Our bodies
Davidson, Ellis A.
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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1869 Excerpt: ... the other, sharp and short. Then a pause, and then the sounds again. The first sound is caused by the contraction of the walls of the ventricles, and the second by the closing of the semi-lunar valves, which I have already mentioned. The movement of the pulse in the wrist follows immediately after the first sound, and at the same time the heart is forced against the walls of the chest, and this is what is called the "beating" of the heart. The circulation of the blood was discovered by Dr. Harvey between 1619 and 1628. How our Blood is Purified in the Lungs. In the last lesson you have seen that the blood is carried by the pulmonary artery to the lungs, and we will now consider the means by which it is there purified. You must first, then, understand that when air has entered our mouth it passes down the Trachea, or windpipe, which, you will remember is the lower part of the larynx. This canal passes down into the chest, and then divides into two large branches, called Bronchial Tubes (see Fig. 21), one of which passes into each lung, and there they divide again and again into numerous smaller branches, which spread about in eveiy direction. These tubes are very wonderful in their struc ture, and afford only another specimen of the wisdom and mercy of our Divine Creator. In order to guard against their being pressed flat by the continual action of the chest, rings or plates, formed of cartilage, are placed in them, E 2 which serve to keep them open. A similar arrangement, on an infinitely smaller scale, exists in the tubes which carry air over the body of the tiniest insect. rig. 21. The Larynx, Trachea, and Lung. (One lung is removed to show the bronchial tubes.) When the bronchial tubes have spread about like the branches and twigs of trees, th...
RareBooksClub.com
2012-05-14
24 pages