Ames test is a simple method to test mutagenicity of a compound, which is suggested by Dr. Ames. It uses several strains of the bacterium Salmonella typhimurium that carry mutations in genes involved in histidine synthesis, so that they require histidine for growth. The variable being tested is the mutagens ability to cause a reversion to growth on a histidine-free medium. [Bruce N. Ames, E. G. Gurney, James A. Miller, and H. Bartsch (1973). Carcinogens as Frameshift Mutagens: Metabolites and Derivatives of 2-acetylaminofluorene and other Aromatic Amine Carcinogens. PNAS 69: 3128-213] [ Ames,B.N. et al. PNAS. 1972, 69, 3128. ]