Section Staining for Electron Microscopy

Epon epoxy resin was introduced as an embedding medium for biological electron microscopy largely through the independent efforts of Finck (1) and Luft (2). The usual recipe involves three components: Epon 812 resin (Epikote 812, in England), an anhydride hardener, and an accelerator such as DMP-30. Since the combination of Epon with dodecenyl succinic anhydride (DDSA) was thought to produce a rather soft cured resin, the addition of a second hardener was recommended. Finck used hexahydrophthalic anhydride (HHPA), while Luft used methyl nadic anhydride (MNA). HHPA is solid at room temperature, so it must be warmed to enable mixing with Epon. Some Epon-HHPA mixtures tend to crystallize on storage. Since these inconveniences are avoided with MNA-containing mixtures, the author has for several years made exclusive use of a mixture of Epon 812, MNA, and DDSA for embedding tissues, employing the proportion 70 per cent Luft's mixture A (Epon-DDSA) and 30 per cent Luft's mixture B (Epon-MNA). Similar mixtures are in preferential use in many laboratories. Recent experiments have indicated an impor-