The leech has been used in medicine from remote antiquity as a moderate blood-letter; and it is still so used, though more rarely than formerly.
LEECH, the common name of members of the Hirudinea, a division of Chaetopod worms. It is doubtful whether the medicinal leech, Hirudo medicinalis, which is rarer in England than on the continent of Europe, or the horse leech, Aulastoma gulo, often confused with it, has the best right to the original possession of this name.
Pike led an exploring expedition as far north as Leech Lake and took formal possession of the Minnesota region for the United States.
But at present the word "leech" is applied to every member of the group Hirudinea, for the general structure and classification of which see Chaetopoda.