Experiment 118. To show that the air we expire is warm. Breathe on a thermometer for a few minutes. The mercury will rise rapidly.
Experiment 119. To show that expired air is moist. Breathe on a mirror, or a knife blade, or any polished metallic surface, and note the deposit of moisture.
Experiment 120. To show that the expired air contains carbon dioxid. Put a glass tube into a bottle of lime water and breathe through the tube. The A liquid will soon become cloudy, because the carbon dioxid of the expired air throws down the lime held in solution.
Experiment 121. “A substitute for a clinical thermometer may be readily contrived by taking an ordinary house thermometer from its tin case, and cutting off the lower part of the scale so that the bulb may project freely. With this instrument the pupils may take their own and each other’s temperatures, and it will be found that whatever the season of the year or the temperature of the room, the thermometer in the mouth will record about 99° F. Care must, of course, be taken to keep the thermometer in the mouth till it ceases to rise, and to read while it is still in position.”—Professor H. P. Bowditch.
Experiment 122. To illustrate the manner in which the movements of inspiration cause the air to enter the lungs. Fit up an apparatus, as represented in Fig. 95, in which a stout glass tube is provided with a sound cork, B, and also an air-tight piston, D, resembling that of an ordinary syringe. A short tube, A, passing through the cork, has a small India-rubber bag, C, tied to it. Fit the cork in the tube while the piston is near the top. Now, by lowering the piston we increase the capacity of the cavity containing the bag. The pressure outside the bag is thus lowered, and air rushes into it through the tube, A, till a balance is restored. The bag is thus stretched. As soon as we let go the piston, the elasticity of the bag, being free to act, Movements of drives out the air just taken in, and the piston returns to its former place.
Fig. 95. Apparatus for Illustrating the Movements of Respiration.
It will be noticed that in this experiment the elastic bag and its tube represent the lungs and trachea; and the glass vessel enclosing it, the thorax.
For additional experiments on the mechanics of respiration, see [Chapter XV].