SUBPOPULATIONS OF BLOOD LYMPHOCYTES DEMONSTRATED BY QUANTITATIVE CYTOCHEMISTRY

The cell coats of glutaraldehyde-fixed blood lymphocytes from guinea pigs have been stained with Thorotrast and examined by electron microscopy. The lymphocytes have been classified into three groups with respect to the concentration and distribution of colloidal particles over their surfaces. The average number of particles per micron length of cell surface membrane, the particle density, has then been measured for each class of cells. These values are distributed into two clusters separated by a gap. A new statistical test for bimodality has been devised to evaluate the significance of such a gap in terms of its "dip intensity." The results of this analysis demonstrate the existence of at least two distinct populations of blood lymphocytes, indistinguishable by other morphologic criteria.