Differentiation of the segmented tubular nephron and excretory duct during lamprey metamorphosis
- John H. Youson
- Anatomy and Embryology
Small s t ructures or lesions are frequently difficult to find and identify for electron microscopic study. Pathologists in par t icular need an orderly procedure to reduce the t ime spent in random searching. In the method described here a relat ively large block of tissue, which is expected to contain the desired focus, is initially fixed and embedded. From the methacryla te-embedded tissue a thick section is then cut and stained for a few seconds with toluidine blue. When the lesion or s t ructure is located with the l ight microscope, the block is t r immed to a small area including the lesion and then sections are cut for electron microscopy. This method offers several advantages. I t enables rapid localization of desired lesions whilc sectioning. I t ensures t h a t the lesion is in t ha t portion of the block t r immed for th in sections. The small area of the sections ul t imate ly used reduces the t ime spent with the electron microscope hunt ing for the lesion and it also facilitates cut t ing the th innest sections. In addit ion, the method allows determinat ion of the dep th and adequacy of the zone of opt imal fixation in the original block. Examinat ion of such sections by light microscopy often reveals details not seen in usual paraffin sections. E nhancem en t of detail may be obtained wit h phase microscopy, as others have observed. Various s taining procedures have been adapted by others for osmium-fixed tissues embedded in methacry la te (1 4). These do not seem to have both the rapidi ty and clarity of the method described here. Some more t ime-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.