1. Cleland, W. P. (1956). J. thorac. Surg., 32, 813.
2. Engberg, H., and Hansen, J. L. (1953). Acta tuberc. scand., 28, 45.
3. Gaensler, E. A., Cugell, D. W., Lindgren, I., Verstraeten, J. M., Smith, S. S., and Strieder, J. W. (1955). J. thorac. Surg., 29, 163.
4. Jackson, C. A., and McCann, J. J. (1956). Tubercle (Lond.), 37, 36.
5. Laird, R., and Stephens, T. W. (1953). Ibid., 34, 68.