Area changes in slices of rat brain during preparation for histology or electron microscopy

Cerebral slices cut from rat brain, either 2-3 mm or 0.27 mm thick, were used to study the effect of embedding and freezing. Paraffin wax sections 6 micrometer thick were mounted and stained with haematoxylin and eosin or Marsland et al.'s (1954) silver stain, and their areas were examined at each step. Embedding in paraffin wax of slices 2-3 mm thick, or in Epon of slices 0.27 mm thick, caused a diminution of their areas by 20-30%. Staining of paraffin wax sections did not alter their areas. Glycerol alone at 15% concentration had no effect on the areas, but at 30% concentration they were diminished by approximately 20%. Diminution of the areas of glycerol treated slices 0.27 mm thick also occurred when they were transferred to liquid N2 or to isopentane, but the areas increased after glycerol was replaced by Freon 12. It was concluded that embedding or freezing cerebral slices caused changes in their areas, but that staining of sections after they had been embedded, sectioned and mounted did not.