In Masson Trichrome, which component differentiates the stain?

Study for the CAMLPR Histology Practice Test. Study with flashcards and multiple choice questions, each question has hints and explanations. Get ready for your exam!

The key idea is that the differentiating step in Masson Trichrome is done with a phosphomolybdic–phosphotungstic acid solution. This reagent selectively removes the red stain from non-collagen components after the initial staining, so that when the next dye is applied, collagen-rich areas take up the blue (or green) dye while other tissues do not. This creates the clear color separation: collagen appears blue/green, muscle red, nuclei dark. Bouin's fixative, Weigert's iron hematoxylin, and the final collagen stain (blue or green) serve their roles at other points in the protocol, but the differentiating action is specifically the phosphomolybdic–phosphotungstic acid step.