An animation shows how the vocal cords change in position to produce a change in the pitch of the voice. Illustrations show the structure and function of the lungs from different angles, and an animation shows the inflation of the lungs during ordinary breathing and during vigorous exercise. A man is shown breathing into an apparatus that inflates as he breathes. Parts of the lung are shown, including the trachea, bronchi and bronchial tubes, and then close up drawings of the branching tip of a bronchial tube and alveoli. An illustration of the wall between two alveoli also shows the epithelial cells, the capillary wall, air space on each side of the wall, red blood corpuscles, and an animation then shows the blood giving off carbon dioxide and taking up oxygen. The film ends with shots of men rowing and swimming.