Panel 43. The rubella virus is a small enveloped virus (about 1/50000th of a millimeter in diameter), containing an icosahedral capsid. In this photograph obtained by negative staining, the envelope has been colored in purple, and the capsid colored in green. The capsid is not visible in all viruses, only in those that have been slightly permeabilized during deposition on the electron microscopy grid, allowing the metal salt to penetrate the particle. This virus is strictly human.