1. Vogt, M., J. Physiol., 123, 451 (1954).
2. Amin, A. H., Crawford, T. B. B., and Gaddum, J. H., J. Physiol., 126, 596 (1954).
3. Sheth, U. K., and Borison, H. L., J. Pharmacol. Exp. Therap., 130, 411 (1960).
4. Clark, W. G., and Borison, H. L., Pharmacologist, 4 (1962).
5. Villablanca, J., and Myers, R. D., Acta physiol. latinoamer. (in the press).