1. Adler, T.K.: The comparative potencies of codeine and its demethylated metabolites after intraventricular injection in the mouse. J. Pharmacol. exp. Ther. 140, 155 (1963).
2. Ariens, E.J.: Receptor theory and structure-action-relationships. Advanc. Drug Res. 3, 235–285 (1966).
3. Beckett, A.H.: Analgesics and their antagonists: some steric and chemical considerations. J. Pharm. Pharmacol. 8, 848–859 (1956).
4. Blane, G.F., Dobbs, H.E.: Distribution of tritium labelled etorphine (M 99) and dihydromorphine in pregnant rats at term. Brit. J. Pharmacol. 30, 166–172 (1967).
5. Boura, A.L.A., Fitzgerald, A.E.: The pharmacology of N-(-cyclopropyl-methyl)-19-isopentyl-norovinol hydrochloride. A potent and long lasting central depressant. Brit. J. Pharmacol. 26, 301–321 (1966).