CHAPTER VII. EXERCISE.-ORGANS OF LOCOMOTION IN DIFFERENT ANIMALS. MIND. MUSCLES AND MUSCULAR ACTION.-OCCUPATIONS.-GYMNASTICS. IN the preceding chapters I have considered the action of the different vital stimulants-light, heat, air, water, and food-in maintaining the life and health of man. In this, the concluding chapter, I shall consider man in his active and passive life, and indicate a few principles relating to exercise and repose. Loco All animals are furnished with organs by which they are enabled to move either the whole or parts of their bodies, and thus, bring the means of subsistence within their reach, or roam about in search of it. motion is effected in different ways in different animals; in some, the whole body is engaged in effecting the movement, in others, special organs are provided for the purpose. The meduse, or jelly-fishes, swim about by contracting the concave side of their body upon the water, the resistance of which impels them onward. The cuttle-fish and some others are furnished with a cavity, which, when they are in the quiescent state, is filled with water; this, when desirous of moving, they force out in a jet. The earth-worm, and other animals of the same order, effect progression by successive contractions of different portions of the body. The leech has two suckers, one at its head, the other at its tail: in moving, it elongates the body, fixes itself at some point in advance by the sucker attached to the head, draws the rest of the body towards this point, holds on by the tail-sucker while it again elongates its body, and by a series of such evolutions gets along pretty glibly. The movement of the snail is effected in a somewhat similar manner. Most animals have, however, special organs of locomotion. The bodies of animalcules are furnished with countless hair-like appendages, called cilia, which can be seen only with the aid of a powerful microscope: by the rapid vibrations of these, they are propelled quickly through the water. The star-fish is furnished with numerous locomotive organs, consisting of tubes with suckers at the extremity: when the animal is at rest these tubes are retracted within the body; when in progression, they become injected with fluid. from the digestive cavity, and project externally. Most insects are possessed of wings as well as legs, so that they can either fly or crawl: the muscular power, the variety and precision of movement, exhibited by these little creatures, are indeed most remarkable. The crustaceans, as the lobster and crab, have feet by which they either swim or crawl; the tail, however, is the organ chiefly used by the lobster in swimming. The locomotive organs in the three classes of vertebrate animals-the fishes, birds, and mammals, -are four in number, and are called limbs. BB These consist of certain bony portions to which muscles are attached and upon which they act; and scarcely anything in nature presents greater evidence of unity of design, and skill in application, than the manner in which these component parts are shaped and modified so as to meet an almost endless variety of purposes. Out of the same anatomical elements the Creator has formed the fins by which the fish ensures and regulates his course through the waters, the wings by which the bird sails through the air or soars upward to the sky, the members differently formed in each order of mammals, constituting fore-legs in some and arms in others, enabling one animal to bound or run, another to seize and tear, a third to climb, a fourth to burrow into the earth, and, so admirably fashioned in man, as to give him the highest dexterity of action, and enable him, under the direction of his mind, to exert a controlling influence over the external world. Motion is produced by the alternate contraction and relaxation of muscles. These constitute the fulness, the firm fleshy portion of limbs, and consist of delicate fibres arranged parallel to each other in bundles. Each little bundle entering into the formation of a muscle is made up of countless delicate fibres, which, when examined under a high magnifying power, have a beaded appearance, and are marked by transverse lines. The interstices between the bundles, and the spaces between muscles are filled up with cellular tissue and fat: the former is so loose as not to interfere with the play of the muscle, and the latter forms a soft, protective medium, and gives The roundness and symmetry to the limbs. muscles are enclosed in sheaths, which prevent their undue action, and obviate any unsightly bulging during their contraction. They also, in most cases, terminate in firm, silvery cords or bands called tendons: by thus making the force to act at some distance, the symmetry and lightness of the limb is not sacrificed. Thus the muscles which produce the principal movements of the hand and foot are situated in the fore-arm and the calf of the leg, and by this arrangement the beauty and varied action of these members is secured. The contractility of muscles depends upon the action of a stimulus, which ordinarily consists of the nervous influence transmitted from the brain through the nerves, with branches of which each muscle is supplied. Upon these nerves depend the isolated and also the concerted action of muscles. The nutrition of muscles is further provided for by a free supply of bloodvessels. There are more than four hundred muscles in the human body, and they may be regarded as so many servants ready to do the mind's bidding, and as forming the medium of its intercourse with the world without. "Their chief purpose is," as Dr. A. Combe remarks, "to enable us to carry into effect the various resolutions and designs,—or volitions, as they are termed by philosophers, which have been formed by the mind. The muscles, accordingly, form the grand instruments by which man acts, and is acted upon by the external world. Whatever impression is made upon him by any other living creature is effected by the aid of muscular power. When the infant clings to its mother's bosom, it is by calling its little muscles into play. When its cries assail her ear, and alarm her feelings, it is by muscular action they are produced. When she flies to its relief, or lulls it to sleep by some simple chant, her muscles are still the medium by which her sympathy and affection are expressed. Life itself is sustained by the constant exercise of muscular power; and were either the heart or the muscles of respiration to forget their part, even for a few minutes, existence would be at an end. Without the concurrence of the muscular power, man's grandest conceptions and most energetic resolutions would remain equally unknown and unfulfilled. Without muscular power, wherewith to communicate with their fellow-men, Shakspeare and Milton would have remained mute as the statues which now represent their bodily form, and the immortal creations of their minds would have been lost to the world for ever. Mind is, no doubt, the high and directing power; but without obedient muscles, ready at a call to minister to its wants, mind would remain isolated in the midst of creation, and could neither speak, nor hear, nor touch. Amid the loss of children and friends, and even amid the wreck of worlds, mind, without muscles to express its feelings, would look on in apparent apathy, even when its affections were torn, and its sufferings were most intense."* Since muscular action results from the impulse of the will conveyed through the nerves, it follows that it must bear a pretty direct relation to The Principles of Physiology applied to the Preservation of Health, by A. Combe, M.D. |