1. Cells were grown for two generations in a culture medium containing tritiated thymidine
1. Thymidine consists of the base thymine, which is used by E.coli to make nucleotides for DNA replication
2. Tritiated thymidine contains tritium, a radioactive isotope of hydrogen
3. Hence, E.coli incorporated these bases into their DNA d replication, making it fully radioactive after a few generations
2. Cell walls were digested by the enzyme lysozyme, releasing the free-flowing DNA
3. DNA was fixed into position onto a dialysis membrane
4. Thin film of photographic emulsion was applied to the surface of the membrane an left in darkness for two months
1. Some of the tritium atoms in the DNA decayed and emitted high energy electrons, which reacted with the film
5. After two months, the film was developed an examined in a microscope
1. Visible black dot appeared at each point where a tritium atom decayed, showing the length and shape of DNA