Figure 4: ABO Blood typing each row shows the appearance of a drop of blood mixed with anti-A and anti-B antisera. Blood cell becomes clumped if they possess the antigens for the antiserum (top row left, second row right third row both) but otherwise remain uniformly mixed. Thus type A agglutinates only in anti-A; type B agglutinates in anti-B; type AB agglutinates in both and type O agglutinates in neither of them.