2i6 



How a Complex Anmal Uses Food unit iv 



Rubber stopper 



Toy balloon 



Rubber sheet 



Fig. 232 A smiple model to illustrate breath- 

 ing. How does this model differ from the chest 

 cavity with its lungs? {See Exercise 5.) 



backbone. Fasten pieces of stiff 

 wire two inches apart at right 

 angles to this board. Bend the 

 wires until they almost meet 

 in front. The \\ ires are to be 

 connected in front by another 

 strip, representing the breast 

 bone. If the wires are fastened 

 loosely, they can be moved so 

 that they slope downward at 

 an angle. This is the position 

 of the ribs after air has been 

 exhaled. Raise the ribs. What 

 happens to the breast bone? 

 What happens to the size of 

 the cavity? (A simple two- 

 dimensional model may be 

 made by using strips of cardboard and brass fasteners. Try it.) 



5. How can you demonstrate the part played by air pressure in breath- 

 ing? See Figure 232. Attach two rubber balloons to a Y-tube. Push the 

 other end of the tube through a one-hole stopper that has been placed 

 in the neck of a bell jar. The balloons are to hang down in the jar. Cover 

 the large open end of the jar with rubber sheeting. The connection be- 

 tween sheeting and jar must be air tight. Make this model "breathe." Ex- 

 plain fully. What happens? 



6. How does exhaled air differ from inhaled air? Before you perform 

 this experiment make sure you know what percentages of oxygen and 

 carbon dioxide are normally present in the air. Blow your breath into a 

 rubber balloon. Notice how much the balloon has expanded. Then permit 

 it to empty itself under the surface of limewater in a jar. Now pump air 

 into the balloon until it is as large as it was before. Empty it into lime- 

 water in another jar. Examine both jars. What conclusion do you draw? 

 Now light a candle. Invert a jar over it. Notice how long the candle bums 

 (use a watch). Collect exhaled air in a jar of the same size (over water). 

 Invert this jar over a burning candle. How long does the candle burn? 

 What conclusions do you draw? Prepare a report. 



7. What is the effect of exercise on the rate of breathing? How often 

 do you breathe in a minute while sitting quietly? Do setting-up exercises 

 for one minute and then count the number of times you breathe in a 

 minute. Explain. Compare your results with those obtained by others. 



Further Activity in Biology 



Find out the best method of artificial respiration and demonstrate it to 

 the class. (Consult Boy Scout Ha?idbook or American Red Cross Maimal.) 



