Leech in the context of "Hirudo medicinalis"

Bloodletting (or blood-letting) is the deliberate withdrawal of blood from a patient to prevent or cure illness and disease. Bloodletting, whether by a physician or by leeches, was based on an ancient system of medicine in which blood and other bodily fluids were regarded as "humors" that had to remain in proper balance to maintain health. It was the most common medical practice performed by surgeons from antiquity until the late 19th century, a span of over 2,000 years. In Europe, the practice continued to be relatively common until the end of the 19th century. The practice has been abandoned by modern-style medicine for all except a few very specific medical conditions. In the beginning of the 19th century, studies had begun to show the harmful effects of bloodletting.

The modern term phlebotomy refers to the drawing of blood for laboratory analysis or blood transfusion. Therapeutic phlebotomy refers to the drawing of a unit of blood in specific cases like hemochromatosis, polycythemia vera, porphyria cutanea tarda, etc., to reduce the number of red blood cells. The traditional medical practice of bloodletting is considered a pseudoscience, though the method is still commonly used in forms of alternative medicine.

The annelids (/ˈænəlɪdz/), also known as the segmented worms, are animals that comprise the phylum Annelida (/əˈnɛlɪdə/; from Latin anellus 'little ring'). The phylum contains over 22,000 extant species, including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecologies – some in marine environments as distinct as tidal zones and hydrothermal vents, others in fresh water, and yet others in moist terrestrial environments.

The annelids are bilaterally symmetrical, triploblastic, coelomate, invertebrate organisms. They also have parapodia for locomotion. Most textbooks still use the traditional division into Polychaetes (almost all marine), Oligochaetes (which include earthworms) and Hirudinea (leech-like species). Cladistic research since 1997 has radically changed this scheme, viewing leeches as a sub-group of oligochaetes and oligochaetes as a sub-group of polychaetes. In addition, the Pogonophora, Echiura and Sipuncula, previously regarded as separate phyla, are now regarded as sub-groups of polychaetes. Annelids are considered members of the Lophotrochozoa, a "super-phylum" of protostomes that also includes molluscs, brachiopods, and nemerteans.

A living medicine is a type of biologic that consists of a living organism that is used to treat a disease. This usually takes the form of a cell (animal, bacterial, or fungal) or a virus that has been genetically engineered to possess therapeutic properties that is injected into a patient. Perhaps the oldest use of a living medicine is the use of leeches for bloodletting, though living medicines have advanced tremendously since that time.

Examples of living medicines include cellular therapeutics (including immunotherapeutics), phage therapeutics, and bacterial therapeutics, a subset of the latter being probiotics.

Hematophagy (sometimes spelled haematophagy or hematophagia) is the practice by certain animals of feeding on blood (from the Greek words αἷμα haima "blood" and φαγεῖν phagein "to eat"). Since blood is a fluid tissue rich in nutritious proteins and lipids that can be taken without great effort, hematophagy is a preferred form of feeding for many small animals, such as worms and arthropods. Some intestinal nematodes, such as Ancylostomatids, feed on blood extracted from the capillaries of the gut, and about 75 percent of all species of leeches (e.g., Hirudo medicinalis) are hematophagous. The spider Evarcha culicivora feeds indirectly on vertebrate blood by specializing on blood-filled female mosquitoes as their preferred prey. Some fish, such as lampreys and candirus; mammals, especially vampire bats; and birds, including the vampire finch, Hood mockingbird, Tristan thrush, and oxpeckers, also practice hematophagy.

The barber surgeon was one of the most common European medical practitioners of the Middle Ages, generally charged with caring for soldiers during and after battle. In this era, surgery was seldom conducted by physicians. Instead, barbers, who possessed razors and dexterity, were responsible for tasks ranging from cutting hair to pulling teeth to amputating limbs.

In this period, surgical mortality was very high due to blood loss, shock and infection. Yet, since doctors thought that bloodletting to balance "humours" would improve health, barbers also used bloodletting razors and applied leeches. Meanwhile, physicians considered themselves to be above surgery. Physicians mostly observed during surgery and offered consulting, but otherwise often chose academia or working in universities.

In usage in the Southern United States, a bayou (/ˈbaɪ.uː, ˈbaɪ.oʊ/ ) is a body of water typically found in a flat, low-lying area. It may refer to an extremely slow-moving stream, river (often with a poorly defined shoreline), marshy lake, wetland, or creek. They typically contain brackish water highly conducive to fish life and plankton. Bayous are commonly found in the Gulf Coast region of the southern United States, especially in the Mississippi River Delta, though they also exist elsewhere.

A bayou is often an anabranch or minor braid of a braided channel that is slower than the mainstem, usually becoming boggy and stagnant. Though fauna varies by region, many bayous are home to crawfish, certain species of shrimp, other shellfish, and leeches, catfish, frogs, toads, salamanders, newts, American alligators, turtles, and snakes such as watersnakes, swampsnakes, mudsnakes, crayfish snakes, and cottonmouths. Common birds include anhingas, egrets, herons, spoonbills, as well as many other species.

An anticoagulant, commonly known as a blood thinner, is a chemical substance that prevents or reduces the coagulation of blood, prolonging the clotting time. Some occur naturally in blood-eating animals, such as leeches and mosquitoes, which help keep the bite area unclotted long enough for the animal to obtain blood.

As a class of medications, anticoagulants are used in therapy for thrombotic disorders. Oral anticoagulants (OACs) are taken by many people in pill or tablet form, and various intravenous anticoagulant dosage forms are used in hospitals. Some anticoagulants are used in medical equipment, such as sample tubes, blood transfusion bags, heart–lung machines, and dialysis equipment. One of the first anticoagulants, warfarin, was initially approved as a rodenticide.