This collection of Carothers' letters was written to and preserved by a close friend, Wilko Gustav Machentanz (1895-1973), with whom Carothers roomed for two of his years at Tarkio College. The bulk of the letters were written between 1917 and 1922, before Carothers became absorbed in his doctoral studies, although the two corresponded as late as 1936.

The letters are especially valuable for the light they shed on Carothers' youth. Carothers wrote candidly to Machentanz regarding his interests, emotions, social life, and study. The letters note Carothers' interest in music and Romantic authors, and describe early episodes of depression. There are also copies of Carothers' wedding invitation and the program for a Tarkio College production of Booth Tarkington's "The Man from Home," directed by Miss Bertha Machentanz, in which both Carothers and Machetanz played minor roles.

The collection concludes with a 1947 exchange of letters between Machentanz, now a lawyer in California, and Betty Jo Travis of Chicago, who had requested information for a paper on Carothers. Machentanz provides a brief but incisive character sketch and a short history of their relationship.

The letters and envelopes bear pencil notations by Robert Secor, who had used them in preparing his own biography of Carothers, which was left incomplete at his death in 2001.