HELPS IN LESSON PREPARATION 325 



more or less than the average? 4. Give the meaning of 

 ceaseless, tide, continually, page 98. 5. Mention the prin- 

 cipal components of air. 6. About what part of pure 

 air is oxygen? 7. Why does a furnace fire or a lamp 

 light go out when the draughts are closed? 8. State how 

 our bodies are like furnaces and engines. 9. What is 

 produced by the union of oxygen and the tissues of our 

 bodies? 10. What component of air serves to dilute 

 the oxygen? 11. State the proportion of carbonic acid 

 gas in pure air. 12. What amount of carbonic acid gas 

 in air is the upper limit of safety? Give the meaning of 

 imagine and representing, page 102. 13. How can you 

 judge whether or not the air of a vat or well is dangerous 

 to breathe? 14. What poisonous gas is produced by the 

 union of oxygen and the tissues of our bodies? 15. Which 

 has the more moisture, warm air or cold air? 16. What 

 is insensible perspiration? 17. Explain why we often 

 feel more uncomfortable on moist summer days than we 

 do on days that are hotter but not as moist. 18. Give 

 synonyms of penetrating, remotest, relative position, page 

 104; of extremely, vital, inflated, museum, and elasticity, page 

 105. 19. Give the meaning of comprehend, tracing, ap- 

 proach, and contain, page 106. 20. What are the capillaries? 

 21. How many separate chambers has the heart? What 

 are they called? 22. Of what use is the heart? 23. In 

 the water system of a great city, what corresponds to the 

 arteries of our body? What to the veins? 24. How is 

 the blood kept from flowing backward? 25. What is 

 meant by the circulation f 26. Tell what is said about the 

 number of times the heart beats per minute. 27. How is 

 oxygen carried from the lungs to the tissues of the body ? 

 How is the carbonic acid gas brought from various parts 

 of the body to the lungs? 28. Where does the blood 

 exchange its carbonic acid gas for oxygen? 29. Give the 



