1. Campbell, W., C., and M. (1952).
2. Battilana D., G. (1948). Rev.
3. Bonham-Carter, R. E., and Lovel, K. W. (1953). Great Ormond St. J., 6, 93.
4. Bonham-Carter, R. E., and Lovel, K. W. and Walker, C. H. M. (1955). Lancet, 268, 272.
5. Brown, J. W., Heath, D., and Whitaker, W. (1955). Circulation, 12, 819.