American Society for Clinical Pathology (ASCP) Histotechnician Certification Practice Exam

The Eosin stain is a vital component of histological staining protocols, often used in conjunction with Hematoxylin. While Hematoxylin primarily stains nucleic acids—like DNA in the nucleus—Eosin targets the cytoplasmic components of cells. The unique property of Eosin is that it stains basic (or eosinophilic) structures within the cytoplasm, imparting a pink color. These structures typically include proteins, cytoplasmic organelles, and other cellular components that are rich in amino acids.

This distinct pink staining is crucial in providing contrast to the blue-purple staining of the nuclei, allowing for better visualization and differentiation of cellular structures under a microscope. This capability is essential for pathologists to evaluate the morphology of tissues and identify potential abnormalities. Though other cellular components and structures may be involved in histology, the primary effect of Eosin is specifically on the cytoplasmic components, justifying the selection of this answer.