Conceptions of the causes of ill health show marked historical changes. With the recognition of the social problems attendant on industrialization, investigators in England and France studied the influence on health of poverty, occupation, housing and other factors. In Germany a group of physicians, Virchow prominent among them, subscribed to the view that social and economic conditions have an important effect on health and disease and must be subjected to scientific investigation (Virchow 1958). These investigations should form the basis of health policy (Morris 1974).