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:
1. The swelling of the tube (pulse) as the water is forced into it. (This is best observed by placing the fingers on the tube.)
[pg 063]2. The forcing of water from the pointed tubs during the interval when no pressure is being applied from the bulb. Compare with the action of the arteries when blood is forced into them from the ventricles.
Repeat the experiment, using a long glass tube terminating in a point instead of the rubber tube. (In fitting the glass tube to the bulb use a very short rubber tube.) Observe and account for the differences in the flow of water through the inelastic tube.
To show the Advantage of Valves in the Veins.—Attach an open glass tube one foot in length to each end of the rubber tube used in the preceding experiment and fill with water (by sucking) to within about six inches of the end. Lay on the table with the glass tubes secured in an upright position (Fig. 26). Now compress the tube with the hand, noting that the water rises in both tubes, being pushed in both directions. This effect is similar to that produced on the blood when a vein having no valves is compressed.
Fig. 26.—Simple apparatus for showing advantage of valves in veins.
Now imitate the action of a valve by clamping the tube at one point, or by closing it by pressure from the finger, and then compressing with the hand some portion of the tube on the table. Observe in this instance that the water is all pushed in the same direction. The movement of the water is now like the effect produced on the blood in veins having valves when the veins are compressed.
To show the Position of the Valves in the Veins.—Exercise the arm and hand for a moment to increase the blood supply. Expose the forearm and examine the veins on its surface. With a finger, stroke one of the veins toward the heart, noting that, as the blood is pushed along on one side of the finger the blood follows on the other side. Now stroke the vein toward the hand. Places are found beyond which the blood does not follow the finger. These mark the positions of valves.
To show Effect of Exercise upon the Circulation.—1. With a finger on the "pulse" at the wrist or temple, count the number of heart beats during a period of one minute under the following conditions: (a) when sitting; (b) when standing; (c) after active exercise, as running. What relation, if any, do these observations indicate between the general activity of the body and the work of the heart?