1. Ashburn,5F. S., Sewell, W.' H., and Huggins, C. E. (1956). J. thorac. Surg., 31, 618.
2. Botham,' R. J., Dracopoulos, T. T., and Gale, J. W. (1960). Ibid., 39, 202.
3. Chamberlain, J.'M., McNeill, T. M., Parnassa, P., and Edsall, J. R. (1959). Ibid., 38, 727.
4. Chardack,iWJM.,'and MacCallum, J. D. (1953). Ibid., 25, 402.
5. Chardack,iWJM.,'and MacCallum, J. D. (1956). Ibid., 31, 535.