The group composed a manifesto, written by Kirchner, stated that "Anyone who directly and honestly reproduces that force which impels him to create belongs to us."
Kirchner then returned to Berlin and continued to work, producing many paintings including Self Portrait as a Soldier (1915), until he was admitted to Dr Kohnstamm’s sanatorium in Königstein in Taunus in December 1915 where he was diagnosed with a strong dependency on Verenol and alcoholism. I n a letter to Dr. Karl Hagemann, a friend and patron, Kirchner writes: "After lengthy struggles I now find myself here for a time to put my mind into some kind of order. It is a terribly difficult thing, of course, to be among strangers so much of the day. But perhaps I’ll be able to see and create something new. For the time being, I would like more peace and absolute seclusion. Of course, I long more and more for my work and my studio. Theories may be all very well for keeping a spiritual balance, but they are grey and shadowy compared with work and life"
He also writes "A Painter's Credo" where he states: "There is an intellectual guardianship over the world, it is man…. This is the last judgement, before them you stand….. They help you when you work. You can thank them only through work. When you want to die, they sometimes appear to you. When you are completely empty and completely open, you belong to them"