17. Why do the lungs of people who live in cities become of a gray color? 18. How would you convince a person that a bedroom should be aired? [Footnote: "If the condensed breath collected on the cool windowpanes of a room where a number of persons have been assembled, be burned, a smell as of singed hair will show the presence of organic matter; and if the condensed breath be allowed to remain on the windows for a few days, it will be found, on examination by the microscope, that it is alive with animalculæ."] 19. What persons are most liable to catarrhs, consumption, etc.? 20. If a person is plunged under water, will it enter his lungs? 21. Are bed curtains healthful? 22. Why do some people take "short breaths" after a meal? 23 What is the special value of public parks? 24. Can a person become used to bad air, so that it will not injure him? 25. Why do we gape when we are sleepy? 26. Is a fashionable waist a model of art in sculpture or painting? 27. Should a fireplace be closed? [Footnote: Thousands of lives would be saved if all fireplaces were kept open. If you are so fortunate as to have a fireplace in your room, paint it when not in use, put a bouquet of fresh flowers in it every morning, if you please, or do anything to make it attractive, but never _close it_; better use the fireboards for kindling wood. It would be scarcely more absurd to take a piece of elegantly-tinted court-plaster and stop up the nose, trusting to the accidental opening and shutting of the mouth for fresh air, because you thought it spoiled the looks of your face to have two such great, ugly holes in it, than to stop your fireplace with elegantly-tinted paper, or a Japanese fan, because it looks better.--Leeds.] 28. Why does embarrassment or fright cause a stammerer to stutter still more painfully? 29. In the organs of voice, what parts have somewhat the same effect as the case of a violin and the sounding-board of a piano? 30. Why should we be careful not to "take the breath of a sick person"? 31. What special care should be taken with regard to keeping a cellar clean? 32. How is the air strained as it passes into the lungs? 33. Can one really "draw the air into his lungs"? 34. How often do we breathe? 35. Describe some approved method of ventilation. 36. What is at once the floor of the chest and the roof of the abdomen? 37. What would you do in a case of apparent death by drowning, or by coal gas? (See p. 264.) 38. What would you do in a case of croup, while the doctor was coming? (See p. 260.) 39. How would you treat a severe burn? (See p. 257.) 40. Describe the various ways in which the water in a well is liable to become unwholesome. FIG. 34. [Illustration] V. THE CIRCULATION.