 transform bovin cell vitro inocul simian viru 40 nucleic acid cell bovin embryon lung tissu cultur inocul simian viru 40 sv 40 phenol extract high titer suspens sv 40 viru nucleic acid prepar induc prolif morpholog chang characterist sv 40 transform non-infect control cultur cultur inocul prepar nucleic acid expos dnase maintain condit infect cultur regular fibroblast growth cell line rapidli grow transform cell attempt isol viru transform cell neg minut amount viru recov occasion passag 