242 RESPIRATION AND EXCRETION 



cord any changes. Breathe gently on any glass or polished metal 

 surface. Note what happens. 



Take a moderate breath, and force air (tidal air) by means of a 

 glass tube through limewater. Notice what occurs. Note dia- 

 gram. 



Force the last part of a deep expiration (reserve air) through 

 limewater. Note result. 



Fill a glass jar with expired air by the downward displacement of 

 water. Invert the jar, keeping it covered. Remove the cover, 

 and introduce into the jar a lighted pine splinter. Does it con- 

 tinue to burn? What does this indicate? Why? (Air loses 

 about one fourth of its oxygen while in the lungs.) 



Conclusion. — 1. What are the changes that take place in blood 

 in the lungs? 



2. What does air gain in the lungs? What does it lose? 



3. What is one reason for deep breathing? 



Problem 209 : To find the capacity of the lungs. (After Davi- 

 son.) 



Materials. — Gallon bottle, cork, curved glass tubing, and a 

 large pan. 



Method. — Fill the bottle with water, place water in the pan, 

 and invert the bottle in the pan. Remove the cork, insert the 

 end of the tubing under the bottle, fill the lungs to the fullest 

 capacity, and force air into the bottle. 



Observations. — How much water flows 'from the bottle? 

 What has taken place ? Place a mark on the bottle so as to show 

 the point to which you drove out the water by means of air. 

 Now with a graduate fill the bottle with water to the point dis- 

 placed. Measure the amount of water. 



Conclusion. — How much air do you conclude your lungs can 

 hold if 100 cubic inches remain in the lungs after you have ex- 

 pelled all you were able? Remember a gallon contains 231 

 cubic inches. 



Problem 210 : To study the mechanics of respiration. 

 Method and Observations. — Notice the movements of the 

 body when inhaling and exhaling in an ordinary breath and an 



