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Interior of laboratory for the 1911 Anglo-American Expedition to Pikes Peak

Alveolar CO2 pressure (thick line); alveolar O2 pressure (thin line). Horizontal interrupted lines represent the mean normal alveolar CO2 and oxygen pressures at sea level (ie, Oxford and New Haven). (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.)