T H E Retention of Immunizing Power by the Shope Papilloma after Exposure to Ultraviolet Radiation

Shope (1) found that domestic rabbits bearing his papilloma were generally immune to reinoculation with the virus, an observation that has been amply confirmed by Kidd, Beard, and Rous ( 2 , 3 ) and by Ladewig (4). Where the animals were not totally resistant the presence of a partial immunity was indicated by the development of but few warts at the site of the second inoculation and by an increase in the length of the incubation period. Immunity was attributed by Shope to antibodies in the blood serum which generally neutralized the virus completely. According to Kidd, Beard, and Rous ( 3 ) these protective agencies develop within a few weeks after the warts appear and are roughly proportional, on the whole, to the area of skin involved. They prevent reinfection, but do not inhibit papillomas that are already established, the occasional regression of a wart being ascribed by Rous and Beard (S), and by Kidd ( 6 ) , to some influence directed against the cell rather than against the virus itself. No domestic rabbit was found naturally refractory to inoculation of the virus on scarified skin, either by Shope or by Beard and Rous (7 ) . Attempting to induce resistance in the absence of a growing tumor, Shope (8) injected extracts of his papilloma info the peritoneal cavity, among other sites, for the virus elicits a neoplasm only in the epidermis. Two C.C. of a 5 per cent extract, repeated eight days later, caused partial or complete resistance to the virus when this was rubbed into the abraded skin twenty days after the second immunizing injection. But despite the precaution of a fresh needle for each animal, in order to avoid infecting the epidermis at the inoculation site, 1 of the 3 treated rabbits developed papillomas at the point where the needle had entered the skin. The injections resulted in immunity, but it was impossible to decide whether this had been elicited by the virus introduced into the peritoneal cavity or by papillomas accidentally induced during the procedure. In subsequent experiments the dilemma was solved by excising the skin immediately surrounding the needle puncture two days after each injection. This procedure, though effective, is laborious, and it was with the object of simplifying the technic that the experiments which are to be described in the following paragraphs were undertaken. Although the work of previous investigators, whom they quote, had suggested that a virus made avirulent by ultraviolkt light loses its immunizing power, Hodes, Lavin, and Webster (9) found that when rabies virus was exposed for from forty-five to sixty minutes to a mercury vapor lamp at a distance of 12.5 cm. infectivity was abolished without entire loss of antigenicity,