Increased RBC count and pulmonary respiration in cold-adapted frogs.

1. Haematological and respiratory parameters (including RBC count, CO2 content and percentage oxygen saturation) were studied in coldacclimated (12 ± 1 °C) and normal frogs (23 + 2 °C). 2. Seasonal variation in RBC count was found, the count being higher in January than in September. Females showed higher counts than males. Coldacclimation resulted in the elevation of counts in all seasons and in both sexes, and was accompanied by a rise in haemoglobin content. 3. Cold-acclimated frogs retained a higher oxygen saturation in the truncus arteriosus than in the cutaneous vein, the carbon dioxide content of the truncus being also reduced in acclimated frogs. The OJCOj ratios were thus higher in the truncus than in the cutaneous vein. 4. Cold-acclimated frogs released more COa through the lungs. 5. It is suggested that a change in the mode of respiration occurs when the frogs are acclimated to cold.