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Abstract
Respiratory behavior (ratio of diving to surface time) of a frog (Rana ridibunda)in response to changes in water temperature and oxygen partial pressure, was studied in the laboratory. Venous blood was withdrawn from the vena angularisin the mouth at the end of the observation sessions and blood hemoglobin saturation was determined with a hemoximeter. It was observed that diving duration was inversely related to temperature. Saturation of blood hemoglobin in hypoxic (N2; <50 mmHg O2) condition took 45 min to decrease from35% to 10%. When bath oxygen partial pressure was maintained at constant temperature, frogs did not surface until hemoglobin oxygen saturation decreased to below 10%. The skin is the main avenue for the elimination of metabolic carbon dioxide in amphibia, but is also an important avenue for oxygen diffusion in water. The experiments show that oxygen accessibility by diffusion through the skin is an important determinant of the respiratory behavior in the frog, but it becomes limited at extreme ambient conditions.