Two methods were employed in a study to ascertain whether the identification of a specific bacterial antigen or antibodies activated by it could be the means of determining rheumatic fever activity. The first method was by a hemolytic test with patient's serum as the antibody source and artificially sensitized sheep erythrocytes as the antigen. The second method was by an agglutination test using rabbit antiserum and patient's erythrocytes sensitized in vivo as the antigen. Clinical correlations were obtained with 78 rheumatic fever patients. There were 77 control cases. The methods proved practical in ascertaining rheumatic fever activity or quiescence and in distinguishing rheumatic fever from other disease processes.
The principle of a specific antigen-antibody reaction has been the basis of numerous tests to identify infectious diseases.* Erythrocytes that have been coated or sensitized by an antigen react with a specific antiserum prepared from that antigen to produce agglutination of the