Autoradiographic thymidine-3H activity after successive steps of the Feulgen reaction.

Autoradiographs were prepared of sections of the ovary of Dytiscus marginalis labelled with thymidine-3H after each successive step of the Feulgen reaction and after treatment with each separate component of the Schiff's reagent. Results of grain counts over ovarian nurse cells showed that losses of thymidine-3H activity occur not only during hydrolysis but also during the successive steps of the Feulgen reaction. It is suggested that the latter decrease in radioactivity may depend on the extraction of fragments of apurinic acid from the sections. An emulsion desensitizing effect has also been observed in sections stained with basic fuchsin alone; this effect appears, however, to be strongly counteracted by the metabisulphite present in the Schiff's reagent.