. The physiology of domestic animals ... Physiology, Comparative; Veterinary physiology. RESPIRATION. 573 until equilibrium is produced (Fig. 246). On the other hand, if the forces which produce enlargement of the thorax cease to act, the elasticity of the lungs, together with that of the cartilages of the ribs, is now sufficient to produce a return of the thorax to its original volume. The lungs, therefore, now decrease in volume, and as a consequence the air within them tends to become compressed, and, as a result, a portion of the air is expelled through the air-passages to the external atm
. The physiology of domestic animals ... Physiology, Comparative; Veterinary physiology. RESPIRATION. 573 until equilibrium is produced (Fig. 246). On the other hand, if the forces which produce enlargement of the thorax cease to act, the elasticity of the lungs, together with that of the cartilages of the ribs, is now sufficient to produce a return of the thorax to its original volume. The lungs, therefore, now decrease in volume, and as a consequence the air within them tends to become compressed, and, as a result, a portion of the air is expelled through the air-passages to the external atmosphere. The expansion of the thorax constitutes inspiration; the contraction of the thorax constitutes expiration. As the tension of air in the lungs becomes decreased through inspiration, fresh air enters the lungs which is less charged with the ' carbon dioxide than that previously present in the lungs, while it is also. Fig. 246.—Diagrammatic Representation of the Relations between the Lungs and the Thoracic Cavity, after Funke. (Beaunis.) The bell-jar, 1, represents the thorax; the rubber membrane, 4, the diaphragm; the membrane, 6, the soft parts of an intercostal space ; 2, the trachea, terminating in two rnbber bulbs representing the lungs ; 3, a manometer for measuring the pressure within the bell-jar. In the figure to the left the atmospheric pressure within the bell-jar is the same as on the outside, and the mercury in the manometer stands at the same level in both arms. If the rubber membrane, 4, is drawn downward by the button, 5, the cavity of the bell-jar is increased and the atmospheric pressure diminished, as shown by the manometer and the depressed space. 6. The negative pressure thus produced leads to the entrance of air through the tube, 2, into the rubber bulbs, which consequently expand. The action of the diaphragm in producing inspiration is precisely similar. richer in oxygen. By diffusion, from the inequality of these gaseous tensions, we have oxygen
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