Luria and Delbrück (1943)—the Fluctuation Test. It's an excellent description and there's a personal touch.
John Dennehy [The Fluctuation Test and Jonathan Eisen [Luria and Delbrück] also picked the same paper. That means it must really be a "must-read"! (I agree.)
Given that the early history of molecular biology is no longer being taught, I imagine that there are quite a few of you who have never heard of Max Delbrück (1906-1981) or Salvador Luria (1912-1991) in spite of the fact they are Nobel prize winners. Here's some of my posts on them ....
The Velvet Underground of Molecular Biology
Nobel Laureates Max Delbrück, Alfred D. Hershey, Salvador E. Luria