1. Cohen, S., and Milstein, C., Adv. in Immunol. (in the press).
2. Hilschmann, N., Hoppe-Seyler Phys. Chem., 348, 1077 (1967).
3. Hood, L., Gray, W. R., Sanders, B. G., and Dreyer, W. J., Cold Spring Harbor Symp. on Quant. Biol. (in the press).
4. Milstein, C., Biochem. J., 101, 352 (1956).
5. Putnam, F. W., Titani, K., and Whitley, E., Proc. Roy. Soc., B, 166, 124 (1966).