CHAPTER I

OF THE STRUCTURE OF THE HUMAN BODY

1. As man ought to know himself best, we begin our treatise here. And first, let us contemplate the human body. The parts of this are either solid or fluid. Those of the solid, of which the rest are formed, are termed similar parts. Such as fibres, bones, membranes, ligaments, arteries, veins, lymphatic vessels, nerves, flesh, muscles, tendons: and those general coverings of the body, the cuticle, the skin, fat, and the paniculus carnosus.

2. A FIBRE is a kind of slender thread, of which all the other parts of the body are woven: according to the difference of which, the substance of the fibres is different also.

Earth, as an element, is a solid, opaque, angular, friable sub­stance, of such small volatile particles, that it readily diffuses itself through air and water, and resides invisibly in them. And earth eagerly imbibing both air and water, by their means forms the permanent basis and growth of all mineral, vegetable, and animal bodies.

These earthly particles have their connexion and power of cohesion, not from themselves, or a mere contact, but from the intermediate glue placed betwixt them.

That this glue is composed of oil, combined with water, by the vital attrision in animals, appears from the chemical analysis of bones and hair; from the jelly ‘of bones, ivory, and horns; and from the nature of our aliments themselves. Nor is there any kind of glue that .could more powerfully join the parts of animals, as we experience in fish-glue, and that of joiners or cabinet makers.

Earthly particles then cohering longitudinally, and tied together by an intervening cohesive glue, compose one of the least or most simple fibres; such as we have a knowledge of rather from reason than sense.

The finest microscopes have been hitherto insufficient to lead us to a sight of the smallest moving and nervous fibrils, and still less can we ever expect from them, to get any sensible idea of the mechanism by which sensation and motion are effected.

But the least fibres which appear to the sight, are of two kinds.

Of these two kinds of fibres, as we shall presently see, we may distinguish the former by the title of filamentary, and the latter of membranous.

* The first kind of these fibres is lineal, namely, such a form as makes their length considerably large in proportion to their breadth; and which, by disposing of the elementary particles in a right line, must of course lay them generally parallel with the neighbouring or contiguous fibres. Examples of such fibres we see in the bones, and most easily in those of a foetus; and Jike­wise in the tendons, ligaments and muscles; only we must here always remember, that the eye never reaches to the smallest fibres, but to larger ones made up of the smallest, and like to them in slenderness, placed together in a rectilineal course. That these are not different from the smallest fibres, we are persuaded by the most accurate microscopes of Muyses and Lewenloeck; by which the muscular fibres, divided even to the last, appear simi­lar to the larger, till, at length, they . seem mere lines, like spiders threads.

The second kind of fibres arc those winch are conjoined with a breadth frequently larger than their length.

From what has been said, we may admire nature no less for her wise economy than simplicity, in thus forming all that variety of parts we see in an animal, from one simple mass of clay or slimy matter, compounded of earth and glue; from whence the body is not only augmented from a single point in the ovum to its full growth and stature; but like the timbers of a ship, is also every day repaired during life, till at length, not two jots of the old or first materials remain. This renovation of parts is made slower in some constitutions, and in some organs, than in others. How quickly the animal humours, with the hair, nails, &c. are re­newed, every one knows: and we may venture to say, that once in three years the change is universal; at the end of which time, though a man remains the same identical person, he is not the same matter.

3. But we proceed from these simple fibres, to the next least compounded solid which they compose; viz. the cellular web-like. substance.

This is made up partly of the simple fibres, and partly by an infinite number of little plates or’ scales, which, joined in various directions, intercept small cells and web-like spaces; and by extending round every, even the least moving solid parts of the body, conjoins them altogether in such a manner as not only sustains, but allows them a free and ample motion.

The extension of this substance, not only with the skin round the whole body, but also round every viscus or organ, and round every individual moving fibre or vessel of them, into the cavities of the bones, and even the substance of the brain and its medulla, is a modern and wonderful discovery. This substance, in its ulti­mate state being composed of simple membranes, when compact­ed and convoluted, gives birth to the least or most simple vessels, which again reflected through plates of the same substance compacted together, make compound and vascular membranes; to the consideration of which we next proceed.

Out of this cellular substance compacted by a concretion of the membranous plates or partitions, and pressed together by the force of the incumbent muscles, and distending fluids, arise other broad and flat plates or skins in various parts of the body; which being generally disposed in one and the same direction, seem to have a better right to the name of membrane than the former; and these being convoluted into cones and cylinders, pervaded by a flux of some juice or liquors brought to them; put on the name of vessels, or else being extended round some space that is in a plane, parrallel to itself, we call it a tunic or coat.

This cellular substance in the human body, is found through­out the whole; wherever any vessel or moving muscular fibre can be traced, and this without the least exception, that I know of, in any part whatever. flut so far as we can trace, it hardly ever admits of any fat into the cells; which are rather moistened by a watery vapour, somewhat oily, exhaled out of the arteries and received again into the veins.

Its plates or scales are still more loose and open where it divides the muscles and all their fibres (even to the ultimate fibre); and likewise where it surrounds and sustains the least vessels with their free motion. That within the cavities of the bones is also made up of boney plates, with membranous ones intermixed; and lastly, it is the most loose and open of all, round the surface of the body on all sides, betwixt the muscles and the skin.

Through this cellular substance the small vessels are spread, and ramified in all parts of the body; from whose arterial extre­mities the fat is deposited into the cells, and afterwards absorbed by the venal orifices. This passage from the arteries, into the adipose cells, is so free and short, that there must needs be very large mouths by which they open, and by which they give admittance to injected mercury, air, or water. The oily fat, in this substance, is separated and expelled from the artery; not by any long ducts, but by transuding on all sides through the whole extent of the vessel. How quickly it is collected from the arteries, appears from the speedy renovation of it, by a returning fatness after acute diseases.

With regard to the sponge-like communications of this substance, it is remarkable, the intervals or spaces betwixt the plates or scales that make up their sides in the cellular membrane, are every where open, and form one continuous cavity throughout the whole body.

That out of this substance, joined with vessels, nerves, mus­cular and tendinous fibres (a great part of all which are before formed of this substance only), all the viscera, all the muscles and glands, with their ligaments arid capsules, are entirely composed; and that only from the different length, tension, quantity or proportion of this, the diversity of our glands, and viscera arises; and lastly, that this alone makes up by far the greatest part of the whole body, we are certain, if the whole be not formed out of the cellular filaments, of this kind.

4. The hardest part of the body, white and void of sense, is termed a BONE- The bones are covered with a thin skin, called the periosteum, extremely sensible.

The bones consist of thin plates, lying one upon another ; and these again, of fibres running lengthways; some to the extremity of the bone, some not so far. Yet none of them terminate there; but are continued transversely, and as it were arched, the fibres of one side meeting and uniting with those of the other, and this at each extremity.

These plates are differently disposed in different bones: in those that have a large cavity, they are contiguous on each side,. and very closely united. In those whose cavities are small, many of the inner plates arc distant from each other; having little long cells between them. In bones whose plates are con­tiguous, there are pores through and between them (beside those for the blood-vessels). The first pierce them transversely, from the cavity to the external surface of each plate. The second run lengthways between . the plates, and diffuse an oil with which they are supplied by the transverse pores.

The bones are generally bigger at each end than in the mid­dle, that the joints may be firm, and the bones not so easily dis-located. But to strengthen the middle of the bone, the fibres there are more closely compacted. Likewise, the bone, being large and hollow, is not so easily broke, as if it had been solid and smaller : for of two bones of equal length and equal number of fibres, that is stronger which has the larger diameter.

The blood-vessels usually enter the ends of the bones; the ar­teries at one end, the veins at the other. The medullary vessels commonly enter the sides of the bone, and that obliquely.

The marrow is covered with a membrane, wherein are inclos­ed little bags. In these’ bags are glandulous bladders, serving both to screen the marrow from the blood, and to receive it. Both these and the bags have passages into each other, whereby the marrow has free course. It. passes first through the trans­verse pores of the first internal plate into the longitudinal ones. Thence it proceeds into other transverse pores, when it alters its course again, and exsudes farther. Thus it passes alternately through and between the plates, till it is diffused throughout. In this manner it is diffused through bones, whose plates are contiguous. But where the plates are at a distance, the small cells contain glands, which directly supply the plates with marrow.

The marrow not only serves to keep the substance of the bone moist, but to lubricate the joints, and to hinder the ends of the bone, from being worn or over-heated with motion. It also moistens the ligaments, which tie them to each other: as do likewise the glands found in all the joints. The back-bone hath these two things peculiarly remarkable: I. Its different articulations from the other joints of the body. For here most of the Joints are fiat, and withal guarded with asperities and hollows, made for catching and holding; so as firmly to lock and keep the joints from luxations, but withal to afford them such a motion, as is necessary for the incurvations of the body. 2. The difference of its own joints in the neck, back and loins. In the neck the two upper vertebra, are curiously made, and jointed (different from’ the rest) for the commodious and easy bending and turning the head every way. In the thorax, and back, the joints are more close and firm; and in the loins more lax and pliant; also the knobs and sockets are turned a quite contrary way, to answer the’ occasions, the body hath to bend more there, than higher in the back. ‘So that its structure is the very best that can be contrived; for’ had it been all bone, we could have had no motion in our body; had it been two or three bones articulated for motion, the medulla spinalis must have been necessarily bruised at every angle or joint; besides, time whole would not have been so pliable, for the several postures we have occasion to put ourselves in. if it had been made of several bones without intervening carti­lages, we should have had no more use of it, than if it had been but one bone. If each vertebra had had its own distinct carti­lage, it might have been easily dislocated. And lastly, the oblique processes of each superior and inferior ‘vertebra, keep time middle one, that it can neither be thrust backwards nor forwards to compress the medulla spinalis

The pelvis made in the belly by time ilium, ossa coxendicia, and pubis, is larger in a female than in a male skeleton, that there may be more room for the laying of the viscera and fatus. So the cartilage bracing the two sharebones, is twice thicker and laxer in women than in men. As also is the cartilage that ties time os sacrum to its vertebra; and all, to give way to the passage of the foetus. -.

Another considerable difference is, in the cartilaginous produc­tion of the seven long ribs, whereby they are braced to the breast­bone. These are harder and firmer in’ women than in men ; the better to support the weight of the breasts, the sucking infants, &c.

It is remarkable in the joints, and a manifest act of caution and design, 1. That although the motion of the limbs be circular, yet the centre of that motion is not in a point, but an ample sperficies. In a point, the bones would wear and penetrate one another, and the joints would be exceeding weak. But the joint consisting of two large superficies, concave and convex, some furrowed and ridged, some like a ball and socket, and all lubri­cated with an oily substance; they are incomparably prepared both for motion and strength. 2. That time bones next the joints are not spungy, as their extremities commonly are, nor hard and brittle; but capped with a strong, tough, smooth, cartilagin­ous substance, serving both for strength and motion.

For affording this oily matter there are glandules very com­modiously placed near the joints, so as not to suffer too great compression by the motion of time neighbouring bones, and yet to receive a due pressure, to cause a sufficient emission of the oil into the joints. Another thing considerable is, that time excre­tory ducts of the mucilaginous glands have some length in their passage from the glands to their mouths; which is a good con­trivance, to prevent their mouth being oppressed by the mucilage, and also to hinder the too plentiful effusion thereof, but yet to afford a due expressure of it at all times, and on all occa­sions; particularly in -violent and long-continued motions of the joints, when there is a greater than ordinary expense of it.

That the nourishment .taken, is continually conveyed through, the bones, as well as the flesh, appears from an easy experiment. Mix red liquor with the ‘food of any animal, and in a short time the bones are died red. When madder root was mixed with the food of a cock, which died after sixteen days, all his bones were red, the internal parts as well as the external. And the most solid parts were the most deeply tinc­tured; in swine, the teeth above all’ the rest.

5. Annexed to the bones are the CARTILAGES, white, flexible and smooth; most of which in process of time become bones, hard and quite void of sense.

A cartilage is an elastic substance, uniformly compact and somewhat transparent, harder and more brittle than a ligament, softer than a bone. It is covered with a fine membrane, folded over the bone, from where the ligament is inserted. Every joint is inserted with a membrane, which forms a complete bag, and covers every thing within the articulation. The blood-vessels are so small, that they do not admit the red globules, and are demonstrable only in very young subjects. All round the neck of the bone, there are numerous arteries and veins which spread into smaller branches, and communicate with each other. These divide into still smaller branches on the adjoining surface, as they run toward the centre of the cartilage. We can seldom trace them into its substance, because they end abruptly, at time edge of the cartilage. The larger vessels plunge in by num­berless small holes, and disperse themselves into branches between the cartilage and bone. From these again there arise many short, but small twigs, which shoot toward the outward surface, This distribution of time blood-vessels is very peculiar, and calculated for obviating great inconveniences. Had they run on the outward surface, the pressure and motion of the two car­tilages must have occasioned frequent obstructions and inflammations. But by creeping round the cartilaginous brim, where there is little friction, or under the cartilage, where there is none, they are perfectly well defended from all such accidents.

Cartilages are admirably contrived for all the purposes of motion. By their uniform surface they move one upon another with ease: by their soft, smooth and slippery surface, mutual abrasion is prevented. By their flexibility, the contiguous sur­faces are constantly adapted to each other. By their elasticity, the violence of any shock, which might happen in running, jumping, or the like, is broken; which must have been extremely pernicious, if the hard surfaces of bones had been immediately contiguous. ‘The cartilaginous fibres appear calculated chiefly for this last advantage.. To conclude, the insensibility of these cartilages, is less wisely designed, that by this means the ne­cessary motions of the body may be performed without pain.

6. The various parts of the body. are clothed with MEMBRANES, which are whitish tunicles, extremely thin and flexible, composed of fibres interwoven with each other, as a piece of cloth is of threads. They are fastened together by a kind of cartilages, which are termed ‘ligaments. -

7. An ARTERY is a hollow canal, composed of fibres closely twisted together, which conveys the blood from the cavity of the heart to all the, parts of the body. All the arteries spring from two, the aorta or great artery, and the pulmonary artery. The latter conveys time blood from the right ventricle of the heart, through the lungs, into the left ventricle. ‘The former conveys it from the left, to all other parts of the body.

The arteries ordinarily Consist of three COATS or membranes. The, outermost has been generally thought to be composed of fine blood-vessels. The second is muscular, and made of firm and strong circular, or rather spiral fibres: of which there are more or fewer strata, as the artery is larger or smaller. These fibres are extremely elastic. The inmost coat is a fine dense, transparent membrane, containing the blood, which otherwise would easily ooze through the spiral fibre,

On a more accurate examination it has been found, that the outermost coat of all arteries is a cellular substance, composed of’ fine, pellucid membranes, which may be stretched, even sud­denly to a great extent without breaking. And they as suddenly collapse, when that stretching force is removed. These cells contain an oily liquor which their coats secern from the branches of the artery that are spread over them, This cellular substance of the arteries serves to connect them with the surrounding part, without hindering their actions or motions. It gives a safe passage to the vessels of their other coats, and supplies oil for lubricating them. There is also another cellular substance, between the membranes and the muscular coat.

All the arteries begin with a larger trunk, and grow less and less till they are no longer seen by the naked eye. Hence they are continued till, they inosculate with the veins, and so form one uninterrupted channel.

They appear white, because their coats are of so dense a con­texture, that the blood is not visible through them. This pro­ceeding from wider to narrower canals, is continually obstructed in its passage. But being pushed ‘on from behind, it distends the coats, and causes that leaping motion called the PULSE. By this, as well as by their whiteness, arteries arc distinguished from veins.

The pulse of a. healthy person, rising in the morning, beats 65 in a minute; but after the fatigue of the day, it will in the even­ing beat 80 in that time’ and again, by the night’s rest or sleep, it will become less frequent, till in the morning you will find it return to 65. For the voluntary motions of the muscles, and actions of the external and internal senses, urge the venal blood on to the heart, which, being thereby oftener stimulated, makes more frequent contractions. This is the cause of those par­oxysms or fits of increase, observable in all fevers towards the evening. For sleep not only retards the motion of the blood, but of all the other humours and actions in the body.

It is one Of the curious observations of Dr. Hales, that the pulse is quicker in small animals. He found the pulse of a horse slower by half than in a man, viz. 32 only in a minute; whereas in a dog, the pulse beat 97 in that time. And this we see is conformable to the blood’s heat, measured by the mercu­rial thermometer of Fahrenheit's scale, For the blood in oxen, horses, and other large animals at rest, being five or six degrees cooler than in us, will not rise to our heat, but by labour; whereas, dogs, cats, and fowls, are five or six degrees hotter than we (viz, about 102); and the latter, when sitting or brooding on their eggs for young, are still four or’ five degrees hotter, viz. 107 or 108, which is commonly the heat of our blood in the fit of an ague; where it is observable, that during the greatest sense of cold chill, time blood is three or four degrees hotter than in health, after which it gains four or five degrees more in the height of the hot fit, viz. 104 or 105 degrees; but in ardent fevers, where the pulse beats 140, the heat of blood will still be four or five degrees higher, viz. 110; i. e. two or three degrees more than equal to a brooding hen.

The pulse is more quick in children, and becomes slower in persons as they grow older. Time salient point of an OVUM beats 134 in a minute. New born infants have their pulse 120, and from thence down to old age it grows slower, to 60 in a minute. A feverish pulse begins at 96 per minute; it is excessive at 130 or 140, which is the number of the pulse with which a person dies. The pulse beats slower in winter, and quicker in summer, by about ten strokes per minute; and under the torrid zone, it grows quicker, to 120.

8. A VEIN is a hollow canal, which receives the blood from the artery, and conveys it back to the heart. The chief veins are. three, the vena cava, which pours the blood through a wide passage into the right ventricle of . the heart; the pulmonary vein, which in like manner’ pours it into the left ventricle; and the vena porta, which does not, like the two former, end in a large. trunk; but spreads itself at each extremity into numerous’ branches.

In the cavity of the veins, there. are certain thin tunicles, which are termed VALVES. These, during the regular motion of the blood, lie close to the side of the inner coat: but in case of any obstruction, recede from it and close the passage, to prevent the blood’s falling back.

9. The LYMPHATIC VESSELS are small canals full of valves, consisting of a thin, transparent tunic, which convey an ex­tremely clear liquid into the mass of blood. Probably these’ (as well as the veins) and all the other vessels, are only continua­tions of the arteries.

It has been lately discovered, that the lymphatic vessels have two coats; betwixt which there are innumerable fine filaments, containing a nutricious juice, which is conveyed into all parts of the body, by a motion from the centre to the circumference, and returns through the inner pipes, of the same watery vessels. But this juice when returning, is no more water or dew, but fer­ment; and the vessels may be termed ferment-vessels. This ferment is conveyed into the blood, by a motion from the cir­cumference to the centre.

The lymphatics carry their dewy particles through the glan­dules, which lie between the two coats. Jim the lowermost end of these glandules, the ferment-vessels take their rise. Most of the juice of the lymphatic-vessels is discharged between the coats of the veins, arteries, and vessels, in the mesentery; to be conveyed into all parts of the body, both internal and external. Even in bearing females, the fruit is not nourished by blood, but by this nutricious juice: the remaining part of which, is trans­mitted into time blood through the thoracic duct and jugular veins. -

10. A NERVE is a whitish, round, slender body, arising from the brain, which is supposed to convey the animal spirits to all parts of the body. What these spirits are, none can shew: nay, we are not sure they have any being. For none can certainly tell, whether the nerves are hollow canals, or only solid threads, enclosed in proper integuments.

11. The fibrous, soft, reddish part of the body is termed FLESH. All fleshy fibres are hollow, and divided through their whole length into little caverns, wherein the blood is detained, as occasion requires.

12. A GLAND is a soft and spungy body, which separates some particular liquid from the blood. The larger glands contain arteries, veins, and lymphatic vessels: but the glands of the intes­tines are ònly the tops of the arteries.

There is a kind of DOWN in the cavity of every gland, which probably does the office of a filter, and is that whereby a particu­lar humour is separated from the blood.

The structure of time down-vessel is different according to the different purposes of nature. Sometimes the liquor filtrated through it, falls drop by drop on a membrane, to which one end of the vessel is fastened, as where it is designed only to moisten the part. Sometimes many of these down-vessels spread over the inner surface of a membranous cell, into which they all pour their liquor, which is discharged at a small orifice.

These vessels are often of a great length, though they take up little room, being wound over one another, sometimes in a single knot, and sometimes in several, enclosed in a common membrane. And hence is the distinction of glands into conglobate and conglomerate.

A conglobate gland is a little, smooth body, wrapt up in a fine, double skin; with only an artery and nerve passing in, and a vein and excretory duct going out.

A conglomerate gland is an irregular assemblage of several simple glands, which are tied together and wrapt up under one common membrane.

13. A MUSCLE is a bundle of fibres joined and fastened together, with their proper veins, arteries and nerves. It is divided into little cells by transverse fibres, parrallel to each one, whereby it may be contracted and shortened, or relaxed and lengthened again. ‘ Its extreme parts arc more closely compacted,, which we term tendons. By these time muscles are connected with the neighbouring parts. A muscle generally consists of three parts: the upper, termed the head, the middle, termed the belly, and the lower part, or tail.

Every muscle is divisible into smaller muscles, and those into other still smaller; and so on, beyond all imagination. The last and smallest parts are muscular fibres. But there is no assign­able point in any muscle, wherein there is not some nerve. And here all the nerves disappear (in other parts their extremities expand into membranes). It is therefore probable that the muscular fibres, are only the nervous continued.

14. The CUTICLE, or SCARF-SKIN, is an extremely thin and transparent membrane, void of sense, and covering the skin all over, sticking fast to its surface, to which it is also tied by the vessels that feed it. It consists of several layers of exceeding small scales, which cover one another where it is thick, But in the lips, where it is extremely thin, they little more than touch one another.

In some creatures (as fishes), these scales are only the excre­tory ducts of the’ glands of the skin. In others, those glands have their proper ducts, opening between the scales.

It is supposed, there arc in one scale 500 excretory ducts, and. and that a grain of sand will cover 250 scales. If so, a grain of sand will cover 125,000 of our pores.

The cuticle serves to defend the nerves of the skin, both front the air, which would dry and make them less sensible, and from rough and hard bodies, which would make a painful impression on the naked nerve.

Negroes have a skin between the cuticle and the true skin. They are born white; but the middle skin, in a little time, turns black, and gives that colour to the whole body.

But who can account for the following case? Sir Charles Wager had a boy about eleven years old, who was born in Virgi­nia, of negro parents. Till he was three years old, he was like other black children. He then, without any distemper, began to have little white specks upon his neck and breast. These increased with his years, both in number and bigness, so that from the tipper part of his neck, quite down to his knees, he was dappled with white spots, some of them broader than the’ palm of a man’s hand. They were wonderfully white, equal to the skin of the fairest lady, only somewhat paler. His face, arms and legs were perfectly black. He was exceedingly active, sprightly, and more ingenious, than. is common among that generation.

Perhaps the following fact is no less difficult to be accounted for: A negro woman, cook to colonel Barnes, in Maryland, about forty years of age, remarkably healthy, had her skin as dark as that of the most swarthy African. But that part of it next her finger nails, about fifteen years ago, became white. Her mouth soon underwent the same change, which has since gradually extended over the whole body. At present, four parts in five of her skin are white, smooth and transparent, as in a fair European, elegantly shewing the ramifications of the subjacent blood­vessels. The other parts daily lose their blackness, and partake­ of the prevailing colour. The neck and back retain most of their pristine hue; the head, face, breast, legs and arms are all white. Her face and breast, when anger or shame has been excited in her, have been observed immediately to glow with blushes. This is the naked fact; but upon what principles of philosophy can we account for it? ‘

The SKIN covers almost all, the whole body, and is formed of whitish fibres, intermixt with mumberless ‘branches of nerves, veins and arteries. On its surface are many furrows, or indented lines, having generally hairs on each side, and pores, or little holes of various sizes, serving for the transpiration of superfluous particles. Under the skin lie the subcutaneous glands, which are supposed’ to transmit through the pores an insensible steam, commonly believed to be of the same kind with what, when sensi­bly thrown out, is called sweat.

The PORES in our hands and feet are very remarkable. Survey with a glass the palm of your hand, well washed, and you may perceive innumerable little ridges, of equal bigness and distance, every where running parallel with each other: these are very observable on the ends and first joints of the fingers and thumb, and near its root, a little above the wrist.

On these ridges stand the pores, all in even rows. Through a good glass every pore looks like a fountain. The sweat may be seen to stand therein, as clear as rock water. The ridges are so placed, that they may better suit with the use and motion of the hand: those on the lower side of each triangle, to the bending in of the fingers: those on the other two sides, and on the elliptic ridges, to the pressure of the hand or fingers’ ends, against any body, requiring them to yield to the right and left.

The pores are placed on these ridges, not in the furrows between them, that their structure may be less liable to be injured by compression, whereby the furrows only are dilated or contracted: the ridges constantly maintaining themselves; and so the pores are unaltered. For’ the same reason the pores are very large, that they may be the better preserved; though the skin be never so much compressed and condensed, by the constant labour of the hand: and so those on the feet, that they may be preserved, notwithstanding the compression of the skin, by the weight of the whole body.

Through the pores there continually transudes a subtle vapour from every point of the body, being what redounds of the aliment, comminuted to the highest degree, and sent to repair every particle of it. And the matter thus evacuated is more than is thrown out by all the Other passages together.

A person of middle age found what he perspired was five ­eighths of the food taken in: so that there remained only three eighths for nourishment and all other evacuations. He observed also that so much is perspired in one day, as passes by stool in fourteen; and more particularly, that in a night’s time about sixteen ounces are usually thrown out by urine, four by stool, and about forty by insensible perspiration.

If a. man eats and drinks eight pounds in a day, five pounds of it pass by perspiration: namely, about one pound within five hours after eating (perspiration being least of all soon after eating); from the fifth to the twelfth hour, about three pounds; and from the twelfth to the sixteenth, scarcely , half a pound. Exercise increases perspiration much; but it is naturally less in women than men.

While this steam flows from our body, it constantly imbibes a supply of moisture from the air, which serves to keep all its parts soft, pliant and fit for motion. Hence, from the greater moisture of the air, we perspire less in winter than in summer, and in rainy weather than in fair. Live, therefore, if possible, in a clean house, arid in a pure, dry air.

This inhalation is very considerable. Dr. Keil found his body to have imbibed in one night eighteen ounces of moisture. And on a sudden change of weather from dry to wet, the inspiration sometimes exceeds the expiration: there being absorbent veins, which accompany the numberless arteries from which the per­spiration is discharged. To time matter thus imbibed, not the obstruction of the pores, he ascribes what we term a COLD-Sweating cures this, by throwing out the noxious matter which was imbibed before.

The cutaneous vessels both exhaling and inhaling, are capable of contraction and relaxation, by the power of the nerves. This appears from the effects of the passions, which if joyful, increase the circulation, and relax the exhaling vessels. Those passions, on the contrary, which are sorrowful, and retard the circulation, contract the exhaling vessels, as appears from the dryness and corrugation of the skin, like a goose-skin after frights; and from a diarrhoea caused by fear. But the same affections seem to open the inhaling vessels; whence the variolus or pestilential conta­gions are easily contracted by fear.

Time benefits of insensible perspiration are so great, that life cannot be preserved without it. And the subtilty, equability and plenty of wlmt we perspire, are the grand symptoms of health.

But how little do we know even of our own frame! It has hitherto passed as an unquestionable truth, that the same matter which passes by insensible perspiration, passing in great quanti­ties, is sweat. Whereas an ingenious physician, Dr. Rogers, has found by numerous experiments, that a person perspires abun­dantly less, when he sweats, than when he does not: that one who perspires twenty-four ounces in seven hours sleep, if he sweats, does not perspire above six. This he tried many times, and never found it to fail. Whence he infers, 1. That it is not the same matter which is evacuated by insensible perspiration and by sweat: 2. That it is not evacuated through the same pores: 3. That the sweat-pores are abundantly larger and fewer, than those which serve insensible perspiration: 4. That sweat greatly hinders that perspiration, both by covering those pores with a clammy liquor, and by constringing them so that they cannot open; which must be the case, when the sweat-pores are dilated. What a field does this open!

Some queries proposed concerning perspiration, by an inge­nious writer, seem to deserve a serious consideration. 1. “ Why do carnivorous animals sweat so little? A fox hunted almost to death never sweats. 2. Why do those which feed on vegetables perspire so much? Horses and cows for example. We may often see them involved in a cloud of their own vapours, yea, almost covered with froth. 3. Flow can animals, whose natural food is vegetables, be kept alive and in health, in very cold cli­mates, by purely animal food ? Cows in Iceland and Norway, are fed in winter upon fish-bones.” I would beg leave to ask, 4. Do the sweat-pores only, imbibe? Or those also, which serve for insensible perspiration?

15. FAT, a whitish, oily substance, void of sense, is secreted from the blood, and lodged in small, oval, membranous bags, which shoot out of the arteries. It is found in various parts, but chiefly under the skin, where, unless a man be emaciated, it runs co-extended with the skin over most parts of the body.

Fat is secerned from the arterial blood by the ADIPOSE GLANDS, and transmitted again from the membranous cells to the blood through the veins. It seems to be a portion of the blood coagulated by the nitrous air mixed with it in the lungs. Artificial fat is made, by mixing, for some days, oil of olives with spirit of nitre. Hence divers animals grow fat in frosty weather, the air then abounding with nitre.

The uses of the fat are various; as to facilitate the motions of the muscles in all the parts, lessen their attrition against each other, and prevent a stiffness or rigidity; it fills up the intermediate spaces between the muscles in such a manner, with the cavities about many of the viscera, that it readily yields to their motions, and yet supports them when at rest; it serves as a stratum or bed to conduct and defend the vessels in their course to all parts ; it gives an uniform extension to the skin, and serv­ing as a cushion to ease the weight of the body in many parts, at the same time it renders the whole of a comely, agreeable shape: it probably, by returning and mixing with many of the humours; abates their acrimony; it has a principal share in form­ing the matter of the bile, and by transuding through the cartilaginous incrustations of the bones, it mWes with the articular lini­ment or synovia; also by exhaling in a living person from the mesentery, mesocolon, omentum, and round time kidnies, it lubri­cates the surfaces of the viscera with an oily, emollient vapour, and by interposing betwixt their integuments, prevents their growing one to another.

Yet too much fat is a real disease, which hinders the motion of the lungs, entangles the most active particles of the blood, and naturally creates dulness and heaviness. You may cure this, by following three plain rules eat and drink little ; sleep little work much.

16 The fourth general integument is the PANNICULUS cAR­NOsus, which in some parts is of a fleshy substance; in others, a mere membrane, lying just under the fat.

17. The dissimilar parts arc composed of the similar. The chief of these is the HEAD. The cavity of time SKULL is nearly filled with a soft substance, termed in general, time BRAIN. But this is properly that part of it which lies forward. The hinder part, considerably smaller, is called the cerebellum. Under both, but chiefly the latter, and springing from the internal sub­stance of both, is the medulla oblongata.

The skull is divided into two plates, one laid over the other. Between these is a spongeous substance, made of bony fibres detached from each plate. Hereby the skull is made not only lighter, but far less liable to fractures.

The skull is covered with a membrane called the PERICRANIUM. This has several holes, which give passage to the spinal marrow, the nerves, arteries and veins. But these fill them so nicely, that nothing can pass into or out of the head, but through these vessels, It is round,, that it may contain the more; but a little de­pressed and longish, advancing out behind, and flatted Qf the sides, which contributes to the enlargement of the sight and hearing.

It is divided into pieces by four sutures. This makes it less liable to break, gives passage to the membranes of the pericra­nium, and vent to the matter of insensible perspiration.

18. All these are involved in two membranes, the inner, called pia mater, extremely thin; and time outer, called dura mater, considerably harder and thicker. Where they involve the cerebellum, there is interposed between them the arach­noides, a very subtle arid transparent membrane, which descend ing through the hinder part of the skull, together with them involves the whole spinal marrow.

19. The outer part of the brain, called the cortex or bark,’ is of an ashy or greyish colour. It is formed from the minute branches of the neighbouring arteries, which being wove toge­ther in the pia mater, enclose the inner part, ordinarily to the thickness of about half an inch.

It consists, therefore of innumerable little glands, contiguous to each other (supposed to secern the animal spirits), which are of themselves oval; but by their mutual pressure become angular, and run waving with each other.

The inner part, called thç medulla, is white, and terminates in another medullary substance, very white and hard, called the corflus callosum. The medulla is thought to consist of fine tubes, which when collected into little bundles, and covered with membranes, are termed nerves.

20. To trace this a little farther. From every point of he outer brain arise minute fibres, which in their progress uniting together, are easily perceptible. These constitute the substance of the inner brain, and of the spinal marrow. In their farther progress they are distinguished by coats, detached from the two membranes of the brain, into several bundles called NERVES, resembling so many horse-tails, each wrapt up in a double tunic.

Several of these part from time rest, in the brain itself, of which there are ten pair; one on each side. From the spinal marrow there arise thirty pair more. All these, while within the skull or the spine, are pulpous; but afterwards harden, acquire a coat, and spread through the smallest points of the solid parts of the body. Their coats are every where furnished with blood­vessels, lymphatics, and vesicles of a very tight texture, which serve to collect, strengthen, and contract their fibres. And if we consider, 1. The great bulk of the brain, cerebellum, and spinal marrow, whereof the whole substance goes to constitute nerves, being continued into, and ending in them: 2. The great number of nerves distributed hence, throughout the whole body: 3. That the brain and spinal marrow are the basis of an embryo, whence the other parts are afterwards formed; and lastly, that there is scarce any part of the body which does not feel or move; it may seem not altogether improbable, that all the solid parts of the body, are woven out of nervous fibres, and wholly consist of them.

21. The brain is divided into four ventricles. Near the rise of the fourth there is a round hole, over which is suspended the pineal gland, so called from its resembling the shape of a pine apple. It is furnished with veins and arteries, and enclosed in a thin membrane, derived from the Jzia mater. Des Cartes imagined this to be the seat of the soul; but without any solid reason. Nor has any one yet been able to discover, what is the use of it. Is it such a reservoir of blood for extraordinary occasions, as some imagine the spleen to be?

The brain is abundantly bigger in proportion in man than in other animals. In other animals, it is commonly biggest, cæteria /zari bus, in those that have most sagacity.

There are in the brain multitudes of Vessels, SO extremely small, that if a globule of blood (a million of which exceed not a grain of sand in bigness) were divided into 500 parts, those parts would be too large to pass through them. And these vessels are as large in the brain of a sparrow as in that of an ox. Nor is there any difference between the brain of a large animal and a small, but that one contains far more of these vessels than the other. But the globules of the fluid passing through them arc in all animals of the same size.

The outer part of a turkey’s brain is a very clear and transpa­rent, oily matter. Innumerable fine blood-vessels are spread through every part of this. And if a small part is cut, there flows out a small globule of pellucid fluid.

The brain is not absolutely necessary to animal life. Infants have been born, and lived some time without any. We have an authentic account from Paris, of a child that survived the birth four days, not only without a brain, but even a head: instead of which it had a mass of flesh, somewhat like liver. In 1673, a child was born alive without any brain, cerebellum, or medulla oblongata; the skull being solid: nor had it any communication with the spinal marrow. Mr. du Verney took out the brain and cerebellum of a pigeon: yet it lived and walked about. Mons. Chirac took out the brain of a dog; yet he lived. On taking out the cerebellum, he seemed dead; but revived when he blew into the lungs, and continued alive an hour. Nay, there are many instances of insects living a long time, after their head is cut off. Hence it appears, that the spinal marrow alone may, for a season, suffice both for life, sensation and motion.

Are there distinct provisions for the vital or spontaneous, and for the animal or voluntary actions? And does the cerebellum furnish the heart, and other vital organs, with nerves, while the brain supplies the nerves, which go out to the organs of sense and voluntary motion? This is an elegant system, but is every where confuted by anatomy. From the cerebellum, time fifth pair of nerves is manifestly produced; but this goes to the tongue, to the muscles of the outward ear, of the eye, and of the nose, which are parts, all of them either moved by the will, or else destined to sensation. Again, from one and the same nerve there are vital branches sent to the heart and lungs, and others that arc animal and voluntary to the larynx, or sensitive in the stomach. Lastly, the repeated accounts of injuries to the cere­bellum, being so speedily fatal, are not altogether true; for that both wounds and scirrhosities of this part have been sustained without any fatality ,to the patient, may be affirmed by certain experience.

22. The EYES next offer themselves to our observation, guarded by the eye-lids, eye-lashes, and eye-brows. The eye­lids consist of the cuticle, the skin, a thin expansion of the fianniculus carnosus, and an inward coat. A palisade of short, but stiff hairs grows out of their cartilaginous edge, both to break the too fierce impression of the rays of light, and to pre­vent any thing from getting into the eye, when open. These hairs only grow to a convenient length, and their points stand out of the way; those of the upper eye-lids being bent upward, and those of the lower, downward. Mean time the eye-brows hinder sweat, or any thing else which might be hurtful, from f ailing down from the forehead.

Both time eye-lids are moveable; but chiefly the upper. Animals which have hard eyes, as lobsters, need none, and therefore have no eye-lids. But most brutes have an additional eye-lid, called the nictitating membrane, which draws like a curtain, to wipe off what might incommode the eye. The monkey indeed has it not, as being furnished with hands like a man.

23. The eye can move upward, downward, to either side, and round, either toward the right or left. For these six motions, six muscles are allotted, which spread their tendons far’ into the eye. At each inner corner of the eye, there is a gland with two or three ducts, which opening on the inner surface of the eye.. lid, keep the eye-ball moist, to facilitate its motion. By these glands, tears also are secerned. The eye is connected with the surrounding bones by the tunica adnata, commonly called the white of the eye: in the midst of which is a large hole for the tunica cornea, through which the iris and pupil appear. The whole ball of the eye rises from the optic nerve, and is formed of three coats, propagated from it, and as many humours: two of which, have each a coat of its own also. The eye therefore has five coats in all: three common, and two to contain their several humours.

24. The outermost coat, proceeding from the dura mater, and surrounding the whole eye, is termed the sclerotica: the fore-part of it being transparent like horn, is thence stiled the cornea. This is more convex than the rest of the eye. It is composed of several parallel plates, which are nourished by many blood-vessels; but so fine as not to hinder the smallest rays of light. It has an exquisite sense, that on the least touch of any thing, the tears may be expressed, to wash off any filth, which by adhering to it might render it dim or cloudy. The rest of the scierotica is opaque, and of the same colour with the dura mater.

The second coat is called the uvea. It is much thinner than ‘the former, though thicker than the pia mater, from which it proceeds. In time forepart of it is a round hole, which with the chrystalline humour interposed, constitutes the pupil, surrounded by the iris, so named from its supposed resemblance to time colours of the rainbow. The third and inmost coat is termed the retina. It is extremely thin and soft, and darker-coloured than time lower part of the optic nerve, of which it is a con­tinuation.

“If it be questioned,” says Dr. Hailer, “whether the object is painted upon time retina, or upon time choroides; we answer, this late supposition is inconsistent with known observation, by which the retina is evidently a most sensible expansion of the nerve, while the choroides has only a few nerves, with small vessels, which are certainly blind. It is also opposed by the great variety of the choroides in different animals, while the constant uniformity of the retina is equally remarkable; to which add the black membrane, that is interposed between time retina and choroides, in some kinds of fish. Finally, anatomy demon­strates, that the choroides is seated in the blind part of the eye, but is itself of a white colour.”

25. The AQUEOIJS HUMOUR, resembling the colour and consistence of Water, lies in the forepart of the eye, just behind the cornea; its interior surface is convex; the other, a little concave. Whence this humour is derived we cannot tell’; but its source must be plentiful: for if the coat containing it be so wounded that all the humour runs out, it needs only to keep the eye close for a season, and the wound will heal, and the humour recruit.

Indeed an eminent Italian affirms, that he has slit the pupil of divers animals, and squeezed out all the humours, and has after­wards restored them perfectly to sight; nay, that the eyes of many, instead of being damaged thereby, seemed more lively and vigorous than before.

The second humour, termed, improperly enough, the chrys­talline, consists of many thousand filaments, tending from the circumference to the’ centre, and closely woven together. It is a little convex before, and more behind. It serves to refract the rays of light, so that they may meet and form an image, on the bottom of the eye. It is set in the forepart of the vitreous humour’, like a diamond in its collet, and is retained there by a membrane that surrounds it, thence called its apsula. It is toward the outside like a jelly; but toward the centre as hard as salt. Time figure of tire outer part is varied by a ligament annext, which can make it either more or less convex, or move it to or from the retina. And this is absolutely necessary in order to distinct vision: for as the rays of distant objects diverge less than those of nearer objects, the chrystalline must either be made less convex, or be set farther from the retina.

When dried, it appears to consist of a vast number of thin, round scales, one upon another, 2000 of which have been counted in one chrystalline. Each of these consists of a single fibre, wound this way and that, in a stupendous manner, so as to run several courses, and meet in as many centres, and yet not inter­fere or cross in any place.

The third, which is termed the VITREOUS HUMOUR, is not unlike melted glass. It is covered with an exceeding thin coat. The forepart is concave, as receiving the chrystalline; the other side is convex.

The whole apparatus of the eye tends to this, that there be produced in the bottom of it, a distinct collection of all the rays, which proceeding from any point of an object, penetrate the chrystalline humour, that so an image of that object may be painted there. In order to this, the rays striking on the cornea, are reflected toward the perpendicular, and thus directed through the pupil to the chrystalline. Mean time the iris, contracting or dilating the pupil, admits fewer or more rays, as the object is more or less vivid.

Now the flatter the cornea is, the fewer rays does it collect and transmit to the chrystalline, and those more diverging. The rounder it is, the more rays does it collect and transmit, and those more converging. It is too flat In old men; it is too round in them that are short sight-sighted. Time rays transmitted through the pupil to the chrystalline humour, are there refracted anew, collected and rendered converging, and those that come from the same point, are thrown in one point on the bottom of the eye. But if the chrystalline be too dense, the focus, or point wherein they unite, will be too near; if that be not dense enough, it will be too remote. And this is another cause of short-sighted.. ness, or the contrary defect.

In all vision both the eyes are used at once. And both together (as any one will find upon trial) behold an object in another situ­ation than either of them apart would do. Hence, a gentleman who had one of his eyes struck out, for some months after was apt to mistake the situation of things; and when he attempted to pour liquors into phials, often poured them quite beside the neck of the phials.

Two eyes greatly contribute, if not to distinct, at least to extensive vision. When an object is placed at a moderate distance, by the means of both eyes to see a larger share of it than we possibly could with one; the right eye seeing a greater portion of its right side, and the left eye of its correspondent side. Thus both eyes in some measure see round the object; and it is this that gives it in nature, that bold relieve, or swelling, with which it appears; and which no painting, how exquisite soever, can attain to. The ‘painter must be contented with shading on a flat surface; but the eyes, in observing nature, do not behold’ the shading only, but a part of the figure also, that lies behind those very shadings, which gives it that swelling, which painters can never fully imitate.

There is another defect, which either of the eyes, taken singly, would have, but which is corrected, by having the organ double. In either eye there is a point, which has no vision, so that if one of them only is employed in seeing, there is a part of time object to which it is always totally blind. This is that part of the optic nerve where its vein and artery run: that point of the object that is painted there, must continue unseen. To be convinced of this, we have only to try a very easy experiment. If we take three black patches, and stick them upon a white wall, about a foot distant from each other, each about as high as the eye that is to observe them; then retiring six or seven feet back, and shutting one eye, by trying sometime, we shall find, that while we distinctly behold the black spots that are to the right and left, that which is in the middle remains totally unseen. When we bring that part of the eye, where the optic artery runs, to fall upon the object, it will become invisible. This defect, in either eye, is corrected by both, since the part of the object that is unseen by one, will be dis­tinctly perceived by the other.

The form of the eye is the most commodious which can be imagined. It is fitest both to contain the humours within, and to receive the images of objects from. without. Was it square, or of any multangular form, some of its parts would lie too far off, and some too nigh those lenticular humours, which by their refractions cause vision. But by means of this form, the humours are fitly placed to perform their office of refraction, and the little darkened cell neatly adapted to receive the image of the object.

Again: as it is necessary for the eye to move various ways, in order to adjust itself to various objects; soby this figure it is well prepared for such motions, and can %Ixh ease direct itself as occasion requires.

No less commodious is the situation of the eye: in the most eminent part of the body, and near the most sensible part, the brain. By its eminence in the body, it can take in the more objects: and by ‘its situation in the head, beside its nearness to the brain, it is most conveniently placed for defence and security. In the hand it might have been more ready for service: but to how many dangers would it. have been exposed? The same may be said, as to its site in any other part but where it is. But the head is a part that seems contrived and made, chiefly for the use of the principle senses.

Some odd circumstances relative to the eyes, are related by a physician in the “Philosophical Transactions.”

“A person had no visible disease in his eyes, yet could not see, unless he squeezed his nose with his fingers, or saddled it with narrow spectacles, and then he saw very well.

“A maid, 23 years old, could see very well, but no colour besides white or black. She could sometimes, in the greatest darkness, see to read almost a quarter of an hour.

“A saddler’s daughter had an imposthume, which broke in the corner of her eyes; and out of it there came about thirty stones, as big as small pearls.

“A young man in Suffolk, about twenty years of age, has. all the day a clear and strong sight. But when twilight comes, he is quite blind; nor can he see any thing at all, either by fire-light or candle-light. No glasses give him any help. He has been thus, ever since he can remember. This cloudiness comes gradually upon him, like a mist, as day-light declines. It is just the same, both in summer and winter, and at all times of the moon.

“When I was about sixty my sight was so decayed, that I could not distinguish men from women. I received no help from any glasses, till I took spectacles with the largest circles. Close to the upper. semicircle on both sides, I cut the bone, and taking out the glasses, put black Spanish leather, taper-wise, into the emptied circles. These took in my whole eye at the wider end, and through the nai’rower end I can read the smallest print. Into this end I can only put my little finger, not quite to the first joint. But they may be made wider or narrower, and longer or shorter, as best fits every eye.

“At first I could not bear them above two hours at a time: now I can use them above twelve hours in twenty-four. And they prove a great help to those who are purblind, who have weak eyes, or decayed with age. But for’ the purblind they must be made shorter: longer for eyes. decayed with age.

“Instead of leather, they may be made of paper, coloured black and pasted on; and with inner folds to be drawn out, from one inch to three.”

In some men the iris has a faculty of darting out light. Dr. Willis mentions one, who, after drinking wine plentifully, could see to read in the darkest night. And Pliny records of Tiberias Cesar, that if he waked in the night, he could see every thing for awhile, as in the broad day-light. Dr. Briggs gives a parallel instance of a gentleman in Bedfordshire.

We find various substitutes for the use of the eyes, in many blind persons. In. some the defect has been supplied, by an excellent gift of remembering what they had seen; in some by ft delicate sense of smelling; in others, by a fine sense of hearing. So Richard Clutterbuck, of Redborough, in Gloucestershire, who was stone-blind, had so curious an ear, that he could hear the fine sand of an hour-glass fall. In some it has been supplied by an exquisite sense of feeling: so that the same Richard Clutter-buck was able to perform all sorts of curious works. lie could not only take a watch in pieces, and set it together again, but could also make all sorts of stringed instruments ol music. He likewise played on them by notes cut in their usual form, and set upon protuberant lines on the wood. Yet even this hardly came up to the skill of Van Eyck, the organist of Utrecht, who, though he had been blind from two years old, played on all sorts of instruments,

Others have been able to take a face by the touch, and mould it in wax with the utmost exactness: as was the blind sculptor, who thus took the likeness of the duke de Bracciano, and made a marble statue of king Charles the first, extremely well.

26. But more than all this, some persons have been able ‘even to distinguish colours by the touch. Peter of Maestricht, though perfectly blind, distinguished by his touch the different colours of cloth. John Vermaasen, of Utrecht, did the same; judging by the different degrees of roughness which he felt.

Yet blind persons, even though they distinguish them by the touch, have no idea of visible objects. Thus the gentleman couched by Dr. Chesselden; he had no idea of distance, but imagined all the objects he saw, touched his eyes, in the same manner as those he felt did his skin.

An extract from Dr. Chesselden’s account of this person, will not be unacceptable to the curious.

“ This young gentleman could, in a strong light, distinguish black, white, and scarlet. Yet tire faint ideas he had of them before he was couched, did not suffice to make him know them after. He now thought scarlet the most beautiful of all colours. Of others, the most gay, were the most pleasing. But the first time he saw black, he was very uneasy; yet after awhile he was reconciled to it. When he first saw, no objects were so agreeable to him as those that were smooth and regular: although he knew not the shape of any thing, nor could distinguish one from another, either by its shape or size. Being told what those things were, whose forms he knew by feeling, he would carefully observe, that he might know them again. Thus having often forgot which was the cat and which the dog, he was ashamed to ask; but catching the cat, which he knew by feeling, he looked at her stedfastly, and said, “ So, puss, I shall know you another time.” He was surprised that the things or persons he liked best, did not appear most agreeable to his sight, expecting that what was most pleasing to his other senses, would be so to his sight also.

We thought he soon knew the nature of pictures; but found afterward we were mistaken: for’ it was two months after the operation, before he discovered that they represented solid bodies. Even then he was no less surprised, expecting they would feel like the things they represented. He was amazed, that those parts, which by their light and shade appeared round and uneven, should feel like the rest, and asked, which was the lying sense, feeling or seeing? Being shewn his father’s picture, drawn in miniature, and told what it was, he acknowledged the. likeness; but asked, how it could be, that so large a face should be contained in so little room? Saying, it would have seemed as impossible to him, as to put a bushel of any thing into a pint. But even blindness, he observed, had this advan­tage, that lie could go any where hi the dark, better than those that could see. And after’ he was couched he did not lose it, but could go all about the house without a light. Every new object gave him new delight, such as he wanted words to ex­press. He was particularly delighted when he first saw a large prospect, and called it a new kind of seeing. Being afterwards couched in his other eye, he said that objects appeared larger to this eye; though not so large as they did to the other, when it was newly couched. But looking on them with both eyes, they seemed twice as large as if he looked with that only."

27. I would beg leave to propose a few queries here, to which I have not found a satisfactory answer.

1. Why do we see things false with one eye? Particularly with regard to their situation.

2. How do the two eyes compound the rays of light, so as to see right?

3. Why do we not see all things double?

4. Since all things are painted upside down on the bottom of the eye, why do we not see them so?

28. We now proceed to the EAR, formed with exquisite wisdom, for the reception of sounds. The OUTWARD EAR consist­ing of an oval cartilage, externally convex, concave within, leads by various windings to tire meatus auditorius, which is first catilaginous, and then bony. It is filled with a viscid mat­ter, called the EAR-WAX, which is supplied from the vessels placed in the skin, surrounding the meatus, to hinder any hurtful animal from creeping into tire car. The meatus is closed within by a thin, dry, transparent membrane, affixt to a bony circle, which is called the membrana tympani. Behind it is that cavity of the os petrosum, which is termed the DRUM.

The outward ear has two parts, that which stands out from the head, called the AURICLE, and the narrow passage which enters the skull, called meatus auditorius.

The auricle is furrowed with divers winding canals, which receive and collect the various undulations of the air. They who have lost this, hear very confusedly, unless they use a trumpet, or form a cavity round the ear with their hands.

It is a wise provision, that tire substance of the auricle is car­tilaginous. Had it been bone, it would have been troublesome, and might by many accidents have been broken off. If flesh, it would neither have remained expanded, nor so well have received or conveyed the sounds. Rather it would have blunted them, and retarded their progress into tire organ. But being hard, and curiously smooth and winding, sounds find an easy passage, with a regular refraction, as in a well-built arch.

It is observable, that in infants in the womb, and newly-born, the meatus auditorius is close shut up, Partly by the construction of the passage, and partly by a glutinous substance, whereby the drum is guarded against the water in the secun­dine, and against tire injuries of the air, as soon as the infant is born.

It is remarkable, that in the ear of most, if not all animals, where the meatus auditorius is long enough to afford harbour to EAR-WIGS, or other insects, ear-wax is constantly to be found. But in birds, whose cars are covered with feathers, and where the drum lies but a little within the skull, no car-wax is found, because none is necessary to the ears so well guarded, and so little tunnelled.

29. In this, besides a little branch of nerves, there are four little bones, two passages, and two windows. Three of those bones, from some imagined resemblance, are stiled the hammer, the anvil, and the staple: the fourth is termed, the orbicular bone. These are fastened by strong ligaments to each other, and to the neighbouring parts. The passages go from the side of the drum: one of which, termed the labyrinth, by a very winding way, carries a part of the auditory nerve to the exter­nal muscles of the head. The other passes from the bottom of the drum to the palate; whereby not only air, if needful, may be received, but the defect of hearing, in some measure supplied by speaking to the mouth,

The LABYRINTH contains, besides the entrance, three bony, semicircular cavities, and a bony canal, in the form of a screw, divided into two parts, from the top to the bottom. The laby­rinth is lined throughout with a thin membrane, furnished with veins, arteries and nerves. And this membrane may not impro­bably be the organ of hearing.

The curious structure of the labyrinth and screw, tend to make the weakest sounds audible. Those canals, by their wind­ing, contain large portions of the auditory nerve, upon every point of which, at once the sound being imprest, becomes audi­ble; and by their narrowness the sounds are hindered from dilating, which. must have weakened them proportionably.

The strength of the impression is likewise increased, by the elasticity of the sides of the bony canal; which receiving the first impulses of the air, reverberate them on the auditory nerve.

The AUDITORY NERVES are distributed, one to the ear, the other to the eye, tongue, and parts adjoining. By the distribu­tion thereof to different parts, an admirable consent is esta­blished between them. Hence it is, that most animals hearing a strange sound, erect their ears to catch it, open their eyes, and are ready with their mouth, to shriek or call for help. A farther use of this nervous communication between the ear and the mouth, is, that the voice may correspond with the hear­ing, and be a kind of echo thereof: and that what is heard with one of these nerves, may readily be expressed by the help of the other.

And now, what less than an infinitely wise God, could contrive so fine an organ, and such a medium, so susceptible of every impression, that the sense of hearing hath occasion for, to empower all animals to express their meaning to each other, with endless variety? Yea, what less could form such an economy as that of music is? So that the medium conveys the melodious vibration of every animal voice or well-tuned instru­ment, and the ear receives them, to allay the perturbations, and calm and cheer the heart of man!

Though the ear be the ordinary organ of hearing, yet it is not the only one. We may hear by the teeth: for if one end of a knife be applied to a spinnet, and the other held between the teeth, the music will be distinctly heard, though the ears he ever so closely stopped. Yet this is not properly by the teeth, but by the auditory nerve which passes from the drum to the palate.

In those who are born deaf, the eyes may in some measure serve in the place of ears. Some can understand what is said, by nicely observing the lips and tongue of the speaker: and may even accustom themselves to use their own, till they learn a kind of speech. Thus a physician at Amsterdam taught several children, born deal;, to understand what was said, and to give pertinent answers.

Mr. Goddy’s daughter, of Geneva, lost her hearing at two years old. Yet by observing the lips of others, she had acquired many words, whereby she would talk whole clays with those that could understand her. But she knew nothing of what was said, unless she saw the mouth of the speaker: so that if they wanted to speak to her in the night, they were obliged to light a candle. Only she knew what her sister said even in the dark, by laying her hand on her mouth.

But.’ many deaf persons can hear, if a loud noise be made while you speak. Dr. Willis mentions one, who, if a drum was heat in the room, could hear very clearly. So that her husband hired a drummer for his servant, and by that means conversed with her daily.

30. The NOSTRILS are made not of flesh or bone, but of carti­lage, the better to be kept open, and as occasion requires, to’ be dilated or contracted: for which purpose they are furnished with proper and curious muscles. The tubes therein growing narrower and narrower, lead into several little cells and winding cavities, covered with a soft coat, and provided with arteries, veins, glands, and filaments of the olfactory nerves. This there­fore is without all doubt the proper organ of smelling.

And forasmuch as it is by breathing, that the odorant par­ticles are drawn in, the laming with which the upper part of the nose is barricaded, serve two excellent purposes; partly to prevent any thing hurtful from entering the breathing passages in our sleep, for which end likewise the hairs placed at the entrance of the nostrils serve, and partly to receive the divari­cations of the olfactory nerves, which are here thick spread, and by this means meet the smells entering with the breath.

Each of the CARTILAGINOUS LAMINÆ is divided into many others, folded into a spiral line. The os cribro8um is made up of the extremities of these; the holes therein being the intervals between them. They are designed to uphold the inner tunic of the nose, which is folded round about together with these lamina that by its great expansion it may receive a greater number of the odorant particles. For the same reason, it is furnished with many small glands, which open into it, and moisten it with a slimy exsudation, fitted to entangle and detain the subtile effluvia that touch it. And not only the number, but also the length of these laminæ, is of great use for the strength of smelling. Fr this purpose most beasts, which either hunt, or distinguish their food by smell, have not their nose in the middle of their face, like a man, but prolonged to the very end.

31. The TONGUE has for its basis that forked bone, called the os gutturis. It consists of various muscles interwoven together, that it may be fit for various kinds of motion. To these are added very many small branches of nerves, which pass through time middle of it to the outside, and being gathered into little bundles constitute those papilla, which makes its surface rough and uneven. Besides these, there appear also on the sur­face of the tongue, certain pointed fibres, not unlike the ends of birds’ claws, inclining toward the basis of it, with which are interspersed innumerable salival glands. And all these are in their several ways subservient to the sense of tasting.

It has been generally supposed, that the tongue is essentially necessary to the formation of speech. But as sure as we have been of this, it is an entire mistake. A child in Essex, sonic years ago, had her tongue entirely cut out, by reason of an incurable canker. She was then three years old. Twenty years after, it was reported, that she was able to speak. To be satis­fied hereof, Mr. Benjamin Boddington, Turkey-merchant, of Ipswich, with two other gentlemen, went to. Wickham Market, where the young woman then lived, whose case they thus describe.

“ We have this day been at Wickham Market, to satisfy ourselves concerning Margaret Cutting. We examined her mouth with the greatest exactness, but found no part of the tongue remaining; nor was there any uvula. The passage down the throat is a circular open hole, large enough to admit a small nutmeg.

“Notwithstanding this, she swallowed both solids and fluids, as well as we could do. and in the Same manner. Yea, and she talked as fluently as other persons do. She pronounced letters and syllables very articulately, even those which seem neces­šarily to require the help of the tongue, as d, 1, t, w. She read to us in a book distinctly; she sings very prettily; nay, and she distinguishes tastes, and can tell the least difference either in taste or smell.”

But is it possible to teach any one to speak, who has been deaf and dumb from his birth?

It is. Dr. Wallis taught such an one to speak: Mr. Daniel Whaley, of Northampton. He was present before the royal society, May 21, 1662, and did there pronounce, distinctly enough, such words as the company proposed to him: indeed not altogether with the usual tone, yet sõ as easily to be under­stood. In a year, which was the time he stayed with Dr. Wallis, he read over great part of the English bible, and learned to ex­press himself intelligibly in common affairs, to understand letters written to him, and to answer them. And in the presence of many foreigners, he has not only read English and Latin to them, but has pronounced the most -difficult words in their languages, which they could propose to him.

The doctor has since done’ the same for Mr. Alexander Pop­ham, a gentleman of a fair estate.

But we have an instance of dumbness cured in a .shorter time. Henry Axford, son of Henry Axford, in the Devizes, at twenty-eight years of age, perceived a hoarseness, and in about six days became quite speechles; not only unable to speak articulately, but to utter the least sound with his tongue. His cold went off, but he remained absolutely speechless; and the advice of all the neighbouring physicians did not help him.

He continued totally dumb for four years, till in July, 1 741, being at Stoke, in returning homeward at night, he fell from his horse, and was taken up and put to bed in a house on the road. He soon fell asleep, and dreamed he was fallen into a vessel of boiling wort. Struggling with all his might to call for help, he actually did call aloud, and recovered the use of his tongue from that moment, as perfectly as ever he had it in his life.

Perhaps, therefore, there is truth in that ancient story, con­cerning the son of king Croesus: namely, having been dumb from his birth, he never had spoke at all, till in the battle, seeing a man ready to kill his father, his tongue was loosed, and he cried out aloud “soldier, spare the king !“

The time of cutting the teeth is usually from the seventh to the seventeenth month. It is commonly preceded by an itching of the gums, and by convulsions, fevers, and looseness: most of which symptoms happen to birds also, upon moulting or casting their feathers. The seed of the teeth is a mucous matter, like the white of an egg, contained in the cells of the jaw-bone, which grows harder and bigger till it breaks through the gum.

The part of the tooth which stands out of the gum, is covered with a peculiar substance called ENAMEL. It is composed of an infinity of little tubes, which grow on the bone by their root. If any part of this be broken off, so that the bone be left bare, it grows carious; there being no bone which will bear the air.

We may farther observe, 1. That the teeth only, of all the bones, grow in length during a man’s whole life: which is pro­videntially designed, to repair the waste that is continually made by attrition; 2. That the teeth are the only bones which are not covered with that exquisitely sensible membrane, the perios teum; 3. That they are harder and firmer than any other bone, that they may be more durable and fit to chew the most solid aliments; 4. That for their nourishment, there is a cavity con­trived in each side of the jaw-bone, in which are lodged an artery, a vein, and a nerve, which through smaller cavities send their twigs to every tooth; 5. That as infants are designed to live on milk for some months, they are so long without any teeth:

whereas animals that need them, have them sooner, and some are even born with them. 6. The different shape of the teeth is remarkable: the fore-teeth are formed broad, and with a thin and sharp edge, like chissels, to cut off a morsel from any solid food. The next, one on each side, are stronger, deeper-rooted, and more pointed, to tear tougher aliments; the rest are made fiat and broad at top, and withal somewhat uneven, that thereby they may retain, grind and mix the aliment. 7. Because biting and chewing require much strength, partly in the teeth themselves, partly in the instruments that move the lower jaw, which alone is moveable; nature has given it strong muscles, which make it bear forcibly against the upper jaw: and has not only fixt each tooth in a distinct cavity, as in a close, strong and deep socket; but has given holdfasts to the several sorts of teeth, suitable to the stress that is to be laid upon them. So whereas the cutters and eye-teeth have only one root, the grinders, designed for harder work, have three: in the upper jaw often four, because they are pendulous, and the substance of the jaw somewhat softer. 8. The situation of the teeth is most convenient. The grinders are behind, near the centre of motion, because chewing requires a consider­able force: the cutters before, ready for their easier work.

32. The PALATE is of a bony substance, .a little concave, anti clothed with a thick membrane, which has the same kind of nervous papilla and small glands, that are seen in the surface of the tongue; and hence it is qualified to assist the taste as well as the speech.

It would be endless to specify the curious mechanism of all the parts that concur to form the voice; however let us note two things: 1. There are thirteen muscles provided for moving the live cartilages of the wind-pipe. 2. It is amazing that the glottis (the upper part of the wind.pipe), can so exquisitely contract or dilate itself, to form all notes. “ Suppose,” says Dr. Keil, “the greatest distance of the two sides of the glottis to be one-tenth of an inch, in sounding twelve notes, to which the voice easily reaches, this line must be divided into twelve parts, each of which gives the aperture requisite for such a note. But if we consider the subdivision of notes into which the voice can run, the motion of the sides of the glottis is still vastly nicer: for if of two chords, sounding exactly unisons, one be shortened but the two-thousandth part of its length, a just ear will perceive the disagreement, and a good voice will sound the difference; and yet this is only the one-hundredth and ninety-sixth part of a note. But suppose the voice can divide only into a hundred parts, it follows, that the different apertures of the glottis, actually divide the tenth part of an inch, into twelve hundred parts, the effect of each of which produces a sensible alteration upon a good ear.”

33. The UVULA is a round, oblong, fleshy substance, suspended near the passage from the mouth into the nostrils, and probably designed to hinder the cold air from rushing too fast into the lungs, as well as to prevent the food we swallow from regurgi­tating into the nostrils.

The TONSILS, or almonds of the ear, are two small glands, placed at the root of the tongue, which supply an humour, to keep the mouth and the tongue continually moist.

The WIND-PIPE is wonderful in its conformation, because con tinual respiration is necessary; it is made with annular cartilages, to keep it constantly open, that its sides may not fall together; and lest, when we swallow, any particle of food should fall in, which might cause convulsions, or even death, it has a strong shutter, or lid, called the epiglottis, which, whenever we eat or drink, falls down of itself, and covers it close, so that no crum or drop can enter. It is for the more convenient bending of our necks, that the wind-pipe is not made of one entire continued cartilage, but of many circular ones.

What is farther remarkable in these cartilages is, that all the way where they are contiguous to the gullet, they are membran­ous, to give an easy passage to the food; but after that, they are, some completely round, some triangular. Another thing observ­able is, in the wind-pipe, the cartilages run parallel to each other; but, in the lungs, the lower-parts of the superior carti­lages, receive the upper parts of the inferior: hereby enabling them to contract themselves in expiration, and to dilate in inspi­ration.

34. The HAIRS all hollow. The root of each hair is fixt in a mucous globule, of an oval figure, which often adheres to it, when it is pulled up by the root. They are jointed like a reed or cane, and shoot out into small branches. They serve not only for a covering, but also for the excretion and expiration of an oily matter.

Every hair does properly live, and receive nourishment like the other parts. The roots do not turn white or grey in age, any sooner than the extremes; but the whole of each hair changes colour at once. Or, to speak more properly, the hairs of another colour fall off, and white ones grow in their place.

But extreme fear may turn the hair grey, or even white in a short space. So it was in that famous instance some years ago. A nobleman, in Germany, was condemned to die, and ordered for execution in the morning. During the night, in ten or twelve hours time, all his hair turned white as flax. The emperor being informed of this, said, “he has suffered enough ;“ and pardoned him.

Since that time, there has been an instance of one of our own countrymen, who being ship-wrecked, saved himself on a small rock, surrounded by the sea. A boat took him off after he had stayed there four hours. But in that space his hair was turned quite white.

Perhaps a still stranger instance of this kind is related in the duke of Sully’s memoirs. “Henry IV. told the marquis De ha Force, that the moment he was informed Henry the III. had published an edict (in July, 1585), ordering all the Hugonots either to go to mass, or to abandon the kingdom in six months, his mustaches tm-ned suddenly white on that side of Ins face which he supported with his hand.”

Its life is a peculiar kind, and approaches to the nature of vegetation. Hairs grow much as plants grow out of the earth, or as some plants grow upon others: from wimich they draw their nourishment, and yet each has its life distinct from the other. So hair derives its food from some juices in the body; but not from the nutricious juices. Accordingly the hair may live and grow, while the body is starved to death,

That hair may grow, merely as an excressence of the vegeta­ble kind, appears from that memorable case recited by Mr. Hook, of a body which, having been buried forty-three years, was found in a manner wholly converted into hair. The woman was buried in a coffin of wood, and lay the lowest of three in the same grave. Time others being removed, and this coffin appearing, it was observed that much hair came though the clefts of it; on removing the lid, the whole appeared a very surprising sight. There was time whole figure of the corpse, exhibiting time eyes, mouth, ears, and every part. But. from the crown of the head, even to the sole of the foot, it was covered over with a very thick set hair; long, and much curled, The people, amazed at this appearance, went to touch the corpse; but the shape fell away, as it was handled, leaving only a quantity of shapeless hair; but neither flesh nor bones, only a small part of the great toe of the right foot.

Each hair consists of several smaller ones, wrapt up in one common covering. They send out branches at the joints. The root lies pretty deep in the skin: and by this they imbibe their proper nourishment, from the adjacent humours. Their extremes also split into two or three branches, especially if they are very dry, or too long. So that what appears a single hair to the naked eye, to the microscope appears a brush. They are grey on the fore part of the head first, particularly about the temples: the back part affords them nourisimment longer. For the same reason they fall from the crown of time head first. Their thickness depends on the size of the pores they issue from: if these are small, the hair is fine, If the pores be straight, the hairs are straight; if oblique or sinuous, the hairs are curled.

All hairs appear round. But the microscope discovers some of them to be square, others triangular; which diversity of figures arises merely from the diversity of the pores. Their length depends on the quantity of homours proper to feed them, and their colour on the quality. And hence the colour usually differs in the different stages of life.

The hair of a’ mouse is a transparent tube, with a pith of small fibres convolved, running in some hairs spirally, in some transversely, in others from top to bottom.

The NAILS are of the nature and fabric of the cuticle, like which, they are also insensible, and renewable, after being cut or fallen off. They are placed upon the backs of the ends of the fingers and toes, which they support to make a due resistance in the apprehension of objects, having the nervous papillary bodies, that serve the organ of touch, placed under their lower surface. They arise with a square root, intermixed with the periosteum, a little before the last joints, from betwixt the outer and inner stratum of the skin, and, passing on soft, go out by a lunar cleft in the external plate of the skin, where the cuticle returns back, and enters into a close adhesion with the root of the nail, together with which it is extended as an outer covering.

35. We proceed to the middle cavity of the body. Herein the principal part is the HEART, consisting of a strong tendon, extended obliquely from the basis or broader part, to the cone, into which ,the fleshy fibres are inserted, in an elegant series, with a spiral bending, one half opposite to, and crossing the other: by which means the grand muscle is admirably fitted both to receive and to propel time blood. It has two great cavities, usually termed the vENTRICLES of the heart. They are divided from each other by an intermediate part called the sep­turn, constituted by the same fibres, which is convex on the side next the right ventricle, and concave on time other. The vena cava is inserted in time .right ventricle, and two inches from its insertion, divides into time upper and lower. The former brings the blood into it from tile upper; the latter, from the lower parts of the body. The PULMONARY ARTERY carries the blood from that ventricle into the lungs, which the PULMONARY VEIN brings from thence into the left ventricle. At the upper side of these veins, ,there is added to each ventricle, a kind of purse called the AURICLE, which is a hollow muscle of the same struc­ture as the heart, in order to stay the blood, that it pour not too violently into the ventricle. Before the orifices of the veins of the heart, there are triangular valves’, and semilunar in the orifices of the arteries, to hinder the reflux of time blood, from the ventricles into the veins, and from the arteries into the ventricles In a healthy person, the heart contracts little less than five thousand times in an hour.

36. The heart is covered with a fine membrane; and near the base of it, on the outside, there is a little fat, probably designed to facilitate its motion. It is placed near the middle of the breast; only its cone inclines a little to the left: It hangs by its base on veins and arteries, communicating with all parts of the body. The other part of it is loose in the PERICARDIUM, that it may be the more commodiously’ constringed arid dilated. The pericardium is a kind of membrane, that like a kind of purse, loosely encloses the heart. The shape of it is suited to that of the heart, and it contains a thin, saltish, reddish humour, exuding from the arteries.

The brain has an alternate contraction and dilation, answer­ing those of the heart- It is highly probable, the weight of time atmosphere is the counterpoise to the contractile force of the heart. That of the brain being not near so strong, does not need so strong a counterpoise.

In the basis of the heart, in some animals, there is a bone fre­quently found. Such an one was found in the heart of pope Urban. Probably it was only the tendons of the heart ossified.

Wounds of the heart are not always so immediately mortal as is generally supposed. A soldier was brought into one of the hospitals in Paris, with a wound in the upper part of the left breast. lie seemed very well for three days: but on the fourth was taken with a fever and difficulty of breathing, and died on the tenth. On ‘opening the body, it was found the sword had pierced the pericardium, traversed the right ventricle of the heart in its lower part, pierced the pericardium on the opposite side, and gone through the diaphragm, and an inch deep into, the liver.

37. The heart is placed in the middle of the LUNGS, which consist of two parts, the right and left lobe. Each of these is divided into two other lobes; one of these frequently into three, sometimes into four, by fisãures, sometimes deeper, sometimes shallower, running from the interior margin towards the back part. The lungs are divided into cells, which are no other than expansions of the small branches of the trachea or wind-pipe. And there is an easy passage from one branch into many cells, and again into it from them all. Time upper part of the trachea opens into the mouth; the lower, divided into two branches, shoots out into various ramifications, which are termed bronchia. And these little canals running on, constitute the lungs, whose cells are wonderfully connected together, and intermixed with numberless branches of veins and arteries.

The upper end of the trachea is called the LARYNX. At the fourth vertebre of the back, it divides and enters the lungs. Its cartilages, ranged at small and equal distances, are smaller and smaller as they approach the lungs.

These cartilages have two membranes. The external, com­posed of circular fibres, covers the whole trachea. That which lines it within, consists of three distinct membranes: the first woven of two orders of fibres, part longitudinal, to shorten it by drawing the cartilages together; part circular, to contract them. Both these together, with the external membrane, assist in breathing, coughing, and varying the tone of voice. The second membrane is glandulous; and its glands opening into time cavity of the trachea, separate a liquor which moistens and defends it from the acrimony of time air. The third is a net-work of nerves, veins, and arteries.

The organs which form the voice of man, have not been accu­rately observed by the ancients. As the trachea bears some resemblance to a flute, they considered the voice according to the sounds of that instrument. Mr. Dodart was the first who she wed the glottis to be the chief organ in producing it, and considered it both as a string and wind instrument, far more perfect than any which art can produce.

The organs which form the various voices of other animals, are likewise worthy of our attention. Those of each species have peculiar sounds, whereby they understand each other. Wherein do these organs resemble ours? and wherein do they differ?

The human voice is almost wholly formed by the glottis, and various tones are produced by time various modifications of it. But all these. depend on one only: the separation and junction of its lips. This comprehends two circumstances, time one capital and primitive; tim