Columbia subject headings:
Harvard subject headings:
Du Bois-Reymond, Emil, 1818-1896--Correspondence.
Humboldt, Alexander von, 1769-1859--Correspondence.
Physiologists--Germany--Correspondence.
Scientists--Germany--Correspondence.
Princeton subject headings:
Du Bois-Reymond, Emil, 1818-1896--Correspondence.
Humboldt, Alexander von, 1769-1859--Correspondence.
Physiologists--Germany--Correspondence.
Scientists--Germany--Correspondence.