1. Thirteen cases of non-paralytic poliomyelitis infection in chimpanzees are described. Nine of these animals were excreting virus in. their stools at periods of from 3 days to 8 weeks following inoculation.

2. All animals killed during the acute stage showed lesions in the brain distributed in centers usually involved in, and compatible with the presence of, poliomyelitic infection. In 2 chimpanzees typical cord lesions were also present. No lesions were found in the brains of 4 control chimpanzees which had had no virus contact as far as known. The occurrence of a purely systemic or peripheral form of poliomyelitis, without lesions in the central nervous system, has thus not been established.

3. Four instances of arrest of the pathological process near the portal of entry into the brain, indicating partial resistance, are included in this series. One was a chimpanzee inoculated intranasally (A1-75) who had severe tuberculosis at the time of inoculation. The second was an animal convalescent after intracerebral inoculation (A1-74), who sustained a second infection limited to the olfactory bulbs when inoculated intranasally 2 months later with homologous virus. The third (A5-01) was inoculated orally with human stool, but contammation of the olfactory area resulted with infection of the olfactory bulbs and of the forebrain; virus was present in the stools of this animal. The fourth chimpanzee (A48) had suffered an initial non-paralytic attack after stomach tube inoculation, followed by a second attack about 9 months later after oral inoculation with part of the same virus-containing pool (human stools). The second attack consisted of a facial paralysis, with arrest of the pathological process near the facial nucleus.

4. Although cerebral lesions were light in some of the non-paralytic and inapparent infections, their presence in all indicates the action of virus on the central nervous system with the possibihty of production of at least partial local resistance. It is not unreasonable to assume that this may occur in inapparent human cases, although the point is, of course, not susceptible to critical proof in man.

5. The degree of severity of pathological involvement in non-paralytic cases varies from a fully developed distribution of lesions in brain and spinal cord in some chimpanzees, to mild and scattered lesions in the brains of others. This suggests that if the extent of pathological reaction is an indicator of subsequent local resistance to reinfection, the degree of protection afforded by a non-paralytic attack of poliomyelitis to even homologous virus must be variable.

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