Embedding in epoxy resins for ultrathin sectioning in electron microscopy.

Fixed tissue is dehydrated with tertiary butyl alcohol overnight. The following day it is cleared in toluene, infiltrated and embedded in Araldite resin-hardener-accelerator mixture without dibutyl phthalate, and polymerized at 60° C. More rapid than previous techniques, this method gives blocks which do not fracture unduly on trimming and provides sections of soft tissues at 1 μ for phase contrast microscopy, as well as ultrathin sections which cut as easily with glass knives as sections of methacrylate. Araldite manufactured in the U.S.A. and in England are different. Satisfactory proportions for the American are: hardener DDSA, 3.5 ml; casting resin 6005, 5.0 ml; accelerator B, 0.12 ml. For the British product, these are: hardener 964 B, 5.0 ml; casting resin M, 5.0 ml; accelerator 964 C, 0.25 ml. The use of 2% agar for orienting small specimens in Araldite is feasible. Mallory's borax-methylene blue has been applied to the staining of Araldite sections as thin as 0.5 μ mounted on glass slides.