EPITOMEOFGALVANISM.
This part of our subject has been calledanimal electricity, by the greater part of those persons who have written upon it;—but this name seems to be improper; for, as an author of reputation on the subject, remarks, “it has by no means been proved that these phenomena depend either upon electricity or animal life.” While this is the case, it is certainly best to distinguish this science by the name of its inventor Louis Galvani. He was an Italian, and professor of anatomy at Bologna, when he made the discovery of Galvanism, which was entirely accidental, as will appear in the following account.
Whilst Galvani was one day employed in dissecting a frog, in a room where some of his friends were amusing themselves with electrical experiments, one of them happened to draw a spark from the conductor, at the same time that the professor touched one of the nerves of the animal. The consequence was, that the animal’swhole body was instantly shaken by a violent convulsion. Astonished at the phenomenon, and at first imagining that it might be owing to his having wounded the nerve, the professor pricked it with the point of his knife, to assure himself whether or not this was the case; but no motion of the frog’s body was produced. He now touched the nerve with the instrument as at first, and directed a spark to be taken at the same time from the machine, on which the contractions were renewed. Upon a third trial the animal remained motionless; but observing that he held his knife by the handle, which was made of ivory, he changed it for a metallic one, and immediately the movements took place, which never was the case when he used an electric, or non-conducting substance.
After having made a great many similar experiments with the electrical machine, he resolved to prosecute the subject with atmospheric electricity. With this view he raised a conductor on the roof of his house, from which he brought an iron wire into his room.—To this he attached metal conductors, connected with the nerves of the animals, destined to be the subjects of his experiments: and to their legs he fastened wires which reached the floor. These experiments were not confined to frogs alone. Different animals, both of cold and warm blood, were subjected to them; and in all of them considerable movements were excited whenever it lightened. These movements preceded thunder, and corresponded with its intensity and repetition; and even when no lightning appeared, the movements took place when any strong cloud passed over the apparatus.—That all these appearances were produced by the electric fluid was obvious.
Having soon after this suspended some frogs, from the iron palisades which surrounded his garden, by means of metallic hooks fixed in the spines of their backs, he observed that their muscles contracted frequently and involuntarily, as if from a shock of electricity. Not doubting that the contractions depended on the electric fluid, he at first suspected that they were connected with changes in the state of the atmosphere. He soon found, however, that this was not the case; and having varied, in many different ways, the circumstances in which the frogs were placed, he at length discovered that he could produce the movements at pleasure, by touching the animals with two different metals, which at the same time touched one another, either immediately, or by the intervention of some other substance capable of conducting electricity.
Almost every animal can be made to produce these muscular contractions by the Galvanic power, but those calledcold bloodedare the best. Thusfrogshave been found the most convenient, both on account of their size and abundance. They also retain their muscular irritability to the Galvanic influence longer than most other animals, and it is asserted that strong convulsions can be produced in them many hours after the brain and spinal marrow have been destroyed; andalso that when pretty far advanced in the process of putrefaction they are capable of Galvanic excitement.
No contractions have been produced in animals killed bycorrosive sublimate, nor in those which have beenstarvedto death: but a very slight motion can be made to appear in those killed byopium, theelectric shock, orazotic gas.
With regard to the metals used to effect these motions, almost any two will answer the purpose; but the most powerful are the following, viz.
Those which have the most power are placed first; that is zinc and gold, will produce greater muscular contractions than tin and silver, or tin and gold, and so of the rest.
The process by which these wonderful appearances are produced consists in effecting, by means of the Galvanic apparatus, a communication between a nerve and a muscle, in any part of an animal body. The part of the animal upon which the experiment is to be performed is denominated theanimal arc: and the Galvanic instruments which form the communication between the muscle and the nerve, are called theexcitatory arc. This latter generally consists of three pieces; one fixed to the muscle, another to the nerve, and a third forming a communication between both. This last, called thecommunicator, may be made of the same metal with either of the others, or be different from both.The best communicators or conductors, are the following.—The list begins with the most perfect.
The metallic ores are not so good conductors as the purified metals, and their conducting power varies, according to the nature of the ores.
The metallic salts are tolerably good conductors.
Dr. Valli observed that human bodies are not all equally good conductors. Out of four persons in a company, he found that when two of them formed the circuit of communication between the nerve and muscles of a frog, the motions took place very readily. When the third person formed the circuit, the motions were very weak; but that, when the fourth person formed the communication, no motion took place. This experiment, he adds, was often repeated with the same success. The effect however may be owing to the different dryness of the skin.
Vitriolic acid, and even alcohol, appear to conduct the Galvanic influence rather better than water.
The veins and arteries are not so good conductors as the nerves; for when a blood-vessel forms part of the circuitof communication, the contractions will take place only when ramifications of the nerves are adhering to it, and if these be carefully separated, the motion will not take place. The same thing may be said of the tendons, the bones, and the membranes; for when either of those parts is separated from the body, and is introduced into the circle of communication between the muscles and nerves of a prepared frog, no motion will ensue; excepting, indeed, when those parts are full of moisture and in immediate contact with the nerve.
Professor Volta’s first contrivance for manifesting Galvanism in a more vigorous manner than had hitherto been done, was what he called acouronne de tasses. This consisted of tumblers of glass, half filled with water, or salt and water. These glasses or tumblers, were so placed that a metallic arc, in form of a C, could be fixed with one leg in one glass, and the other in the next glass. On one end of each arc, was fastened a small plate of silver or copper, and on the other end, a similar plate of zinc or tin. These plates were immersed in the fluid contained in the tumblers.—Thus in the water of every glass there was a plate of silver or copper, and another plate of zinc or tin. The metallic arcs were formed of any good conductor. When thirty or forty of these glasses were prepared, the experimenter put one of his hands into the fluid contained in the first glass, and the other hand into that in the last: when this was done a shock, something like the electrical one, wasexperienced, and would recur as often as the circuit was interrupted and completed.
Mr. Volta remarks, thatalkaline solutionsare used to the most advantage when one of the metals is tin and the other silver or copper; but that where zinc is substituted for tin, salt water is preferable.
After this discovery, Volta invented a much more convenient instrument, which, besides other advantages over the former, was more powerful and less expensive. The instrument is called theGalvanic pile, and very often theVoltaic pile, from its inventor. It is made in the following manner—Take a number of circular plates of copper, or silver and an equal number of tin or zinc of the same dimensions. Next provide a like number of round pieces of paste-board, leather, or any other substance capable of retaining moisture for a considerable time. This leather, cloth or other substance, must be rather smaller than the metal plates and, when used, well moistened with salt and water. Now form a pile, by laying alternately the zinc over the silver, and, the cloth or other moistened substance, over the zinc; and so on successively.—By thus continuing the series to forty or fifty plates, a Galvanic pile will be constructed. If the pile is intended to be of any considerable height, it ought to be secured by pillars of varnished baked wood; or strong glass tubes.
To get the shock, one hand must touch the bottom, and the other the top plate.—The hands should be wet, as the cuticle or external part of the skin is a bad conductor.
Shocks may be received by applying the hands in this manner, as long as the leather, or other substanceinterposed between the zinc and silver, continues moist; but as soon as it becomes dry the operation closes.
The drying of the substance was a great inconvenience in the Voltaic pile, and the inventor proposed, as a remedy for this, to station the metallic plates at a greater distance from one another, and to fill up the cells or intervals between them with a saline solution. Mr. Cruickshank, an English chemist at Woolwich, improved this construction.—Histroughas it is called, is made thus.—
Get a wooden trough, made of hard baked mahogany, about thirty inches long, and four or five wide and deep.—On the inside let there be cut in the sides and bottom, and at equal distances from one another, as many grooves, as the number of plates required to be put into the trough;—the grooves of a size to admit the plates. The plates are to be cemented[18]separately to each of the grooves, so that no fluid can pass from one cell to another. In this instrument the plates are constructed by soldering a plate of zinc to one of copper. The zinc, or which is the same thing, the spelter of the shops, should be melted in a vessel which exposes but a small surface to the action of the air, otherwise it would absorb oxygen so rapidly as to be converted into the flowers of zinc.—The melted metal should be poured as soon as possible into a mould of the proper size, made of stone or brass.—It is not necessary that the plates of copper should be more than one tenth of the thickness of those of zinc.
The two plates are commonly soldered, not through their whole extent, but about one fourth of an inchfrom the edge; so that at the edge their union may be complete.
Care must be taken that all the plates be cemented to the trough in the same direction; so as to have the copper side of every plate opposite to the zinc side of the next.
The liquid employed to fill up the cells between the plates, is formed by diluting muriatic acid with water, in the proportion of one ounce of the former to a pint of the latter. When the trough is not in use, it should be emptied of this solution (which may be preserved for subsequent experiments, unless saturated with the metals) and then rinsed clean with fresh water.
This construction is preferable to the Voltaic pile, for experiments in which it is necessary to have the Galvanic action for a length of time. But for occasional experiments the pile is more convenient; as the trough, if suffered to remain long without the fluid, is apt to crack and separate the cement from the plates, which renders it necessary to cement them again.
When several batteries are required, they should be disposed in the same order as if they all constituted one trough, (observing through the whole series to keep the zinc surfaces constantly opposed to the copper ones,) and connected together by some metallic substance, such as a piece of sheet lead, or tin-foil, about half the width of the trough. Batteries combined in this way should all be, as nearly as possible, of the same power. For if a bad battery be united to five good ones, each of the same number of plates, the effect of the whole will be equal only to six times that of the bad one—as in electrical batteries, if three jars of different sizes be charged together,the whole charge will be equal to only three times that of the smallest jar.
Every sensible heart must be shocked with the idea of torturing defenceless animals, merely to gratify an idle curiosity. The chapter which we shall now lay before the reader is founded entirely on the assertions of other writers upon this subject; to which, however, we have not the least doubt that the fullest credit is due. But we have not chosen to prove the veracity of their statements by our own experiments, believing that any small additional knowledge we might possibly have obtained in this way, would have been purchased at too great a price—the sacrifice of feeling and humanity.
Take a living frog, and after amputating the hind legs, (for they are the best, on account of the number of joints) let the largest nerve, called thecrural nerve, be laid bare, and surrounded with a slip of tin-foil, or a piece of sheet lead—then lay a piece of zinc, or other metal different from that on the nerve, in contact with the neighbouring muscles; form a communication by another piece of zinc, or other good conductor, between the metal in contact with the muscle and thearmedpart of the nerve, and violent contractions will be produced in the limb.
There is another method of producing these convulsions, which has been preferred on account of its simplicity.—Itis by forming a communication between a nerve, armed as above, and an adjoining muscle, by a piece of zinc, without the assistance of a communicator.—This was one of the first methods of Galvanizing frogs, before the invention of the pile and trough. But since these discoveries, frogs have been made to show more violent convulsions.
We now proceed to relate some of the conclusions which have been drawn from the experiments on frogs.
1. The contractions produced in the limb of a frog are stronger the farther the metal is placed from the origin of the nerve.
2. When the metal has remained for some time on a particular part of the nerve the motion will cease; but it may be renewed by changing the position of the metal, and carrying it lower on the nerve.
3. Contractions may be produced in the prepared limb of a frog, by putting it in water, and then bringing two metals in contact with each other, at a short distance from the limb.
4. Only those muscles to which the nerves lead suffer contraction from the Galvanic influence.
5. When a contraction has taken place in any muscle, no other will follow while the metals remain in contact.—In order to renew the motions, therefore, the metals must be separated and joined again.
6. Galvanic excitement, instead of destroying the irritability of a muscle, gives it an additional support. Dr. Valli, an Italian physician, has fully confirmed this principle by the following experiment. “Having prepared the wing of a fowl, or the paw of a cat or dog, I subjected it to the customary trial. At the expirationof half an hour, I armed the other wing of the fowl, or the other paw of the cat or dog, and had recourse to my exciting arc.—The latter wing or paw, however, did not give any sign of electricity, (for he conceived the motion to be occasioned by electricity,) while the parts which had been subjected in the first instance to the experiment, still continued in a convulsed and agitated state.”
7. Galvanic experiments do not succeed so well in a room crowded with persons, as when only two or three individuals are present.
8. Galvanic contractions are more powerful the instant the animal is deprived of life, than some time after; and therefore more violent agitations can be produced in the living animal.
9. Volta concluded that Galvanism was generated by the metal, and not by the animal upon which he operated.
These are the principal remarks which we think worth noticing. If they do not content the reader, we must refer him to Wilkinson on Galvanism; where he will find a detail of almost every thing that happened in the Galvanic world till the time he wrote.
The first experiments which we shall mention were performed by Mr. Cruickshank, with the Galvanic pile. He employed plates of zinc and silver, 1.6 inches square, and the number of plates of both metals varied from forty to a hundred, according to the power required.The lower end of the pile we shall denominate thesilverend, because the plate at the bottom is of silver, and the upper end thezincend, because the uppermost plate is of zinc. The first experiment of Mr. Cruickshank with the Galvanic pile, was upon water and silver wires. These wires were passed through corks, fitted into a glass tube filled with water, and projected about one third of the way, on both sides, into the tube; so that the space between the inner ends of the wires was one third of the length of the tube. One of the corks was made perfectly tight by cement. The tube was then placed upright in a tumbler of water, with the uncemented end downwards.
As soon as a communication was made between the extremities of the pile by the wires, small air bubbles began to ascend from the wire connected with the silver end, and a white cloud made its appearance at the wire proceeding from the zinc end.—The cloud gradually increased, assuming a darker colour, and at last it became purple, and even black. A few air bubbles were likewise observed upon this wire, which ascended from it; but when the pile acted well, a considerable stream of air could be perceived.—When this gas was examined, it was found to be a mixture of hydrogen and oxygen, in the proportion of three parts of the former to one of the latter. No great reliance, however, can be placed on the accuracy of this analysis. The wire proceeding from the zinc end, was found much corroded, and looked as if a portion of it had been dissolved.
Mr. Cruickshank supposed the cloud formed round the wire of the zinc end to be the muriate of silver, proceeding from the silver wire which had been somehowdissolved, and afterwards precipitated in this state, by the muriatic salts contained in the common water.
The next experiment was with distilled water, a tincture of litmus, and silver wires, as before. The apparatus being adjusted in the manner above described, and one wire connected with one end of the pile, while the other touched the other end, gas immediately arose from both wires, but in greater quantity from the one connected with the silver plate. In a short time the whole fluid below the point of the wire from the zinc plate, became red, and the fluid below the wire from the silver plate, looked of a deeper blue. Distilled water tinged with Brazil wood, soon became of as deep a purple as could be produced by ammonia.—From the two last experiments, Mr. Cruickshank was led to suppose, that anacid, probably the nitrous, is produced at the wire connected with the zinc plate, and analkali, probably ammonia, at the one connected with the silver end of the pile.
As hydrogen gas, whether heated or in its natural state, reduces metallic oxyds, Mr. Cruickshank resolved to subject solutions of metallic oxyds to the hydrogen gas which was produced by the pile.—The result answered his expectation, for in a minute or two after the communication was formed, fine metallic needles or crystals, something resembling a feather, were perceived round the wire connected with the silver plate.—The oxygen too which escaped from the metal, and that generated from the fluid used in the solution, was commonly pure, when an excess of acid was added to take up the alkali.—The acetite of lead and the sulphate of copper, were among the oxyds experimented upon, but whatever the metal was, the resultscoincided. These experiments were made in a tube like the preceding ones.—A number of experiments were made by the same gentleman upon theearths, but we shall not detail them; we must content ourselves with some conclusions drawn from his observations.
1. Hydrogen gas, mixed with a small portion of oxygen and ammonia, is somehow disengaged at the wire communicating with the silver extremity of the pile; and this effect is equally produced, whatever the nature of the metallic wire may be, provided the fluid operated upon bewater.
2. When metallic solutions are used, the same wire which separates the hydrogen gas, revives the metallic calx, and deposits it at its extremity, in its pure metallic state; in this case no hydrogen is disengaged. The wire employed for this purpose may be of any metal.
3. Of the earthy solutions, only those of magnesia and argill are decomposed by the wire: a circumstance which strongly favours the production of ammonia.
The pile with which these experiments were made consisted of thirty-six plates of silver, and an equal number of zinc ones, between which were interposed disks of flannel, moistened with a solution of the muriate of ammonia.—Each plate had a diameter of ten inches, or contained 78.58 square inches;—consequently the whole surface of silver in the pile, reckoningonly one side, was 2828.57 square inches, and that of zinc the same.
With this instrument, in December 1801, gold, silver, copper, tin, lead and zinc were deflagrated with surprising facility. The gold burned with a vivid white light, inclining a little to blue, and deposited an oxyd of a deep purplish-brown colour.—The silver gave a vivid flame of a greenish hue, and extremely brilliant. Its oxyd was of a blackish colour. The copper presented phenomena similar to those which attended the gold.—Lead gave a very vivid light, of a dilute bluish purple.—The tin afforded a light similar to that of the gold, but burnt with much less energy; probably because the leaves were thicker. The zinc gave a blueish white flame, which was edged, at the moment of contact, with red. It was more difficult to inflame than any of the preceding metals, but the leaves were likewise much thicker. The oxyds of the four last metals were not examined.
Water was poured upon the upper plate of the pile, so as to form astanding pool; and several pieces of the same kind of metals with those before experimented upon, were presented to the plate through this aqueous medium, and were deflagrated. They afforded a flame of the same colour as when they were brought to the bare plate.—A vapour was sometimes perceptible immediately after the deflagration, and was supposed to arise from a portion of water converted into steam by the intense heat.
It is very remarkable that the shocks taken from this pile, which produced such astonishing effects upon metals, could be received with but very trifling inconvenience, through the human body.
Besides these experiments, which were made by a society of gentlemen, a variety of others were performed, from which nearly the same conclusions were deduced.—Two other facts, however, deserve notice.
1. When metallic leaves are deflagrated in carbonic-acid gas, the flame is weak: but when in oxygen gas, the communication between the upper and under plates of the pile is no sooner formed, than the metallic leaves are destroyed with one sudden flash.
2. When metals are subjected to Galvanism in an exhausted receiver, they emit light but are not oxydated.
It is hardly necessary to mention, that every experiment made by means of the Galvanic pile may be performed, with equal success, with the trough. The experiments related in this chapter may be effected by the pile, but they cannot be done with the same convenience as when troughs are used. The battery[19]employed in these experiments consisted of sixty pieces of silver, and a like number of zinc, each two and a quarter inches square. The shock produced by this trough, by means of two metallic conductors, was distinctly felt in the shoulders, and the contraction or spasm wasso violent, as to render the operator unable to hold the conductors, when in contact with the plates by which the trough terminated each way.—A sensation resembling that produced by hot water, was at the same time felt in the wrists and fore-arm.
A small steel wire, which was used for the conductor to form the communication, upon its contact with the plates, produced a vivid spark and bright scintillations.—When a piece of phosphorus was placed upon the end of this wire, and made a part of the circuit, it was instantly inflamed.
Another battery of the same size being connected with the one above described, gun-powder was fired, and gold leaf deflagrated without any perceptible residuum—being probably volatilised by the heat occasioned by the experiment.
Mr. Davy, secretary of the Royal Society, placed a small piece of pure potash (which had previously been exposed to the atmosphere, so as to render it a conductor of the Galvanic fluid,) upon an insulated plate of platina, connected with the negative[20]end of a battery, of the power of two hundred and fifty plates, six inches by four, in a state of intense activity.—A wire communicating with the positive end, was brought in contact with the upper surface of the alkali. The whole apparatus was in the open air. Under these circumstances a vivid action was soon perceived.—The potash began to fuse at both points where the fluid acted upon it.—There was a violent effervescence at the uppersurface:—at the lower or negative surface there was no liberation of elastic fluid, but there appeared small metallic globules, very much resembling quick-silver. Some of these globules burned with an explosion and a bright flame, as soon as they were formed, while others remained which were merely tarnished; and finally a white film was formed over their surfaces, which was afterwards found to be pure potash.
Soda was acted upon in the same manner as potash, and exhibited the same results; but its decomposition required a stronger action of the battery, or it was necessary that the soda should be in smaller pieces than the potash.
The metallic globules produced from the potash remained fluids in the open air, at the time of their production; but those from soda, though fluid at the time of their formation, upon cooling, became solid, having much the lustre of silver. The alkalies could be made to produce metallic results in vacuo.
Since Mr. Davy’s first experiments on this subject, several others have been made, much in the same manner, upon the earths. Messrs. Pontin and Berzelius, two Swedish chemists, have succeeded in obtaining metallic amalgams from lime, magnesia, strontites and barytes; but they could produce no such effect on alumine and silex. Mr. Davy however effected this, by a battery of 36000 square inches.—He also improved upon their other discoveries. He, by distillation, drove off the mercury from the amalgamated metals which they obtained from the earths, and procured a pure metal.
Ammonia was also found to contain a metal. This discovery inclines one to believe, that the air we breathe contains metal in a gaseous state, as azote, which is acomponent part of ammonia, forms a large portion of our atmosphere.
When compounds, soluble in water, were put into water contained in agate cups, and subjected to the action of Galvanism, their decomposition was rapid.—A solution of the sulphate of potash, being put into two cups and Galvanised by fifty pair of plates, for four hours, the acid was found by itself in the cup connected with the positive end of the battery, and the alkaline basis in the cup communicating with the negative end. Similar phenomena took place in solutions of sulphate of soda, nitrate of potash, nitrate of barytes, phosphate of soda, sulphate, succinates, oxalate and benzoate of ammonia; also with alum. When muriatic salts were used, they afforded oxymuriatic acid. When metallic solutions were employed, metallic crystals and an oxyd were deposited on the negative wire, and a great excess of acid was found in the positive cup.—Strong solutions afforded signs of decomposition quicker than weaker ones.
We could enumerate a variety of similar experiments, but the limits of our work forbid it.
Place a piece of zinc upon your tongue, and a piece of silver between your cheek and upper jaw; then move your tongue so as to bring the two metals in contactwith each other, and you will perceive a very curious sensation upon your tongue, accompanied by a cool sub-acid taste,[21]and at the same time you will see aflash of light, whether your eyes be open or closed. The sub-acid taste resembles, in a degree, that produced by electricity.[22]
Place a tin or pewter bason filled with clean water upon a silver mug: with both your hands, which must previously be wet with a solution of salt in water, grasp the silver vessel, and put your tongue into the water, taking care not to touch the tin or pewter vessel with any part of your body; you will now perceive an acid taste; which will be more sensible, if you withdraw your hands from the silver vessel while your tongue remains in the water, and then replace them.
To prove that Earth-Worms have a nervous system.
Place an earth-worm upon a plate of zinc, resting on a larger plate of silver.—The animal, as soon as it approaches the silver, seems to be repulsed by a painful sensation, and at last becomes fatigued by its repeated and fruitless exertions to make its escape, which nothing apparently prevents.
This evidently proves that the animal is provided with a nervous system, as experiments have proved that Galvanic irritation is excited only in the nerves.
We have already remarked, that a sub-acid taste is perceptible when two different metals are applied to the tongue and fauces: it has also been found that Galvanism affects the taste, when two differentfluidsand a single metal are in contact with the tongue. Upon this principle a variety of known facts have been accounted for.—For example—It has long been observed that beer, cyder, &c. when drunk from a tin or silver vessel, were more palatable than when received from a vessel of glass, or any other substance not metallic. The supposed explanation of this, is as follows.—When the outer extremity of the vessel is applied to the under lip, rendered moist by the saliva, and the tongue is extended so as to be in contact with the liquid contained in the vessel, a Galvanic arc is formed, which produces the brisk and lively taste.
It has been supposed, by persons fond of this theory, that snuff, when taken from a metallic box, excites a more agreeable sensation than when taken from a box of tortoise shell, or leather.
The fact that a silver spoon becomes discoloured by being used for eating eggs, is familiar to every one. This, also, is attributed to the Galvanic action. By experiment, sulphur has been discovered in both the albumen and yolk of an egg.—The Galvanic combination is between the sulphur of the egg, the silver spoon, and the saliva; for no tarnish is produced on the spoon when it is immersed in either the albumen or yolk; and that part of the spoon which enters the mouth is most discoloured. In every Galvanic experiment, water is decomposed into its constituent parts, hydrogen and oxygen gases. These things being premised, the fact is easily accounted for.—The hydrogen, which before the operation is nascent in the water, (which holds the sulphur in solution) now readily unites with the sulphur, and forms sulphurated hydrogen gas, which produces the tarnish on the silver.[23]
We shall mention a few other common appearances, and leave the solution to the ingenuity of the reader.
When copper sheathing is fastened on a ship with iron nails, the nails, and particularly the copper, are found to be corroded about the places of contact.
Works of metal, the parts of which are joined by a solder of a different metal, are observed to tarnish about the places where the different metals meet. A seam which has been soldered so accurately that it cannotbe perceived by the eye, may be discovered by passing the tongue over it.
This part of Galvanism has been particularly attended to by Humboldt, a German. He first observed the irritability of the vegetable fibre.
Remarking the great similarity of appearance between the substance of mushrooms and the muscular fibre, he wished to ascertain whether they possessed a similar power of contraction. He accordingly made a considerable number of experiments, from which he concluded that the different kinds of mushrooms, which in becoming putrid emit an animal insipid cadaverous smell, are as perfect conductors in the Galvanic chain as the organs of animals. His experiments likewise proved that they possessed irritability.
Mr. Humboldt afterwards directed his inquiries to themannerin which Galvanism acted upon the irritable fibre, which, as we have already mentioned, he first observed. These experiments, however, were unsuccessful. We shall not therefore relate them.
The effects of Galvanism on vegetation are supposed to be deleterious, as will appear from the following extract from the “Monthly Magazine.”
“It often happens, that some of the limbs of fruit trees, trained against a wall, are blighted and die; while others remain in a healthy and flourishing state. This evil is, by gardeners, generally attributed to the effects of lightning. But, if this were the case, would not the violentaction of the electric fluid produce a laceration of the branch and stalk of the tree? No such effect is to be perceived. It therefore appears to me, that we must seek some other cause for this evil, and I flatter myself that I have discovered the real one.
A few years since, when Galvanism was first introduced to public notice, I constructed a pile, consisting of about one hundred plates of copper and as many of zinc, each about two inches square. Among other experiments, I applied it to the branch of a tender plant, (a species of the ficoides.) Having left it for about an hour, on my return I found the branch withered, and hanging close to the stalk. It immediately occurred to me, that Galvanism might be the cause of the above mentioned defect in wall fruit trees, occasioned by the oxydation of the nails, by which they are oftentimes fastened (for I conceive Galvanism to be produced, in a greater or less degree, by every metal passing into a state of oxydation.) Recollecting that the limb of a cherry tree in my garden had, nearly a year before, been fastened to the wall with an iron cramp, I instantly examined it, and found it dead; though, when fastened, it was a flourishing, healthy limb, at least an inch in diameter, and nine feet in length.
I have since examined several peach and nectarine trees; and wherever I discovered a limb dead, I invariably found that one or more of the nails which fastened it were incontact with the bark. A limb of a peach tree puzzled me for some time. It was dead, but I could not perceive that any of the nails were in contact with it, (the scraps of cloth being left pretty long.) After a narrow search, however, I found the mud, of which the wall was built, considerably stained with rust, immediatelyunder the branch: and on digging into the wall with my knife, I brought the hidden mischief to light.—It was part of a very large spike nail, and which lay about an inch below the surface.
On mentioning some of those circumstances to a friend, he observed, that about a year before, he had fastened some currant trees to a wall, with iron hooks. On examination, almost every limb so fastened,was dead.
The effect of the Galvanism in these cases will probably be found to be greater in rainy seasons, as the oxydation then goes on more rapidly than it does at other times.
Hence it appears that, in training fruit trees, wooden pegs or cramps, should be used instead of iron; or else, that care should be taken that the iron do not touch or come near to a limb.
Galvanism, like electricity, has been applied to the human body, for the purpose of removing complaints, and apparently with equal success.
The ingenious Galvani, immediately after his discovery of Galvanism, (or as he called it,animal electricity,) attempted to explain the causes of several diseases by it. Thus in a complaint where there was a total loss of contractile power, as the paralysis, he ascribed the cause to the interposition of a non-conducting substance, which prevented the passage of the Galvanic fluid from the nerve to the muscle, and from themuscle to the nerve. “If artificial electricity (says he,) be conveyed to the head, the nerves or spinal marrow, by means of the conductor of the Leyden phial, paralysis, apoplexy, and even death, will be induced, according as the phial is charged with a greater or less quantity of the electric fluid.—If such effects result fromcommonelectricity, may it not be presumed that a sudden afflux ofanimalelectricity towards the brain, may be productive of the most fatal consequences.”
But omitting, as wholly conjectural and unsatisfactory, alltheoriesrelating to the effect which Galvanism has upon the animal œconomy, we shall proceed to relate known facts, and the method of applying Galvanism for the relief of certain morbid affections of the human body.
The general mode of operating with Galvanism, is to apply small portions of it at first, and gradually to increase the shock, as circumstances may dictate. It has been customary to remove the cuticle (by means of a blister or otherwise,) from the parts of the body to which the wires, communicating with the two extremities of the battery, are to be applied. This method, which was adopted because the cuticle is a very bad conductor, gave excruciating pain to the patient. Mr. Wilkinson has found it unnecessary, as by moistening the parts, and applying pieces of gold leaf or Dutch-metal, he has succeeded in producing the desired effect. During an operation, one of the conducting wires should be kept in contact with one of the metallic leaves, while the other conductor is to be removed, immediately after it has been brought in contact with the other metallic-leaf—and then replaced and removed successively.
The negative wire of a battery is the most powerful, and it is necessary in some cases to attend to this fact.
In a short time after Galvanism has been applied to a part of the body, a redness becomes perceptible about the part; and if the application be continued too long, vesications and ulcerations will be produced. These symptoms are a little troublesome at first, but do not require any particular treatment for their cure.
Galvanism should be applied twice in twenty four hours, otherwise it is supposed the intervals would be so long, as to prevent any good effects which might arise from it.
We shall now enumerate some disorders in which Galvanism has proved beneficial. Inparalytic affectionsit has afforded considerable relief.—Two instances ofmental derangementare recorded by professor Aldini, nephew to Galvani, in which its effects were truly surprising.—One of them afforded an instance of a gradual diminution of the mental energies, which ultimately sunk into stupidity. The other was of an opposite nature:—the system was in a state of violent excitement, and the patient raving and unmanageable.
Inrheumatism,spasmodic affections, anddeafness, where it does not arise from a natural defect in the organ, Galvanism has been applied generally with advantage. But the most astonishing effects of this wonderful principle have been displayed in cases ofsuspended animation. Mr. Humboldt made the first experiments relative to this part of our subject, on apparently dead linnets. He put a piece of zinc into the bill, and thrust a sharp piece of silver into the bird, near the other extremity of the body—he then formed a communicationbetween the two, by an iron wire. “What (exclaims he) was my surprise, when I perceived, the moment the contact took place, the linnet open its eyes, stand erect on its feet, and flutter its wings; it again breathed during six or eight minutes, and then expired tranquilly.”
Galvanism is now applied to persons apparently dead, from drowning, hanging, or exposure to noxious gases. In such cases, the body should be divested of its clothing, and placed in a warm bed nearly approaching the natural temperature, and at the same time slight Galvanic shocks should be passed through the body, in such a direction as to affect the heart.—Thus by combining this, with the usual means, the most advantageous consequences may be expected. It may be laid down as a principle, that, in all cases where animation is suspended, and the principle of irritability not destroyed, the stimulus of Galvanism and electricity, if prudently employed, may rouse the dormant energies of vitality, and restore the system to its natural state of activity.
It has been supposed by many, that the phenomena of Galvanism and electricity depend upon thesamecause. Others, however, controvert this opinion, and affirm that Galvanism is a fluidsui generis. That there is a great similarity between some of the phenomena of Galvanism and those of the electric fluid, isevident; but this analogy cannot be traced in every instance.
It is not our province to enter into this controversy; we shall only relate a few facts upon which it is founded, and leave the speculative reader to draw from them his own conclusions.
Both Galvanism and electricity exhibit light, in their passage from one conductor to another, through an intervening space of air.
Both affect an electrometer.
The deflagration of metals may be produced by either.
Electricity, as well as Galvanism, produces muscular contractions in animals, a short time after death.
Somegoodconductors of electricity are not good conductors of Galvanism; as was shewn by Dr. Fowler.
The manner of exciting Galvanism is different from that of exciting electricity;—the former being collected most copiously fromconductors, and the latter fromnon-conductors.
The electric fluid affects the sense of smelling—but no smell has ever been observed from Galvanism.
The electric shock operates on the body by a sudden and percussive effect—while the one which followsthe Galvanic process seems to arise from a constant current, attended by a jarring and tremulous sensation.
In the decomposition of water by Galvanism, hydrogen gas is formed at one of the wires, and oxygen at the other. In that by electricity, both gases arise from the same wire.