Efficiency of Electrical Energy Production by Surviving Frog Skin,Measured by Iodine Coulometer. ∗

Abstract

Surviving frog skin is the seat of an electrical potential which has been related to factors affecting its metabolic activity. 1 2 To determine the efficiency of electrical energy production through an external circuit by surviving frog skin it is necessary to measure the joules of electrical energy and the oxygen consumption of the skin during the same interval of time. An iodine coulometer 3 of low resistance (18–22 ohms) with sufficient electrode area to minimize polarization within the range of skin potentials, was employed to integrate the quantity of current passing through the external circuit. The coulometer was calibrated against known, constant current densities for measured intervals with a microammeter in series as a check. Average voltage was determined with a standard potentiometer by readings at 5 to 10 minute intervals.

The oxygen consumption was found by difference between initial and final oxygen concentrations in 25 ml samples of the Ringer's solution surrounding the skin, using the Winkler method for analysis.

Experiments were carried out in duplicate on symmetrical pieces of frog skin (Rana catesbiana) of 24 cm² area. Each piece of skin was clamped between a pair of iso-electric cup electrodes with 60 ml of Ringer's solution on each side. The electrodes were of lead amalgam-lead chloride covered by a surface layer of saline agar. The external circuit consisted of Ringer's solution, the electrodes, a coulometer and a microammeter in series. A potentiometer was connected across the electrode terminals.

Results of a typical one-hour determination at 25°C: The coulometer measured 1.497 coulombs. The average potential for 6 readings was 0.039 volts. The oxygen consumption was 0.239 ml at standard temperature and pressure. The respiratory quotient of the isolated skin was not determined. The highest and lowest respiratory quotients for the intact frog range from 0.94 to 0.72 4 .