Brilliant cresyl blue is a

supravital stain Supravital staining is a method of staining used in microscopy to examine living cells that have been removed from an organism. It differs from intravital staining, which is done by injecting or otherwise introducing the stain into the body. Thu ...

used for counting

reticulocyte Reticulocytes are immature red blood cells (RBCs). In the process of erythropoiesis (red blood cell formation), reticulocytes develop and mature in the bone marrow and then circulate for about a day in the blood stream before developing into mat ...

s. It is classified as an oxazine dye. N95 dust masks, eye shields, and gloves must all be worn when handling the chemical.

References

{{heterocyclic-stub Chlorides Zinc compounds Oxazine dyes Phenoxazines