The measurement of rectal and testis temperature in conscious mice, with observations on the effect of direct heating

The application of Newton's law of cooling to freshly killed mice was found not to measure accurately their rectal or testis temperature. Improvements in the fitting process gave satisfactory results for rectal temperature only. A diffusion model was applied to testis cooling but was of no avail. Finally a satisfactory correction factor was determined empirically. This method was applied to conscious mice whose hindquarters were immersed in a stirred oilbath at 34 to 42 degrees C for 1 h, and to controls. It was found that both rectal and testis temperatures increased with bath temperature, producing a graph with a slope of only 0.5, indicating a regulatory capacity. Conscious mice, but not anaesthetised, can maintain a testis temperature of 39 degrees C in a bath at 42 degrees C.