T H E Roentgen Radiation of Papilloma Virus (shope)

A benign, infectiqus, cutaneous tumor of rabbits, the Shope papilloma, is caused by a virus that upon inoculation in either domestic or cottontail rabbits induces papiUomas with great regularity (1). These tumors are not infrequently followed by cancers (2-6). On attempted recovery of the virus from these two varieties of rabbits, however, a marked difference in host reactivity becomes apparent; for the virus, which is readily recoverable from cottontail rabbits, is not recoverable, or but rarely recoverable, from domestic rabbits (1, 7-9). This finding does not prove, of course, that the virus is absent from the papillomas of domestic rabbits. On the contrary, some immunological evidence for its presence in such papillomas and in the cancers derived from them has been presented (10, 11). If a virus were not present in the cells of papillomas on domestic rabbits, such papillomas might be expected to react to Roentgen radiation as non-infectious tumors do. This, indeed, has been shown to be the case (12). On the other hand, if a virus were contained in the tumor cells, the outcome following irradiation might be expected to be quite different. Obviously, therefore, it is important to learn the effect of Roentgen radiation on the virus itself. Data bearing on these points have been briefly recorded by Lacassagne (13) and ourselves (14, 15). The work from our laboratory that dealt with the effects of Roentgen radiation on papillomas in vivo has been amplified by further experimentation and presented in full (12). I t was concluded that the curative effect of x-rays on domestic-rabbit papillomas (Shope) results from the direct action of the Roentgen radiation on the rabbit's cells rather than on the virus. The studies described in the present paper deal with the effect of Roentgen radiation in vitro on cell-free suspensions of papilloma virus derived from cottontail rabbits. The experiments were designed to determine the dosage necessary to render papilloma virus non-infectious for both cottontail and domes-