The effect of temperature on the circulation of the isolated perfused rabbit ear.

Isolated rabbit ears were perfused with Ringer solution, and the rates of flow were measured by a micro flow-gauge. It was found that changes in flow produced by changes in temperature of the ear (amounting to two and a half times between 40° and 0° C), could be quantitatively explained by changes in the viscosity of the perfusion solution with temperature. No evidence of a “hunting reaction” to cold could be demonstrated either with or without a temperature gradient in the ear. The residual “critical closing pressure” of the isolated rabbit ear was shown to be independent of temperature. It is concluded that in the isolated perfused rabbit ear the temperature effects on circulation are entirely explicable in terms of viscosity changes, and that in the intact innervated ear, viscosity effects also underlie, but do not completely explain the observed changes with temperature.