1. Drescher, J., and Schrader, K., Amer. J. Hyg., 79, 218 (1964).
2. Tyrrell, D. A. J., Head, B., and Dimic, M., Brit. J. Exp. Path., 48, 513 (1966).
3. Drescher, J., and Gillissen, A., Zbl. F. Bakt. I. Orig., 200, 480 (1966).
4. Gillissen, G., and Drescher, J., Zbl. F. Bakt. I. Orig., 201, 65 (1966).
5. WHO Tech. Rep. Ser., No. 71, 23 (1953).