1. Ardeman, S., and Chanarin, I. (1963). Lancet, 2, 1350.
2. Irvine, W. J. (1966). Clin. exp. Immunol., 1, 99.
3. Davies, S. H., Haynes, R. C., and Scarth, L. (1965). Lancet, 2, 397. R0dbro, P., Christiansen, P. M., and Schwartz, M. (1965). Ibid., 2, 1200.
4. Spray, G. H. (1955). Clin. Sci., 14, 661.
5. Wangel, A. G., and Callender, S. T. (1965). Brit. med. J., 1, 1409.