Which of the following are non-additive fixatives?

• A. Alcohols and Acetone
• B. Formalin
• C. Osmium tetroxide
• D. Glutaraldehyde

Answer: (A)

Non-additive fixatives preserve tissue mainly by coagulating proteins or removing water, without introducing additional chemicals that remain in the tissue. Alcohols and acetone fit this idea because they fix by dehydrating and precipitating proteins, rather than forming new chemical bonds or depositing metals in the specimen.

Osmium tetroxide, on the other hand, fixes lipids by reacting with them and leaves osmium in the tissue, effectively adding material to the specimen. Glutaraldehyde and formalin fix tissues by cross-linking proteins, which also introduces new chemical bonds and components into the tissue. This cross-linking and addition of material are why those are considered additive fixatives.

So, alcohols and acetone are the non-additive option.