- Date: 14th century
- 1 a archaic : sharp
- b obsolete : sour
avid, keen, anxious, athirst mean moved by a strong and urgent desire or interest. eager implies ardor and enthusiasm and sometimes impatience at delay or restraint <eager to get started>. avid adds to eager the implication of insatiability or greed <avid for new thrills>. keen suggests intensity of interest and quick responsiveness in action <keen on the latest fashions>. anxious emphasizes fear of frustration or failure or disappointment <anxious not to make a social blunder>. athirst stresses yearning but not necessarily readiness for action <athirst for adventure>.
Hormesis (from Greek hórmēsis "rapid motion, eagerness," from ancient Greek hormáein "to set in motion, impel, urge on") is the term for generally-favorable biological responses to low exposures to toxins and other stressors. A pollutant or toxin showing hormesis thus has the opposite effect in small doses as in large doses. A related concept is Mithridatism, which refers to the willful exposure to toxins in an attempt to develop immunity against them.
In toxicology, hormesis is a dose response phenomenon characterized by a low dose stimulation, high dose inhibition, resulting in either a J-shaped or an inverted U-shaped dose response. Such environmental factors that would seem to produce positive responses have also been termed “eustress”.
However, whether hormesis is common or important is controversial. At least one peer-reviewed article accepts the idea, claiming that over 600 substances show a U-shaped dose-response relationship. Calaberese and Baldwin wrote:
One percent (195 out of 20,285) of the published articles contained 668 dose-response relationships that met the entry criteria.
The biochemical mechanisms by which hormesis works are not well understood. It is conjectured that low doses of toxins or other stressors might activate the repair mechanisms of the body. The repair process fixes not only the damage caused by the toxin, but also other low-level damage that might have accumulated before without triggering the repair mechanism.