The study begins with an examination of the biographic forces at work in the emergence of the mid-nineteenth-century concept of unitary psychosis in Germany. Specifically, it sketches the Pietistic worldview of Albert Zeller and his abiding interest in affective symptoms, explains the motivations behind the publication of his best-seller about the (in)famous Seeress of Prevorst (Friederike Hauffe), contextualizes his critique of Romantic psychiatry, and recounts his visits to numerous mental asylums throughout Europe in 1832/1833. It also untangles the specific intellectual lineages that contributed to Zeller’s concept of unitary psychosis, especially the impact of such seminal—albeit mostly ignored or forgotten—figures such as J. H. F. Autenrieth, J. C. Reil, F. Schleiermacher, J.-É. Esquirol, J. C. A. Heinroth, and J. Guislain. It then turns to the reception of Zeller’s concept of unitary psychosis first and foremost in the work of Wilhelm Griesinger. It points to key differences in their respective understanding of the term—differences that mark the threshold dividing a Romantic and naturalistic interpretations of unitary psychosis. The final three sections turn to the different derivatives or spin-offs of the concept of unitary psychosis as it began to fracture in the 1860s. The first of these derivatives was advanced in 1859 by Heinrich Neumann, who sought to appropriate and redefine the concept in a materialistic and positivistic key. The second derivative is traced to Karl Ludwig Kahlbaum’s attempt at a wholesale terminological and symptomatological transformation of psychiatric nosology. Kahlbaum’s vanguard study on the Grouping of Mental Illnesses (1863) effectively swallowed, but left undigested, the concept of unitary psychosis, simply redefining it as vesania typica and ranking it alongside several other clinical categories. Kahlbaum thereby effectively paved the way to Kraepelinian psychiatry and the delineation of specific clinical entities. Finally, the last section treats a belated third derivative which was put forth by the obscure but influential alienist Rudolf Arndt, who in the 1880s strove to reduce all mental phenomena to a single, universal, neurophysiological “twitching” law, which he believed governed all manifestations of psychosis.