A Method of Enumeration of Individual Marrow Elements for Research Purposes
J. Sharp, E. L. Feinmann, JOHN FREDERICK WILKINSON · Biometrics · 1952
IN any study requiring the assessment of quantitative changes of a particular cell type in a suspension of mixed marrow elements, a method is essential whereby these cells may be counted with a known degree of accuracy. This problem was encountered in experiments designed to investigate the possible presence of a factor in pernicious anaemia serum affecting the rate of maturation of erythroblasts cultured in vitro, as reported by several workers (Rusznyak et al 1947, Lajtha 1950, Thompson 1950). Our results are presented elsewhere (Feinmann, Sharp and Wilkinson, 1952). In these experiments it was necessary to count absolute numbers of certain erythroblasts to a known degree of accuracy in order to determine whether observed differences in changes in their numbers on culture in different media were significant. The method of counting is described in detail since, with suitable modification, it has more general application. When it is not possible to count directly the number of cells in a known volume of fluid, the absolute number of a cell type per unit volume is derived by determining its proportion on smears and relating this to the total cell count. It is well known that in smears prepared on slides, the larger cells appear more frequently at the ends and edges of the smear than in the centre (Stephens et al 1920, Napier 1922, Gyllenswaird 1929, Boveri 1939, Dacie 1950). Methods of sampling of the slide, giving reasonably constant estimates of the proportion of a cell type on smears from one blood sample, have been devised (Dacie 1950). Our problem required the assessment of proportions of normal and megaloblastic erythroblasts in a marrow suspension, initially and after a period of incubation; during this incubation there might be not only a change in the relative propor-