1. Artificial antigens containing the azobenzyl glycosides of the disaccharide cellobiose and the aldobionic acid, cellobiuronic acid, give rise in rabbits to antibodies which are specific and characteristic of the saccharide constituent. The antiserum to cellobiuronic acid shows broader serological cross reactions than does that to cellobiose.
2. An antiserum to the cellobiuronic acid antigen precipitates the capsular polysaccharide of Type III Pneumococcus when the latter is combined with a heterologous protein.
3. The cellobiuronic acid test antigen precipitates vigorously in antipneumococcus sera Types II, III, and VIII. The mechanism of these reactions is discussed.