method of enhancing the contrast in tissue sections at the microscopic level. Stains and dyes are used in histology (study of tissue under a microscope) and in the medical fields of histopathology, hematology and cytopathology, the main focus of  staining is the diagnosis of disease at the microscopic level. Dyes and stains can be used to examine biological tissues, the accumulation of cells or organelles within single cells.