The concentration of carbon dioxide in the expired air is determined routinely during the estimation of basal metabolism by the open circuit method. This concentration is dependent on the relation of the volume of respired air to the rate of production or elimination of carbon dioxide. The physiologic relation between respiration and the production of carbon dioxide has been summarized by Henderson1:
The control of breathing... involves many factors: oxygen, carbon dioxide, blood alkali and H ions, and particularly the sensitivity of the respiratory center under a wide range of conditions and influences. For conditions of health the accepted teaching is that of Haldane and his collaborators. It can be summarized in the statement that a normal man... breathes... volumes of air that are closely proportional to the amounts of carbon dioxide that are produced in his tissues. When he sits still, the amount of energy liberated in his