The collection consists of correspondence, notes, memoranda, extracts from publications, reprints, drafts of essays, poems, magazine and newspaper articles, comic strips, popular songs, and other material on bioluminescence, collected principally between 1945-1959 for his History of Luminescence from the Earliest Times until 1900 (American Philosophical Society Memoirs 44, 1957). Other topics are chemistry, military medicine, natural history, and professional associations.

In addition to extensive correspondence, there are numerous laboratory notes, lecture notes, drafts of published papers, reports. This material documents Long's career, with much on his work with diabetes, including the International Diabetes Federation. His 1950 trip to Japan as an advisor to Japanese medical schools on medical education is also documented. In addition, there is substantial material on the Yale University Department of Physiology and the School of Medicine.