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Horner's syndrome
Horner's syndrome (oculosympathetic paresis) is the triad of miosis, ptosis, and anhidrosis from disruption of the three-neuron sympathetic pathway to the eye; described by Horner in 1869, confirmed with apraclonidine or cocaine testing, and localized with hydroxyamphetamine.
Hornet
Hornet: large eusocial predatory wasps of the genus Vespa (Vespinae), also loosely applied to Dolichovespula maculata. Includes Vespa crabro, invasive Vespa velutina, and the eradicated US population of Vespa mandarinia.
Hornet attacks and mass envenomation
Hornet attacks and mass envenomation is illness from many stings at once, driven by venom dose rather than allergy, most often from the Asian giant hornet.
Hornet predation on honey bees
Hornet predation on honey bees is the hunting of foragers and hive raids by hornets, chiefly the northern giant hornet, which can destroy a colony in hours.
Horntail
Horntail (Siricidae), also called wood wasp: large nonstinging hymenopteran wood-boring wasp; about 122 species; females inject eggs plus Amylostereum fungus into dying trees; Sirex noctilio is an invasive pine pest.
Hornwort
Hornworts (Anthocerotophyta) are a bryophyte division of about 220 species with a horn-shaped, continuously growing sporophyte, single chloroplasts with pyrenoids, and Nostoc cyanobacterial symbiosis, sister to liverworts plus mosses.
Hornworts of Great Britain
The hornworts of Great Britain are the four species of the plant division Anthocerotophyta recorded in the country, most often on bare, damp arable clay and loam.
Hornworts of Ireland
The hornworts of Ireland are the hornwort plants recorded from Ireland: three confirmed taxa, Anthoceros agrestis, Anthoceros punctatus, and Phaeoceros laevis, with Phaeoceros carolinianus unresolved.
Horse
The horse (Equus caballus) is a large domesticated, hoofed, grazing mammal kept worldwide for riding, draft work, sport, and companionship; all modern breeds descend from a steppe lineage of 4,200 years ago.
Horse breed
Horse breed: a recognized population of domestic horses defined by FAO criteria of visible traits or accepted separate identity; shaped by domestication 5,500 years ago, a Pontic-Caspian lineage dominant since 4,200 years ago, closed stud books, and conservation concerns.
Horse colic
Horse colic (equine colic) is abdominal pain in horses, usually gastrointestinal, and the leading equine emergency. About 90% of cases resolve medically; surgical cases have 55–80% short-term survival. Key signs: pain, heart rate over 40 bpm, reduced gut sounds.
Horse gait
Horse gait: the hoof-fall patterns of equine movement. Natural gaits are walk, trot, canter, gallop; gaited horses perform ambling gaits via the DMRT3_Ser301STOP mutation, traced to Medieval England (850–900 AD).
Horse hoof
Horse hoof: the keratinized capsule (wall, sole, frog) of the equine foot, suspending the coffin bone via about 600 laminae; grows ~3/8 inch monthly, and conventional shoeing measurably restricts heel expansion versus barefoot.
Horse teeth
Horse teeth are hypsodont, continuously erupting teeth adapted to grazing, with 2–4 mm yearly wear offset by eruption; care includes floating and wolf tooth removal, practiced since 1150 BCE Mongolia.
Horse trailer
Horse trailer (UK: horse box; Australia: horse float): a towed vehicle for carrying horses. Key facts: first recorded use 1771 for racehorse Eclipse; straight vs slant load; gooseneck hitches; 3,500 kg UK licence rules; butt bar safety.
Horseradish
Horseradish (Armoracia rusticana), a Brassicaceae perennial from southeastern Europe and western Asia, grown over 3,000 years for its pungent taproot; allyl isothiocyanate from sinigrin gives the heat, and it substitutes for wasabi.
Horseradish peroxidase
Horseradish peroxidase (HRP, EC 1.11.1.7) is a heme glycoprotein enzyme from horseradish roots (Armoracia rusticana), the standard reporter enzyme in ELISA, Western blot, and immunohistochemistry, with isoenzyme C1A (34 kDa) best studied.
Horses in the United States
Horses in the United States, about 6.65 million strong, descend from animals Spanish colonists reintroduced in the 1490s, and the equine industry adds $177 billion a year to the economy.
Horses in World War I
Horses in World War I: British Army draught, pack and cavalry horses, 1914-1918. Over 368,000 on the Western Front by 1917; 75 percent of deaths from disease or exhaustion; Remount Department spent £67.5 million procuring them.
Horses in World War II
Horses in World War II: belligerents used millions of horses, chiefly for hauling artillery and supplies. Germany employed about 2.8 million horses and lost over 1.55 million; the US and Britain mechanized, with the mule leading US animal transport.
Horseshoe bat
Horseshoe bats (Rhinolophidae, genus Rhinolophus) are Old World insectivorous bats with a horseshoe-shaped noseleaf, high-duty-cycle constant-frequency echolocation, Doppler shift compensation, about 106–112 species, and roles as SARS-like coronavirus reservoirs.
Horseshoe crab
Horseshoe crab (Limulus polyphemus and three Asian Tachypleus/Carcinoscorpius species): ancient chelicerate arthropods, not true crabs, with 450-million-year fossil record; blue blood supplies the LAL endotoxin test; American species Vulnerable, tri-spine Endangered.
Horseshoe kidney
Horseshoe kidney, a congenital renal fusion anomaly (fused kidney, renal fusion), joins both kidneys at the lower poles via an isthmus; affects about 1 in 500 people, causing stones, PUJ obstruction, reflux, and elevated malignancy risk.
Horst Kessler
Horst Kessler is a German bioorganic chemist, professor at the Technical University of Munich from 1989 to 2008, known for cyclic peptide conformational analysis and RGD-based integrin ligands.
Horticultural Hall, Boston
Horticultural Hall, Boston, was a granite exhibition hall at 100–102 Tremont Street built for the Massachusetts Horticultural Society in 1864 and demolished in 1901, replaced by a Back Bay hall.
Horticultural Hall, Melbourne
Horticultural Hall, known as Horti Hall, is a two-storey brick exhibition and assembly hall at 31–33 Victoria Street, Melbourne, built in 1873 and now home to Victorian Opera.
Horticultural Hall, Toronto
Horticultural Hall, formally the Horticulture Building, is a 1907 Beaux-Arts exhibition pavilion on the Canadian National Exhibition grounds in Toronto, designed by George W. Gouinlock to replace the burned Crystal Palace.
Horticultural Therapy
Horticultural therapy is the use of plants and gardening activities, guided by a trained therapist, to promote healing and rehabilitation; it became a distinct profession in the mid-twentieth century.
Horticulture
Horticulture, or horticultural science, is the branch of agriculture devoted to intensively grown plants for food, medicine, and visual enjoyment, including fruits, vegetables, flowers, and ornamentals.
Hospice
Hospice: comfort-focused end-of-life care for terminally ill patients and families, rooted in Cicely Saunders' 1967 St Christopher's Hospice and a US Medicare benefit since 1982; four care levels, 6-month prognosis certification, over $23 billion in annual Medicare spending.