Abstract
A new method is proposed to study the secondary structure of deoxyribonucleic acid (DNA) in situ in fixed chromatin. It is based on acriflavine staining and on differentiation with a nitrous acid solution of the fixed cytologic preparation. The presence of green fluorescence after this treatment is regarded as indicative of double stranded DNA. Experiments are described with DNA-acriflavine mixtures in solution, DNA-agar models and cytologic preparations submitted to different pretreatments. The feasibility and limitations of the method are discussed in the light of the results reported upon.