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.
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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?
Experiment 21. Modifications of the Breath.—Write I, E, or IE after each word in this list, according as inspiration, expiration, or both, are involved in the action. (Test with sham acts if possible.) Sighing, sobbing, crying (of a child), coughing, laughing, yawning, sneezing, hiccoughing, snoring.
Experiment 22. Effects of Exercise.—Count and record the rates of breathing before and after vigorous exercise.
Experiment 23. Comparative Study.—Observe and record the rate and manner of breathing of cow, horse, dog, cat, etc. Is the air drawn in or sent out more quickly? Is there a pause? If so, after which stage of breathing?
Experiment 24. Emergency Drill.—Resuscitation from drowning, etc. See Coleman's "Elements of Physiology," page 356.
Necessity for Breathing and for Specialized Organs of Breathing.—The body is a self-regulating machine which
possesses energy. This energy, like that of steam engines,
arises from oxidation which takes place continually, but at
a varying rate. Food for fuel is taken at intervals, but
oxygen must be taken in continually. Man breathes about
eighteen times per minute. The blood in the tissues soon
becomes dark because of loss of oxygen and absorption of
carbon dioxid. It is then pumped through the heart to
the organ which has the function of absorbing oxygen
and giving off carbon dioxid (Fig. 67). In some animals,
as the ameba and the earthworm, the surface of the body
suffices for breathing. This cell breathing is the true
essential respiration; it is universal among living things,
