1. Coutard, H., Amer. J. Roentgenol., 28, 313 (1932).
2. Barth, G., Bohmer, D., and Wachsmann, F., Strahlentherapie, 109, 599 (1959).
3. Barth, G., Graebner, H., and Wachsmann, F., Strahlentherapie, 112, 280 (1960).
4. Mallender, L. J., J. Faculty Radiol., 1, 267 (1950).
5. Churchill-Davidson, I., and Johnson, E., Brit. Med. J., i, 1465 (1954).