The white mouse, the guinea pig, the calf, and probably the rat, were found to be susceptible to infection with the virus of rabbit pox. Serial transmission of the virus in mice by brain to brain passage was characterized by a fatal outcome usually on the 5th or 6th day after inoculation. Infection of the guinea pig was accomplished by intratesticular injection and the virus was continued to the 2nd passage in this species. Guinea pigs developed a well marked cutaneous reaction from the intradermal injection of both rabbit and guinea pig tissue virus. Active virus was demonstrated in the testicles of rats 8 days after intratesticular injection by rabbit subinoculation. In the calf inoculation of the scarified skin was followed by the development of large papular lesions with marked hemorrhage and necrosis. The results of the investigations on the etiology of rabbit pox and of the experimentally induced infection reported in this and the four preceding papers (1-4) are discussed with special reference to the relation of pox virus to other viruses and of rabbit pox to other pock diseases.