By the 1940s the ideas of inheritance and mutation were generally accepted, though the role of DNA as the hereditary material had not yet been established. It was thought that bacteria were somehow different and could develop heritable genetic mutations depending on the circumstances they found themselves: in short, was the mutation in bacteria pre-adaptive (pre-existent) or post-adaptive (directed adaption)? Luria in particular was obsessed with this idea and was determined to test it. He conceived the experiment at a faculty dance at Indiana University while watching a slot machine.