dybbuk \'di-bok\ In Jewish folklore, a disembodied human spirit that must wander restlessly, burdened by former sins, until it inhabits the body of a living person. Belief in such spirits was common in eastern Europe in the 16th-17th century. Individuals thought to be possessed by a dyb¬ buk were taken to a ba'al shem, who would carry out a rite of exorcism. The mystic Isaac ben Solomon Luria helped promote belief in dybbukim with his doctrine of the transmigration of souls. The folklorist S. Ansky depicted such a spirit in his classic Yiddish drama The Dybbuk (c. 1916).
Dyck, Anthony Van See Anthony Van Dyck
dye Any of a class of intensely coloured complex organic compounds used to colour textiles, leather, paper, and other materials. Dyes known to the ancients came from plants such as indigo and madder (see madder family) or from the shells of mollusks; today most dyes are made from coal tar and petrochemicals. The chemical structure of dyes is relatively easy to modify, so many new colours and types of dyes have been syn¬ thesized. Dye molecules are deposited from solution onto materials in such a way that they cannot be removed by the original solvent. Fibre- reactive dyes form a covalent bond with the fibre. Other dyes require prior application of a mordant, an inorganic material that causes the dye to pre¬ cipitate as an insoluble salt. Another technique is vat dyeing, in which a soluble colourless compound is absorbed by the fibres, then oxidized (see oxidation-reduction) to the insoluble coloured compound, making it remarkably resistant to the fading effects of washing, light, and chemi¬ cals. See also azo dye.
Dylan \'dil-3n. Bob orig. Robert Allen Zimmerman (b. May 24,
1941, Duluth, Minn., U.S.) U.S. singer and songwriter. He grew up in the iron-range town of Hibbing, Minn., adopted the name of the poet Dylan Thomas, and traveled to New York in search of idol Woody Guthrie. In the early 1960s he performed professionally in Greenwich Village coffee¬ houses and released albums that made him the darling of critics and folk music devotees. “Blowin’ in the Wind” and “The Times They Are a-Changin’” became anthems of the civil rights movement. In 1965 he adopted electrically amplified instruments and the rhythms of rock and roll in a major departure. The landmark albums Highway 61 Revisited (1965) and Blonde on Blonde (1966) established him as a leading figure in rock music, and his lyrics, influenced partly by the Beat movement, brought poetic complexity to pop music. After a motorcycle accident in 1966, he underwent another musical turnabout and released several albums (notably Nashville Skyline, 1969) characterized by country music elements and a muted, reflective tone. Among the most praised of his many later albums are Blood on the Tracks (1975), Time Out of Mind (1997) and Love and Theft (2001). He is perhaps the most admired and influential American songwriter of his time.
dynamics Branch of mechanics that deals with the motion of objects in relation to force, mass, momentum, and energy. Dynamics can be divided into two branches, kinematics and kinetics. The foundations of dynamics were laid by Galileo, who derived the law of motion for falling bodies and was the first to recognize that all changes of velocity of a body are the result of forces. Isaac Newton formulated this observation in his sec¬ ond law of motion (see Newton's laws of motion).
dynamite Blasting explosive, patented in 1867 by Alfred P. Nobel. Dyna¬ mite is based on nitroglycerin but is much safer to handle than nitroglyc¬ erin alone. By mixing the nitroglycerin with kieselguhr, a porous silica- containing earth, in proportions that left an essentially dry and granular material, Nobel produced a solid that was resistant to shock but readily explodable by heat or sudden impact. Later, wood pulp was substituted
Dutchman's-pipe (Aristolochia durior).
AJ. HUXLEY
© 2006 Encyclopaedia Britannica, Inc.
dysentery ► Dzerzhinsky I 585
as the absorbent, and sodium nitrate was added as an oxidizing agent to increase the strength of the explosive.
dysentery \'di-s 3 n-,ter-e\ Infectious intestinal disorder. It is character¬ ized by inflammation, abdominal pain and straining, and diarrhea, often containing blood and mucus. Dysentery is spread in food or water con¬ taminated by feces, often by infected individuals with unwashed hands. Bacillary dysentery (shigellosis), caused by Shigella bacteria, may be mild or may be sudden, severe, and fatal. Fluid loss causes dehydration. Advanced stages include chronic large-intestine ulceration. It is treated with antibiotics, fluid replacement, and sometimes blood transfusion. Amoebic (or amebic) dysentery, caused by the amoeba Entamoeba his¬ tolytica, has two forms, one much like bacillary dysentery and the other chronic and intermittent, sometimes with large-intestine ulcerations. It is treated with drugs that kill the amoeba.
dyslexia \dis-'lek-se-o\ Chronic neurological disorder causing inability or great difficulty in learning to read or spell, despite normal intelligence. It inhibits recognition and processing of graphic symbols, particularly those pertaining to language. Symptoms, including very poor reading skills, reversed word and letter sequences, and illegible handwriting, usu¬ ally become evident in the early school years. With early recognition and specialized approaches to teaching reading, most dyslexics can learn to read. Anomalies have recently been found in reading-related pathways in the brains of dyslexic persons.
dysmenorrhea N.dis-.me-no-'re-sV Pain or cramps before or during menstruation. In primary dysmenorrhea, caused by endocrine imbalances, severity varies widely. Irritability, fatigue, backache, or nausea may also occur. Long assumed to be psychosomatic, it is now known to be due to
excess prostaglandins, which contract the uterus, causing cramps. Pain relievers that block prostaglandin formation can decrease its severity, which may also be eased after childbearing. Secondary dysmenorrhea is caused by other disorders, including genital obstructions, pelvic inflam¬ mation, infection, polyps, or tumours. Treatment is directed toward the underlying disorder.
dysphasia See aphasia
dysplasia \dis-'pla-zho\ Abnormal formation of a bodily structure or tissue, usually bone, that may occur in any part of the body. Several types are well-defined diseases in humans. In the most common, epiphyseal dysplasia, the ends of children’s bones (epiphyses) grow and harden very slowly; dwarfism often results (sometimes only in the legs), and degen¬ erative joint disease usually develops by middle age. Large dogs bred for narrow hips may have hip dysplasia, with abnormalities involving the head of the thighbone and the hip socket.
Dyushambe See Dushanbe
Dzerzhinsky \dyir-'zhen-ske\, Feliks (Edmundovich) (b. Sept. 11, 1877, Dzerzhinovo, near Minsk, Russian Empire—d. July 20, 1926, Mos¬ cow, Russia, U.S.S.R.) Russian Bolshevik leader, head of the first Soviet secret-police organization. Son of a Polish nobleman, he was repeatedly arrested for revolutionary activities beginning in 1897. After the Russian Revolution of 1917, he headed the newly created Cheka, which became Soviet Russia’s security-police agency. He organized the first concentra¬ tion camps in Russia and acquired a reputation as a ruthless and fanatical communist. In 1924 he was given control of the Supreme Economic Council.
© 2006 Encyclopaedia Britannica, Inc.
586 I E. coli ► Early
E. coli \'ko-,lI\ in full Escherichia coli Yesh-o-'ri-ke-o-'ko-JU Species of bacterium that inhabits the stomach and intestines. E. coli can be trans¬ mitted by water, milk, food, or flies and other insects. Mutations can lead to strains that cause diarrhea by giving off toxins, invading the intestinal lining, or sticking to the intestinal wall. Therapy consists largely of fluid replacement, though specific drugs are effective in some cases. The ill¬ ness is usually self-limiting, with no evidence of long-lasting effects. However, one dangerous strain causes bloody diarrhea, kidney failure, and death in extreme cases. Proper cooking of meat, washing of produce, and pasteurization of cider prevent infection from contaminated food sources.