1. Armstrong, D., Jepson, J. B., Keele, C. A., and Stewart, J. W., J. Physiol., 135, 350 (1957).
2. Margolis, J., J. Physiol., 137, 95 (1957).
3. Stewart, J. W. (personal communication).
4. Ratnoff, O. D., and Colopy, J. E., J. Clin. Invest., 34, 602 (1955).
5. Biggs, R., Sharp, A. A., Margolis, J., Hardisty, R. M., Stewart, J. W., and Davidson, W. M., Brit. J. Haematol (in the press).