Meselson and Stahl found that DNA of the first generation of bacteria was hybrid or intermediate (N15 N14). The second generation of bacteria, after 40 minutes, contained two types of DNA, 50% light (N14 N14) and 50% intermediate (N14 N15). The third generation of bacteria after 60 minutes contained two types of DNA, 25% intermediate (N15 N14) and 75% light (N14 N14) in 1:3 ratio. The fourth-generation after 80 minutes contained 12.5% N15 N14 and 87.5% N14N14 DNA in a 1:7 ratio.