LESSON II. THE BONES, AND THE INJURIES TO WHICH THEY 1. THE bones are composed of both animal and earthy materials. The animal part gives them life, and the earthy part gives them strength; and both kinds of material are supplied by the blood. If, then, there be but little blood in the system, or if it move slowly and feebly, it will not supply a sufficient quantity of this building material. 2. In infancy the bones, being then composed mostly of animal matter, are soft and yielding; but as the child advances in years they become gradually firmer, stronger, and harder, and in very old age they sometimes become so brittle as to be easily broken. So readily do the bones in early life yield to pressure, that they are often permanently bent out of shape by careless or ignorant management; and deformity,' poor health, and sometimes early death, are the unfortunate results. 3. The spinal column, in its natural position, curves backward and forward, but not from side to side. This arrangement of the bones, when connected with the cushion-like cartilages between them, gives to the body great ease and elasticity of movement, and prevents many injuries to which it would otherwise be exposed. 4. The natural position of the body is always the correct one; and when by accident or design the body is allowed to grow differently, one of God's laws is violated, and we are sure to be punished for it. In the growth of our bodies we may aid nature, but we can not with safety act in opposition to it. We may cultivate the habit of sitting and walking in an erect position, and thereby aid nature in providing for the proper growth of the spinal column. 5. But children often sit at their desks in the school-room, or stand during recitation, in a stooping position, or one that allows the body to curve sidewise. The bones gradually harden or grow in this position, until at length a confirmed stoop or a curvature3 of the spine is produced, and the body loses that erect posture which is essential not only to manly beauty, but to health also. By this carelessness an important law of nature is violated, and deformity and suffering are the penalty paid for it. (See Figs. 2 and 3). 6. Many of the Chinese, thinking that a very small foot is a great beauty, bandage the feet of their female children so as to prevent the growth of the bones. The feet then, after a great amount of suffering, become mere awkward stumps, scarcely able to support the body, and almost wholly incapable of being used in walking. Some of the North American Indians flatten the foreheads of their children by pressure, because they think a very flat forehead is a mark of beauty; and some mothers, even among civilized and Christian people, have the equally bad taste and cruelty to compress1 and distort the bodies of their daughters, by cords and bandages, to make their waists smaller than their Maker designed them. The results of this cruel and wicked practice, when long persevered in, are weak, miserable, deformed bodies, and, frequently, wasting consumption and early death. 7. The bones are found to increase in size and strength, the same as other parts of the body, by a proper amount of exercise; while they become weak by inaction, and finally dwindle away. Thus the bones of the laboring man are hard and strong, while the bones of those who neglect exercise are loose in texture, weak, and deficient in size. The cause of these results is, that exercise makes the blood flow more A person who sits facing an ascending desk should sit in an erect position, as in Fig. 3, and not allow the body to curve sidewise, as in Fig. 2. For the purposes of writing, however, a level table, and right side to the table, with an erect position, and paper square with the table, are perhaps preferable; although many writing masters still adhere to the old rule, "left side to the desk," which necessitates a leaning posture, and imposes a continual strain upon the muscles which support the back. 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. 3 CURV ́-A-TŪRE, bending. 14 €ŎM-PRESS', to press together; to make smaller. 5 CON-SUMP'-TION, a disease of the lungs attended with wasting of the flesh. 16 ЄON-DUCE', promote; contribute; lead to. LESSON III. 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 mus cles 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 being 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 c 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 of 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 worthless. removing that which is old and 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. |