CONDITIONS INFLUENCING THE INTENSITY OF THE FEULGEN REACTION

Hydrolysis in 5 N hydrochloric acid at room temperature is preferable to the conventional Feulgen hydrolysis in 1 N HCl at 60°C. The intensities achieved are less critically dependent on time and temperature and the maximum Feulgen values obtained may be significantly higher than after the latter procedure. However, the shape of the 5 N hydrolysis curve is dependent on the fixative and preparative procedures used and it may vary from experiment to experiment. The small lymphocyte, which has previously been found by several workers to bind about 10% less Feulgen dye than other diploid cells, was found to have a similar lower Feulgen intensity after 5 N HCl hydrolysis at room temperature. Isolating leukocyte nuclei or extracting their acid-soluble nuclear proteins failed to cause a significant elevation in the amount of Feulgen dye found.