1. Hunt, D. E., J. Bact., 88, 893 (1964).
2. Mertz, E. T., in Elementary Biochemistry, 68 (Burgess Publishing Company, Minneapolis, Minnesota, 1960).
3. Salton, M. R., J. Gen. Microbiol., 5, 391 (1951).
4. Heinmets, F., Lehman, J., Taylor, W. W., and Kathan, R. H., J. Bact., 511 (1954).
5. Frobisher, jun., M., in Fundamentals of Bacteriology, sixth ed., 132 (W. B. Saunders Company, Philadelphia, 1957).