Abstract
An "oximeter," intended primarily for measuring colorimetrically the oxygenation of circulating blood in living tissues, has been tested on blood contained in glass absorption cells. The instrument reading is shown to depend not only on oxygenation but also on the total amount of pigment (haemoglobin) in the light path, and thus a single calibration curve is only acceptable if this amount is constant. Comparison of the optical density of whole blood with a sample in which the haemoglobin has been released from the corpuscles into homogeneous solution reveals the large contribution to the total light extinction which derives from scattering effects in whole blood. This factor, together with instrumental deficiencies, limits severely the accuracy of measurements with this type of oximeter on blood within the circulation, and the accuracy of the method on whole blood in glass absorption cells is estimated as ±8% oxygen saturation.