1. Thomasson, H. J., Intern. Z. Vitaminforsch., 25, 62 (1953).
2. Iongh, H. de, and Thomasson, H. J., Nature, 178, 1051 (1956).
3. Klenk, E., and Bongard, W., Z. physiol. Chem., 291, 104 (1952). Klenk, E., and Lindlar, F., Z. physiol. Chem., 299, 74 (1955).
4. Mead, J. F., and Howton, D. R., J. Biol. Chem., 229, 575 (1957). Howton, D. R., and Mead, J. F., ibid., 235, 3386 (1960).