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Psychedelic drug

Psychedelics are a subclass of hallucinogenic drugs whose primary effect is to trigger non-ordinary mental states (known as psychedelic experiences or "trips") and a perceived "expansion of consciousness". Also referred to as classic hallucinogens or serotonergic hallucinogens, the term psychedelic is sometimes used more broadly to include various types of hallucinogens, such as those which are atypical or adjacent to psychedelia like salvia and MDMA, respectively.

Classic psychedelics generally cause specific psychological, visual, and auditory changes, and oftentimes a substantially altered state of consciousness. They have had the largest influence on science and culture, and include mescaline, LSD, psilocybin, and DMT.

Most psychedelic drugs fall into one of the three families of chemical compounds: tryptamines, phenethylamines, or lysergamides (LSD is considered both a tryptamine and lysergamide). They act via serotonin 2A receptor agonism. When compounds bind to serotonin 5-HT2A receptors, they modulate the activity of key circuits in the brain involved with sensory perception and cognition. However, the exact nature of how psychedelics induce changes in perception and cognition via the 5-HT2A receptor is still unknown. The psychedelic experience is often compared to non-ordinary forms of consciousness such as those experienced in meditation, mystical experiences, and near-death experiences, which also appear to be partially underpinned by altered default mode network activity. The phenomenon of ego death is often described as a key feature of the psychedelic experience.

Many psychedelic drugs are illegal worldwide under the UN conventions, with occasional exceptions for religious use or research contexts. Despite these controls, recreational use of psychedelics is common. Legal barriers have made the scientific study of psychedelics more difficult. Research has been conducted, however, and studies show that psychedelics are physiologically safe and rarely lead to addiction. Studies conducted using psilocybin in a psychotherapeutic setting reveal that psychedelic drugs may assist with treating depression, alcohol addiction, and nicotine addiction. Although further research is needed, existing results suggest that psychedelics could be effective treatments for certain forms of psychopathology. A 2022 survey found that 28% of Americans had used a psychedelic at some point in their life.

Etymology and nomenclature
The term psychedelic was coined by the psychiatrist Humphrey Osmond during written correspondence with author Aldous Huxley and presented to the New York Academy of Sciences by Osmond in 1957. It is irregularly derived from the Greek words ψυχή (psychḗ, meaning 'mind, soul') and δηλείν (dēleín, meaning 'to manifest'), with the intended meaning "mind manifesting" or alternatively "soul manifesting", and the implication that psychedelics can reveal unused potentials of the human mind. The term was loathed by American ethnobotanist Richard Schultes but championed by American psychologist Timothy Leary.

Aldous Huxley had suggested his own coinage phanerothyme (Greek phaneroein- "to make manifest or visible" and Greek thymos "soul", thus "to reveal the soul") to Osmond in 1956. Recently, the term entheogen (meaning "that which produces the divine within") has come into use to denote the use of psychedelic drugs, as well as various other types of psychoactive substances, in a religious, spiritual, and mystical context.

In 2004, David E. Nichols wrote the following about the nomenclature used for psychedelic drugs:

"Many different names have been proposed over the years for this drug class. The famous German toxicologist Louis Lewin used the name phantastica earlier in this century, and as we shall see later, such a descriptor is not so farfetched. The most popular names—hallucinogen, psychotomimetic, and psychedelic ('mind manifesting')—have often been used interchangeably. Hallucinogen is now, however, the most common designation in the scientific literature, although it is an inaccurate descriptor of the actual effects of these drugs. In the lay press, the term psychedelic is still the most popular and has held sway for nearly four decades. Most recently, there has been a movement in nonscientific circles to recognize the ability of these substances to provoke mystical experiences and evoke feelings of spiritual significance. Thus, the term entheogen, derived from the Greek word entheos, which means 'god within', was introduced by Ruck et al. and has seen increasing use. This term suggests that these substances reveal or allow a connection to the 'divine within'. Although it seems unlikely that this name will ever be accepted in formal scientific circles, its use has dramatically increased in the popular media and on internet sites. Indeed, in much of the counterculture that uses these substances, entheogen has replaced psychedelic as the name of choice and we may expect to see this trend continue."

Robin Carhart-Harris and Guy Goodwin write that the term psychedelic is preferable to hallucinogen for describing classical psychedelics because of the term hallucinogen's "arguably misleading emphasis on these compounds' hallucinogenic properties."

While the term psychedelic is most commonly used to refer only to serotonergic hallucinogens, it is sometimes used for a much broader range of drugs, including empathogen–entactogens, dissociatives, and atypical hallucinogens/psychoactives such as Amanita muscaria, Cannabis sativa, Nymphaea nouchali and Salvia divinorum. Thus, the term serotonergic psychedelic is sometimes used for the narrower class. It is important to check the definition of a given source. This article uses the more common, narrower definition of psychedelic.

Examples

 * 2C-B (2,5-dimethoxy-4-bromophenethylamine) is a substituted phenethylamine first synthesised in 1974 by Alexander Shulgin. 2C-B is both a psychedelic and a mild entactogen, with its psychedelic effects increasing and its entactogenic effects decreasing with dosage. 2C-B is the most well known compound in the 2C family, their general structure being discovered as a result of modifying the structure of mescaline.
 * DMT (N,N-dimethyltryptamine) is an indole alkaloid found in various species of plants. Traditionally it is consumed by tribes in South America in the form of ayahuasca. A brew is used that consists of DMT-containing plants as well as plants containing MAOIs, specifically harmaline, which allows DMT to be consumed orally without being rendered inactive by monoamine oxidase enzymes in the digestive system. In the Western world DMT is more commonly consumed via the vaporisation of freebase DMT. Whereas Ayahuasca typically lasts for several hours, inhalation has an onset measured in seconds and has effects measured in minutes, being significantly more intense. Particularly in vaporised form, DMT has the ability to cause users to enter a hallucinatory realm fully detached from reality, being typically characterised by hyperbolic geometry, and described as defying visual or verbal description. Users have also reported encountering and communicating with entitites within this hallucinatory state. DMT is the archetypal substituted tryptamine, being the structural scaffold of psilocybin and – to a lesser extent – the lysergamides.
 * LSD (Lysergic acid diethylamide) is a derivative of lysergic acid, which is obtained from the hydrolysis of ergotamine. Ergotamine is an alkaloid found in the fungus Claviceps purpurea, which primarily infects rye. LSD is both the prototypical psychedelic and the prototypical lysergamide. As a lysergamide, LSD contains both a tryptamine and phenethylamine group within its structure. As a result of containing a phenethylamine group LSD agonises dopamine receptors as well as serotonin receptors, making it more energetic in effect in contrast to the more sedating effects of psilocin, which is not a dopamine agonist.
 * Mescaline (3,4,5-trimethoxyphenethylamine) is a phenethylamine alkaloid found in various species of cacti, the best-known of these being peyote (Lophophora williamsii) and the San Pedro cactus (Trichocereus macrogonus var. pachanoi, syn. Echinopsis pachanoi). Mescaline has effects comparable to those of LSD and psilocybin, albeit with a greater emphasis on colors and patterns. Ceremonial San Pedro use seems to be characterized by relatively strong spiritual experiences, and low incidence of challenging experiences.
 * Psilocin (4-HO-DMT) is the dephosphorylated active metabolite of the indole alkaloid psilocybin and a substituted tryptamine, which is produced in over 200 species of fungi. Of the Classical psychedelics psilocybin has attracted the greatest academic interest regarding its ability to manifest mystical experiences, although all psychedelics are capable of doing so to variable degrees. O-Acetylpsilocin (4-AcO-DMT) is an acetylated analog of psilocin. Additionally, replacement of a methyl group at the dimethylated nitrogen with an isopropyl or ethyl group yields 4-HO-MIPT and 4-HO-MET, respectively.

Traditional
A number of frequently mentioned or traditional psychedelics such as Ayahuasca (which contains DMT), San Pedro, Peyote, and Peruvian torch (which all contain mescaline), Psilocybe mushrooms (which contain psilocin/psilocybin) and Tabernanthe iboga (which contains the unique psychedelic ibogaine) all have a long and extensive history of spiritual, shamanic and traditional usage by indigenous peoples in various world regions, particularly in Latin America, but also Gabon, Africa in the case of iboga. Different countries and/or regions have come to be associated with traditional or spiritual use of particular psychedelics, such as the ancient and entheogenic use of psilocybe mushrooms by the native Mazatec people of Oaxaca, Mexico or the use of the ayahuasca brew in the Amazon basin, particularly in Peru for spiritual and physical healing as well as for religious festivals. Peyote has also been used for several thousand years in the Rio Grande Valley in North America by native tribes as an entheogen. In the Andean region of South America, the San Pedro cactus (Trichocereus macrogonus var. pachanoi, syn. Echinopsis pachanoi) has a long history of use, possibly as a traditional medicine. Archaeological studies have found evidence of use going back two thousand years, to Moche culture, Nazca culture, and Chavín culture. Although authorities of the Roman Catholic church attempted to suppress its use after the Spanish conquest, this failed, as shown by the Christian element in the common name "San Pedro cactus" – Saint Peter cactus. The name has its origin in the belief that just as St Peter holds the keys to heaven, the effects of the cactus allow users "to reach heaven while still on earth." In 2022, the Peruvian Ministry of Culture declared the traditional use of San Pedro cactus in northern Peru as cultural heritage.

Although people of Western culture have tended to use psychedelics for either psychotherapeutic or recreational reasons, most indigenous cultures, particularly in South America, have seemingly tended to use psychedelics for more supernatural reasons such as divination. This can often be related to "healing" or health as well but typically in the context of finding out what is wrong with the individual, such as using psychedelic states to "identify" a disease and/or its cause, locate lost objects, and identify a victim or even perpetrator of sorcery. In some cultures and regions, even psychedelics themselves, such as ayahuasca and the psychedelic lichen of eastern Ecuador (Dictyonema huaorani) that supposedly contains both 5-MeO-DMT and psilocybin, have also been used by witches and sorcerers to conduct their malicious magic, similarly to nightshade deliriants like brugmansia and latua.

Psychedelic therapy
Psychedelic therapy (or psychedelic-assisted therapy) is the proposed use of psychedelic drugs to treat mental disorders. As of 2021, psychedelic drugs are controlled substances in most countries and psychedelic therapy is not legally available outside clinical trials, with some exceptions.

The procedure for psychedelic therapy differs from that of therapies using conventional psychiatric medications. While conventional medications are usually taken without supervision at least once daily, in contemporary psychedelic therapy the drug is administered in a single session (or sometimes up to three sessions) in a therapeutic context. The therapeutic team prepares the patient for the experience beforehand and helps them integrate insights from the drug experience afterwards. After ingesting the drug, the patient normally wears eyeshades and listens to music to facilitate focus on the psychedelic experience, with the therapeutic team interrupting only to provide reassurance if adverse effects such as anxiety or disorientation arise.

As of 2022, the body of high-quality evidence on psychedelic therapy remains relatively small and more, larger studies are needed to reliably show the effectiveness and safety of psychedelic therapy's various forms and applications. On the basis of favorable early results, ongoing research is examining proposed psychedelic therapies for conditions including major depressive disorder, and anxiety and depression linked to terminal illness. The United States Food and Drug Administration has granted "breakthrough therapy" status, which expedites the assessment of promising drug therapies for potential approval, to psilocybin therapy for treatment-resistant depression and major depressive disorder.

Recreational
Recreational use of psychedelics has been common since the psychedelic era of the mid-1960s and continues to play a role in various festivals and events, including Burning Man. A survey published in 2013 found that 13.4% of American adults had used a psychedelic.

A June 2024 report by the RAND Corporation suggests psilocybin mushrooms may be the most prevalent psychedelic drug among adults in the United States. The RAND national survey indicated that 3.1% of U.S. adults reported using psilocybin in the past year. Roughly 12% of respondents acknowledged lifetime use of psilocybin, while a similar percentage reported having used LSD at some point in their lives. MDMA, also known as ecstasy, showed a lower prevalence of use at 7.6%. Notably, less than 1% of U.S. adults reported using any psychedelic drugs within the past month.

Microdosing
Psychedelic microdosing is the practice of using sub-threshold doses (microdoses) of psychedelics in an attempt to improve creativity, boost physical energy level, emotional balance, increase performance on problems-solving tasks and to treat anxiety, depression and addiction. The practice of microdosing has become more widespread in the 21st century with more people claiming long-term benefits from the practice.

A 2022 study recognized signatures of psilocybin microdosing in natural language and concluded that low amount of psychedelics have potential for application, and ecological observation of microdosing schedules.

Pharmacology
While the method of action of psychedelics is not fully understood, they are known to show affinities for various 5-HT (serotonin) receptors in different ways and levels, and may be classified by their activity at different 5-HT sub-types, particularly 5-HT1A, 5-HT2A, and 5-HT2C. It is almost unanimously agreed that psychedelics produce their effect by acting as strong partial agonists at the 5-HT2A receptors. How this produces the psychedelic experience is unclear, but it is likely that it acts by increasing excitation in the cortex, possibly by specifically facilitating input from the thalamus, the major relay for sensory information input to the cortex. Additionally, researchers discovered that many psychedelics are potent psychoplastogens, compounds capable of promoting rapid and sustained neural plasticity.

Tryptamines
Tryptamine, along with other trace amines, is found in the central nervous system of mammals. It is hypothesized to play a role as a neuromodulator on classical monoamine neurotransmitters, such as dopamine, serotonin, norepinephrine and epinephrine. Tryptamine acts as a non-selective serotonin receptor agonist to activate serotonin receptors, and a serotonin–norepinephrine–dopamine releasing agent (SNDRA) to release more monoamine neurotransmitter, with a preference for evoking serotonin and dopamine release over norepinephrine (epinephrine) release. Psychedelic tryptamines found in nature include psilocin, DMT, 5-MeO-DMT, and tryptamines that have been synthesized in the laboratory include 4-HO-MET, 4-HO-MiPT, and 5-MeO-DALT.

Phenethylamines
Phenethylamine is also a trace amine but to a lesser extent acts as a neurotransmitter in the human central nervous system (CNS). Phenethylamine instead regulates monoamine neurotransmission by binding to trace amine-associated receptor 1 (TAAR1), which plays a significant role in regulating neurotransmission in dopamine, norepinephrine, and serotonin neurons in the CNS and inhibiting vesicular monoamine transporter 2 (VMAT2) in monoamine neurons. When VMAT2 is inhibited monoamine neurotransmitters such as dopamine cannot be released into the synapse via typical release mechanisms. Mescaline is a naturally occurring psychedelic protoalkaloid of the substituted phenethylamine class.

Lysergamides
Amides of lysergic acid are collectively known as lysergamides, and include a number of compounds with potent agonist and/or antagonist activity at various serotonin and dopamine receptors. The structure of lysergamides contains the structure of both tryptamines and phenethylamines. LSD (Lysergic Acid Diethylamide) is one of many lysergamides. A wide range of lysergamides have emerged in recent years, inspired by existing scientific literature. Others, have appeared from chemical research. 1P-LSD is a derivative and functional analogue of LSD and a homologue of ALD-52. It modifies the LSD molecule by adding a propionyl group to the nitrogen atom of LSD's indole.

Psychedelic experiences
Although several attempts have been made, starting in the 19th and 20th centuries, to define common phenomenological structures of the effects produced by classic psychedelics, a universally accepted taxonomy does not yet exist. At lower doses, features of psychedelic experiences include sensory alterations, such as the warping of surfaces, shape suggestibility, pareidolia and color variations. Users often report intense colors that they have not previously experienced, and repetitive geometric shapes or form constants are common as well. Higher doses often cause intense and fundamental alterations of sensory (notably visual) perception, such as synesthesia or the experience of additional spatial or temporal dimensions. Tryptamines are well documented to cause classic psychedelic states, such as increased empathy, visual distortions (drifting, morphing, breathing, melting of various surfaces and objects), auditory hallucinations, ego dissolution or ego death with high enough dose, mystical, transpersonal and spiritual experiences, autonomous "entity" encounters, time distortion, closed eye hallucinations and complete detachment from reality with a high enough dose. Luis Luna describes psychedelic experiences as having a distinctly gnosis-like quality, and says that they offer "learning experiences that elevate consciousness and can make a profound contribution to personal development." Czech psychiatrist Stanislav Grof studied the effects of psychedelics like LSD early in his career and said of the experience, that it commonly includes "complex revelatory insights into the nature of existence… typically accompanied by a sense of certainty that this knowledge is ultimately more relevant and 'real' than the perceptions and beliefs we share in everyday life." Traditionally, the standard model for the subjective phenomenological effects of psychedelics has typically been based on LSD, with anything that is considered "psychedelic" evidently being compared to it and its specific effects.

During a speech on his 100th birthday, the inventor of LSD, Albert Hofmann said of the drug: "It gave me an inner joy, an open mindedness, a gratefulness, open eyes and an internal sensitivity for the miracles of creation... I think that in human evolution it has never been as necessary to have this substance LSD. It is just a tool to turn us into what we are supposed to be." With certain psychedelics and experiences, a user may also experience an "afterglow" of improved mood or perceived mental state for days or even weeks after ingestion in some cases. In 1898, the English writer and intellectual Havelock Ellis reported a heightened perceptual sensitivity to "the more delicate phenomena of light and shade and color" for a prolonged period of time after his exposure to mescaline. Good trips are reportedly deeply pleasurable, and typically involve intense joy or euphoria, a greater appreciation for life, reduced anxiety, a sense of spiritual enlightenment, and a sense of belonging or interconnectedness with the universe. Negative experiences, colloquially known as "bad trips," evoke an array of dark emotions, such as irrational fear, anxiety, panic, paranoia, dread, distrustfulness, hopelessness, and even suicidal ideation. While it is impossible to predict when a bad trip will occur, one's mood, surroundings, sleep, hydration, social setting, and other factors can be controlled (colloquially referred to as "set and setting") to minimize the risk of a bad trip. The concept of "set and setting" also generally appears to be more applicable to psychedelics than to other types of hallucinogens such as deliriants, hypnotics and dissociative anesthetics.

Classic psychedelics are considered to be those found in nature like psilocybin, DMT, mescaline, and LSD which is derived from naturally occurring ergotamine, and non-classic psychedelics are considered to be newer analogs and derivatives of pharmacophore lysergamides, tryptamine, and phenethylamine structures like 2C-B. Many of these psychedelics cause remarkably similar effects, despite their different chemical structure. However, many users report that the three major families have subjectively different qualities in the "feel" of the experience, which are difficult to describe. Some compounds, such as 2C-B, have extremely tight "dose curves", meaning the difference in dose between a non-event and an overwhelming disconnection from reality can be very slight. There can also be very substantial differences between the drugs; for instance, 5-MeO-DMT rarely produces the visual effects typical of other psychedelics.

Potential adverse effects
Despite the contrary perception of much of the public, psychedelic drugs are not addictive and are physiologically safe. As of 2016, there have been no known deaths due to overdose of LSD, psilocybin, or mescaline.

Risks do exist during an unsupervised psychedelic experience, however; Ira Byock wrote in 2018 in the Journal of Palliative Medicine that psilocybin is safe when administered to a properly screened patient and supervised by a qualified professional with appropriate set and setting. However, he called for an "abundance of caution" because in the absence of these conditions a range of negative reactions is possible, including "fear, a prolonged sense of dread, or full panic." He notes that driving or even walking in public can be dangerous during a psychedelic experience because of impaired hand-eye coordination and fine motor control. In some cases, individuals taking psychedelics have performed dangerous or fatal acts because they believed they possessed superhuman powers.

Psilocybin-induced states of mind share features with states experienced in psychosis, and while a causal relationship between psilocybin and the onset of psychosis has not been established as of 2011, researchers have called for investigation of the relationship. Many of the persistent negative perceptions of psychological risks are unsupported by the currently available scientific evidence, with the majority of reported adverse effects not being observed in a regulated and/or medical context. A population study on associations between psychedelic use and mental illness published in 2013 found no evidence that psychedelic use was associated with increased prevalence of any mental illness.

Using psychedelics poses certain risks of re-experiencing of the drug's effects, including flashbacks and hallucinogen persisting perception disorder (HPPD). These non-psychotic effects are poorly studied, but the permanent symptoms (also called "endless trip") are considered to be rare.

Serotonin syndrome can be caused by combining psychedelics with other serotonergic drugs, including certain antidepressants, opioids, CNS stimulants (e.g. MDMA), 5-HT1 agonists (e.g. triptans), herbs and others.

Potential therapeutic effects
Psychedelic substances which may have therapeutic uses include psilocybin, LSD, and mescaline. During the 1950s and 1960s, lack of informed consent in some scientific trials on psychedelics led to significant, long-lasting harm to some participants. Since then, research regarding the effectiveness of psychedelic therapy has been conducted under strict ethical guidelines, with fully informed consent and a pre-screening to avoid people with psychosis taking part. Although the history behind these substances has hindered research into their potential medicinal value, scientists are now able to conduct studies and renew research that was halted in the 1970s. Some research has shown that these substances have helped people with such mental disorders as obsessive-compulsive disorder (OCD), post-traumatic stress disorder (PTSD), alcoholism, depression, and cluster headaches.

It has long been known that psychedelics promote neurite growth and neuroplasticity and are potent psychoplastogens. There is evidence that psychedelics induce molecular and cellular adaptations related to neuroplasticity and that these could potentially underlie therapeutic benefits. Psychedelics have also been shown to have potent anti-inflammatory activity and therapeutic effects in animal models of inflammatory diseases including asthma, and cardiovascular disease and diabetes.

Surrounding culture

Psychedelic culture includes manifestations such as psychedelic music, psychedelic art, psychedelic literature, psychedelic film, and psychedelic festivals. Examples of psychedelic music would be rock bands like the Grateful Dead, Jefferson Airplane and The Beatles. Many psychedelic bands and elements of the psychedelic subculture originated in San Francisco during the mid to late 1960s.

Legal status
Many psychedelics are classified under Schedule I of the United Nations Convention on Psychotropic Substances of 1971 as drugs with the greatest potential to cause harm and no acceptable medical uses. In addition, many countries have analogue laws; for example, in the United States, the Federal Analogue Act of 1986 automatically forbids any drugs sharing similar chemical structures or chemical formulas to illicit or prohibited substances if sold for human consumption.

U.S. states such as Oregon and Colorado have also instituted decriminalization and legalization measures of psychedelics and states like New Hampshire are attempting to do the same. J.D. Tuccille argues that increasing rates of use of psychedelics in defiance of the law are likely to result in more widespread legalization and decriminalization of the substances in the United States (as has happened with alcohol and cannabis).

title: Psychedelic drug


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Vaccinium

Vaccinium is a common and widespread genus of shrubs or dwarf shrubs in the heath family (Ericaceae). The fruits of many species are eaten by humans and some are of commercial importance, including the cranberry, blueberry, bilberry (whortleberry), lingonberry (cowberry), and huckleberry. Like many other ericaceous plants, they are generally restricted to acidic soils.

Description
The plant structure varies between species: some trail along the ground, some are dwarf shrubs, and some are larger shrubs perhaps 1 to 2 m tall. Some tropical species are epiphytic. Stems are usually woody. Flowers are epigynous with fused petals, and have long styles that protrude from their bell-shaped corollas. Stamens have anthers with extended tube-like structures called "awns" through which pollen falls when mature. Inflorescences can be axillary or terminal. The fruit develops from an inferior ovary, and is a four- or five-parted berry; it is usually brightly coloured, often being red or bluish with purple juice. Roots are commonly mycorrhizal, which likely help the plants to access nutrients such as nitrogen and phosphorus in the acidic, nutrient-poor soils they inhabit.

Taxonomy
The genus was first described scientifically by Carl Linnaeus in 1753. The name Vaccinium was used in classical Latin for a plant, possibly the bilberry or a hyacinth, and may be derived from the Latin bacca, berry, although its ultimate derivation is obscure. It is not the same word as Vaccinum "of or pertaining to cows".

The taxonomy of the genus is complex, and still under investigation. Genetic analyses indicates that the genus Vaccinium is not monophyletic. A number of the Asian species are more closely related to Agapetes than to other Vaccinium species. A second group includes most of Orthaea and Notopora, at least some of Gaylussacia (huckleberry), and a number of species from Vaccinium, such as V. crassifolium. Other parts of Vaccinium form other groups, sometimes together with species of other genera. The taxonomy of Vaccinium can either be resolved by enlarging the genus to include the entirety of the tribe Vaccinieae, or by breaking the genus up into several different genera.

Two fossil seeds of V. minutulum have been extracted from borehole samples of the Middle Miocene freshwater deposits in Nowy Sacz Basin, West Carpathians, Poland.

Subgenera
A classification predating molecular phylogeny divides Vaccinium into subgenera, and several sections:

 * Subgenus Oxycoccus: The cranberries, with slender, trailing, wiry non-woody shoots and strongly reflexed flower petals. Some botanists treat Oxycoccus as a distinct genus.
 * Sect. Oxycoccus
 * Vaccinium macrocarpon – American cranberry
 * Vaccinium oxycoccos – common cranberry
 * Vaccinium microcarpum – small bog cranberry
 * Sect. Oxycoccoides
 * Vaccinium erythrocarpum – southern mountain cranberry
 * Vaccinium japonicum – mountain blueberry
 * Subgenus Vaccinium: All the other species, with thicker, upright woody shoots and bell-shaped flowers
 * Sect. Batodendron
 * Vaccinium arboreum – sparkleberry
 * Vaccinium crassifolium – creeping blueberry
 * Sect. Brachyceratium
 * Vaccinium dependens
 * Sect. Bracteata
 * Vaccinium acrobracteatum
 * Vaccinium barandanum
 * Vaccinium bracteatum
 * Vaccinium coriaceum
 * Vaccinium cornigerum
 * Vaccinium cruentum
 * Vaccinium hooglandii
 * Vaccinium horizontale
 * Vaccinium laurifolium
 * Vaccinium lucidum
 * Vaccinium myrtoides
 * Vaccinium phillyreoides
 * Vaccinium reticulatovenosum
 * Vaccinium sparsum
 * Vaccinium varingifolium
 * Sect. Ciliata
 * Vaccinium ciliatum
 * Vaccinium oldhamii - Japanese blueberry
 * Sect. Cinctosandra
 * Vaccinium exul
 * Sect. Conchophyllum
 * Vaccinium corymbodendron
 * Vaccinium delavayi
 * Vaccinium emarginatum
 * Vaccinium griffithianum
 * Vaccinium moupinense – Himalayan blueberry
 * Vaccinium neilgherrense
 * Vaccinium nummularia
 * Vaccinium retusum
 * Sect. Cyanococcus – typical North American blueberries
 * Vaccinium angustifolium – lowbush blueberry - also known as Vaccinium stenophyllum
 * Vaccinium boreale – northern blueberry
 * Vaccinium caesariense – New Jersey blueberry
 * Vaccinium corymbosum – highbush blueberry
 * Vaccinium darrowii – evergreen blueberry
 * Vaccinium elliottii – Elliott's blueberry
 * Vaccinium formosum
 * Vaccinium fuscatum – black highbush blueberry; syn. V. atrococcum
 * Vaccinium hirsutum
 * Vaccinium myrsinites – evergreen blueberry
 * Vaccinium myrtilloides – Canadian blueberry
 * Vaccinium pallidum Ait. – dryland blueberry (images ); syn. V. vacillans Torr.
 * Vaccinium simulatum
 * Vaccinium tenellum
 * Vaccinium virgatum – rabbiteye blueberry; syn. V. ashei
 * Sect. Eococcus
 * Vaccinium fragile
 * Sect. Epigynium
 * Vaccinium vacciniaceum
 * Sect. Galeopetalum
 * Vaccinium chunii
 * Vaccinium dunalianum
 * Vaccinium glaucoalbum
 * Vaccinium sikkimense (may not be treated as a separate species from V. glaucoalbum)
 * Vaccinium urceolatum
 * Sect. Hemimyrtillus
 * Vaccinium arctostaphylos
 * Vaccinium cylindraceum
 * Vaccinium hirtum
 * Vaccinium padifolium – Madeira blueberry
 * Vaccinium smallii
 * Sect. Koreanum
 * Vaccinium koreanum – Korean blueberry
 * Sect. Myrtillus (including sect. Macropelma) – bilberries and relatives. Monophyly of this section has been confirmed by matK and nuclear ribosomal ITS sequence data.
 * Vaccinium calycinum Sm. – ʻōhelo kau laʻau (Hawaii)
 * Vaccinium cereum (L.f.) Forst.f. – east Polynesian blueberry, Pacific blueberry
 * Vaccinium cespitosum – dwarf bilberry
 * Vaccinium deliciosum – Cascade bilberry, Cascade blueberry, blueleaf huckleberry
 * Vaccinium dentatum Sm. – ʻōhelo (Hawaii)
 * Vaccinium membranaceum – square-twig blueberry, thinleaf huckleberry, tall huckleberry, big huckleberry, mountain huckleberry, "black huckleberry"
 * Vaccinium myrtillus – common bilberry, blue whortleberry, blaeberry, fraughan, hurtleberry
 * Vaccinium ovalifolium – Alaska blueberry, early blueberry, oval-leaf blueberry
 * Vaccinium parvifolium – red huckleberry
 * Vaccinium praestans – krasnika (красника), Kamchatka bilberry
 * Vaccinium reticulatum – ʻōhelo ʻai (Hawaii)
 * Vaccinium scoparium – grouse whortleberry, grouseberry, littleleaf huckleberry
 * Vaccinium shastense - Shasta huckleberry
 * Sect. Neurodesia
 * Vaccinium crenatum
 * Sect. Oarianthe
 * Vaccinium ambyandrum
 * Vaccinium cyclopense
 * Sect. Oreades
 * Vaccinium poasanum
 * Sect. Pachyanthum
 * Vaccinium fissiflorum
 * Sect. Polycodium
 * Vaccinium stamineum L. – deerberry; syn. V. caesium (eastern North America) (images )
 * Sect. Pyxothamnus
 * Vaccinium consanguineum
 * Vaccinium floribundum
 * Vaccinium meridionale
 * Vaccinium ovatum Pursh – California huckleberry (or evergreen huckleberry) (coastal western North America). First collected and described for western science by Meriwether Lewis.
 * Sect. Vaccinium
 * Vaccinium uliginosum L. – northern (or bog) bilberry (or blueberry); syn. V. occidentale (northern North America and Eurasia)
 * Sect. Vitis-idaea
 * Vaccinium vitis-idaea L. – partridgeberry, cowberry, redberry, red whortleberry, or lingonberry (northern North America and Eurasia)

Distribution and habitat
The genus contains about 450 species, which are found mostly in the cooler areas of the Northern Hemisphere, although there are tropical species from areas as widely separated as Madagascar and Hawaii. The genus is distributed worldwide except for Australia and Antarctica, but areas of great Vaccinium diversity include the montane regions of North and South America, as well as Southeast Asia. Species are still being discovered in the Andes.

Plants of this group typically require acidic soils, and as wild plants they live in habitats such as heath, bog and acidic woodland (for example, blueberries under oaks or pines). Blueberry plants are commonly found in oak-heath forests in eastern North America. Vaccinium is found in both successional and stable sites, and is fire-adapted in many regions, withstanding low-intensity burns, and re-sprouting from rhizomes when above-ground tissues are burned off.

Ecology
Vaccinium species are used as food plants by the larvae of a number of Lepidoptera (butterfly and moth) species. Berries of North American species nourish a variety of mammals and birds, notably including the grizzly bear.

Cultivation
Blueberries (sect. Cyanococcus) and cranberries (sect. Oxycoccus) are relatively newly cultivated plants, and are largely unchanged from their wild relatives. Genetic breeding of blueberries began around the turn of the 20th century, and was spearheaded by Frederick Coville who performed many cross-breeding trials and produced dozens of new blueberry cultivars. He often tested new cultivars for their flavor, claiming after a long day of tasting that "all blueberries taste the same, and all taste sour."

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Vaccinium


text:
Hermann von Helmholtz

Hermann Ludwig Ferdinand von Helmholtz (31 August 1821 – 8 September 1894) was a German physicist and physician who made significant contributions in several scientific fields, particularly hydrodynamic stability. The Helmholtz Association, the largest German association of research institutions, is named in his honour.

In the fields of physiology and psychology, Helmholtz is known for his mathematics concerning the eye, theories of vision, ideas on the visual perception of space, colour vision research, the sensation of tone, perceptions of sound, and empiricism in the physiology of perception. In physics, he is known for his theories on the conservation of energy and on the electrical double layer, work in electrodynamics, chemical thermodynamics, and on a mechanical foundation of thermodynamics. As a philosopher, he is known for his philosophy of science, ideas on the relation between the laws of perception and the laws of nature, the science of aesthetics, and ideas on the civilizing power of science.

Early years
Helmholtz was born in Potsdam, the son of the local gymnasium headmaster, Ferdinand Helmholtz, who had studied classical philology and philosophy, and who was a close friend of the publisher and philosopher Immanuel Hermann Fichte. Helmholtz's work was influenced by the philosophy of Johann Gottlieb Fichte and Immanuel Kant. He tried to trace their theories in empirical matters like physiology.

As a young man, Helmholtz was interested in natural science, but his father wanted him to study medicine. Helmholtz earned a medical doctorate at Medicinisch-chirurgisches Friedrich-Wilhelm-Institute in 1842 and served a one-year internship at the Charité hospital (because there was financial support for medical students).

Trained primarily in physiology, Helmholtz wrote on many other topics, ranging from theoretical physics to the age of the Earth, and to the origin of the Solar System.

University posts
Helmholtz's first academic position was as a teacher of anatomy at the Academy of Arts in Berlin in 1848. He then moved to take a post of associate professor of physiology at the Prussian University of Königsberg, where he was appointed in 1849. In 1855 he accepted a full professorship of anatomy and physiology at the University of Bonn. He was not particularly happy in Bonn, however, and three years later he transferred to the University of Heidelberg, in Baden, where he served as professor of physiology. In 1871 he accepted his final university position, as professor of physics at the Friedrich Wilhelm University in Berlin.

Mechanics
His first important scientific achievement, an 1847 treatise on the conservation of energy, was written in the context of his medical studies and philosophical background. His work on energy conservation came about while studying muscle metabolism. He tried to demonstrate that no energy is lost in muscle movement, motivated by the implication that there were no vital forces necessary to move a muscle. This was a rejection of the speculative tradition of Naturphilosophie and vitalism which was at that time a dominant philosophical paradigm in German physiology. He was working against the argument, promoted by some vitalists, that "living force" can power a machine indefinitely.

Drawing on the earlier work of Sadi Carnot, Benoît Paul Émile Clapeyron and James Prescott Joule, he postulated a relationship between mechanics, heat, light, electricity and magnetism by treating them all as manifestations of a single force, or energy in today's terminology. He published his theories in his book Über die Erhaltung der Kraft (On the Conservation of Force, 1847).

In the 1850s and 60s, building on the publications of William Thomson, Helmholtz and William Rankine popularized the idea of the heat death of the universe.

In fluid dynamics, Helmholtz made several contributions, including Helmholtz's theorems for vortex dynamics in inviscid fluids.

Sensory physiology
Helmholtz was a pioneer in the scientific study of human vision and audition. Inspired by psychophysics, he was interested in the relationships between measurable physical stimuli and their correspondent human perceptions. For example, the amplitude of a sound wave can be varied, causing the sound to appear louder or softer, but a linear step in sound pressure amplitude does not result in a linear step in perceived loudness. The physical sound needs to be increased exponentially in order for equal steps to seem linear, a fact that is used in current electronic devices to control volume. Helmholtz paved the way in experimental studies on the relationship between the physical energy (physics) and its appreciation (psychology), with the goal in mind to develop "psychophysical laws".

The sensory physiology of Helmholtz was the basis of the work of Wilhelm Wundt, a student of Helmholtz, who is considered one of the founders of experimental psychology. More explicitly than Helmholtz, Wundt described his research as a form of empirical philosophy and as a study of the mind as something separate. Helmholtz had, in his early repudiation of Naturphilosophie, stressed the importance of materialism, and was focusing more on the unity of "mind" and body.

Ophthalmic optics
In 1851, Helmholtz revolutionized the field of ophthalmology with the invention of the ophthalmoscope; an instrument used to examine the inside of the human eye. This made him world-famous overnight. Helmholtz's interests at that time were increasingly focused on the physiology of the senses. His main publication, titled Handbuch der Physiologischen Optik (Handbook of Physiological Optics or Treatise on Physiological Optics; English translation of the 3rd volume here), provided empirical theories on depth perception, colour vision, and motion perception, and became the fundamental reference work in his field during the second half of the nineteenth century. In the third and final volume, published in 1867, Helmholtz described the importance of unconscious inferences for perception. The Handbuch was first translated into English under the editorship of James P. C. Southall on behalf of the Optical Society of America in 1924–5. His theory of accommodation went unchallenged until the final decade of the 20th century.

Helmholtz continued to work for several decades on several editions of the handbook, frequently updating his work because of his dispute with Ewald Hering who held opposite views on spatial and colour vision. This dispute divided the discipline of physiology during the second half of the 1800s.

Nerve physiology
In 1849, while at Königsberg, Helmholtz measured the speed at which the signal is carried along a nerve fibre. At that time most people believed that nerve signals passed along nerves immeasurably fast. He used a recently dissected sciatic nerve of a frog and the calf muscle to which it attached. He used a galvanometer as a sensitive timing device, attaching a mirror to the needle to reflect a light beam across the room to a scale which gave much greater sensitivity. Helmholtz reported transmission speeds in the range of 24.6 – 38.4 meters per second.

Acoustics and aesthetics

In 1863, Helmholtz published Sensations of Tone, once again demonstrating his interest in the physics of perception. This book influenced musicologists into the twentieth century. Helmholtz invented the Helmholtz resonator to identify the various frequencies or pitches of the pure sine wave components of complex sounds containing multiple tones.

Helmholtz showed that different combinations of resonators could mimic vowel sounds: Alexander Graham Bell in particular was interested in this but, not being able to read German, misconstrued Helmholtz's diagrams as meaning that Helmholtz had transmitted multiple frequencies by wire—which would allow multiplexing of telegraph signals—whereas, in reality, electrical power was used only to keep the resonators in motion. Bell failed to reproduce what he thought Helmholtz had done but later said that, had he been able to read German, he would not have gone on to invent the telephone on the harmonic telegraph principle.

The translation by Alexander J. Ellis was first published in 1875 (the first English edition was from the 1870 third German edition; Ellis's second English edition from the 1877 fourth German edition was published in 1885; the 1895 and 1912 third and fourth English editions were reprints of the second).

Electromagnetism
Helmholtz studied the phenomena of electrical oscillations from 1869 to 1871, and in a lecture delivered to the Naturhistorisch-medizinischen Vereins zu Heidelberg (Natural History and Medical Association of Heidelberg) on 30 April 1869, titled On Electrical Oscillations he indicated that the perceptible damped electrical oscillations in a coil joined up with a Leyden jar were about 1/50th of a second in duration.

In 1871, Helmholtz moved from Heidelberg to Berlin to become a professor of physics. He became interested in electromagnetism, and the Helmholtz equation is named for him. Although he did not make major contributions to this field, his student Heinrich Rudolf Hertz became famous as the first to demonstrate electromagnetic radiation. Oliver Heaviside criticised Helmholtz's electromagnetic theory because it allowed the existence of longitudinal waves. Based on work on Maxwell's equations, Heaviside pronounced that longitudinal waves could not exist in a vacuum or a homogeneous medium. Heaviside did not note, however, that longitudinal electromagnetic waves can exist at a boundary or in an enclosed space.

Philosophy
Helmholtz wavered between empiricism and transcendentalism in his philosophy of science.

Quotation
Whoever, in the pursuit of science, seeks after immediate practical utility may rest assured that he seeks in vain. — Academic Discourse (Heidelberg 1862)

Students and associates
Other students and research associates of Helmholtz at Berlin included Max Planck, Heinrich Kayser, Eugen Goldstein, Wilhelm Wien, Arthur König, Henry Augustus Rowland, Albert A. Michelson, Wilhelm Wundt, Fernando Sanford and Michael I. Pupin. Leo Koenigsberger, who was his colleague from 1869 to 1871 in Heidelberg, wrote the definitive biography of him in 1902.

Honours and legacy

 * In 1873, Helmholtz was elected as a member of the American Philosophical Society.
 * In 1881, Helmholtz was elected Honorary Fellow of the Royal College of Surgeons in Ireland.
 * On 10 November 1881, he was awarded the Légion d'honneur: au grade de Commandeur, or Level 3 – a senior grade. (No. 2173).
 * In 1883, Professor Helmholtz was honoured by the Emperor, being raised to the nobility, or Adel. The Adelung meant that he and his family were now styled: von Helmholtz. The distinction was not a peerage or title, but it was hereditary and conferred a certain social cachet.
 * Helmholtz was conferred with Honorary Membership of the Institution of Engineers and Shipbuilders in Scotland in 1884.
 * The largest German association of research institutions, the Helmholtz Association, is named after him.
 * The asteroid 11573 Helmholtz and the lunar crater Helmholtz as well as the crater Helmholtz on Mars were named in his honour.
 * In Charlottenburg, Berlin, the street Helmholtzstraße is named after von Helmholtz.

Translated works

 * On the Conservation of Force (1847) HathiTrust
 * On the Conservation of Force (1895) Introduction to a Series of Lectures Delivered at Carlsruhe in the Winter of 1862–1863, English translation
 * On the Sensations of Tone as a Physiological Basis for the Theory of Music (downloadable from California Digital Library) Third Edition of English Translation, based on Fourth German Edition of 1877, By Hermann von Helmholtz, Alexander John Ellis, Published by Longmans, Green, 1895, 576 pages
 * On the Sensations of Tone as a Physiological Basis for the Theory of Music (downloadable from Google Books) Fourth Edition, By Hermann von Helmholtz, Alexander John Ellis, Published by Longmans, Green, 1912, 575 pages
 * Treatise on Physiological Optics (1910) three volumes. English translation by Optical Society of America (1924–25).
 * Popular lectures on scientific subjects (1885)
 * Popular lectures on scientific subjects second series (1908)
 * Treatise on Physiological Optics (1910) three volumes. English translation by Optical Society of America (1924–25).
 * Popular lectures on scientific subjects (1885)
 * Popular lectures on scientific subjects second series (1908)

title: Hermann von Helmholtz


text:
Vitaceae

The Vitaceae are a family of flowering plants, with 14 genera and around 910 known species, including common plants such as grapevines (Vitis spp.) and Virginia creeper (Parthenocissus quinquefolia). The family name is derived from the genus Vitis.

Most Vitis species have 38 chromosomes (n=19), but 40 (n=20) in subgenus Muscadinia, while Ampelocissus, Parthenocissus, and Ampelopsis also have 40 chromosomes (n=20) and Cissus has 24 chromosomes (n=12).

The family is economically important as the berries of Vitis species, commonly known as grapes, are an important fruit crop and, when fermented, produce wine.

Species of the genus Tetrastigma serve as hosts to parasitic plants in the family Rafflesiaceae.

Taxonomy
The name sometimes appears as Vitidaceae, but Vitaceae is a conserved name and therefore has priority over both Vitidaceae and another name sometimes found in the older literature, Ampelidaceae. In the APG III system (2009) onwards, the family is placed in its own order, Vitales. Molecular phylogenetic studies place the Vitales as the most basal clade in the rosids. In the Cronquist system, the family was placed near the family Rhamnaceae in order Rhamnales.

Plants of the World Online currently includes the following genera, placed in two subfamilies:

Leeoideae

 * Leea D.Royen : previously placed in its own monotypic family, Leeaceae, was included in Vitaceae by APG IV (2016) and the Angiosperm Phylogeny Website.

Vitoideae
Five tribes are now recognised in this subfamily:
 * Ampelopsideae
 * 1) Ampelopsis A.Rich. ex Michx. (pepper-vines)
 * 2) Clematicissus Planch.
 * 3) Nekemias Raf.
 * 4) Rhoicissus Planch.
 * Cayratieae
 * 1) Acareosperma Gagnep.
 * 2) Afrocayratia J.Wen, L.M.Lu, Rabarij. & Z.D.Chen
 * 3) Causonis Raf.
 * 4) Cayratia Juss.
 * 5) Cyphostemma (Planch.) Alston
 * 6) Pseudocayratia J.Wen, L.M.Lu & Z.D.Chen
 * 7) Tetrastigma (Miq.) Planch.
 * Cisseae
 * 1) Cissus L. (treebinds) - widespread in  tropics & subtropics
 * Parthenocisseae
 * 1) Parthenocissus Planch.
 * 2) Yua C.L.Li
 * Viteae
 * 1) Ampelocissus Planch.
 * 2) Vitis L. (includes grape vine)
 * tribe incertae sedis
 * 1) Pterisanthes Blume (Indochina, Malesia)

Earliest fossil history
Well preserved-fruits of Indovitis chitaleyae containing seeds with similar morphology to the Vitaceae have been recovered from Late Cretaceous Deccan Intertrappean beds of several sites in central India. These fruits and their dispersed seeds found in the same sediments, about 66 million years old, represent the oldest known fossils of the grape family. The fossil fruits containing 4 to 6 seeds are very similar to extant Vitis.

title: Vitaceae


text:
Henri Labrouste

Pierre-François-Henri Labrouste (11 May 1801 – 24 June 1875) was a French architect from the famous École des Beaux-Arts school of architecture. After a six-year stay in Rome, Labrouste established an architectural training workshop, which soon became known for rationalism. He became noted for his use of iron-frame construction and was one of the first to realize the importance of its use.

Biography
Born in Paris, Labrouste was one of five children of, a lawyer and politician from Bordeaux and Anne-Dominique Gourg (1764-1851), daughter and granddaughter of cognac merchants. He entered the Collège Sainte-Barbe as a student in 1809. He was then admitted into the second class and the Lebas-Vaudoyer workshop in the École Royale des Beaux Arts in 1819. In 1820, he was promoted to the first class. Competing for the Grand Prix, Labrouste was awarded second place (the Palais de Justice scored first) by Guillaume-Abel Blouet in 1821. In 1823, he won the departmental prize and worked as a lieutenant-inspector (sous-inspecteur) for the director Étienne-Hippolyte Godde during the construction of the Saint-Pierre-du-Gros-Caillou parish in Paris. In 1824 Labrouste won the competition with a design of a Court of Appeals (Cour de cassation). In November, he left Paris for Italy, visiting Turin, Milan, Lodi, Piacenza, Parma, Modena, Bologna, Florence and Arezzo.

In July 1835 in Paris he was present at the scene when Giuseppe Marco Fieschi attempted the assassination of King Louis-Philippe using a home-made, multi-barrel gun fired from an upstairs window. Although the King only received a minor injury, 18 people were killed, including Henri's father, Alexandre Labrouste.

Stay in Rome
Receiving a pension or stipend from the French government for five years, he and the other Académie française laureates stayed in the Medici Villa in Rome. The directors of the Académie stated in correspondence in French about the laureates that, in their studies of antiquity, they "must research the laws of proportion and reduce them to formulas to be used by masters and students in Paris."

His work was the subject of "Henri Labrouste: Structure Brought to Light," the first solo exhibition in the U.S. of his work, at The Museum of Modern Art in New York City.

His buildings include:
 * Sainte-Geneviève Library, Paris, built between 1843 and 1850
 * The Salle Labrouste, a reading room in the Bibliothèque Nationale de France in the Rue de Richelieu, Paris, and built between 1862 and 1868.

title: Henri Labrouste


text:
Ewald Hering

Karl Ewald Konstantin Hering (5 August 1834 – 26 January 1918) was a German physiologist who did much research in color vision, binocular perception, eye movements, and hyperacuity. He proposed opponent color theory in 1892.

Born in Alt-Gersdorf, Kingdom of Saxony, Hering studied at the University of Leipzig and became the first rector of the German Charles-Ferdinand University in Prague.

Early years
Hering was born in Alt-Gersdorf in Saxony, Germany. He probably grew up in a poor family, son of a Lutheran pastor. Hering attended gymnasium in Zittau and entered the university of Leipzig in 1853. There he studied philosophy, zoology and medicine. He completed an M.D. degree in 1860.

It is somewhat unclear how Hering trained to do research. At the time Johannes Peter Müller was perhaps the most famous physiologist in Germany. Hering seems to have applied for studying under his direction but was rejected, which might have contributed to his animosity towards Hermann von Helmholtz, Müller's protégé. However, in Leipzig, E. H. Weber and G. T. Fechner were conducting groundbreaking studies founding what would become the field of psychophysics. Although there is no evidence that Hering ever studied under their direction, in his later years he proudly acknowledged himself a "student of Fechner".

After graduating, Hering practiced as a physician in Leipzig. Despite having little time to do research and having even scarcer financial resources, he turned to binocular vision (using both eyes together) and the problem of the horopter (the points in space that project on anatomically identical points on the two retinas). There, he surprised the scientific community when he published, as a completely unknown scientist, his own mathematical derivation of the horopter independently from Hermann von Helmholtz, who was by then considered one of the best German scientists and mathematicians. Hering went as far as ridiculing Helmholtz's (unimportant) mathematical errors in his derivation of the horopter.

University posts
Hering was subsequently appointed professor of physiology at the military academy of Vienna until 1870. With better resources he conducted important studies in physiology, in particular on the cardiac and respiratory systems. In 1870, he succeeded Jan Evangelista Purkinje at the university of Prague where he remained for the next 25 years. There he became involved in fierce arguments between nationalistic Czechs who wanted the university taught in the language of the land, and a minority of German professors. Eventually a separate German university, Charles-Ferdinand University, was created in 1882 and Hering became its first rector.

In his late years, Hering returned to Germany, where he became professor at the university of Leipzig in 1895, aged 61. He retired in 1915 and died of tuberculosis three years later. He was an atheist.

Binocular vision

Hering studied a broad range of subjects in vision, among them his outstanding studies on binocular vision. He derived, almost simultaneously with Helmholtz, the theoretical shape of the horopter. Despite identical results, Hering's derivation was far more modern and elegant, using recently developed projective geometry. Indeed, Helmholtz himself qualified Hering's approach as "very elegant, comprehensive and complete". Subsequently, Hering empirically estimated the shape of the horopter. Alongside with Helmholtz and Hillebrand, he noticed that the empirical horopter does not match the theoretical horopter, a phenomenon now named the Hering–Hillebrand deviation.

Hering is also well known for his Law of Visual Direction which describes the perceived egocentric direction of an object from an observer. Unbeknownst to Hering and other visual scientists of the time, a similar law had been proposed by Alhazen (1021) and Wells (1792) although both their laws were different.

Hyperacuity
Hering did seminal work on what we now  call hyperacuity: spatial resolution in certain visual tasks that exceeds visual acuity by about an order of magnitude. In his famous 1899 treatise "On the Limits of Visual Acuity" he summarized empirical data published 1863 by Alfred Wilhelm Volkmann and Ernst Anton Wülfing 1892 who found that there are visual tasks in which  spatial resolution goes well below the size of receptor cells in the central retina. In an explanatory model, Hering superimposed a Vernier acuity stimulus – a disalignment among two line segments – onto an idealized receptor array. He argued that, by a mechanism of integration across small eye movements, the location information signalled by the involved receptors is coded to a much higher precision than would be possible by a single receptor, an explanation that still holds up today.

Eye movements

Hering further studied eye movements. He developed the Hering's law of equal innervation to describe the conjugacy of eye movements in animals. According to this law eye movements are always equal in intensity in the two eyes but not in direction. Eye movements can therefore be either conjugate (in the same direction such as saccades or smooth pursuit) or disjunctive (such as vergence eye movements). Hering's law of equal innervation is best described by Müller's stimulus where the fixation point changes position in 1 eye but not the other eye. Simplicity conducts that only the misaligned eye should move to refoveate. Hering's law predicts that because the eyes must always move by equal amounts, both eyes should move in the new binocular direction of the target (see Hering's law of visual direction above), then move in opposite direction to adjust vergence to that of the target. In other words, the eye in which the target did not move will move away and then back at the target. This prediction was experimentally confirmed by Yarbus in his seminal work on eye movements. However it is now known that strong deviations from Hering's law exist.

Color theory
Hering disagreed with the leading theory developed primarily by Thomas Young, James Clerk Maxwell and Hermann von Helmholtz. Young proposed that color vision is based on three primary colors: red, green, and blue. Maxwell demonstrated that any color can be matched by a mixture of three primary colors. This was interpreted by Helmholtz as proof that humans perceive colors through three types of receptors, while white and black would reflect the amount of light.

Hering instead held that the visual system works based on a system of color opponency. His evidence stemmed from color-adaptation experiments and the linguistic observation that certain color names cannot be combined into one. In this model, colors are perceived through mechanisms sensitive to three pairs of opponent colors: red-green, yellow-blue and white-black.

Johannes von Kries published in 1905 the zone theory that synthesizes both descriptions as one, where the Young-Helmholtz theory describes the interaction of light with receptors and Hering the image processing stage. Later, in 1925, Erwin Schrödinger published a paper inspired by von Kries, titled On the relation of the four color to the three color theory. There he probes a formal relationship between the two color theories.

Both theories have solid empirical evidence. The conundrum was resolved by the discovery of color-opponent ganglion cells in the retina and lateral geniculate nucleus. We now know that the human eye possesses three types of color-sensitive receptors (as proposed by Young, Maxwell, and Helmholtz) which then combine their signals in three color-opponent channels as proposed by Hering. Thus, both the Hering and Young-Helmholtz theories are correct.

Physiology
Hering made significant contributions to the field of physiology as well as psychology. In particular he demonstrated with his student Breuer the Hering–Breuer reflex, or that artificially inflating the lungs triggers an automatic signal triggering expiration. Then deflating the lungs in turns triggers a new signal inducing respiration. That is, inspirations and expirations are an endless reflex loop triggering each other. He also showed the Traube-Hering reflex, or that inflating the lungs triggers an acceleration of the heart.

Other research
In 1861, Hering described an optical illusion which now bears his name – the Hering illusion. When two straight and parallel lines are presented in front of radial background (similar to the spokes of a bicycle), the lines appear as if they were bowed outwards. The Orbison illusion is one of its variants, while the Wundt illusion produces a similar, but inverted effect.

Hering first suggested the idea of organic memory in an 1870 lecture for the Imperial Academy of Science in Vienna. Hering took influence from the idea of inheritance of acquired characteristics and suggested that memories could be passed on through generations by germ cells.

The Hering-Helmholtz controversy
Hering spent most of his life arguing violently with Helmholtz. The controversy was not only scientific but also philosophical; Hering was a nativist, Helmholtz an empiricist. Helmholtz also came from a higher social class and was always considered a prodigy, whereas Hering had to go through a harder time in his early career. Hering and Helmholtz disagreed on almost everything and the controversy lasted long after the end of both of their lives. Hering however was by far the more aggressive of the two, and was always prompt to point out any mistake that Helmholtz might have made, sometimes even going so far as to insult him ("It is likely that the great Helmholtz in his dozing state..."). Helmholtz's faction (though probably not Helmholtz himself) spread rumors which accorded to Hering the need for help to do his mathematical work and that he was clinically insane ("He has been, as I have heard, mentally ill").

Publications

 * The Theory of Binocular Vision [Die Lehre Vom Binocularen Sehen] (1868/1977)
 * Spatial Sense and Movements of the Eye [Der Raumsinn und die Bewegungen des Auges] (1879/1942)
 * On the Limits of Visual Acuity. [Ueber die Grenzen der Sehschärfe]  (1899/2018)
 * Outlines of a Theory of the Light Sense [Grundzüge der Lehre vom Lichtsinn] (1905/1964)
 * Handbuch der Physiologie (1879)
 * On Memory and the Specific Energies of the Nervous System (1897)

title: Ewald Hering