A vital stain in a casual usage may mean a stain that can be applied on living cells without killing them.
Vital stains have been useful for diagnostic and surgical techniques in a variety of medical specialties.
Very bulky or highly charged stains that don't cross live plasma membrane are used as vital stains and supravital stains are those that are either small or are pumped actively into live cells.
Since supravital and intravital nature of the staining depends on the dye, a combination of supravital and vital dyes can also be used in a sophisticated way to better classify cells into distinct subsets (e.g. viable, dead, dying etc.
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