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Tasting and Feeling

Written in 1881

Currents of electricity passed through the limbs affect the nerves with certain painful sensations, and cause muscles to undergo involuntary contractions. The sudden rush of even a small charge of electricity from a Leyden jar charged to a high potential, or from an induction coil, gives a sharp and painful shock.

The current from a few strong Grove's cells, conveyed through the body by grasping the terminals with moistened hands, gives a very different kind of sensation, not at all agreeable, of a prickling in the joints of the arms and shoulders. It does not produce any spasmodic contractions, except it be in nervous or weakly persons, at the sudden making and breaking of the circuit.

After the discovery of the shock of the Leyden jar by Cunĉus1 in 1745, many experiments have been tried. Louis XV. of France caused an electric shock from a battery of Leyden jars to be administered to 700 Carthusian monks joined hand in hand, with prodigious effect. Franklin killed a turkey by a shock from a Leyden jar.

In 1752 Sulzer remarked that "if you join two pieces of lead and silver, then lay them upon the tongue, you will notice a certain taste resembling that of green vitriol2, while each piece apart produces no such sensation." This galvanic taste, not then suspected to have any connection with electricity, may be experienced by placing a silver coin on the tongue and a steel pen under it, the edges of them being brought into metallic contact. The same taste is noticed if the two wires from the poles of a voltaic cell are placed in contact with the tongue.

Ritter discovered that a feeble current transmitted through the eyeball produces a sensation as of a bright flash of light by its sudden stimulation of the optic nerve. Dr. Hunter3 saw flashes of light when a piece of metal placed under the tongue was touched against another which touched the moist tissues of the eye. Volta and Ritter heard musical sounds when a current was passed through the ears. Humboldt4 found a sensation to be produced in the organs of smell when a current was passed from the nostril to the soft palate.

The following experiment shows the effect of feeble currents on cold-blooded creatures. If a copper (or silver) coin be laid on a piece of sheet zinc, and a common garden snail be set to crawl over the zinc, directly it comes in contact with the copper it will suddenly pull in its horns, and shrink in its body. If it is set to crawl over two copper wires, which are then placed in contact with a feeble voltaic cell, it immediately announces the establishment of a current by a similar contraction. It will scarcely be credited that a certain Jules Alix once seriously proposed a system of telegraphy based on this phenomenon. Limbs of frogs as prepared by Galvani In 1678 Swammerdam5 showed to the Grand Duke of Tuscany that when a portion of muscle of a frog's leg hanging by a thread of nerve bound with a silver wire was held over a copper support so that both nerve and wire touched the copper, the muscle immediately contracted. More than a century later Galvani's6 attention was drawn to the subject by his observation of spasmodic contractions in the legs of freshly-killed frogs under the influence of the "return-shock" experienced every time a neighbouring electric machine was discharged. Unaware of Swammerdam's experiment, he discovered in 1786 the fact (leading ultimately to the discovery of the Voltaic Pile) that when nerve and muscle touch two dissimilar metals in contact with one another a contraction of the muscle takes place.

Frogs limbs correctly prepared form an excessively delicate galvanoscope: with them, for example, the excessively delicate induction currents of the telephone can be shown, though the most sensitive galvanometers barely detect them. Galvani and Aldini proved that other creatures undergo like effects. With a voltaic pile of 100 pairs Aldini experimented on newly killed sheep, oxen and rabbits and found them to spasmodic muscular contractions. Humboldt proved the same on fishes; and Zanotti, by sending a current through a newly killed grasshopper, caused it to emit its familiar chirp.

Nobili showed that when the nerve and muscle of a frog were respectively connected with the terminals of a delicate galvanometer, a current is produced which lasts several hours. He even arranged a number of frogs' legs in series, like the cells of a battery, and thus increased the current.

Aldini, and later Dr. Ure of Glasgow, experimented on the bodies of executed criminals, with a success terrible to behold. The facial muscles underwent horrible contortions, and the chest heaved with the contraction of the diaphragm. This has suggested the employment of electric currents as an adjunct in reviving persons who have been drowned. The small muscles attached to the roots of the hairs of the head appear to be markedly sensitive to electrical conditions from the readiness with which electrification causes the hair to stand on end.

Du Bois Reymond proved that the contraction of muscles produces currents. He dipped the tips of his fore-fingers into two cups of salt water communicating with the galvanometer terminals. A sudden contraction of the muscles of either arm produced a current from the contracted towards the uncontracted muscles. Dewar has shown that when light falls upon the retina of the eye an electric current is set up in the optic nerve.

By 1881 electric currents had been successfully employed as an adjunct in restoring persons rescued from drowning. Since the discovery of the Leyden jar many attempts have been made to establish an electrical medical treatment. Discontinuous currents, particularly those furnished by small induction coils and magneto-electric machines, are employed by practitioners to stimulate the nerves in paralysis and other affections.

It is not out of place here to enter an earnest caution against the numerous quack doctors who deceive the unwary with magnetic and galvanic "appliances". It many cases these much-advertised shams have done incalculable harm; in the very few cases where some fancied good has accrued the curative agent is probably not magnetism, but flannel!

From "Electricity and Magnetism" by Silvanus P. Thompson, B.A., D.Sc., F.R.A.S. Macmillan and Co., London, 1881.

Readers are seriously urged not to try any of these experiments either on themselves, on others or on any animals.

1. Cunĉus also spelt Cuneus: see article "Early Condensers" in January 1998 newsletter.
2. Vitriol: Sulphuric acid or any of its salts.
3. Hunter, John (1728 - 1793). British Surgeon and anatomist.
4. Humboldt, Friedrich Heinrich Alexander Von (1769 - 1859). German naturalist.
5. Swammerdam, Jan (1637 - 1680). Dutch naturalist, qualified in medicine at Leyden University, specialising in entomology.
6. Galvani, Luigi (1737 - 1798). Italian physiologist, professor of anatomy at Bologna University.

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