Egg albumin embedding: A procedure compatible with neurological staining techniques

Abstract

A water-soluble embedding medium for frozen sections of central nervous system and peripheral nerves which will tolerate on-the-slide alcohol dehydration, xylene clearing and synthetic resin mounting can be prepared by dissolving 20 gm of powdered egg albumin in 30 ml of distilled water. Formalin-fixed, thoroughly washed tissue is immersed in the albumin solution for several hours and then embedded in it. For embedding, a two-layered box is constructed with an inner layer of vegetable parchment paper. This is supported by an outer layer of aluminum foil with 6-8 perforations about 0.5 nun in diameter in its bottom. Hardening of the tissue-albumin block is achieved by formalin dialysis through the parchment paper when the box is stood for 24-48 hr in a layer of 25% formalin that wets only the bottom of the box. Frozen sections from such blocks are compatible with Nauta silver impregnations for degenerating axons, Cajal's gold chloride-sublimate for astrocytes and Pen-field's modified silver carbonate for oligodendroglia and microglia. These, as well as Nissl and myelin sheath preparations show minimal shrinkage and distortion.