Which of the following is NOT a common fixative in histopathology?

Fluorescein is not a common fixative used in histopathology. Fixatives are substances used to preserve tissues and cells, maintaining their structure and preventing decomposition prior to examination under a microscope. The standard fixatives in histopathology include formalin, acetic acid, and alcohol, which are recognized for their effectiveness in preserving cellular morphology and functionality.

Formalin, for instance, is widely utilized because it cross-links proteins, effectively preserving tissue architecture. Acetic acid is often used in combination with other fixatives to stabilize nuclear proteins, particularly in cytology samples. Alcohol, particularly ethanol, is known for its ability to dehydrate tissues and coagulate proteins, serving as a reliable fixative for many tissue types.

In contrast, fluorescein is a fluorescent dye primarily used as a stain rather than a fixative. It is used to label tissues or cells for microscopic visualization but does not serve the preservation function essential in histopathological processing. Therefore, fluorescein distinctly differs from the other options, which are integral to the fixation process in histopathology.