Cellular size of bone marrow cells from rats and beagle dogs

The usefulness of cellular size measurement for differentiating erythroid and myeloid cells was investigated using rat and canine bone marrow film prepared by the Cytospin method and Wright-Giemsa staining. 1. In the erythroid series, basophilic and polychromatic erythroblasts were distinguishable in terms of cellular diameter; i.e., 99% of rat and 95% of canine polychromatic erythroblasts were distributed in a range < or = 9.5 microns, at which basophilic erythroblasts did not exist. 2. In the myeloid series, myelocytes and metamyelocytes were to some extent distinguishable by their diameters; in rats, myelocytes (75% of the population) were > or = 13.5 microns, and metamyelocytes (61%) < or = 11 microns; and in dogs, myelocytes (45%) were > or = 16 microns, and metamyelocytes (66%) < or = 12 microns. 3. With regard to the metamyelocytes and myelocytes existing in the same range, their nuclear sizes (width) allowed further differentiation; in rats, the nuclear width of myelocytes (87%) was > or = 5 microns, and that of metamyelocytes (84%) < 5 microns; and in dogs, myelocytes (96%) > or = 7 microns, and metamyelocytes (88%) < 7 microns. The present results indicate that cellular size, together with nuclear size, contribute to distinguish the active mitotic group from less- or non-mitotic group in erythroids and myeloids, thus being helpful for toxicological evaluation on chemicals.