Before Carl Hauptmann turned to literature, he wrote ›Metaphysik in der modernen Physiologie‹ (Metaphysics in Modern Physiology) between 1886 and 1892. This is a scientific study which deals with the relationship between body and soul. In this study, he shows that physiological research during the preceding fifty years had clung to a way of metaphysical thinking which was believed to have been long-forgotten and advocates regarding physical and mental processes as functions of matter which have equal value. This early work by Carl Hauptmann is characterized by a strong analytical talent, a fine sense of irony and a deliberate linguistic form.