1. Abassy, M.A. (1937).Biochem. J., 31, 339.
2. Borst, J. G. G. (1948).Acta med. Scand., 130, Supp. 207.
3. Cathcart, E. S. and Williams, I.T.D. (1955).Clin. Sci., 14, 121.
4. Evans, W. (1938).Lancet, i, 308.
5. Kenawy, M. R., El-Habawy El-Mohandis, M. M., El-Dine Rohayer H. K. and Abdel-Wahab El-Sheehy (1952).Int. Z. Vitaminforsch., 24, 40.