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3. R. Melzack and P.D. Wall, ‘Pain Mechanisms: A New Theory’, Science, 150 (1965): 971–9.
4. H. Merskey ‘Psychological Aspects of Pain’, Postgraduate Medical Journal, 44 (1968): 297–306
5. E. Cassell, The Nature of Suffering and the Goals of Medicine (New York: Oxford University Press, 1991), 30–46.