Evaluation of Feulgen reaction performed on unfixed smears.

Feulgen reaction--both the original one with Schiff reagent and the modified one with toluidine- or methylene blue, pH = 4.0--can be carried out on air-dried smears without fixing. Hydrolysis--5 n HCl at room temperature should be 15 to 20 min for the original and 5 to 10 min--for the modified reaction. Binding of the dyes is stoichiometric in both cases.