Observations on the behavior of MHV (Pr) in the cerebral tissue of Princeton and Swiss weanling mice indicated a limited neurotropism. The virus migrated to the brain on intraperitoneal injection and was established there by cranial passage, though with difficulty in Swiss mice. Intracerebral multiplication was rarely followed by outward signs of nervous disorder. A slight pathologic reaction occurred in the brains of intracerebrally injected Princeton mice, but it was negligible compared with that of the ensuing hepatitis. In Swiss mice, injected intracerebrally with a mixture of MHV (Pr) and Eperythrozoon coccoides, a related virus with restricted pathogenicity and host range, possibly a mutant, was isolated from the liver and brain.

MHV (C), an actively hepatotropic virus recovered from leukemic Balb C mice, was much more neurotropic than MHV (Pr). Intracerebral injection of Balb C and Swiss weanling mice was attended by marked leptomeningeal and encephalitic lesions. Paralysis of the extremities occurred in some of the animals. The virus was essentially inactive in Princeton mice. During the intracerebral passage of MHV (C) in Swiss mice a pleuropneumonia-like organism was isolated from the brain. In conjunction with the virus this organism produced a vigorous leukocytic reaction.

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