Sudansprachen

A historical reconstruction of West Sudanic was published in 1927, and in his 1935 'Charakter und Einteilung der Sudansprachen' he conclusively established the relationship between Bantu and West Sudanic.

His most important later publication Die westlichen Sudansprachen 1927a divided these into East and West Sudanic languages and laid the basis for what would become Niger–Congo.