It has been repeatedly shown by many investigators1that when the virus of poliomyelitis is instilled intranasally in rhesus monkeys it enters the central nervous system by way of the olfactory nerves and bulbs. Our purpose in the present communication is to describe the pathologic changes produced by the virus in its passage through the olfactory bulbs and to present evidence that these changes occur only when the virus has reached the bulbs from the periphery by way of the olfactory nerves and not when the invasion of the central nervous system is by other pathways. Experimental poliomyelitis in rhesus monkeys was produced almost constantly by instilling 1 cc. of a 10 per cent virus suspension (M. V. strain) into each nostril on one day and repeating the process forty-eight hours later. With this procedure the first rise of temperature occurs between the fourth and sixth days and paralysis