It was subsequently found that the Czech serologist Jan Janský had independently pioneered the classification of human blood into four groups in 1907, but Landsteiner 's independent discovery had been accepted by the scientific world while Janský remained then in relative obscurity. However, in 1921 an American medical commission acknowledged Janský 's classification. Jan Janský is nowadays credited with the first classification of blood into the four types (I, II, III, IV).
who proposed every person has specific blood group
Czech serologist Jan Janský