This paper discusses the oxygen intake during exercise while breathing oxygen-rich mixtures, with a focus on possible errors in measurement. The study, conducted by K. Furusawa, re-observed previous findings by A. V. Hill, C. N. H. Long, and H. Lupton, showing that maximal oxygen intake can increase by up to 50% when breathing oxygen-rich mixtures compared to air. The method used involved the Douglas bag and Haldane apparatus to measure expired air. A major concern was contamination of expired gases by air, which could significantly affect results. A calculation demonstrated that even small amounts of air contamination could lead to a noticeable decrease in measured oxygen intake. The study also considered the possibility of nitrogen equilibrium changes, but found this effect to be negligible compared to the main issue of air leakage. The experiments were conducted with strict precautions to prevent air leakage, including testing mouthpieces and ensuring tight seals. The results showed a significant increase in oxygen intake when breathing oxygen-rich mixtures, with the highest values recorded for a subject (K.F.) being 87.3 c.c. per minute per kgm. This increase is attributed to an increased circulation rate, possibly due to the heart muscle itself. The study confirms that breathing oxygen-rich mixtures can significantly increase oxygen intake during exercise, and that this effect is likely due to enhanced blood circulation rather than arterial blood saturation. The paper acknowledges the contributions of Prof. A. V. Hill and other researchers involved in the experiments.This paper discusses the oxygen intake during exercise while breathing oxygen-rich mixtures, with a focus on possible errors in measurement. The study, conducted by K. Furusawa, re-observed previous findings by A. V. Hill, C. N. H. Long, and H. Lupton, showing that maximal oxygen intake can increase by up to 50% when breathing oxygen-rich mixtures compared to air. The method used involved the Douglas bag and Haldane apparatus to measure expired air. A major concern was contamination of expired gases by air, which could significantly affect results. A calculation demonstrated that even small amounts of air contamination could lead to a noticeable decrease in measured oxygen intake. The study also considered the possibility of nitrogen equilibrium changes, but found this effect to be negligible compared to the main issue of air leakage. The experiments were conducted with strict precautions to prevent air leakage, including testing mouthpieces and ensuring tight seals. The results showed a significant increase in oxygen intake when breathing oxygen-rich mixtures, with the highest values recorded for a subject (K.F.) being 87.3 c.c. per minute per kgm. This increase is attributed to an increased circulation rate, possibly due to the heart muscle itself. The study confirms that breathing oxygen-rich mixtures can significantly increase oxygen intake during exercise, and that this effect is likely due to enhanced blood circulation rather than arterial blood saturation. The paper acknowledges the contributions of Prof. A. V. Hill and other researchers involved in the experiments.