Effect of N -methyl N -nitroso Urethane on Amoebae

N -METHYL N -nitroso urethane (MNU) is a potent carcinogen which produces tumours in rats and mice after a few or even single doses 1–4 . The possibility that experiments using single cells might give some indication of site and mode of action within the cell led to the following investigation of the effects of MNU on the large free-living mono-nucleate amoeba, Amoeba proteus . These unicellular animals are particularly useful for such studies 5–7 , as they can be grown singly (the fate of each treated amoeba can be followed and studies made on clones arising from them) and they survive well after micrurgy, for example, transfer of nucleus from one individual to another 8 .