Lyell was largely responsible for the general acceptance of the concept of uniformitarianism in geology.
Lyly \'li-le\, John (b. 1554?, Kent,
Eng.—d. November 1606, London) English writer. Educated at Oxford, Lyly gained fame in London with two prose romances, Euphues (1578) and Euphues and His England (1580). The novels inspired euphuism, an elegant, extravagant Elizabethan literary style, and made Lyly the first English prose stylist to leave an enduring impression on the language. As a dramatist he also contributed to the development of prose dialogue in English comedy, a genre to which he devoted himself almost exclusively after 1580. Endimion (performed 1588) is considered his finest play.
Lyme disease Tick-borne bacterial disease. It was identified in 1975 and named for Old Lyme, Conn. It is caused by a spirochete, Borrelia burgdorferi, transmitted by ticks, which pick it up in the blood of infected animals, mostly deer. Humans can be bitten by ticks in tall grass or fallen leaves. Lyme disease has three stages: a target-shaped rash, often with flulike symptoms; migrating arthritic pain and neurological symptoms (disturbances to memory, vision, or locomotion); and crippling arthritis with symptoms like those of multiple sclerosis and sometimes with facial paralysis, meningitis, or memory loss. Most cases do not progress beyond the first stage, but those that do reach the third stage within two years. Prevention involves avoiding tick bites. Diagnosis can be difficult, espe¬ cially if the initial rash is not noticed. Early antibiotic treatment can pre¬ vent progression. Advanced cases need more powerful antibiotics, and symptoms may recur.
lymph Pale fluid that bathes tissues, maintaining fluid balance and removing bacteria. It enters the blood system at a vein under the collar¬ bone that it reaches via channels and ducts, being driven through them mainly by surrounding muscle activity. The lymphatic organs (spleen and thymus) and lymph nodes filter out bacteria and other particles the lymph takes up from body tissues. Lymph contains lymphocytes and macrophages, the primary cells of the immune system. See also lymphatic system.
lymph node Small, rounded mass of lymphoid tissue contained in con¬ nective tissue. They occur all along lymphatic vessels, with clusters in cer¬ tain areas (e.g., neck, groin, armpits). They filter bacteria and other foreign materials out of lymph and expose them to lymphocytes and macrophages that can engulf them; these cells multiply in response to accumulation of such materials, which is why lymph nodes swell during infections. The nodes also produce lymphocytes and antibodies, to be carried by lymph throughout the lymphatic system. In Hodgkin disease and other lymphomas, malignant lymph cells proliferate, causing lymph node enlargement. Other cancers often invade lymphatic vessels, which can carry cells from the
tumour to lymph nodes, where they are trapped and grow into secondary tumours. Lymph nodes are therefore removed in cancer surgery to detect or prevent tumour spread.
lymphatic system System of lymph nodes, vessels, and nodules and lym¬ phoid tissue, including the thymus, spleen, tonsils, and bone marrow, through which lymph circulates and is filtered. Its primary function is to return pro¬ teins, waste products, and fluids to the blood; molecules too big to enter the capillaries pass through the more permeable walls of lymphatic vessels. Valves keep lymph flowing in one direction, more slowly than blood and at a lower pressure. The lymphatic system also has a role in the immune system. Nodes filter bacteria and foreign matter from lymph. Smaller nodules, which often produce lymphocytes, form in areas more exposed to such mate¬ rials. They can merge and become permanent, as in the tonsils. Blockage of a lymph vessel may cause fluid to collect in the tissues, producing lymphe¬ dema (tissue swelling). Other lymphatic system disorders include lympho¬ cytic LEUKEMIAS and LYMPHOMA. See also RETICULOENDOTHELIAL SYSTEM.
lymphocyte Type of leukocyte fundamental to the immune system, regu¬ lating and participating in acquired immunity. Each has receptor mol¬ ecules on its surface that bind to a specific antigen. The two primary types, B cells and T cells, originate from stem cells in bone aaarrow and travel to lymphoid tissues. When a B cell binds to an antigen, it multiplies to form a clone of identical cells.
Some of these, acted on by helper T cells, differentiate into plasma cells that produce antibodies against the antigen. Others (memory cells) mul¬ tiply, providing long-term immunity to the antigen.
lymphoid tissue Cells, tissues, and organs composing the immune sys¬ tem, including the bone aaarrow, thymus, spleen, and lymph nodes. The most highly organized components are the thymus and lymph nodes, and the least organized are the cells that wander in the loose connective-tissue spaces under membranes lining most body systems, where they can estab¬ lish lymph nodules (local lymphocyte production centre) in response to antigens. The most common lymphoid tissue cell is the lymphocyte. Oth¬ ers are macrophages, which engulf foreign materials and probably alter them to initiate the immune response, and reticular cells, which produce and maintain thin networks of fibres as a framework for most lymphoid organs. See also immunity; lymphatic system.
lymphoma \lim-'fo-m9\ Any of a group of malignant diseases (see cancer) that usually start in the lymph nodes or lymphoid tissues. The two major types, Hodgkin disease and non-Hodgkin lymphoma, each have sev¬ eral subtypes. Diagnosis of either type requires biopsy, usually from the lymph nodes. Non-Hodgkin lymphomas may be diffuse (widespread) or nodular (concentrated in nodules); nodular lymphomas generally develop more slowly.
Lynch, David (b. Jan. 20, 1946, Missoula, Mont., U.S.) U.S. director. Trained as an artist, he studied in Europe and began experimenting with film in the late 1960s. In 1977 he made his first feature, Eraserhead, a grotesque and nightmarish film that became a cult favourite. He directed the critically acclaimed The Elephant Man (1980), the science-fiction Dune (1984), and the bizarre mystery Blue Velvet (1986). He was noted for his disturbing and dark view of life. His later films include Wild at Heart (1990, Golden Palm), Lost Highway (1997), The Straight Story (1999), and Mulholland Drive (2001). He also created the offbeat televi¬ sion series Twin Peaks (1990-91).
lynching Execution of a presumed offender by a mob without trial, under the pretense of administering justice. It sometimes involves tortur¬ ing the victim and mutilating the body. Lynching has often occurred under unsettled social conditions. The term derives from the name of Charles Lynch, a Virginian who headed an irregular court to persecute loyalists during the American Revolution. In the United States, lynching was widely used in the post-Reconstruction South against blacks, often to intimidate other blacks from exercising their civil rights.
Lynd Vlind\, Robert (Stoughton); and Lynd, Helen orig. Helen Merrell (respectively b. Sept. 26, 1892, New Albany, Ind., U.S.—d. Nov.
Charles Lyell, detail of a replica in oil by Lowes Cato Dickinson, 1883; in the National Portrait Gallery, London.
Human lymphocyte (phase-contrast microphotograph).
MANFRED KAGE-PETER ARNOLD
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1, 1970, Warren, Conn.; b. March 17, 1894, La Grange, Ill., U.S.—d. Jan. 30, 1982, Warren, Ohio) U.S. sociologists. The Lynds taught for several decades at Columbia University and Sarah Lawrence College, respectively. In their collaboration on the studies Middletown (1929) and Middletown in Transition (1937), classics of sociological literature as well as popular suc¬ cesses, they became the first scholars to apply the methods of cultural anthropology to the study of a modern Western city (Muncie, Ind.).