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 studying or working with something in its natural or original location rather than moving it elsewhere. This approach preserves environmental factors and relationships that might be lost whenmaterials orspecimens are relocated to controlled settings. In comparison,ex situ methods involve removing materials or specimens for study, preservation, or modification under controlled conditions, often at the expense of their original context. The earliest recorded use ofin situ in English dates back to the mid-17th century. Its appearance inscientific literature grew from the late 19th century onward, beginning in medicine and engineering and later spreading to a wide range of disciplines.
Thenatural sciences typically usein situ methods to studyphenomena in their original context. Ingeology, field studies ofsoil composition androck formations may provide direct insights into Earth's processes. Biologists observe organisms in their naturalhabitats to understand behaviors and ecological interactions that cannot be reproduced in a laboratory. Inchemistry andexperimental physics,in situ techniques make it possible to watch substances andreactions as they occur, capturing transient phenomena in real time.
The scope of these methodologies extends intoapplied sciences and thehumanities. Inaerospace engineering,in situ inspections and monitoring systems evaluate performance without interrupting operations. Environmental scientists useecosystem monitoring in the field to gather reliable data with minimal disturbance. In medicine, especiallyoncology,carcinoma in situ describes early-stage cancers that remain localized at their site of origin.Space exploration relies onin situ methods to conduct direct observational studies and data collection oncelestial bodies, avoiding the challenges ofsample-return missions. Inarchaeology,in situ generally refers toartifacts and features found in undisturbed depositional settings, where recording spatial andstratigraphic relationships preserves information about past human activities. In art,in situ refers to works created or displayed in dialogue with their surroundings:site-specific projects, such asenvironmental sculptures or architectural installations, are conceived for particular locations.
The termin situ does not appear inClassical Latin. Its earliest recorded use is inLate Latin, with the first known instance in the writings ofAugustine of Hippo (354–430 AD).[4]: 1536 [c] It became widely used inMedieval Latin.[4]: 1536 In English, the earliest known usage dates to the mid-17th century; theOxford English Dictionary cites the first appearance in 1648, in William Molins' anatomical textMyskotomia.[1] The usages 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 In situ entered French medical discourse by 1877 in theJournal de médecine et de chirurgie pratiques ('Journal of Practical Medicine and Surgery').[6] 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.[7][8]
The concept ofin situ incontemporary art developed in the late 1960s and 1970s as a framework for artworks created specifically for a given space.[9]: 160–162 By the mid-1980s, the term 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
Inastronomy,in situ measurement involves collecting data directly at or near acelestial object using spacecraft or instruments physically present at the location.[10] For example, theParker Solar Probe conductsin situ studies ofSun's atmosphere,[11] while theCassini–Huygens mission similarly analyzedSaturn'smagnetosphere.[12]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.[13][14]
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.[15][16]
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.[17][18]
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,[d] which may pose safety risks if isolated.[21]: 872 Another example is theCorey–Chaykovsky reagent, a sulfurylide, is generatedin situ bydeprotonating sulfoniumhalides with a strongbase.[22][23] 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.[24]
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.[25][26][27]
Inelectrochemistry,in situ experiments are performed under the normal operating conditions of anelectrochemical cell, with theelectrode maintained at a controlledpotential (typically by apotentiostat).[28] 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.[28][29][30]
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;[31] speckle shearinginterferometry (shearography), which analyzes surface deformation patterns but requires carefully controlled environmental conditions;[32] andultrasonic testing, which usessound waves to detect internal defects incomposite materials but can be time-intensive for large structures.[33] Despite these individual limitations, the integration of these complementary techniques enhances overall diagnostic accuracy.[34] 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.[34]
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.[35][36]
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.[37]: 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.[38]
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.[39]: 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.[39]: 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.[40][41][42]
Ingeotechnical engineering, the termin situ describessoil in its natural, undisturbed state,[43]: 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.[44][45]
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.[46][47] Examples include athletes viewing biometric data on smartwatches to improve their performance[48] or a presenter looking at tips on a smart glass to reduce their speaking rate during a speech.[49]
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).[50] 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.[51]
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,[52] in contrast toerosion, which involves the removal and relocation of materials by agents such as wind, water, or ice.[53]Soil formed from the weathering of underlyingbedrock is an example of anin situ formation.[54]: 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.[55][56][57]
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.[58] Historically, oceanographers usedreversing thermometers, which were inverted at specific depths to trapmercury and preserve temperature readings for subsequent analysis.[59] These instruments have been largely replaced byCTD devices andexpendable bathythermographs.[60]
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.[61] For example,radiosondes, carried aloft byweather balloons, measure atmospheric parameters such as temperature, humidity, and pressure as they ascend through theatmosphere,[54]: 396 whileanemometers, typically positioned at ground level or on towers, recordwind speed anddirection at specific locations.[62] 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.[63]
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[e]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 situTEM/STEM experiments may include mechanical loading, pressure, temperature variation, electricalbiasing, radiation, and environmental exposure to gases, liquids, ormagnetic fields, individually or in combination. These conditions allow researchers to study atomic-level processes—such asphase transformations, chemical reactions, ormechanical deformations—thereby providing insights into material properties and behavior essential for advances in materials science.[64][65]
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). These expressions facilitate concise communication of experimental and clinical contexts, much like abbreviations.In situ is widely used in medicine to describe phenomena or processes occurring in their original location. Its applications spanoncology, measurement acquisition,medical simulation, and anatomical examination. Because of its versatility across such varied uses, one study has describedin situ as among the most productive Latin expressions in contemporary medical discourse.[66]
In oncology,in situ is applied in the context ofcarcinomain situ (CIS), a term describing abnormal cells confined to their original location withoutinvasion of surrounding tissue.[66][67] The earliest known use of the term dates back to 1932 in the writing of U.S. surgical pathologistAlbert C. Broders.[7] Broders introduced both the term and the concept, and the concept ofCIS was initially controversial.[8]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.[68][69] 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.[70]
Beyond oncology,in situ is used in fields where maintaining natural anatomical or physiological positions is essential.[66] 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".[71] 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.[72][73] 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 situmachine perfusion involves perfusing the organ outside the donor's body, typically after it has been removed.[74][75][f]
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).[76] 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.[77]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 asSAGD the primary method of extraction.[78]
Inurban planning,in situ upgrading is an approach to and method of upgradinginformal settlements.[79]
Inarchaeology, the termin situ has been used variably to describeartifacts orfeatures found undisturbed since deposition; however, its definition remains contested. Scholars distinguish between a broad usage, referring to materials recovered through controlledexcavation, and a stricter usage applied only to those discovered in undisturbed depositional settings.[80] Between these poles lies a continuum of depositional scenarios, from sealed habitation floors to slope orfluvial deposits, meaning that whether an object is trulyin situ depends on site-specific formation processes and the degree to whichstratigraphic as well as spatial relationships can be reconstructed.[80] Recording the exactspatial coordinates, stratigraphic position, and surrounding matrix of depositional materials is necessary for understanding past human activities and historical processes. While artifacts are often removed for analysis, certain archaeological features—such ashearths,postholes, andarchitectural foundations—have to be thoroughly documented in place to preserve their contextual information during excavation.[81]: 121 This documentation relies on various methods, including detailed field notes, scaledtechnical drawings,cartographic representation, and high-resolution photographic records. Current archaeological practice incorporates advanced digital technologies, including3D laser scanning,photogrammetry,unmanned aerial vehicles, andGeographic Information Systems (GIS), to capture complex spatial relationships.[82] Artifacts found outside their original context (ex situ), often due to natural disturbances or amateur excavations, have less interpretive value, but may provide clues about the spatial distribution and typological characteristics of unexcavatedin situ deposits, guiding future excavation efforts.[83][84]
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.[81]: 558 [† 1]: 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.[† 1]: 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.[85]
.jpg)
The concept ofin situ incontemporary art developed in the late 1960s and 1970s, referring to works created for a specific site. Such works incorporate the site's physical, historical, political, and sociological characteristics as integral elements of their composition.[9]: 160–162 This approach contrasts with autonomous artistic production, where artworks are conceived independently of their display location.[86] Theoretical discussions, particularly in the writings and practice of Frenchconceptual artist and sculptorDaniel Buren, have addressed the dynamic relationship between artistic intervention and its surrounding environment.[9]: 161 [87]
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. Another example is theland art movement, wherein artists such asRobert Smithson andMichael Heizer integrated their works directly into natural landscapes.[86] In contemporaryaesthetic discourse,in situ describes practices that reinforce the fundamental unity between an artwork and its site.[9]: 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.[88]: 283–285 [† 2][† 3]
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.[89]: 115–117 [90]: 2
Inlinguistics, particularly insyntax, an element is described asin situ when it is pronounced in the same position where it receives itssemantic interpretation. This concept is especially relevant in the analysis ofwh- questions across languages. For example, inMandarin Chinese andKurdish, wh-elements remainin situ, producing structures analogous to "John bought what?" where theinterrogative word occupies the same syntactic position as the directobject would in adeclarative sentence ("John bought bread").[91][92] By contrast, languages like English and French typically employwh-movement, where the interrogative element is displaced from its base position to the beginning of the clause, as in "What did John buy?" Here, the wh-wordwhat has moved from its original post-verbal position to the sentence-initial position, leaving behind a trace or gap in the object position. Thistypological distinction betweenin situ wh-elements and moved wh-elements represents one of the fundamental parameters of variation in natural language syntax and has been extensively studied withingenerative grammar frameworks.
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.[93]: 54 [94]: 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.[95]: 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.[96]
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.[97]
[…] To findeSacer (not dissected afore this Body) you must raiseDorsi Longissimus andSacrolumbus from their membranous origination atOs Ileon,Os Sacrum, and from theSpines of theLumbi, and immediately under that, will appear this inSitu, and in clearing him well, you will remove the scruple some make of the origination ofSemispinatus andSpinatus, one beginning where the other ends.
Utque ad causam referatur exemplum; naturae humanae generalitas institutionum infra se locatarum genus quoddam est; haec velut species habet, in situ, in membris, in ordinibus, in motibus, vel aliis id genus.[5]
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.