One of the longest living perennial mushrooms in the world, Agarikon (Fomes officinalis) can live for an astounding 50 years or more, a fact that's all the more impressive because it only grows on trees that are already old to begin with. Agarikon's survival is therefore dependent on our rapidly vanishing old growth forests.
The earliest written record of any mushroom used medicinally can be found in the Materia Medica from 65 B.C., where Fomes officinalis was listed by Greek physician Dioscorides as a tuberculosis remedy.  Other oral and written traditions from Poland and elsewhere in Europe indicate that Fomes officinalis was the most important medicinal mushroom in ancient Europe.
Unfortunately, Agarikon (Fomes officinalis) is no longer a European folk remedy. It may actually be extinct in Europe today, due to its requirement of old growth forests. In fact, it is mostly extinct in North America as well; except for Washington State's last remaining old growth rain forests. Hopefully this last refuge will be preserved for future generations. If not, at least the precious genetic material of this potentially powerful medicinal mushroom can be saved through cultivation. Two U.S. companies that currently cultivate and sell Fomes officinalis are Mushroom Harvest out of Ohio and Paul Stamets' Washington based business Fungi Perfecti.
The traditional therapeutic use of Fomes officinalis included pneumonia and, as previously mentioned, tuberculosis (Mycobacterium tuberculosis). It was also used for muscular and skeletal pain in the form of a poultice.
In 2002, an article by K. Grzywnowics was published in the International Journal of Medicinal Mushrooms supporting this information. Titled Medicinal mushrooms in Polish folk medicine, it states that Fomes officinalis was indeed used to treat lung conditions, including asthma and coughing, as well as painful skeletal conditions such as rheumatoid arthritis. Polish healers considered it an elixir for long life. In addition to lung and musculoskeletal conditions, it was also used to treat infected wounds and open bleeding. 
In North America, it is believed that Agarikon extract was used by Native Americans as protection from smallpox and other diseases brought over by the Europeans. But there is no definite written record of this information. The Haida Native American mythological tradition also retains a connection between Agarikon and the female creator spirit Raven, and with female sexuality.
Two mentions in modern scientific literature include Agarikon extract with other mushrooms that elicit a strong immune enhancing effect in subjects. [148, 149]
Finally, it should be noted that in spite of its common name synonyms "Quinine Fungus" or "Quinine Conk," Agarikon does not contain the compound quinine and is not effective in the use against malaria.
Note: The statements on this page have not been evaluated by the Food and Drug Administration. This article is not intended to diagnose, treat, cure or prevent any disease. Never use any medicinal mushroom or herb without prior approval by medical doctor.
Credits: Thank you, Paul Stamets, for research references.