A Regulated Differential Fluorometer for the Assay of Oxidative Metabolism in Intact Tissues

A fluorometer is described which records the difference in intensity of the light emitted by a fluorescing sample (the biological specimen) and by a reference material. Stabilization of the instrument was achieved by feedback to maintain constant signal level from the reference source in the presence of severe changes in the intensity of the excitation light. Illumination and comparison of the two fluorescent intensities occurs at half the frequency of the ac driving the mercury arc lamp. The necessity for this feature strongly implies that mutually independent fluctuations occur between the intensities of the two arc-lamp flashes for each ac cycle.