RESPIRATION 115 



enter the vein from either direction; the finger prevents its 

 flow toward the heart, while the valves in the vein prevent the 

 flow in the opposite direction. Remove the finger; result? 



c. Wind a string tightly about a finger, and note what takes 

 place. What vessels carry blood into the finger? What ones 

 carry it out? Which of these is closed by the string? Why 

 is it important that arteries should not be near the surface? 



d. Ask a physician to show you a stethoscope and the way it 

 " works." With it study the heart-beat of some member of 

 your family. What sounds does the heart make? 



e. From a butcher get the heart of a sheep or calf, with the 

 lungs and trachea attached if possible. Examine the blood 

 vessels connected with the heart. Study their position by the 

 aid of Fig. 284, 375, of the text. Distinguish the arteries 

 from the veins by the differences in thickness, strength, and 

 elasticity. Distinguish the ventricles from the auricles. In 

 what part of the heart are the ventricles? Why are their walls 

 so thick? 



/. If your specimen of the heart has the lungs attached, 

 examine them. Are they heavy or light? Are they of exactly 

 the same shape? What is their color? What is the shape and 

 structure of the trachea? What keeps it in shape? 



EXERCISE 105 

 RESPIRATION 



Apparatus and Materials. Watch, measuring tape, 2-qt. fruit 

 jar, deep pan of water, glass tube, graduated cylinder, small-mouth 

 bottle with bottom removed (Ex. 84), touch paper. 



a. .Read 381 to 391, inclusive, of the text. For the test 

 for the presence of carbon dioxide in exhaled air, recall Exercise 

 15, b. Test for water in exhaled air by blowing the breath into 

 a cold bottle or against a cold window pane. What happens? 



