The fonds contains original and typescript letters, manuscript notes, newspaper clippings, journal extracts, reminiscences and more, assembled by Harvey Cushing chiefly between 1920 and 1924 during the course of his research for the biography of William Osler. For the biography, Cushing collected and retyped over 7500 pieces of Osler's correspondence, among which are some original letters.

The fonds is separated into three series: Manuscripts, Working Notes and Osler's Correspondence. It also contains photographs, annual reports, publications, clippings, one watercolor painting, one postcard. Osler's correspondence is further arranged in three subseries based chronologically.

Macdonell's papers comprise a journal for 1793-1795, which L.R. Masson entitled "Assinoboines-Rivière Qu'appelle", and an account of the Red River, approximately 1797.