Factors which influence light microscopic visualization of biological material in sections prepared for electron microscopy

Epoxy-embedded biological material, sectioned for conventional or high-voltage electron microscopy, can be visualized within the section with good contrast and detail by phase-contrast or dark-field light microscopy. The (phase) contrast of such material is not substantially influenced by the type of embedding resin or section support substrate. It is, however, influenced by the type of fixation, by heavy metal (uranyl and lead) staining and by the section thickness. After screening ultrathin and semithin sections for content with the light microscope, one need stain and examine only those grids containing sections of interest. This approach eliminates the need to screen sections with the electron microscope and, in some cases, the need to stain non-useful sections. This time-saving procedure is particularly useful for studies requiring ultrastructural examination of a selected area or structure which is large enough to be visualized with the light microscope but which comprises only a small volume of the embedded material.