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2. Baird, D. and Illsley, R. (1953). Ibid., 46, 53.
3. Douglas, J. W. B. (1950). J. Obstet. Gynaec. Brit. Emp., 57, 143.
4. "Classification of Occupations;Ferguson, T.; Logan, J.C.;Glasg. med. J; Joint Committee of the Royal College of Obstetricians and GynaecDlogists and the,1953