A new, variable phase contrast microscope, the PolanretTM, has been developed which is particularly suited to the optical screening of thin sections for electron microscopy with regard to tissue orientation and section quality.

By preliminary examination, defects in preparation of the specimen can be discovered immediately after sectioning and prior to staining or examination with the electron microscope. Such examination of unprocessed sections which are thinner than conventional light microscopy sections is possible because the Polanret TM system can make exceptionally small differences in optical path. Using the PolanretTM microscope, the phase and amplitude can be adjusted continuously so as to achieve optimum specimen contrast. The microscope can thus be used to visualize specimen defects and intracellular details in a way which conventional phase microscopy is unable to do.

This preliminary screening technique was evaluated for its usefulness in detecting microtome knife defects, i.e., scratches and chatter, so that corrective measures could be taken.