In situ[a] is aLatin phrase meaning 'in place' or 'on site', derived fromin ('in') andsitu (ablative ofsitus,lit. 'place').[3] The term refers to the examination or occurrence of a process within its original context, without relocation. The term is widely used across disciplines to denote methods, observations, or interventions carried out in their natural or intended environment. By contrast,ex situ methods involve the removal or displacement of materials,specimens, or processes for study, preservation, or modification in a controlled setting, often at the cost of contextual integrity. The earliest known use ofin situ in the English language dates back to the mid-17th century. In scientific literature, its usage increased from the late 19th century onward, initially in medicine and engineering.
Thenatural sciences typically usein situ methods to studyphenomena in their original context. Ingeology, field analysis ofsoil composition androck formations provides direct insights into Earth's processes. Biologicalfield research observesorganisms in their naturalhabitats, revealing behaviors and ecological interactions that cannot be replicated in a laboratory. Inchemistry andexperimental physics,in situ techniques allow scientists to observesubstances and reactions as they occur, capturing dynamic processes in real time.
In situ methods have applications in diverse fields ofapplied science. In theaerospace industry,in situ inspection protocols and monitoring systems assess operational performance without disrupting functionality.Environmental science employsin situecosystem monitoring to collect accurate data without artificial interference. In medicine, particularlyoncology,carcinomain situ refers to early-stage cancers that remain confined to their point of origin. This classification, indicating noinvasion of surrounding tissues, plays a crucial role in determiningtreatment plans andprognosis.Space exploration relies onin situ research methods to conduct direct observational studies and data collection oncelestial bodies, avoiding the challenges ofsample-return missions.
In thehumanities,in situ methodologies preserve contextual authenticity.Archaeology maintains the spatial relationships and environmental conditions ofartifacts atexcavation sites, allowing for more accurate historical interpretation. Inart theory and practice, thein situ principle informs both creation and exhibition.Site-specific artworks, such asenvironmental sculptures or architecturalinstallations, are designed to integrate seamlessly with their surroundings, emphasizing the relationship between artistic expression and its cultural or environmental context.
The termin situ is not found inClassical Latin. Its earliest recorded use is inLate Latin during the 4th century, with the first known instance byAugustine of Hippo. The term became widely used inMedieval Latin.[4]: 1536 The term's earliest known use in the English language dates back to the mid-17th century. TheOxford English Dictionary cites its first appearance in 1648 in the writings of William Molins, author of the anatomical textMyskotomia.[1] The usage ofin situ inscientific literature increased from the late 19th century onward, initially in medicine and engineering, includinggeological surveys andpetroleum extraction. During this period, the term described analyses conducted within the living human body or insideoil wells, among other applications.[4]: 1534 Thecompound termcarcinoma in situ, referring to abnormalcells that confined to their original location without invasion of surroundingtissue, was first used in a 1932 paper by U.S. surgical pathologistAlbert C. Broders.[5][6]
The concept ofin situ incontemporary art emerged as a framework in the late 1960s and 1970s, referring to artworks created specifically for a particular space.[7]: 160–162 By the mid-1980s,in situ was adopted inmaterials science, particularly in the field ofheterogeneous catalysis, where acatalyst in onephase facilitates achemical reaction in a different phase. Its usage later expanded beyond catalysis and is now applied across various disciplines within materials science.[4]: 1534 As of August 2022[update], the termin situ had been used in more than 910,000 scientific publications since 1874, whileex situ had appeared in over 29,000 scientific publications since 1958.[4]: 1535 In situ remains one of the most widely used and versatile Latin terms in contemporary medical discourse.[8]
Inastronomy,in situ measurement involves collecting data directly at or near acelestial object using spacecraft or instruments physically present at the location.[9] For example, theParker Solar Probe conductsin situ studies ofSun's atmosphere,[10] while theCassini–Huygens mission similarly analyzedSaturn'smagnetosphere.[11]In situ formation refers to astronomical objects that formed at their current locations without significant migration. Some theories propose that planets, such as Earth, formed in their present orbits rather than moving from elsewhere.Star clusters may form within their host galaxy, rather than being accreted from external sources.[12][13]
Incell biology,in situ techniques allow the examination ofcells ortissues within their native environment, preserving their natural structure and context. These approaches contrast with techniques requiring the extraction or isolation of cellular components. One example isin situ hybridization (ISH), a technique designed to identify and localize specificnucleic acid sequences within intact cells or tissue sections. ISH employs labeled probes, which are strands ofnucleic acids engineered to bind selectively to target sequences. These probes are tagged with detectable markers, such asfluorophores orradioactive isotopes, enabling visualization of the precise spatial distribution of the targetedDNA orRNA. By maintaining the structural integrity of the sample, the technique facilitates mapping of genetic material within its original cellular or tissue framework.[14][15]
In biologicalfield research, the termin situ refers to the study of livingorganisms within their naturalhabitat. This includes collecting biological samples, conducting experiments, measuring abiotic factors, and documentingecological or behavioral observations without relocating the subject.[16][17]
Inorganic chemistry,in situ refers to processes that take place within thereaction mixture without isolatingintermediates. This approach is useful for handling unstablecompounds that decompose rapidly, and enhanceslaboratory safety by eliminating the need to isolate potentially hazardous intermediates. In one-pot synthetic sequences,in situ work-up modifications enable multiple reaction steps to proceed within a single vessel, reducing exposure to unstable or hazardous substances, such asazide intermediates,[b] which may pose safety risks if isolated.[20]: 872 Another example is theCorey–Chaykovsky reagent, a sulfurylide, is generatedin situ bydeprotonating sulfoniumhalides with a strongbase.[21][22] This approach is used because unstablized sulfur ylides are highly reactive. If isolated, the ylide could decompose or losereactivity, making its direct generation and use in the reaction mixture more practical.[23]
Analytical techniques such asnuclear magnetic resonance (NMR) spectroscopy,Raman spectroscopy, andmass spectrometry facilitate real-time monitoring ofin situ reactions. These methods enable researchers to detect short-lived substances that form during a reaction, such as intermediates that might not be stable enough to isolate, and adjust conditions to improve the process—all without disturbing the reaction itself.[24][25][26]
Inelectrochemistry,in situ experiments are performed under the normal operating conditions of anelectrochemical cell, with theelectrode maintained at a controlledpotential (typically by apotentiostat).[27] By contrast,ex situ experiments occur outside those operating conditions, usually without potential control—for example, after the electrode has been removed from the cell or left atopen-circuit. Maintaining potential control inin situ measurements preserves the electrochemical environment at the electrode–electrolyte interface, ensuring that thedouble layer and ongoingelectron-transfer reactions remain intact at a given electrode potential.[27][28][29]
In aerospacestructural health monitoring,in situ inspection involves diagnostic techniques that assess components within their operational environments, avoiding the need for disassembly or service interruptions. Thenondestructive testing (NDT) methods commonly used forin situ damage detection includeinfrared thermography, which measuresthermal emissions to identify structural anomalies but is less effective on low-emissivity materials;[30] speckle shearinginterferometry (shearography), which analyzes surface deformation patterns but requires carefully controlled environmental conditions;[31] andultrasonic testing, which usessound waves to detect internal defects incomposite materials but can be time-intensive for large structures.[32] Despite these individual limitations, the integration of these complementary techniques enhances overall diagnostic accuracy.[33] Another approach involves real-time monitoring usingalternating current (AC) anddirect current (DC) sensor arrays. These systems detect structural degradation, including matrix discontinuities, interlaminardelaminations, and fiberfractures, by analyzing variations inelectrical resistance andcapacitance withincomposite laminate structures.[33]
Futurespace exploration andterraforming efforts may depend onin situ resource utilization, reducing reliance on Earth-based supplies. Proposed missions, such asOrion andMars Direct, have explored this approach by leveraging locally available materials. The Orion space vehicle was once considered for propulsion using fuel extracted from the Moon, while Mars Direct relies on theSabatier reaction to synthesizemethane and water from atmosphericcarbon dioxide and hydrogen on Mars.[34][35]
Inbiological engineering,in situ describes experimental treatments applied tocells ortissues while they remain intact, rather than using extracts. It also refers toassays or manipulations performed on whole tissues without disrupting their natural structure.[36]: 295–296
Inbiomedical engineering,in situ polymerization is used to produce proteinnanogels, which serve as a versatile platform for the storage and release oftherapeutic proteins. This approach has applications incancer treatment, vaccination, diagnostics,regenerative medicine, and therapies for loss-of-function genetic diseases.[37]
Inconstruction engineering,in situ construction refers to building work carried out directly on-site usingraw materials, as opposed toprefabrication, where components are manufactured off-site and assembled on-site.In situ concrete is poured at its final location, offering structural stability compared to precast construction.[38]: 117–119 In wall construction,reinforcing bars are assembled first, followed by the installation offormwork to contain the poured concrete. Once the concrete has cured, the formwork is removed, leaving the wall in place.[38]: 117 Prefabrication, by contrast, enhances efficiency by reducing on-site labor and accelerating project timelines, though it requires precise pre-planning and incurs higher manufacturing and transportation costs.[39][40][41]
Ingeotechnical engineering, the termin situ describessoil in its natural, undisturbed state,[42]: 15 as opposed tofill material, which has been excavated and relocated. The differences between undisturbed soil and fill material affect how well a site can support structures, install underground utilities, and managewater drainage. Proper assessment of soil conditions is necessary to prevent issues such as uneven settling, unstablefoundations, and poorwater infiltration.[43][44]
Incomputer science,in situ refers to the use of technology anduser interfaces to provide continuous access to situationally relevant information across different locations and contexts.[45][46] Examples include athletes viewing biometric data on smartwatches to improve their performance[47] or a presenter looking at tips on a smart glass to reduce their speaking rate during a speech.[48]
Analgorithm is said to be anin situ algorithm, or in-place algorithm, if the extra amount of memory required to execute the algorithm isO(1),[49] that is, does not exceed a constant no matter how large the input. Typically such an algorithm operates ondata objects directly in place rather than making copies of them.
Withbig data, in situ data would mean bringing the computation to where data is located, rather than the other way like in traditional RDBMS systems where data is moved to computational space.[50] This is also known asin-situ processing.
InEarth sciences, particularly ingeomorphology,in situ refers to natural materials or processes occurring at their point of origin without being transported. An example isweathering, in which rocks undergo physical or chemical disintegration in place,[51] in contrast toerosion, which involves the removal and relocation of materials by agents such as wind, water, or ice.[52]Soil formed from the weathering of underlyingbedrock is an example of anin situ formation.[53]: 246 In situ measurements, such as those ofsoil moisture, rock stress,groundwater trends, orradiation levels, are conducted on-site to provide direct data. These measurements are often essential for validatingremote sensing data, such assatellite imagery, which is widely used for large-scaleenvironmental monitoring but may requirein situ confirmation to ensure accuracy.[54][55][56]
Inoceanography,in situ observational methods involve direct measurements of oceanic conditions, typically conducted during shipboard surveys. These methods employ specialized instruments, such as theConductivity, Temperature, and Depth (CTD) device, which records parameters such assalinity, temperature,pressure, andbiogeochemical properties likeoxygen saturation.[57] Historically, oceanographers usedreversing thermometers, which were inverted at specific depths to trapmercury and preserve temperature readings for subsequent analysis.[58] These instruments have been largely replaced by CTD devices andexpendable bathythermographs.[59]
Inatmospheric sciences,in situ measurements refer to observations of atmospheric properties obtained using instruments placed within the environment being studied. Aircraft, balloons, and rockets are used to carry some of these instruments, allowing for direct interaction with the air to collect data.[60] For example,radiosondes, carried aloft byweather balloons, measure atmospheric parameters such as temperature, humidity, and pressure as they ascend through theatmosphere,[53]: 396 whileanemometers, typically positioned at ground level or on towers, recordwind speed anddirection at specific locations.[61] In contrast, remote sensing techniques, such asweather radar and satellite observations, collect atmospheric data from a distance by usingelectromagnetic radiation to infer properties without direct contact with the atmosphere.[62]
By the mid-1980s, the termin situ was adopted inmaterials science, particularly in the field ofheterogeneous catalysis, where acatalyst in onephase facilitates achemical reaction in a different phase. The term later expanded beyond catalysis and is now applied across various disciplines of materials science, alongside the opposite designationex situ.[4]: 1534 For example,in situ describes the study of asample maintained in asteady state[c]condition within a controlled environment, where specific parameters such as temperature orpressure are regulated. This approach allows researchers to observe materials under conditions that replicate their functional states. Examples include a sample held at a fixed temperature inside acryostat, anelectrode material operating within anelectric battery, or a specimen enclosed within a sealed container to protect it from external influences.[4]: 1532
Intransmission electron microscopy (TEM) andscanning transmission electron microscopy (STEM),in situ refers to the observation of materials as they are exposed to external stimuli within the microscope, under conditions that mimic their natural environments. This enables real-time observation of material behavior at thenanoscale. External stimuli inin situ TEM/STEM experiments include mechanical loading and pressure, temperature changes, electrical currents (biasing),radiation, and environmental factors—such as exposure to gas, liquid, andmagnetic field—or any combination of these. These conditions allow researchers to study atomic-level processes such asphase transformations, chemical reactions, ormechanical deformations, providing insights into material behavior and properties essential for advancements in materials science.[63][64]
Inmedical terminology,in situ belongs to a group of two-wordLatin expressions, includingin vitro ('within the glass', e.g., laboratory experiments),in vivo ('within the living', e.g., experiments on livingorganisms), andex vivo ('out of the living', e.g., experiments onextracted tissues), which facilitate communication of experimental or clinical contexts. Like abbreviations, these terms convey essential information concisely.In situ is a widely employed term in the medical field, used to describe phenomena or processes as they occur in their original location. It is applied in diverse contexts such asoncology, measurement acquisition,medical simulation, and anatomical examination. Because of its versatility across these varied applications,in situ is considered one of the most productive Latin expressions in contemporary medical discourse.[8]
In oncology,in situ is commonly applied in the context ofcarcinomain situ (CIS), a term describing abnormal cells confined to their original location withoutinvasion of surrounding tissue.[8][65] The earliest known use of the term dates back to 1932 in the writing of U.S. surgical pathologistAlbert C. Broders.[5] Broders introduced both the term and the concept, and the concept of carcinomain situ was initially controversial.[6] CIS is a critical term in earlycancer diagnosis, as it signifies a non-invasive stage, allowing for more targeted interventions such as localized excision or monitoring—before potential progression to invasive cancer.[66][67] Melanomain situ is an early, localized form ofmelanoma, a type of malignantskin cancer. In this stage, the cancerousmelanocytes—the pigment-producing cells that give skin its color—are confined to theepidermis, the outermost layer of the skin. The melanoma has not yet penetrated into the deeperdermal layers or metastasized to other parts of the body.[68]
Beyond oncology,in situ is used in fields where maintaining natural anatomical or physiological positions is essential.[8] Inorthopedic surgery, the term refers to procedures that preserve the natural alignment or position of bones or joints. For example,orthopedic plates or screws may be placed without altering the bone's original structure, as in "[the patient] was treated operatively with anin situ cannulated hip screw fixation".[69] Incardiothoracic surgery,in situ often describes techniques whereblood vessels are utilized in their original anatomical position for surgical purposes. For example, theinternal thoracic artery can be left attached to thesubclavian artery while rerouting blood flow to bypass occludedcoronary arteries and improve heart circulation.[70][71] Inorgan transplantation,in situ is used to describe procedures performed within the donor's body to preserve organ viability.In situperfusion is a technique employed during organ retrieval to restore blood flow to organs while they remain in their original location. This method minimizesischemic injury and preserves organ viability for transplantation. In contrast,ex situ machine perfusion involves perfusing the organ outside the donor's body, typically after it has been removed.[72][73]
Inpetroleum engineering,in situ techniques involve the application of heat orsolvents to extractheavy crude oil orbitumen from reservoirs located beneath theEarth's surface. Severalin situ methods exist, but those that utilize heat, particularly steam, have proven to be the most effective foroil sands extraction. The most widely usedin situ technique issteam-assisted gravity drainage (SAGD).[74] This method employs two horizontal wells: the upper well injects steam to heat the bitumen, reducing its viscosity, while the lower well collects the mobilized oil for extraction.[75] SAGD has gained prominence in the Canadian province ofAlberta, due to its efficiency in recovering bitumen from deep reservoirs. Approximately 80% of Alberta's oil sands deposits are located at depths that renderopen-pit mining impractical, makingin situ techniques such as SAGD the primary method of extraction.[76]
Inurban planning,in situ upgrading is an approach to and method of upgradinginformal settlements.[77]
Inarchaeology, the termin situ refers toartifacts and other materials that remain in their original depositional context, undisturbed since their initial placement. Recording the exactspatial coordinates,stratigraphic position, and surrounding matrix ofin situ materials is crucial for reconstructing past human activities and historical processes. While artifacts are often removed for analysis, certainarchaeological features—such ashearths,postholes, andarchitectural foundations—must be thoroughly documented in place to preserve their contextual information duringexcavation.[78]: 121 This documentation relies on various methods, including detailed field notes, scaledtechnical drawings,cartographic representation, and high-resolution photographic documentation. Current archaeological practice incorporates advanced digital technologies, including3D laser scanning,photogrammetry,unmanned aerial vehicles, andGeographic Information Systems (GIS), to capture complex spatial relationships.[79] Artifacts found outside their original context (ex situ), often due to natural disturbances or unrecorded excavations, have less interpretive value. However, these displaced materials can still provide clues about the spatial distribution and typological characteristics of unexcavatedin situ deposits, guiding future excavation efforts.[80][81]
TheConvention on the Protection of the Underwater Cultural Heritage sets mandatory guidelines for signatory states regarding the treatment ofunderwater shipwrecks. One of its key principles is thatin situ preservation is the preferred approach.[78]: 558 [82]: 13 This policy is based on the unique conditions of underwater environments, where lowoxygen levels and stable temperatures help preserve artifacts over long periods. Removing artifacts from these conditions and exposing them to the atmosphere often accelerates deterioration, particularly theoxidation of iron-based materials.[82]: 5
Inmortuary archaeology,in situ documentation involves systematically recording and cataloging human remains in their original depositional positions. These remains are often embedded in complex matrices ofsediment, clothing, and associated artifacts. Excavatingmass graves presents additional challenges, as they may contain hundreds of individuals. Before identifying individuals or determining causes of death, archaeologists must carefully document spatial relationships and contextual details to preserveforensic and historical information.[83]
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The concept ofin situ incontemporary art emerged as a framework in the late 1960s and 1970s, referring to artworks created specifically for a particular space. These works integrate the site's physical, historical, political, and sociological characteristics as essential elements of their composition.[7]: 160–162 This approach contrasts with autonomous artistic production, where artworks are independent of their eventual display locations.[84] Theoretical discussions, particularly in the writings and practice of Frenchconceptual artist and sculptorDaniel Buren, have emphasized the dynamic relationship between artistic intervention and its surrounding environment.[7]: 161
The site-specificinstallations ofChristo and Jeanne-Claude exemplify the application ofin situ principles in art. Their large-scale interventions such asThe Pont Neuf Wrapped (1985) andWrapped Reichstag (1995) involved the systematic wrapping of buildings and landscape elements in fabric, temporarily transforming familiar spaces and altering public perception. The concept ofin situ art further evolved with theland art movement, wherein artists such asRobert Smithson andMichael Heizer integrated their works directly into natural landscapes and created an inseparable connection between the artwork and its environment.[84] In contemporary aesthetic discourse,in situ has expanded into a broader theoretical construct, describing artistic practices that reinforce the fundamental unity between a work and its site.[7]: 160–161
Inlegal contexts,in situ is often used for its literal sense, meaning 'in its original place'. InHong Kong,in-situland exchange refers to a mechanism whereby landowners can swap their existing or expired land leases for new grants covering the same land parcel. This approach facilitatesredevelopment—such as modernizing buildings or increasing land usage density—in a crowded, land-scarce environment without displacing ownership from the original location. The Hong Kong government, through theDevelopment Bureau andLands Department, has implemented arrangements to expedite lease modifications and land exchanges.[85]: 283–285 [86][87]
Inpublic international law, the termin situ is used to distinguish between a government that exercises effective control over a state's territory and population and agovernment-in-exile, which operates from outside its national borders. A governmentin situ is thede facto governing authority, while a government-in-exile may still claim legitimacy despite lacking territorial control. The recognition of a government generally depends on its ability to maintain authority over its state, though exceptions exist, particularly when a government-in-exile is displaced due to unlawfulforeign occupation.[88]: 115–117 [89]: 2
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Inlinguistics, particularly insyntax, an element is said to bein situ if it is pronounced in the same position where it is interpreted. For example, in languages such asChinese,wh-elements remainin situ, as in a structure comparable to "John bought what?", wherewhat occupies the same position as thegrammatical object in the affirmative counterpart ("John bought bread"). In contrast, English typically employswh-movement, as seen in "What did John buy?", where the wh-element is displaced from its original position.
Ineconomics,in situ storage refers to the practice of retaining a product, usually anatural resource, in its original location rather than extracting and storing it elsewhere. This method avoids directout-of-pocket costs, such as those for transportation or storage facilities, with the primary expense being theopportunity cost of delaying potentialrevenue. It applies to resources like oil and gas left unextracted in wells,minerals andgemstones remaining underground, and timber left standing until extraction is economically favorable. Certain agricultural products, such ashay, can be storedin situ under suitable conditions.[90]: 54 [91]: 35
Inpsychology,in situ typically refers to studies conducted in a natural or real-world setting, as opposed to a controlled laboratory environment. This approach allows researchers to observe and measure psychological processes as they occur, increasingecological validity—though often at the expense of experimental control over variables.[92]: 84–85
Ingastronomy,in situ refers to the art of cooking with the different resources that are available at the site of the event. Here a person is not going to the restaurant, but the restaurant comes to the person's home.[93]
In situ leaching orin situ recovery refers to the mining technique of injectinglixiviant underground to dissolve ore and bringing the pregnant leach solution to surface for extraction. Commonly used in uranium mining but has also been used for copper mining.[94]
The fields and particles instruments took "in situ" (on site) direct sensing measurements [...]
Weathering may be defined as the disintegration or decomposition of rocksin situ. [...] But the main mass of the rock remainsin situ and is not transported.