1. Beams, A. J., and Harmos 0. (1949). Amer. J. Med., 7, 425.
2. Cole, R., and MacCallum, W. G. (1918). J. Amer. med. Ass., 70, 1146.
3. Dingle, J. H., Abernethy, T. J., Badger, G. F., Buddingh, G. J., Feller, A. E., Langmuir, A. D., Ruegsegger, J. M., and Wood, W. B. (1944). Amer. J. Hyg., 39, 67.
4. Drew, W. R. M., Samuel, E., and Ball, M. (1943). Lancet, 1, 761.
5. Durck, H. (1896-7). Dtsch. Arch. klin. Med., 58, 368.