RICHMOND, Virginia, USA, 10 November 2026 — Emil Kraepelin, the German psychiatrist whose concept of manic-depressive illness became one of the most influential diagnoses in the history of the field, was famously sparing with citations. So, when a new peer-reviewed Thought Leaders Invited Review in Genomic Psychiatry points out that, across the first five editions of his textbook, his chapter on the periodic psychoses carried exactly one reference on its opening page, the obvious question follows. Who earned it?
The answer is a name almost no one remembers. Ludwig Kirn published a 115-page monograph in 1878 titled “The Periodic Psychoses: A Clinical Treatise.” Kraepelin cited it from his first edition in 1883 through his fifth in 1896, and when later editions added other references, Kirn was always listed first. Yet, the review authors report, no detailed examination of the book had ever appeared in German or English. Eric Engstrom, a leading historian of nineteenth-century German psychiatry, supports that conclusion.
A citation hiding in plain sight
Kirn himself is something of a ghost. Born in 1839, he qualified in medicine at Heidelberg in 1861, trained in psychiatry at the Illenau asylum, and was extraordinary Professor of Psychiatry in Freiburg from 1883 to 1886 before turning to forensic medicine. His end caused a sensation. In 1899, months after he disappeared, his body was found in the Reuss river at Andermatt, Switzerland. The death was recorded as accidental, though the review notes he had been suffering from mental health problems and may have died by suicide.
The review, by Kenneth S. Kendler, MD, of the Department of Psychiatry at Virginia Commonwealth University, and Astrid Klee, of the Department of Germanic Languages and Literatures at the University of Toronto, sets out to repair that neglect. Astrid Klee translated the entire monograph into English, with Dr. Kendler assisting and reviewing the translation, and the complete text is available as an online appendix. The article then walks through the book section by section, reproduces three of its case histories, and asks what the young Kraepelin took from it.
“Nineteenth-century medical German had no systematized psychiatric vocabulary,” said Astrid Klee. “Many terms belonged to a particular period, and sometimes to a particular physician, so each one had to be read against the usage of its author and the historical context in which he wrote.”
Before bipolar disorder had a name
The story begins in France. In 1854, Falret and Baillarger each published what are credited as the first clear descriptions of what would become the current concept of bipolar disorder: Falret called it la folie circulaire, circular insanity, and Baillarger la folie à double forme, insanity with a double form. Baillarger went further, setting intermittent melancholy, intermittent mania, and double-form madness side by side as three distinct entities.
Kirn, writing nearly a quarter century later, became the bridge. The review authors argue that he gave German-speaking readers among the first, and certainly the most extensive and clinically oriented, summaries of this French literature, and that he did not simply repeat it. He expanded it with observations from his own patients. How does an idea cross a border? Sometimes it needs a translator of concepts as much as of words.
Nineteen patients, one recurring pattern
What kind of illness returns, again and again, wearing the same clothes? Kirn divided the periodic psychoses into those of “direct central origin,” arising from within, and those “triggered” by external events. The central forms he split again by the length of attacks, long or short, and by clinical form: periodic mania, periodic melancholia, and cyclical psychosis. Nineteen case reports form his clinical cohort. Of 21 closely observed cases, 16 had pronounced mental disorders in their families, and Kirn placed hereditary predisposition first among causes, comparing it to a germ that lies dormant before maturing into disease.
What gives the book its life, by the account of the review authors, is its eye. Kirn noticed that patients tended to relive the same episode with uncanny fidelity. One worker demanded a reward for his labor at the start of every attack. Another always sang the same song. A third struck up the guitar; a fourth adorned his hat with a feather. That sameness, Kirn wrote, was almost pathognomonic, close to a diagnosis in itself. In cyclical psychosis, he observed, “a double life takes place,” two completely different personalities alternating, one quick-pulsed and eager for action, the other pale, passive, and diminished.
“Kirn wrote with real clinical vividness,” said Astrid Klee. “His patients remain recognizable as individuals on the page, each repeating the same gestures and moods from one attack to the next.”
Ideas that arrived two decades early
Is remission the same as recovery? Kirn thought not, and several of his convictions read as strikingly modern, the synthesis shows. He insisted that the underlying illness persisted between attacks, quiet but present. He warned against judging a patient from a single cross-sectional look and urged clinicians to follow the disorder from its beginning, comparing observations over time, the longitudinal approach that became central to the diagnostic system Kraepelin proposed some 20 years later. He separated milder manias from severe forms in which consciousness and thinking broke down, a distinction Kraepelin recognized in 1899 and that Carlson and Goodwin rediscovered in their 1973 work on the stages of mania. And he suspected why periodic melancholia seemed so rare in his wards: milder cases, he wrote, likely escaped the observation of the institution altogether.
“Longitudinal follow-up is central to the diagnostic system Kraepelin built,” said Dr. Kendler, the corresponding author. “Yet some 20 years earlier, Kirn was already warning that a single cross-sectional assessment of a patient in remission could mislead, and that the disorder had to be explored from its beginning.”
Tracing the fingerprints on Kraepelin
How much of a textbook belongs to the books its author read? In his first edition of 1883, a 27-year-old Kraepelin described periodic psychoses as rooted in the organism itself, separated them from externally driven recurrences such as alcoholic agitation, named heredity as the most important cause, and distinguished three clinical pictures: periodic mania, periodic melancholia, and circular insanity. He noted the short melancholic stage before mania, the slight diminution of intellect or emotional life after repeated episodes, and attacks that corresponded to one another down to the smallest details. Each element echoes Kirn. Given the likely poor French of Kraepelin, the authors judge it unlikely that he studied Falret and Baillarger directly, and a good deal of what he knew of them came through Kirn.
Could Kraepelin have drawn on other German sources instead? The review weighs them: a three-page note by Griesinger in 1855, a largely conceptual 12-page essay on cyclical insanity by Kahlbaum in 1882, and a 12-page section by Schüle that leaned heavily on degeneration theory. Kraepelin followed the organization of Kirn instead, with no mention of degeneration. Kirn alone held the citation.
“For five editions, Kraepelin cited one source in that chapter, and his early account follows the structure of Kirn closely,” said Dr. Kendler. “We feel the evidence is strong that his early concepts of periodic psychoses were substantially influenced by Kirn, and likely based on his reading of the monograph.”
Where the trail runs cold
The authors frame their conclusion as strong but not certain, and they are frank about its edges. The patients were most likely housed at Illenau, an inference drawn from the references of Kirn to observing patients there, which means the cohort reflects institutional care rather than the milder cases that never needed hospitalization. Kraepelin also did not remain a disciple. Between his second and sixth editions he moved steadily away from Kirn, and his creation of manic-depressive insanity in 1899 rested on rejecting two central theses of the monograph: he united circular, manic, and melancholic forms into a single syndrome, and he brought most ordinary, non-circular cases of mania and melancholia into it as well.
One puzzle stays open. Mania and melancholia had been described for centuries, yet Kirn never addressed how his periodic forms related to those classical syndromes. That omission, the review notes, anticipated the very question Kraepelin would struggle with as he built his larger category in the late 1890s. Why would so careful an observer leave the most obvious door unopened?
Why an old book still matters
Why should a monograph nearly a century and a half old matter outside a history seminar? Because diagnostic categories are not unearthed like fossils. They are assembled, by particular people reading particular books. The review places Kirn squarely in that assembly, carrying French observations into German psychiatry and into the hands of Kraepelin. Some intellectual debts are paid promptly. This one has waited since 1878 to be acknowledged.
The peer-reviewed Thought Leaders Invited Review in Genomic Psychiatry titled “Ludwig Kirn’s 1878 Monograph: ‘The Periodic Psychoses (“Die Periodischen Psychosen”): A Clinical Treatise’,” is freely available via Open Access, starting on 10 November 2026 in Genomic Psychiatry at the following hyperlink: https://doi.org/10.61373/gp026i.0057 .
The full reference for citation purposes is: Kendler KS, Klee A. Ludwig Kirn’s 1878 Monograph: ‘The Periodic Psychoses (“Die Periodischen Psychosen”): A Clinical Treatise’. Genomic Psychiatry 2026. DOI: https://doi.org/10.61373/gp026i.0057 . Epub 2026 Nov 10.
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Ludwig Kirn’s 1878 Monograph: “The Periodic Psychoses (“Die Periodischen Psychosen”): A clinical treatise”
10-Nov-2026
The authors declare no conflict of interest.