Ecbovirus type SA-l, a bovine enterovirus, has been purified and crystallized and its chemical composition, physical characteristics and morphology studied. The virus particles have a mean diameter of 230Å, a sedimentation constant of 152S, a diffusion constant of approximately 1.7 x 10⁻⁷ cm² sec⁻¹ and a particle weight of about 6.1 x 10⁶ daltons. Its capsid consists of a number of identical subunits, probably 32, arranged in icosahedral symmetry and enclosing the nucleic acid component which comprises about 30 per cent of the total weight.
Infective ribonucleic acid could only be isolated from infected cells. It has a sedimentation constant of approximately 37S corresponding to a molecular weight of about 2 x 10⁶, and consists of single-stranded RNA. The presence of a small amount of infective double-stranded RNA could also be demonstrated. In its physical characteristics and appearance, therefore, the virus is practically indistinguishable from polio- and other enteroviruses. The small differences in size found by different authors for various enteroviruses are probably insignificant and due to experimental error.