Air drying as a preparatory factor in cytology: investigation of its influence on dye uptake and dye binding

The effect of air-drying on cytological material is investigated in this article. Smears of rat liver were fixed completely wet and, after air drying, postfixed in ethanol, methanol/formaldehyde/acetic acid (MFA), and formaldehyde. Staining was performed with the thionin-Feulgen procedure, a standard Romanowsky-Giemsa stain with azure B-eosin Y and a Papanicolaou staining variant. The image analysis system IBAS 2000 was applied to evaluate objective criteria of the changes caused by air drying the chromatin texture. Nuclear absorption was measured with a Vickers M 85a Microdensitometer. Air-drying had striking effects on size and shape of cell nuclei (spreading), on the structure of the nuclear chromatin (chromatin condensation), and on the chromaticity coordinates (hue, saturation, and intensity of nuclear staining). The variations of the chromatin texture and dye-substrate affinity are attributed to alterations of the tertiary structure of the nuclear proteins.