Shadow Casting of Stained Virus Bodies to Enhance Visibility by Light Microscopy

Materials used for study were viral smears or ultra-thin sections containing viral cell inclusions. They were stained with the Feulgen reaction and other cytochemical procedures. Stained preparations were dried and then shadow-cast with metallic chromium for 30 seconds in a bell jar with a vacuum of at least 0.1 µ (10^-4mm.) of mercury, and placed at a shadowing angle of 10-12°. Shadow-cast preparations were cleared with xylene and mounted in Canada balsam. Dried smears or deparaffinized sections without staining were suited to this method also. A virus which stained indistinctly with cytochemical procedures alone could be adapted to visible light microscopy by shadowing, and in addition, used for observations on its chemical composition.