Studies on Depolarization of Light at Microscope Lens Surfaces

The uniqueness of polarization microscopy lies in the use of light beams with controlled states of polarization. With such beams, optical properties such as birefringence, dichroism, and optical activity are detectable, and optical constants are determinable in an exceedingly small sample volume. Since birefringence and dichroism generally reflect the arrangement or properties of material the dimensions of which lie below the limit of resolution of the light microscope, the polarizing microscope can in principle be used for studying the optically unresolvable "submicroscopic structures" of cells and tissues. Such studies can be made directly on living cells and the submicroscopic events followed as the cells undergo physiological activities. In contrast, the electron microscope gives a vastly improved resolving power and enables a direct visualization of the submicroscopic structures, but only after their fixation and desiccation. The two instruments, therefore, are complementary to one another, and together they make up for each other's shortcomings. Indeed Sj6strand (9, p. 511) has commented on these aspects of electron microscopy, concluding that " . . . the polarized light microscope should be the standard equipment of the electron microscopists. But it has to be used on living cells and it has to be equipped for analyzing very weak birefringence . . . . " Although potentially endowed with such desirable and unique attributes, the polarizing microscope has not yet been used very extensively for studying living cells. This is not due to the absence of a submicroscopic organization in cells, for such has been amply demonstrated by recent electron microscope