Volumes and cellularity in populations of hematopoietic clones.

Volumes of hematopoietic spleen colonies were estimated by measuring parameters of superimposed triaxial ellipsoids. Observations were made on groups of colonies that contained only undifferentiated cells or had differentiated to varying degrees into purely erythropoietic, purely granulocytic or purely megakaryocytic colonies. The average volume occupied by one cell and surrounding matrix, the so-called single cell space, was determined for each type of colony. The estimated colony cellularity was then computed from the measured colony volume and the tabulated single cell space. The techniques of measurement are described. Formulas are provided to estimate mean and variance of volumes and their cell contents. Data on the distribution of spleen colony size and cellularity after seven days of growth are given.