Quantitative Serologic anti Isotopic Studies on the Rh 0

S ALINE AGGLUTINATION REACTIONS of variable strength among Rh positive bloods were reported soon after the discovery of the Rh factor.”2 Wieners suggested that these D variant types were determined by special “intermediate” Rh genes and Stratton2 postulated that this weak D antigen was elaborated by a new allele, D’, at the D-d locus. The only blood types which could he classified as DL variants, prior to the development of the antiglobulin test, were those that showed weak to negative reactions with a substantial number of saline anti-D agglutinating sera. With the development of the antiglobulin technic, D” varieties were recognized, which failed to agglutinate in all saline serums hut which would do so when tested with an incomplete antiserum by the antiglobulin technic.4’5 These second varieties of Du were termed “low grade” in contrast to the first or “high grade” ‘arieties#{176} Renton and Hancock7’M’#{176} showed that less incomplete anti-D is needed to inhibit the saline agglutination of D” cells as compared with conventional D positive cells. They attribtmted this phenomenon to a decreased “strength” of the surface antigen. It appears that the context in which they used “strength”