Paracelsus, regarded by many as the father of toxicology, is often paraphrased to have said that the poison is in the dose ["Alle Ding sind Gifft und nichts ohn Gifft. Allein die Dosis macht das ein Ding kein Gifft ist." (All things are poison and are not poison; only the dose makes a thing not a poison)]. With this statement, Paracelsus considered the apparent safety of toxicants at low doses. Moreover, some substances, although toxic at higher doses, can be stimulatory or even beneficial at low doses. This is the case with compounds such as pharmaceuticals that are used for their beneficial effects, as well as with compounds such as pesticides that are normally used as toxicants. This stimulatory effect of a low dose of a toxicant is called hormesis. Although this phenomenon was recognized earlier, the term hormesis was first used by Southam and Erlich (1943) to describe the effect of an oak bark compound that promoted fungal growth at low doses, but strongly inhibited it at higher doses. They coined this term using the Greek word "hormo" (to excite), the same root used in the word hormone.