AN EMBEDDING TECHNIQUE FOR ELECTRON MICROSCOPY USING EPON 812

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Abstract
EPON 812 may be used for dehydration with little effect on the fine structure of a variety of cells. Endoplasmic reticulum and other organelles appear undamaged. The exact mechanism of tissue dehydration by ascending concentrations of EPON 812 is not clear but it is probably similar to that of alcohol. Because EPON 812 is miscible with water (40% by volume), the initial dehydration mixture should contain slightly less than 40% water. The specimen may be transferred from the buffered rinse solution to 100% EPON 812 without deleterious effect on the fine structure. EPON 812 has limited lipid-solvent properties; however, the acid anhydrides and tertiary amine accelerators employed for its polymerization may add to this solvent effect. This effect appears to be much less drastic than that of the conventional solvents employed for routine dehydration, thus making EPON 812 a promising agent for the study of lipid-soluble, histochemical reaction products at the electron microscope level. Sectioning of the embedded material presents several problems; however, with careful attention to technique sufficiently thin sections can be obtained. Prolonging the impregnation period and the polymerization time seems to improve the sectioning properties of the final block. Sections obtained demonstrate considerably less contrast than comparable sections from tissue embedded in methacrylate, presumably because the EPON does not sublime in the electron beam. The decrease in contrast can be overcome by subsequent staining with heavy metals.

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