1. L. P. Naidovich, B. K. Rostotskii, and P. N. Kibal'chich, Farmatsiya, No. 5, 1970.
2. C. Rudel, Arch. Pharm.,229, 631, 1891.
3. H. Pommerehne, Arch. Pharm.,233, 127, 1895.
4. H. M. Jordin, Arch. Pharm.,240, 146, 1902.
5. T. A. Henry, The Plant Alkaloids [Russian translation], Moscow, 1956, p. 340.