Measurement of the Refractive Index of Cytoplasmic Inclusions in Living Cells by the Interference Microscope

Abstract

A METHOD of measuring the refractive index of living cytoplasm by phase-contrast microscopy was recently developed by Dr. R. Barer and his associates^1,2. This method consisted essentially of suspending cells in an isotonic protein medium of the same refractive index as the cytoplasm, which then, by phase-contrast, appeared to match the background in brightness and consequently was almost invisible. This formed the starting-point for the present investigation. Phase-contrast cannot normally be employed for the refractometry of cytoplasmic inclusions, since the refractive index of the cytoplasm that surrounds them cannot be varied at will like that of the medium in which the cells are suspended. When the cytoplasm matches the suspension-medium in brightness, a cell-inclusion that appears brighter will generally have a lower refractive index than the cytoplasm, and conversely; but no accurate quantitative estimate can be made.