A reliable and easily sectioned epoxy embedding medium

Sections for electron and light microscopy were easily prepared from mixtures of Dow Epoxy Resins 332 and 732 (D.E.R. 332 and D.E.R. 732) cured with dodecenyl succinic anhydride (DDSA) and DMP‐30. The most useful formula contained 46.7% D.E.R. 332, 20% D.E.R. 732, and 33.3% DDSA, plus 2% DMP‐30. Stronger sections were derived from a preparation containing 31.6% D.E.R. 332, 15.8% D.E.R. 732, and 52.6% DDSA, plus 2% DMP‐30. Harder resins were made by reducing the amount of D.E.R. 732 incorporated in the mixtures. When prolonged infiltration was required polymerization was slowed by substituting DMP‐10 in place of the more reactive DMP‐30. Compressed sections were easily restored to their proper size by the vapors of chloroform, dichloroethylene or xylene. The sections were strong enough to withstand intense electron beams on bare 150 mesh copper grids. The inherent contrast was good without staining, but additional contrast was obtained by brief treatment with aqueous solutions of lead or uranyl salts. Sections for light microscopy could be stained by water soluble basic dyes.