What are leeches used for?

Leeches suck blood and it was believed that leeches would actually suck the bad blood/diseased blood out of your body. Today leeches are used after reattachment of body parts, particularly fingers and toes. The leeches relieve the congestion of blood in the affected parts. The leeches also put a chemical into the blood in the area of the attachment that prevents blood from clotting.