In rhesus and cynomolgus monkeys without signs or symptoms of poliomyelitis, a comparison of the incidence, numbers, size, and character of lesions in certain peripheral ganglia (gasserian, nodose, superior cervical sympathetic, and celiac) was made between 9 "new" animals sacrificed 1 to 3 days after arrival in a laboratory devoted exclusively to poliomyelitis research, and 17 "old" animals housed there without special isolation precautions for periods ranging from 17 days to 10½ months. The comparison showed that the "old" animals had more infiltrative lesions of various sizes than the "new" and that neuronophagia occurred in 65 per cent of the "old" animals as compared with none in the "new."

The heaviest and most frequent involvement occurred in the gasserian and superior cervical sympathetic ganglia, while that of the nodose (vagal afferent) ganglia was somewhat less, and that of the celiac ganglia was still less and without neurophagia. The ganglia of the VII and IX cranial nerves were also examined and showed no lesions of note.

Reasons are presented for believing that the lesions were of centripetal and not of centrifugal origin.

The lesions, while not positively identified as poliomyelitic, were of similar morphology, were presumably due to an infective neurotropic agent, and were acquired under conditions of potential exposure to poliomyelitis virus.

The possibility is suggested that the asymptomatic acquisition of neurotropic lesions in this group of casually exposed monkeys can be comparable to the acquisition of "subclinical" poliomyelitis in man.

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