The debated problem of gastro-intestinal versusrespiratory mode of infection in poliomyelitis has been restudied by several investigators recently, with conflicting findings. Kling and Levaditi in Europe carried out experiments from 1929 to 1933, which led them to the conclusion that the digestive tract affords a ready entrance of the virus of the disease into the body. They believe that the substitution of Macacus cynomolgus for Macacus rhesus as the animal of choice for the tests supports this point of view. Toomey in the United States has arrived at a similar conclusion, not by employing a particular species of monkey for experiment, but by the use of drastic measures of inoculation, which insure that the virus makes contact with the unmyelinated nerve fibers embedded in the intestinal wall. Toomey's methods are so severe and artificial that his results cannot be regarded as simulating a natural mode of infection.
We have repeated the tests of Kling and Levaditi, but in a far more comprehensive manner than was followed by them, and, like Clark and his associates who early repeated them, we have failed to confirm them. Indeed, we do not find Macacus cynomolgusand rhesus to differ in any essential way in their response to the presence of the virus of poliomyelitis in the body. Cynomolgido not respond to virus introduced into the stomach when contamination of the buccal and nasal cavities is avoided; they respond, as do rhesi, to virus directly injected into the intestine when virus passes into the intestinal wall and makes the necessary nerve fiber contact. Both Macacus cynomolgus and Macacus rhesus which have resisted feedings of virus are subject to nasal instillations of the same strains of virus and in the same degree.
On the basis of the experiments reported in this paper we can reaffirm the conclusion previously arrived at by ourselves, and confirmed independently by investigators in Europe and America, namely that the only established portal of entry of the virus of poliomyelitis into the central nervous system of man is the nasal membrane, and especially the olfactory nervous areas in that membrane.