Columbia subject headings:
Authors, German--20th century--Correspondence.
Authors, Swiss--20th century--Correspondence.
Hesse, Hermann, 1877-1962--Correspondence.
Humm, Rudolf Jakob, 1895-1977--Correspondence.
Harvard subject headings:
Authors, German--20th century--Correspondence
Authors, Swiss--20th century--Correspondence
Hesse, Hermann, 1877-1962.--Correspondence.
Humm, Rudolf Jakob, 1859---Correspondence.
Princeton subject headings:
Authors, German--20th century--Correspondence.
Authors, Swiss--20th century--Correspondence.
Hesse, Hermann, 1877-1962. Correspondence.
Humm, Rudolf Jakob, 1859---Correspondence.