owing to the bodies being poffeffed of too large or too fmall a quantity of this fubtil fluid, which is perhaps the vehicle of all our feelings. It is known, that in damp and hazy weather, when this fire is blunted and abforbed by the humidity, it's activity is leffened, and what is collected is foon diffipated; then our fpirits are more languid, and our fenfibility is lefs acute. And in the fierce wind at Naples, when the air feems totally deprived of it, the whole fyftem is unftrung, and the nerves feem to lofe both their tenfion and elafticity, till the north-west wind awakens the activity of the animating power, which foon reftores the tone, and enlivens all nature, which feemed to droop and languifh in it's abfence: nor can this appear furprifing, if it is from the different state of this fire in the human body, that the ftrictum and laxum proceeds, and not from any alteration in the fibres themselves, or their being more or less braced up, (among which bracers cold has been reckoned one,) though the mufcular parts of an animal are more braced when they are hot, and relaxed when they are cold.

From the perpetual electricity of the atmo fphere, which is no longer a problem, as it's exiftence and agency in that mafs of air which furrounds our globe, has been afcertained by numerous, clear, and decifive experiments, it feems but juft to infer, that it must exert a certain influence on all the beings contained therein, and principally on organized bodies, among which the human frame claims the pre-eminence.

But there is no neceffity for deductions from a general view of nature, for we are now in poffeffion of facts, which prove, that it is a principal agent in promoting the functions of animated beings; as in the gymnotus electricus torpedo, and filurus clecuicus. For the fimilitude eftablished

between

between the electrical fluid of these animals, and that of nature at large, is fuch, that in a physical sense they may be confidered as the same.

OF THE LATER EXPERIMENTS ON ANIMAL ELEC

TRICITY,

When Mr. Walsh first attributed the fenfations produced by the torpedo, &c. to electricity, his opinions, and the inferences deduced from his experiments, were vehemently oppofed by moft of the best electricians of the day: the conceptions of these men being limited to the minutiae of experiments, they were incapable of grafping a more extenfive fubject; or one that was not in all refpects conformable to the appearances they were used to. Whereas a juft view of things fhould have prepared them to expect various anomalies, while they were inveftigating the nature of an invisible and fubtil agent, fubject to a variety of modifications from the fubftance through which it paffes, or with which it may be combined. Hence in the purfuit of animal electricity, you must not expect to meet with every electric fign, as from the very nature of it's connection with animated beings, it will certainly acquire properties that are not to be found when it is difengaged therefrom.

Before I relate any of the experiments of Valli, &c. I fhall lay before you thofe principles which I conceive will throw great light on the fubject of animal electricity, and by which they may be reconciled to the general agency of nature. You have feen by a great variety of experiments, that electricity is always first rendered fenfible by a folution of continuity; you have also every reason to fuppofe, that the electric matter is carrying on it's most important functions, when we are unable

Ee 3

to

to perceive any figns of electricity; you have feen that the electric matter, and what we term electricity, are not infeparable beings, that the one may fubfift, when the other ceafes to appear. As the air may occupy a fpace without producing found; fo the electric matter may refide in a body, without exhibiting any electric figns. We know allo by universal obfervation, as well as partial experiments, that there is a principle in all bodies, which is continually endeavouring to extend their form, but whofe energies are continually counteracted by an exterior force. Now it must be evident, that every folution of continuity will give an opportunity for this expansive, dilating fubftance to escape, when it puts on new and unexpected appearances. Now as we know this expanding fubftance is fire, and have a proof, that on it's escape it exhibits electric figns, we have a further confirmation of the identity of these elements.

I think this view of the subject is in itself a fufficient refutation of Dr. Munro's attempt to prove, that the nervous fluid or energy is not the fame with the electrical;* though many other arguments may be adduced to answer the fame purpose.

His difficulty in conceiving how the electrical fluid can be accumulated within our nervous fyftem is not greater than that of conceiving how it is accumulated amidst a condu&ting fluid in the torpedo, &c.; nor indeed than of it's being accumulated in the Leyden phial, as glass is now known to be permeable thereto. But the difficulty with respect to animals vanifhes, when we confider that electrical appearance's are occafioned by a fate of the fluid altogether different from that under which it exifts in the animal frame; when it is in the latter, it's

* Munro's Experiments on the Nervous System.

it's powers are united, and it's operations imperceptible; when it appears as electricity, it's powers are divided, and fome of their effects rendered fenfible.

So far as mechanical stimuli have any relation to fire, fo far they will be in fome degree similar to the ele&rical fluid, and act in the fame manner; for ftimulants act only as they are the vehicles of fire. The fecond objection therefore of the professor falls to the ground. The fame reasoning applies to his fixth objection.

His fourth reafon, fo far from proving that the nervous and electrical fluids are not the fame, may be confidered as a clear proof of their identity, for the two electrical powers always act in oppofite directions.

On the fame principle the nervous energy (the electrical fluid in it's united state) cannot pass readily up or down a nerve that has been tied or cut, for the tying or cutting the nerve changes the ftate of the fluid.

Before I proceed to give you an account of the experiments relating to animal electricity, I fhall lay before you fome remarks of the Rev. Mr. William Jones, from whom we have already profited fo much in the courfe of thefe Lectures, and which are intimately connected with our fubject. As the force of the electrical fluid (fays he) is principally exerted on the nerves and tendons of the body, there is reafon to believe that this Auid is the fame with that fomething, which many phyficians have difcourfed upon, under the name of animal fpirits. The nerves do not appear as if they were defigned to admit any animal fluid or liquor, unlefs it be an indolent lymph neceffary to Ee 4 keep

Jones's Effay on the Firft Principles of Natural Philofophy,

P. 266,

keep them moift: but their pellucidity indicates that they are properly adapted to give a direct paffage to the fluid light; for they are transparent, and that not tranfverfely, but longitudinally, or in the direction of their fibres. This Mr. Jones obferved accidentally, as fome eyes of fheep and oxen, which he had procured for diffection, lay on the table; one of thefe eyes bone in the day time, much in the fame manner as the eyes of fome animals do in the dark; on examining into this círcumftance, he found that if his hand were interpofed between the nearest window and the extremity of the optic nerve (a part of which, nearly an inch in length, remained with the eye, and was accidentally pointed towards the window) the light immediately disappeared."

From this he was led to confider, whether the light that appears in the eyes of fome animals in the night time, is really a reflection of light from the eye, as is commonly fuppofed; or whether it does not rather pafs into the eye, through the optic nerve, from the body of the animal? It is not easy to conceive how this fhining can be occafioned by a reflection of light from the choroides in the bottom of the eye, when the light to be reflected (as in a dark night) is not vifible before it's entrance into the eye. If a candle be held before the eyes of a dog, and you place yourself in the line of reflection, the light will be vifibly reflected from his eyes, because the illumination is fufficiently ftrong: but when there is no vifible illumination at all, how fhould it account for the like effect? Whence it is more reasonable, that this appearance fhould be owing to a light from within the body of the animal, which being weaker than the light of the day, but ftronger than the light of the night, is vifible in the night, but not in the day. The light of other bodies which shine in the dark is inherent in those

bodies,