From wikipedia section on the medical uses of leeches [wiki]:
The leech has long been used in medicine, although today its use is mainly limited to limb reattachment procedures instead of the wide-ranging medical use in the past. Leeches have proven highly effective at preventing venous congestion after the surgical re-attachment of fingers, toes, ears and other parts of the body. The word leech either comes directly from or was influenced by the Old English word for "physician", l[ae]ce, which is related to Old High German lahhi and Old Irish liaig.
And where would you keep your leeches? In a pretty pink jar, of course.