1. Rabbits and guinea pigs are susceptible to psittacosis virus introduced intracerebrally. By means of brain to brain passages in these animals the active agent is capable of propagation indefinitely.

2. Serial passages of the virus through rabbits and guinea pigs do not cause the active agent to lose its pathogenicity for parrots and mice.

3. The chief clinical evidences of infection in rabbits and guinea pigs following intracranial inoculation of the virus are fever and loss of weight. The pathological changes are characterized by a mild meningo-encephalitis, and fatty degeneration, focal necrosis, and infarction of the liver.

4. Rabbits upon recovery from an attack of psittacosis are actively immune.

5. Two strains of virus, human and parrot, were found to be immunologically similar.

6. No evidence was obtained to show that human convalescent serum possesses an appreciable amount of neutralizing substances.

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