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briskly, and deposits in the bony structure an increased quantity of such materials as bone is made of.
8. But, on the other hand, if a child be put to severe, continued labor, the bones will fill up and harden too rapidly before they attain their natural growth, and the child will be dwarfed in stature. If exercise be taken with moderation, it will conduce to the growth and strength of the whole body; but if it be too violent, and be too long continued without the intervals of rest which nature requires, it will be productive of evil. Here, as elsewhere, the true rule is, "Excess in nothing; moderation in all things."
1 DE-FORM'-I-TY, crookedness; distortion.
2 E-LAS-TIC-I-TY, a springy or elastic condition of the body.
3 CURV'-A-TŪRE, bending.
14 COM-PRESS', to press together; to make smaller.
5 CON-SUMP'-TION, a disease of the lungs at-
ORGANS THAT MOVE THE BODY.-THE MUSCLES.
1. WHILE the bones give support and general form to the body, the instruments by which it is moved are the muscles. They are what in animals is known as flesh, or lean meat, as distinguished from fat, bone, sinew,' or cartilage. The muscles are made of bundles of very fine threads, called muscular fibres, placed side by side, and bound up in a thin skin-like covering or sheath. All these threads are elastic, so that when they are stretched out they incline to shrink back again, like India-rubber. At the ends of the muscles these threads are changed into strong tendons or cords, which are firmly fastened to the bones.
2. The muscles are spread all over the body. In the limbs they are placed around the bones, one end of a muscle be⚫ing usually attached by its tendon to one bone, and the other
end to another. In the trunk or body they are spread out to inclose cavities;2 and there they constitute a defensive wall, readily yielding to pressure, but resuming their original position when the pressure is removed.
3. There are more than five hundred muscles in the human
body, of various shapes, bound around, twining among, and lapping over each other, and running in almost every possible direction, according to their various uses. Every movement that is made by any part of the body requires the action of at least two muscles, one to draw the part one way, and the opposing muscle to yield to the movement, or to draw the part back again. The muscles are directed how to act by the nerves, which run from the brain to all parts of the body.
4. We can not swallow our food, draw the breath, move the eyes or head, bend the body, or move the limbs, without the employment of numerous muscles. It is by their action that the farmer cultivates his fields, the mechanic wields his tools, the sportsman pursues his game, the orator gives ut
Fig. 4, showing the bones, and only two of the muscles of the arm, is a representation of the manner in which all the joints of the body are moved. Here h is the upper bone of the arm, and ra and u the bones of the fore-arm. When the muscle b contracts, the muscle c relaxes, and the fore-arm is raised, turning on the joint d. When e contracts, and b relaxes, the fore-arm is extended.
In Fig. 5 are shown the muscles of the arm. The muscles marked 5 and 6 are used in moving the wrist. The one marked 8 extends all the fingers; while another, on the other side of the arm, closes them. The one marked 9 moves the little finger; 13 turns the hand sidewise, and also moves the arm; 10 and 14 turn the hand; 15 is the strong band that holds the muscles firmly in place around the wrist.
Fig. 6 shows a number of the small muscular fibres, a, a, b, torn from larger bundles. These are magnified two hundred times their real size. These fibres are really formed of little cells connected with each other.
At Fig. 7 is a greatly magnified representation of three of the
muscular fibres cut across (transversely), and showing the shape of the cells. Pressure has caused these cells to lose their rounded shape.
terance to his thoughts, the lady touches the keys of the piano, and the young are whirled in the mazy dance. It will readily be seen, therefore, how much the pleasures and the employments of life depend upon their healthy action.
5. Some of the muscles, such as those which move the fingers, limbs, and trunk, act under the government of the will; but others, such as those which are used in breathing, and those used in moving the blood through the system, act wholly without the necessity of mental control. The former are called voluntary, and the latter involuntary muscles. Can any reason be given why the involuntary muscles should not be under the control of the will?
6. Like all other parts of the body, the muscles are nourished by the blood, one set of blood-vessels, the arteries, carrying the nourishing particles where they are needed, and another set, the veins, removing the decayed portions that are no longer of any use. Thus the blood is constantly depositing new matter, and removing that which is old and worthless.
7. The materials of which a muscle is composed are constantly passing away, like water under the influence of the noonday sun, and if no exercise be given to the muscle it soon becomes thin and flabby,3 it grows weak, and ere long loses its power of action. In this case the waste of matter is greater than the supply. But if proper exercise be given to the muscle, the movement of the blood in the artery which nourishes it is quickened, an abundant supply of nourishment is provided, and the muscle attains its perfect shape and full power of action. If only a few of the muscles of the body are exercised, they alone become firm, compact, and strong, while the others dwindle away.
8. The effect of vigorous exercise of one set of muscles is seen in the arms of the blacksmith, which not only increase in size, but become firm and hard; while, perhaps, other muscles of the body, called less frequently into use, are feebly developed. The hands and arms of the student are usually small and soft, and of a sickly hue, merely because, not being accustomed to vigorous exercise, they do not receive a suitable supply of nourishment.
9. The same law prevails throughout the entire body. If little or no exercise be taken, the whole body will be literally starved; for while the blood flows in a sluggish stream it very poorly performs its office of building up the system and keeping it in repair.
10. Yet, notwithstanding the importance of exercise, several cautions are necessary respecting it. The young, especially, should be guarded against taking too severe exer cise, and against continuing it too long; for there is a point beyond which the muscles will be enfeebled, rather than strengthened, by exertion. Their healthy condition requires that exercise should be moderate at the commencement, and never continued so as to produce a feeling of exhaustion.
"Begin with gentle toils; and as your limbs
When, all at once, from indolence to toil
12. An erect attitude while sitting, standing, or walking, is found to be most conducive to health, and to be attended with far less exhaustion of the muscles than a stooping position; for in the former case the muscles, being well balanced, mutually support each other. The spinal column should be kept erect, so far as possible, whatever occupations we may be engaged in, and the shoulders should be kept thrown back, that the chest may become broad and full. If a stooping posture be acquired in youth, we may be very certain that the deformity will continue to increase throughout life.
13. But whether the body be at rest, or in action, no one position of the muscles should be continued until weariness results from it. How often is it noticed that small children, after sitting a short time, become restless. Nature is warn
ing them of the danger of violating her laws. A sitting or a standing posture occasions a continued strain upon certain sets of muscles; and rest, or change of position, is required for their relief. To one who has long been sitting, walking or running will often give the needed rest. We may learn from this the importance of giving to young and feeble children at school frequent out-door recreation."
14. Moreover, the muscles should be exercised in pure air, and in the light, neither immediately before nor immediately after severe mental toil; and they should be rested gradually, by continuing some gentle exercise, when they have been vigorously used, and are greatly fatigued. They should never be so compressed by bandages or clothing as to restrain their free motions, unless the desire be to starve them into premature decay. The pressure of tight dresses, in females, enfeebles the muscles, and is a common cause of projecting shoulders, curvature of the spinal column, and consumption. What then shall we say of those fashions and modes of dress that violate all physiological laws? May they not justly be regarded as enemies of the human race?
"Knowest thou the nature of the human frame,
The proofs of boundless wisdom there displayed'?
How every tendon acts upon its bone,
And how the nerves receive their nicer tone'?
1 SIN'-EW (sin'-nu), a tendon.
2 CAV'-I-TIES, hollows.
3 FLAB'-BY, Soft; hanging loose.
4 VIG'-OR-OUS, active; powerful.
7 REC-RE-A-TION, amusement; diversion.
8 PRE-MA-TURE, before the proper time.
9 PHYS-I-O-LOG'-I-CAL, pertaining to the laws of physiology or health.
10 VI-BRA'-TION, supposed motion of the nervous fluid.
11 BAL'-SAM, here used for the blood.
5 DE-VĚL'-OPED, filled out in size.
6 EX-HAUST -ION, weariness; deprived of strength.