A Comparison of the Tar Tumors of Rabbits and the Virus-Induced Tumors

Abstract

By tarring the ears of domestic and cottontail rabbits tumors have been procured for comparison with others experimentally induced with the Shope virus. 1 The tarred rabbits were strictly isolated.

The growths caused by virus regularly developed from the surface epidermis and were papillomas varying little in structure, whereas not a few of those consequent on tarring originated from the skin appendages, with result in a wider morphological variety. The tar papillomas were scattered, discrete and often punctate in origin; so too were the papillomas due to virus when this had been appropriately inoculated. The growths due to tarring appeared only after it had been repeated often enough to cause general hyperplasia of the epithelium, together with complex connective tissue alterations; and many of them retrogressed after tarring was stopped. The virus tumors, on the other hand, arose on the basis of the slight epidermal trauma incident to inoculation, and their progression was followed, not preceded, by connective tissue changes. The virus evidently needed no help,—though the growths it caused could be stimulated to rapid enlargement by connective tissue disturbances experimentally induced. 2 The unknown cause of the tar papillomas, on the other hand, was effective only when epithelial and connective-tissue disturbances had long existed, becoming independent thereof only after the growths had undergone considerable development, and often not even then. The tar papillomas were structurally much more irregular than early virus papillomas, as would follow from the disturbance of the underlying connective tissue, which was of a sort to bring about corresponding irregularities in the virus tumors. The surface of the tar papillomas often underwent maceration because covered, whereas the exposed surface of the virus growths consisted of dry, keratinized material.

When due allowance had been made for these differing conditions of incidence and growth, the resemblance between the tar and virus papillomas was found to be close.