Since the pioneer work of Novinsky (1876), the venereal tumor of the dog has attracted the attention of many authors in cancer etiology on account of several interesting characters: the tumor usually develops in the external genitalia of both sexes of dogs; it is naturally transmissible from dog to dog through copulation, and experimentally by artificial means; the survival duration of tumor-bearing animals is comparatively long; metastasis of the tumor seldom occurs; animals once attacked by the disease seem to gain immunity to some extent.