Methacarn substitutes methyl for ethyl alcohol in Carnoy's solution; what effect does this substitution have?

• A. It hardens and shrinks less than Carnoy's
• B. It fixes faster
• C. It increases shrinkage
• D. It changes color of tissue

Answer: (A)

Replacing ethanol with methanol in Carnoy's solution changes how aggressively the tissue is dehydrated. Ethanol-based Carnoy’s causes strong dehydration, leading to notable hardening and shrinkage. Using methanol instead makes the dehydration milder, so tissues fix with less shrinkage and less hardening, while still preserving morphology well because the other components (chloroform and acetic acid) continue to precipitate proteins and aid fixation. This is why the substitution tends to produce a result that shrinks and hardens less than the original Carnoy’s fixative.