1. Azo, K., and Yoshida, R., Proc. First Int. Congr. Soil Sci., 3, 150 (1928).
2. Jensen, V., and Petersen, E. J., Roy. Vet. and Agric. Coll., Copenhagen, Den., Yearbook, 107 (1955).
3. Petersen, E. J., Roy. Vet. and Agric. Coll., Copenhagen, Den., Yearbook, 70 (1959).
4. Eisenstark, A., Ward, C. B., and Kyle, T. S., J. Bact., 60, 525 (1950).
5. Lawson, G. J., and Stacey, M., J. Chem. Soc., 1925 (1954).