What effect does acetic acid have when added to ethanol in "bloody" specimens?

When acetic acid is added to ethanol in "bloody" specimens, it plays a critical role in the preparation of the sample for microscopic examination. Specifically, acetic acid fixes the diagnostic cells by denaturing proteins and preserving cellular structures. This fixation process is essential as it helps maintain the integrity of the cells and allows for more accurate morphological assessment.

Moreover, acetic acid has the property of lysing red blood cells (RBCs). The lysis of RBCs is beneficial in bloody specimens because it clears the background, making it easier to visualize the diagnostic cells, such as white blood cells or other cellular components of interest. By breaking down the red blood cells while preserving the other cellular elements, acetic acid aids in better histological evaluation and diagnosis.

Thus, the action of acetic acid in this context is crucial for enhancing the clarity and quality of the specimen by fixing relevant cells and lysing unwanted RBCs, which supports the rationale behind the correct answer.