The Identification of Labelled Structures on Autoradiographs

Abstract

THERE is no agreed method of deciding whether or not a given structure is radioactive from its autoradiograph. Some authors require that a cell, for instance, should have five or more overlying grains to be considered labelled, whereas others are satisfied with three or four grains. By setting such an arbitrary limit, the experimenter risks accepting as labelled some non-radioactive cells which, by chance, have a higher number of background grains over them, and risks rejecting as unlabelled those radioactive cells which have failed to give rise to the requisite number of grains over them. In an ideal preparation with very low background and high grain densities over radioactive structures, the error introduced by this arbitrary definition of labelling is likely to be small. The smaller the differences between the mean grain densities over background and over the radioactive sources, however, the greater this error becomes.