The Concept of Anxiety
All of Kierkegaard's books have either a preface, dedication, or prayer at the beginning. This book includes a lengthy introduction. "The Concept of Anxiety" was published on exactly the same date as "Prefaces", June 17, 1844. Both books deal with Hegel’s idea of mediation. Mediation is a common thread throughout Kierkegaard’s works. His work up to this point was to show that faith was being mediated by knowledge. Here he takes up the questions of sin and guilt.
Theodor Ziehen
Ziehen published nearly 450 works on psychology, neurology, anatomy, et al. He was author of a textbook titled "Die Geisteskrankheiten des Kindesalters" (Mental Diseases of Childhood), a book that reportedly was the first systematic work on child psychiatry in Germany. He also penned "Psychiatrie für Ärzte und Studirende", a textbook that was published in four editions between 1894 and 1911. In his writings, Ziehen is credited with introducing the terms "affective psychosis" and "psychopathic constitution".