1. Gaarder, A., Jansen, J., Laland, S., Hellem, A. J., and Owren, P. A., Nature, 192, 531 (1961).
2. Born, G. V. R., and Cross, M. J., Nature, 197, 974 (1963).
3. Hellem, A. J., Scand. J. Clin. Lab. Invest., 12, Suppl. 51 (1960).
4. Williamson, J. R., Prog. Med. Lab. Tech. (edit. by Baker, S.), 41 (Butterworth and Co., Ltd., London, in the press).
5. Regoli, D., and Clark, V., Nature, 200, 546 (1963).