A patient with diabetes mellitus, in the wards of the Peter Bent Brigham Hospital, was observed to have a slight but definite cyanosis, for which no explanation could be found. A sample of venous blood from the arm revealed on analysis a marked increase in the oxygen unsaturation. The venous oxygen unsaturation of several other diabetic patients was found to be similarly though not so markedly increased, and it seemed worth while to study a small group of these patients in this respect.
Accordingly, samples of anticubital venous blood were taken without stasis and under oil from thirty-four unselected diabetic patients, while the patients were at rest in bed, and the samples were analyzed by the method of Van Slyke and Stadie1 for oxygen content and oxygen capacity, the oxygen unsaturation being calculated by subtracting the oxygen content from the oxygen capacity. Duplicate analyses were made in each case. It