 He studied at the University of Berlin, and later practiced medicine at the Charité in Berlin.He admired the works of physiologist Ivan Petrovich Pavlov, and with internist Friedrich Kraus, he published a book on electrocardiography titled "Das Elektrokardiogramm des gesunden und kranken Menschen".In 1914, at the onset of World War I, Nicolai composed an anti-war treatise called "Manifesto to the Europeans".