. The eclectic guide to health; or, Physiology and hygiene ... gs, placed one above another, withthe open part behind. These ringskeep the trachea open. The bronchialtubes are similar to the trachea instructure, but they are smaller andhave thinner walls. The air-cellshave extremely thin membranous walls,which separate the air within them fromthe blood in the capillaries of the are many millions of cells, sothat their entire surface for the absorp-tion of the air is very great. Fig. 41shows how the bronchial tubes end in clusters of lining of the air-passages is very
. The eclectic guide to health; or, Physiology and hygiene ... gs, placed one above another, withthe open part behind. These ringskeep the trachea open. The bronchialtubes are similar to the trachea instructure, but they are smaller andhave thinner walls. The air-cellshave extremely thin membranous walls,which separate the air within them fromthe blood in the capillaries of the are many millions of cells, sothat their entire surface for the absorp-tion of the air is very great. Fig. 41shows how the bronchial tubes end in clusters of lining of the air-passages is very sensitive, especially inthe larynx and trachea, so that any foreign body that maybe drawn into them causes pain and violent coughing untilit is expelled. The lining of the bronchial tubes is coveredwith a peculiar hair-like kind of cells, called cilia, whichaid in removing dust from the lungs. 96. The lungs are two large, soft lobes that fill thechest. The lungs are formed of the bronchial tubes andair-cells, and of the blood-vessels of the pulmonic circula-. Fig. 41. Cluster or Air-cells. — of Bronchial Tube. 2. AirCell. RESPIRATION. 95 tion. Soft, fibrous tissue fills between these various tubes,to support and bind the whole together. These two greatsets of passages, the one for the air, the other for the blood,are arranged as closely together as possible, so as to exposethe blood to the action of the air. The outside of the lungsis covered with a delicate membrane, called the smooth membrane also lines the inner surface of thechest. In all movements of the lungs these two smoothmembranes rub together, so that all frictionis avoided. 97. The movements of the chest,that cause the air to flow into and out ofthe lungs, are produced by the action ofthe diaphragm and intercostal diaphragm is a thin, broad, circularpartition across the body, separating theabdomen from the chest. It forms thebottom of the chest, and is arched upward,like an inverted s
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