SEROLOGICAL REACTIONS WITH A VIRUS CAUSING RAB- BIT PAPILLOMAS WHICH BECOME CANCEROUS I. T~sTs oF THE BLOOD OF ANIMALS CARRYING TIIE PAPILLOMA BY

The cutaneous papillomas induced in domestic rabbits with a virus procured from western cottontails (1) have the immediate attributes of tumors (2), and they frequently become cancerous (3). The problem of the relation of the virus to the neoplastic activities is com-pUcated by a singular difficulty. Though readily obtained from most of the naturally occurring papillomas of cottontails, it cannot ordinarily be recovered from the far more vigorous growths induced with it in domestic rabbits. Recently indeed, Shope (4) has secured virus strains with which the disease can be serially transmitted in such animals, and it should be possible to make direct tests for the presence of these in any cancers that may develop as result of their action. But the large material thus far studied by us,-comprising more than 150 instances of malignant change in all,-has been provided by the inoculation of domestic rabbits with virus strains irrecoverable from either the papillomas or the cancers, by any of the various means thus far employed. For this reason recourse has been had to a sero-logical method to determine the presence of the virus. Shope noted that rabbits carrying the papilloma proved more or less resistant on reinoculation, and that their sera exerted a neutralizing influence when mixed with the virus in vitro (1). We have titrated the antiviral power, investigated the conditions of its development, and sought for it in the blood of animals carrying tumors of various sorts. The findings will be recorded in two associated papers.