The idea is somewhat startling that the dust, which is blown in our faces on a windy day, once formed a part of living beings as active, intelligent, and full of life as ourselves; that the very water we drink has entered into strange and curious combinations.

From the human system, water passes into the air in enormous quantities. The tiny flower that blooms almost unseen and which we may crush by a step, the grass covering the earth with its velvet mantle, the flowering shrub and the foliage of the mighty forest tree, all throw into the atmosphere which envelops the earth a vast amount of moisture. This, collecting in the upper regions of the air, descends again in refreshing showers, or distils upon the earth in gentle dew.

Who can say whether the crystal fluid, which we quaff with such delicious pleasure, may not once have sparkled, on the leaf of a rose, or glittered on the swarthy brow of an African sweating at his daily toil beneath a scorching sun. The air, that great reservoir, which surrounds us on all sides, covers alike the negro and the prince, and mingles together the drop which falls from the brow of the dying monarch, and the tear of suffering in the hovel of the poor and lowly. In that vast republic there is no distinction, all are alike.

Man from his infancy to his grave is constantly undergoing change. There are at work within him forces, ever active, never tiring, until the heart ceases to beat and death and decay commence. Yet this change in health is attended with no pain, hut is the simple and beautiful process of nature, bringing new materials to take the place of worn out particles, keeping alive within us that process of combustion, which warms us in winter and cools us in summer, the derangement of which causes disease and death.

We are to look in this and the following chapter, at the physical organization of man, and unfold step by step, the most wonderful and beautiful mechanism, which ever came from the hand of the Eternal. We are to unveil for a time the human frame, and gaze upon bone, and blood, and muscle, and nerve, and tissue, and examine the various parts which make up this beautiful structure, and inquire into their organization, form and use, the process of health, of regeneration and decay, of life and death. We are to lift the curtain of nature and gaze into her secret chambers. We shall find these chambers irradiated with a pure and holy light, and, stamped upon all, the impress of the most perfect wisdom. We shall learn here a lesson of simplicity, truth and harmony, and admire the wisdom and love of that Being who made so perfect and beautiful an earthly habitation for the deathless soul.

In examining the human system we shall look,

1st, at its bony frame-work, or skeleton.

2d, The muscles.

3d, The brain and nervous system.

4th, The organs connected with respiration and circulation.

5th, The organs connected with digestion, secretion, excretion and reproduction. 1st, The Bones or Skeleton. The bony frame-work of the human system consists of two hundred and eight pieces. [See plate 2, fig. 1.] Of these, eight compose the skull - viz. The frontal-bone or forehead, the two parietal bones, forming the sides of the cranium and meeting at a line directly on the top of the skull, the occipital forming the back part of the skull, the temporal, the lower part of the sides of the head around the ears, and the ethnoid and sphenoid. The former passes from one temporal bone to the other across the base of the cranium, and the other is situated in the middle of the anterior portion of the cranium. These bones form a cavity for the brain, which is thus in its bony covering guarded in the most perfect manner from external violence. The edges of the bones are as it were dove-tailed into each other; they are soft and capable of expansion in infancy, but in after life become solid. The bones of the cranium as well as those of the face are perforated in several places, so that the nerves may pass out from the brain and perform their functions.

The Face. The bones of the face are fourteen in number. The two nasal hones, form the arch or bridge of the nose; the vomer separates the two passages; the two malar bones, form the prominence of the cheek and are generally called check bones. The superior maxillary bone, forms the upper jaw, and the inferior maxillary bone, the lower jaw. Of the teeth we shall treat when speaking of their diseases.

The Trunk. We are now to notice that curiously contrived and beautifully arranged column, which, while it supports the head and trunk, holding in the centre that great nerve (spinal marrow) which passes off from the brain and gives out other branches to almost every part of the body, still permits us to bend in every direction with the most perfect ease.

This column [Plate 2, fig. 3,) is composed of twenty-four distinct bones with projections, which, forming a canal behind the body of the vertebra for the spinal marrow, serve also to bind the bones together and as attachments for the muscles. Between the joints of the vertebras is a highly elastic cartilaginous tissue, which serves as a cushion to break the jar which would otherwise be felt in the brain at every step. With the aid of this elastic cushion and the backward and forward curve of the spine, no direct motion is communicated to the head. The first seven bones are called cervical or neck bones, 5, then follow twelve dorsal bones, 6, then five lumbar vertebras, 7, and last the sacrum and coccyx. We have thus the spinal column supporting the head as well as giving form and support to the trunk, but another bony cavity is required to contain and guard those vital organs, the lungs and heart. We therefore find them placed in the chest or thorax [Fig. 4,] which when well developed adds so much to the beauty and noble appearance of the human race. This cavity is formed by twenty-four ribs. Twelve on each side, starting from the twelve dorsal vertebrae and coming forward in a curve, seven of the upper ones on each side unite directly by means of a cartilage with a bone in front, 2, called the sternum or breast-bone. Three lower ones united by a cartilage are called false-ribs, and the two remaining without anterior connection are called floating ribs. The natural form of the chest then resembles a pyramid or cone, the apex of which is at the top. It is not unusual in these days of fashion and artificial beauty, to find the order reversed, and the apex at the bottom. Rest assured, however, that nature's ways are the best, and that she generally contrives to punish severely those, who with fool-hardy temerity seek to fetter or restrain her movements. We have another bony cavity or basin forming the lower extremity of the trunk, essential to the support of the abdomen, as well as to those organs placed in its vicinity. This is called the pelvis [Plate 2, fig. 6.] There are posteriorly two bones forming the lower extremity of the spinal column, and sometimes called false vertebrae - viz., the sacrum and coccyx, 3. 5. From these proceed anteriorly in the form of a curve, a larger bone on either side, called the innominata, meeting in front at what is called the pubis. The upper portion of these bones, 7. 8. are known as the hip-bones, the lower portion, 9. 10. as the seat-bones.