SUMMARY

The virus of vesicular stomatitis is shown to exist as a system of several particle forms. Two major particles, the ‘bullet ’ and ‘cap’, appear in electron micrographs in various states as outer structural layers are absent or lost. High infectivity is not associated with particles of one form. The distribution of particle forms is apparently determined by cultural condi-tions and is not significantly modified by the preparative procedures employed. The morphology of the several components of the virus system is described