Name a fixative that will leave the tissue protein uncoagulated.

• A. Osmium tetroxide
• B. Formalin
• C. Bromine fixative
• D. Acetone

Answer: (A)

Osmium tetroxide fixes lipids by oxidizing them and stabilizing membranes, and it does not cause proteins to coagulate. Because it acts mainly on lipids rather than denaturing or precipitating proteins, tissue proteins remain uncoagulated compared with fixatives that denature or precipitate proteins. Formalin cross-links proteins, acetone dehydrates and precipitates proteins, and bromine fixatives would also alter proteins more than osmium tetroxide. This lipid-focused fixation makes osmium tetroxide the best choice when you want to avoid protein coagulation.