1. Barrett, N. R., and Elkington, J. St. C. (1938). Brit. J. Surg., 26, 314.
2. Clagett, 0. T., McDonald, J. R., and Schmidt, H. W. (1952). J.
3. Ehrenhaft, J. L., Sensenig, D. M., and Lawrence, M. S. (1960). Ibid., 40, 393.
4. Kahn, D. S., Glay, A., and Madore, P. (1959). Ibid., 38, 225.
5. Kerr, W. F., and Nohl. H. C. (1961). Thorax, 16, 180. Klemperer. P., and Rabin, C. B. (1931). Arch. Path. Lab. Med., 11, 385.