1. Witkin, E. M., Genetics, 32, 221 (1947).
2. Rörsch, A., Edelman, A., Kamp, C. v. d., and Cohen, J. A., Biochim. Biophys. Acta, 61, 278 (1962).
3. Grula, E. A., J. Bact., 80, 375 (1960).
4. Webb, M. J., Gen. Microbiol., 3, 410 (1949).
5. Ryter, A., and Jacob, F., C.R. Acad. Sci., 257, 3060 (1963).