Read Ebook: Hygienic Physiology : with Special Reference to the Use of Alcoholic Drinks and Narcotics by Steele Joel Dorman

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FIG. 4.

The peculiar structure and form of the skull afford a perfect shelter for the brain--an organ so delicate that, if unprotected, an ordinary blow would destroy it. Its oval or egg shape adapts it to resist pressure. The smaller and stronger end is in front, where the danger is greatest. Projections before and behind shield the less protected parts. The hard plates are not easy to penetrate. The spongy packing deadens every blow. The separate pieces with their curious joinings disperse any jar which one may receive, and also prevent fractures from spreading.

FIG. 5.

The frequent openings in this strong bone box afford safe avenues for the passage of numerous nerves and vessels which communicate between the brain and the rest of the body.

FIG. 6.

THE SPINE consists of twenty-four bones, between which are placed pads of cartilage. A canal is hollowed out of the column for the safe passage of the spinal cord. Projections at the back and on either side are abundant for the attachment of the muscles. The packing acts as a cushion to prevent any jar from reaching the brain when we jump or run, while the double curve of the spine also tends to disperse the force of a fall. Thus on every side the utmost caution is taken to guard that precious gem in its casket.

THE PERFECTION OF THE SPINE surpasses all human contrivances. Its various uses seem a bundle of contradictions. A chain of twenty-four bones is made so stiff that it will bear a heavy burden, and so flexible that it will bend like rubber; yet, all the while, it transmits no shock, and even hides a delicate nerve within that would thrill with the slightest touch. Resting upon it, the brain is borne without a tremor; and, clinging to it, the vital organs are carried without fear of harm.

FIG. 7.

FIG. 8.

THE RIBS, also twenty-four in number, are arranged in pairs on each side of the chest. At the back, they are all attached to the spine. In front, the upper seven pairs are tied by cartilages to the breastbone ; three are fastened to each other and to the cartilage above, and two, the floating ribs, are loose.

The natural form of the chest is that of a cone diminishing upward. But, owing to the tightness of the clothing commonly worn, the reverse is often the case. The long, slender ribs give lightness, the arched form confers strength, and the cartilages impart elasticity,--properties essential to the protection of the delicate organs within, and to freedom of motion in respiration.

FIG. 9.

FIG. 10.

THE SHOULDER BLADE is a thin, flat, triangular bone, fitted to the top and back of the chest, and designed to give a foundation for the muscles of the shoulder.

FIG. 11.

FIG. 12.

The first bone of each finger is so attached to the corresponding metacarpal bone as to move in several directions upon it, but the other phalanges form hinge joints.

The fingers are named in order: the thumb, the index, the middle, the ring, and the little finger. Their different lengths cause them to fit the hollow of the hand when it is closed, and probably enable us more easily to grasp objects of varying size. If the hand clasps a ball, the tips of the fingers will be in a straight line.

The hand in its perfection belongs only to man. Its elegance of outline, delicacy of mold, and beauty of color have made it the study of artists; while its exquisite mobility and adaptation as a perfect instrument have led many philosophers to attribute man's superiority even more to the hand than to the mind.

FIG. 13.

THE CAUSE OF THESE DEFORMITIES is found in the shape and size of fashionable boots and shoes. The sole ought to be large enough for full play of motion, the uppers should not crowd the toes, and the heels should be low, flat, and broad. As it is, there is a constant warfare between Nature and our shoemakers, and we are the victims. The narrow point in front pinches our toes, and compels them to override one another; the narrow sole compresses the arch; while the high heel, by throwing all the weight forward on the toes, strains the ankle, and, by sending the pressure where Nature did not design it to fall, causes that joint to become enlarged. The body bends forward to meet the demand of this new motion, and thus loses its uprightness and beauty, making our gait stiff and ungraceful.

PRACTICAL QUESTIONS.

THE MUSCLES.

HOLMES.

ANALYSIS OF THE MUSCLES.

FIG. 14.

THE MUSCLES.

THE USE OF THE MUSCLES.--The skeleton is the image of death. Its unsightly appearance instinctively repels us. We have seen, however, what uses it subserves in the body, and how the ugly-looking bones abound in nice contrivances and ingenious workmanship. In life, the framework is hidden by the flesh. This covering is a mass of muscles, which by their arrangement and their properties not only give form and symmetry to the body, but also produce its varied movements.

In Fig. 14, we see the large exterior muscles. Beneath these are many others; while deeply hidden within are tiny, delicate ones, too small to be seen with the naked eye. There are, in all, about five hundred, each having its special use, and all working in exquisite harmony and perfection.

CONTRACTILITY.--The peculiar property of the muscles is their power of contraction, whereby they decrease in length and increase in thickness. This may be caused by an effort of the will, by cold, by a sharp blow, etc. It does not cease at death, but, in certain cold-blooded animals, a contraction of the muscles is often noticed long after the head has been cut off.

ARRANGEMENT OF THE MUSCLES. --The muscles are nearly all arranged in pairs, each with its antagonist, so that, as they contract and expand alternately, the bone to which they are attached is moved to and fro.

If you grasp the arm tightly with your hand just above the elbow joint, and bend the forearm, you will feel the muscle on the inside swell, and become hard and prominent, while the outside muscle will be relaxed. Now straighten the arm, and the swelling and hardness of the inside muscle will vanish, while the outside one will, in turn, become rigid. So, also, if you clasp the arm just below the elbow, and then open and shut the fingers, you can feel the alternate expanding and relaxing of the muscles on opposite sides of the arms.

If the muscles on one side of the face become palsied, those on the other side will draw the mouth that way. Squinting is caused by one of the straight muscles of the eye contracting more strongly than its antagonist.

FIG. 15.

The binding of so many threads into one bundle confers great strength, according to a mechanical principle that we see exemplified in suspension bridges, where the weight is sustained, not by bars of iron, but by small wires twisted into massive ropes.

FIG. 16.

THE TENDONS.--The ends of the muscles are generally attached to the bone by strong, flexible, but inelastic tendons. The muscular fibers spring from the sides of the tendon, so that more of them can act upon the bone than if they went directly to it. Besides, the small, insensible tendon can better bear the exposure of passing over a joint, and be more easily lodged in some protecting groove, than the broad, sensitive muscle. This mode of attachment gives to the limbs strength, and elegance of form. Thus, for example, if the large muscles of the arm extended to the hand, they would make it bulky and clumsy. The tendons, however, reach only to the wrist, whence fine cords pass to the fingers .

Here we notice two other admirable arrangements. 1. If the long tendons at the wrist on contracting should rise, projections would be made and thus the beauty of the slender joint be marred. To prevent this, a stout band or bracelet of ligament holds them down to their place. 2. In order to allow the tendon which moves the last joint of the finger to pass through, the tendon which moves the second joint divides at its attachment to the bone . This is the most economical mode of packing the muscles, as any other practicable arrangement would increase the bulk of the slender finger.

FIG. 17.

Since the tendon can not always pull in the direction of the desired motion, some contrivance is necessary to meet the want. The tendon belonging to one of the muscles of the eye, for example, passes through a ring of cartilage, and thus a rotary motion is secured.

FIG. 18.

FIG. 19.

The nearer the power is applied to the resistance, the more easily the work is done. In the lower jaw, for example, the jaw is the weight, the fulcrum is the hinge joint at the back, and the muscles on each side are the power. They act much closer to the resistance than those in the hand, since here we desire force, and there, speed.

FIG. 20.

HOW WE STAND ERECT.--The joints play so easily, and the center of gravity in the body is so far above the foot, that the skeleton can not of itself hold our bodies upright. Thus it requires the action of many muscles to maintain this position. The head so rests upon the spine as to tend to fall in front, but the muscles of the neck steady it in its place. The hips incline forward, but are held erect by the strong muscles of the back. The trunk is nicely balanced on the head of the thigh bones. The great muscles of the thigh acting over the kneepan tend to bend the body forward, but the muscles of the calf neutralize this action. The ankle, the knee, and the hip lie in nearly the same line, and thus the weight of the body rests directly on the keystone of the arch of the foot. So perfectly do these muscles act that we never think of them until science calls our attention to the subject, and yet to acquire the necessary skill to use them in our infancy needed patient lessons, much time, and many hard knocks.

FIG. 21.

HOW WE WALK.--Walking is as complex an act as standing. It is really a perilous performance, which has become safe only because of constant practice. We see how violent it is when we run against a post in the dark, and find with what headlong force we were hurling ourselves forward. Holmes has well defined walking as a perpetual falling with a constant self-recovery. Standing on one foot, we let the body fall forward, while we swing the other leg ahead like a pendulum. Planting that foot on the ground, to save the body from falling farther, we then swing the first foot forward again to repeat the same operation.

The shorter the pendulum, the more rapidly it vibrates; and so short- legged people take quicker and shorter steps than long-legged ones. We are shorter when walking than when standing still, because of this falling forward to take a step in advance.

In running, we incline the body more, and so, as it were, fall faster. When we walk, one foot is on the ground all the time, and there is an instant when both feet are planted upon it; but in running there is an interval of time in each step when both feet are off the ground, and the body is wholly unsupported. As we step alternately with the feet, we are inclined to turn the body first to one side and then to the other. This movement is sometimes counterbalanced by swinging the hand on the opposite side.

Violent exercise, however, is injurious, since we then tear down faster than nature can build up. Feats of strength are not only hurtful, but dangerous. Often the muscles are strained or ruptured, and blood vessels burst in the effort to outdo one's companions.

No education is complete which fails to provide for the development of the muscles. Recesses should be as strictly devoted to play as study hours are to work. Were gymnastics or calisthenics as regular an exercise as grammar or arithmetic, fewer pupils would be compelled to leave school on account of ill health; while spinal curvatures, weak backs, and ungraceful gaits would no longer characterize so many of our best institutions.

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