1. Graves, J. H., and Cunliffe, H. R., Proc. US Line Stock Sanit. Ass., 63, 340 (1960).
2. Burrows, R., Bull. Off. Int. Epizoot., 61, 1251 (1964).
3. Madin, S. H., and Traum, J., Bact. Rev., 19, 6 (1955).
4. Wawrzkiewicz, J., Smale, C. J., and Brown, F., Arch. Ges. Virusforsch. (in the press).
5. Zee, Y. C., and Hackett, A. J., Arch. Ges. Virusforsch., 20, 473 (1967).