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The oxygen saturation of arterial blood in man can be measured continuously in situ by means of bichromatic photoelectric colorimetry of the intact fully flushed ear. The accuracy of the device as determined by gas analysis of arterial blood samples is from 3 to 8 percent. The entire optical and photoelectric system, comprising a miniature lamp bulb, two color filters, and two selenium barrier-layer photo-cells, weighs 30 grams, and slips over the shell of the ear. One of the color filters transmits a wave-length band which is equally absorbed by oxy- and reduced hemoglobin, thus providing a means of measuring the amount of total hemoglobin in the optical path, independent of its degree of oxygen saturation. The other color is very differently absorbed by the two hemoglobin forms. Several direct reading forms of the instrument are discussed.
G. A. Millikan (Thu,) studied this question.