An immunologist is conducting an experiment to understand precipitation reactions. He notes that on adding excessive amount of antibody to a serum sample containing small amount of antigen, the amount of precipitate formed is less, compared to adding smaller amount of antibody to the same sample. What is this phenomenon called?

Lattice hypothesis explains this: In precipitation reactions, the amount of precipitate formed is greatly influenced by the relative propoions of antigens and antibodies. Pro-zone phenomenon: It is caused by excessive antibody in the test system. (Weak or even absent precipitation and a false negative test) Zone of equivalence: Antigen and antibody are in optimum propoions and maximum precipitation occurs. Post-zone phenomenon: Presence of excessive antigen in the test system. (Weaker or even absent precipitation) Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition