tricity, should be entirely altered, if it be intended to represent the scale of the conducting and exciting forces of these substances, in whatever relates to galvanism. Liver of sulphur, the alkaline solutions, lime-water, and the oxygenated muriatic acid, ought to be ranked before all other substances, metals and charcoal excepted, and immediately after them. The blood also should be considered as possessing a great degree of energy. I have convinced myself, hy repeated experiments, made attentively, and with the most scrupulous exactitude, that alkaline solutions, lime-water, the oxygenated muriatic acid, and, more particularly, liver of sulphur, produce, when brought into reciprocal action, effects equally powerful with those of two heterogeneous metals; and that, in all the cases in which the recurrence of the contractions is ascribed to an increase of irritability, produced by a chemical action, it would be much better to ascribe this effect to the irritating property of these substances, as they constitute a part of the galvanic chain.

48. They form, in a manner, a series of metallic exciting arcs; and ought to be ranked among those which have the greatest affinity with metallic substances, that is, with zinc and lead. It is on this account that their effects are so obvious, when they are combined with gold, silver, and metallic minerals. They are also very efficacious in the reproduction of the contractions, when, instead of being applied in an immediate way to the nerves, they are simply made to correspond with them by the means of conductors. The blood and the bile ought also to be comprehended in the same class, although their effect may not be equally powerful.

49. It is well known that it suffices, for the production of convulsive movements in a very irritable frog, to employ a homogeneous metal, for instance a silver discharger, by which a communication is formed between the muscles and the nerves. These convulsive movements are principally produced by the metals denominated noble; but, more especially, by metallic minerals, such as pyrites and galena, or sulphuric ore of lead. When I had formed a communication between the nerve and the prepared thigh of a frog, by the means of a piece of pyrites, the convulsions were produced, and were more particularly manifested when that substance touched the blood-vessels belonging to the nerves. When a chain was established in the thigh, and the mineral substance and nerve had ceased to produce any effect, the convulsions were reproduced, although feebly, by interposing in the chain a piece of moistened sponge, which formed, in a manner, a coating to the nerves. These effects were not usually, however, of any long duration. By moistening, afterwards, the nerve with a drop of blood taken from the frog subjected to the experiments, or, what amounts to the same thing, from any other, and afterwards touching the blood in question with a metallic exciter of silver or copper, placed on the thigh, very powerful convulsions were instantly produced.

50. Here the susceptibility of irritation was evidently augmented by the moistening of the nerve with the blood. It was even so to such a

degree, that a galvanic irritation of the feeblest kind became very powerfully augmented. This augmentation of the contractions was not, however, to be ascribed to an immediate influence of the blood on the nerve, and on the irritability seeing that the same phenomena were manifested, precisely in the same way, when the blood, instead of being immediately applied to the nerve, was simply laid on a bit of sponge, or on any other conducting body, placed over it. The success of the above experiments depended entirely on the immediate contact of the blood; since, whenever the nerve, or the sponge, was touched at the parts distant from it, the effect did not ensue. To the presence of the blood ought more particularly to be ascribed the properties of animal substances, considered as members of the galvanic chain.

51. In this latter point of view, the heart of the frog, still replete with blood, displayed very singular effects, at a time when the irritability was extinguished to such a degree, that certain heterogeneous metals, such as gold and silver, or silver and copper, no longer produced any effect when brought in contact. I was enabled to reproduce very forcible contractions, by placing the heart of a frog on its nerve, and by forming a communication between it and the thigh of the animal, by the means of a metallic exciting arc either of gold or silver. In this manner I established a galvanic chain, in the composition of which one metallic exciter only was to be found. In another instance, it was very remarkable, that the moment the heart was touched, either by silver or by pyrites, it remained tranquil, notwithstanding the thigh of the animal was in a convulsed state, the regularity of the system of the pulsations not being in any degree interrupted. Other parts of the frog, for instance, portions of its liver, its bowels, &c., which contain a less proportion of blood, did not possess an equal efficacy; but the heart itself was surpassed by the blood presented in substance, and more particularly in a concrete state. It was surprising to see the mode in which I could, by the means of a drop of blood, bestow on the nerve its vital energy; and also to observe that this drop of blood, without undergoing any sensible diminution or change, still continued to render the same service.

52. Whatever may be the effect, however, which the blood produces, it is still surpassed by the alkalies, by the oxygenated muriatic acid, and, more particularly, by the liver of sulphur, when metallic exciters of the first class, that is, the minerals and noble metals, together with the other metallic substances, and the regulus of antimony, cease to produce any effect, in conjunction with the blood with which the nerve has been moistened. After having wiped it dry, and substituted for the blood a single drop of the deliquescent oil of tartar, very powerful convulsive movements may be produced, by a recurrence to the above metallic exciting substances. This galvanic chain, consisting of muscles, silver, pyrites, or regulus of antimony, and of an alkali and a nerve, is as efficacious as a chain formed by muscles, silver, iron, or tin, conjointly with a nerve. The deliquescent oil of tartar

my

53. Professor Pfaff goes on to say that the following experiments merit a particular notice. I laid a portion of muscular flesh on the nerve of a frog, on which two heterogeneous metals, silver and copper, had ceased to produce any effect, and having touched the nerve with a silver probe, which was applied to the thigh, was not enabled to produce any contractions. I now poured a drop of the deliquescent oil of tartar on the muscular flesh, and, as soon as the silver probe was brought in contact with this alkaline substance, very strong convulsive movements were displayed. I laid another portion of muscular flesh on the preceding one, and brought the exciter towards it, but without being enabled to produce the contractions. Scarcely, however, had this latter portion of muscle been moistened and touched, as in the former instance, than they were renewed. In this way I was enabled to form several layers of a different nature; and the effect above pointed out took place as often as the silver, or, what was still better, the pyrites and the regulus of antimony, came in immediate contact with the alkali. The nerve having been moistened with the deliquescent oil of tartar, a very feeble galvanic irritation, produced either by gold and silver, or by silver and copper, became highly exalted, even when the convulsions had not been previously excited. It remains, however, to be ascertained, whether, in this case, the deliquescent oil of tartar did not act as the most efficacious coating of the nerve. It is in this way that silver and copper produce fresh contractions, when, after the nerve has been coated with zinc, and the thigh of the animal laid on silver, a communication is formed between them by the means of copper. In such a case, indeed, the effect is not owing to the joint operation of the copper and silver, but, on the other hand, to that of the silver and zinc, by which the humid animal parts are immediately coated. Would not an effect exactly similar be produced, if the nerve were to be moistened with the deliquescent oil of tartar? Does not this alkali, in surrounding the nerve, become a more efficacious coating than the zinc; and, on the application of feeble exciters, such as copper and silver, does not the zinc itself act more powerfully by the means of an alkali, with which it is simply connected by the copper, as an intermediate conductor?

54. These doubts are very far from being removed by M. Humboldt's experiments. Supposing the deliquescent oil of tartar to act by producing an augmentation of irritability, this effect ought also to be produced when the nerve has been carefully dried, before the application

On

however, is what I have not found in any of experiments. M. Humboldt constantly applied his weakest exciters, whilst the nerves were still moistened with the deliquescent oil of tartar, or with any other chemical substance calculated to augment the susceptibility of irritation. this head, let the different parts of his work in which he treats of the increase of this susceptibility by the alkalies, be compared. He sets out by saying: "I showed the galvanic flashes to several persons who could not perceive them in the experiments made by Mr. G. Hunter, by rubbing their gums, on the upper jaw, with an alkaline solution. Two pieces of gold, applied to wounds on the back, were found to possess great efficacy, when the wounds had been touched with the deliquescent oil of tartar.' A little farther he observes: When the principal trunks of the nerves of an organ are carefully prepared, and enveloped in moist bits of bladder, in such a way as that the irritating humidity simply moistens the muscular flesh, and the few fine nervous filaments it contains, an increase of irritability is rarely to be observed, at the same time that it is constantly produced, when the above principal trunks are moistened beneath the muscles.' Again, he says in the following page: The vital principle will be restored in the thighs of frogs exhausted by galvanic experiments, by the means of the oxygenated muriatic acid, in such a way as that the irritation of metals will again produce its effect. It is remarkable, that the contractions become more powerful, when a great portion of the nerve is moistened, and touched directly by the silver.' Such are the extracts I have chosen to cite from Humboldt's work. Now, let it be observed, that, in all the above cases, and more particularly in the experiments relative to the influence of chemical substances on the irritability of the animal fibre, the nerves were constantly moistened by these substances. They must consequently, whenever the metals were applied, operate likewise as links, or members, of the galvanic chain. The consequences must therefore be uncertain at the least.

55. I could not observe any remarkable difference in the alkalies, considered as links of the galvanic chain. The deliquescent oil of tartar appeared, however, to be somewhat more efficacious than the other substances of this nature. The effects of lime-water were not so powerful : it appeared, as it were, to preserve a medium between the alkalies and the substances to which an inferior rank is assigned. The oxygenated muriatic acid appeared to be pretty nearly as active as the deliquescent oil of tartar. In a few cases only the latter fluid produced spasmodic contractions of a longer duration. I observed likewise, in several instances in which I employed the oxygenated muriatic acid, a phenomenon which the metallic coatings of the nerves had often displayed, namely, that the contractions were manifested at no other time than when the contact of the nerve, moistened with a drop of the oxygenated muriatic acid, ceased. Here, likewise, the effects seemed to depend entirely on the immediate presence and application of

the oxygenated muriatic acid. As soon as a drop of this liquid is poured on a portion of muscular flesh, laid on the nerve, the movements are invariably reproduced.'

56. Having entered into this detail of the objections of M. Pfaff to the theory of Humboldt, we may now proceed to the analysis of a very curious memoir, read by M. Lehot at the French National Institute. Its object is to demonstrate particularly, not only the circulation of a very subtile fluid in the galvanic chain, but likewise that, in the application of the different chains to the animal arcs, there are unequivocal signs of the direction of the motion of that fluid, insomuch that it is possible to determine a priori, in a considerable number of different chains, the direction of the current. Being acquainted with this direction, as well as with the nature of the different parts of the chain, the author of the memoir in question observes, that it is reciprocally possible, in certain cases at least, to determine their respective position; and also, by the interposition of new substances in the chain, or by a change in the disposition of the parts of which it is composed, to give a particular direction to the galvanic fluid, and even to bring it into a state of repose.

57. The comprehension of these phenomena is connected with a fact which seemed to have escaped the notice of the different physiologists, namely, that the galvanic fluid is accumulated in the passage from the organs to the coatings. By a due attention to this fact, the nature of the metallic substances may likewise be distinguished at the distance of several yards. The galvanic influence will be sufficient to determine this. The following are the principal results of the interesting experiments made by M. Lehot.

58. Experiment I.-If the thigh of a frog recently prepared be held in one of the hands, and the nerve be brought in contact with a piece of zinc, the extremity of which is immersed in mercury, the moment the fingers of the other hand are dipped in that fluid powerful contractions will be manifested in the thigh of the animal. The same result will be obtained as often as one of the following substances, namely zinc, lead, tin, mercury, bismuth, copper, silver, or plumbago, is employed as a coating to the fingers; and one of those by which it is preceded, in the foregoing series, as a coating to the nerve. With respect to the precaution of moistening the fingers, it is absolutely indispensable; for which reason, whenever they are described as terminating one of the extremities of the arc, they are to be constantly supposed to be in a humid

state.

59. Experiment II.-If, on the other hand, the nerve be brought in contact with the mercury, and if that metal be touched with a piece of zinc, held in the moistened hand, either the contractions will not be produced, or they will be extremely feeble, provided there still be a certain share of susceptibility in the part. By separating, however, the nerve from the mercury, or, in general, by breaking the chain at any given point whatever, the contractile movements will take place. The same results will be obtained, as often as one of the metals belonging to the se

ries pointed out in the preceding experiment, is employed as a coating to the fingers; and one of those by which it is followed in that series, as a coating to the nerve. Thus, if the nerve be coated with lead, and the fingers with zinc, there will not be any contraction when these two metals are brought in contact; but, if the chain be destroyed at any given point, the contractions will be manifested. If, on the other hand, the nerve being still coated with lead, the fingers be coated with silver, when the chain is formed, the galvanic contractions will take place.

60. Experiment III.-If a flat surface of zinc be laid on the tongue, and touched with a piece of silver, held between the moistened fingers, a particular savor will instantly be perceived. Much has been said on the subject of this phenomenon, but it has been nowhere noticed, that it likewise takes place whenever the tongue is coated with any one of the metallic substances pointed out in the first experiment, and the fingers with one of those by which it is followed in the series. If, however, after the chain has been formed, it be interrupted, the savor will be no longer manifest.

61. Experiment IV.-If a piece of silver be laid on the tongue, and a portion of zinc be held between the moistened fingers, as soon as the latter is brought in contact with the silver, there will not be any distinguishable sensation, or, at the least, it will be very slight. As often, however, as the chain is interrupted in any given point whatever, the savor will be perceptible. It will not in this case be so strong as in the preceding experiment, and will be more slowly communicated.

62. The same result will be obtained, as often as one of the metals pointed out in the first experiment is employed as a coating to the tongue, and one of those by which it is preceded in the list, as a coating to the fingers. Thus, by coating the tongue with lead, and the fingers with zinc, and by bringing the two metals in contact, the savor will not ensue; but, by interrupting the chain at any given point, it will be very perceptible. On the contrary, if, the tongue being still coated with the lead, the fingers be coated with silver, instead of zinc, and the chain established, the sensation will be instantly perceived.

63. Experiment V.-If the thigh of a frog be laid on a plate of silver, and the nerve on a surface of zinc or lead, the moment the coatings are brought in contact, powerful contractions will be produced. The same thing will happen whenever the coating of the nerve is made to consist of a metal selected from among those which are pointed out in the first experiment; and that of the muscle, of another metal following it in the series.

64. Experiment VI.-If the muscle be armed with zinc, and the nerve with silver, the contractions will not ensue until the moment the chain is interrupted. When portions of copper, iron, bismuth, and lead are substituted for the silver, the same results are obtained.

65. In the first, third, and fifth, of the preceding experiments, it must have been observed, tha

the phenomena were manifested the moment the galvanic circle was formed. The fluid contained in the part of the chain was put in motion, and penetrated instantly either to the tongue or to the nerve. By reversing the chain, a contrary direction must have been given to the current, seeing that the phenomena which were manifested in the second, fourth, and sixth experiments, that is, those in which the galvanic influence was not perceptible until the instant when the chain was interrupted, were to be ascribed to a portion of the fluid, accumulated either in the tongue or in the nerves, at the points of contact of these organs with their coatings. Now, to the end that the fluid should have been thus accumulated, it was necessary that it should have penetrated the above organs in the direction of the muscle towards the nerves, or of the fingers towards the tongue. It is thus demonstrated, that the accumulation of the fluid is a sure characteristic of the direction of the current, by the help of which it may in all cases be determined.

66. In conformity to the experiments which have been detailed above, and to the galvanic facts previously known and established, it would appear that the following principles may be laid

down.

67. (1.) That all exciting substances contain the galvanic fluid; but that its quantity is very considerable in humid substances, and in the organs of animals, which have a very small capacity for that fluid, when compared with metallic sub

stances.

68. (2.) That, when two exciting substances are brought together, a new distribution of the galvanic fluid takes place; the substance which has the least capacity losing a portion of the fluid, on which the other substance seizes. Metallic and carbonated substances, disposed in the following order,-zinc, lead, tin, mercury, bismuth, copper, silver, and plumbago, act in such a manner as that any one of them, when brought in contact with one of those by which it is followed, seizes on a portion of the fluid the latter con

tains.

69. (3.) When the galvanic fluid penetrates the tongue, in directing itself from its extremity towards its root, it causes in the latter part a particular savor, which is more or less strong, according to the greater or less quantity of the fluid, and to the susceptibility of the organ. But when its direction is such, that it tends to flow out of the animal arc by the tongue, it occasions a much weaker savor, which differs from the former in proportion as the quantity of the fluid put in motion is less. As the fluid, however, finds some difficulty in quitting the tongue, it partly accumulates in that organ; and when the cause that has given rise to this accumulation ceases, then the fluid, in returning towards the root of the tongue, occasions there the galvanic savor in question.

70. (4.) When the galvanic fluid, distributed by the nerves, penetrates into the muscular substance of the organs of living animals, recently separated from the animals themselves, contractions are produced in the parts it permeates. The susceptibility being exalted, if the fluid inherent in the organ should, from any cause

whatever, be unequally distributed, and accumulated at the particular points, muscular movements will ensue. But if the susceptibility is weakened, the contractions can no longer take place, unless by the aid of a fluid extraneous to the organ.

71. At the earliest stage of the diminution of the susceptibility of the organs, the contractions are displayed, whatever may be the direction of the fluid by which they are permeated. But when the susceptibility is weakened still more, the direction of the current ceases to be indifferent. When the fluid is directed in such a way as to pass from the nervous ramifications to the nerves themselves, the contractile movements are much weaker than when it receives a contrary direction; and in the former case a portion of the fluid becomes accumulated at the point where it has a tendency to flow out from the nerve. This accumulation, and this difference in the effect of the current, by which the organ is penetrated in one direction or in another, are greater in proportion as the susceptibility is less, and as the quantity of the fluid put in motion is smaller. Thus, when the susceptibility is greatly enfeebled, notwithstanding the contractions may ensue, when the fluid penetrates into the organs, in the direction leading from the nerve to the muscle, they cease altogether when it permeates them in a contrary direction, it being then almost completely accumulated in the organ. The cause which has given rise to this accumulation having ceased, the fluid returns into its accustomed channel, and, having penetrated the organs in the most favorable direction, occasions in them the muscular movements.

72. (5.) If a communication be established between two points of an animal organ, with the help of a chain composed of different substances, disposed in such a way as that it may not be symmetrical, relatively to the nature of the parts of which it is composed, the fluid, being unequally solicited on the one hand and on the other, puts itself in motion, and forms a current directed towards the preponderating force.

73. (6.) If all the parts of the chain, by which a communication is established between two points of a system of organs either nervous or muscular, be reversed, a current will be produced having a contrary direction to the former.

74. (7.) When the chain is symmetrical, relatively to the nature of the parts of which it is composed, the fluid, being equally solicited on all sides, will forbear to display any movement.

75. (8.) and lastly. When a chain, which is calculated by its nature to give motion to the galvanic fluid, is destroyed, that is, when an insulating body is interposed, the fluid, which had been accumulated in the organ by the formation of the chain, returns to its original situation, and a current is formed into a contrary direction to the first.

76. These principles, which form the basis of M. Lehot's, theory of galvanism, are likewise confirmed by the following experiments :

77. If the thigh of a frog be held in one of the hands, and the nerve coated with zinc, at the same time that the person who makes the experiment has his tongue armed with silver, the

thigh of the frog will contract as soon as the two metals are brought in contact; but the experimenter will not be sensible of any savor, or of a very slight one at the most. By interrupting, however, the chain, he will perceive a very distinct savor, and the thigh of the frog will cease to contract. If, on the other hand, he coats his tongue with zinc, and the nerve with silver, the peculiar taste will be manifested at the moment of the contact; and the thigh, provided its incitability has been weakened, will preserve a state of perfect immobility.

78. By the interruption of the chain, the muscular movements will be again apparent, without any manifestation of the galvanic taste. It will appear that this ought necessarily to happen, when it is considered that, as soon as the chain is formed, the current of the fluid takes a direction from the silver to the zinc, and, having penetrated in a direct and immediate way into the nerve, produces contractions in the muscle, at the same time that it crosses the body of the person by whom the experiment is made, and accumulates on his tongue, without his being sensible of any particular savor. When, however, the chain is interrupted, the accumulated fluid returns to the parts it had quitted, and the savor on the tongue becomes manifest. If the tongue be coated with zine, and the nerve with silver, the current being impelled in a contrary direction, the phenomena which take place are diametrically opposite.

79. If two persons, holding each other by the hand, arm the tongue, one of them with zinc, and the other with silver, as soon as they bring the two metallic substances in contact, the one who has the tongue coated with zinc is sensible of the savor; but this does not happen to the other. If they afterwards separate the zinc from the silver, the one who felt the savor at the time when the chain was formed, will cease to be sensible of it on its being thus interrupted; at the same time that it will be rendered manifest on the tongue of the other.

80. Finally, the animal arc may be terminated by two nerves. Thus, by placing the two thighs of a frog on a plate of glass, and establishing a communication between their muscles, by the help of a flat piece of metal, coating, at the same time, the nerve of one of them with zinc, and the other with silver; the thigh which is armed with zinc will contract the moment a cominunication is established between the two coatings, by the means of a rod of zinc or silver; the incitability of the other thigh having been weakened, the limb will remain motionless. By interrupting the chain, however, the muscular movements will be displayed in the latter, and the former will resume a state of repose.

81. The same disposition being made as in the second experiment, and the chain established, if a given point of the muscle be brought in contact with the mercury. without deranging the contact of the nerve; or if a communication be established between the muscle and the mercury, or between the muscle and the zinc, by the means of a metallic substance, the muscular movements will be instantly manifested. These thenomena are occasioned by the fluid accumu

lated at the point of contact between the nerve and its coating, which fluid returns into the muscle, and there gives rise to the contractions. This is shewn in the following manner :-If, while the communicating metallic substance still touches the muscle and the mercury, or the muscle and the zinc, the latter be detached from the mercury, the contractions will not ensue, as would have happened if the fluid accumulated by the original chain, at the point of contact of the nerve and its coating, had remained there.

82. If the thigh of a frog, prepared in the customary manner, be held in one of the hands, and the nerves, as well as a few points of the muscle, be brought in contact with the mercury, the moment that fluid is touched by a bar of zinc, held in the other hand, previously moistened, violent contractions will be produced in the limb of the animal. This experiment consequently presents phenomena entirely different from those which were the result of the second experiment. The fluid, instead of having been accumulated in the nerve, appears to have flowed out by the muscle, and to have there occasioned the contractions. Such a degree of incitability may be induced, that the contractions may be altogether subdued by the double contact of the nerve and the muscle, as well in forming as in interrupting the chain.

83. If the same disposition having been made as in the sixth experiment, not only the nerve, but likewise the muscle, be made to touch the piece of silver, leaving it, however, in constant contact with the zinc, violent contractions will be manifested as soon as a communication is established between the zinc and the silver, by the means of a conducting substance. By substituting for the silver either copper, plumbago, or lead, the same phenomenon will be obtained.

84. The current which is formed in a chain composed of three metallic substances, is constantly directed towards the extreme metal stationed in front of the metal at the other extremity of the chain. The direction of the current cannot therefore depend, in any degree, on the metal by which the middle space is occupied.

85. In the chain composed of metallic and humid substances, where there are only two or three heterogeneous metals in immediate contact, the current is directed in the same way as it would be if these metals were to be regarded as independent of the rest of the chain.

86. Having placed a thin plate of zinc at the bottom of a vessel filled with water, and brought the tongue in contact with the extremity of a bar of tin, the other extremity of which is made to touch the plate of zinc; if another bar of the same metal, of the same dimensions with the preceding one, be held in one of the hands, and its extremity plunged in the water, there will not be any perceptible savor. In reality, the current is, in this instance, directed in such a way as to pass through the fingers, crossing the body of the person by whom the experiment is made, to accumulate itself on the tongue. But as soon as the second bar of tin is plunged more deeply in the water, so as to touch the zinc, the savor becomes perceptible. This phenomenon, which had not hitherto been noticed, is, according