A virus has been isolated from the tissues of a pigeon with visceral lesions that were characterized by focal necrosis of parenchymatous tissue, by the presence in affected cells of intranuclear inclusions of the herpetic type, and by secondary inflammatory reaction. This newly recognized virus, which has been tentatively called the I.N.I. agent is pathogenic for pigeons and embryonated eggs but is avirulent for rabbits, guinea pigs, and mice. The virus is smaller than the agent of psittacosis and is immunologically different from it.
The I.N.I. agent and psittacosis virus were both of etiological importance in an epizootic among pigeons. Some birds were infected simultaneously with the two agents while others were infected with only one.