Sections stained with the Luxol fast blue-cresyl echt violet technique show bluish purple myelin and a diffuse rose-purple background. The most likely explanation is that

• A. Cresyl echt violet was not acidified
• B. Luxol fast blue was too concentrated
• C. Sections were cut too thick
• D. The slide was not warmed

Answer: (A)

In this stain, the blue Luxol fast blue specifically marks myelin, so seeing bluish-purple myelin shows the myelin staining worked. The Cresyl echt violet serves as the counterstain to highlight cell bodies, and it must be acidified to yield selective staining and a clean background. If Cresyl echt violet was not acidified, the counterstain would spread more diffusely through the tissue, giving a rose-purple, diffuse background instead of a well-differentiated, pale background with clearly stained cell bodies. Thus the diffuse background points to a lack of acidification of the Cresyl echt violet. The other options would produce different issues (too strong a blue overall, thick sections causing diffusion, or poor uptake without warming) rather than the specific rose-purple background described.