f the limewater
to a milky white color proves the presence of carbon dioxide.

[Fig. 50]

Fig. 50--*Apparatus* for showing changes which air undergoes while in the
lungs.

2. The effects illustrated in experiment 1 may be shown in a somewhat more
striking manner as follows: Fill two bottles of the same size each one
fourth full of limewater and fit each with a two-holed rubber stopper
(Fig. 50). Fit into each stopper one short and one long glass tube, the
long tube extending below the limewater. Connect the short tube of one
bottle and the long tube of the other bottle with a Y-tube. Now breathe
slowly three or four times through the Y-tube. It will be found that the
inspired air passes through one bottle and the expired air through the
other. Compare the effect upon the limewater in the two bottles. Insert a
small burning splinter into the top of each bottle and note result. What
differences between inspired and expired air are thus shown?

3. Blow the breath against a cold window pane. Note and account for the
collection of moisture.

4. Note the temperature of the room as shown by a thermometer. Now breathe
several times upon the bulb, noting the rise in the mercury. What does
this experiment show the body to be losing through the breath?

*To show Changes in the Thoracic Cavity.*--1. To a yard- or meter-stick,
attach two vertical strips, each about eight inches long, as shown in Fig.
51. The piece at the end should be secured firmly in place by screws or
nails. The other should be movable. With this contrivance measure the
sideward and forward expansion of a boy's thorax. Take the diameter first
during a complete inspiration and then during a complete expiration,
reading the difference. Compare the forward with the sideward expansion.

[Fig. 51]

Fig. 51--*Apparatus* for measuring chest expansion.

2. With a tape-line take the circumference of the chest when all the air
possible has been expelled from the lungs. Take it again when the lungs
have been fully inflated. The difference is now read as the chest
expansion.

[Fig. 52]

Fig. 52--*Simple apparatus* for illustrating the action of the diaphragm.

*To illustrate the Action of the Diaphragm.*--Remove the bottom from a
large bottle having a small neck. (Scratch a deep mark with a file and
hold on t