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The 1903 Flyer was the first aircraft to make a successful, controllable, heavier-than-air flight. View the Flyer at different angles, the customized lightweight motor, and other related images for a complete picture of this breakthrough in aircraft…

A major plant hormone that plays an important role in plant growth and development. Abscisic acid (ABA), with a chemical formula of C15H20O4 (Fig. 1), is one of the most significant hormones found in plants. It is responsible for regulating various…

Habituation to a specific practice, such as drinking alcoholic beverages or using drugs (for example, heroin, cocaine, or amphetamines), and disorders characterized by the chronic use of a drug, alcohol, or similar substance. Addiction and addictive…

Malfunctions of the paired adrenal glands. The paired adrenal glands are complex endocrine organs in proximity to the kidneys (see illustration), and disorders of the adrenal glands can have serious consequences. Under specific circumstances,…

A variety of chalcedonic quartz that is distinguished by the presence of color banding in curved or irregular patterns (Fig. 1). Most agate used for ornamental purposes is composed of two or more tones or intensities of brownish-red, often…

Any disorder of recognition. Agnosia is a rare neurological condition in which an individual fails to recognize and identify persons or objects (see illustration). Typically, agnosia is the result of damage to specific areas of the brain.…

The cross section of a body that is placed in an airstream to produce a useful aerodynamic force in the most efficient manner possible. The cross sections of wings, helicopter rotor blades (Fig. 1), propeller blades, windmill blades, compressor and…

A sodium-rich plagioclase feldspar mineral whose composition extends over the range Ab100An0 to Ab90An10, where Ab (= albite) is NaAlSi3O8 and An (= anorthite) is CaAl2Si2O8 (see illustration). Albite occurs in crustal igneous rocks as a major…

Substances formed by the addition of one or more elements, usually metals, to aluminum. The principal alloying elements in aluminum-base alloys are magnesium (Mg), silicon (Si), copper (Cu), zinc (Zn), and manganese (Mn) [Fig. 1]. In wrought…

A disease of the nervous system characterized by a progressive dementia that leads to profound impairment in cognition and behavior. Dementia occurs in a number of brain diseases where the impairment in cognitive abilities represents a decline from…

Most commonly, a generic name for all fossil resins, although it has been restricted by some to refer only to succinite, the mineralogical species of fossil resin that includes most of the Baltic Coast deposits. The time necessary to transform resin…

A lithium aluminum phosphate mineral of basic formula LiAl(PO4)(F). The structure of amblygonite consists of phosphate (PO4) groups of tetrahedra and AlO6 groups of octahedra. Each PO4 tetrahedron is connected to an AlO6 octahedron. Corner-sharing…

The transparent purple to violet variety of the mineral quartz. Although quartz is perhaps the commonest gem mineral known, amethyst (see illustration) is rare in the deep colors that characterize fine quality. Amethyst is usually colored unevenly…

A significant, yet relatively selective loss of memory. Amnesia is a type of memory loss, often resulting from brain disease or injury (see illustration). The inability to remember can be temporary or permanent. In general, amnesia can be…

A nesosilicate mineral, composition Al2SiO5, crystallizing in the orthorhombic system. Andalusite (Fig. 1) occurs commonly in large, nearly square prismatic crystals. The variety chiastolite has inclusions of dark-colored carbonaceous material…

A plagioclase feldspar with composition Ab70An30 to Ab50An50 (Ab = NaAlSi3O8; An = CaAl2Si2O8). Andesine (see illustration) occurs primarily in igneous rocks, often in a glassy matrix as small, chemically zoned, lathlike crystals known as…

Loss of sensation with or without loss of consciousness. Anesthesia is used to prevent pain during surgery and other medical procedures. There are several ways of producing anesthesia, with the choice dependent on the type of surgery and the medical…

A mineral with the chemical composition PbSO4. Anglesite occurs in white or gray, orthorhombic, tabular or prismatic crystals or compact masses (see illustration). It is a common secondary mineral, usually formed by the oxidation of galena. Fracture…

A mineral with the chemical composition CaSO4. Anhydrite (anhydrous calcium sulfate) occurs commonly in white and grayish granular masses, rarely in large, orthorhombic crystals (see illustration). Fracture is uneven and luster is pearly to…

The formation of new animal individuals, which may occur by asexual or sexual means. All animals must reproduce asexually or sexually to create new individuals of their species. In asexual reproduction, a single parent can produce offspring that are…

The calcium-rich plagioclase feldspar with composition Ab0An100 to Ab10An90 (Ab = NaAlSi3O8; An = CaAl2Si2O8). Anorthite (see illustration) occurs in olivine-rich igneous rocks and rare volcanic ejecta (for example, at Mount Vesuvius, Italy, and…

An ongoing current event in which a large number of living species are threatened with extinction or are going extinct because of environmentally destructive human activities. The Earth is presently in the midst of a mass extinction event. In the…

One of the three living orders of the class Amphibia, encompassing the frogs and toads. Anura is the largest order of amphibians (class Amphibia), containing more than 7000 species of frogs (Fig. 1) and toads. Because members of the order Anura…

A disorder of language acquired as a result of brain disease. Aphasia is impairment in the use of spoken or written language caused by brain disorders (see illustration) that cannot be explained by paralysis or incoordination of the articulatory…

An impairment in the performance of voluntary actions despite intact motor power and coordination, sensation and perception, and comprehension. Apraxia is a neurological condition in which there is difficulty with skilled tasks or learned movements…

One of three naturally occurring mineral forms of calcium carbonate (CaCO3). The other forms (or polymorphs) are the abundant mineral calcite and the relatively rare mineral vaterite. Still other forms of calcium carbonate are known, but only as…

Arenite (rock composed of sand-size fragments) that contains a high proportion of feldspar in addition to quartz and other detrital minerals. Arkose is also known as feldspathic sandstone. Although there is no universal agreement, many geologists…

Any treatment or procedure that includes the in-vitro handling of oocytes (immature ova or egg cells) and sperm or embryos for the purpose of establishing a pregnancy. Assisted reproductive technology (ART) is undertaken as a treatment of…

A group of monoclinic calcic pyroxenes which have the general chemical formula (Ca,Mg,Fe)(Mg,Fe)-Si2O6, in which calcium is the dominant cation in the first cation position. Monoclinic pyroxene with substantial iron or magnesium in place of calcium…

A neurodevelopmental condition that impairs the way that a person relates to and communicates with other people. Persons with autism have difficulties with social communication and interaction. They also can have unusual behaviors, such as…

A basic carbonate of copper with the chemical formula Cu3(OH)2(CO3)2. Azurite is normally associated with copper ores and often occurs with malachite. Azurite is monoclinic. It may be massive or may occur in tabular, prismatic, or equant crystals…

A mineral with chemical composition BaSO4. It is isostructural with celestite, SrSO4, and anglesite, PbSO4. Barite is orthorhombic, space group Pnma, a = 0.887 nanometer, b = 0.545 nm, c = 0.714 nm. The illustration shows typical crystals. Barite…

The most common volcanic rock on Earth. Basalt is an igneous rock characterized by small grain size (less than about 5 mm) and approximately equal proportions of calcium-rich plagioclase feldspar and calcium-rich pyroxene, with less than about 20%…

The primary ore used to produce aluminum metal and alumina (Al2O3). Bauxite (see illustration) is a naturally occurring weathering product composed of one or more aluminum hydroxide minerals, such as gibbsite [Al(OH)3], boehmite [AlO(OH)], and…

A structural member that is fabricated from metal, reinforced or prestressed concrete, wood, fiber-reinforced plastic, or other construction materials and that resists loads perpendicular to its longitudinal axis. A beam's length is usually much…

Any of several leguminous plants, or their seeds, long utilized as food by humans or livestock. There are more than 40,000 varieties of beans, with only a small number of these being mass-produced for human or animal consumption. In particular,…

The most common beryllium mineral. Beryl, Al2[Be3Si6O18], crystallizes in the hexagonal system with space group P6/mcc. The crystal structure consists of six-membered rings of corner-sharing silicon-oxygen (SiO4) tetrahedra cross-linked by…

Minerals containing beryllium as an essential component. Over 50 beryllium minerals (Fig. 1) have been identified, even though beryllium is a scarce element in the Earth's crust. The unusual combination of low charge (+2) and small ionic radius…

An integrated device consisting of a biological recognition element and a transducer capable of detecting the biological reaction and converting it into a signal that can be processed. Ideally, the sensor should be self-contained, so that it is not…

An iron-magnesium-rich layer silicate; it is also known as black mica. Biotite (see illustration) is the most abundant of the mica group of minerals. The name is derived from that of the French chemist J. Biot. The formula for the ideal end member,…

A distinctive, fine-grained mudrock that derives its dark color from an unusually high content of organic matter, ranging from around 2% to over 50% of the weight of the rock (typical shales contain less than 1% organic matter). Most black shales…

A taxonomic order of insects comprising the cockroaches and termites. The order Blattodea, also referred to as Blattaria, contains at least 4500 species of cockroaches (Fig. 1) and 3000 species of termites. Previously, termites were assigned to a…

Regional metamorphism with the highest pressures and lowest temperatures, commonly above 500 megapascals (5 kilobars) and below 400°C (750°F). Metamorphic rocks of the relatively uncommon blueschist facies contain assemblages of minerals that record…

The branch of biological science that embraces the study of plants and plant life. Botany is the scientific study of plants (see illustration), encompassing investigations of plant anatomy, physiology, genetics, phylogeny, ecology, pathology, and…

A clastic rock composed of angular gravel-size fragments; the consolidated equivalent of rubble. The designation gravel-size refers to a mean particle diameter greater than 2 mm, which means that 50% or more of the particles (by volume) are this…

Terrestrial and aquatic animals that are capable of excavating holes in the ground for protection from adverse environmental conditions, as well as for storing food. Burrowing animals are uniquely adapted species, having the capacity to dig burrows…

A mineral composed of calcium carbonate (CaCO3). Calcite is one of the most common minerals found in the Earth's crust. Calcite (Fig. 1) may be found in a great variety of sedimentary, metamorphic, and igneous rocks. It is also an important…

A hormone, the only known secretory product of the parenchymal or C cells of the mammalian thyroid and of the ultimobranchial glands of lower animal forms. The hormone calcitonin (also referred to as thyrocalcitonin) has been isolated and…

A member of the mammalian family Camelidae in the order Artiodactyla. Camels are even-toed, hoofed mammals (ungulates). There are three extant camel species: the Bactrian camel (Camelus bactrianus; Fig. 1), the wild Bactrian camel (C. ferus), and…

A type of carved gemstone in which the background is cut away to leave the subject in relief. Often cameos are cut from stones in which the coloring is layered, resulting in a figure of one color and a background of another. The term cameo (see…

The common name for a malignant neoplasm or tumor. Cancer is a serious medical condition that develops when the orderly relationship of cell division and cell differentiation becomes disordered, leading to the development of neoplasms. Neoplasms are…

Cells within a tumor that possess the capacity to self-renew and cause the heterogeneous lineages of cancerous cells that comprise the tumor. Cancer stem cells (CSCs) typically represent a small percentage of all cells in a tumor (rarely more than…

A firm, resilient connective tissue of vertebrates and some invertebrates. Cartilage (see illustration) is an important structural element found in the bodies of vertebrates and some invertebrates. It is a resistant, elastic connective tissue that…

A coarse, erect, annual herb plant, Ricinus communis, belonging to the spurge family (Euphorbiaceae). The castor plant (Ricinus communis) is a member of the spurge family (Euphorbiaceae) in the order Malpighiales. The plant varies greatly in height…

The mechanism by which cells in a multicellular organism become specialized to perform specific functions in a variety of tissues and organs. Cell differentiation is the process through which cells are transformed into divergent types of cells…

The movement of cells, the movement of materials within cells, and changes in cell shape (including cell division). Cell motility is an important facet of cell biology, encompassing the movement of individual cells, the coordinated movement of many…

The organizing and compartmentation of eukaryotic cells. Eukaryotic cells are divided into several compartments, and each compartment has a characteristic structure, biochemical composition, and function (Fig. 1). These compartments are called…

The field concerning the interactions among cells and molecules of the immune system, and how such interactions contribute to the recognition and elimination of pathogens. Humans (and vertebrates in general) possess a range of nonspecific mechanical…

Mitosis is the series of visible changes that occur in the nucleus and chromosomes of non-gamete-producing plant and animal cells as they divide. This Image Gallery exhibit depicts these events using state-of-the art microscopy and digital image…

Any member of the grass family (Poaceae or Gramineae) that produces edible grains usable as food by humans and livestock. Cereals are important cultivated crops. Common cereals include rice, wheat, barley, oats, maize (corn), sorghum, rye, and…

The administration of chemical substances for the treatment of disease, especially cancer, or for the prevention of aberrant growth of cells or tissues (neoplasms). In general, chemotherapy is the use of chemicals to treat any disease, but the term…

A mineral having composition BeAl2O4 and crystallizing in the orthorhombic system. Chrysoberyl crystals (see illustration) are usually tabular parallel to the front pinacoid and frequently in pseudohexagonal twins. There is good prismatic cleavage.…

An evergreen shrub or small tree, particularly Cinnamomum verum, and the spice obtained from the plant's bark. The cinnamon plant (see illustration) is a member of the laurel family (Lauraceae) in the order Laurales. Native to Sri Lanka, the…

The collective processes by which metabolic materials are transported from one region of an organism to another region. The circulatory system, often termed the cardiovascular system, is responsible for the functions of circulation, allowing…

Pathologies and abnormal conditions that involve the circulatory system. Circulation disorders include both localized disturbances of circulation and diseases of the circulatory system (Fig. 1). Circulation 1 Illustration of the thickening and…

The major fibrous protein in animals. Collagen is present in all types of multicellular animals and is probably the most abundant animal protein in nature. It is estimated that collagen accounts for about 30% of the total human body protein.…

Any device connected internally or externally to a computer and used in the transfer of data to or from a computer. A personal computer (PC) processes information. Data (unprocessed information) must get into the computer, and the processed…

Structural or functional abnormalities of the body that develop during embryogenesis and the fetal period; also called birth defects. Congenital anomalies, or birth defects, are conditions present at or from birth that deviate from the body's normal…

One of the four primary tissues of the body. Connective tissue (Fig. 1) provides the solid foundation required for underpinning, binding, and protecting tissues and organs of the body. Connective tissue differs from the other three tissues…

Any of a group of diseases involving connective tissue as the pathological target. Connective tissue comprises one of the primary tissues of the body and is distinguished by an abundance of fibrillar and nonfibrillar extracellular components, which…

The response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral skeleton visible. Corals (Fig. 1) are animals that live in a partnership (symbiosis) with…

Any of a group of viruses that cause upper and lower respiratory tract diseases, gastroenteritis, hepatitis, and central nervous system infections in birds and mammals, including humans. Coronaviruses (Fig. 1) comprise a major group of common animal…

A genome-engineering technique that allows precise targeting of specific stretches of genetic code and editing of DNA at designated locations. The CRISPR/Cas9 system has been used as a general tool to engineer the genomes of many different…

A member of a class of proteins containing hemes as prosthetic groups that catalyze oxidation–reduction reactions. Cytochromes are heme-containing proteins (see illustration) that play vital roles in electron transport within cells. It should be…

Marine animal life inhabiting the portion of the oceans below the upper limit of the continental slopes. The marine animals that make up the deep-sea fauna live below the photic zone of the oceans. In general, the deep sea may be regarded as that…

Inflammation of the skin; also known as eczema. Dermatitis, or eczema, is a general medical term that describes irritation or inflammation of the skin. Typically, the inflammation of the skin involves redness and scaling (see illustration). In acute…

From the inspiration of a toy helicoptor to glider tests at Kitty Hawk, North Carolina, view photographic documentation of the Wright Brothers' attempts at human flight and the stages toward a final successful aircraft. View launches and landings,…

The branch of genetics that studies how genes control embryonic development. Advances in the field of developmental genetics have emphasized the degree of conservation throughout evolution of the genes (basic units in inheritance consisting of DNA)…

A cycloaddition reaction between a diene and a dienophile. The simplest Diels-Alder reaction (O. Diels and K. Alder, 1928) occurs between butadiene and ethylene and is often referred to as a [4+2] cycloaddition. The numbers, four and two in…

A deleterious set of responses occurring at the subcellular level, stimulated by infection, injury, or genetic or developmental errors, and manifested in altered structure or functioning of the affected organism. Disease is considered to be a…

Various species of diving, air-breathing animals. Diving animals, which are found in every class of terrestrial vertebrates (amphibians, reptiles, birds, and mammals), are air-breathing species that have almost complete freedom in the aquatic…

The Mesozoic Era (about 250 to 65 million years ago) is a geologic time period that is known as the "Age of the Dinosaurs." However, paleontologists are finding more evidence of varied abundance of life during this age, tracing the common ancestor…

The biological study of insects that have a direct influence on humanity. Economic entomology is a subdiscipline of entomology (the biological science that deals with the investigation of insects) and focuses on the effects of insects on human…

A condition in space in the vicinity of an electrically charged body such that the forces due to the charge are detectable. An electric field (or electrostatic field) exists in a region if an electric charge at rest in the region experiences a force…

The controlled induction of a grand mal seizure under anesthesia to treat individuals suffering from certain psychiatric illnesses. Electroconvulsive therapy (ECT; Fig. 1) was introduced as a treatment for psychiatric disorders by the Italian…

The common name for three living species of mammals in the family Elephantidae (order Proboscidea). Elephants are extant members of the mammalian family Elephantidae, which is one of several families included in the order Proboscidea. The remaining…

A pathology characterized by abnormal enlargement of air spaces distal to the terminal bronchioles in the lung. Emphysema (see illustration) is a pathologic condition distinguished by loss of elasticity of the lung. The primary cause of this loss of…

The study of the glands of internal secretion—the endocrine glands—and the hormones that they synthesize and secrete. Endocrinology is the field of medicine and physiology concerned with the endocrine system, which regulates hormones (chemical…

A family of endogenous peptides with morphinelike action present within the central nervous system. The enkephalins were the first group of endorphins to be identified. They were discovered in 1975 and opened research into a wide number of centrally…

The occurrence of cases of disease in excess of what is usually expected for a given period of time. An epidemic is a breakout of disease affecting unusually large numbers of people within a community or population. When an epidemic spreads…

A hormone, also known as adrenaline, that is an important adrenal secretion. Epinephrine, or adrenaline, is an important secretion from the adrenal medulla (the inner part of the adrenal glands). In 1901, Jokichi Takamine isolated epinephrine in…

The common name for the steroid hormone 17β-estradiol. Estrogen (17β-estradiol; Fig. 1) is an important steroid hormone that aids mammalian sexual and reproductive development. In mammalian females, estrogen maintains secondary sex characters and…

Planets beyond our solar system. For millennia, humankind has known about most of the major planets in our solar system because these worlds are visible to the naked eye. Exoplanets, however, were not indisputably known until 1995, when astronomers…

Disorders of form and function that affect the eye. Eye disorders and diseases are pathological conditions of the eye. Some conditions can result in vision loss and even blindness. In contrast, others are less severe and temporary, being resolved by…

The segment of horticulture concerned with the commercial production, marketing, and sale of plants grown and used for decorative or display purposes. Floriculture is a branch of horticulture, that is, the art and science of growing plants,…

Any interaction between objects that causes motion. Fundamentally, objects interact through the four known physical forces: gravity, electromagnetism, and the strong and weak nuclear interactions. In practice, however, many of the forces worked with…

The science, art, and practice of managing and using the natural resources that occur on and in association with forested lands. Forestry is the management of forested lands (see illustration). It involves the planning and implementation of…

The intentional production of new genes and alteration of genomes by the deletion, substitution, or addition of new genetic material. Genetic engineering involves the artificial recombination of nucleic acid molecules in the test tube; their…

Plants that have altered genetic material (DNA) through recombinant DNA (rDNA) manipulation. Genetic engineering of plants allows for very specific genetic changes to be made to a plant's deoxyribonucleic acid (DNA), as opposed to the random…

Commercially grown plants that have altered genetic material through artificial recombinant manipulation. Genetic modification is the latest scientific tool for developing improved crop varieties. Such genetically modified (GM) crops can help to…