This medium is recommended for differential and selective isolation of Salmonella and Shigella species from pathological specimens, suspected foodstuffs etc. Lactose is the fermentable carbohydrate. Brilliant green, bile salts and thiosulphate selectively inhibit gram-positive and coliform organisms. Production of H2S gas is detected as an insoluble black precipitate of ferrous sulphide, formed upon reaction of H2S with ferric ions or ferric citrate.