BRIEF [O.A.] Bühlmann, Manfred Author: Bühlmann, Manfred Recipient: Haeckel, Ernst Dating: 22.03.1916
BRIEF [O.A.] Bühlmann, Manfred Author: Bühlmann, Manfred Recipient: Haeckel, Ernst Dating: 15.04.1916
BRIEF [O.A.] Bühlmann, Manfred Author: Bühlmann, Manfred Recipient: Haeckel, Ernst Dating: 09.03.1917