1. Roitt, I. M., and Doniach, D., Brit. Med. Bull., 23, 66 (1967).
2. Cohen, I. R., Globerson, A., and Feldman, M., J. Exp. Med., 133, 834 (1971).
3. Cohen, I. R., and Wekerle, H., Science, 176, 1324 (1972).
4. Cohen, I. R., and Wekerle, H., in Proceedings of the Fourth International Conference on Lymphatic Tissues and Germinal Centers in Immune Reactions (edit, by Jankovic, B. D.) (Plenum Press, New York, in the press).
5. Wekerle, H., Cohen, I. R., and Feldman, M., Nature New Biology, 241, 25 (1973).