SUMMARY of EXPERIMENTS made on ANIMALS with METALLINE SUBSTANCES.
I shall now proceed to state the several circumstances I have observed, in my Experiments, which more directly lead us to judge of the Nature and Cause of Animal Electricity.
1. When two Plates of different Metalline Substances, particularly of Zinc and Gold, between which a living Frog is placed, are brought into contact with each other, those Muscles, which are farther from the Brain and Spinal Marrow than the Metals, are convulsed: and this effect follows, although the Animal and Metals are placed on an inverted glass jar, and that a stick of sealing wax is interposed between the hand of the Operator and the Metals; that is, although the Animal, with the Metals, be insulated.
I have further observed, that the Metals, disposed as above described, excite convulsions in the Legs, after all the parts of the Frog have been divided transversely at the Pelvis, providing only that they are, thereafter, laid in contact with each other.
2. When all the parts of a living Frog, except the large Nerves called Sciatic, are cut transversely at the Pelvis, and the fore part of the Animal is laid on a plate of Zinc, supported by glass, and the hind Legs on glass; if a gold Probe be applied so as to touch the Zinc and one of the Legs; or a piece of Metal put under one of the Legs; the Muscles of both Legs will be convulsed.
The event is the same, after the Body of the Frog has been cut transversely about the middle of the Spine: or when the Legs are laid on the Zinc and the Spine on Glass.
If a piece of perforated dry Paper is placed between the gold Probe and the Muscles, there will be no convulsions; but wet Paper interposed does not prevent the convulsions.
On separating the gold Probe from the Muscles there are no convulsions.
3. If, after the Animal and Metals are placed as above described, the joining of the two Legs at the Ossa Pubis is cut, that Leg only will be convulsed with which the gold is in contact.
4. The Spine of the Frog with the Zinc being placed on one glass, and the Legs on another glass, if the gold, supported by one hand, which we shall call the Right Hand, be applied to the Zinc alone, and not to the Legs, these are not convulsed. But if the Operator applies his left hand to the Legs, or if a bystander, communicating with the Operator by the medium of the floor only, touches them, they are convulsed. If a stick of sealing-wax be interposed between his right hand and the gold, or between his left hand and the Legs; or, if the bystander, touching the Legs, is insulated, by standing on a stool supported by glass feet, the Legs will not be convulsed. If the insulated bystander touches the Legs with one hand, and the Operator with his other hand, the Legs are immediately convulsed.
5. After cutting the Spine transversely under the fifth Vertebra, and all the parts of the Pelvis, except the Sciatic Nerves, and laying the Spine on Zinc supported by glass, and the Legs on glass; if gold be applied to the Zinc, and then to one of the Sciatic Nerves, both Legs, if they have not been separated from each other at the Ossa Pubis, will be convulsed[11]. And this happens although a stick of sealing-wax be interposed between the hand of the Operator and the gold Probe, and although no Metalline Substance touches the Legs.
This Experiment succeeds after denuding the Sciatic Nerves for the length of an inch, and wiping them dry; and it continues to succeed for an hour or more, and till the Nerves are evidently discoloured and shrunk in their size. And, after that, although we wet the Nerves, their powers are not restored; shewing that the influence had been conveyed not by wetness on the surface of the Nerves, but by the particular matter of which Nerves are composed.
The event is the same, when the upper ends of the Sciatic Nerves are cut away from the Spine, and laid on the Zinc.
6. After preparing the Frog and placing the Metals as in last Experiment, if a piece of thin dry Paper, pierced with a number of small holes, be interposed between the gold Probe and the Sciatic Nerves, the Legs will not be convulsed. But, if the Paper be wetted, although it is not perforated, the Legs will be convulsed.
After preparing a Frog, as in last Experiment, and laying the Spine on one glass, and the Legs on another, if the Zinc be laid on a third glass, and the gold Probe applied to it and to the Sciatic Nerves, the Legs will not be convulsed.
8. If the Spine and hind Legs, connected by the Sciatic Nerves, are all laid on the same plate of Zinc, supported by glass, the Legs are not convulsed on touching the Zinc with the gold Probe held in the right hand, although the left hand is applied to the Legs.
9. If several Frogs, prepared as above described, are laid upon glass, in a straight line touching each other, and that the first Frog is supported on Zinc, and the last upon Gold; if one end of a brass wire is applied to the Zinc, and the other end of it to the Gold; the Muscles of all the Frogs will be convulsed. The event is the same, although a stick of sealing-wax be interposed between the hand of the Operator and the brass wire: that is, although the Frog with the Metals be insulated.
10. When Frogs are prepared as in last Experiment, and the Spine of the first of them laid on Zinc, and the last supported by the left hand of the Operator, if with a gold Probe, held in his right hand, he touches the Zinc, the Muscles of all the Frogs will be convulsed. But if the hind Legs, as well as the Spine, of the first Frog be laid on the Zinc, the Muscles of that Frog will not be convulsed.
11. After a Frog was prepared as before described, I cut the Sciatic Nerves where they are about to enter the Thighs, and laid their cut ends in contact with the Muscles, and then touched the Zinc and Nerves with a gold Probe, without exciting convulsions in the Thighs or Legs.
12. After cutting the Sciatic Nerves, I tied together their divided parts, and then touched the Zinc and Nerves above the Ligature, with the Gold, without finding that the Legs were convulsed, when the Zinc supporting the Spine was laid on one glass and the Legs on another: but when the Metals and parts of the Frog were laid on a wet Table, the Muscles of the Leg were convulsed.
13. When the Sciatic Nerves have been cut and rejoined by Ligature, if while the Gold is, with one hand, applied to the Zinc and Nerves, above the Ligature, the other hand touches the Feet, the Legs are convulsed.
14. If the two hind Legs of a Frog are separated from each other, and their Sciatic Nerves afterwards tied to each other; if one of the Legs be laid on Zinc supported by glass, and the other Leg on glass, when, with one hand, the Toes of one of the Legs are touched, whilst with the other hand a gold Probe is applied to the Zinc and Nerve of the Leg which it supports, this Leg only will be convulsed. But if the gold Probe touching the Zinc be applied to the Nerve of the most distant Leg, both Legs will be convulsed.
15. I found it was not necessary, in order to excite convulsions, that either of the Metals should be in contact with the living Nerve or living Flesh of the Frog; for if, after separating from each other the hind Legs of a Frog, and cutting transversely the upper part of their Sciatic Nerves, I laid a piece of putrid or boiled beef between their Sciatic Nerves, and two other pieces of putrid or boiled beef between their Toes and a plate of Zinc; if, with the point of a gold Probe, the side of which was applied to the piece of beef placed between the Sciatic Nerves, I touched the Zinc, both Legs were convulsed.
16. In like manner, when I placed alternately, in a straight line, a number of dead and living Frogs touching each other, and in the living Frogs cut, at their Pelvis, all the parts but the Sciatic Nerves; if, with my left hand I touched a dead Frog at one end of the line, and with a gold Probe, held in my right hand, I touched a plate of Zinc, on which a dead Frog was laid at the other end of the line or chain of Frogs, the Muscles of all the living Frogs were convulsed.
17. When a chain of living and dead Frogs was formed, as in the two last Experiments, but without cutting at their Pelvis all the parts but the Nerves; on applying the gold to the Zinc, convulsions of the Muscles were not excited.
18. It has been found, that, if a plate of Zinc is applied to the upper part of the point of the Tongue, and a plate of Silver to its under part, on bringing the two Metals into contact with each other, a pungent disagreeable feeling, which it is difficult to describe, is produced in the point of the Tongue. And if a plate of Zinc is placed between the upper lip and the gums, and a plate of gold applied to the upper or under part of the Tongue, on bringing these two Metals into contact with each other, the person imagines that he sees a flash of lightning, which, however, a bystander in a dark room does not perceive; and the person performing the Experiment perceives the flash, though he is hoodwinked.
It has been alleged, that the Flash happens before the two Metals touch each other, and is repeated on separating them; but these facts appear to me very doubtful, as I do not find that a Flash is produced when a piece of Cambric-paper, in which a number of holes is pierced with a pin, is interposed between the Zinc and Silver, although the Paper does not in thickness exceed 1/1500 part of an inch.
After performing this Experiment repeatedly, I constantly felt a pain in my upper jaw at the place to which the Zinc had been applied, which continued for an hour or more: And in one Experiment after I had applied a blunt Probe of Zinc to the Septum Narium, and repeatedly touched with it a Crown piece of Silver applied to the Tongue, and thereby produced the appearance of a Flash, several drops of Blood fell from that Nostril; and Dr Fowler, after making such an Experiment on his Ears, observed a similar effect[12].
I have farther observed, that although the previous application of a second plate of Silver to one half of the plate of Zinc, does not prevent the Flash when the other half of the plate of Zinc, touching the Tongue, is brought into contact with the first piece of Silver placed between the lip and the gum; yet if the Zinc and Silver are in the first place applied to each other, then placed between the lip and gum, and, after this, touched with the Tongue, there is no appearance of a Flash, although some degree of pungency and a disagreeable sensation is perceived by the Tongue: and a mixed mass, composed of one part of Zinc and two parts of Quicksilver, or a mass composed of three parts of Zinc and one of Silver, incorporated in a furnace, have not the effect, when they are applied to Nerves, of exciting convulsions of the Muscles in which the Nerves terminate.
I have also found, that two thick pieces of raw or boiled flesh, one between the Zinc and Tongue, and the other between the Silver and Tongue, do not prevent the disagreeable pungent sensation when the two Metals touch: and, in like manner, that the interpolation of two pieces of flesh between the Zinc and Tongue, and between the Silver and the upper Lip, does not prevent the appearance of a flash, on bringing the two Metals into contact.
19. I put a very thick plate of Zinc into a vessel with water, and placed, near to it, in the water, the under part of the Spine and the hind Legs of a Frog, after cutting all the parts at the Pelvis except the Sciatic Nerves. I then touched the Zinc with a gold Probe, and found, that, when I touched that part of the Zinc which was above the water, the Legs of the Frog were not affected; but when I touched that part of the Zinc which was below the surface of the water, the Legs of the Frog were convulsed[13].
I next put into the water one of the hind Legs of a dead Frog, and its other Leg into an adjoining vessel with water. Into the opposite side of the second vessel, I put one of the hind Legs of a living Frog, in which all the parts at the Pelvis, except the Sciatic Nerves, were cut; and into a third glass vessel with water, I put its other Leg. When I now touched that part of the Zinc, which was below the surface of the water with a gold Probe, the Legs were not convulsed; but, if I, at the same time, dipped the finger of my other hand into the water contained in the third vessel, they were convulsed: when, instead of my finger, I dipped into the water a stick of sealing-wax, held in my other hand, the Legs were not convulsed.
I found, by the three following Experiments, that the Muscles are convulsed, whether the Influence, produced by the application of the Metals, passes upwards or downwards along the Nerves.
20. I cut four living Frogs transversely at the middle part of their Spines, and threw away the fore parts of their Bodies and their Abdominal Viscera.
I next cut, at their Pelves all the Parts but the Sciatic Nerves; and at their Knees, I cut all the Parts but the Crural Nerves; and, in all of them, I cut asunder the joining of the two hind Legs at their Ossa Pubis. I then laid the Legs of all of them in a straight line, supported on different Glass Vessels inverted, in such a manner that the Foot of one Frog touched the Foot of the next to it.
Having then placed a Plate of Zinc under the Foot of the first Frog, and holding in my left hand the Foot of the fourth or last Frog, I touched the Zinc with a gold Probe which I held in my right hand; and found that all the Muscles of the Loins, Thighs and Legs of the four Frogs were convulsed.
21. When I placed the two Frogs in the middle, with their Spines contiguous to each other, and the Feet of both touching the Spines of the other two Frogs forming the Extremities of the Chain, and of course the Feet of one of these resting on the Zinc, and the Feet of the other supported by my left hand: On touching the Zinc with the gold Probe held in my right hand, all the Muscles of the Frogs were, as before, convulsed.
22. When I now turned aside the right Legs of all the Frogs, so that they did not form a Chain by touching the next Frogs; the right Legs were not convulsed.
It is evident, that in whatever direction we suppose the influence to have passed in its Circle, it must, in Experiment 20th, have passed up one Leg and down the other in the same Frog: And, in Experiment 21st, if it passed from one end of the Chain to the other end of it, it must have passed upwards in two of the Frogs, and downwards in the other two; or if the influence passed from the two ends of the Chain towards its middle, where the Spines of the two middlemost Frogs were contiguous, it must have passed upwards in all of them.
23. When after cutting four living Frogs transversely at the middle of their Spines, but without cutting at their Pelves all the Parts but the Sciatic Nerves, I placed the hind Parts of them in a Chain, as in Experiments 20th, 21st and 22d, the Muscles were not convulsed on applying the Gold to the Zinc.
I next found, that after placing in contact with each other the several Muscles which had been cut transversely in Experiments 20th, 21st and 22d, allowing the Nerves to remain undivided, the muscles were not convulsed when I touched the Plate of Zinc with the gold Probe held in my right hand, although I touched the other end of the Chain of Frogs with my left hand.
The reason why the Muscles were convulsed in Experiments 20th, 21st and 22d, and not in Experiment 23d, evidently is, that in the former, the influence was concentrated in the Nerve, in the latter the influence was diffused; that is, was in part conveyed by other Organs, as well as by the Trunks of the Nerves.
24. After finding that I could readily excite Convulsions in the hind Legs of a Frog, without cutting it, by laying its Back on a Plate of Zinc, and introducing a gold Probe within its Intestinum Rectum and touching the Zinc with the side of the Probe, I produced two or three hundred Convulsions, succeeding each other quickly, and observed that its Legs were, by these means, so much weakened, that it could not jump, and crawled with difficulty, but in a few minutes it recovered nearly the full force of its Muscles.
In other Frogs I passed a gold Wire between their Sciatic Nerves and Os Sacrum, and twisted together the two ends of the Wire over the Backs of the Animals. I then put them into a Zinc Vessel filled with Water, or into a Glass Vessel filled with Water, in the bottom of which I laid a large Plate of Zinc: So that every time the Animals by moving separated the Gold from the Zinc, and again brought them into contact, their hind Legs were convulsed. I allowed them to remain three or four days in this situation, and found that their Limbs were weakened considerably, but not exhausted of their Power of Motion; and, after removing the gold Wire, the Limbs by degrees recovered their strength.
I made the same Experiment on those Frogs in which I had, six weeks before, cut out, from behind, all that part of their Spinal Marrow which is covered by the six undermost Vertebræ, and found, several days after the Frogs had been subjected to the Experiment, that, by pinching their Sciatic and Femoral Nerves, and still more readily by the application of the Gold and Zinc, weak convulsions of the Muscles were excited.
25. After Frogs were prepared as above described, by cutting their Spines transversely, and then all the parts of their Pelves, except their Sciatic Nerves, I found that slight Electrical Shocks, or a Leyden Phial discharged directly through the Limbs of a Frog, or indirectly by the medium of water, produced convulsions in their Muscles, exactly resembling those excited by the Metals. And when, after moderate Electrical Shocks had been passed repeatedly through their Legs, the Metals were applied to their Nerves, in the manner before mentioned, the Muscles were convulsed. I found, likewise, that after cutting the Nerves transversely, and tying them together, Electrical Shocks were conducted by the Nerves, and occasioned convulsions of the Muscles.
When I had killed Frogs, by discharging through them, from their foreheads to their hind feet, large Leyden Phials highly charged, I found their Nerves or Muscles, or both, so much deranged, that feeble convulsions only could be excited by pinching the Nerves, or by applying the Metals to them.