Gas transit times in the pig lung.

1. A method of measuring the time taken by a front of gas to pass from the carina to individual small airways in the lung is described. 2. This method has been used to investigate the movement of a gas front through hollow lung casts, excised lungs, and excised lungs subjected to a gradient of pleural pressure. 3. The results obtained support the suggestion of morphometric studies that the asymmetrical anatomy of the bronchial tree plays a part in the uneven distribution of ventilation in the lung. 4. The effect of a gradient of pleural pressure over the surface of the upright lung was to increase the time taken by a gas front to reach dependent regions.