Mitosis is a process that sorts and evenly distributes a cell's genetic instructions to the nuclei of two daughter cells during cell division. Mitosis distributes identical DNA instructions to new cells when the old cell divides. Growth is based on cell division and mitosis. Some cells in the body—such as nerve and skeletal muscle cells—cannot divide, and they stay with us for…
Mockingbirds, thrashers, and catbirds are 31 species of medium-sized birds that are sometimes known as mimid thrushes, in the family Mimidae. This is an American family of birds, occurring widely from southern Argentina and Chile, through to southern Canada. The usual habitat of mimids is brushlands, forest edges, shrubby riparian areas, and recently disturbed forests. Mimids range in body length …
The mode of a set of numbers is the number that occurs most frequently. There may be more than one mode. In the set (1,4,5,7), all four numbers are modes. But in the set (1,4,4,6), 4 is the only mode. The mode is one of the measures of central tendency, the others being the mean and the median. …
Modular arithmetic derives from the concept of congruence modulo m, written symbolically as where a and b are any integers and m is a positive integer greater than 1. This means that a - b is divisible by m. For example, since 36 - 16 = 20 is divisible by 5. Likewise 11 ≡38 (mod 9) because 11-38 = -27 is divisible by 9. The concept of congruence was first used by Carl Friedrich Ga…
Mohs' hardness scale provides an index and relative measure of mineral hardness (i.e., resistance to abrasion). In 1812, German geologist Frierich Mohs (1773–1839) devised a scale with specimen minerals that offered comparison of hardness qualities that allows the assignment of a Mohs hardness number to a mineral. Mohs' scale utilizes ten specific representative materials that…
The New World monkeys of Central and South America belong to the family Cebidae and to the family Callitrichidae (the marmosets and tamarins). The Cebidae, or capuchin-like monkeys, are distinguished from the marmosets and tamarins by their possession of nails instead of claws on most fingers and toes, and three molars instead of two on either side of each jaw. Finally, cebids tend to give birth t…
Molds are fungi that are microscopic in size. Even though they can approximate bacteria in size, molds are eukaryotic organisms. That is, their genetic material is enclosed within a specialized membrane that lies in the interior of the organism. Molds are present in virtually every environment that has been examined. Molds grow indoors and outdoors and, depending on the species, can grow year-roun…
A standard unit for counting numbers of particles is needed in chemistry, because atoms and molecules react with one another particle by particle. The amount of a chemical reaction—how much of the chemicals are used up or produced—is determined by the numbers of particles that are reacting. Weighing the chemicals wouldn't tell us anything very meaningful unless we knew how to …
Mole-rats are small, fossorial rodents, which means they spend their entire lives underground in a sealed burrow system. Native to Africa, these little animals are found from the southernmost tip of the continent to about 10 degrees north of the equator. Mole-rats make up the family Bathyergidae, which includes 12 species in five genera (not to be confused with an unrelated family Spalacidae, cont…
Molecular biology is the study of biological molecules and the molecular basis of structure and function in living organisms. Molecular biology is an interdisciplinary approach to understanding biological functions and regulation at the level of molecules such as nucleic acids, proteins, and carbohydrates. Following the rapid advances in biological science brought about by the development and adva…
Earthly and heavenly motions were of great interest to Newton. Applying an acute sense for asking the right questions with reasoning, Newton formulated three laws which allowed a complete analysis (mathematical) of dynamics, relating all aspects of motion to basic causes, force and mass. So influential was Newton's work that it is referred to as the first revolution in physics. …
The molecular formula specifies the actual number of atoms of each element in a molecule. It is important to remember that the molecular formula—in contrast to the simpler empirical formula that specifies only the relative number of atoms or moles present in a compound—identifies the actual number of atoms present in a molecule. More information is required to construct a molecular f…
Newts are lizard-shaped animals with a tail in the amphibian order Caudata (or Urodela), in the superfamily Salamandroidea, which also includes the salamanders. The distinction between newts and salamanders is not always obvious since both have a tail in the larval stage and the adult stage. However, newts do not have costal grooves on the sides of their body, they are less slippery than salamande…
The arrangement of atoms within a molecule determines not only the shape of the molecule, but also many of its physical properties. In many cases, dealing with molecules of biological significance, the spatial arrangement of atoms determines whether or not the molecule—or the compound containing the molecule—is "biologically active" (e.g., whether a drug containing a pa…
To know more about "molecular weights," one must first become familiar with the concept of "atomic weights." Because an element (e.g., carbon, oxygen, sulfur, etc.) often exists as a mixture of two or more (stable and unstable forms) natural isotopes that have the same number of protons but differ in the number of neutrons, atomic masses of these isotopes are slightly d…
The niche is an important ecological notion that considers the role that an organism or species plays in its community. Important aspects of the niche are environmental tolerance, use of resources, activities, and interactions with other organisms. Niche is an integrating concept because it considers organisms within the context of their biological tolerance of environmental extremes but is signif…
Nicotine is so highly addictive that the American Psychiatric Association includes it in their diagnostic manual under substance dependence. Nicotine addiction is also very difficult to break—only 5% of those who attempt to quit smoking are successful on their first try, and only 3% can kick the habit for a whole year. Only 10% of smokers are not addicted. To relieve the physical and psycho…
Night vision enhancement scopes or devices enable machines or people to form images when illumination in the visible band of the electromagnetic spectrum is inadequate. Although it is not possible to form images in absolute darkness, that is, in the absence of any electromagnetic radiation whatsoever, it is possible to form images from radiation wavelengths to which the human eye is insensitive, o…
It was not until knowledge about atoms and elements was gained that the make-up of the millions of different substances around us was understood. All the scientific knowledge we have today indicates that these different substances are made from only 92 different kinds of atoms that make up the naturally occurring elements. These atoms are able to join together in millions of different combinations…
Moles are small burrowing animals of the order Insectivora, mammals with teeth designed for crushing the outer shells of insects. The true moles and desmans (water-living moles) make up the family Talpidae, which inhabit most of North America and northern Eurasia. The similar golden moles of Africa, south of the Sahara, make up the family Chrysochloridae. Moles vary from 1-3 in (24-75 mm) in lengt…
Mollusks (phylum Mollusca) are the second largest group of invertebrates (the arthropods being the largest), with over 100,000 species. They are characterized by a head with sense organs and mouth, a muscular foot, a visceral hump containing the digestive and reproductive organs, and an envelope of tissue (the mantle) that usually secretes a hard, protective shell. Practically all of the shells fo…
Momentum is a property of motion that in classical physics is a vector (directional) quantity that in closed systems is conserved during collisions. In Newtonian physics momentum is measured as the product of the mass and component velocity of a body. For massless particles (e.g., photons) moving at the speed of light (v = c) the momentum (p) is equal to Planck's constant divided by the wav…
The family of plants known as nightshades is also known as the Solanacene. It is a large group of plants composed of more than 2,000 species and 75 different genera. Most nightshades are herbs, but some species are shrubs, vines, or trees. Most of the members of the nightshade family are native to parts of Central and South America, but about 100 nightshades can be found in North America. Some spe…
The monarch or old-world flycatchers are about 400 species of arboreal, insectivorous songbirds that make up the family Muscicapidae. There are three subfamilies in this group: the monarch and paradise flycatchers (Monarchinae), the fantails (Rhipidurinae), and the typical flycatchers (Muscicapinae). Some taxonomists consider these to be separate families, but they are treated as a single group he…
Nitric acid is also formed from the reaction of nitrogen oxides produced during the combustion (burning) of fossil fuels in automobile engines. These nitrogen oxides react with water in the atmosphere and form nitric acid, one cause of acid rain. High levels of nitrates in drinking water can contribute to the formation of nitrosamines, a group of carcinogenic (cancer causing) compounds. …
Mongooses are African and Asian carnivores of the family Herpestidae. They are small, long, slender mammals, some of which are most widely known for their willingness and skill in attacking and killing poisonous snakes. In the past, members of the mongoose family have been included with the weasels (family Mustelidae), and sometimes the mongooses are included with civets and genets (family Viverri…
Nitrification is an aerobic microbial process by which specialized bacteria oxidize ammonium to nitrite and then to nitrate. Nitrification is a very important part of the nitrogen cycle, because for most plants nitrate is the preferred chemical form of nitrogen uptake from soil or water. …
Monitor lizards include 24 living species of large lizards in the genus Varanus, family Varanidae. Monitors inhabit tropical and sub-tropical regions of Africa, Asia, and Australia. Monitors are among the most advanced of the lizards, in terms of achieving an active, predaceous lifestyle. The largest species of monitor, and the world's largest lizard, is the extremely impressive Komodo drag…
Monkeys are tree-dwelling mammals that, along with prosimians, apes, and humans, make up the order Primata of the primates. The primate suborder Anthropoidea includes two different infraorders: the Platyrrhini, comprised of New World monkeys, marmosets and tamarins; and the Catarrhini, the Old World monkeys, apes, and humans. The major division between New World and Old World monkeys, in addition …
Monoculture refers to the practice of cultivating an agricultural species or tree under conditions where other species are absent or virtually absent. This is done in order to lessen the intensity of competition on growth of the desired crop species. …
Nitrogen is the non-metallic chemical element of atomic number 7, with a symbol N, atomic weight 14.0067, specific gravity 0.96737 (compared to air), melting point -345.74°F (-209.86°C), boiling point -320.44°F (-195.8°C). Nitrogen is a non-metallic element located in group 15 of the periodic table. It has two stable isotopes: nitrogen-14, with an abundance of 99.634%, …
A monomer is a molecule or compound, usually containing carbon, with a relatively low molecular weight and simple structure; monomers form the fundamental building blocks of polymers, synthetic resins, and elastomers. Thus, vinylidene chloride is the monomer from which polyvinylidene chloride is made, and styrene is the monomer from which polystyrene resins are produced. One of the simplest monome…
The identification of MSG began with the isolation of glutamic acid from a mass of wheat protein, called gluten, in 1886. The chemical structure of glutamic acid, a naturally occurring amino acid, was later identified in 1890. The flavor enhancing ability of MSG was discovered by the Japanese chemist Ikeda Kibunae (1864-1936). From a kelplike seaweed, which was traditionally used to add flavor to …
The order Monotremata (one-holed creatures) is comprised of two families, the Ornithorhynchidae, including the platypus, and the Tachyglossidae, including the long- and short-beaked spiny anteaters or echidnas. Monotremes are found only in Australia, Tasmania, and New Guinea. Monotremes are a derivative of an ancient mammal stock but there is no direct evidence of what it might have been. Monotrem…
Mathematics, in the very broadest sense, is the systematic study of relationships in the physical world and relationships between symbols which need not pertain to the real world. In relation to the world, mathematics is the language of science. It operates within the laws and constraints of science as it examines physical phenomena. Unlike science, however, mathematics has no constraints. So in r…
Nitrogen is a critically important nutrient for organisms, being one of the most abundant elements in their tissues, and an integral component of many biochemicals, including amino acids, proteins, and nucleic acids. The availability of biologically useful forms of nitrogen is a common limiting factor in the productivity of plants. This is especially true of plants growing in terrestrial and marin…
A matrix is a rectangular array of numbers or number-like elements: These rules for adding and subtracting matrices give matrix addition the same properties as ordinary addition and subtraction. It is closed (among matrices of the same size), commutative, and associative. There is an additive identity (the matrix consisting entirely of zeros) and an additive inverse: This latter def…
In 1804, the English scientist John Dalton formulated the atomic theory, which set out some fundamental characteristics of matter, and which is still used today. According to this theory, matter is composed of extremely small particles called atoms, which can be neither created nor destroyed. Atoms can, however, attach themselves (bond) to each other in various arrangements to form molecules. A ma…
The Maunder minimum is the name given to a period of extreme solar inactivity that occurred between 1645 and 1710. Of particular interest is that this period of inactivity corresponds closely to one of the coldest periods of the so-called "Little Ice Age" in Europe, a time of long, cold winters that caused severe hardships in the pre-industrial revolution world. This has led scientis…
A monsoon is a seasonal change in the direction of the prevailing wind. This wind shift typically brings about a marked change in local weather. Monsoons are often associated with rainy seasons in the tropics (the areas of Earth within 23.5° latitude of the equator) and the subtropics (areas between 23.5° and about 35° latitude, both north and south). In these areas, life is c…
Finding the maxima and minima, both absolute and relative, of various functions represents an important class of problems solvable by use of differential calculus. The theory behind finding maximum and minimum values of a function is based on the fact that the derivative of a function is equal to the slope of the tangent. When the values of a function increase as the value of the independent varia…
Mayflies, or shadflies, are aquatic insects in the order Ephemeroptera. There are several thousand species of mayflies, distributed among 20 families. Mayflies have a relatively protracted nymphal stage, which occurs in freshwater habitats. The adults are a short-lived stage during which dense aggregations of animals engage in a frenzied procreation, needed to perennate the species in its local ha…
As late as the 1950s, most of the sounds on this planet were probably still of natural origin rather than derived from technological sources. Today, however, the opposite appears to be true. Cars, trucks, lawn mowers, leaf blowers, chain saws, power drills, television, radio, video games, computers... the list of noise makers in our modern life is almost endless, and our world keeps getting noisie…
The mean is also known as the average. It is one of the measures of central tendency, the others being the mode and median. …
The median is a measure of central tendency, like an average. It is a way of describing a group of items or characteristics instead of mentioning all of them. If the items are arranged in ascending order of magnitude, the median is the value of the middle item. If there is an odd number of items in the group, the median can be found precisely. For example, assume that 27 test scores are arranged f…
Earth's moon is a roughly spherical, rocky body orbiting Earth at an average distance of 238,000 mi (382,942 km). Its diameter is about one-fourth Earth's diameter. Compared to moons of other planets, this is a The first footprint on the moon's surface, made by astronaut Neil A. Armstrong on July 20, 1969, shows the fineness of the lunar soil. The soil is produced when moon…
Medical genetics is a multi-dimensional study of medically significant human genetic variation. Molecular diagnostics is the newest specialty field in genetics and allows a better understanding of heredity and disease at the molecular level. Disorders due to mutations as small as a single base change in the DNA can now be explained. Once the mutation is known, clinical laboratory testing can usual…
The mooneye is a freshwater fish with very large eyes. Usually measuring between 16-21 in (40-51 cm) long, it has a deep, laterally thin body. Because it generally resembles a shad or herring, the mooneye has acquired such common names as toothed herring, big-eyed shad, or white shad. Mooneyes can be distinguished from shads and herrings by the presence of well-developed teeth on their jaws and to…
The moose (Alces alces), also known as elk in Europe, is a horse-sized, northern species of deer that occurs in the boreal and north-temperate forests of both North America and Eurasia. At one time, the Eurasian and American moose were considered to be separate species, but these animals are fully interfertile and are now thought to be the same species. However, there are many geographically disti…
Non-Euclidean geometry refers to certain types of geometry which differ from plane and solid geometry which dominated the realm of mathematics for several centuries. There are other types of geometry which do not assume all of Euclid's postulates such as hyperbolic geometry, elliptic geometry, spherical geometry, descriptive geometry, differential geometry, geometric algebra, and multidimen…
Morphine has similar painkilling properties to endorphins and enkephalins, a group of amino acid compounds produced in the pituitary gland. The molecular structure of morphine is so much like that of endorphins that it is able to bind to and occupy specialized receptor sites located in various pain centers in the central nervous system. Morphine also alters the release of neurotransmitters. The pe…
Non-point sources refer to situations in which there are numerous, relatively small sources of emission of gases, metals, pesticides, nutrients, or other substances into the environment. Collectively, these many sources can comprise a regional emission of large quantities of Non-point sources. Illustration by Hans & Cassidy. Courtesy of Gale Group. pollutants into the environment. Ho…
A nonmetal is a chemical element that generally does not conduct heat or electricity very well, is usually a solid or a gas at normal temperatures, and (for solids) is difficult to reshape by pounding or beating. Nonmetals include elements such as carbon, sulfur, oxygen, and nitrogen. They are normally defined in contrast to metals, which are bright, shiny, solid elements (with one exception) that…
Meiosis, also known as reduction division, consists of two successive cell divisions in diploid cells. The two cell divisions are similar to mitosis, but differ in that the chromosomes are duplicated only once, not twice. The end result of meiosis is four daughter cells, each of them haploid. Since meiosis only occurs in the sex organs (gonads), the daughter cells are the gametes (spermatozoa or o…
Mosquitoes belong to an order of insects called Diptera, which includes the common house fly. All together, the Diptera order, the flies, are responsible for carrying diseases to more than 50% of the world's population. Some 120,000 species of Dipteran flies have been catalogued, which includes more than 2,500 species of mosquitoes. More than 15,000 species of flies and 150 species of mosqu…
Cell membranes or plasma membranes surround cells, separating the cytoplasm and organelles on the inside from the extracellular fluid on the outside. Several cell organelles (mitochondria, endoplasmic reticulum, and Golgi bodies) are also bounded by membranes. The membrane allows a cell or organelle to maintain a constant internal environment, usually one that is quite different from the medium su…
The landmass occupied by the present-day countries of Canada, the United States, and the Republic of Mexico make up North America. Greenland (Kalaallit Nunaat), an island landmass to the northeast of Canada, is also included in North America, for it has been attached to Canada for almost two billion years. Plate tectonics is the main force of nature responsible for the geologic history of North Am…
The mosses are the largest of the three classes in the plant phylum Bryophyta. They have been divided into three subclasses: the true mosses (Bryideae), the peat mosses (Sphagnideae), and the granite mosses (Andreaeideae). The familiar small, green, and "leafy" moss plant is known as the gametophyte. This haploid multicellular phase is dominant in the moss life cycle. The mosses are …
Moss animals, polyzoa, or ectoprocts (phylum Bryozoa) are some of the most abundant and widespread organisms in the animal kingdom. A considerable amount of confusion has surrounded the taxonomic arrangement of the moss animals. A similar, although not so diverse, group of animals known as entoprocts have now been distinguished in their own phylum, Entoprocta. The vast majority of moss animals are…
Moths, along with butterflies, belong to the order Lepidoptera, the second largest order of insects. They possess two pairs of wings covered with microscopic, overlapping scales having distinctive colors and patterns. The body and legs are covered with scales, or with long, hairlike bristles. The adult lepidopteran lacks mandibles (found in most other insects); it feeds on liquids, mostly nectar, …
The process by which something moves from one position to another is referred to as motion; that is, a changing position involving time, velocity and acceleration. Motions can be classified as linear or translational (motion along a straight line), rotational (motion about some axis), or curvilinear (a combination of linear and rotational). A detailed description of all aspects of motion is called…
Memory refers to the mental systems and processes involved in storing and recalling information about stimuli that are no longer present, as well as to all of the information that is stored. Memory is essential to healthy human functioning, and it can be said that every mental process involves some aspect of memory. Indeed, the ancient Greek philosopher Cicero once described memory as "the …
Mendelian genetics is the study of simple patterns of inheritance. Gregor Mendel (1822-1884), an Austrian monk was the first to publish an extensive study of how various traits are passed from parent to progeny. He studied simple garden pea plants, plotting in detail their various physical traits, and studying how combinations of various parental traits produced particular traits in the progeny. F…
Motion pictures, also called film, cinema or movies, are a series of images, recorded on strips of film, that create the illusion of continuous motion. A series of rapidly shown images appear to move because of a phenomena called the persistence of vision. The eye does not react instantly to changes in its field of vision. In fact, the eye continues to "see" an image for 1/10-1/20 of…
The megapodes, or moundbuilders, are a fascinating group of birds found in Australia, New Guinea and its surrounding islands, eastern Indonesia, and the Philippines. Also known as "thermometer birds," scrubfowl, or brush turkeys, 22 species are recognized (seven genera) in the family Megapodiidae. A wide range of habitats are occupied by these species, ranging from semi-arid scrublan…
Meningitis is a potentially fatal inflammation of the meninges, the thin, membranous covering of the brain and the spinal cord. Meningitis is most commonly caused by infection (by bacteria, viruses, or fungi), although it can also be caused by bleeding into the meninges, cancer, or diseases of the immune system. …
Menopause is the stage in the female life cycle during which menstrual cycles stop. On average, menopause occurs at age 51, and generally takes from five to seven years from start to finish. For years, the menopausal stage was rarely talked about in public. Beginning in the 1960s, physicians began treating menopause aggressively as a medical problem, using estrogen hormones. Contemporary debate fo…
A mountain is a large-scale topographic feature that is set apart from the local landscape by being much higher in elevation (topographic means having to do with the shape of the land surface). When the edge of a plate of Earth's crust runs over another plate, forcing the lower plate deep into Earth's elastic interior, a long, curved mountain chain of volcanos usually forms on the fo…
The menstrual cycle technically refers to the cyclic changes that take place in the lining of the human uterus over the course of approximately 28 days in adult females. These cycle changes are associated with cyclic changes in the ovaries and in the brain and ovarian hormones. The term "menstrual" comes from the Latin word menses, meaning month. The purpose of the cyclic changes is …
Mousebirds, or colies, are six species of non-migratory birds of sub-Saharan Africa, making up the family Colidae. Their usual habitat is open brushlands, savannas, and forest edges. Mousebirds are about 11-14 in (29-36 cm) long, at least one-half of which is made up of their long tail. This structure is composed of ten feathers of variable, but graduated length, the longest being in the center of…
Mercurous chloride has been most often used as a treatment for intestinal worms. In the past, large doses were often used to stimulate the intestines and remove blockages, although it is rarely used in medicine today due to the toxicity of mercury. When it is used as a laxative, if the treatment fails to work, large doses of other laxatives and water must be used to insure that no mercury is allow…
The mulberry family occurs primarily in tropical and semi-tropical regions, and includes a wide variety of herbs, shrubs, and trees, characterized by a milky sap and reduced, unisexual flowers. This family includes 40 genera and 1,000 species, of which 500 species are members of the fig genus, Ficus. The Moraceae is a member of the order Urticales, class Magnoliopsida (the dicotyledons), division …
Mercury is a metallic chemical element identified by the symbol Hg on the periodic table. It is silver in color and, unlike other metals, is liquid at room temperature. The ancient name for mercury was quicksilver, meaning "living" silver. This name reflected mercury's lustrous silver color and its unusually lively behavior: when it is poured onto a smooth surface, it forms be…
Multiple personality disorder (MPD) is a chronic and recurrent emotional illness. A person with MPD plays host to two or more personalities. Each identity has its own unique style of viewing and understanding the world and may have its own name. These distinct personalities periodically control that person's behavior as if several people were alternately sharing the same body. Because those…
Multiplication is often described as repeated addition. For example, the product 3 × 4 is equal to the sum, 4 + 4 + 4, of three 4s. The law on which this is based is the distributive law: a(b + c) = ab + ac. In this instance, the law is applied to 4(1 + 1 + 1), which gives 4(1) + 4(1) + 4(1) or 4 + 4 + 4. When one or both of the multipliers are not natural numbers, the law still applies, 0.…
The Murchison meteorite was a meteorite that entered Earth's atmosphere in September 1969. The meteor fragmented before impact and remnants were recovered near Murchison, Australia (located about 60 mi [96.5 km] north of Melbourne). The fragments recovered dated to nearly five billion years ago—to the time greater than the estimated age of Earth. In addition to interest generated by …
Mercury is the closest planet to the Sun. It is a small world only slightly larger than Earth's Moon. Next to the planet Pluto, Mercury is one of the least explored planets within our solar system. Visited only once in all the years of solar system exploration (three brief fly-bys of Mariner 10 during 1974–75), only about 45% of Mercury's surface has been imaged from nearby. A…
Muscle relaxants are drugs that are administered to relax muscles. They are given to relieve the discomfort of muscle spasm or involuntary muscle contracture and also in cases of surgery to relax muscles and provide easier access for the surgeon. Some nonprescription drugs are available to combat painful contraction of the uterus during a woman's menstrual period. Muscles can be divided int…
The prefix "meso-" means "in between" or "intermediate." Mesoscopic systems are those that are larger than atoms and yet very much smaller than the largescale everyday objects that we can see and touch. They are a thousand to a hundred thousand times smaller than the diameter of a human hair and they range in size from several hundred nanometers or billion…
The phylum Mesozoa comprises a small group of parasitic animals that are related to flatworms—a widely dispersed group of free-living and parasitic organisms. Some 50 species have been identified in this phylum to date, all of which are exclusively marine in their lifestyle. Relatively few detailed studies have been conducted on the behavior and life cycles of these species and their taxono…
The muscular system is the body's network of tissues for both conscious and unconscious movement. Movement is generated through the contraction and relaxation of specific muscles. Some muscles, like those in the arms and legs, are involved in voluntary movements such as raising a hand or flexing the foot. Other muscles are involuntary and function without conscious effort. Voluntary muscles…
Metabolic disorders are diseases caused by errors in metabolism. The term "metabolism" refers to the sum of the chemical reactions in the body. Metabolic problems can be traced to numerous metabolic pathways found in cells throughout the body. Metabolic reactions are categorized into two types, anabolic and catabolic. Anabolic reactions construct complex molecules from simple molecul…
Metabolism refers to the highly integrated network of chemical reactions by which living cells grow and sustain themselves. This network is composed of two major types of pathways: anabolism and catabolism. Anabolism uses energy stored in the form of adenosine triphosphate (ATP) to build larger molecules from smaller molecules. Catabolic reactions degrade larger molecules in order to produce ATP a…
A material is called a metal based on the way it reacts to other elements. Metallic elements characteristically form positive ions when their compounds are in solution. Their oxides form hydroxides rather than acids with water. Nearly three-fourths of the elements in each group of the periodic table are metals except for the Group 17 (halogen) and Group 18 (noble gas) elements. Most metals form cr…
The term composition (from the Latin com, together, and ponere, to put) is commonly applied in Western music to a notated work, and in non-Western systems to a consistently united progression or organization of sounds. Although Western music compositions have been defined by their narrative structure (i.e., progression toward a climax, etc.) a more accurate definition, encompassing modern Western …
Metal fatigue is the process by which a material is slowly damaged by stresses and strains that are less than those needed to actually break the material apart. For example, a steel wire might be used to suspend weights that are less than the amount needed to cause the wire to break apart (its tensile strength). Over time, however, those weights might slowly cause defects to develop in the steel. …
Mushrooms are the fruiting bodies of certain species of higher fungi. The vegetative tissues of these fungi consists of immense lengths of microscopic, thread-like hyphae, and their aggregations known as mycelium, which grow in surface soils, organic debris, and in association with plant roots. Strictly speaking, a mushroom is the sporulating or fruiting body of a fungus in the division Basidiomyc…
Muskoxen or muskox (Ovibos moschatus) are a species of large mammal in the family Bovidae, which also includes cattle, buffalo, antelope, sheep, and goats. The muskox is anatomically intermediate between sheep and cattle, and there has been taxonomic debate over which of these two groups the muskox should be more closely aligned with. As a result, its genus, Ovibos, is a composite of the scientifi…
The muskrat or musquash (Ondatra zibethicus) is a relatively large, amphibious rodent that is native to North America. The northern range of the muskrat reaches as far as the limits of the boreal forest from Alaska to Labrador and Newfoundland. The southern range of the muskrat extends through much of the United States as far south as northern Baja California, although not in the coastal plains of…
The term metal production refers to all of the processes involved in the conversion of a raw material, such as a metallic ore, to a final form in which the metal can be used for some commercial or industrial purpose. In some instances, metal production involves relatively few steps since the metal already occurs in an elemental form in nature. Such is the case with gold, silver, platinum, and othe…
Materialism is the generic name of a variety of doctrines that deny the existence of non-material substances. Materialism may be either a metaphysical or a methodological concept. In its most coherent and radical form, it is a type of monism, the metaphysical position stating that there is only one principle—matter and its properties—in terms of which all reality is to be explained. …
Metallurgy is the science and technology of metals. As indicated in Table 1, the recorded history of metal working goes back over 6,000 years. Chemical or extractive metallurgy is concerned with the extraction of metals from ores and with the refining of metals. Physical metallurgy is concerned with the physical and mechanical properties of metals as affected by composition, mechanical working, an…
The mustard family, or Brassicaceae, contains about 3,000 species of plants. These plants occur widely on all continents except Antarctica and in a wide range of habitats from tundra and desert to forests of all types. Most species in the mustard family occur in the temperate zones, and many occur in the alpine or arctic tundra. The flowers of members of the Brassicaceae have four petals arranged …
This article comprises a compact survey of the development of mathematics from ancient times until the early twentieth century. The treatment is broadly chronological, and most of it is concerned with Europe. …
Mustard gas is a substance used in chemical warfare. It is the popular name for the compound with the chemical designation 1,1-thiobis(2-chloroethane) (chemical formula: Cl-CH2-CH2-S-CH2-CH2-Cl). Mustard gas has a number of other names by which it has been known over the years, including H, yprite, sulfur mustard and Kampstoff Lost. Because the impure substance is said to have an odor similar to t…
Matriarchy is usually defined as a political system in which women are the dominant political actors, as opposed to patriarchy, in which men are the exclusive or primary heads of families, social groups, or political states. But matriarchy has always been a controversial term, since whenever it is mentioned, there are debates about whether matriarchies are imagined utopias or real societies, wheth…
The mechanical philosophy was a philosophy of nature, popular in the seventeenth century, that sought to explain all natural phenomena in terms of matter and motion without recourse to any kind of action at a distance (cause and effect without any physical contact). During the sixteenth and seventeenth centuries, many natural philosophers rejected Aristotelianism, which had provided the form of an…
Metamorphic grade is a scale denoting the level of pressure and temperature involved in forming a particular metamorphic rock. The scale is based on the first appearance of particular minerals, known as index minerals. Because each mineral crystallizes within a limited pressure and temperature range, the presence of particular index minerals indicates the relatively specific set of conditions that…
The term media history is almost a tautology when the historic is distinguished from the prehistoric by the presence of recording media. History is always already mediated. A distinct domain of historiography whose object is human communication technologies will to this extent always be tempted to assimilate all human history to itself. Among late-twentieth-and early-twenty-first-century media his…
Metamorphic rock is rock that has changed from one type of rock into another. The word metamorphic (from Greek) means "of changing form." Metamorphic rock is produced from either igneous rock (rock formed from the cooling and hardening of magma) or sedimentary rock (rock formed from compressed and solidified layers of organic or inorganic matter). Most of Earth's crust is made…
In most of early medieval Europe, only a few classical medical treatises survived, primarily in the libraries of monastic institutions, and most medical practitioners had little education. The outcome was a split between theory and practice. In China there was no such split. Almost all of the literature, including works on doctrinal foundations, was written by practitioners. The Inner Canon define…
The ancient Greeks had many ways of healing the sick. Plant gatherers and drug sellers, especially of herbal medicines, were the key people in the establishment of the vast Greek pharmacopoeia. Women healers had their own special categorization. And there were two groups making up a motley crew specializing in diagnosis and treatment calling on the gods and their evil relatives. One constant in Gr…
The systematic doctrines of ayurvedic medicine included a humoral theory somewhat akin to that of Hippocrates and Galen. Indian medicine admitted three humoral substances, namely, wind, bile, and phlegm. However, a certain indecision is visible within the tradition as to the status of blood, which shared with the humors the critical feature of being able to cause illness through becoming corrupt, …
While terrorism has arisen in a variety of cultures and historical periods, much of the world's attention on this phenomenon in the late twentieth and early twenty-first centuries has centered on the Middle East. Middle Eastern terrorism emerged in Western consciousness during the 1970s, primarily through the rise of secular leftist and nationalist groups among Palestinian exiles, which tar…
Metamorphism is the process by which the structure and mineral content of rocks transform in response to changes in temperature, pressure, fluid content (gas or water), or a combination of these. Because the minerals that make up rocks are stable only within certain ranges of temperature and pressure, large changes in these conditions cause minerals to change chemically or to change shape, or both…
Islamic medicine refers to the range of health-promoting beliefs common to and actions taken in Muslim societies, whether by Muslims or others. As with other traditional medical systems, Muslim medicine was composed of several subsystems, each involving a unique etiology and practice and each enjoying a different legitimacy. These subsystems were not independent of each other and none enjoyed comp…
In the living cell, deoxyribonucleic acid (DNA) undergoes frequent chemical change, especially when it is being replicated. Most of these changes are quickly repaired. Those that are not, result in a mutation. Thus, mutation is a failure of DNA repair. Mutagens are chemicals or physical factors (such as radiation) that increase the rate of mutation in the cells of bacteria, plants, and animals (in…
Many religious traditions have practices that could possibly be labeled meditation. In Judaism, Christianity, and Islam, these practices are usually associated with prayer, contemplation, or recitation of sacred texts. In the religious traditions of the Native Americans, Australian aboriginals, Siberian peoples, and many others, what could be identified as meditation techniques are incorporated wi…
Mutagenesis is the induction of genetic change in a cell by the alterations in the cell's genetic material (usually deoxyribonucleic acid [DNA]). This change or alteration can subsequently be inherited from one cell to the next. While many mutations are benign, some can be detrimental and cause human genetic disease. If the mutation occurs in a gamete (sex cell), the genetic alteration may …
Meme is indeed an interesting and apt subject to include in a dictionary of the history of ideas, for it is nothing less than a meta-concept for describing the transmission of knowledge among persons and cultures. Memetics—the study of memes—is, briefly stated, evolutionary theory applied to ideas. The word itself was coined by the British biologist Richard Dawkins in his 1976 book T…
The history of the idea of memory is associated with the cultural uses of two kinds of memory, episodic and semantic. Episodic memory concerns the conscious recall of particular events. Interest in its nature dates from antiquity, and mnemonic techniques for strengthening memory's resources, known as the "art of memory," were developed as rhetorical skills. Semantic memory dea…
Most human cultures, perhaps all, have accounts of gender relations, explaining and illustrating what it is to be a woman or a man, and how women and men are interrelated. The forms taken by these accounts vary greatly—ancestor myths, moral exhortation, exemplary narratives, drama, social science, philosophical speculation, and visual imagery. In many, there is a specific account of the dom…
Metamorphosis is the transition in overall body pattern that occurs during the life history of some animals following birth or hatching. Two well-known examples are the development of caterpillars into butterflies and tadpoles into frogs. Metamorphosis is considered an indirect form of development, in that a metamorphic animal passes through morphologically distinct stages before reaching the adul…
The concept of mestizaje expresses the tensions, contradictions, and ambiguities of its birth in the New World. More important, it is a concept that continues to have spiritual and aesthetic dimensions. Mestizaje refers to racial and/or cultural mixing of Amerindians with Europeans, but the literal connotation of the word does not illuminate its theoretical applications and its more recent transfo…
Meteorology is a science that studies the processes and phenomena of the atmosphere. Meteorology is subdivided into many specialty areas including—but not limited to—physical meteorology (dealing with physical aspects of the atmosphere such as rain or cloud formation, or rainbows and mirages), synoptic meteorology (the analysis and forecast of large-scale weather systems), dynamic me…
A mutation is the alteration in the composition in deoxyribonucleic acid (DNA). Mutations that are inherited can change the character of a species. Living organisms rely upon change as a means of adapting to new environments or conditions. Change is a crucial survival mechanism. Evolution hinges on the appearance and inheritance of mutations. Mutations are the source of genetic variation in humans…
The dominant Aristotelian idea of metaphor is not, however, either a balanced opposition or mixture of metaphor's two primary aspects. Of the two, Aristotle chooses to emphasize the formal view—perhaps because it confirms the primacy of reason and cooperates with his systematic and pedagogical motives. The philosophical and cultural consequences of Aristotle's formal emphasis …
Mutualism is a biological interaction that is beneficial to both parties. Most mutualisms are facultative, meaning the partners can successfully live apart. However, some mutualisms are so intimate that the interacting species can no longer live without each other; they have a mutually obligate interdependence. Many mutualisms are fascinating in their intricacies and reciprocal usefulness as is ap…
In the early twenty-first century metaphysics is a term used fairly loosely to describe philosophical investigation of the fundamental constituents of reality. But, in the Middle Ages, there was great debate about what was the subject of metaphysics, and that controversy had ancient roots. …
Metaphysics, in its most basic sense, is an account of what exists. It may include accounts of what sorts of things exist; of what really exists as opposed to what merely appears to exist; of what exists necessarily rather than by accident; of what it is that underlies everything else; or of the most general laws governing existing things. This article will describe some of the most important meta…
Microcosm and macrocosm are two aspects of a theory developed by ancient Greek philosophers to describe human beings and their place in the universe. These early thinkers viewed the individual human being as a little world (mikros kosmos) whose composition and structure correspond to that of the universe, or great world (makros kosmos, or megas kosmos). Kosmos at this time meant "order�…
A "fungus root" or mycorrhiza (plural: mycorrhizae) is a fungus living in a mutually beneficial symbiosis (or mutualism) with the roots of a vascular plant. In this intimate relationship, the fungus benefits from access to energy-containing carbohydrates, proteins, and other organic nutrients excreted by, or contained in, the roots while the host plant benefits from an enhanced suppl…
Natural resources, unlike man-made resources, exist independently of human labor. These resources are, however, not unlimited and must be used with care. Some natural resources are called "fund resources" because they can be exhausted through use, like the burning of fossil fuels. Other fund resources such as metals can be dissipated or wasted if they are discarded instead of being r…
Historically, migration has been a way of life in Africa. Over the generations African people have migrated in response to demographic, economic, political, and other factors, including environmental disasters and conflicts. The histories of many African communities record their migratory movements from one area to another or the incursions of more powerful migrant groups who conquered and reorgan…
Mycotoxins are toxic substances produced by molds and fungi, such as mushrooms. These toxic substances, known as secondary metabolites, are by-products of metabolism that are inessential to fungal growth. Although some mycotoxins can be used for medicinal purposes, most are poisonous if eaten in sufficient quantity. Numerous mycotoxins have been studied and identified. Of particular interest are m…
Migration is a central aspect of human existence. This is evident from the debate about the origins of the human species, which spread, according to the evidence, from Africa across all continents. On the level of ideas and prejudices, this has resulted in racialized debates about white distinctiveness and Afrocentrism. In prehistoric times, some thirty to forty thousand years ago, human beings m…
Amerindians, Pilgrim fathers, immigrants, slaves, Asian–Americans, Hispanics—all denote historical population groups in the United States and in the Americas, but each group is placed in a different frame of reference. All of them arrived as migrants with norms, values, and belief systems of their ancestors and premigration society as a whole. Before immigrating they also had experie…
The word meteor is derived from the Greek meteron, meaning something high up. Today, however, the term is used to describe the light phenomena produced by the entry of objects into Earth's atmosphere. A meteoroid is defined to be any solid object moving in interplanetary space smaller than a few meters in diameter. A visual meteor, or shooting star, is produced whenever a sandgrain-sized me…
Millenarianism refers to religious beliefs about a thousand-year period at the end of the world. This period, the millennium (from two Latin words, mille, thousand, and annum, year), is described in the Bible's Book of Revelation (20:1–6). Millenarians, while believing that Christ's Second Coming will usher in this earthly kingdom for the faithful, differ on the timing of the …
By contrast, the Shiite messianic vision was based upon the return of the Twelfth Imam (descended from the Prophet Muhammad), who went into occultation in 874. The Twelfth Imam will arise either in the east, as in the Sunni version, or in Mecca in some other versions and will similarly purify the Muslim world and take vengeance upon those who have oppressed the Shiites. However, in both the Sunni …
Mynah or myna birds are species in the family Sturnidae, which also includes many species of starlings. The distinction between starlings and mynahs is not always clear, and these common names are sometimes used interchangeably. However, as considered here, the mynahs are tropical, Asian species, the most prominent of which are in the genus Acridotheres and Gracula. The word mynah is derived from …
The history of humankind is replete with the desire for better times, a more just order, and leaders who can bring their people into a better world, often having to defeat or destroy a world that is viewed as unjust and inequitable. These desires have frequently been fueled by faith or have taken specifically religious forms; and in addition have often been organized around or contained elements o…
The science of mind is the empirical and theoretical search for the foundations of our mental lives. Unlike other subjects of scientific investigation, such as stars or rocks, human mental lives defy easy definition. Yet few would dispute that such a definition would have to encompass consciousness, emotions, reasoning, language, memory, and perception. As far back as ancient Greece, one can find …
The term minority group and its opposite, majority group, have been widely used both among social scientists and the general public in recent decades. In social scientific (and often popular) use of these terms, they do not usually refer per se to a numerical minority or majority. Rather, the social-scientific meaning of a minority group is a group that is assigned an inferior status in society, o…
In both the New and Old Worlds many genera of the myrtle family (Myrtaceae) unfurl their waxy, leathery leaves. Containing both trees and shrubs, this angiosperm family takes its name from the shrub Myrtus, which is found near the Mediterranean, in North Africa, and in South America. Other well known genera from the Myrtaceae include ornamentals such as Leptospermum (Australian tea tree), Eucalypt…
Miracles, miracle workers, and their stories are found in the life and literature of all ancient societies and are not limited to religious texts. In ancient Greece figures like Epimenides, Pythagoras, and Apollonius of Tyana were all renowned for working miracles. To this day, healing remains the form that most claimed miracles take, and many of these miracles are associated with visitations to t…
The metric system of measurement is an internationally agreed-upon set of units for expressing the amounts of various quantities such as length, mass, time, temperature, and so on. Whenever we measure something, from the weight of a sack of potatoes to the distance to the moon, we must express the result as a number of specific units: for example, pounds and miles in the English system of measurem…
A movement of indeterminate origin and span, modernism nevertheless retains the distinctiveness of a major episode in the history of culture. Its most renowned manifestations performed a radical break with the dominant arts of the nineteenth century. They were direct provocations to prevailing norms: norms of beauty, of the representational integrity of the human body, of the continuity of forms, …
Modernism (sometimes referred to as modern art or, even less precisely, as modernity in the arts) is a term for various experimental languages in the arts with multiple meanings and conflicting aims, and was ascendant from the 1880s to the 1960s (although certain artistic techniques and tactics of early modernist art, such as collage and photomontage, have enjoyed a potent afterlife since the 1960…
Modernity is best understood as a condition, rather than as the designation for some particular period of time. Aspects of the modern condition can arise at any time and place, but they are most generally associated with historical trends arising out of Cartesian philosophy, industrial capitalism, revolutionary politics, and the cultural changes of the turn of the nineteenth century. The main less…
The debates and controversies over modernity, from its origins in sixteenth-and seventeenth-century western Europe to the various sites of its deployment following the formation of colonial empires, have given rise to an abundance of literature. Non-Western societies, by and large, in the formation of their cultural, political, economic, and social identities and their reactions to it, have approp…
Modernity (kindaisei in Japanese, and xiandaixing in Chinese) is a relatively recent term in the intellectual vocabulary of East Asia, becoming current only after World War II. Differing conceptions of "the modern" start much earlier, when terms long available in both languages acquired new connotations, as the region felt the impact of the West. The classical Chinese jin (close, nea…
The term modernization conjures images of social change in the direction of general improvement over the past. In contemporary social sciences, the notion has been the basis of a theoretical orientation—variously referred to as modernization theory, approach, paradigm, or framework—to the study of the development of Third World or underdeveloped societies. The conception of developme…
For roughly one decade until the second half of the 1960s, modernization theory was in vogue in the social sciences, especially in the United States. The word modernization appeared widely in titles, the concept was commonly invoked in efforts to explain long-term change, and it figured in critiques of Marxist theory and discussions of Cold War differences over how newly independent countries shou…
Mice are small fury mammals, usually living on the ground, with bright beady eyes, rounded ears, and long tails. Mice live all around the world, in almost every habitat, and are a very important part of nature. They are typically vegetarians, often eating seeds and grain, but some species have developed much more comprehensive diets. Known for their high rates of reproduction, females are normally…
Few reliable details are known of the life of Mozi. Most scholars agree that he was a person of relatively humble origin from one of the eastern Chinese states (either Song, Qi, or Lu). Like Confucius, he traveled through neighboring states in search of better appointments, but apparently to no avail. Even more than Confucius, he succeeded as an educator and organizer, turning his followers into a…
Monarchy derives from a Greek term that refers literally to rule by one person (as distinct from oligarchy, rule by the few, or democracy, rule by the people). Among political systems of a post-tribal nature, monarchy is certainly the most common form of human governance globally throughout human history. While the modern Western world tends to venerate nonmonarchic constitutions of the pastȁ…
Nanotechnology describes technologies where the component parts can measure just a few atomic diameters (generally around a millionth of a millimeter). The general goal of nanotechnology research programs is to reduce complex and sophisticated machinery into very small operational units. Nanotechnology involves the development of techniques to build machines from atoms and molecules. The name come…
It was only in 661 at the accession of Mu'awiya that the Umayyad caliphate (661–750) became the first Islamic dynastic and caliphal monarchy. Knowledge of the Umayyad family is difficult to extract from the generally negative portrayal of them in later historical sources, but one criticism of them did highlight the fact that they were considered by some to be temporal kings (Ar., mul…
A narcotic is a substance that produces insensibility, or a stuporous state. The most notable characteristics of narcotics are their ability to decrease the perception of pain and alter the reaction to pain, and their extremely addictive properties. Narcotics often induce a state of euphoria or extreme well being. The word narcotic is derived from the Greek word narké (meaning stupor), and …
The "idea of monasticism" invites a misconception, because monasticism is not an idea but a practice. It is a discipline of life, encapsulated in a vow to obey a rule. Monasticism is not a theory about the good life, and still less an escape from practicality, but rather a commitment to live according to a rule handed down from a founder. In its classical Western form deriving from S…
In 1887 two American scientists, physicist Albert Michelson and physical chemist Edward Morley, performed an experiment that was designed to detect the motion of Earth through a hypothetical medium known as the luminiferous ether, which was thought to be present throughout space. They made their measurements with a very sensitive optical instrument now called a Michelson interferometer. Their obse…
Monism is the doctrine that there is only one principle in terms of which all reality is to be explained. Doctrines differ as to the nature and activity of this principle and its relations to the appearance and experience of multiplicity. Monists explain multiplicity or plurality in the world either as derivative from the one principle or as an illusion. Monism is found in philosophical, religious…
Microorganisms include prokaryotes like bacteria, unicellular or mycelial eukaryotes e.g., yeasts and other fungi, and viruses, notably bacterial viruses (bacteriophages). Microbial genetics is concerned with the transmission of hereditary characters in microorganisms. Microbial genetics has played a unique role in developing the fields of molecular and cell biology and also has found applications…
Sentimentalism, of which moral sense theory was a part, initially had a short run. Until the end of the twentieth century, all the major versions of the theory were produced within a sixty-year period in eighteenth-century Britain. Anthony Ashley Cooper, third earl of Shaftesbury (1671–1713), initiated the sentimentalist line of thought with his theory that morality is grounded in the refle…
Climate is the set of characteristic temperatures, humidities, sunshine, winds, and other weather conditions that prevail over large areas of space for long periods of time. Microclimate refers to a climate that holds over a very small area. Microclimates usually are slight modifications of the main background climate altered by features in the landscape. A forest creates a microclimate within the…
Motherhood the world over is commonly understood in terms of a generic terminology. Regardless of country, clime, or class, age-old mythologies in all cultures eulogize motherhood and impart to it an importance that goes well beyond the physical act of birthing. At the level of twenty-first-century popular culture, however, motherhood and maternity have been appropriated by modern-day consumerism,…
Microorganisms are minute organisms of microscopic dimensions, too small to be seen by the eye alone. To be viewed, microorganisms must be magnified by an optical or electron microscope. The most common types of microorganisms are viruses, bacteria, blue-green bacteria, some algae, some fungi, yeasts, and protozoans. Viruses, bacteria, and blue-green bacteria are all prokaryotes, meaning that they…
George Steiner has described culture as a matrix of recurrent and interrelated elements, a motor fueled by revolving constants. Broadly speaking, cultural literacy relies on our ability to recognize these constants—in literature, music, painting, or any other form of cultural production—and to work out relationships between them, to translate and recycle the meaning we inherit from t…
A motif is a small but recognizable musical unit. The motif might consist merely of a series of pitches or a distinctive rhythm, or it might be harmonically conceived; quite often, pitch and rhythm are combined in a motif to create a discrete melodic fragment. No matter what its constituent elements, the motif needs to be repeated before it can be recognized as a unit. The repetition may be nearly…
Multiculturalism means different things to different people. For some it is directly linked to the politics of recognition and of difference (Taylor). In this regard, it concerns an appreciation of the necessity to deal with diversity in ways that affirm the value of different cultures and to respect the various claims made by minority groups. For others, multiculturalism concerns an explicit poli…
It is often assumed that museums have been a permanent feature of society, simply because they contain some of the oldest things in the world. In fact, in their current form, museums are surprisingly recent in origin, almost entirely Western in conception, internally confused about their identity, and unsure of their future role. The British Museum, effectively the mother of all modern museums, wa…
Natural fibers may be of animal, vegetable, or mineral origin. Although the annual production of vegetable fibers outweighs that of animal or mineral fibers, all have long been useful to humans. Animal hair fibers consist of a protein known as keratin. It has a composition similar to human hair. Keratin proteins are actually crystalline copolymers of nylon, where the repeating units are amino acid…
The phrase anthropology of music is most closely associated with Alan P. Merriam's 1964 landmark book bearing this title. In this prescriptive text, influential through the 1980s, Merriam defines ethnomusicology as the study of music in culture in relation to the mutual interactions of sound, behavior, and concepts. In consonance with many ethnomusicologists to this day, Mieczyslaw Kolinski…
A microscope magnifies and resolves the image of an object that otherwise would be invisible to the naked eye, or whose detail could not be resolved using the unaided eye. These objects include such items as human skin, the eye of a fly, cells of a living organism, microorganisms such as bacteria, protozoa and viruses, individual molecules, and atoms. Some of the above objects are large enough to …
Musical performance is an organized presentation of musical sounds (and, arguably, controlled silences), usually for the entertainment, edification, or enrichment of listeners. The parameters of a performance are often determined by culturally understood boundaries—symphony audiences disregard the warming up and tuning of orchestral musicians, whereas listeners to Indian classical music und…
Musicology is the scholarly study of music, where music can be considered either as a fixed object of investigation or as a process whose participants are the composer, the performer, and the listener. As a field of knowledge, it encompasses every aspect of the aesthetic, physical, psychological, and cultural dimensions of the musical art. In practice, consequently, the discipline includes not jus…
The term mysticism represents a modern approach to a cultural path rooted in antiquity, and given anthropological considerations it is timeless. Mysticism usually concerns any work, study, or praxis that aims at transcendence (the experiencing "self" moving beyond normal limits) or union with the divine. It was (is) often private or even secret, perhaps involving special teachers. To…
Natural gas is a mixture of hydrocarbons (molecules that contain only carbon and hydrogen) and gases (most notably methane, ethane, propane, and butane) that exist naturally in rocks beneath the surface of the earth. It is widely used as a heating source, and in some cases specific portions of the natural gas are used as starting materials in industrial processes. Natural gas is the product of the…
Since the Baroque age, the concept of mysticism (first in French, la mystique) has been used to describe religious phenomena that can hardly be restricted to a certain geographical space or a certain epoch. These phenomena are primarily symbolic expressions (in act, speech, literature, art, music, etc.), of persons trying to communicate knowledge that has been gained through mystical experiences. …
The natural numbers are the ordinary numbers, 1, 2, 3,... with which we count. Sometimes they are called "the counting numbers." They have been called "natural" because much of our experience from infancy deals with discrete objects such as fingers, balls, peanuts, etc. We quickly, if not naturally, learn to count them. The mathematician Kronecker is reported to have sa…
The mystical dimension of the Islamic religious tradition has roots in the divinely revealed text of the Koran. One passage often pointed to in this regard is the "Light Verse" (24:35), in which God is described as the Light of a blessed lamp, lit by a burning oil "neither of the East nor the West." One episode from the Koran, involving the prophet Moses, provided key e…
There are a number of mystical movements within Islam, but by far the dominant tradition is that of Sufism, one of the most dynamic and interesting dimensions of Islamic religious and cultural expression. Sufism is an umbrella term for a variety of philosophical, social, and literary phenomena occurring within the Islamic world. In its narrowest sense, the term refers to a number of schools of Isl…
Microscopy is the science of producing and observing images of objects that cannot be seen by the unaided eye. A microscope is an instrument which produces the image. The primary function of a microscope is to resolve, that is distinguish, two closely spaced objects as separate. The secondary function of a microscope is to magnify. Microscopy has developed into an exciting field with numerous appl…
Kabbalah is a Hebrew term that has many meanings. Its basic meaning is derived from the root QBL, which means to receive, and thus the term means "reception." In rabbinic literature it stands mainly for a tradition that is received orally. However, beginning in the tenth century, testimonies appeared for a more specific form of Kabbalah: an esoteric tradition dealing basically with …
The term mysticism typically denotes a complex of beliefs and practices related to the personal experience of the divine. Much, although not all, mystical thought and practice derives from or draws upon formal religious doctrines, emphasizing reflective, introspective, and meditative practices as the keys to cultivating perception and awareness that will ultimately lead to knowledge of and communi…
The study of myth across the disciplines is united by the questions asked. The main questions are those of origin, function, and subject matter. Origin in this context means why and how myth arises; function, why and how myth persists. The answer to the why of origin and function is usually a need, which myth arises to fulfill and persists by continuing to fulfill. What that need is varies from th…
Although the study of narrative goes back as far as Aristotle's Poetics, narrative theory emerged as a distinct field of inquiry only in the second half of the twentieth century. At that point, work on the theory of the novel intersected with structuralism's project of writing the grammar of stories and storytelling. This intersection in turn opened out to other streams of traffic in…
Nautical archaeology is the branch of archaeology concerned with the excavation, identification, and study of the remains of sunken ships. The techniques used in nautical archaeology can be applied to the study of submerged ports, lost cities, sacrificial wells, and other underwater sites. The ocean conceals a vast number of unexplored, and potentially valuable, archaeological sites. But the techn…
Natio derives from the Latin verb to be born (nasci) and refers to societies constituted by (assumed) common birth or descent, a meaning akin to the English word race. …
Microtechnology is the use of compact, or very small, technical devices. Microtechnology embraces microcomputer parts, space microdevices, microsurgery, and microelectronics. Both microfilm and microfiche, which store information on film, are also examples of microtechnology; microfiche generally stores more than microfilm. The term "micro," derived from the Greek word mikros, meanin…
Advanced by Massachusetts Institute of Technology Professor Richard P. Binzel in 1995, the Torino scale is a revision of the Near-Earth Object Hazard Index. In 1999, the International Conference on Near-Earth objects adopted the scale at a meeting in Turino (Turin), Italy (from which the name of the scale is derived). The Torino scale is used to portray the threat to Earth of an impact with a part…
The professionalization of history in nineteenth-and twentieth-century European universities was so closely related to the construction of the nation-state that national histories came to be seen as the only objective form of historical writing—indeed, criticism of national histories was seen not only as unpatriotic, but as a threat to the integrity of the historical profession and its clai…
Nectar is a sweet, pleasant-tasting liquid secreted by nectaries. These are specialized organs located inside flowers, and also outside. For example, the "glands" on leaf stalks of cherry (Prunus) and wattle (Acacia) trees are nectaries. The nectar produced inside flowers attracts crawling or flying insects, birds, or mammals. As a result of feeding on nectar, these visitors may tran…
Nationalism is one of the most significant political ideas of the nineteenth and twentieth centuries, at the heart of worldwide and local conflicts penetrating every region of the globe. It can be defined simply as a political ideology that aims to bring about or to increase the political representation or power of "the nation" and has appeared in many forms in a wide variety of circ…
Negative is a term in mathematics that usually means "opposite." An electron's charge is called negative not because it is "below" but because it is opposite that of a proton. A surface with negative curvature bulges in from the point of view of someone on one side of the surface but bulges out from the point of view of someone on the other side. A line with nega…
The topic of African nationalism has been repeatedly contested and redefined over the past century. At the end of the nineteenth century, the European powers divided the continent and ruled virtually all of Africa, and African nations lost their sovereignty. During the 1950s and 1960s, when Africans began to seriously resist colonial rule, Africa underwent a major transformation and each colony ev…
Literary critics and historians use cultural nationalism to refer to collective practices that form modern political communities within, unsanctioned by, or even undercutting state authority. Such collective practices include the "high" culture disseminated via public media, established in publicly funded institutions such as universities and museums; as well as the "low…
Nationalism is generally regarded as a recent development in the Middle East, a contingent phenomenon produced by the unique conditions of the modern era. Prior to the nineteenth century, concepts of collective identity and allegiance appear to have been defined primarily on the basis of lineage, locale, or religion—communities of sentiment and solidarity either smaller or larger than the n…
Microwaves are radio signals with a very short wavelength. Microwave signals can be focused by antennas just as a searchlight concentrates light into a narrow beam. Signals are transmitted directly from a source to a receiver site. Reliable microwave signal range does not extend very far beyond the visible horizon. If microwave signals were visible to the eye, cities would be seen to be crisscross…
Nationalism in music has traditionally been described as a late-nineteenth-century phenomenon associated with countries or regions aspiring to nationhood whose composers strove to wed a national (most often folk-based) musical idiom to existing "main-stream" genres. Some of these accounts begin with Frédéric Chopin (1810–1849), but he is more often understood as �…
Before Europeans from a variety of countries began arriving on the shores of the two continents of the western hemisphere in the late fifteenth century, there were no "Indians." At that point in time, millions of human beings, members of hundreds of distinctive societies speaking mutually unintelligible languages, inhabited the lands between Alaska and Patagonia. The category of per…
Natural history, the study of natural objects, has been a feature of all literate civilizations. In the Western tradition, starting with Aristotle, natural history has engaged scholars and has been an important feature of Western literature. The perspective with which writers have approached natural objects, and the aspects of interest to them, have varied as much as their cultures. Natural histor…
Naturalism was one of a wave of "isms" that swept through the cultural world of the late nineteenth century. Its most vocal advocate was the French author Émile Zola (1840–1902), a prolific novelist, dramatist, essayist, and critic. Highly controversial in the period between the heyday of realism (1830–1860) and the emergence of early forms of modernism at the end …
Migraine is a type of headache marked by severe head pain lasting several hours or more. Migraine is an intense, often debilitating type of headache. Migraines affect as many as 24 million people in the United States, and are responsible for billions of dollars in lost work, poor job performance, and direct medical costs. Approximately 18% of women and 6% of men experience at least one migraine at…
Naturalism, a term widely used in the nineteenth century, was employed by novelists, artists, and art critics as a synonym for realism. But, in fact, naturalism was a much more complex term. The term derived from the theory of positivism developed by the French philosopher Auguste Comte (1798–1857). The roots of scientific naturalism, emerging from the eighteenth century and coming to frui…
Natural jurisprudential approaches to ethics have proved difficult to integrate into the historiography of philosophy because of just this same ambiguous relationship to history itself. On the one hand, natural law was viewed as a set of eternal verities presented by God to humanity in finished and perfect shape, and found embodied in the moral and civil order as evidence of its divine fashioning,…
The primary sense of the term natural theology rests on the contrast between natural and revealed knowledge. Natural theology concerns knowledge of the existence and attributes of God arrived at using only the natural faculties of sense and reason. Philosophical arguments for the existence, intelligence, power, and goodness of God based on the order and beauty of the world, or on purely intellectu…
No interpretation of the idea of nature is good for all people in all places at all times. The interpretive position here reflects pivotal conceptual developments of the nineteenth and twentieth centuries. Charles Darwin's century brought home forcefully the reality of time, of evolutionary process that ultimately transforms all things. Darwin's contemporary T. H. Huxley believed tha…
Naturphilosophie refers both to the specific philosophical program Friedrich Wilhelm Joseph von Schelling (1775–1854) initiated with his Ideen zu einer Philosophie der Natur (1797; Ideas for a philosophy of nature) and to the movement during the German Romantic period that Schelling's work is said to have spawned. The context of both is the achievement of Immanuel Kant (1724–1…
An aesthetic and literary movement inaugurated in the 1930s that centers on the creative potential of black consciousness, negritude was one of the premier cultural phenomena of the twentieth century. Curiously, negritude has no originating text as such; it took root and flourished in Paris in the mid-1930s, fed by the writings of two black scholars from the French colonies, Aimé Césaire…
Migration is the act of moving from one place to another, and is often associated with seasonal movements of animals between their breeding territory and a wintering range. This activity is most readily observed in birds, but has been documented in many other animals as well, including insects, fish, whales, and other mammals. Migration is a complex behavior that involves timing, navigation and ot…
Neptune is the eighth planet from the Sun and about four times the size of Earth. Astronomers consider Neptune to form with Uranus a subgroup of the Jovian planets (Jupiter, Saturn, Uranus, and Neptune). Neptune and Uranus are similar in size, mass, periods of their rotation, the overall features of their magnetic fields, and ring systems. However they differ in the structure of their atmospheres …
Neocolonialism can be defined as the continuation of the economic model of colonialism after a colonized territory has achieved formal political independence. This concept was applied most commonly to Africa in the latter half of the twentieth century. European countries had colonized most of the continent in the late nineteenth century, instituting a system of economic exploitation in which Afric…
Mildews are whitish fungi that grow on moist surfaces. Some mildews are parasites growing on the surface of plant foliage or fruits. Other mildews grow on the moistened surfaces of materials made from plant or animal tissues, such as wood, paper, clothing, or leather. The downy mildews are in the fungal family Peronosporaceae. These fungi can only exist as parasites, and under conditions favorable…
Nerve growth factor (NGF) is a polypeptide, a molecule composed of several amino acid units that has a protein-like behavior, but is not as complex as a protein in structure. NGF increases the growth of nerve cells, especially those in the peripheral nervous system, and directs the growth and orientation of nerve cell axons (processes which carry impulses away from the nerve cell body to adjoining…
The concept of neoliberalism is an interesting one in that, first, it is a label commonly used by its opponents rather than by its adherents. As with all such labels, the tendency for caricature may at times overtake the need for faithful rendition of the underlying idea. As the term implies, neoliberalism refers to what some view as a new form of liberalism, and what others view as a mere reasser…
Milkweeds are various species of perennial plants in the family Asclepiadaceae, a mostly tropical group that contains more than 1,800 species. Most species in this Milkweed in seed. JLM Visuals. Reproduced by permission. family are herbaceous, but others are woody climbers, shrubs, or small trees. The foliage and stems of milkweeds are often succulent, and when they are broken they weep a whi…
In contrast to the endocrine system that achieves long-term control via chemical (hormonal) mechanisms, the nervous system relies on more rapid mechanisms of chemical and electrical transmission to propagate signals and commands. The rapid conduction of impulses is essential in allowing the nervous system to mediate short-term and near immediate communication and control between various body syste…
Neoplatonism initially had a negative connotation. Enlightenment historians developed the term to dissociate the Platonists of the late Roman Empire from Plato, believing that they had distorted his philosophy beyond all recognition by their eclecticism. Jacob Brucker (Historia critica philosophiae, 1742–1744) branded them "the Eclectic Sect" before A. F. Büsching (Grundr…
The New Criticism is the name given to the work of a school of formalist-oriented Anglo-American literary critics whose writings appeared in the years following World War I and came to prominence in the 1940s and 1950s. John Crowe Ransom (1888–1974) coined the moniker itself in his 1941 study The New Criticism, in which he provided an overview of the work of key "New" Critics,…
A standard definition of Newtonianism or Newtonian philosophy found in early eighteenth-century dictionaries such as John Harris's Lexicon Technicum (5th ed., 1736) is: "The doctrine of the universe, and particularly of the heavenly bodies; their laws, affections, etc., as delivered by Sir Isaac Newton." An almost identical definition appears around thirty years later in the E…
In a history that spans more than two and a half centuries, the term nihilism has been employed to denote a wide range of phenomena. It has been variously used to express contempt or horror on the one side, approval and admiration on the other. In the twentieth and twenty-first centuries, it has almost always been an emotional and axiological term, frequently employed to cut off debate on a moral …
While numerous types of migrating peoples can be referred to as nomads, this entry focuses on pastoral nomadism, defined as human cultures that depend solely or primarily on herds of domesticated animals. People in these cultures as a result are required to relocate their homes to new pastures on a regular basis in order to sustain these herds—what anthropologists call transhumance. Such no…
On a clear, moonless night, away from the bright lights of the city, the Milky Way is visible—a fuzzy, milky band stretching across the sky. The Milky Way is the plane of our galaxy, a vast spinning carousel of a few hundred billion stars. Our solar system is located about half way between the center and the edge of this 120,000-light-year diameter pancake shaped galactic disk. The "…
Gandhian nonviolence (ahimsa) is an active civic virtue that habitually disposes individuals, social groups, and political authorities to resist violence through non-violent means and to resolve conflicts using peaceful methods. It recognizes violence as a fact and nonviolence as a norm of social life. Its normative character arises from the assumed natural sociability of human beings. Its focal p…
A classic experiment in molecular biology and genetics, the Miller-Urey experiment, established that the conditions that existed in Earth's primitive atmosphere were sufficient to produce amino acids, the subunits of proteins comprising and required by living organisms. In essence, the Miller-Urey experiment fundamentally established that Earth's primitive atmosphere was capable of p…
Millipedes are long, cylindrical, segmented, many-legged terrestrial arthropods in the class Diplopoda, in total comprising about 10,000 species. The common name of these animals is derived from the Latin word for "thousand legs," although most species actually have fewer than 200 legs, and some as few as about 60. Millipedes have an elongate, almost cylindrical body form, with two s…
The nervous system coordinates behavior and helps to maintain the internal stability of animals. It may be as simple as the nerve net of Cnidarians or as complex as the centralized system of mammals. In all nervous systems the functional unit is the nerve cell or neuron, a cell specialized to transmit and receive a stimulus. …
Mimicry may broadly be defined as imitation or copying of an action or image. In biological systems, mimicry specifically refers to the fascinating resemblance of an organism, called the "mimic," to another somewhat distantly related organism, called the "model." The set of mimic and model species involved is often referred to as a mimicry complex. Usually through escap…
Mineralogy is the branch of geology concerned with the study of minerals. A mineral is a naturally occurring, homogeneous solid with a definite chemical composition and a highly ordered atomic structure. A homogeneous substance is one that can be divided into repeating units that are exactly the same. A mineral, by definition, cannot be a liquid or a gas. The chemical composition of a mineral is d…
When humans are in good health, the nervous system and musculature work together so smoothly there is little awareness of how efficiently this complicated biochemical machine functions. Neuromuscular diseases include a vast and bewildering array of related and unrelated disorders that have a certain similarity of symptoms in that both nerves and muscles are usually impaired. This term is usually a…
In ordinary usage, minerals are the natural, non-living materials that compose rocks and are mined from Earth. Examples are metals, gemstones, clays, and ores. The scientific definition of a mineral is more limited. To be considered a mineral, a substance must be solid under ordinary conditions, thus excluding petroleum and water. Minerals must be single, homogeneous (uniform) substances. Therefor…
Neurons are nerve cells (neurocytes), which, together with neuroglial cells, comprise the nervous tissue making up the nervous system. The neuron is the integral element of our five senses and of countless other physical, regulatory, and mental faculties, including memory and consciousness. A neuron consists of a nerve cell body (or soma), an elongated projection (axon), and short branching fibers…
Neuroscience is the study of the nervous system and its components. Neuroscientists may examine the nervous systems of humans and higher animals as well as simple multicellular nervous systems, or investigate nervous phenomenon at the cellular, organelle, or molecular level. Neuroscience principally originated with three European scientists working at the end of the nineteenth and the beginning of…
Mining is the process by which ores or related materials are extracted from the Earth. Ore is defined as a rock or mineral, generally metallic, which can be mined, processed, transported, and sold at a profit. Therefore, the classification of an Earth material as ore depends as much on economics and technology as geology. Nonmetallic substances that are commonly mined but not considered to be ores…
Minks are carnivores in the family Mustelidae, which also includes badgers, weasels, marten, and otters. Mink are closely related to the weasels and ermine, and are included in the same genus (Mustela spp.). Mink have a long, compact body, with relatively short legs, webbed toes, and a long, bushy tail. Minks are larger and more stout than other animals in the weasel group. Male minks are consider…
Neurosurgery is a medical specialty concerned with the diagnosis and treatment of the central and peripheral nervous system. The nervous system is composed of the brain, spinal cord and spinal column, as well as the nerves that travel through all parts of the body (hands, legs, arms, face). Neurosurgeons treat degenerative and congenital diseases of the spine, pain from pinched nerves in the neck,…
Minnows are a diverse group of about 1,600 species of small exclusively freshwater fish in the family Cyprinidae. The most familiar of these fish are carp, minnows, tenche, and barbs. Species in the minnow family occur in Africa, Asia, Europe, and North America. In addition, some cultivated and game species have also been introduced to South America, New Guinea, Australia, New Zealand, and some ot…
Neurotransmitters are chemical agents secreted at the end of axons of nerve cells that diffuse across the synaptic gap and transmit information to adjoining cells such as neurons, muscle cells, and glands, by altering their electrical state or activity. There are many neurotransmitters with a variety of structures and functions; two of the principle ones are acetylcholine and norepinephrine. Since…
There are many thousands of minor planets, also termed miniplanets or asteroids, within our solar system. They vary in size from a foot or so in diameter to hundreds of miles in diameter. The majority of asteroids, the main-belt asteroids, circle the Sun in a donutshaped region between the orbits of the planets Jupiter and Mars. Several other asteroid families have been identified, including a lar…
In chemistry, the process in which an acid and a basereact with each other to form a salt and water is known as neutralization. Just as a neutral color contains no vivid colors and a neutral person has no strong opinions, a neutralization reaction between an acidic and a basic (alkaline) solution lessens the acidic and basic properties of both solutions. Taking an antacid to settle a sour stomach,…
The virtuoso demands that composers placed on musicians at the end of the 1800s were but a foretaste of things to come in the twentieth century. Members of the orchestra were complaining that the music of contemporary composers was unplayable because of the enormous difficulty of complex orchestral writing styles. With the Paris premiere of Igor Stravinsky's "Le Sacre Du Printemps&#x…
Neutrinos are elusive subatomic particles that result from certain nuclear reactions. Neutrinos have no electrical charge and only a tiny mass, travel at nearly the speed of light, come in three types—electron neutrinos, muon neutrinos, and tau neutrinos—and barely interact with normal matter. Because their interaction rate is so low, neutrinos produced in the core of the Sun fly dir…
The mint family (Labiatae or Lamiaceae) is a large group of dicotyledonous plants occurring worldwide in all types of climates except in extreme arctic and antarctic conditions. There are about 3,000 species in the mint family and 200 genera. The most diverse groups are the genus Salvia with 500 species, Hyptis with 350 species, and Scutellaria, Coleus, Plectranthus, and Stachys, each with 200 spe…
The longest continuous presence of man in space began in 1989, with the Russian launch of a 20.4 ton cylinder that formed the core of the space station called Mir. By 1996, a total of six modules had been linked to complete the sprawling station, which has been likened to a spaceborne assembly of tinkertoys. To build Mir, the Russians drew from lessons learned with the Salyut stations of the 1970s…
The atom's structure has a nucleus at the center, surrounded by a cloud of electrons. Inside the nucleus are two types of particles, neutrons (electrically neutral) and protons (positively charged). Under special experimental conditions, neutrons can be released from the nucleus. They are useful for creating new radioactive materials or for producing large amounts of nuclear energy. The ato…
Any reflective material can act as a mirror, because it will throw back enough light to form an image of its surroundings. The surface may be a plane, concave or convex. Planar or flat mirrors present a virtual image that reverses the object being reflected. Curved surfaces act more like lenses, without the aberrations to which glass lenses are prone. Nowadays such surfaces can be made from glass,…
Neutron activation analysis is an analytical technique for determining the elements present in a material as well as the amount of each element in the sample. The technique is based on a well-known reaction from nuclear chemistry. When an element is bombarded with neutrons, some of the atoms of that element may capture neutrons and incorporate them into their nuclei. Those atoms that do so have th…
Miscibility means how completely two or more liquids dissolve in each other. It is a qualitative rather than quantitative observation—miscible, partially miscible, not miscible. (To state exactly how miscible two liquids were, a scientist would use the larger concept of solubility, usually in a specific weight or volume per liter of solution.) Two completely miscible liquids will form a hom…
Mistletoe belongs to the family Viscaceae and to the genus Viscum, Phoradendron, or Arceuthobium. Most commonly, mistletoe refers to either the Eurasian shrub Viscum album or one of the American species, such as Phoradendron flavescens. Mistletoe grows on the trunks and branches of a wide variety of trees. Mistletoe is an evergreen, and its stems have numerous branches. The plants have tough, oblo…
Mites are tiny arthropods in the order Acari (or Acarina), which also includes the somewhat larger ticks. The Acari is in the class Arachnida, which also encompasses the spiders and scorpions. Arachnids have four pairs of segmented legs, a body divided into a cephalothorax (that is, a united head and thorax), and abdomen, and they have a simple respiratory apparatus consisting of tracheae and/or b…
A neutron star is the dead remnant of a massive star. A massive star ends its life as a supernova, a catastrophic explosion that flings the star's outer layers into space, leaving only the core behind. If the mass of the core is between 1.4 and 2.5 times the mass of the Sun, it will become a neutron star, a solid mass of neutrons a hundred trillion times more dense than water. Neutron stars…
