The infected cells were passaged so that the virus could be isolated . cpe were observed from passage 2 to passage 9 postinfection . the cultured virus supernatants were harvested when cpe were observed in 3 / 4 infected cells 接种后的胚肺细胞从第二代到第九代均出现细胞病变，当接毒细胞有3 4出现细胞病变时，收集培养的细胞，制作超薄切片进行电镜观察，发现了病毒样粒子。
