The rôle played by the blood and circulatory system in the gaseous metabolism of the body has constituted the subject of numerous investigations. These fall naturally into two groups. One comprises researches into the oxygen carrying capacity of the hemoglobin and the other group embraces studies on the volume flow of blood. The necessity for a wide range of functional adaptation is apparent when we recall that during severe exercise the amount of oxygen required may be seven or eight times greater than that which suffices under resting conditions.
Barcroft, Haldane and their co-workers demonstrated the reserve power of the hemoglobin by showing that under ordinary conditions oxyhemoglobin gives up approximately only one-third of its oxygen to the tissues but may, when the demand exists, give up much more. Studies on the volume flow of blood, which have been facilitated by the nitrous oxid method of Krogh and Lindhard, indicate