1. "Report No. 20 of the;de Blecourt, J.J.; Basart, A.H.M.,1953
2. de Blecourt, J. J., and Basart, A. H. M. (1954). T. Soc. Geneesk., 32, 219.
3. Bohman, F. (1948). Acta med. scand., 132, 150.
4. Dahlberg, G., and Grubb, I. (1951). Acta genet. statist. med., 2, 42.
5. Kalbak, K. (1953). Ibid., 12, 306.