Tritium-labelled Araldite as an internal standard for quantitative autoradiography using the electron microscope

A method is described for making quantitative measurements of radioactivity from electron-microscope autoradiographs. Autoradiographs are made from sections of tissue which contain a seam of tritium-labelled Araldite of known radioactivity. The latter serves as an internal standard and an estimate of the tissue activity is obtained by comparing the tissue grain density with that over the standard. The method can avoid many of the problems which are commonly encountered in making quantitative measurements of tissue radioactivity.