Used primarily in histology and microbiology for staining procedures, especially in the Ziehl-Neelsen acid-fast staining technique. It helps identify acid-fast bacteria such as Mycobacterium species, which cause diseases like tuberculosis and leprosy. The stain penetrates the waxy cell walls of these bacteria when heated, allowing them to retain the red color while background tissues are counterstained. Also used in some fungal staining protocols due to its affinity for chitin in fungal cell walls. Its strong coloring properties make it effective for microscopic examination of tissue sections and smears where clear differentiation of pathogens is required.