This collection consists of letters from doctors, relating to medicine and medical publications and editing, as well as medical organizations. Most significant of the correspondence is that with John Shaw Billings (ca. 60 letters).

These papers reflect Isaac Hays' interests and activities in the medical profession and as an editor. His interest in paleontology, especially in the controversy with G. W. Featherstonhaugh, is also represented. There is one separate volume (77 letters) containing correspondence about natural history and naturalists, written to Hays by C. L. Bonaparte, George Ord, Thomas Say, and Charles A. Lesueur. The correspondence in the larger collection, however, contains much material on the American Journal of the Medical Sciences, particularly illuminated in the correspondence with John D. Godman. The I. Minis Hays material consists of letters from doctors, relating to medicine and medical publications and editing, as well as medical organizations. Most significant of the correspondence is that with John Shaw Billings (ca. 60 letters).

Ernst Krackowizer (1821-1875), father-in-law to the anthropologist Franz Boas (APS 1903), was an Austrian born surgeon who fled Vienna to New York following his involvement as captain of the Academic Legion during the Revolution of 1848. Krackowizer was an active member of New York medical community, helping to found the German Dispensary and Hospital, later renamed Lenox Hill Hospital. During the Civil War, Krackowizer assisted the Union Army as a volunteer surgeon and inspector of military hospitals. Krackowizer is claimed to have been the first on whom the anesthetic effects of chloroform were tested in Vienna and the first to use a laryngoscope in the United States. This collection is comprised of the personal papers of Ernst Krackowizer including diplomas, certificates, correspondence, diaries, and photographs, which document his life and medical career. Krackowizer's experience in the Revolution of 1848 and subsequent flight from Vienna trough Germany to the United States is well detailed in his correspondence to his fiancée and later wife, Emilie Forster, and in his diaries, which make up a significant portion of this collection. Krackowizer firsthand description of the early use of chloroform and the laryngoscope are included, as well as materials documenting his involvement as a volunteer surgeon and hospital inspector during the Civil War. Additionally, the Krackowizer Papers contain material written by others reference the life and work of Ernst Krackowizer.