March 23, 1900

Karl Landsteiner

Landsteiner publishes an early observation of human blood agglutination

Blood typing began as a footnote whose author was not yet sure whether the clumping reflected permanent human differences or illness.

A footnote in a 1900 bacteriology journal

Karl Landsteiner's paper on the antifermentative, lytic and agglutinating effects of blood serum and lymph appeared in 1900, in volume 27, issue 10/11 of Centralblatt für Bakteriologie, Parasitenkunde und Infektionskrankheiten, at pages 357–362.

In a footnote he reported that serum from healthy people could agglutinate red cells from other healthy people — normal blood visibly clumping merely because serum and cells came from different people.

He left open whether the effect reflected innate individual differences or illness and infection.

Not yet a typing system

The 1900 notice did not classify the ABO types. Landsteiner published the classification of three groups by their agglutinating properties in 1901.

Alfred von Decastello and Adriano Sturli demonstrated a fourth group in 1902; they had no part in the 1900 footnote.

The system arrived in stages: an observation in 1900, three classified groups in 1901, a fourth reported by other investigators in 1902.

Why the date will not narrow to a day

The 23 March date appears in derivative day-by-day chronologies. Landsteiner's own 1901 paper identifies the earlier Centralblatt report as appearing in February 1900; beyond the month, the consulted journal catalogues, the Josephinum's museum record, scholarly histories and Nobel sources establish only the year and issue 10/11.

No consulted source establishes an exact publication day, so 23 March remains unsupported — and the entry also conflates the 1900 footnote with the 1901 classification.

Landsteiner received the Nobel Prize in Physiology or Medicine in 1930 for discovering human blood groups; the prize does not validate a March publication day.

Sources

Researched 23 Aug 2026 6 sources 2 audit passes, 1 issue open Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree; the research places it at 1900.

What the sources leave uncertain

The listed date, March 23, appears in derivative day-by-day chronologies, but the consulted journal catalogues, museum record, scholarly histories, and Nobel sources establish only the year 1900 and issue 10/11—not an independently verified publication day.
Because the precise day is unsupported and the event description conflates the 1900 footnote with the 1901 classification, the best-supported date is given as 1900.