1. Motulsky, A. G., Human Biol., 32, 28 (1960).
2. Flatz, G., and Nelson, E. R., Med. Arts Sci., 14, 130 (1960).
3. Vella, F., Experientia, 17, 181 (1961).
4. Motulsky, A. G., and Campbell, J. M., Blood (in the press).
5. Kidson, C., Nature, 190, 1120 (1961).