Physiology and Hygiene for Secondary Schools by Francis M. Walters;A.M.
page 47 of 527 (08%)
page 47 of 527 (08%)
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correspond to the contractions of the heart.
No other single discovery with reference to the human body has proved of such great importance. A knowledge of the nature and purpose of the circulation was the necessary first step in understanding the plan of the body and the method of maintaining life, and physiology as a science dates from the time of Harveyâs discovery. *Organs of Circulation.*âThe organs of circulation, or blood vessels, are of four kinds, named the heart, the arteries, the capillaries, and the veins. They serve as contrivances both for holding the blood and for keeping it in motion through the body. The heart, which is the chief organ for propelling the blood, acts as a force pump, while the arteries and veins serve as tubes for conveying the blood from place to place. Moreover, the blood vessels are so connected that the blood moves through them in a regular order, performing two well-defined circuits. [Fig. 13] Fig. 13â*Heart* in position in thoracic cavity. Dotted lines show positin of diaphragm and of margins of lungs. *The Heart.*âThe human heart, roughly speaking, is about the size of the clenched fist of the individual owner. It is situated very near the center of the thoracic cavity and is almost completely surrounded by the lungs. It is cone-shaped and is so suspended that the small end hangs downward, forward, and a little to the left. When from excitement, or other cause, one becomes conscious of the movements of the heart, these appear to be in |
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