In the top half of the diagram, the viral organisms have combined with a specific antibody present in the antiserum sample, thereby, rendering the viruses unable to combine with the RBCs. Hence, a small button-shaped droplet of RBCs remains at the bottom of the well. In the lower half of the diagram, variables have changed. In this case, no virus specific antibodies have been added to the reaction, leaving the virions to combine with the RBCs, due to the affinity their surface proteins have for the RBC surface proteins. The result is agglutination of the RBCs, as evidenced by the lacy, or lattice clumping pattern visible in the well’s bottom.