Steady-state measurements of respiration rate with an oxygen electrode.

The respirometer is shown in Fig. 1. The cathode was made from gold wire of 0.51 mm diam which was coated with glass of low melting point (4). After mounting the cathode as shown in Fig. 1, the gold and its glass coating were ground to a flat surface and polished using a series of carborundum grinding powders. The cathode was maintained at -0.45 V with respect to the calomel electrode. The electrode current was measured with a Keithley model 15OA microvolt-amperometer (Keithley Instruments, Cleveland, OH 44139). The buffer was 0.01 M succinate at pH 6.0, made with glass-distilled water. At low oxygen tensions, 0.01 M KC1 was used as an electrolyte, but at atmospheric oxygen tension, 0.1 M KC1 was required to prevent appreciable electrolyte resistance between the electrodes. Stirring was done with a magnet rotated at 2000 rpm under the respirometer. The slot along the inner joint of the respirometer was just large enough to accommodate a 26-gauge hypodermic needle. This needle was connected to a syringe pump, and airequilibrated buffer was pumped into the respirometer at a constant rate. The syringe pump was constructed by attaching the chart drive of a Health/Schlumberger model EU-20B recorder (Health/Schlumberger Instruments, Benton Harbor, MI 49022) to the rack and pinion gear