Determinations of phosphor-us-containing compounds of the whole brain tissue taken from normal mice and from mice suffering from polio-encephalitis produced by the MM poliomyelitis virus did not reveal any significant differences in the inorganic, acid soluble, lipid, nucleic acid, “protein residue” or total phosphorus fractions. Nor did they show any significant differences in the desoxyribosenucleic acid content as determined by the diphenylamine reaction. However, the content of ribosenueleic acid as determined by the orcinol-HCl reaction was significantly reduced in infected brains as compared with normal mouse brain tissue.