Demonstration of an antigen – antibody reaction by overlaying antiserum with toxin or bacterial extract, a ring of white precipitate appearing at the junction if the serum contains the homologous antibody.
A test in which two dissolved substances in a solution join to form a visible solid. The results depend on the strength of the attraction between the Fab fragment on the antibody and the corresponding epitope on the antigen (affinity) and on the stability of the complex (antibody avidity). The test demonstrates how immune complexes form in the circulation and are deposited in blood vessel walls.
A serological examination that visibly displays the reaction between a soluble antigen and antibody through the development of a precipitate is known as a precipitin test. This test can be performed in a variety of ways, such as in agar or via droplets on slides or petri dishes. The identification of the precipitate is made easier by the addition of polystyrene latex particles in the latex test, red blood corpuscles in the haemagglutination test, or by using crude sap in the chloroplast agglutination test.