Older serologic methods for the diagnosis of tuberculosis are unsatisfactory. Serums from patients with active tuberculosis often fail to react. Serums from normal persons often give positive reactions. These difficulties presumably arise from lack of a suitable reacting antigen. An improved antigen was therefore suggested by Middlebrook and Dubos,1 consisting of the water-soluble (rich in polysaccharide) fraction of mammalian tubercle bacilli adsorbed on sheep erythrocytes. Serums from tuberculous patients give specific hemagglutinations with these activated erythrocytes.
A modification of this antigen is currently proposed by Rothbard2 and associates of Montefiore Hospital, New York City. Instead of the "polysaccharide" extract of tubercle bacilli, they exposed sheep erythrocytes to more readily available, concentrated old tuberculin, which undoubtedly contains the polysaccharide fraction. To make the test, the patient's serum is heat inactivated and then freed from interfering antibodies by adsorption on normal sheep erythrocytes. In control tests with the resulting reduced