Electrical impedance changes of the cat's foot pad in relation to sweat secretion and reabsorption.

Impedance across the cat's foot pad, the glands being at rest, has a high quite constant value in a given preparation. Stimulation of the sudomotor nerves causes a decrease to a low constant value. After cessation of stimulation impedance returns slowly over a course that is linear with respect to the logarithm of time. The resistive and capacitative components vary with each other. Sweat reabsorption during recovery progresses linearly with respect to time. Hence impedance varies as the logarithm of reabsorption, and therefore as the mean level of sweat columns in the ducts. This relation can be accommodated by supposing that the sweat duct epithelium resembles a core conductor. An electrical model constructed on this principle is shown to behave as does the foot pad. During stimulation at a fixed frequency impedance change varies as the logarithm of duration showing that the amount of sweat produced per impulse at a given frequency is a constant. With frequency of a fixed number of stimuli varied the impedance change varies with it in a manner consistent with the view that the amount of sweat produced per impulse is a constant regardless of frequency.