Hematoxylin P.T.A. reagent is used for staining collagen, muscle tissue (excellent diferentiation between smooth and striated muscle tissue), Nemaline rods (present in certain skeletal muscle diseases), fibrin (visible in tissues with fresh damage, in acute inflammatory reactions), glial fibres (display of gliosis in central nervous system), certain elastic fibers, cartilage and bone matrix. Tungsten from the excessive phosphotungstic acid in the reagent binds all the available hematein and creates blue pigment that selectively stains skeletal striated muscles, fibrin, nuclei and certain other elements. The remainder of the phosphotungstic acid stains red-brown structures such as collagen. Hematoxylin P.T.A. is a component of Hematoxylin P.T.A. kit.