A person can build up immunity to a particular venom through frequent low and increasing doses (about every 21 days), but this immunity is only in effect while he or she is undergoing the dose regime. According to Greek history, King Mithridates did this in order to protect himself against attempts of poisoning, therefore this procedure is often called mithridatism. However, cytotoxic venom causes injury even at low doses meant to build resistance and the long-term effects of venom dosing in general have not been studied. Thus, there is no practical purpose or favorable cost/benefit ratio for this, except for people like zoo handlers, researchers, and circus artists who deal closely with venomous animals. Mithridatism has been tried with success in Australia and Brazil and total immunity has been achieved even to multiple bites of extremely venomous cobras and pit vipers.