title: Heterogeneity of strain R avian (erythroblastosis) virus.
mesh_terms: D000818:Animals; D001354:Avian Leukosis Virus / Q000145:classification* / Q000276:immunology / Q000472:pathogenicity; D001358:Avian Sarcoma Viruses; D002471:Cell Transformation, Neoplastic; D002642:Chick Embryo; D046508:Culture Techniques; D009500:Neutralization Tests; D014762:Viral Interference; D014776:Virus Cultivation