1. Cameron, A. (1959). Brit. med. J., 2, 1291.
2. Cardell, B. S., and Hanley, T. (1951). J. Path. Bact., 63, 587.
3. Cooke, W. T., Cloake, P. C. P., Govan, A. D. T., and Colbeck, J. C. (1946). Quart. J. Med., New Series, Vol 15, 39, 47.
4. Harrison, C. V. (1948). J. clin. Path., 1, 197.
5. Harrison, R. J., Harrison, C. V., and Kopelman, H. (1955). Brit. med. J., 2, 1593.