Abstract
Recent reports have described the similarities and differences in the composition and occurrence of infectious virions and empty capsids (or top components) of several small RNA viruses (Maizel, Philips & Summers, 1967; Longley & Leberman, 1966; Fabiyi, Engler & Martin, 1964; Halperen, Eggers & Tamm, 1964). A previous report (Breese & Graves, 1966) on observations of crystalline arrays of foot-and-mouth disease virus type A, strain 119, has been followed by extensive experimentation with three field strains from Argentina (A1, O2 and C3, CANEFA), which have had fewer tissue culture passages. An effort was made to find a combination of multiplicity of infection, time of harvest, and cell culture which would regularly result in the observation of crystalline arrays of virus particles. During the course of these studies, the A1 strain was found to form arrays of both complete and recently described empty particles.