Karl Landsteiner in 1901 identified 4 human blood groups based on the presence in their erythrocytes of special proteins agglutinogens and agglutinin antibodies contained in the plasma. Determination of blood groups is necessary for blood transfusion, otherwise an agglutination reaction, adhesion and destruction of erythrocytes may occur.
Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.