sleep Natural periodic suspension of consciousness during which the powers of the body are restored. Humans normally sleep at night, whereas nocturnal species sleep during the day. The average human sleep require¬ ment is about 7.5 hours. Sleep is divided into two main types, REM (rapid-eye-movement) and NREM (non-REM); each recurs cyclically several times during a normal period of sleep. REM sleep is character¬ ized by increased neuronal activity of the forebrain and midbrain, by depressed muscle tone, and by dreaming (see dream), rapid eye move¬ ments, and vascular congestion of the sex organs. NREM sleep is divided into four stages, the last of which is the deep, restorative, quiet sleep commonly associated with “a good night’s rest.” See also insomnia, nar¬ colepsy.
sleeping sickness Protozoal disease transmitted by the bite of the tsetse fly. Two forms, caused by different species of the genus Trypanosoma, occur in separate regions in Africa. The parasite enters the bloodstream and invades the lymph nodes and spleen, which become swollen, soft, and tender. Irregular fever and delayed pain sensation develop. In the Rhode¬ sian form, the patient soon dies of massive toxemia. The Gambian type progresses to brain and spinal cord invasion, causing severe headache, mental and physical fatigue, spastic or flaccid paralysis, chorea, and pro¬ found sleepiness, followed over two or three years by emaciation, coma, and death. Some patients develop a tolerance but still carry the trypano¬ somes. The earlier drug treatment begins, the greater the chance of recov¬ ery. Sleeping sickness is still prevalent in parts of Africa despite efforts to control it.
Slidell \sli-'del\, John (b. 1793, New York, N.Y., U.S.—d. July 29, 1871, London, Eng.) U.S. and Confederate diplomat. He practiced law in New Orleans from 1819, then served in the U.S. House of Representa¬ tives (1843—45) and Senate (1853-61). In the American Civil War he joined the Confederate foreign service. En route to France to seek sup¬ port for the Confederacy, he and James Murray Mason were seized from the British steamer Trent by a Union vessel (see Trent Affair).
Slim, William (Joseph), 1st Viscount Slim (of Yarralumla and Bishopston) (b. Aug. 6, 1891, Bristol, Gloucestershire, Eng.—d. Dec. 14, 1970, London) British general. He served with the British army in World War I and with the Indian army from 1920. In World War II he commanded Indian troops in East Africa and the Middle East (1940—41). As commander of the 1st Burma Corps (1942), he led a 900-mi (1,450- km) retreat from superior Japanese forces in Burma to India. In 1944 he led forces to repel a Japanese invasion of northern India; in 1945 he retook Burma from the Japanese. Promoted to field marshal (1948), he served as chief of the Imperial General Staff (1948-52) and later as governor- general of Australia (1953-60).
slime mold Any of about 500 species of primitive organisms that con¬ tain true nuclei and resemble both protists and fungi (see fungus). Origi¬ nally grouped within the kingdom Fungi, some classification systems consider slime molds to be in the kingdom Protista. They typically thrive in dark, cool, moist conditions such as on forest floors. Bacteria, yeast, molds, and fungi provide the main source of slime-mold nutrition. The complex life cycle of slime molds, exhibiting complete alternation of generations, may clarify the early evolution of both plant and animal cells. In the presence of water a tiny spore releases a mass of cytoplasm called a swarm cell, which later develops into an amoebalike creeping cell called a myxamoeba. Both swarm cells and myxamoebas can fuse in sexual union; the resulting fertilized cell, or plasmodium, grows through nuclear division and forms a spore case, which, when it dries, disintegrates and releases spores to begin the cycle again.
slippery elm or red elm Large-leaved elm (Ulmus rubra or U.fulva ) of eastern North America that has hard wood and fragrant inner bark. A gluelike substance in the inner bark has long been steeped in water as a remedy for throat ailments, powdered for use in poultices, and chewed as a thirst quencher, among other uses. It has received renewed attention in recent years as part of alternative medicine’s herbal pharmacopoeia, pre¬ scribed for a wide variety of ailments.
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slipware ► Slovakia I 1767
slipware Pottery that has been treated with semiliquid clay, or slip. The technique was originally used to cover defects in body colour, but later evolved into decorative tech¬ niques such as sgraffito, carving, painting, trailing, marbling, and inlay. In sgraffito a pattern is incised through the slip to reveal the differ¬ ent body colour underneath. The Staffordshire potters in 17th-century Britain were famous for the decora¬ tive figures, flowers, and patterns they created by using dotted and trailed slip.
Sloan, Alfred P(ritchard), Jr.
(b. May 23, 1875, New Haven,
Conn., U.S.—d. Feb. 17, 1966, New York, N.Y.) U.S. corporate execu¬ tive. He began his career at the Hyatt Roller Bearing Co. in New Jersey and became its president at age 26.
Hyatt was later acquired by General Motors Corp. (GM), and Sloan rose to become president and chief executive officer of GM in 1923. Under his leadership it surpassed Ford Motor Co. in sales and became the largest corporation in the world. He served as chairman of the board from 1937 to his retirement in 1956. A noted philanthropist, he endowed the Alfred P. Sloan Foundation and contributed to the Sloan-Kettering Cancer Cen¬ ter in New York and to the school of management at the Massachusetts Institute of Technology.
Sloan, John (French) (b. Aug. 2, 1871, Lock Haven, Pa., U.S.—d. Sept. 7, 1951, Hanover, N.H.) U.S. artist. He worked as a commercial newspaper artist in Philadelphia, where he studied with Robert Henri. He followed Henri to New York City, where in 1908 with six others they exhibited as The Eight. Sloan’s realistic urban paintings gave rise to the epithet Ash Can school. Works such as Sunday, Women Drying Their Hair (1912) and Backyards, Greenwich Village (1914) are sympathetic por¬ trayals of working men and women; occasionally he evoked a mood of romantic melancholy.
Slocum, Joshua (b. Feb. 20, 1844, Wilmot, Nova Scotia, Can.— disappeared 1909/10, at sea) Canadian seaman and adventurer. He worked his way up from ship’s cook to captain of a trading vessel by 1869. Wrecked with his family on the Brazilian coast in 1886, he built a canoe from the wreckage and paddled back to New York. He set sail from Bos¬ ton in 1895 in a 36-ft, 9-in. (11.2-m) fishing boat. In three years, two months, and two days, he sailed 46,000 mi (74,000 km) in a circuitous route ending in Newport, R.I, becoming the first man in recorded history to sail around the world singlehandedly. He wrote several books, includ¬ ing the classic Sailing Alone Around the World. In 1909 he set sail for Grand Cayman from New England and was lost at sea.
Slonimsky, Nicolas (b. April 27, 1894, St. Petersburg, Russia—d. Dec. 25, 1995, Los Angeles, Calif., U.S.) Russian-bom U.S. musicolo¬ gist, conductor, and composer. He left the Soviet Union after studies at the St. Petersburg Conservatory and settled in the U.S. in 1923. In the 1930s he conducted premieres of works by Charles Ives, Edgard Varese, and others. In Music Since 1900 (1937) he chronicled the century’s musi¬ cal life day by day. His Lexicon of Musical Invective (1952) collected wrongheaded musical criticism. His Thesaurus of Scales and Melodic Patterns (1947) was an inspiration to numerous composers. He edited four editions of Baker’s Dictionary of Music and Musicians (1958-92). His commodious scholarship was undertaken with zest and humour, and near the end of his long life he was lionized by Frank Zappa and other musi¬ cians.
slope Numerical measure of a line’s inclination relative to the horizontal. In analytic geometry, the slope of any line, ray, or line segment is the ratio of the vertical to the horizontal distance between any two points on it (“slope equals rise over run”). In differential calculus, the slope of a line tan¬ gent to the graph of a function is given by that function’s derivative and rep¬ resents the instantaneous rate of change of the function with respect to change in the independent variable. In the graph of a position function (rep¬ resenting the distance traveled by an object plotted against elapsed time), the slope of a tangent line represents the object’s instantaneous velocity.