Polyvinyl Alcohol with Cadmium Iodide and Fructose as an Aqueous Mounting Medium

An aqueous histologic and cytologic mounting medium containing polyvinyl alcohol, cadmium iodide and fructose is described. It is used in the preparation of permanent slides and may be applied to sections stained and rinsed in water or in any concentration of ethyl alcohol. The medium forms a hard, tough, quick-drying film which adheres well to the slide and cover glass. It is nonfluorescent, clear, optically homogeneous, and isotropic; it does not admit bubbles under the cover glass or crystallize on drying. It prevents or minimizes the bleeding of many stains from the sections; a list of 60 dyes, mostly basic, is given. The fresh medium has a pH of 4.4. The refractive index of the fresh medium is n_D²⁰ 1.4674; the dried film is n_D 1.6020 which may be lowered to n_D 1.5150 by decreasing the cadmium iodide in the formula. The viscosity at 25°C. is 7,299 centipoises. The medium has the following composition: distilled water, 40 g.; cadmium iodide, 34 g.; polyvinyl alcohol (Elvanol 51-05, du Pont's low viscosity grade) 18 g.; fructose, 8 g. The medium is prepared as follows: wash the polyvinyl alcohol with absolute methyl alcohol; dry and then grind in a mortar; dissolve the cadmium iodide in the water; add the polyvinyl alcohol while stirring with a speed-controlled motor-driven mixer; heat to 75°C. on a water bath with continuous stirring until dissolved; remove from the water bath and add the fructose while stirring; replace water lost by evaporation. The medium is ready for use when the foam has dispersed after standing.