The Physical Properties of the Frog Lung. ∗

Abstract

The respiration of the frog has been studied by several investigators. Ventilatory movements have been described ( 1 , 2 , 3 ) and the diffusion of gases has been studied. Krogh( 4 ) found that most of the carbon dioxide was eliminated through the skin while most of the oxygen was absorbed through the lungs. The lung of the frog is a simple saccular organ. Ventilation occurs under positive pressure. Air is forced into the lungs by muscular contraction of the floor of the mouth and retained in the lungs by closure of the glottis. Mechanisms by which the frog empties its lungs are not thoroughly understood although contraction of the smooth muscle in the wall of the lung is probably the major factor.

The physical properties of the frog lung have not been studied previously. An understanding of the mechanical behavior of the frog lung is of importance because of its structure. Theories of the mechanical behavior of mammalian lungs entail a consideration of forces arising from the tissue and forces arising from the air fluid interfaces throughout the lung. Data have been obtained from the lungs of frogs for interpretation in the light of these theories.

Materials and methods. Adult male frogs (Rana pipiens) weighing 24 to 42 g were pithed. The lungs and heart were removed and the vessels ligated. Pressure and volume were measured under static conditions with air and with liquid (Ringer's solution) filling. The lung was cannulated with a 20 cm length of polyethylene tubing type PE160. In the Ringer's solution experiments, the polyethylene tubing served as a manometer. Volume displacement inside the tubing was 100 cm/ ml. Capillarity was insignificant. A calibrated tuberculin-type syringe was used to measure volume to the nearest 0.01 ml. Pressure equilibrated rapidly so all pressure measurements were made within 15 seconds following each change in volume.