[1] Cheville, N. F. (1975). In Cytopathology in Viral Diseases, Monographs in Virology, Vol. . 10, Melnick, J. L., editor, S. Karger, Basel, Munchen, Paris, London, New York and Sydney, 124-127.
[2] Helmboldt, C. F., and Jungherr, E. L. (1955). Amer. J. vet. Res. 16, 463-469.
[3] Karstad, L., and Budd, J. (1964). Canad. vet. J. 5, 326-330.
[4] Kirk, R. W. (1977). In Current Veterinary Therapy VI. Small Animal Practice, W. B. Saunders Comp., Philadelphia, London and Toronto, 1385.
[5] McCullough, B., Krakowka, S., and Koestner, . A. (1974). Amer. J. Path. 74, 155-170.