1. Weatherall, D. J., Pembrey, M. E., and Pritchard, J., Clinics in Haemat., 3, 467 (1974).
2. Schroeder, W. A., et al., Proc. natn. Acad. Sci. U.S.A., 60, 537 (1968).
3. Schroeder, W. A., and Huisman, T. H. J., Twelfth. Int. Cong. Haematol., Plenary Sessions, 26, Lehmanns, Munich (1970).
4. Weatherall, D. J., and Mclntyre, P. A., Br. J. Haemat., 13, 106 (1967).
5. Alexander, P., Nature, 235, 137 (1972).