Abstract
Continuous-flow zonal ultracentrifugation is now established as an invaluable technique for rapidly concentrating, and largely purifying, milligram amounts of infectious virus from very large volumes of tissue culture fluid (Cline, Nunley & Anderson, 1966; Toplin, 1967; Cline et al. 1967; Fox et al. 1967). The quantities of virus thus obtainable are potentially of use for chemical and physical studies of virus nucleic acid and protein or for production of vaccines. However, for many purposes, sufficient virus can be obtained from volumes of tissue culture fluid of the order of 1 l., whereas continuous-flow zonal rotors are most suited for handling volumes of 5 l. and upwards. Moreover, a continuous-flow rotor is a specialized piece of equipment and so is available in relatively few laboratories. Batch-type zonal rotors, on the other hand, are much more widely available since they are used for separating a variety of subcellular components (Anderson et al. 1967).