A survey of the significance of the Rh factor.

LLOWING Landsteiner’s brilliant description in I9oo-19o1” 2 of the four blood groups, transfusions gradually became on the whole a safe and routine procedure. However, intragroup transfusion reactions were still observed in two groups of cases: (0 patients who had previously received a series of uneventful transfusions, and (2.) women at the very first transfusion associated with pregnancy. It was for a long time suspected that differences other than the 4 blood groups were responsible for isoimmunization and the production of new antibodies, but the actual demonstration of immune isoagglutinins was very seldom observed. In the course of the study of this material, an entirely new field of clinical importance was opened by the discovery of the role of fetal blood in isoimmunization, a subject hitherto of theoretical interest only.