1. Anderson, W. F., and Cowan, N. R. (1955). Lancet, 2, 239.
2. Bainton, J. H. (1932). Amer. Heart J., 7, 331.
3. Bakwin, H., and Bakwin, R. M. (1935). Amer. J. Dis. Child., 49, 861.
4. Bedford, D. E., and Treadgold, H. A. (1931). Lancet, 2, 836.
5. Comeau, W. J., and White, P. D. (1942). Amer. J. Roentgenol., 47, 665.