1. The respiration of luminous bacteria has been studied by colorimetric and manometric methods. 2. Limulus oxyhaemocyanin has been used as a colorimetric indicator of oxygen consumption and indicator dyes were used for colorimetric determination of carbon dioxide production. 3. The Thunberg-Winterstein microrespirometer has been used for the measurement of the rate of oxygen consumption by luminous bacteria at different partial pressures of oxygen. 4. The effect of oxygen concentration upon oxygen consumption has been followed from equilibrium with air to low pressures of oxygen. 5. Luminous bacteria consume oxygen and produce carbon dioxide independent of oxygen pressures from equilibrium with air (152 mm.) to approximately 22.80 mm. oxygen or 0.03 atmosphere. 6. Dimming of a suspension of luminous bacteria occurs when oxygen tension is lowered to approximately 2 mm. Hg (0.0026 atmosphere) and when the rate of respiration becomes diminished one-half. 7. Pure nitrogen stops respiratory activity and pure oxygen irreversibly inhibits oxygen consumption. 8. The curve for rate of oxygen consumption with oxygen concentration is similar to curves for adsorption of gasses at catalytic surfaces, and agrees with the Langmuir equation for the expression of the amount of gas adsorbed in unimolecular layer at catalytic surfaces with gas pressure. 9. A constant and maximum rate of oxygen consumption occurs in small cells when oxygen concentration becomes sufficient to entirely saturate the surface of the oxidative catalyst of the cell.

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Some recent work, notably that of Dixon and Elliott, 1 has indicated that not all cells and tissues are completely cyanide-sensitive in the sense that they reduce their rate of respiration in the presence of cyanides. Alien ~ has pointed out that not all the respiratory exchange in Planaria m a y be inhibited b y cyanides. This has indicated that there m a y be other oxidation systems in the cells besides those affected by cyanides. Lund ~ found some years ago that K C N had little or no effect on oxygen consumption b y Paramecium. We proposed to reinvestigate this question and to determine if iron is present in the protoplasm of Paramecium, acting as the respiration catalyst according to the theory of Warburg, and to note if addition of iron would cause an increase in the rate of respiration in the Paramecium.All of the present experiments have involved the measurement of oxygen consumption in the Thunberg-Winterstein microrespirometer. Using the type of respiratory vessel illustrated in Fig. 1, it was a simple matter to remove or add organisms in various culture media and solutions. In all experiments a preliminary determination was made of the rate of oxygen consumption before cyanide was added to the sample of Paramecium. The comparative rates of oxygen consumption indicated the intensity of total oxidation within the cells under experimental conditions.To test the apparatus and the methods employed, two experimental runs were made on the same sample of Paramecium suspended in tap water. It was found that they consumed the same amount of oxygen over the same period of time. When 1 cc. of a 2 cc. sample of organisms was removed, and replaced with 1 cc. of distilled water without organisms, the respiration rate of the sample was re-1 Dixon, M., and EUiott, K. A. C., Biochem.

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