1. Baron, D. N. (1963). Proc. roy. Soc. Med., 56, 173.
2. Bell, J. L., and Baron, D. N. (1960). Clin. chim. Acta, 5, 740.
3. Bennett, H. D., Frankel, J. J., Bedinger, P., and Baker, L. A. (1950).
4. Berk, J. E., Shay, H., Ritter, J. A., and Siplet, H. (1948). Gastroenterology, 11, 658.
5. Dunnet, W. N. (1963). Brit. med. J., 1, 1187.