pores arife, from the external furface of the skin, NERVOUS PAPILLE, very minute and contiguous to each other, by which the office of touch is performed.

These are defended by a mucous fubftance * spread between the EXTERNAL and INTERNAL SKIN, which being every where pierced through by these papillæ, receives the name of RETE MUCOSUM.

Befides the pain confequent upon injuries done to the skin, the primary object of fenfation in thefe PAPILLÆ feems to be hardness and softness: fuch bodies as give way to the touch, we call foft; others, which resist preffure, so as to cause the skin to yield under them, we call hard. And how happily is this sense tempered between the two extremes; being neither too acute nor too obtufe!

By the touch, we correct the error of vifion. Naturally every object we fee appears to be within our reach, for a child, who has as yet made but little use of

* This gluey matter, soon after birth, grows of a yellow tinge, which increases in our riper age. It is darker, as the climate is hot, and as we become more exposed to it, and under the line it is of a perfect black colour, forming the chief contrast between black and white men. Dr. BEDDOES, in the prefence of fome pupils who attended his chemical lectures at Oxford, having directed a black to immerse his hand in diluted oxygenated marine acid, the hand quickly became milky white; but the piebald negro refifted any further attempts. On the contrary, a French phyfician, it is faid, by giving a reverend divine filver diffolved in the nitrous acid, converted him wholly into a black. Vide Dr. Beddoes' Works, and La Medicine Eclairée par les Sciences.

his fenfe of feeling, would equally grasp at the moon as at objects within his reach. Mr. CHESELDEN, having couched a boy of thirteen for a cataract, who had hitherto been blind, and thus at once restored him to fight, has curiously marked the progress of his recovery. He was, at first, couched only in one of his eyes; and, when he saw for the first time, he was fo far from judging of distances, that he fuppofed his eyes touched every object that he faw, in the fame manner as his hands might be faid to feel them. It may be for this reason that we often see horfes frighted at things, which they have not become acquainted with by means of their noftrils, which ferve them in fome refpects like our hands.

It has been remarked, that even brutes are intelligent in proportion to the accuracy of their feeling, or as their extremities approach in resemblance to the human hand. The horse and the bull, whofe feet are covered with callous hoofs, are less intelligent than the dog, and the dog is inferior in accutenefs to the ape, who poffeffes a rude kind of hand.

This fenfe is the peculiar amufement of infants, and, as we before obferved, perfects the fense of vifion.

SECT. XVII.

OF PAIN.

BUT different from this, and conftituting another species of feeling, are those sensations arifing from different disturbances in the animal machine.

All these various fenfations are fo diftinct one from another, that scarce any two parts of the body feel the fame fpecies of pain. The bead-ach, tooth-ach, ear-ach, though ranged under one general name, are yet very different kinds of fenfation. The pain which the bowels feel in colics, is totally different from any of thefe; and the affection of the stomach, called sickness *, is peculiar to that part, this organ being liable to other fpecies of pain alfo. Again, the pain felt in the breast from the breath being ftraitened, has no kind of analogy with any of thefe, the breaft being alfo fubject to other pains, inflammation, and the like. Nor are the feveral modes

*Sickness arifes from fenfation: hence it is always preceded by nausea. Van Swieten relates that SYDENHAM was once fick on seeing a putrid dead dog; coming past the fame place many years afterwards, he felt a fimilar inclination to vomit. Hence if we cut the par vagum, the nerve leading to the ftomach, no fickness can be excited in the dog by the most violent emetics.

of pain, to which our perishing bodies are subject in all their diverse parts, eafily to be enumerated *. But these variations principally merit our attention, as the different fenfations in the pains the fame part is fubject to, may, fo far as they can be defcribed, point out the cause of each, and direct to the proper methods for removing them.

Thefe ftimulate in proportion to their intensity and the fenfibility of the part affected, and accordingly convey their impreffion to the fenforium, which has a power even to stifle a part of the stimulus by refignation, or else add to it by the impatience of the will.

*It is not meant that the nerves are different, but that they are like the nerves administering to taste, differently affected according to the stimuli applied; and poffefs also a difference in fenfation, arifing from the variety of ructure in those organs to which they are connected. Vide the Sect. ON THE SENTIENT PRINCIPLE.

SECT. XVIII.

OF THE SENSATION OF HEAT AND COLD,

THERE are many experiments in chemical writers, that evince the exiftence of HEAT as a fluid clement, which covers and pervades all bodies, and is attracted by the folutions of fome of them, and is detruded from the combination of others. Thus from the combinations of metals with acids, and from those combinations of animal fluids, which are termed fecretions, this fluid matter of heat is given out amongst the neighbouring bodies; and in the folutions of falts in water, or of water in air, it is abforbed from the bodies that furround them; whilst in its facility in paffing through metallic bodies, and its diffi culty in pervading refins and glass, it refembles the properties of the ELECTRIC AURA; and is like that excited by frittion, and feems like that to gravitate amongst other bodies in its uncombined fiate, and to find its equilibrium*.

There is no circumftance of more confequence in the animal œconomy than a due proportion of this fluid of heat; for the digestion of our nutriment, and the con

*Vide page 282.

verfion