A photoelectric ear densitometer for continuously recording the arterial concentration of T-1824 in the dye-dilution method.

To eliminate the collection of serial samples of arterial blood an instrument has been developed which records dye-dilution curves by measuring changes in optical density of a segment of a heatflushed ear. Comparison with curves from arterial samples shows close similarity in the shape of the curves, and good agreement between the cardiac outputs calculated from them. Other advantages of the technic are the relatively small close of dj'e needed, the linear relation between deflection of the recording galvanometer and changes in dye concentration in the blood, and the fact that determinations can be repeated several times at intervals of three or four minutes.