valve from above. Compare the two sides of the heart, part for part.

9. Separate the aorta from the other blood vessels and cut it entirely
free from the heart, care being taken to leave enough of the heart
attached to the artery to insure the semilunar valve’s being left in good
condition. After tying or plugging up the holes in the sides of the
artery, pour water into the small end and observe the closing of the
semilunar valve. Repeat the experiment until the action of the valve is
understood. Sketch the artery, showing the valve in a closed condition.

*To illustrate the Action of a Ventricle.*—Procure a syringe bulb with an
opening at each end. Connect a rubber tube with each opening, letting the
tubes reach into two tumblers containing water. By alternately compressing
and releasing the bulb, water is pumped from one vessel into the other.
The bulb may be taken to represent one of the ventricles. What action of
the ventricle is represented by compressing the bulb? By releasing the
pressure? Show by a sectional drawing the arrangement of the valves in the
syringe bulb.

[Fig. 25]


Fig. 25—Illustrating elasticity of arteries.


*To show the Advantage of the Elasticity of Arteries.*—Connect the syringe
bulb used in the last experiment with a rubber tube three or four feet in
length and having rather thin walls. In the opposite end of the rubber
tube insert a short glass tube which has been drawn (by heating) to a fine
point (Fig. 25). Pump water into the rubber tube, observing: