Bloodletting (or blood-letting) - the withdrawal of blood to alleviate or take precautions towards an illness(es). The ancient practice was originally derived form a system, which considered blood and other bodily fluids as "humors". Bodily fluids, in this system, were required to maintain a proper balance to stay in good health. They were partially correct, but they didn't know about electrolytes or the specific elements broken down in the blood or bodily fluids.
Bloodletting was, at one time, the most common medical practice performed by physicians from its origins until as late as the late 19th century in most parts of the world. That would be for about 2,000 years. The practice is now rarely performed save for a small number of specific conditions. Its been speculated that in its heyday, bloodletting in and of itself was beneficial to some degree for those suffering form hypertension as it could temporarily reduce blood pressure by reducing blood volume. However, that's not a fact and should probably not be something you try at home, lol!
I'm gonna let you in on an interesting fact. I'm not sure how many of you know this, but do you know that the barber pole with the blue and red swirls in it that spins around on the front of a barber shop is a reminder of the days when the symbol existed to let you know that you could go into said shop to undergo bloodletting?
Leeching - In medieval and at the beginning of modern medicine and even sometimes now, the medicinal leech (Hirudo medicinalis, Hirudo verbana, Hirudo troctina, and Hirudo orientalis) were used to remove blood to aid in the balance of the "humors". (The four humors of ancient medical philosophy were blood, phlegm, black bile, and yellow bile.) Any sickness that caused the subject's skin to become red such as with fever and inflammation, was thought to have been caused by too much blood in the body. Also, an individual who was overly animated, hyper, or agitated was thought to be suffering from an excess of blood. This type of behavior was referred to as "sanguine".
Sanguine now has a different meaning than it did in medieval times, meaning more optimistic or excited or blood red in color. In medieval terms, the word had a very different meaning. It meant having the temperament and ruddy complexion, which was thought to be because a person was dominated by this humor; blood, sort of overly-passionate. The use of leeches began to become less widespread towards the end of the 19th century.
Leech therapy began its use again in the 1970's as a tool used in microsurgery. They were and still are utilized to regulate circulation to salvage skin grafts and other tissue threatened by postoperative venous congestion, particularly in finger reattachment and reconstructive surgery of the ear, nose, lip, and eyelid.
Other uses are for varicose veins, muscle cramps, thrombophlebitis, and osteoarthritis, among a myriad of different conditions. The therapeutic effect does not stem from the blood taken, but instead from continued, steady bleeding from the wound left after the leech has detached, as well as the anesthetizing, anti-inflammatory, and vasodilating properties of the secreted leech saliva. The most common complication from leech treatment is prolonged bleeding, which can be easily remedied. However, a couple of risks do exist; allergic reactions and bacterial infections.