1. Casals, J., Ninth Intern. Cong. Microbiol. Moscow, Symposia, 441 (1966).
2. WHO Scientific Group, Technical Report Series, No. 369 (1967).
3. Ann. Inst. Pasteur, 109, 625 (1965).
4. Atoynatan, T., and Hsiung, G. D., Proc. Soc. Exp. Biol. and Med., 116, 852 (1964).
5. Haldane, J. B. S., Nature, 187, 879 (1960).