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