Causal theories suggest that the infant may have immature or hypersensitive lungs, may have a defect in brain-stem control of breathing, or may be rebreathing carbon dioxide. Recent studies have shown persistent high levels of an infant form of hemoglobin in babies with known risk factors for the condition.

SIDS victims are thought to have brief episodes of apnea (breathing stoppage) before the fatal one. An alarm system that detects breathing abnormalities is sometimes used with infants suspected of being prone to SIDS. The American Academy of Pediatrics has recommended that babies be laid to sleep on their backs or sides.

Research into the near-death experience was pioneered by Raymond Moody, who published Life After Life in 1975 after studying 150 people who had had such experiences. He and other scientists, such as cardiologist Michael Sabom, found that possible physiological and psychological causes for the phenomenon, including lack of oxygen to the brain, the influence of anesthetics, disruptions in neurotransmitter release, and prior expectations, could not sufficiently account for the experiences these people described. Their findings and a belief in a spiritual explanation for the phenomenon have been supported by Elisabeth Kübler-Ross, who pioneered the study of death and dying in the United States beginning in the late 1960s.

Near-death experience is an emotional issue, believed to be a profound spiritual experience by some and criticized as wish fulfillment by others. Many skeptical scientists believe that it is a simple physiological event misconstrued by people who have a compelling psychological need or who are comforted by interpreting the experience in terms of their religious or spiritual beliefs.

Somatic death is characterized by the discontinuance of cardiac activity and respiration, and eventually leads to the death of all body cells from lack of oxygen, although for approximately six minutes after somatic death—a period referred to as clinical death—a person whose vital organs have not been damaged may be revived. However, achievements of modern biomedical technology have enabled the physician to artificially maintain critical functions for indefinite periods.

Somatic death is followed by a number of irreversible changes that are of legal importance, especially in estimating the time of death. These include rigor mortis, livor mortis (discoloration of the body due to settling of blood), algor mortis (cooling of the body), autolysis (breakdown of tissue by enzymes liberated by that tissue after death), and putrefaction (invasion of the body by organisms from the gastrointestinal tract).

Brain death, which is now a legal condition in most states for declared death, requires that the following be absent for at least 12 hours: behavioral or reflex motor functions above the neck, including pupillary reflexes to testing jaw reflex, gag reflex, response to noxious stimuli, and any spontaneous respiratory movement. Purely spinal reflexes can remain. If the patient has agreed to be an organ donor, the observation period can be shortened to 6 hours.

As a result of recent refinements in organ transplantation (see transplantation, medical) techniques, the need has arisen to more precisely define medical death. The current definition is that of a 1981 U.S. presidential commission, which recommended that death be defined as "irreversible cessation of all functions of the entire brain, including the brain stem," the brain stem being that part of the brain that controls breathing and other basic body functions. Some feel, however, that people in persistent vegetative states, i.e., people who have brain-stem function but have lost higher brain functions (vision, abstract thought, personality), should be considered dead and allowed, through living wills or relatives, to donate organs.

See euthanasia; funeral customs; vital statistics.

Death Valley was named by gold seekers who undertook to cross this desolate region in 1849 on their way to the California gold fields. The valley yielded gold and silver in the 1850s, and in the 1880s borax was discovered and taken out by mule-drawn wagons. The valley was much publicized by the American adventurer Walter Scott ("Death Valley Scotty"), and it remains a popular tourist attraction. Death Valley National Park, 3,367,628 acres (1,363,412 hectares), a protected region of Death Valley, was established as a national monument in 1933 and designated a national park in 1994. See also National Parks and Monuments (table).

Large, aggressive shark (Carcharodon carcharias, family Lamnidae), considered the species most dangerous to humans. It is found in tropical and temperate regions of all oceans and is noted for its voracious appetite. Its diet includes fishes, sea turtles, birds, sea lions, small whales, carcasses, and ships' garbage. The great white is heavy-bodied and has a crescent-shaped tail and large, saw-edged, triangular teeth. It can reach a length of more than 20 ft (6 m) and is generally gray, bluish, or brownish, with the colour shading suddenly into a whitish belly. Though it is widely feared, only a few hundred humans are known to have ever been killed by the great white shark.

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Unexpected death of an apparently well infant. It occurs almost always during sleep at night and usually at 2–4 months of age. Sleeping facedown and exposure to cigarette smoke have been implicated. It is more common in cases of premature birth, low birth weight, and poor prenatal care. Many cases that would once have been labeled SIDS prove to be due to suffocation in bedding or overheating. Some babies who die of SIDS have been found to have brain stem abnormalities that interfere with their response to high levels of carbon dioxide in the blood.

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Mechanism that allows cells to self-destruct when stimulated by the appropriate trigger. It may be initiated when a cell is no longer needed, when a cell becomes a threat to the organism's health, or for other reasons. The aberrant inhibition or initiation of apoptosis contributes to many disease processes, including cancer. Though embryologists had long been familiar with the process of programmed cell death, not until 1972 was the mechanism's broader significance recognized. Apoptosis is distinguished from necrosis, a form of cell death that results from injury.

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Execution of an offender sentenced to death after conviction by a court of law of a criminal offense. Capital punishment for murder, treason, arson, and rape was widely employed in ancient Greece, and the Romans also used it for a wide range of offenses. It also has been sanctioned at one time or another by most of the world's major religions. In 1794 the U.S. state of Pennsylvania became the first jurisdiction to restrict the death penalty to first-degree murder, and in 1846 Michigan abolished capital punishment for all murders and other common crimes. In 1863 Venezuela became the first country to abolish capital punishment for all crimes. Portugal was the first European country to abolish the death penalty (1867). By the mid-1960s some 25 countries had abolished the death penalty for murder. During the last third of the 20th century, the number of abolitionist countries increased more than threefold. Despite the movement toward abolition, many countries have retained capital punishment, and some have extended its scope. In the U.S., the federal government and roughly three-fourths of the states retain the death penalty, and death sentences are regularly carried out in China, Saudi Arabia, Singapore, and Iran. Supporters of the death penalty claim that life imprisonment is not an effective deterrent to criminal behaviour. Opponents maintain that the death penalty has never been an effective deterrent, that errors sometimes lead to the execution of innocent persons, and that capital punishment is imposed inequitably, mostly on the poor and on racial minorities.

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Medieval allegorical concept of the all-conquering and equalizing power of death, expressed in the drama, poetry, music, and visual arts of western Europe, mainly in the late Middle Ages. It is a literary or pictorial representation of a procession or dance of both living and dead figures, the living arranged in order of their rank, from pope and emperor to child, clerk, and hermit, and the dead leading them to the grave. It was given impetus by the Black Death and the Hundred Years' War. Though depictions declined after the 16th century, the theme was revived in literature and music of the 19th–20th centuries.

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Valley, southeastern California, U.S. The lowest, hottest, driest portion of North America, it is about 140 mi (225 km) long and 5–15 mi (8–24 km) wide. The Amargosa River flows into it from the south and contains a small pool, Badwater, near which is the lowest point in North America at 282 ft (86 m) below sea level. Death Valley was formerly an obstacle to pioneer settlers (hence its name); it later was a centre of borax mining. Declared a national monument in 1933, it was made a national park in 1994; the park covers 5,269 sq mi (13,648 sq km) and extends into Nevada.

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Fierce and widespread outbreak of plague, probably bubonic and pneumonic, that ravaged Europe during the 14th century. The epidemic originated in Asia and was transmitted to Europeans in 1347 when a Turkic army besieging a Genoese trading post in the Crimea catapulted plague-infested corpses into the town. It spread from the Mediterranean ports and ravaged all of Europe between 1347 and 1351. Renewed outbreaks occurred in 1361–63, 1369–71, 1374–75, 1390, and 1400. Towns and cities were more heavily hit than the countryside, and whole communities were sometimes destroyed. Much of Europe's economy was devastated. About one-third of the European population, or a total of 25 million people, died in the Black Death.

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