poison sumac: see poison ivy.

poison oak: see poison ivy.

poison ivy, poison oak, and poison sumac, woody vines and trailing or erect shrubs of the family Anacardiaceae (sumac family), native to North America. They are sometimes considered as several species of Rhus, the sumac genus, but are usually distinguished as Toxicodendron radicans (poison ivy and poison oak) and the larger T. vernix (poison sumac). The whitish berrylike fruits often persist through winter. The leaves of T. radicans are composed of three smooth leaflets. Both species have vivid red autumn foliage. Poison oak is a name generally used in the South and West for the bushy kinds.

The irritant principle, urushiol, is present in almost all parts of the plant. Direct or indirect contact (clothing, tools, or animals that have touched the plant, or smoke from burning the plants) sets off a skin eruption that may vary from simple itching inflammation to watery blisters, depending upon the sensitivity of the individual. The eruption appears within a day to two weeks depending upon sensitivity. It begins on the portion of the body that has come in contact with the plant, usually the hands, which then can spread it to the face and other areas. Washing contaminated skin as soon as possible after contact can reduce the severity of symptoms. These plants are classified in the division Magnoliophyta, class Magnoliopsida, order Sapindales, family Anacardiaceae.

poison hemlock, lethally poisonous herbaceous plant (Conium maculatum) of the family Umbelliferae (parsley family). It has rank, finely divided foliage, flat-topped clusters of small white flowers, and a hollow, purple-mottled stem. Although native to the Old World, it is now naturalized and common in parts of the United States. The poisonous principle (the alkaloid coniine) causes paralysis, convulsions, and eventual death. Poison hemlock was used in ancient Greece in executions; a famous example was the philosopher Socrates. The related water hemlock (any species of Cicuta) is similar in appearance and as poisonous. C. maculata, called also musquash-root, spotted cowbane, and beaver poison, is the common species of E North America. The evergreen trees called hemlock are unrelated. Poison hemlock is classified in the division Magnoliophyta, class Magnoliopsida, order Apiales, family Umbelliferae.

poison glands: see venom.

poison gas, any of various gases sometimes used in warfare or riot control because of their poisonous or corrosive nature. These gases may be roughly grouped according to the portal of entry into the body and their physiological effects. Vesicants (blister gases) produce blisters on all body surfaces (see lewisite; mustard gas); lacrimators (tear gas) produce severe eye irritation; sternutators (vomiting gases) cause nausea; nerve gases inhibit proper nerve function; and lung irritants attack the respiratory tract, causing pulmonary edema. By the middle of the 19th cent. the possibility of the use of poison gas as a weapon was already envisaged and was viewed by most people with a peculiar horror—a feeling that has persisted. The first effective use of poison gas came in World War I, when the Germans released (1915) chlorine gas against the Allies in the Ypres sector of the Western Front. The success was immediate, but the attackers, uncertain as to the effect, failed to pursue the retreating French. Shortly afterward protective measures (see gas mask) were introduced as both sides used gas more extensively. The gas shell (much more suitable than wind-blown gas) was introduced by the French. Gas did not have any dominant influence on the course of the war, but it did seem to point toward wide-scale use in the future. However, except for the use of poison gas by the Italians in the war against Ethiopia (1935-36) and by the Japanese against Chinese guerrillas (1937-42), poison gas was not employed in warfare after World War I out of fear of retribution, even though the military powers of the world continued to develop new gases. Poison gas was used in the Iran-Iraq War, and Iraq has used poison gas on its own civilians, in particular the Kurds. In the Persian Gulf War, the UN troops were equipped with antidotes for nerve gas, protective clothing, and gas masks in case Iraq used poison gas. The 1989 treaty between the United States and the USSR provided for an end to production of poison gas and the beginning of destruction of current stockpiles. See also chemical warfare.

poison, any agent that may produce chemically an injurious or deadly effect when introduced into the body in sufficient quantity. Some poisons can be deadly in minute quantities, others only if relatively large amounts are involved. Factors of importance in determining the severity of a poison include the nature of the poison itself, the concentration and amount, the route of administration, the length of exposure, and the age, size, and physical health of the individual. If poisoning is suspected a physician or poison control center should be called immediately. The remainder of the poison and its container should be saved; the label may list ingredients, first aid measures, or antidotes. For most ingested poisons emptying the stomach is the most important treatment; vomiting is best accomplished in the conscious individual by administering syrup of ipecac with large quantities of water. The major exceptions to this treatment are in cases of ingestion of corrosives, such as lye, and certain hydrocarbons, such as kerosene. In corrosive ingestions a small amount of milk may be given, but vomiting should not be induced since the damage that may have already been sustained by the mucous membranes of the esophagus and stomach may advance to perforation; the patient should be seen by a physician as soon as possible. Hydrocarbons are extremely volatile, and the dangers of their being aspirated into the lungs when vomiting is induced are greater than their toxicity if absorbed into the body. In gas or vapor poisoning the patient should be carried to a nonpolluted atmosphere; artificial respiration should be employed if necessary. If any poison has been absorbed through the skin, all contaminated garments should be removed immediately and the skin washed with soap and water. Poisoning is a significant cause of accidental death in children and is best treated by prevention; potential poisons in the home should be stored in locked cabinets. In chemistry, poison refers to a substance that inhibits or slows a chemical reaction. See separate articles on botulism; carbon monoxide; food poisoning; lead poisoning; mercury poisoning; poison gas; poison ivy; snakebite; toxin.

Poison Affair, in French history, scandal implicating a number of prominent persons at the court of King Louis XIV. It began with the trial of Marie Madeleine d'Aubray, marquise de Brinvilliers (c.1630-76). She conspired with her lover, Godin de Sainte-Croix, an army captain, to poison her father and two brothers in order to secure the family fortune and to end interference in her adulterous relationship. Her husband escaped the same fate by his complaisance. An investigation was made, and the marquise fled abroad, but in 1676 she was arrested at Liège. The affair greatly worked on the popular imagination, and there were rumors that she had tried out her poisons on hospital patients. She was beheaded and then burned. The Brinvilliers trial attracted attention to other mysterious deaths. Parisian society had been seized by a fad for spiritualist séances, fortune-telling, and the use of love potions. Some of the quack practitioners undoubtedly also sold poison (called "inheritance powders" at the time); after their arrest they furnished the police with lists of their clients, who often were guilty merely of having their palms read or of buying an aphrodisiac, and accused them of complicity in their crimes. The most celebrated case was that of La Voisin, a midwife and fortune-teller whose real name was Catherine Deshayes Monvoisin and whose clientele included the marquise de Montespan, Olympe Mancini (niece of Cardinal Mazarin and mother of Prince Eugene of Savoy), her sister Marie Anne Mancini, and Marshal Luxembourg (duke and peer of France and one of the military heroes of the time). No formal charges were made against any of these, and there is no evidence that they were seriously implicated, yet a permanent stain was left on their names. La Voisin was burned as a poisoner and a sorceress in 1680. A special court, the chambre ardente [burning court], was instituted to judge cases of poisoning and witchcraft, and the poison epidemic came to an end in France. The affair was symptomatic of the witchcraft trials of the period throughout Europe and in New England; however, the judicial investigation was conducted generally with far more regularity and far less hysteria than elsewhere.

Either of two North American species of white-fruited woody vines or shrubs of the sumac, or cashew, family. The species found in eastern North America (Toxicodendron radicans) is abundant; a western species, known as poison oak, is less common. Both species are sometimes classified as genus Rhus. A key identifier is leaves with three mitten-shaped leaflets. Contact with urushiol, an oil produced by the plant, can cause severe inflammation and blistering of human skin. Urushiol may be carried from the plant on clothing, shoes, tools, or soil; by animals; or by smoke from burning plants. Because urushiol is nonvolatile, a reaction may result from wearing clothing a year or more after its contact with the plant.

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Any of several poisonous herbaceous plants of the parsley family, especially Conium maculatum, believed to be the plant that killed Socrates. It is now common in the U.S. as well as in Europe. A tall biennial, this plant has green stems spotted with red or purple, large compound leaves, and white flowers. Though the poison is concentrated in the seeds, the entire plant is dangerous to livestock when fresh. Despite their common name, poison hemlocks are not conifers (see hemlock). Water hemlocks (Cicuta species) are similar and also dangerous.

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Any substance (natural or synthetic) that, at a certain dosage, damages living tissues and injures or kills. Poisons spontaneously produced by living organisms are often called toxins, venoms if produced by animals. Poisons may be ingested, inhaled, injected, or absorbed through the skin. They do not always have an all-or-none effect; degrees of poisoning may occur, and at a given dose some substances are far more toxic than others (e.g., a pinch of potassium cyanide can kill, whereas a single dose of ordinary table salt must be massive to kill). Poisoning may be acute (a single dose does significant damage) or chronic (repeated or continuous doses produce an eventual effect, as with chemical carcinogens). The effects produced by poisons may be local (hives, blisters, inflammation) or systemic (hemorrhage, convulsions, vomiting, diarrhea, clouding of the senses, paralysis, respiratory or cardiac arrest). Agricultural pesticides are often poisonous to humans. Some industrial chemicals can be very toxic or carcinogenic. Most therapeutic drugs and health-care products can be poisons if taken inappropriately or in excess. Most forms of radiation can be toxic (see radiation injury). Seealso antidote; arsenic poisoning; fish poisoning; food poisoning; lead poisoning; medicinal poisoning; mercury poisoning; mushroom poisoning.

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