Toxicology is the scientific study of poisons (or toxins). Major topics in toxicology include the detection and chemical analysis of poisons, the study of the metabolic effects of these substances on organisms, and the investigation of methods for treatment of poisoning. The Swiss physician and alchemist Philippus Aureolus, also known as Paracelsus (1493-1541) and said to be the father of the mode…
Trace elements are chemicals that are required by organisms in very small quantities for proper physiological and biochemical functioning. Trace elements commonly occur in organisms in concentrations smaller than about 0.001% of the dry weight (less than 10 parts per million, or ppm). Listed in alphabetical order, the most commonly required trace elements for healthy animal or plant nutrition are:…
The basic sense of the term tradition remains quite close to its etymological roots. The Latin noun traditio describes the handing over of an item or an idea, while the English tradition refers to a social or cultural institution that is handed down from the past. This much seems straightforward. Sacrificing cattle, singing at graduation, celebrating the New Year with fireworks: all these appear q…
Trains were developed during the Industrial Revolution and were arguably that period's most important product. In many ways railroads made the Industrial Revolution possible. Factories could not run without a constant supply of raw materials, or without a method of moving goods to market. More than anything, the progress of the railroads depended on the development of motive power, which wa…
The medical use of drugs to reduce or relieve anxiety has given rise to a group of medications called an tianxiety agents. These agents include anxiolytics, tranquilizers, and sedatives. Tranquilizers were formerly grouped as either "minor" tranquilizers or "major" tranquilizers. The word major stands for "major psychiatric illness," not heavily sedating o…
A transducer is a device which converts one form of energy to another. Typically, one of these forms is electrical while the other is either mechanical, optical, or thermal. Transducers are usually classified as either input or output devices, depending on the direction in which they transfer energy or information. Input transducers convert some property or effect into an electrical signal, while …
A transformer is an electrical device which changes or transforms an alternating current (AC) signal from A high voltage transformer. Photograph by Tardos Camesi. Stock Market. Reproduced by permission. one level to another. The device typically consists of two sets of insulated wire, coiled around a common iron core. Electrical power is applied to one of these coils, called the primary c…
The term transgenics refers to the process of transferring genetic information from one organism to another. By introducing new genetic material into a cell or individual, a transgenic organism is created that has new characteristics it did not have before. The genes transferred from one organism or cell to another are called transgenes. The development of biotechnological techniques has led to th…
A transistor is a small, solid device capable of amplifying and switching electrical signals. A transistor can be manufactured using a wide variety of materials; most transistors utilize the unique semiconducting properties of silicon or germanium that has been selectively contaminated with other elements (e.g., arsenic, phosophorus, boron, gallium). A transistor is controlled by voltages communic…
The concept of transitivity goes back at least 2,300 years. In the Elements, Euclid includes it as one of his "common notions." He says, "Things which are equal to the same thing are also equal to one another." As Euclid puts it, if a = b and c = b, then a = c, which is equivalent to the modern version, which has "b = c" rather than "c = b." …
What may summarily be called translation has been practiced in many parts of the world for centuries and even millennia. The rendering of Buddhist texts into literary Chinese and the Latinization of the Bible in the first millennium are two instances of celebrated achievements in the long history of translation. There are countless cases where translations are known to have played a decisive role …
A translation is one of the three transformations that move a figure in the plane without changing its size or shape. (The other two are rotations and reflections.) In a translation, the figure is moved in a single direction without turning it or flipping it over. A translation can, of course, be combined with the two other rigid motions (as transformations which preserve a figure's size an…
A surgical transplant involves the removal of body parts, organs, or tissues from one person and implanting them into the body of another person. Although the idea of transplantation to cure disease dates back several centuries, transplantation has been considered a viable therapy for only a few decades. The relatively recent growth in transplantation stems primarily from expanding knowledge about…
A trapezoid is a four-sided, two-dimensional polygon. With four sides, a trapezoid is a quadrilateral, just as a square or rectangle or parallelogram. Unlike those forms, however, a trapezoid does not necessarily have to have parallel sides. In other words, all rectangles are trapezoids, but not all trapezoids are rectangles. A trapezium is a subset of trapezoids in which at least two sides are pa…
The genre of epic structures the oldest European travel narratives extant, from the voyages of Ulysses to that of Beowulf. The epic as a form connects travel to conflict and cultural threat, as well as to the landscape of fantasy and to the epic hero. Just as the epic hero is larger and more marvelous than life, so the epic landscape is both marvelous and dangerous. The epic hero and those who acc…
Although the word treaty can be etymologically traced back to the Latin tractus, meaning treatment, handling, discussion, and management, there was no Latin word with that root having the notion of an (international) agreement. If anything, tractus sometimes had the sense of a disagreement, of a violent handling of affairs, such as the dragging by the hair of the priestess of Apollo. A common Lati…
The tree shrews (order Scandentia, family Tupaiidae) comprise a small number of species that are only found in South and Southeast Asia. Five genera (19 species) are recognized. All occur in forested areas, ranging from India and Southwest China eastward through Malaysia, Indonesia (west of Wallace's Line), and the Philippines. Three genera and 10 species occur on the island of Borneo alone…
The term tribe, derived from the Latin tribus, refers to a group of persons forming a community and claiming descent from a common ancestor. In the Middle East and North Africa, unlike many other parts of the world, claiming tribal affiliation often positively affirms community, identity, and belonging. In the mid-to late twentieth century, nationalist leaders in some regions rejected claims to tr…
Triggerfishes are members of the family Balistidae of the order Tetradontiformes. They derive their name from a unique feature of their dorsal fin. The triggerfish can lock the large dorsal spine in an upright position by supporting it with its smaller secondary spine. This protects the fish from predation by larger fish because the erect spine makes the fish hard to swallow or extract from small …
Fats exist in foods—and are usually stored in the body—as Triglycerides. Recent research relating levels of triglycerides in the blood stream to heart attacks in human presents a sometime confusing picture but a mounting level evidence suggests that, along with other indicators, triglyceride levels can be used to predict heart attack risk, especially in women and diabetics. Although …
Tritium is an isotope of the chemical element hydrogen. It has not only a single proton but also two neutrons in the nucleus of its atoms. Although technically it is still the element hydrogen, it has its own chemical symbol, T. Chemically, tritium reacts in exactly the same manner as hydrogen, although slightly slower because of its greater atomic weight. A tritium atom has almost three times the…
Trogons are about 35 species of beautiful arboreal birds that constitute the family Trogonidae. Trogons have a number of peculiar features in their morphology, and are not thought to be closely related to any other groups of living birds. This is why their family is the only one in the order Trogoniformes. Species of trogons occur throughout the tropical and subtropical parts of the world, a bioge…
Trophic levels describe the various stages within ecological food chains or webs. Examples of trophic levels, all of which will be described below, are primary producers, primary consumers or herbivores, and secondary and higher-level consumers, or predators. Food webs are based on the productivity of photosynthetic organisms, such as blue-green bacteria, algae, and plants. These are autotrophic o…
Tropic birds are three species of pan-tropical seabirds that make up the family Phaethontidae, in the order Pelecaniformes, which also includes the pelicans, anhingas, cormorants, gannets, and boobies. Tropic birds are medium-sized seabirds, weighing about 0.9 lb (0.4 kg), and having a body length of 16-18.9 in (41-48 cm). This length does not include their greatly elongated tail feathers, which a…
Tropical cyclones are large circulating storm systems consisting of multiple bands of intense showers and thunderstorms and extremely high winds. These storm systems develop over warm ocean waters in the tropical regions that lie within about 25° latitude of the equator. Tropical cyclones may begin as isolated thunderstorms. If conditions are right they grow and intensify to form the storm …
Nowhere is the prevalence of certain illnesses more striking than in areas where tropical diseases flourish. In many parts of Africa, South America, and Asia, diseases exist that are rarely seen in the United States. These include malaria, which infects from 300 to 500 million people annually and kills up to 2.7 million people every year, and leishmaniasis, which affects some 12 million people int…
The trout-perch belongs to the family Percopsidae, which includes only one genus—Percopsis—with only two species. The fish is found only in the fresh waters of North America. One species (Percopsis omiscomaycus) is found mainly on the eastern side; the other species, the sandroller (P. Transmontana), is native to the west in the regions around the Columbia River Basin. Both species a…
The true bugs are a large and diverse group of about 35,000 species of insects in the order Hemiptera. About 44 families of bugs occur in North America. Bugs typically have a flattened body, and their folded wings cross over their thorax and abdomen, giving a distinctive, cross-like pattern. Some species of true bugs are of great economic importance as pests of agricultural plants. A few species o…
The true flies are a large and diverse group of commonly observed insects in the order Diptera, comprising more than 100,000 species. About 107 families of flies occur in North America. Flies have distinctive, knob-like structures known as halteres on the back of their thorax. Halteres are highly modified from the hind wings of true flies, while the fore wings are membranous and used for flying. T…
Trumpetfish (Aulostomus maculatus) are bony fish in the family Aulostomidae, found from the Caribbean Sea to as far north as Bermuda. They are named for the trumpet-like shape they exhibit when their mouths are open. Trumpetfish measure up to 2 ft (0.6 m) in length, and have dorsal spines which support separate fins or finlets. They are brownish in color with widespread streaks and spots. Trumpetf…
Tsunami, or seismic sea waves, are a series of very long wavelength ocean waves generated by the sudden displacement of large volumes of water. The generation of tsunami waves is similar to the effect of dropping a solid object, such as a stone, into a pool of water. Waves ripple out from where the stone entered, and thus displaced, the water. In a tsunami, the "stone" comes from und…
Tuataras are unusual, lizard-like animals that are the only living representatives of the order Sphenodonta of the vertebrate class Reptilia. The lineage of the sphenodonts is an ancient one, with a fossil record extending back 200 million years, prior even to the evolution of dinosaurs and the lizards. Until the discovery of tuataras in New Zealand, biologists had believed that this reptilian lin…
A tuber is a swollen, underground storage organ that develops on the roots of certain species of plants. Some types of tubers are highly nutritious, mostly because of their energy content in the form of starch. Agricultural species of plants that develop edible tubers include the white potato (Solanum tuberosum), sweet potato (Ipomoea batatas), tapioca or cassava (Manihot esculenta), and yam (Dios…
Tuberculosis is a disease caused by the bacterium Mycobacterium tuberculosis. The organism infects the lungs and causes a debilitating condition that historically was known as consumption. In the 1970s, scientists considered tuberculosis as largely defeated following the widespread use of antibiotics. Today, multi-drug resistant Mycobacterium tuberculosis has developed, and tuberculosis has reemer…
The true tumbleweeds are various species of herbaceous plants in the amaranth family (Amaranthaceae). These are usually annual plants that develop a spherical, bush-shaped biomass. At the end of the growing season when their small seeds are ripe, the tumbleweeds wither and detach from their base and are blown about by winds, scattering their seeds widely over the surface of the ground. Therefore, …
A tumor (also known as a neoplasm) is an abnormal tissue growth. Neoplasm means "new formation." Tumors can be either malignant (cancerous) or nonmalignant (benign) but either type may require therapy to remove it or reduce its size. In either case the tumor's growth is unregulated by normal body control mechanisms. Usually the growth is not beneficial to the organ in which it…
Tundra is a generic name for a low-growing ecosystem found in climatically stressed environments with short and cool growing seasons. Latitudinal tundra occurs in the Arctic and to a much lesser extent in the Antarctic, where the environments are characterized by cool, short growing seasons. Altitudinal tundra occurs under a similar climatic regime, but at the tops of mountains. After temperature,…
Tunneling, also known as the tunnel effect, is a quantum mechanical phenomenon by which a tiny particle can penetrate a barrier that it could not, by any classical or obvious means, pass. Though seemingly miraculous, the effect does have some intuitive characteristics. For instance, thin barriers allow more particles to tunnel than do thick ones, and low barriers permit more tunneling than do high…
Turacos, or touracos, are 18 species of sub-Saharan birds that make up the family Musophagidae, in the order Cuculiformes, which also includes the cuckoos, anis, coucals, and roadrunner. The usual habitat of turacos is dense tropical forests or forest edges. Turacos do not migrate, although they may move locally. Turacos are medium- to large-sized birds, with a body length of 1.2-2.5 ft (38-76 cm)…
Turbulence is the formation of eddies in a fluid (liquid or gas). It is produced whenever a fluid (under certain conditions) is in contact with a solid and there is relative motion between them; for example: when wind flows past a building or past a mountain; when the ocean flows past an island; when a baseball flies by; when a jet plane moves in the stratosphere; or when a river flows past a brid…
Turtles are familiar, four-legged reptiles whose body is enclosed within a bony shell. Turtles constitute the reptilian order Testudines. The 257 living species inhabit all continents except Antarctica, plus many islands, and there are marine turtles in all tropical and temperate oceans. The turtles are separated into two major groups (subclasses) that can be readily identified by the way they ret…