1. Abruzzo, J. L., and Christian, C. L. (1961). J. exp. Med., 114, 791.
2. Aho, K., and Wager, 0. (1961). Ann. Med. exp. Fenn., 39, 79.
3. Ball, J., De Graaff, R., Valkenburg, H. A., and Westendorp Boerma, F. (1962). Arthr. and Rheum., 5,55.
4. Bartfeld, H. (1960). Ann. intern. Med., 52, 1059.
5. Bloomfield, N. (1960). J. Lab. clin. Med., 55, 73.