All but one of these letters are to Charles Alston, the professor of botany at Edinburgh University, and concern medicine, botany, and science in general. They are dated between 1737 and 1750. One letter is to George Whately, dated 1778.

Nine of these letters are addressed to Sir Alexander Dick of Edinburgh (1763-1768), and relate to Morgan's medical studies, his travels on the Continent, and the founding of the medical department of the College of Physicians. These are copies of originals in possession of Mrs. Dick Cunyngham, Prestonfield House, Edinburgh. In addition there are letters from Morgan to: Petrus Camper, William Smith, Samuel Vaughan, Jr.; and from Peter Collinson to Camper; Camper to Morgan; S. Vaughan Jr. to Camper; and an exchange between Christian F. Michaelis and Camper. These concern Morgan, with mentions of fossils (mastodon bones in America), natural history, comments on Franklin, Jefferson, and Angelica Kauffmann. These are from originals in the Petrus Camper Papers, on deposit (1976) at the University of Amsterdam Library.

This is primarily a collection of letters and manuscripts sent to Wistar by prominent men who were among his many correspondents. These documents reflect his broad interests, including botany, paleontology, medicine, the American Philosophical Society, and André Michaux's plans for exploring the Missouri.

The collection of about 850 items covers the period from 1782 to c. 1936, with the bulk dating to the 1780s to 1840s. The collection is divided into four series. Series I contains correspondence relating to a wide variety of topics, including French and English politics, business, trade, religious matters, and personal affairs. Many of the items are letters of introduction. There is also information on John Vaughan's immigration to America, Joseph Priestley, vaccines and inoculation (with Jefferson's comments on the same), Vaughan's business in Philadelphia, and the American Philosophical Society. Also included in this series are 2 boxes with copies of Vaughan correspondence as well as miscellaneous notes by E. W. Madeira, gathered in the course of his research on Vaughan in the 1930s. Series II consists of three volumes. Included are two of Vaughan's commonplace books. One, entitled, "J. Vaughan's book," May 17, 1779 (47 pp., in Latin; 870/L34), includes mostly Latin notations. The other commonplace book, dated 1783 (ca. 66 pp.; B V 462.c), includes comments on several prominent Americans, such as Benjamin Rush and David Rittenhouse, as well as American society generally. The third volume is a copybook with thirty letters spanning the period 1784 to 1801 (B V462.1). Series III includes material relating to Vaughan's administration of the estate of the Philadelphia merchant Samuel Merrick, 1796-1822 (Vaughan-Merrick Papers, B V462.m; 2 boxes). Series IV consists of correspondence between Vaughan and the DuPont Co. for which he served as agent (B V462.4; photocopies of 73 letters).

Through his craniometic studies of human races, the Philadelphia physician Samuel George Morton (1799-1851) exerted a profound influence on the development of physical anthropology in antebellum America, and made substantial contributions to mineralogy, paleontology, and natural history. Relating primarily to Morton's scientific interests, the Morton Papers include insights into Morton's perspectives on education, medical practice, geology and mineralogy, craniology, paleontology, the Wilkes Exploring Expedition (also known as the United States Exploring Expedition 1838-1842), and his two major monographs, the Crania Americana and Crania Aegyptiaca. Several of the letters were written by Morton in his capacity as corresponding secretary of the Academy of Natural Sciences of Philadelphia. Also included in this collection are Morton's "Some Remarks on the Infrequency of Mixed Offspring Between the European and Australian Races" (1850), Joseph Barclay Pentland's notes on the aborigines of Peru (ca. 1840?), and newspaper clippings on Morton's death; a diary of Morton's trip to the West Indies, 1834, a set of craniological sketches for use in Crania Americana, and a microfilm of letters in private hands, written to Morton, 1838-1844