1. Poliomyelitis virus suspensions were atomized so as to produce dry droplet nuclei which, suspended in air, were introduced into a special infecting chamber and inhaled by test animals, both rhesus and cynomolgus monkeys.
2. Without olfactory blockade, 5 of 7 rhesus and 6 of 7 cynomolgus monkeys developed poliomyelitis of the CNS with entry through the olfactory nerves.
3. With olfactory blockade, 2 of 35 rhesus and 4 of 10 cynomolgus monkeys developed this form of the disease by routes proved by serial sections of the olfactory bulbs not to have been olfactory.
4. The neural pathways of infection from the mucous surfaces to the CNS in the 4 cynomolgus monkeys with blockade were shown in 2 instances to have been the afferent fibers of the trigeminal nerve into the Gasserian ganglion and thence to its central connections in the pons-medulla; in another case this was the probable route. In one instance the pathway consisted of the sympathetic fibers of the nose or nasopharynx into the cervical sympathetic ganglia and thence into the uppermost levels of the thoracic cord. The routes in the 2 rhesus monkeys with non-olfactory takes were not accurately determined but in one there was suggestive evidence of entry through the trigeminal nerve.
5. Study of the peripheral ganglia in a number of exposed cynomolgus and rhesus monkeys, including several with no demonstrated involvement of the CNS, revealed lesions most constantly in the Gasserian ganglia; less so in the cervical sympathetics and still less so in the celiac. In 2 rhesus monkeys dying of other causes a few days after exposure, lesions were limited to the Gasserian ganglia. No evidence was found in any case of passage of infection from the celiac ganglia into the CNS.
6. The importance of the peripheral ganglia as intermediate stations in the centripetal passage of infection from the body surface is again emphasized.
7. Comparison of the present with a previous study suggests that infection by inhalation of virus occurs with greater ease than by ingestion.