1. Meek, R.L, Bowman, P.D. and Daniel, C.W (1977) Exp. Cell Res. 107, 277–284.
2. Bishop J.M. (1985), TIG Sept. 245-249.
3. MacDonald, C. (1989) CRC Reviews in Biotechnology, in press.
4. Hayflick, L (1965), Exp. Cell Res. 37: 614–636.
5. Chang, S.E. (1986), Biochim Biophys Acta 823, 181–194.