Crystal Violet Lactose Agar is recommended for differentiation of pure cultures of pathogenic and nonpathogenic Staphylococci. This medium recommended by Chapman for the differentiation of pure cultures of pathogenic from nonpathogenic strains of Staphylococci. The toxicity of Staphylococci is estimated on the basis of their pigment production, haemolytic and coagulating characteristic. Crystal violet inhibits most of the gram-positive organisms and is markedly inhibitory to Staphylococci. A fair growth can be obtained at a 1: 300,000 concentration of the dye when the medium is inoculated heavily. So, this medium is used for study of pure cultures where a mass inoculation can be used rather than for primary isolation.