The chief characteristics of the blood of the turtle Pseudemys concinna, considered as a system for the transport of oxygen and carbon dioxide, are its low corpuscular content (10 to 22 per cent by volume) and its high concentration of base bound as bicarbonate. These characteristics account fully for the shape and position of the carbon dioxide dissociation curve, the effect of oxygenation and reduction of the hemoglobin upon the carbon dioxide-combining power of the blood, and the distribution of carbon dioxide between the corpuscles and plasma. The oxygen-combining capacity of the turtle corpuscles does not differ from that of an equal volume of human erythrocytes. The oxygen dissociation curve is similar to that of mammalian blood and is affected in like manner by the quantity of carbon dioxide present. Its exact shape and position depend in part upon the number of corpuscles in the blood; in part its characteristics cannot be attributed to known chemical factors.