The teichoic acid of streptococcal Group N, with end groups of galactose phosphate, had been shown to cross-react with antipneumococcal sera of types VI, XIV, XVI, and XXVII. End groups of D-galactose-1-phosphate in the phosphogalactans of Sporobolomyces yeasts made it predictable that these galactans would precipitate the same antipneumococcal sera and also antisera to streptococcal Group N. The predictions were verified, and other unpredicted reactions were found. Precipitation of much of the antibody in an antipneumoccal type XVIII horse serum was shown to be due to O-acetyl-D-galactose residues in the phosphogalactan, in accord with earlier information that an O-acetyl sugar was a principal determinant of S XVIII. The new results identify this sugar as D-galactose. Since it is linked 1,3- in S XVIII, the O-acetyl group in the Sporobolomyces galactan is probably also on a 1,3-linked residue. Another major cross-reaction in anti-S. paratyphi A serum characterizes the galactose residues in the "O" polysaccharide of the bacillus as members of the D-series probably linked in tandem 1,6-, 1,6-; 1,6-, 1,3-; 1,3-, 1,6-; or 1,3-, 1,3-. Reactions of periodate-oxidized-reduced products confirm the conclusions stated above. Quantitative data are given.

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