1. Purchase, H. G. & Burmester, B. R. in Diseases of Poultry (ed. Hofsted, M. S.) 502–568 (Iowa State University Press, 1972).
2. Hanafusa, H. in Comprehensive Virology Vol. 10 (eds Fraenkel-Conrat H. & Wagner, R.) 401–482 (Plenum, New York, 1977).
3. Linial, M. & Blair, D. in Molecular Biology of Tumour Viruses 2nd edn (ed. Weiss, R.) 649–784 (Cold Spring Harbor Laboratory, New York, 1982).
4. Bishop, J. M. & Varmus, H. in Molecular Biology of Tumor Viruses 2nd edn (ed. Weiss, R.) 999–1108 (Cold Spring Harbor Laboratory, New York, 1982).
5. Murphy, J. B. & Rous, P. J. exp. Med. 15, 119–132 (1912).