CHAPTER V
THE CIRCULATION
Experiment 1. Anatomy of Mammalian Heart.—Get a sheep's or beef's heart from the butcher. Get the whole heart, not simply the ventricles (as usually sold). Note the blood vessels, four chambers, thickness of different walls, valves, cords, openings.
Experiment 2. Does Gravity affect the Blood Flow?—Hold the right hand above the head for a few minutes. At the same time let the left hand hang straight down. Then bring the hands together and see which is of a darker red because of containing more blood. Now reverse the position of the hands for a few minutes, and find whether the effect is reversed. (Entire class.)
Experiment 3. Study of Human Blood.—Examine a drop of blood under the microscope, first diluting it with a little saliva. See Fig. 60.
Experiment 4. The Circulation in a Frog.—Wrap a small frog in a moist cloth, lay on a slip of glass, place under the microscope, and study the circulation in the web of its foot.
Experiment 5. (Entire class.) Effect of Exercise upon the Pulse.—Tap a bell as the second hand of a watch begins a minute and let the pupils count the pulse at the radial artery on the wrist above base of thumb. Repeat standing, or after gymnastics or recess. Result?
Experiment 6. The Action of the Valves in the Veins.—Place the tip of the middle finger on one of the large veins of the wrist; with the forefinger then stroke the vein toward the elbow so as to push the blood from a portion of it, keeping both fingers in place. The vein remains empty between the fingers. Lift the finger nearer the heart and no blood enters the vein; there is a valve above which holds it back. Lift the other finger and the vein fills instantly. Stroke a vein toward the hand, and notice that the the veins swell up into little knots where the valves are. Stroke in the reverse direction. Result?
Experiment 7. Finding the Capillary Pressure. This is found by pressing a glass plate or tumbler upon a red part of the skin. When the skin becomes pale the capillary pressure is counterbalanced.
Experiment 8. Emergency Drill.—Let one pupil come forward, mark with blue chalk or pencil the position on his arm of a supposedly cut vein. Let another pupil use means to stop the imagined blood flow.
