Breathing.

Silent with Intertitles. Intertitle: 'Mechanism of breathing' diagrammatic picture illustrating movement of ribs and diaphragm; Intertitle: 'A classroom model shows how the diaphragm helps to enlarge the chest cavity and draw air into the lungs. Man blowing into two balloons in vacuum chamber. Intertitle 'Artificial respiration illustrates the mechanics of breathing,' two men demonstrating this. Intertitle: 'The Air passages', diagrams of nostrils, sinuses, and then illustrated using a skull, showing turbinates, ciliary membranes seen; diagram showing adenoids; tonsils; pharynx; larynx; and trachea. Diagram and model showing function of vocal chords. Diagrams showing the structure and function of the lungs, also showing bronchial tubes and alveoli. Inspiratory excursion at rest and during exercise; air-blood gaseous interchange.