Immunohistochemistry is used to confirm the presence of or to identify certain structures or substances in tissue sections which cannot be identified with conventional staining methods. Such structures include: cells, enzymes, hormones, macromolecules like nucleic acids and polysaccharides. The basis of immunohistochemical staining techniques is the antigen-antibody reaction. This method makes it possible to differentiate, for example, various cells in a tissue section according to their different metabolic products or surfaces. Either the metabolic product or a certain surface component serves as the antigen. In the first step, the antigen reacts with a specific antibody. The resulting antigen-antibody complex is invisible. Therefore, in a further step a second antibody bound to an adjuvant is added and binds to the initial antibody (so-called sandwich procedure). The bound adjuvant makes the antigen-antibody complex visible under the microscope and identifies the sought structure. Adjuvants are: