The MacArthur Papers contain personal and professional correspondence of the father and son as doctors, and also those letters received by Daniel's sister, Julia, and her husband, Frank P. Cook. The Cook letters make up a sizeable portion of the early correspondence.
Some of the first letters of this collection are those from 2nd Lt. A. Fox Cook, Company A, 31st Regiment Wisconsin Volunteer Infantry, to his brother, Frank P. Cook and James J. Hogan of the La Crosse mercantile firm of Hogan and Cook.
There is also a short series of official Orders and letters having to do with Major Daniel MacArthur's participation in the Wisconsin National Guard, and letters to him from Major R. H. Gray who was in France during the First World War.
The last thirty years of correspondence are sprinkled with personal letters of Helen and Louise MacArthur, Daniel's two daughters. Throughout the entire collection are to be found numerous scrolls, diplomas, certificates of membership, etc. pertaining to the medical profession.
