Leech Therapy

Leeches have been used in medicine for thousands of years. Leeches remove blood ("phlebotomize") from their host, and they release pain-killing (anesthetic) and blood-thinning (anticoagulant) substances with their saliva. Live leeches are currently used to treat blood-congested limbs, which otherwise might die or require amputation, if the pooling blood cannot be removed any other way. They are also sometimes used to provide pain relief, and for many other therapeutic effects. 

Leech therapy or Hirudotherapy has a long history. Records indicate that Egyptians used leech therapy 3,500 years ago. Dhanvantari, the Hindu God of Medicine, was first referenced in the 8th century B.C.E., and he is depicted as holding a leech in one of his four hands. Leech treatments were very popular during the Middle Ages. Again leech therapy was commonly practiced in the 1800's by American physicians treating a variety of diseases.Today, medicinal leeches are also used in the treatment of other venous diseases such as thrombophlebitis, as well as angina pectoris, arthritis, hematomas, and even tinnitus.

Info taken from here and here