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common name of breast, and that of thorax in science, from the Latin thorax, (breast) contains the seat of action on which human life directly depends. Here are the lungs, which by the avenue of the wind-pipe receive about 48000 cubic inches of air every hour in successive respirations. In the lungs the air comes immediately in contact with the blood; and it is computed that the whole mass of blood, which may be 50 pounds, or five gallons, receives, fourteen times within the hour, the lifegiving impulse of the air. It is supposed that the whole mass of blood passes through the heart once in every four minutes. From this fact some conception may be formed of the strength of the mechanical action of the heart, which must be sufficient to impel this mass through all the arteries and veins of the system, within that space of time.
There also, is that indescribable power contained in the stomach (an oblong globular sack of eight or ten inches in length, and five or six in depth, which is capable of contraction and expansion) whereby the process is continually going on, to convert the foreign substances passed into it, into living, active, sensitive and perceptive being. In this small cavity, of the breast everything has its appropriate place, and its precise duty, and upon the harmonious action of each and every one, and ceasingly, that which we call life, depends; and that, which is the most admirable of all is, that the vital action of the whole system goes on independently of man's will; and entirely beyond its control. All who have read Paley will remember his striking remark, that the action of the vital organs is not confided to man's care. His ignorance, or improvidence, if it, were so, might soon, and easily, close his career.
64. We have no room to follow out the consequences of this mechanical action. But as there will be occasion to refer to human form and moverment in other places, for other purposes, we must notice the craving want of the stomach that daily returns upon it; that it can and does receive with pleasure, and impu
nity, a given quantity of food in a given time; that the system is known to lose more than half of all it takes in as food, through its three hundred thousand millions of pores of the skin in every twenty-four hours: that continued excess in quantity is the parent of pain, suffering, disease and death: that certain substances, are certain and immediate death; and that certain others, though received through habit, and from craving desire, will occasion a slow, thoughas certain death, involving the gradual destruction of the intellectual power, the moral sense, and of all that distinguishes men from brutes. This criminal indulgence places man far below the brutes, since they are incapable of such depravity.
Proofs drawn from the Senses.
65. It is to the senses of man that we come, with pleasure, in contemplating the power and goodness of the Creator. The eye is commonly selected as the most striking evidence of design, and is emphatically so, as a part of the human system. We cannot undertake to describe this delicate organ for any other purpose than the general one of rendering just homage to the Creator, and of warning all of the interest which they have in knowing its delicacy and of preserving it in a sound condition; and because its action is open in some degree to common observation. It is first to be noticed that the bones which project around the eye, seem to be intended to preserve it from exterior injury. The eyelids are given to close at every intimation of danger, and to guard the eye while we sleep. Between the eyelids, in the open eye, in the exterior front, the first thing we see is the cornea. This word
is taken from the Latin cornu, (horn,) because this part of the eye resembles horn. This is a transparent substance through which light passes into the eye. The cornea is continued all around the globe of the eye; it is only in the front part that it is so called; the continuation around the eye is known by the name of sclerotica, from a Greek word which signifies hardness. As all the coats of the eye but this are soft, and might lose their form, this hardness seems necessary to preserve it.
66. Immediately behind the cornea is a distinct. separate part called the aqueous humor, from the Latin aqua (water), which means, merely, a watery liquid. Immediately behind this humor is the pupil, (commonly called apple of the eye) which is a round dark spot which every one can see with the help of a mirror. The word pupil has no descriptive meaning. It is through this dark spot that the light which comes in at the cornea passes still further into the eye.
67. That colored circle which surrounds the pupil (or apple) and which is either black, hazle, grey, or blue, and from which the eye has its color, is called the iris, which word is the Latin for rainbow. The iris is supposed to have the power of compressing the pupil of the eye by means of minute muscles, or permitting its expansion by relaxing these inuscles so as to adapt the pupil to receive more or less light, as may be necessary; this action of the iris seems to go on mechanically, and without any operation of the will, as any one may know who goes from a lighted room into a dark one. In such case one sees better in a few moments, which is occasioned by the spontaneous action of the iris in providing for the expansion of the pupil. The iris extends also, all around the globe of the eye, inside the sclerotica, but it loses its name after it leaves the front of the eye, and is called choroides, which name is from two Greek words which mean a membrane enclosing something..
68. Immediately behind the pupil lies the crystalline lens; a common burning glass or magnifying
glass, is a lens, from the Latin word lens. Chrystalline (nearly the same word in Latin, Greek, and English) means transparent or clear. This lens in the human eye is a remarkable substance; it is much easier to say what sort of substance it is not, than to say what it is. Its place is in the front centre of the vitreous humor, which is so named from the word vitrum, (glass,) because it resembles melted glass. This humor or liquid fills all the residue of the ball, until it comes in contact with the nerve, called the optic nerve, from a Greek word meaning vision.
69. This nerve is also called the retina, from reta, (a net.) The retina is the seat of vision; that is, it is the part of the eye on which the figure of the objects seen is pictured. The retina is the expansion of the nerve which comes from the brain in a round form about the size of a wheat straw, and as soon as it enters the eye through the opening made for it in the back part of the eye, it expands into this minutely delicate net-work and encloses the vitreous humor, precisely as a globular bottle with a solid neck to it, expands from the neck. To see an object there must be the cornea, the aqueous humor, the pupil, the crhystalline lens, the vitreous humor, and the retina, and all of them must be in a condition to perform their several offices. All of them are of such indescribable delicacy that it is astonishing that they can be preserved for a single day: how much more so is it that they are so generally preserved through all the vicissitudes of life, even to old age. This description of the eye is very general, and very simple. No attempt is made to describe the more minute parts, their nerves, blood-vessels, connexion of parts, general sympathy of the parts; even so far as is known by anatomists. By the most skilful of them, many parts of the eye are very imperfectly understood.
70. Thus far human knowledge goes, and no farther. By what law is it that the eye is so formed that it can see? What is seeing? How is it that the impression
of a figure on the retina conveys a clear and distinct perception to the mind, and makes the object so perceived a subject of memory, and of thought. Who but that Being who framed and preserves the eye, can answer this?
71. The rapid, easy and unfelt motion of the eye, is also a matter of grateful wonder. In the strong and sound, the eye is kept in front, and in its proper place by soft substances, which yield the liquid matter necesary to its action; and the motion depends on muscles which turn the eye in every direction. When these muscles are disproportioned in length, that defect is occasioned which is called cross-eyed. When disease overtakes us, and the waste of the body cannot be supplied, this is felt in the eye, as elsewhere, and the globe of the eye sinks within the socket.
72. The philosophical theory of vision as now received in the world is this: Every object seen, reflects or emits rays of light. These rays, passing through the several departments of the eye, make the figure of the object seen to fall on the retina in an inverted form. In all representations of vision, the rays of light are drawn from the object to the retina. Color too is said to depend on the manner in which rays of light act on the objects which appear colored to our eye. There is no doubt that light is necessary to see the figure and the color of objects. But some one may hereafter be bold enough to doubt, whether this theory of vision is satisfactory. May not the eye have a power of vision to which light is necessary to be sure, but of which light is not the cause? When one is watching the coming on of the morning, or the gradual return of night, there is no gradual change in the coloring of objects. It is not satisfactory to common sense, that objects and persons well known to us, are not the same even in color in the night, and in the day time. We are certain of this, that when there is light from the sun, or light from artificial means, the eye can and does take impressions on the retina of external objects, and that they go thence into the mind. What is 5*