. A healthy body. A textbook on anatomy, physiology, hygiene, alcohol, and narcotics. For use in intermediate grades in public and private schools . act andmove the bones that we are able to run and jump and perform all the movementsof which the body is capable. Fig. 15. Yohmtary muscle,with its blood-vessels. (1) themuscle fibres ; (2) the blood-ves-sels, magnified. The Structure of Muscle. If a piece of boiled, leanmeat, which is voluntary muscle, be examined, it willbe noticed that it readily falls apart into little threadsof tissue ; and with needles these little threads maybe easily divid
. A healthy body. A textbook on anatomy, physiology, hygiene, alcohol, and narcotics. For use in intermediate grades in public and private schools . act andmove the bones that we are able to run and jump and perform all the movementsof which the body is capable. Fig. 15. Yohmtary muscle,with its blood-vessels. (1) themuscle fibres ; (2) the blood-ves-sels, magnified. The Structure of Muscle. If a piece of boiled, leanmeat, which is voluntary muscle, be examined, it willbe noticed that it readily falls apart into little threadsof tissue ; and with needles these little threads maybe easily divided into still smaller threads. If one 4 50 A HEALTHY BODY. of these small threads be placed under the microscope it will be found to consist of many small fibres. (Fig. 15.) Therefore we say that voluntary muscle is made up of many small fibres, all bound together. Our illustration shows four of these fibres, and also the blood-vessels that belong to them. Involuntary muscle is composed of very small cells which are placed close together. The illustration shows them separated from each other, so that their shape may be better seen. (Fig. 16.). The Contraction of Muscle. The muscles are of use to us because they have the power to contract. When a muscle contracts, it becomes thicker, harder, and shorter. (Fig. 17.) That it becomes harder and Fig. 16. The cells of involiintarymuscle^ magnified.
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