Filippo Pacini (1812–1883) was the chair of general and topographical anatomy at the Institute of Higher Studies in Florence — the medical-scientific establishment that would become the modern University of Florence — when the 1854–55 European cholera pandemic reached Tuscany. He was 42 years old. He had spent most of his professional life on histology — the microscopic study of tissue structure — and had already discovered the touch-receptor structures (Pacinian corpuscles) on which the modern neurological understanding of cutaneous sensation is partly based.

The Florence cholera outbreak of summer 1854 gave him fresh cadavers in volume. Within weeks of the first deaths Pacini had performed approximately twenty autopsies on cholera victims and had examined their intestinal tissue under one of the few high-quality compound microscopes then available in Italy.

What he saw

The intestinal mucosa of cholera victims was, in Pacini’s careful description, packed with vast numbers of a small comma-shaped organism approximately 2 micrometres long. The organisms were present in the gut tissue of every cholera victim he examined and absent from the gut tissue of control cadavers (typhoid victims, tuberculosis victims, accident victims) of the same period. The organisms were motile in fresh preparations and substantially identical in morphology across all the samples he examined.

Pacini’s interpretation was direct and correct. The organisms were the cause of cholera. The disease was an infectious illness transmitted by an identifiable microorganism — not a constitutional weakness, not a miasmatic exposure, not an imbalance of the bodily humours.

He named the organism Vibrio cholerae. He published the finding in late 1854 in a short Italian-language treatise titled Osservazioni microscopiche e deduzioni patologiche sul cholera asiatico (Microscopic Observations and Pathological Deductions on Asiatic Cholera). The treatise ran to approximately 40 pages. It included his microscopic drawings of the organisms (which match modern photomicrographs of Vibrio cholerae almost exactly), his autopsy notes, his epidemiological summary of the Florence outbreak, and his explicit conclusion that the organism was the disease’s cause.

What happened to the publication

Nothing.

The Italian scientific community in 1854 was substantially regional — the Risorgimento was still six years from the proclamation of the Kingdom of Italy — and Italian medical publication had limited reach beyond the peninsula. The leading European medical journals of the period (the British Lancet, the French Comptes rendus, the German medical periodical press) did not pick up the Pacini paper. The dominant European miasmatic theory of cholera, championed by the German hygienist Max von Pettenkofer and by most of the British and French public-health establishment, treated bacterial theories of disease causation with substantial scepticism.

Pacini continued to publish on cholera for the next twenty years. His 1865 Sul processo chimico e morboso del cholera refined the original finding with additional clinical evidence. His 1871 Sulla causa specifica del cholera explicitly argued that the disease’s transmission was through contaminated water — eleven years after John Snow’s similar Broad Street pump argument and twelve years before Robert Koch’s Egyptian-Indian rediscovery. None of the later Pacini papers attracted European attention either.

He died in Florence in July 1883 — three months before Koch’s announcement of the cholera bacillus in Berlin. His obituaries in the Italian press noted the Pacinian corpuscles but did not mention the cholera work.

Why Koch got the credit

Koch’s December 1883 announcement of the cholera bacillus — based on the German Cholera Commission’s expedition to Alexandria and Calcutta — used the same microscopic technique, identified the same organism, and reached the same conclusion. Koch was working in German and in the dominant German scientific publication tradition of the period; his work was better-resourced (the Commission had German government funding, dedicated bacteriological laboratory equipment, and the institutional weight of the recently-established Imperial Health Office); his prior demonstration of the tubercle bacillus in 1882 had established his scientific reputation as the leading bacteriologist of his generation.

Koch did know about Pacini. He referenced the Pacini paper in his 1884 follow-up publication, with the-condescending observation that the Italian work had been “premature” and had lacked the systematic bacteriological method that Koch had since developed. The implication — that Pacini had merely seen the organism without proving its causal role — was unfair: Pacini’s 1854 paper had argued the causal role explicitly, on the basis of evidence that was comparable to what Koch presented thirty years later.

The Italian recognition

The Italian medical establishment recognised the Pacini priority during the early 20th century. The standard Italian medical encyclopaedia of the 1920s lists Pacini as the discoverer of Vibrio cholerae; the official Italian biographical dictionary published by the Treccani Institute treats his 1854 paper as the first identification of the organism. International recognition came later.

The decisive change came in 1965, when the International Committee on Bacteriological Nomenclature formally adjudicated the priority question and ruled that the organism should be named Vibrio cholerae Pacini 1854. The Koch nomenclature (Comma bacillus or Vibrio Koch) was retired from the standard taxonomic literature. The current International Code of Nomenclature of Bacteria recognises Pacini as the first describer of the species.

Modern Italian medical history treats the Pacini case as a study in the penalties of writing in the wrong language and the wrong publication tradition. Pacini’s 1854 paper was correct, methodologically rigorous, and complete. It was also in Italian, in an Italian journal, in a period when the publication centre of European bacteriology was 1,200 kilometres north.

He died ten weeks before Koch announced the bacillus in Berlin. He never knew his work would eventually be recognised.