Jan Janský was born on April 3, 1873 in Prague. He was a Czech serologist, neurologist and psychiatrist. He is credited with the first classification of blood into the four types (A, B, AB, O) of the ABO blood group system.
Janský studied medicine at Charles University in Prague. From 1899 he worked in a psychiatric clinic in Prague. In 1914 he was named professor. During World War I Janský served two years as a doctor at the front until a heart attack disabled him. After the war he worked as a neuropsychiatrist in a military Hospital.
Through his psychiatric research, Janský tried to find a correlation between mental diseases and blood diseases. He found no such correlation existed and published a study, Hematologicka studie u psychotiku (1907, Hematological study of psychotics), in which he classified blood into four groups I, II, III, IV. At the time this discovery passed almost unnoticed. In 1921 an American medical commission acknowledged Janský's classification (over that of Karl Landsteiner, who classified blood into only three groups; and was for this (blood types) discovery awarded the Nobel Prize in Physiology or Medicine in 1930). Janský's classification remains in use today.
Janský was also a proponent of voluntary blood donations. He died on September 8, 1921.