Which reagent is applied first in the Masson Trichrome staining sequence?

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!

Bouin's solution is used first in Masson Trichrome because it acts as a fixative that also serves as a mordant to precondition the tissue. This pre-treatment intensifies and clarifies subsequent color separation, helping the later dyes bind in a way that yields crisp, distinct colors for nuclei, cytoplasm/muscle, and especially collagen. After Bouin's, the sequence proceeds with a nuclear stain (to visualize nuclei), then a red stain for cytoplasm/muscle, followed by the differentiating step with phosphomolybdic/phosphotungstic acid, and finally the blue/green stain for collagen. So the initial Bouin's step sets up the tissue for accurate and contrasting staining in the rest of the sequence.