His famous experiment with DelbrÃ 1\/4 ck in 1943 , known as the Luria-Delbr Ã 1\/4 ck experiment , demonstrated that inheritance in bacteria follows Darwinian rather than Lamarckian principles and that mutant genes occurring randomly can still give viral resistance without the virus being present . His famous experiment with DelbrÃ 1\/4 ck in 1943 , known as the Luria-Delbr Ã 1\/4 ck experiment , demonstrated statistically that inheritance in bacteria must follow Darwinian rather than Lamarckian principles and that mutant bacteria occurring randomly can still bestow viral resistance without the virus being present .