While modern medical knowledge has shown that bloodletting does nothing to help cure a person of their ailments, leeches do still serve a purpose. Hospitals around the world continue to use the critters because of some remarkable properties that are hard to replicate synthetically. Chemicals within the saliva of medicinal leeches contain powerful anticoagulation properties. This is essential to allow the creature to feed because it needs a constant flow of blood. In reconstructive surgeries, leeches are often utilized as these chemicals prevent blood clots from forming and ensure that blood flows into the new body parts properly. Without them, the new tissue could die because it would receive no oxygen or nutrients.