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Determination of the total respiratory exchange while walking on a section of flat ground between railroad rails from the 1911 Anglo-American Expedition to Pikes Peak

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C Gordon Douglas is shown breathing into a "Douglas bag." Historically, gas exchange was measured by the "Douglas bag method," which involved collecting exhaled air in large, impermeable canvas bags from which gas fractions and expired volumes could be measured. The Douglas bag method served as the “gold standard” for gas exchange measurements for over a century (Bassett DR Jr, Howley ET, Thompson DL, et al. Validity of inspiratory and expiratory methods of measuring gas exchange with a computerized system. J Appl Physiol [1985] 2001;91[1]:218-24). (Source: Douglas CG, Haldane JS, Henderson Y, Schneider EC. Physiological observations made on Pike's Peak, Colorado, with special reference to adaptation to low barometric pressures. Philosophical Transactions of the Royal Society, Series A 1913;203:185-318.)