1. Intracerebral inoculation of fowl pox virus in young chicks produces a disease characterized by the development of drowsiness and somnolence 4 to 5 days after inoculation. This is followed by spastic paralysis and convulsions on the 6th and 7th day. The majority of inoculated chicks die on the 7th or 8th day.

2. The pathological lesions are found chiefly in the meninges, perivascular structures, the choroid plexus, paranasal sinuses, mastoid cells, the bone marrow of the cranial bones, and the orbital tissues. No affinity for nervous tissue per se develops.

3. In this environment the virus has a high virulence for the choroidal plexus epithelium and acquires the capacity for infecting cells of mesodermal origin. All infected cells of whatever origin undergo a similar structural change. Fowl pox inclusions can be demonstrated within them and they become spherical in shape and detached from each other.

4. The virus has been carried through 14 successive intracerebral passages. The symptoms and lesions in the chicks inoculated with the 14th passage showed no marked difference from those of the first passage. No enhancement of the changes brought about in the virus by the intracerebral environment seems to take place upon repeated passage.

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