The Circulation : Part 7

Physiology and Hygiene for Secondary Schools
by Francis M. Walters

(Page 11 of 29)

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. 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.)

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. 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.

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?

2. Compare the size of the veins on the backs of the hands when they are placed side by side on a table. Then exercise briskly the right hand and arm, clenching and unclenching the fist and flexing the arm at the elbow. Place the hands again side by side and, after waiting a minute, observe the increase in the size of the veins in the hand exercised. How is this accounted for?

To Show the Effect of Gravity on the Circulation. - Hold one hand high above the head, at the same time letting the other hand hang loosely by the side. Observe the difference in the color of the hands and the degree to which the large veins are filled. Repeat the experiment, reversing the position of the hands. What results are observed? In what parts of the body does gravity aid in the return of the blood to the heart? In what parts does it hinder? Where fainting is caused by lack of blood in the brain (the usual cause), is it better to let the patient lie down flat or to force him into a sitting posture?

To study the Circulation in a Frog's Foot (Optional). - A compound microscope is needed in this study and for extended examination it is best to destroy the frog's brain. This is done by inserting some blunt-pointed instrument into the skull cavity from the neck and moving it about. A small frog, on account of the thinness of its webs, gives the best results. It should be attached to a thin board which has an opening in one end over which the web of the foot may be stretched. Threads should extend from two of the toes to pins driven into the board to secure the necessary tension of the web, and the foot and lower leg should be kept moist.

Using a two-thirds-inch objective, observe the branching of the small arteries into the capillaries and the union of the capillaries to form the small veins. The appearance is truly wonderful, but allowance must be made for the fact that the motion of the blood is magnified, as well as the different structures, and that it appears to move much faster than it really does. With a still higher power, the movements of the corpuscles through the capillaries may be studied.

NOTE. - To perform this experiment without destroying the brain, the frog is first carefully wrapped with strips of wet cloth and securely tied to the board. The wrapping, while preventing movements of the frog, must not interfere with the circulation.

D.C. Heath and Co. - Publishers
Original copyright 1909