is the ...
, was researching the
nervous system
In biology, the nervous system is the complex system, highly complex part of an animal that coordinates its behavior, actions and sense, sensory information by transmitting action potential, signals to and from different parts of its body. Th ...
of frogs from around 1780. This research included the muscular response to
opiate
An opiate is an alkaloid substance derived from opium (or poppy straw). It differs from the similar term ''opioid'' in that the latter is used to designate all substances, both natural and synthetic, that bind to opioid receptors in the brain ( ...
s and
static electricity
Static electricity is an imbalance of electric charges within or on the surface of a material. The charge remains until it can move away by an electric current or electrical discharge. The word "static" is used to differentiate it from electric ...
, for which experiments the spinal cord and rear legs of a frog were dissected out together and the skin removed. In 1781, an observation was made while a frog was being dissected. An
electric machine
Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...
discharged just at the moment one of Galvani's assistants touched the
crural nerve of a dissected frog with a scalpel. The frog's legs twitched as the discharge happened. Galvani found that he could make the prepared leg of a frog (see the
''Construction'' section) twitch by connecting a metal circuit from a nerve to a muscle, thus inventing the first frog galvanoscope. Galvani published these results in 1791 in ''De viribus electricitatis''.
An alternative version of the story of the frog response at a distance has the frogs being prepared for a soup on the same table as a running electric machine. Galvani's wife notices the frog twitch when an assistant accidentally touches a nerve and reports the phenomenon to her husband. This story originates with
Jean-Louis Alibert and, according to Piccolino and Bresadola, was probably invented by him.
Galvani, and his nephew
Giovanni Aldini
Giovanni Aldini (10 April 1762 – 17 January 1834) was an Italian physician and physicist born in Bologna. He was a brother of the statesman Count Antonio Aldini (1756–1826). He graduated in physics at University of Bologna in 1782.
He became ...
, used the frog galvanoscope in their electrical experiments.
Carlo Matteucci
Carlo Matteucci (20 June 1811 – 24 June 1868) was an Italian physicist and neurophysiologist who was a pioneer in the study of bioelectricity.
Biography
Carlo Matteucci was born at Forlì, in the province of Romagna, to Vincenzo Matteucci ...
improved the instrument and brought it to wider attention. Galvani used the frog galvanoscope to investigate and promote the theory of ''animal electricity'', that is, that there was a
vital life force in living things that manifested itself as a new kind of electricity.
Alessandro Volta
Alessandro Giuseppe Antonio Anastasio Volta (, ; ; 18 February 1745 – 5 March 1827) was an Italian chemist and physicist who was a pioneer of electricity and Power (physics), power, and is credited as the inventor of the electric battery a ...
opposed this theory, believing that the electricity that Galvani and other proponents were witnessing was due to metal
contact electrification
The triboelectric effect (also known as triboelectricity, triboelectric charging, triboelectrification, or tribocharging) describes electric charge transfer between two objects when they contact or slide against each other. It can occur with d ...
in the circuit. Volta's motivation in inventing the
voltaic pile
upright=1.2, Schematic diagram of a copper–zinc voltaic pile. Each copper–zinc pair had a spacer in the middle, made of cardboard or felt soaked in salt water (the electrolyte). Volta's original piles contained an additional zinc disk at the ...
(the forerunner of the common
zinc–carbon battery
A zinc–carbon battery (or carbon zinc battery in U.S. English) is the generic “heavy duty” disposable battery. It has been overtaken in recent times by the longer-lasting alkaline battery.
A zinc–carbon battery is a dry cell that provi ...
) was largely to enable him to construct a circuit entirely with non-biological material to show that the vital force was not necessary to produce the electrical effects seen in animal experiments. Matteucci, in answer to Volta, and to show that metal contacts were not necessary, constructed a circuit entirely out of biological material, including a
frog battery
A frog battery is an electrochemical battery consisting of a number of dead frogs (or sometimes live ones), which form the cells of the battery connected in a series arrangement. It is a kind of biobattery. It was used in early scientific inv ...
. Neither the animal electricity theory of Galvani nor the contact electrification theory of Volta forms part of modern electrical science. However,
Alan Hodgkin
Sir Alan Lloyd Hodgkin (5 February 1914 – 20 December 1998) was an English physiology, physiologist and biophysics, biophysicist who shared the 1963 Nobel Prize in Physiology or Medicine with Andrew Huxley and John Eccles (neurophysiologist) ...
in the 1930s showed that there is indeed an
ion
An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
ic current flowing in nerves.
[Piccolino & Bresadola, p. 75]
Matteucci used the frog galvanoscope to study the relationship of electricity to muscles, including in freshly amputated human limbs. Matteucci concluded from his measurements that there was an electric current continually flowing from the interior, to the exterior of all muscles. Matteucci's idea was widely accepted by his contemporaries, but this is no longer believed and his results are now explained in terms of
injury potential.
Construction
An entire frog's hind leg is removed from the frog's body with the
sciatic nerve
The sciatic nerve, also called the ischiadic nerve, is a large nerve in humans and other vertebrate animals. It is the largest branch of the sacral plexus and runs alongside the hip joint and down the right lower limb. It is the longest and widest ...
still attached, and possibly also a portion of the
spinal cord
The spinal cord is a long, thin, tubular structure made up of nervous tissue that extends from the medulla oblongata in the lower brainstem to the lumbar region of the vertebral column (backbone) of vertebrate animals. The center of the spinal c ...
. The leg is skinned, and two electrical connections are made. These may be made to the nerve and the foot of the frog's leg by wrapping them with metal wire or foil,
[Hare, p. 4] but a more convenient instrument is Matteucci's arrangement shown in the image. The leg is placed in a glass tube with just the nerve protruding. Connection is made to two different points on the nerve.
[Bird, p. 345]
According to Matteucci, the instrument is most accurate if direct electrical contact with muscle is avoided. That is, connections are made only to the nerve. Matteucci also advises that the nerve should be well stripped and that contacts to it can be made with wet paper in order to avoid using sharp metal probes directly on the nerve.
Operation
When the frog's leg is connected to a circuit with an
electric potential
Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work (physic ...
, the muscles will contract and the leg will twitch briefly. It will twitch again when the circuit is broken.
The instrument is capable of detecting extremely small
voltage
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...
s, and could far surpass other instruments available in the first half of the nineteenth century, including the electromagnetic
galvanometer
A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely. Galvanomet ...
and the
gold-leaf electroscope
The electroscope is an early scientific instrument used to detect the presence of electric charge on a body. It detects this by the movement of a test charge due to the Coulomb electrostatic force on it. The amount of charge on an object is ...
. For this reason, it remained popular long after other instruments became available. The galvanometer was made possible in 1820 by the discovery by
Hans Christian Ørsted
Hans Christian Ørsted (; 14 August 1777 – 9 March 1851), sometimes Transliteration, transliterated as Oersted ( ), was a Danish chemist and physicist who discovered that electric currents create magnetic fields. This phenomenon is known as ...
that electric currents would deflect a compass needle, and the gold-leaf electroscope was even earlier (
Abraham Bennet
Abraham Bennet FRS (baptised 20 December 1749 – buried 9 May 1799) was an English clergyman and physicist, the inventor of the gold-leaf electroscope and developer of an improved magnetometer. Alessandro Volta cited Bennet as a key influence ...
, 1786). Yet
Golding Bird
Golding Bird (9 December 1814 – 27 October 1854) was a British medical doctor and a Fellow of the Royal College of Physicians. He became a great authority on kidney diseases and published a comprehensive paper on urinary deposits in 1 ...
could still write in 1848 that "the irritable muscles of a frog's legs were no less than 56,000 times more delicate a test of electricity than the most sensitive condensing electrometer." The word ''condenser'' used by Bird here means a coil, so named by
Johann Poggendorff by analogy with Volta's term for a
capacitor
In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...
.
The frog galvanoscope can be used to detect the direction of
electric current
An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of electric charge through a surface. The moving particles are called charge c ...
. A frog's leg that has been somewhat desensitised is needed for this. The sensitivity of the instrument is greatest with a freshly prepared leg and then falls off with time, so an older leg is best for this. The response of the leg is greater to currents in one direction than the other and with a suitably desensitised leg it may only respond to currents in one direction. For a current going into the leg from the nerve, the leg will twitch on making the circuit. For a current passing out of the leg, it will twitch on breaking the circuit.
The major drawback of the frog galvanoscope is that the frog leg frequently needs replacing.
[Clarke & Jacyna, citing Matteucci] The leg will continue to respond for up to 44 hours, but after that a fresh one must be prepared.
References
Bibliography
*Clarke, Edwin; Jacyna, L. S., ''Nineteenth-Century Origins of Neuroscientific Concepts'', University of California Press, 1992 .
*Clarke, Edwin; O'Malley, Charles Donald, ''The Human Brain and Spinal Cord: a historical study illustrated by writings from antiquity to the twentieth century'', Norman Publishing, 1996 .
*
Bird, GoldingChapter XX, "Physiological electricity, or galvanism" ''Elements of Natural Philosophy'', London: John Churchill, 1848 .
*Hackmann, Willem D., "Galvanometer", in Bud, Robert; Warner, Deborah Jean (eds), ''Instruments of Science: An Historical Encyclopedia'', pp. 257–259, Taylor & Francis, 1998 .
*
Hare, Robert"Of galvanism, or voltaic electricity" ''A Brief Exposition of the Science of Mechanical Electricity'', Philadelphia: J. G. Auner, 1840 .
*Hellman, Hal, ''Great Feuds in Medicine'', John Wiley and Sons, 2001
*
Keithley, Joseph F., ''The Story of Electrical and Magnetic Measurements: From 500 BC to the 1940s'', IEEE Press, 1999 .
*Piccolino, Marco; Bresadola, Marco, ''Shocking Frogs: Galvani, Volta, and the Electric Origins of Neuroscience'', Oxford University Press, 2013 .
*
Matteucci, Carlobr>
"The muscular current"''Philosophical Transactions'', pp. 283–295, 1845.
*Wilkinson, Charles Henry
''Elements of Galvanism'' London: John Murray, 1804 {{OCLC, 8497530.
Biophysics
History of technology
Electrical meters