"With milky blood the heart is overflown,

Is soothed and sweetened by the social sense."-THOMSON.

and lungs could be touched through the opening without imparting any feeling that they were touched. Harvey says: "When I paid my respects to this young nobleman, he made no concealment, but exposed the left side of his breast, when I saw a cavity into which I could introduce my fingers and thumb. Astonished with the novelty, I again and again explored the wound, and first marvelling at the extraordinary nature of the cure, I set about the examination of the heart. Taking it in one hand and placing the finger of the other on the pulse of the wrist, I satisfied myself that it was indeed the heart which I grasped. I then brought him to the King (Charles I.), that he might behold and touch so extraordinary a thing, and that he might perceive, as I did, that unless when we touched the outer skin, or when he saw our fingers in the cavity, this young nobleman knew not that we touched the heart."

110. Why do the interior organs of the body keep in the places assigned them, when the body itself is moved about in every direction.

Because the various parts are tied or fastened to the body in such a manner as to prevent them slipping from their places.

111. The heart is placed between two soft lobes of the lungs, and is tied to the mediastinum and to the pericardium, which pericardium is not only itself a very strong membrane, but adheres firmly to the duplicature of the mediastinum, and, by its point, to the middle tendon of the diaphragm. The heart is also sustained in its place by the great blood-vessels which issue from it. The lungs are tied to the sternum by the mediastinum before, to the vertebræ by the pleura behind. It seems indeed to be the very use of the mediastinum (which is a membrane that goes straight through the middle of the thorax, from the breast to the back) to keep the contents of the thorax in their places; in particular to hinder one lobe of the lungs from incommoding another, or the parts of the lungs from pressing upon each other when we lie on the side. The liver is fastened in the body by two ligaments; the first, which is large and strong, comes from the covering of the diaphragm, and penetrates the substance of the liver; the second is the umbilical vein, which, after birth, degenerates into a ligament. The first, which is the principal, fixes the liver in its situation whilst the body holds an erect posture; the second prevents it from pressing on the diaphragm when we lie down; and both together sling or suspend the liver when we lie upon our backs, so that it may not compress or obstruct the vein to which belongs the important office of returning the blood from the body to the heart.

"What a piece of work is a man!

How noble in reason! how infinite in faculties.

In form and moving, how express and admirable!

In action, how like an angel! in apprehension, how like a God."

CHAPTER IV.

THE SENSES SEEING, HEARING, SMELLING, TASTING, AND FEELING. 112. Why are the senses of seeing, hearing, tasting, and smelling placed in the head?

Because the head is the most elevated part of the body, and is capable of moving independently of the rest of the fabric. Thus the organs of sense, which put us in connection with the external world, which render us susceptible of pleasure, and which give us notice of the approach of objects capable of exciting pain, are placed where external bodies may be brought most conveniently and completely in contact with them, and where alone they can be efficient as the sentinels of the system.

113. How do we know that the powers of seeing depend more upon the mechanical exercise of the eye itself than upon mental capacity?

Because many persons in certain departments of life, are capable of discerning objects more readily in connection with their pursuits than better informed or more intellectual persons who have seldom or never seen those objects; thus a sailor will descry the various phenomena of the elements, which are invisible to the learned and refined passenger; and the ploughman will point out certain objects in a landscape to the wondering student who has just escaped from his labours. On the other hand, persons who are much accustomed to reading are enabled to take in, as it were, the contents of a whole page of a book, while another person less accustomed to reading has only been able to master two or three lines.

114. Why is it erroneous to suppose that on entering a room we see all the objects in it at once?

Because this apparently simultaneous view arises from the motions

"And in the silence of his calm abode,

In nature's works he worshipped nature's God."

MATILDA HOUSTON.

of the eye, which admit of great objects being successively presented to it with a rapidity of which we are unconscious.

115. It is easy to show that if the eye were without motion, steadily fixed in the socket, the vision would be quickly lost; that objects of the greatest brilliancy would be obscurely seen, or disappear. For example, let us fix the eye on one point-a thing somewhat difficult to do, owing to the very disposition in the eye to be constantly moving; but suppose that by repeated attempts we have at length acquired the power of directing the eye steadily on an object, when we have done so, we shall find that the whole scene becomes more and more obscure, and finally vanishes. Let us fix the eye on the corner of the frame of the principal picture in the room; at first everything around the room will be distinct; in a very little time the impression will become weaker, objects will appear dim, and then the eye will have an almost uncontrollable desire to wander; if this be resisted, the impressions of the figures in the picture will first fade; for a time we shall see the gilded frame alone; but this also will become faint. When we have thus ascertained the fact, if we change the direction of the eye but ever so little, the whole scene will at once again be perfect to us.

116. Why is incessant motion of the eye essential to the continued exercise of the organ?

Because when the eye is fixed upon a point, the lights, shades, and colours of objects continuing to strike upon the same part of the retina, the nerve is exhausted; but when the eye shifts there is a new exercise of the nerve; the part of the retina that was opposed to the lights is now opposed to the shades, and what was opposed to different colours is now opposed to other colours, and the variation in the exciting cause produces a renewed sensation.

117. Why do we know that the ideas we obtain of the size, shape, and distance of objects depend mainly upon the education of the sight?

Because optical illusions, however nearly they resemble realities when they first meet the eye, are satisfactorily proved to have no existence, by the attentive and correct use of that very organ which gave rise to the error.

118. Dr. Cheselden, by a surgical operation, procured sight to a very intelligent person who was born blind, and he observed the manner in which this sense was developed in the young man. "When he saw the light for the first time, he knew so little how to judge of distances, that he believed the objects which he saw

"He that is giddy thinks the world turns round."-SHAKSPERE.

touched his eyes, as the things which he felt touched his skin." During the time of his blindness he had received such an imperfect idea of colours which, by a very strong light, he was then able to distinguish, that a sufficient impression had not been left by which he could again recognise them. Indeed, when he saw them, he said the colours he then saw were not the same as those he had seen formerly; he did not know the form of any object; nor could he distinguish one object from another, however different their size and configuration might be; when objects were shown to him which he had known formerly by the touch, he looked at them with attention, and observed them carefully in order to recognise them again; but as he had too many objects to retain at once, he forgot the greater part of them, and when he first learnt, as he said, to see and to know objects, he forgot a thousand for one that he recollected.

It was two months before he discovered that pictures represented solid bodies; until that time he had considered them as planes and surfaces differently coloured and diversified by a variety of shades; but when he began to conceive that these pictures represented solid bodies, in touching the canvas of the picture with his hand he expected to find something solid upon it, and he was much astonished when, upon touching those parts which seemed round and unequal, he found them flat and smooth like the rest.

He could not support much light at first, and every object seemed very large to him; but after he had seen larger things, he considered the first smaller; he thought there was nothing beyond the limits of his sight. The same operation was performed on the other eye about a year after the first, and it succeeded equally well. At first he saw objects with his second eye much larger than with the other, but not so large, however, as he had seen them with his first eye; and when he looked at the same object with both eyes at once, he said that it appeared twice as large as with the first eye.

119. Why is sight essential to the firmness of most of our attitudes?

Because we judge of the position of our bodies by other bodies which we see around us. Thus, when we are deprived of this means of judging of our equilibrium, as when we are on a house, or any elevated place where we are only surrounded by the air, our standing becomes uncertain, and it sometimes happens that we feel giddy, and cannot stand at all.

120. The utility of sight is still greater if the base of support is very narrow; a rope dancer could not stand erect if he were not constantly directed by the eye as to the position necessary to be preserved, in order that the perpendicular drawn from his centre of gravity may fall upon the base of support. This connection between sight and attitude is further demonstrated by the uncertain postures which blind persons assume.

"Time wasted is existence, used is life,

And bare existence, man, to live ordained,

Wrings and oppresses with enormous weight."-YOUNG.

121. Why does the pupil of the eye contract and dilate? Because when it is necessary to exclude excess of light, the pupil through which the light enters may gradually or wholly exclude it by contraction; and when a large amount of light is desired, the dilation of the pupil in a similar degree ensures the admission of a greater number of rays.

122. The chamber of the eye is a camera-obscura, which, when the light is too small, can enlarge its opening; when too strong, can again contract it; and that without any other assistance than of its own exquisite machinery.

123. Why is a person unable to discern objects when passing from a strongly-illuminated room into one comparatively dark, or into the open air at night?

Because the contraction of the pupil, which was adapted to the strong light to which it had been previously exposed, admits so little light to the retina that no sensation is produced. The pupil, however, after a while dilates, and, admitting more light, objects are perceived which were before invisible.

124. Why does the eye of a person suffer inconvenience and pain in passing from a dark room into a light one?

Because, while the observer remains in the dark or less illuminated room, the pupil is dilated to that degree so as to admit into the eye as great a quantity of light as the structure of the organ allows of. When he passes suddenly into the strongly-illuminated room the flood of light arriving through the widely dilated pupil acts with such violence upon the retina as to produce pain, which necessarily calls for the relief and protection of the organ. The iris, then, by an action peculiar to it, contracts the dimension of the pupil so as to admit proportionally less light, and the eye is gradually opened with impunity.

125. Why is the pupil of the eye so called?

Because if we look into the eye of another we shall perceive a little image of our own face, like a very minute child or pupilhence the name.