Physiology for beginners / by Leonard Hill.

  • Hill, Leonard, Sir, 1866-
Date:
1902
Catalogue details

Licence: In copyright

Credit: Physiology for beginners / by Leonard Hill. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    The difference between inspired and expired air. Expired air contains about five per cent, less oxygen and four per cent, more carbonic acid than atmospheric air. If you blow through a straw into a bottle containing lime-water the latter will turn milky, owing to the carbonic acid in the expired air. The carbonic acid combines with the lime to form a white solid salt, carbonate of lime. If you allow the carbonate of lime to fall to the bottom of the bottle, and then, having poured off the water, add a little hydrochloric acid, you will see the salt effer- vesce. The carbonic acid is driven out by this strong acid and chloride of lime is formed. The following table shows the difference between inspired and expired air :— Composition of 100 pints Composition of 100 pints of inspired air. of expired air. Oxygen . . 21 pints 16 pints Nitrogen . . 79 pints 79 Pints Carbonic acid . a trace 4 pints. The nitrogen does not change, but its presence is necessary to dilute the oxygen. The breath of a man is warmed to the temperature of the body, and appears misty on a cold day owing to the water-vapour which it takes up from the air-tubes. The effect of exercise on the respiration. When a man runs he breathes rapidly, and pants for breath. This is because the muscles are hard at work, giving out carbonic acid, and using up oxygen. The working muscles there- fore need plenty of arterial blood. The rapid movements of respiration not only purify the venous blood but help to bring it back to the heart, and aid the heart in driving it through the lungs. When the lungs expand in inspira- tion not only more air but more blood is drawn into them. When the lungs shrink in expiration not only air but blood is driven out of them. The blood is driven into