1. Campbell, J. (1958). Thorax, 13, 177.
2. Caplan, A. (1953). Ibid.,8, 29.
3. Christiaens, L., Balgairies, E., Foubert, P., Aupetit, J., and Grailles, M. (1954). Rev. Rhum., 21, 1.
4. Clerens, J. (1953). Arch. belges Med. soc., 11, 336.
5. Colinot, E. (1950). Acta physiother. rheum. belg., 5, 185.