Application of the bromophenol blue (BPB) staining method to rat fetal cartilage previously stained with alizarin red S.

The application of a convenient bromophenol blue (BPB) cartilage staining method on rat fetal skeleton, previously stained with alizarin red S, was investigated. This staining method made it possible to observe uncertain cartilage anomalies and unossified caudal vertebrae, which were poorly detected by single staining with alizarin red S. Namely, the anomaly of chondral rib bifurcation was detected and the number of unossified caudal vertebrae in rat fetuses was demonstrated as being identical with adult rat caudal vertebrae. The BPB staining has the notice to make the pH 4 adjusted specimens and has the advantage of fading with water or ethanol at pH 8 without discoloration of alizarin red S on the bones.