1. Belcher, J. R. (1950). Brit. J. Surg., 38, 121.
2. Carter, M. G., and Strieder, J. W. (1950). J. thorac. Surg., 20, 613.
3. Gebauer, P. W. (1950). Ibid., 19, 604.
4. Gravel, J. A. (1954). Ibid., 27, 244.
5. Jackson, T. L., Lefkin, P., Tuttle, W., and Hampton, F. (1949). Ibid., 18, 630.