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Galvani prepared a frog in such a manner, that the legs were connected with the body, only by means of the sciatic nerve; and, in this case, he found the muscular contractions were produced by bringing the muscles of the legs in contact with the upper part of the body.3
Volta having laid bare the muscles and the sciatic nerve in the leg of a frog, just separated from the animal, introduced them into two vessels filled with water, in such a manner, that the muscles were in one glass, and the nerve in the other. He connected the two glasses together, by means of his fingers, when a strong contraction was produced in the limb.4
Humboldt placed the prepared leg of a very vivacious frog upon a plate of glass, and made a contact between the sciatic nerve and the muscles of the foot, by means of a piece of muscular flesh. At the moment of the {222} contact, muscular action was produced, and the experiment was often repeated with success.5
M. Aldini has succeeded in causing contractions in the limbs of frogs, not only by bringing their nerves and muscles in contact with each other, in various modes; but likewise by placing them in contact with the nerves and muscles of warm blooded animals, just deprived of life. One of the most singular of his experiments is this: of two persons, one holds in his hand the lower muscles of the prepared leg of a frog, and the other touches with his fingers the spinal marrow of an animal recently killed. The unoccupied hands are moistened and connected with each other; and the sciatic nerve in the leg of the frog brought in contact with the bared abdominal muscles of the warm blooded animal. At the moment that the circuit is completed, the leg is agitated by strong contractions.
In considering these curious phænomena, it is difficult to account for them, except on the supposition that the animal organs are capable, in certain cases, of exerting an action similar to the metals, in producing galvanic electricity. Living animal bodies, in fact, follow the metals and charcoal, in the order of their conducting powers; they are composed of solids and fluids. And all the analogies on the subject tend to prove, that to form galvanic combinations, nothing more is necessary than the contact of solids and fluids possessed of different conducting powers, and capable of exerting chemical action on each other.
In most cases when muscular contractions are produced in animal organs, by the application of an arc composed of two metals, or of one metal and different fluids, the circulation of the electricity must be supposed {223} to be determined by the action of the inorganic bodies. But when contractions are produced by a single metal, communicating with the organs only be means of water,6 the impulse of the electricity must be attributed to the animal substances; for the arc being simple, and connected at both ends with a similar body, forms only one element of a galvanic combination, of which water is the efficient part: and it can act only as a simple conductor.
The galvanic power of the artificial animal combinations is evidently much feebler, and more transient than that of the metallic combinations; silver and zinc will produce contraction in the muscles of a frog, many hours after it has been insensible to the action of either of them separately used: and, in this case, the effect must be attributed simply to the passage of electricity through the irritable parts; for it takes place whatever be the form of the application.
The muscles and nerves appear to be the exciting parts in animal combinations; but as yet their states of electricity, with regard to each other, have not been ascertained. By connecting a very feeble metallic combination, with a very active animal combination, in two different ways, this problem might perhaps be solved. If, for instance, with an arc of copper and {224} silver, connected with the nerves and muscles in the leg of a frog, by means of water, the action was much stronger when the copper was opposite to the muscle and the silver to the nerve, than in the contrary case; it would be reasonable to conclude, that the nerve bore the same relation to the muscle, as the copper to the silver, i.e. that the nerve was positive, and the muscle negative, &c.
All the facts that we are acquainted with on the subject of galvanism, tend to show, that the same substances which form simple galvanic combinations, are capable when multiplied and alternated with each other, in the proper order, of forming a galvanic battery. In consequence, however, of the susceptibility of animal substances to undergo a change, from the feebleness of the action and other circumstances in the experiment just detailed, it is probable that it will be very difficult, if not impossible, to accumulate galvanic electricity by means of arrangements composed of separate animal organs.7 In the torpedo and gymnotus electricus the electrical instrument is composed wholly of living matter, and its activity is related to the general functions of the animal: and, in the case of the galvanic action of the nerves and muscles of frogs, and warm blood animals, the effect is apparently connected with some remains of {225} vitality; which, as there is great reason to believe, would disappear during the time required for forming compound galvanic combinations.
The heart soon loses its susceptibility to the galvanic stimulus very soon, but the muscular organs, which are connected with large nerves, are capable of being made to contract for a considerable time.
By connecting the pectoral muscles with one end of the pile, and the par vagum and sympathetic nerves, at their origin, with the other end, very powerful muscular action was produced, which caused the phænomena of expiration and inspiration. On the first view of these experiments, we might be induced to hope for some advantages in the application of galvanism in cases of drowning, strangling, &c.; but when we consider that the contractions of most of the muscles, the actions of which are subservient to the vital functions, cannot be produced without laying bare large nerves, our expectations will be but moderate.
"M. Guyton, Member of the National Institute, and {226} Director of the Polytechnic School, read, at the sitting of the National Institute of the 25th of August, a memoir entitled, 'Researches on the pile of Volta' by MM. Hachette et Desormes, Professor in the Polytechnic School.
"This memoir contains two important facts which may be expected to throw great light on the theory of electricity. The first is, that an insulated electrical column, or Nairne's electrical machine, insulated, that is, communicating only with the air, is an inexhaustible source of electricity. The second fact is, that many dry and solid substances, such as pure starch, and the powder of different salts, are capable of occupying the place of the moist substance, in the pile of Volta, and that, in consequence of this discovery, piles may be formed by the mere arrangement of different substances, which are constant and almost unchangeable sources of the electrical fluid."
It is perhaps impossible to judge accurately of the nature of the researches of the French experimenters, from this short notice; and, consequently, any observations upon it may not be found applicable to the memoir itself. It may not, however, be improper to say that there is little novelty in the first fact. It is a new expression of a truth that has been generally admitted.
The second fact, the formation of a pile by means of solid substances only, would, if confirmed, be of the greatest importance in its applications to the theory and operations of galvanic electricity: it would afford a strong argument in favour of Volta' s theory of electromotion; and it would go far to overturn the opinion concerning the dependence of the circulation of galvanic electricity upon chemical changes.
For the purpose of examining the results of MM. {227} Hachette and Desormes, I constructed a pile with double plates of copper and zinc and dry powder of starch in its common state; but when twelve plates had been put together, in the order of copper, zinc, starch, and so on, no effects whatever were perceived; the pile produced no sensation on the tongue, and wires from it occasioned no change in water.
On exposing a pile, composed of copper, zinc and starch, to the atmosphere in a cold and damp cellar; it was found, after two days, to have gained a slight degree of powder. On moistening the starch with a very little water, the electrical action was evolved in the same manner as when wet cloths were employed. The phænomena were the same with a combination of silver and zinc; no effects could be produced from pure dry starch.
It would be unjust to decide concerning the experiments of the French chemists till the details of them are made known; -- but, in the present state of our information, we should be inclined to conceive that they have been misled by the moisture, which, in common cases, adhere very strongly to starch, and to many saline substances.
On exposing a quantity of powdered starch to the gentle heat of a sand-bath, a considerable quantity of water was speedily driven off from it. When dry, it was a perfect non-conductor of electricity; but after being exposed for some hours to a moist atmosphere, it had gained a slight degree of conducting power; which as there is every reason to suppose, was the consequence of its having absorbed moisture. The salts, the earthly substances and the solid vegetable productions, when in a state of perfect dryness, are, in fact, all non-conductors, and as such it appears impossible that they can form elements of the pile of Volta. They have, however, {228} many of them a very strong attraction for moisture, and in common cases when exposed to the atmosphere are always more or less saturated with it. I found, some time ago, that powdered steatite, from the Lizard in Cornwall, in its crude state, when used in a small galvanic pile, instead of the moistened cloth, enabled it to act, though very feebly. But after having been gently heated, it was no longer capable of producing the effect; and in its dry state, a single stratum of it, when placed in any part of an active pile, was sufficient to destroy the circulation of the electricity.
2. [The year 1802.]
3. Humboldt sur le Galvanisme, p. 27.
4. Idem, p. 29.
5. Op. cit. p. 31.
6. The experiment on the production of muscular contraction, by the application of two portions of water, in contact with a single metal, to the organs, was first made by Galvani, and confirmed by Aldini and Humboldt. One form of it, which I have several times employed with success, is this: A piece of silver is made to connect together two glasses, filled with pure water; the leg of a frog, deprived of the skin, is suspended by a bit of silk, in such a way, that the foot and sciatic nerve are nearly parallel. On bringing the muscle in contact with one portion of water, and the nerve in contact with one portion of water, and the nerve in contact with the other, the contraction of the limb is produced. -- D.
7. I attempted to form a galvanic battery, by combining in a circle, upon a plate of glass, ten newly prepared legs of frogs, having the sciatic nerve bared, with drops of water; in the order of muscle, nerve, water; muscle, nerve, water, and so on; but no effect was produced on breaking or completing the circle, by means of one of the legs. When a silver wire was made part of the circle, contractions were produced in the two legs which were nearest to it; but the others were not affected. When a little nitrous acid was added to the water, four of the legs contracted strongly with the silver; but there was no effect with the animal substances alone. -- D.
8. Journal de Physique, Vendémiaire, An. xi.