Use of Geiger Counter for Quantitative Estimation of Phosphorus-32 in Histological Sections

IN a recent communication 1 details were given of a method for the quantitative estimation of radioactive isotopes in histological sections. A similar piece of apparatus was made by me some time ago for investigating the distribution of phosphorus-32 in sections of human enamel. In order to determine exactly what portion of the enamel was over the scanning hole, a low-voltage lamp and mirror were arranged inside the castle to throw a beam of light out through the hole. The mirror was mounted on a sliding rod, so that it could be pulled to one side of the counting tube. A microscope was arranged horizontally to view the scanning hole and the specimen ; the general arrangement is shown in the diagram.