1. Streptococcus viridans is of extremely low virulence for white mice and rabbits.
2. The serum of rabbits, after a series of intravenous injections of dead or living Streptococcus viridans, is poor in complement fixative substance (fixateur of Besredka) for Streptococcus viridans.
3. Antigens prepared from several strains of Streptococcus viridans are relatively poor in fixable substance.
4. The technique of complement fixation tests for infection with Streptococcus viridans is so laborious and difficult that the method will not be available for general clinical work.