Other fixatives used for best carmine include?

• A. Carnoy and Bouin
• B. Formalina and alcohol
• C. Zinc formalin
• D. Osmium tetroxide

Answer: (A)

When using Best's carmine, the tissue's carbohydrate-rich components (such as glycogen and mucopolysaccharides) must be well preserved so the stain can bind effectively. Carnoy’s fixative and Bouin’s fixative are classic choices because they rapidly penetrate and fix tissue while preserving these carbohydrate-containing substances, leading to strong and specific carmine staining. Carnoy’s (ethanol, chloroform, acetic acid) fixes quickly and preserves polysaccharides, while Bouin’s (picric acid, formalin, acetic acid) also retains mucopolysaccharides and glycogen, resulting in consistent staining.

Formalina (neutral buffered formalin) and alcohol can crosslink or dehydrate in ways that mask carbohydrates and diminish carmine uptake, making them less suitable for this stain. Zinc formalin, though a buffered fixative, remains formalin-based and does not offer the same carbohydrate preservation as Carnoy’s or Bouin’s. Osmium tetroxide targets lipids and is used mainly for electron microscopy, not for preserving the carbohydrate-rich components essential for Best’s carmine staining.

So, the best fits are fixatives that preserve carbohydrates and mucopolysaccharides, which is why Carnoy’s and Bouin’s are the preferred options.