Answer
Fig. 18.2
The older theory was to use leeches to remove "bad blood", presumably the cause of many diseases.
Work Step by Step
The new use is to take advantage of the anticoagulant properties of leech saliva to promote blood flow to a tissue, and remove undesirable formed clots.
Leeches, Hirudo medicinalis, produces an anticoagulant polypeptide (hirudin) in their saliva . Hirudin prevents clotting( and causes blood to flow freely) by inhibiting the formation of fibrin. The uses of leeches to remove bad blood ( France 1560s) was less painful than phlebotomy.
