Stain

Add a drop of methylene blue stain and lower a coverslip carefully. The stain makes otherwise colourless structures, particularly nuclei, easier to distinguish.

Many cells and their structures are almost transparent, so a stain increases contrast and makes boundaries easier to distinguish. A coverslip holds the preparation flat, slows drying and keeps the objective away from the liquid.

A suitable liquid or stain is added, and a cover slip is lowered gently over the specimen.

A stain can make otherwise faint cells easier to distinguish because it increases contrast between the specimen and its background. Shape, arrangement, colour after staining and other visible features can then be compared with a key. These observations contribute to identification, although microscopy may be combined with culture or genetic testing when organisms look similar.