ELECTRON MICROSCOPIC PARTICLE COUNTING IN VIROLOGY .1. CENTRIFUGE TUBES FOR DIRECT SEDIMENTATION OF VIRUS ON SPECIMEN GRIDS

In two types of specially designed centrifuge tubes suspensions of vaccinia virus and polystyrene latex particles were sedimented from columns of known height onto coated specimen grids for electron microscopy. The titers of the suspensions were estimated by counting the particles on grid squares of known dimensions. By means of statistical analysis the reliability of the method was determined and compared with the pseudoreplica technique. Both methods proved to be equally reliable; the pseudoreplica technique required considerably more apparatus and longer preparation time. Similar systematic errors are inherent in both techniques. © 1969 Springer-Verlag.