21. Letter from Michael Heidelberger to William C. Boyd, Boston University Publication: Produced: 16 December 1940 Subject(s): PrecipitinsAgglutinationAntigen-Antibody ReactionsAllergy and Immunology Archival Collection: The Michael Heidelberger Papers (Profiles in Science)
22. Letter from Max Delbruck, California Institute of Technology to Michael Heidelberger Publication: Produced: 16 March 1938 Subject(s): Antigen-Antibody ReactionsPrecipitins Archival Collection: The Michael Heidelberger Papers (Profiles in Science)
23. Letter from Michael Heidelberger to Max Delbruck, California Institute of Technology Publication: Produced: 28 March 1938 Subject(s): Antigen-Antibody Reactions Archival Collection: The Michael Heidelberger Papers (Profiles in Science)