The virus-induced papillomas of cottontail as well as domestic rabbits regress completely within a few weeks when exposed to 5,000 r of x-ray irradiation. The x-rays do not immediately kill the papilloma cells, but lead to death by inhibiting cellular division and producing pathological changes in the cells which then continue to differentiate. The virus associated with the growths, however, not only persists in undiminished amount during regression, but often an increased yield of it can be obtained on extraction. The fibroma virus in crude extracts or in vivo is inactivated by far less irradiation than the papilloma virus. 10,000 r destroys 90 per cent or more of the infectivity of the fibroma virus, whereas at least 100,000 r is required to inactivate 50 per cent of the papilloma virus in extracts containing about the same amount of protein. No variant of the papilloma virus or fibroma virus has been encountered as a result of the irradiation.
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机译：当暴露于5,000 r X射线照射下，病毒诱导的棉尾巴乳头状瘤以及家兔在数周内完全消退。 X射线不会立即杀死乳头瘤细胞，而是通过抑制细胞分裂并在细胞中产生病理变化而导致死亡，然后继续分化而导致死亡。然而，与生长相关的病毒不仅在回归过程中以不减少的量持续存在，而且通常在提取时可以获得更高的产量。与乳头状瘤病毒相比，粗提取物或体内的纤维瘤病毒通过更少的辐射灭活。 10,000 r会破坏纤维瘤病毒90％或更多的感染力，而至少需要100,000 r才能灭活含有大约相同量蛋白质的提取物中50％的乳头瘤病毒。辐照未见乳头瘤病毒或纤维瘤病毒的变体。
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