_Experiment 2._ =Anatomy of Lungs.=--Study fresh lungs of sheep, hog, fowl, or frog. Will they float? Will they contract when expanded by air blown in through a quill or other tube? What is the structure of the windpipe? Can you distinguish the arteries from the veins by the stiffness of their walls? Which contain pure blood? Study branching of air tubes. Make a sketch. _Experiment 3._ =Tests of Expired Air.=--Breathe upon a mirror, bright knife blade, or cold window pane. Result? State your conclusion. _Experiment 4._--Carbon dioxid added to limewater will cause a white cloud consisting of particles of limestone. Breathe through a tube or straw or the hollow stem of a reed into clear limewater. Result? Conclusion? (Limewater may be had at druggist’s or made by pouring water upon a lump of unslackened lime and draining it off when lime has settled.) _Experiment 5._ Breathe for several minutes upon the bulb of a thermometer. Result? Conclusion? _Experiment 6._ Breathe a few times into a large, carefully cleaned pickle jar, or a bottle. Cork it tightly, and set it in a warm place for several days. Then uncork and smell the air in it. Result? Conclusion? _Experiment 7._ Pierce a small hole in a card, place card over a wide-mouthed bottle, and breathe into bottle through a tube, lemonade straw, or hollow reed. Pull out straw. Place bottle, mouth downward, on table, and slip out card. Slide bottle to edge of table and lift lighted candle into bottle. Result? _Experiment 8._ Place bottle of fresh air over lighted candle. Result? Conclusion? (See Animal Biology, p. 4.) _Experiment 9._ (School.) =Testing the Air of a Room.=--Fill a fruit jar or large bottle with water, and take it into a room containing many people. Pour out the water. (This insures that all the air now in the jar is air obtained in the room to be tested.) Seal the jar if test is not to be made at once. Test by pouring in two tablespoonfuls of clear limewater and shake. If the limewater turns milky, the ventilation is bad. _Experiment 10._ (Home and school.) =Homemade Current Detector.=--Dangle a bit of paper by means of a spider web or thread from the end of a walking stick or ruler. (Or test with the flame of a candle.) Hold it near cracks of window, above and below doors, and especially before openings intended for entry and exit of air, and test if air moves as desired. _Experiment 11._ =Ventilation of the Schoolroom.=--Let the whole class rise, and with the fingers test cracks around doors and windows. Wherever the air feels cold to the hand the air is entering.