Abstract
1. The influence of certain variables upon the shape of the Feulgen absorption curve of mouse liver nuclei has been studied in situ using cytophotometric equipment. The accuracy and reproduciblity of the cytophotometer was ascertained by various procedures.
2. The absorption curve usually is represented by a primary peak at about 585 mµ and a slight secondary peak at about 550 mµ. Reduction or removal of nuclear protein by extraction or enzymatic procedures does not alter the shape of the curve.
3. Variations in hydrolysis times do not alter the shape of the curve obtained with nuclei fixed in Zenker's fluid. There are some differences indicated around the secondary peak of formalin-fixed tissue following different hydrolysis times.
4. Comparison of absorption curves of nuclei fixed in different fixatives shows negligible differences.
5. There are no differences in the absorption curves of nuclei isolated in one per cent citric acid and in nuclei isolated in 0.88 M sucrose.