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including a reference to those organs of the human body through which those senses operate.

Although the Senses, properly speaking, are, like the Soul, immaterial, that is, not consisting of substance or matter, but of sensations excited in the mind by external objects, and in this respect not proper subjects of anatomy; yet as all their organs are material, they constitute a proper and important branch of anatomical knowledge. The number and names of the Senses are the five following:-SEEING,-HEARING,-SMELLING,TASTING,-and FEELING. These comprehend our whole sources of sensation and knowledge. Without them the mind could have no ideas. The great end of the Senses is to make us acquainted with external objects and their qualities, and our perception of these is accompanied with a belief that they exist, and are what they appear to be.

We commence with

I. THE EYE, which is the Organ of Seeing.

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4.-Rays of light from all parts. B.-Cornea, through which they pass. C.-Crystalline lens, where they are refracted. DD.--Divergent rays. EE.-Retina, upon which the picture is formed. F.-Optic

nerve.

The Eye is a most beautiful and ingeniously constructed object. It may be compared, in its structure, to a telescope, the purpose of both being to collect the rays of light proceeding from the surface of bodies, and to bring those rays to a common centre, by means of a peculiar lens, or glass, into a focus, or given point; and thus to form a very fine image or picture of the object before them.

The Eye may be said to consist of two parts,-the internal and the external, or the Eye itself, and that which surrounds it. The eyes are situated in two bony cavities, or sockets, named orbits, in which they move, and by which they are protected. These orbits have their vacant spaces filled with a loose soft fat, which serves as a proper bed for the eyes to move or rest in. In human beings the eyes are not fixed, like those of some animals; but, by means of six different muscles, can be made to roll about, upwards, downwards, and sideways; and thus we are spared the trouble of turning our heads continually towards the objects we wish to inspect. By these contrivances, the eye, as a natural telescope and microscope, is made to advance, to recede, to move to the right and to the left, and in other directions; and to view near and distant objects with equal distinctness; so that a single eye, by the variety of positions it may assume, performs the office of a thousand. Flies and other insects, whose eyes are immoveable, have several thousands of distinct globes in each eye. In one of the eyes of the common dragon-fly there have been reckoned thirteen thousand five hundred of these lenses; and consequently, in both eyes, twenty-seven thousand, every one of which is capable of forming a distinct image of any object.

The eye itself is a small round ball, covered, for the most part, with three membranes or skins, lying one upon another, something like the rind and the white inner skin of an orange. The first or outer coat, that is, the white of the eye, is called the SCLEROTICA, from its being hard, firm, tough, and opaque, or not transparent. The second under coat is termed the CHOROID. This is a thin, delicate skin; one part of which is filled with a black matter, called pigment, or paint, designed to soften or absorb the rays of light after they have passed the third inner membrane, called the RETINA (fig. E E), which we shall presently describe. The greater cavity of the ball of the eye is filled with a fluid, named the VITREOUS HUMOUR, SO called, as it resembles melted glass. It is something like the white of an egg. This keeps the ball distended, and preserves

its round form.

As you look at your own eye in the looking-glass, or inspect the eye of another, you will perceive, in the centre, a small, dark, round spot. This is the PUPIL, or apple of the eye: Sometimes the pupil is circular, as in man, the dog, the monkey; sometimes in an upright oval form, as in the cat; or in a horizontal oval form, as in the sheep. It is the opening through which the rays of light pass to the retina, (fig. E E,) one of the inner coats of the eye, resembling fine net-work;-retina signifying a net; which is an expansion or enlargement of a nerve at the back part of the eye, called the OPTIC NERVE, (fig. F,) which extends to the brain. The retina is something like a mirror, upon which the objects we see are received or painted. Thus a landscape of many miles in extent, with all its hills, valleys, and plains, trees, flowers, rivers, houses, &c., may be painted upon a space of less than an inch diameter, or the size of a sixpence. Thus the little retina takes portraits of all comers. All creation sits to this silent diminutive artist. Around the small pupil there is, you will perceive, a coloured circle, called the IRIS, or rainbow, from its variegated colours. These colours are in some eyes black, in some brown, in some blue, in some grey. The iris is a membrane resembling a round moveable curtain, designed to regulate the volume of light admitted through the pupil of the eye. The pupil varies in size according to the degree of light to which the eye is exposed. It becomes smaller when the eye is subjected to a strong light; and enlarges when the light is more obscure. You have seen the eye of a cat, when she has been sitting before the fire, or in the sun; the pupil is then contracted almost to a straight line: the same may be said of the owl. So by holding a candle before the eye of a person, you will see the pupil contract or expand according to the distance and strength of the light. When we are in the dark, the pupil becomes very large, (almost as large as the iris,) in order to admit as many rays of light as possible to pass through to the retina. In the front and outside of the iris and

pupil of the eye is a transparent membrane called the CORNEA, (fig. B.) It is a horny substance, and hence its name, (from the Latin word Cornu, a horn.) It projects a little in front of the ball of the eye, something like a watch-glass. Through this, the rays of light (fig. A,) pass to the pupil. The cornea, by age, undergoes several changes. As individuals advance in life, the texture or substance of the cornea becomes more thick and tough than previously. It also becomes flattened, and people require the use of spectacles, to make a sort of artificial cornea.

Just behind the pupil of the eye, and further into the ball, is the CRYSTALLINE LENS, (fig. c,) that is, a firm substance of a jelly-like nature, as clear and transparent as the brightest, purest, crystal. It is in a double convex form, like two watch glasses, put together at their rims or edges. It is about the size of a small damson stone, or the kernel of a hazel nut. This lens serves to refract or break the natural course of the rays of light, (fig. DD,) as they pass through the cornea and the pupil to the retina, and form a perfect image thereon. There is a disease of the eye, called Cataract, in which the crystalline lens becomes dim and dark,-losing its transparency; and as the rays of light can no longer pass through it, the individual so affected becomes blind. An effectual remedy for this complaint is the removal of the lens from its situation, either by pushing it downwards below the pupil; or, by cutting the side of the eye, and squeezing it, and then pushing the lens out of the eye altogether. Even after this is gone, a person may have his sight, though imperfectly, as the light would still pass through the pupil to the retina. This operation can be performed only by the skilful surgeon; and in some instances it occasions but little pain to the subject of it. An experiment of this kind may be easily made by any one. Take a recently dead sheep's eye, and with a lancet or pen knife cut horizontally the cornea: the aqueous humour will at once spurt out. Then squeeze the ball of the eye, and the crystalline lens will come forth,—a beautifully transparent object! On a further incision of the lancet, the vitreous humour will all ooze out, and the eye-ball will collapse or shrivel up, and the retina and black pigment appear. In the space between the cornea and the crystalline lens, there is a transparent fluid, called the AQUEOUS or watery HUMOUR; and between the crystalline lens and the retina is the vitreous humour, which we just now said nearly fills the middle of the eye-ball, and preserves its round shape. The exercise of seeing, then, may be thus further described:-"The rays of light (fig. A), entering from all directions, in passing through the eye, strike first upon the cornea (fig. B), then pass through the aqueous humour, and enter the crystalline lens (fig. c): having arrived there, the rays diverge (fig. D D), or separate, as from a centre, towards the internal circumference, and traversing the vitreous humour, impinge, or strike upon, all parts of the retina (fig. E E); and it is here,— upon the retina,-that the phenomenon understood by the word sight, is effected." If we take a bullock's eye, and cut

off the three coats from the back part, and put a piece of thin white paper over that part, and hold the eye towards the window, or any bright object, we shall see the image of the object depicted upon the paper, in an inverted position: for "there is a curious circumstance connected with this operation of vision; which is, that the image or picture, in front of the eye, is formed on the retina in an inverted position; or, as we should say, upside down. Thus, if I am looking at a horse or a tree, there is a kind of image, or shadow of that horse, or tree, on the retina of my eye, with its lowest part upwards. Why everything seen by the eye does not appear inverted, rather than in its true position, is not known, though many very ingenious theories have been invented to account for it."*

The ball of the eye is filled with various beautiful bloodvessels. In a diseased state, and when inflamed, these vessels are distinctly seen, in what is called a blood-shot eye. Within the orbit, above each inner corner of the eye, there is a gland called the LACHRYMAL GLAND, (from lachryma, a tear,) which secretes the watery fluid called tears, and keeps the eye moist, and clean, and clear. It assists the motion of the eyeball and eye-lids, and preserves the eye from the contact of the atmosphere. At the corner of each eye-lid, near the nose, is a small tube or pipe, about the size of a crow quill, which conveys the water of the eye to the nose. When once the fluid has entered there, it spreads itself upon the inside of the nostrils, and is evaporated by the current of warm air, which, in the course of respiration, is continually passing over it. By strong emotions of the mind, however, this liquid overflows the lower eyelids in tears. How grief or joy excites the lachrymal gland, so as to produce these tears, we know not. Here I quote, from the "Family Friend," a few sentences on "the Philosophy of a Tear."

"Beautiful Tear! whether lingering upon the brink of the eyelid, or darting down the furrows of the care-worn cheek— thou art beautiful in thy simplicity-great, because of thy modesty strong, from thy very weakness. Offspring of sorrow! who will not own thy claim to sympathy? who can resist thy eloquence? who can deny mercy when thou pleadest? Beautiful Tear! It is only when the crystal drop comes forth under the impulse of sorrow-thus speaking the anguish of the mind-that it can properly be called a tear.

*"House I Live in,” p. 121.

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