Lyophilized powder. Reconstitute with 20 ml (100 ml or 1 L) of dH2O before use. The product will give a 10% (v/v) suspension of fixed and killed Staphylococcus aureus, Cowan I strain, in 10 mM phosphate buffered saline, pH 7.4 containing 0.05% thimerosal as preservative.