In medieval and early modern medicine, the medicinal leech ("Hirudo medicinalis" and its congeners "H. verbana", "H. troctina", and "H. orientalis") was used to remove blood from a patient as part of a process to balance the humors that, according to Galen, must be kept in balance for the human body to function properly. (The four humors of ancient medical philosophy were blood, phlegm, black bile, and yellow bile.) Any sickness that caused the subject's skin to become red (e.g. fever and inflammation), so the theory went, must have arisen from too much blood in the body. Similarly, any person whose behavior was strident and sanguine was thought to be suffering from an excess of blood. Leeches were often gathered by leech collectors and were eventually farmed in large numbers. A unique 19th-century "Leech House" survives in Bedale, North Yorkshire on the bank of the Bedale Beck, used to store medicinal leeches until the early 20th century.