May 25, 1956 To the Editor:The May, 1956, issue of the Archives was a worthy monument of a great discovery. The issue gives also credit to the ensuing serological and clinical progress through contributors who took an essential part in the development. I wish, in this connection, to mention one fact that often did not come out clearly in historical sketches, through the years. In dealing with the introduction of alcoholic heart extract as antigen most presentations give a list of several authors without emphasis on the sequence. It must, therefore, be pointed out that the use of this antigen was first demonstrated by K. Landsteiner, R. Muller, and O. Potzl (Wien. klin. Wchnschr.20:1565, 1908). Landsteiner once called this to Bruck's attention who then acknowledged it explicitly (Bruck, C.:Berl. klin. Wchnschr.58:580-81 [May 30] 1921). He stated that mistakenly he had attributed the discovery to Marie and