16. Should a hat be thoroughly ventilated? How?
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?