TWO-EMULSION RADIOAUTOGRAPHY

Two-emulsion radioautography can distinguish between beta particles emitted from C 14 atoms and those originating in H 3 atoms. It uses two layers of sensitized emulsion separated by an inert layer of celloidin: the C 14 beta particles, because of their longer range, are recorded in the second emulsion, but the beta particles from tritium are arrested by the first emulsion. Experiments have shown that the combination of two NTB emulsions separated by a celloidin layer is the most satisfactory. The total thickness of the radioautograph is 19 µ. The first emulsion plus the celloidin layer measure together 12 µ in thickness and decrease by 38% the flux of C 14 beta particles reaching the second emulsion. Staining of the specimen with Mayer's hematoxylin and eosin and celloidin coating follow the exposure and processing of the first emulsion. The second emulsion is applied after the celloidin coating and processed after a suitable second exposure. By using a tritiated precursor of DNA and a C 14 -labeled precursor of RNA or proteins, or viceversa, two-emulsion radioautography can be applied to investigate two distinct metabolic processes occurring at the same time in the same cell.