The experiments reported above indicate that the intranasal instillations of pituitrin S and adrephine, alter susceptibility in the rhesus monkey. One-half to two-thirds of the treated animals resisted intranasal infection, and, moreover, most of the resistant animals which had received combined treatment and virus developed active immunity, as indicated by the presence of neutralizing substance in their serums and by their ability to resist intracerebral infection. We have, it appears, not alone modified in some fashion the usual reaction of this animal to intranasal infection, but we have also successfully vaccinated these animals by the nasal route, so that the response in animals more nearly approaches what we believe to be the response in human beings.

We have no knowledge of the mechanism by means of which pituitrin S and adrephine produce this apparent alteration in susceptibility, but since the outcome of continued exposure to virus in most of the animals treated with these substances results in immunity, we believe that this offers a more hopeful approach toward the control of the disease.

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