1. W. A. Stoll, Schweiz. Arch. Neurol. Psych.68, 279 (1947).
2. E. E. Van Tamelen, Exper.9, 457 (1953).
3. J. Harley-Mason, Chem. and Ind.1954, 251.
4. N. L. Wendler, Exper.10, 338 (1954).
5. R. Robinson,The Structural Relations of Natural Products (Oxford University Press, London 1955).