CHAPTER V 

 THE CIRCULATION 



Experiment i . 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 re- 

 verse 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 vali'e ab<n>e 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 supposedlv cut 

 vein. Let another pupil use means to stop the imagined blood flow. 



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