The main reason you stain a specimen before putting it under the microscope is to get a better look at it, but staining does much more than simply highlight the outlines of cells. Some stains can penetrate cell walls and highlight cell components, and this can help scientists visualize metabolic processes. Stains also help distinguish between live cells and dead ones. Moreover, staining allows scientists count the number of cells of a particular type within a certain biomass. Twenty or more different types of stains exist, and each one has its purpose.