_Experiment 12._ =Dust.=--With a mirror cause a sunbeam to play like a search light into a closed room several hours after it has been swept. Result? Do the same in a room where every window and door were open during sweeping and left open afterwards. Result? Conclusion? Note also the amount of dust on the furniture of each room. _Experiment 13._ =Study of Habitual Quiet Breathing.=--Without any more disturbance of the breathing than can be helped, direct your attention to your breathing while sitting quietly. Record motions of any parts of chest and abdominal walls that may be noticeable. If necessary, lay the hands successively against different parts of the wall to test for motion. Think of another subject, and later repeat observations. _Experiment 14._ =Study of Deep Breathing.=--Place your hands successively upon the front and sides of your chest, waist, and abdomen, while drawing in and sending out deep breaths. What motions of the several parts are observed at each stage? _Experiment 15._ =Study of Elasticity as a Factor in Breathing.=--(1) Notice whether in quiet breathing there is an elastic rebound as the breath goes either in or out. If so, it is due to the elasticity of the cartilages or air cells of lungs, or both. (2) Breathe by inflating the lungs strongly at each breath. Is the air then forced out without effort? (3) Breathe by flattening the chest and abdomen as much as possible at each breath. Does the air then rush in without effort? _Experiment 16._ =Chest Breathing.=--Try to breathe wholly by deep expansions and contractions of chest wall. What motions, if any, are noticed in abdominal wall as breath goes in? As it goes out? (Test motions with hand.) _Experiment 17._ =Abdominal Breathing.=--Try to hold the chest walls still and breathe by strong contraction and expansion of abdomen. Do the chest walls move at all? Neither “chest breathing” nor “abdominal breathing” is the normal way. See text. _Experiment 18._ =Full Breathing.=--Try breathing by outward and inward movement of walls of chest, _waist_, and abdomen. Do you succeed? This is normal breathing. Is the motion greater at the front or the sides of the waist? Put a belt around the waist tight enough to stay in place and repeat. Is the waist motion interfered with? _Experiment 19._ =How the Ribs are Lifted.=--Make a model-like sketch to represent backbone, breastbone, and two ribs, using pins to make joints loose at corners. Use cords for diagonals. What happens when cord _ac_ is pulled? When cord _bd_ is pulled? The cords correspond to the two sets of muscles between the ribs. [Illustration] _Experiment 20._ =Study of Laughing.=--Place the hands upon the waist and abdomen when laughing. What motion occurs at each sound of laugh? Draw in the abdominal wall with a jerk. What is the effect upon the breath?