1. Birnstingl, M. A., Shooter, R. A., and Hunt, M. F. (1952). Brit. med. J,2, 253.
2. Bolton, H., Catchpole, B. N., and Jepson, R. P. (1947). Lancet, 2, 608.
3. Buhr, A. J., and Scott, J. C. (1959). Ibid., 1, 1019.
4. Fairbrother, R. W. (1956). Ibid., 1, 716.
5. Goodier, T. E. W., and Parry, W. R. (1959). Ibid., 1, 356.