THE CIRCULATION 63 



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 / IG ; 26 --~ Simple appa- 



ratus for showing advantage 

 tubes, being pushed in both directions. of va i ves in veins . 



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 in- 

 stance that the water is all pushed in the same direction. The move- 

 ment 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 fore- 

 arm 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. i . 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 : (#) 

 when sitting ; (6) when standing ; (c) after active exercise, as run- 

 ning. 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 



