From The Frankfurt School: Its History, Theories, and Political Significance by Rolf Wiggershaus (Cambridge, 1995).
In the lead up to this paragraph on Jahnn, Wiggershaus describes the lack of an international avant garde in the early fifties in West Germany: "Advanced literary works were rare in the Federal Republic, and remained the preserve of controversial loners." He first discusses Wolfgang Koeppen and his novels Tauben im Gras , Das Treibhaus, and Der Tod in Rom [English translations by Michael Hofmann: Pigeons on the Grass, The Hothouse, and Death in Rome]. About Koeppen, "In the Federal Republic he stood alone. He did not belong to any circle; he did not form a school of any sort." And then:
The case of Hans Henny Jahnn was similar. In the 1920s he had published plays that met with vehement criticism,* as well as one -- unique -- expressionist novel, Perrudja. When 1933 came, his books were banned at once. He went into exile in Denmark, living on the island of Bornholm. In 1949 and 1950 he published Das Holzschiff and the two-volume Niederschrift des Gustav Anias Horn nachdem er 49 Jahre alt geworden war, which formed the prelude and main part of a melancholy and discursive trilogy of novels, Fluss ohne Ufer. In 1956 a slim novel, Die Nacht aus Blei, appeared. During the 1950s, Jahnn, who was also an organ-builder, hormone researcher and editor of early music, as well as a critic of cruelty to animals and extinction of species, devoted most of his energies to the struggle against the atomic bomb. He too was a loner fighting a lost cause in the context of the Federal Republic's 'Restauratorium.' Adorno and Jahnn might have met at the Darmstadt discussions in 1950 on 'The Image of Man in Our Time'; perhaps they did. If they did, then -- in spite of their closeness in terms of the radicality of their criticisms of civilization and their preference for the interrelation between instinct and mind and for humanity to reconsider the way in which it forms a part of creation -- Jahnn's complete lack of refinement and refusal to make concessions to public opinion and social etiquette would at best have shocked Adorno. Jahnn was one of the loners on whom Dialectic of Enlightenment and Minima Moralia had counted, but Horkheimer and Adorno were in reality rather alarmed by people like this.**
*Alfred Kerr described Jahnn's tragedy Medea in the Berliner Tageblatt of 5 May 1926: "This horror story about a young German takes Hofmannsthal's Electra line darkly and orgiastically towards the ultimate bestiality."
**During the second half of the 1960s, a student of Adorno's from the pre-Nazi period, Wilhelm Emrich, lent his support to Jahnn, who had died in 1959. Emrich defended him with great resolution, using Adornoesque arguments.