1. Peptic Ulcer in Denmark, Copenhagen, 1953;Alsted, G.;Lancet,1953
2. Bager, B. (1929). Acta chir. scand., 64, Suppl.
3. Dogra, J. R. (1940). Indian J. med. Res., 28, 145. Doll, R., Jones, F. A., and Buckatzsch, M. (1951). Spec. Rep. Ser.
4. Census 1951. Classification of Occupations;med. Res. Coun. Lond., No. 276. H. M. S. O., London;General Register Office,1956
5. Ginanneschi, G. (1938). Med d. Lavoro, 29, 65.