72 LIVING IN AN OCEAN OF AIR 



per square inch at sea level and decreases as one goes to the top 

 of a high mountain. One breathes much easier on top of a very 

 high mountain because the atmospheric pressure is less. In the 

 lungs the blood takes oxygen and water vapor from the air. None 

 of the nitrogen taken into the lungs is used by the body. The air 

 sacs are those small cavities in which the air is never changed. One 

 generally takes deeper breaths when awake than when asleep. The 

 lungs become empty after making an expiration so that there is no 

 air at all in the pleural cavity. This is why we gasp for breath after 

 running a hard race. 



THE REVIEW SUMMARY 



In preparing a summary of what you have learned in this unit, 

 you will want to place emphasis on the big ideas which have come 

 out of the applications of the facts you have learned and the 

 demonstrations you have seen. These big ideas we call generaliza- 

 tions. For this unit they are as follows : 



1. The gaseous envelope of the earth, called the atmosphere, 

 extends upward for many miles, rapidly becoming less dense at 

 high altitudes. 



2. The air contains elements essential both to plants and 

 animals. 



3. Air can be removed from a closed vessel. 



4. Atmospheric pressure is of great value to man. 



5. The breathing and hence the life of many living things 

 depend upon both the composition and the pressure of the air. 



Before making your review summary, test your knowledge of 

 the facts of the unit by checking over the text so as to be sure 

 you know the facts underlying the generalizations. Then, using 

 the generalizations, the material in the text, and everything you 

 have read, seen, or done yourself, make a summary outline for your 

 notebook. This outline you may use when you make a recitation. 



TESTS ON FUNDAMENTAL CONCEPTS 



Make two vertical columns in your workbook. Head one CORRECT 

 and the other INCORRECT. Under the first place the numbers of all state- 

 ments you believe to be correct. Under the second place all the numbers of 

 the statements you believe to be incorrect. Your grade = right answers X 2, 



