Which of the following is NOT a Romanowsky stain?

Hematoxylin is not classified as a Romanowsky stain. Romanowsky stains, such as Wright's and Giemsa, are primarily used in cytology and hematology for staining blood smears and other cytological preparations. These stains work by combining eosin (an acidic dye) with methylene blue (a basic dye), which gives the cells various colors depending on their structures. This dual staining property aids in highlighting different cellular components and allows for the identification of various cell types based on morphology.

Hematoxylin, on the other hand, is a basic dye that primarily stains the nucleic acids in the cell, particularly cell nuclei, a process commonly used in histology rather than in the Romanowsky staining technique. It does not exhibit the same dual staining effect that characterizes Romanowsky stains. Therefore, identifying hematoxylin as the choice that does not belong to the Romanowsky family is accurate, as it functions differently and is utilized in different applications.