Karl landsteiner placed animal blood in human blood and discovered that the blood clumped. which did his creativity lead to? understanding the process of blood clotting understanding the formation of blood cells understanding the function of antibodies understanding a, b, ab, and o blood groups

His experiments led to the understanding of A, B, AB and O blood groups.

Landsteiner  found that there are substances in the blood, antigens and antibodies, that induce clumping of red blood cells when red cells of one type are added to those of a second type.  He recognized three groups namely A, B and O based on their reactions with each other. A fourth group, AB, was identified a year later by another research team.

 Today application of knowledge of the ABO system  in blood transfusion practice is of enormous importance, because mistakes can have fatal consequences.