This medium is intended for use in sterility testing of substances in accordance with the United States Pharmacopoeia and European Pharmacopoeia. It is a general purpose medium for the cultivation of both fastidious anaerobic and aerobic micro-organisms. Sodium Thioglycollate and L-cystine are included to reduce the medium to ensure anaerobiosis and to inactivate mercury and other heavy metallic compounds. A small amount of agar is added to further reduce the update of oxygen. However, in the event of oxidation, the medium will turn pink due to the presence of the resazurin. Providing only 30% of the medium has turned pink, the Eh may be restored by heating the medium (once only) in a boiling water bath.