Rough Guide to the Identification of
Bacteria of Medical Importance

---

Additional information on acid-fastness

---

To test if a bacterium is 'acid-fast' a microscopic preparation is boiled in a strong solution of carbol fuchsin. Acid-fast cells retain the dye when the preparation is treated with a mineral acid, most often hydrochloric acid. They can do this because of the waxy nature of their envelopes. Other cells need counterstaining before examination in a bright-field microscope.

---