A Rapid Method for Localization of Tissue Structures or Lesions for Electron Microscopy

microscopy. This method offers several advantages. It enables rapid localization of desired lesions whilc sectioning. It ensures that the lesion is in that portion of the block trimmed for thin sections. The small area of the sections ultimately used reduces the time spent with the electron microscope hunting for the lesion and it also facilitates cutting the thinnest sections. In addition, the method allows determination of the depth and adequacy of the zone of optimal fixation in the original block. Examination of such sections by light microscopy often reveals details not seen in usual paraffin sections. Enhancement of detail may be obtained wit h phase microscopy, as others have observed. Various staining procedures have been adapted by others for osmium-fixed tissues embedded in methacrylate (1 4). These do not seem to have both the rapidity and clarity of the method described here. Some more time-consuming special stains may be necessary to identify specific substances or lesions. The facility with which toluidine blue can be removed from the section allows the same slide, if necessary, to be used for other more complex stains.