The effects of the rabbit papilloma virus upon tar tumor tissue are widely various, as the present paper and previous ones attest. It enables some of the benign tar tumors of domestic rabbits (papillomas, carcinomatoids) to establish themselves after implantation,—which they are unable to do under ordinary circumstances, being dependent upon favoring factors; and it may drive them to active proliferation without altering their morphology. Some growths it fails to influence and some it converts into virus papillomas. Often, however, it brings about cytological changes which are indicative of a combination of its influence with that of the undetermined factor motivating the original tumor. The resulting neoplasm exhibits a blend of characteristics.
The virus makes some benign tar tumors become cancerous forthwith, the malignancy developing without intermediate virus papillomatosis. It can be readily imposed upon some of the squamous cell carcinomas which tar elicits in its natural host, the cottontail rabbit, and it may drive such tumors to proliferate faster, or alter them morphologically, or do both. Its stimulating effect is especially pronounced in the case of those tar cancers that are slow-growing.
Since the virus can influence tar cancers markedly, one can scarcely suppose it to be devoid of effect upon the cancers of the same type which derive from the papillomas it has itself engendered. Other implications of the work are discussed.