Estimation of the proportion of cell nuclei in tissue sections falling within tritium-autoradiographic range

Comparisons between the observed proportions of 3H-thymidine-labeled nuclei of different diameter-classes from autoradiographs of thick tissue sections result in gross misrepresentation of the data because the probability that a nucleus in the section falls within the 3H-autoradiographic range depends directly on the diameter of the nucleus in question. A mathematical formula is given to compute the proportion of nuclei in thick sections falling within 3H-range. Standard curves are provided for different values of section thickness, nuclear diameter and 3H-autoradiographic range. The formula is valid for determination of the proportion of all spherical structures falling within a thin slice of a thick section.