"There closely braced,

And neatly fitted, it compresses hard
The prominent and most unsightly bones,
And binds the shoulders flat."-COWPER.

owing to the greater proportion of fluids to that of solids; the younger the age the greater the preponderance of fluids. The human embryo when first perceptible is almost wholly fluid; solid substances are gradually but slowly superadded, and even after birth the preponderance is strictly according to age: for in the infant the fluids abound more than in the child; in the child more than in the youth ; in the youth more than in the adolescent; in the adolescent more than in the adult; and in the adult more than in the aged.

40. The fluids are not only more abundant than the solids, but they are also more important, as they afford the immediate material of the organization of the body; the medium by which its composition and decomposition are effected. They bear nourishment to every part, and by them are carried out of the system its noxious and useless matter.

41. Why is the spinal column flexible?

This flexibility renders the movement of the body free, easy, and varied, and accommodating to the complex combination of motion which may be brought into play at any moment, with the rapidity of the changes of thought, and at the command of the impulses of feeling. If the spinal column were composed of a rigid and immoveable pile of bones, all the other parts of the body, to which they are directly or indirectly attached, would have been rendered stiff and mechanical in their movements, and would not have been able to move, save in a given direction.

42. The degree of flexibility which the spinal column possesses, and the extent to which, by the cultivation of it, it is sometimes actually brought, is exemplified in the positions and contortions of the posture-master and the tumbler. It is acquired by means of the compressible and elastic matter interposed between the several vertebræ. So compressible is this substance that the human body is half-an-inch shorter in the evening than in the morning, having lost by the exertions of the day so much of its stature; yet, so elastic is this matter that the stature lost during the lay is regained by the repose of the night.

43. Why are all the bones of the body covered with a delicate coating, termed periosteum, except the teeth?

Had so exquisitely sensitive a membrane as the periosteum

In human works, though laboured on with pain,
A thousand movements scarce our purpose gain;
In God's one single can its ends produce;

Yet serves to second too some other use."-POPE.

invested the teeth, as it invests every other bone of the body, action, necessary exposure, and irritation would have subjected the animal to continual pain. General as it is, it was not the sort of integument which suited the teeth; what they stood in need of was a strong, hard, insensible defensive coat, and exactly such a covering is given to them, in the ivory enamel which adheres to their surface.

44. Why are the front teeth of the mouth sharp and the back teeth broad and blunted?

Because the office of the former is to cut and separate the food ; while the purpose of the latter is to grind it to a pulp, by which it becomes fitted for the process of digestion.

45. What are the uses, distinct and mutual, of the bones and muscles?

The bones are to the body what the masts and spars are to a ship -they give support and the power of resistance. The muscles, again, are to the bones what the ropes are to the masts and spars ; it is to them that the bones are indebted for the preservation or the change of their position. If the bones or masts are too feeble in proportion to the weight which they are required to sustain, then a deviation from their shape or position takes place; and, on the other hand, if the muscles or ropes are not sufficiently strong and well braced, then insufficiency of support must necessarily result.

46. Early infancy affords an instance of both of the above-mentioned imperfections, the bones being infirm, and the muscles small and destitute of true fleshy fibres. The disease called "Softness of the bones," is an illustration of what may be called a weak mast of the body, which must yield if its muscles be strongly drawn. The state of muscular debility consequent on fever and many acute diseases, or even on sudden fright, is, on the other hand, an instance of the inability of the bones alone to preserve an attitude or execute motion, when the muscular system as weakened by disease.

47. Why is the cylindrical form of the long bones of the body advantages to structure of the human frame?

The superior advantages of this arrangement are illustrated