animal, but on every other body, and in every other direction; this part of the animal being placed at a considerable distance from the conductor, and in certain circumstances. These were, that the animal, thus dissected, should be in contact, or very nearly so, with some metal, or other good conducting substance of a sufficient extent, and still better between two such conductors, the one of them being directed towards the extremity of the said legs of the animal, or some one of the muscles, the other towards the spine, or the nerves. It is also of great advantage that one of these, called the nervous and the muscular conductors, but preferably the latter, should have a free communication with the floor. It is in this position especially that the legs of the animal receive violent shocks, leap up and down rapidly on each spark from the conductor of the machine, though it may be pretty far distant, and though the discharge be not made on either the nervous or muscular conductor, but on some other body, likewise distant from them, and having another communication for transmitting such a charge, as on some person placed in an opposite corner of the room.

Such was the first step, which led him to the fine and grand discovery of an animal electricity, properly so called, appertaining not only to frogs and other cold-blooded animals, but also to all warmblooded animals, as quadrupeds, birds, &c. ; a discovery which makes the subject of the third part of the work quite new and interesting.

It was chance that presented to M. Galvani the phenomenon just described, but at which he was more astonished than he needed to have been, had he given due attention to the effects of electric atmospheres. Yet who could have believed that an electric current, so weak as not to be rendered sensible by the most delicate electrometers, was capable of affecting so powerfully the organs of an animal, and of exciting in its members, cut off many hours before, motions as strong as those of the living animal, as the vigorous springing of the legs, the leaping, &c., not to mention the most violent tonic convulsions?

M. Volta endeavoured to determine the least electric force requisite to produce these effects, as well in a living isolated frog as in one dissected and prepared as before-mentioned, which M. Galvani had omitted to do. M. Volta chose the frog in preference to every other animal, because it is endued with a very durable vitality, and is also very easy to prepare. He also made trial of other small animals for the same purpose, and with nearly the same success. Hence he found, that for the living and entire frog the electricity of a simple middle-sized conductor was sufficient, when it was only capable of giving a very feeble spark, and to raise Henly's electrometer to 5° or 6. When he used a Leyden phial of a middle size, a much weaker charge produced the same effect, viz., such as gave not the least spark, and was quite insensible to the quadrant electrometer, and hardly sensible to Cavallo's electrometer.

All this was for a whole and isolated frog; but for one dissected

and prepared in different ways, especially after Galvani's manner, where the legs are attached to the dorsal spine only by the crural nerves, a still much weaker electricity, whether of the conductor or of the Leyden phial, the fluid being obliged to pass through the narrow passage of the nerves, never failed to excite convulsions, &c. Hence, then, we have, in the legs of the frog attached to the dorsal spine only by the bare nerves, a new kind of electrometer; since the electric charge which, giving no signs by other the most delicate electrometers, gives evident tokens of it by this new means, by what may be called the animal electrometer.

But if, after these experiments, we ought not to be surprised at those of Galvani described in the first and second parts of his work, how can we avoid being so at the very novel and marvellous ones in the third part? by which he obtains the same convulsions and violent motions of the members, without having recourse to any artificial electricity, by the sole application of some conducting arc, of which one extremity touches the muscles, and the other the nerves or the spine of the frog, prepared in the manner aforesaid. This conducting arc may be either wholly metallic or partly metallic, and partly some of the imperfect conductors, as water, or one or more persons, &c. Even wood, walls, the floor, may enter into the circuit, if they be not too dry. The bad conductors, however, do not answer so well, and only for the first moments after the preparation of the frog, as long as the vital forces are in full vigour; after which the good conductors only can be used with success, and soon after we can only succeed with the most excellent ones, namely, with conducting arcs wholly metallic. Galvani successfully extended these experiments, not only to many other cold-blooded animals, but also to quadrupeds and birds, in which he obtained the same results, by means of the same preparations; which consist in disengaging from its coverings one of the principal nerves, where it is inserted into a member susceptible of motion, in arming this nerve with some metallic plate or leaf, and in establishing a communication, by help of a conducting arc, between this arming and the depending muscles. Thus he happily evinced the existence of a true animal electricity in almost all animals. It appears proved, indeed, by these experiments, that the electric fluid has a continual tendency to pass from one part to another of a living organised body, and even of its lopped members, while they retain any remains of vitality; that it has a tendency to pass from the nerves to the muscles, or vice versa, and that muscular motion is due to a like transfusion, more or less rapid. Indeed it seems that there is nothing to be objected either to the thing itself, or to the manner in which M. Galvani explains it, by a kind of discharge similar to that of the Leyden phial.

M. Galvani following up the idea he had formed, after his experiments, and to follow in every point the analogy of the Leyden phial and the conducting arc, pretends that there is naturally an excess of the electric fluid in the nerve, or in the interior of the muscle, and a cor

respondent defect in the exterior, or vice versa; and he supposes, consequently, that one end of that arc ought to communicate with a nerve which he considers as the conducting thread, or knob of the phial, and the other end with the exterior of the muscle. But had he but a little more varied the experiments, as I have done (says M. Volta), he would have seen that this double contact of the nerve and muscle, this imaginary circuit, is not always necessary. He would have found, as I have done, that we can excite the same convulsions and motions in the legs, and the other members of animals, by metallic touchings, either of two parts of a nerve only, or of two muscles, and even of different points of one simple muscle alone.

It is true that we succeed not quite so well in this way as the other, and that in this case we must have recourse to an artifice, which consists in employing two different metals, which is not necessary in experimenting after Galvani's method, at least, while the vitality in the animal, or in its amputated members, is in full vigour; but, in short, since, with the armings of different metals, applied either to the nerves only or to the muscles alone, we succeed in exciting contractions in these, and the motions of the members, we ought to conclude that if there are cases (which appears, however, very doubtful) in which the pretended discharge between the nerve and muscle is the cause of muscular motion, there are also circumstances, and more frequently, in which we obtain the same motions by a quite different way, a quite different circulation, of the electric fluid. Yes, it is a quite different sort of method of the electric fluid, of which we ought rather to say we disturb the equilibrium, than restore it, in that which flows from one part to another of a nerve, or muscle, &c., as well interiorly by their conducting fibres, as exteriorly by means of applied metallic conductors, not in consequence of a respective excess or defect, but by an action proper to these metals, when they are of different kinds. It is thus (says Mr. Volta) that I have discovered a new law, which is not so much a law of animal electricity, as a law of common electricity; to which ought to be attributed most of the phenomena, which would appear, from both Galvani's experiments and mine, to belong to a true spontaneous animal electricity, and which are not so, but are really the effects of a very weak artificial electricity. As to the motion of the muscles, my experiments, varied in all possible ways, show that the motion of the electric fluid excited in the organs does not act immediately on the muscles; that it only excites the nerves, and that these, put in action, excite in their turn the muscles. Whereas Galvani supposes in all cases, that the transfusion of the electric fluid, produced either by artificial electricity or by natural animal electricity, ought to act from the nerves to the muscles, or vice versa. But these ideas are restrained within too narrow limits; for, in varying the experiments in different ways, I have found that neither of these conditions, viz., the laying bare and isolating the nerves, but at the same time touching these and the muscles, to procure the pretended discharge, is absolutely necessary. It is sufficient, for

example, when we have laid bare the sciatic nerve of a dog, or a lamb, &c., to cause an electric current to pass from one part of this nerve to another, even next to it, leaving all the rest untouched and free, as well as the whole leg-it is sufficient, I say, for this, to see excited in this leg the strongest convulsions and motions; and this, whether we employ an artificial electricity, or put in motion the electric fluid in the nerve itself.

M. Volta next relates several experiments of his own, to prove these positions; and then adds, these last preparations lead to those of Galvani, which, indeed, prove that it is better to lay bare the nerves, and still more to detach them round about; but not that this is a necessary condition, since he had obtained the same convulsions and motions of the members by simply laying bare the muscles, and leaving all the nerves enveloped and hid under them in the natural

state.

After these essays on reptiles, birds, and small quadrupeds, I proceeded (says M. Volta) to other and larger animals, rabbits, dogs, lambs, beeves; and not only produced the same effects by all the foregoing methods, but obtained some more remarkable and durable, as the vital heat subsists longer in these large animals and their members. For it must be remarked, that though in most coldblooded animals, and particulary in frogs, vitality subsists in the amputated members many hours, this vitality, which renders them so sensible to the weakest electric irritation, lasts only some minutes in the several members of warm-blooded animals, and commonly disappears before all that animal heat is dissipated.

M. Volta having had such success in his experiments on large and small animals of all kinds, sometimes living and entire, sometimes skinned, decapitated, and dissected in different ways, also in each of their large members cut off, and almost always without Galvani's preparation of laying bare the nerves, he then wished to go further, and practise on the small members, on a muscle only, and on small pieces of muscles; which led to other new discoveries. Thus he cut off sometimes the leg with the thigh of a frog, sometimes the leg only, sometimes the half or quarter of a leg; and having applied, as usual, to a part of the lopped piece the tinsel, and to another part the silver plate, and made the armour communication, he always obtained motions and convulsions. Also the same with the legs or muscles, or any part of them, of a hen or other birds, rabbits, &c. Hence he infers that it is not at all necessary to make a discharge of electric fluid between a nerve and muscle, or to transpose it from the interior to the exterior of this latter by the nerve and the conducting arc, as Galvani supposes: and that it is useless to sustain here an analogy with the Leyden phial.

In like manner, in another experiment, having covered the two thighs of a frog, to exactly the corresponding parts, with two metal leaves, the one of silver, the other of tin, he excited the contractions of the muscles, and the usual motions of the legs as soon as he made a communication between those two armings by the conduct

ing arc. But if two muscles, or two places in one muscle only, be armed alike, viz., with two plates or leaves of the same metal, equal in all respects, and applied alike, then connecting them by the conducting arc, there ensues no convulsion, no motion. But though these effects are constant and general in all quadrupeds, birds, fishes, reptiles and amphibia, which he has tried, it is not less true that worms in general, and many insects, have not the same effect. He tried in vain earth-worms, leeches, slugs, and snails, oysters and many caterpillars; being unable to excite any motion in these by small or moderate sparks, or discharges of artificial electricity. With some difficulty, however, he succeeded with cray-fish, beetles, shrimps, butterflies, and flies.

M. Volta found by his experiments that it was only the muscles subject to the will that are affected by them, and not those of the viscera, that are not usually so subject, as those of the heart, &c. He also shows that the electric fluid acts only mediately on even the voluntary muscles; that it is not even the immediate or efficient cause of the motion of those muscles; and that it is the nerves only that are directly affected, which again act on the muscles, viz., those more immediately connected with them: an assertion which, he says, is rendered evident, and proved by many experiments he had made on the tongue, which led him also to other curious and interesting experi

ments.

Having excited tonic convulsions, and strong motions, in the muscles and in the members, in both large and small animals, without laying bare any nerve, by the simple application of armings of different metals to the muscles stripped of the integuments, M. Volta began to think of attempting the same thing in the human subject. He easily conceived that it would succeed very well in amputated limbs; but how was it to be managed in the entire and living subject? It would be necessary to strip of the integuments, to make deep incisions, to remove even a part of the flesh where the metal plates must be applied. Happily it occurred to him that we have in the tongue a muscle naked, at least destitute of such thick integuments as clothe the exterior parts of the body: a muscle which is easily and voluntarily moveable. On this idea M. Volta made the following experiment on his own tongue. Having covered the tip of the tongue and a part of the upper surface, to the extent of some lines, with tin leaf, (silver paper is best), he applied the convex part of a silver spoon more advanced on the flat of the tongue, and inclined the spoon till its hanIdle came in contact with the tin-foil. Thus M. Volta expected to see the trembling of the tongue, and for that purpose had placed himself before a looking-glass. But the expected motions did not take place; however, he felt instead of it a very unexpected sensation: a pretty sharp taste at the end of the tongue.

M. Volta was at first much surprised at the event; but on a little reflection, he easily conceived that the nerves which terminate at the tip of the tongue, being those destined for the sensation of taste, and not for the motions of this flexible muscle, it was quite natural that