The use of water containing tritium (a radioactive isotope of hydrogen), such that the tritium replaces a stable (i.e. non-radioactive) atom in a compound, making the compound radioactive (e.g. tritium is readily incorporated into DNA during DNA replication). The path taken by such a labelled compound in the biological system can be followed by the radiation it emits (e.g. on an autoradiograph).
Subjects: Zoology and Animal Sciences.