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river, 485 mi (781 km) long, rising in E Miss. and flowing S to Lake Borgne, an inlet of the Gulf of Mexico; its lower section (116 mi/187 km) forms the Miss.-La. boundary. Above Jackson, Miss., the Pearl's largest city, is Ross Barnett Reservoir, one of the state's chief water-storage areas.


Chin. Zhujiang, river, 110 mi (177 km) long, S Guangdong prov., S China. Formed at Guangzhou by the confluence of the Xi and Bei rivers, it flows E then S past Guangzhou and Huangpu island to form a large estuary between Hong Kong and Macau. The river links Guangzhou to Hong Kong and the South China Sea and is one of China's most important waterways and one of the centers of its world trade. It is vitally important to the special economic zones that lie along its estuary, which is crossed by the Hong Kong–Zhuhai–Macau Bridge (opened 2018), the main section of which consists of a 14.2 mi (22.9 km) bridge and 4.2 mi (6.7 km) tunnel. The estuary, which also has been known as the Boca Tigris, is kept open for ocean vessels by dredging.


hard, rounded secretion formed inside the shell of certain mollusks, used as a gem. It is secreted by the epithelial cells of the mantle, a curtain of tissue between the shell and body mass, and is deposited in successive layers around an irritating object—usually a parasite in the case of natural pearls—that gets caught in the soft tissue of the mollusk. The pearl is built up of layers of aragonite or calcite (crystalline forms of calcium carbonate) held together by conchiolin (a horny organic substance); its composition is identical to that of the mother-of-pearlmother-of-pearl
or nacre
, the iridescent substance that forms the lining of the shells of some fresh-water and some salt-water mollusks. Like the pearl it is a secretion of the mantle, composed of alternate layers of calcium carbonate and conchiolin.
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, or nacre, that forms the interior layer of the mollusk shell.

Pearls may be rice-shaped, round, pear-shaped, button-shaped, or irregular (baroque) and are valued in that order. Pearls found attached to the inner surface of the shell are known as blister pearls. The best pearls are usually white, sometimes with a creamy or pinkish tinge, but may be tinted with yellow, green, blue, brown, or black. Black pearls, because of their rarity, are often highly valued. The unique luster, or orient, of pearls depends upon the reflection and refraction of light from the translucent layers and is finer in proportion as the layers are thinner and more numerous. The iridescence which some pearls display is caused by the overlapping of successive layers, which breaks up light falling on the surface. Pearls are not cut or polished like other gems. They are very soft and are injured by acids and heat; as organic products, they are subject to decay.

Commercially valuable pearls are obtained from pearl oysters (especially of the genus Pinctada) and from freshwater pearl mussels (especially of the genus Hyriopsis). The largest natural pearl center is the Persian Gulf, which is said to produce the finest saltwater pearls. Other important sources are the coasts of India, China, Japan, Australia, the Sulu Archipelago, various Pacific islands, Venezuela, and Central America, and the rivers of Europe and North America. In ancient times the Red Sea was an important source.

Nearly all of the world's supply of cultured saltwater pearls is produced by the Japanese, who have perfected the techniques of saltwater pearl cultivation. These pearls are commonly produced by placing a small mother-of-pearl bead enclosed in a piece of mantle tissue in the body of the oyster. The oysters are then placed in cages that are suspended into sheltered bays for the period of time (up to 4 years) required for pearl formation.

Freshwater pearl cultivation is dominated by the Chinese. To produce freshwater pearls, a small piece of mantle tissue from one mussel is placed into a second mussel; shell beads and small seed pearls are also used. The quantity of freshwater pearls produced far exceeds that of saltwater pearls, and freshwater pearls are also significantly cheaper. Although many freshwater pearls are irregular oblong "rice pearls," round and near-round pearls are also produced. Inferior Chinese pearls are crushed and used in cosmetics and medicines.


See N. Landman et al., Pearls (2001).

The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.

What does it mean when you dream about a pearl?

The pearl is sometimes associated with the feminine principle, lunar forces, intuition, and water (all of which are identified with the unconscious). Mother of pearl lining the shell of the abalone suggests a fetus emerging to life. Alternatively, pearls in a dream may symbolize “pearls of wisdom” regarding a new idea or venture or a warning not to “cast your pearls before swine” by compromising oneself or one’s values.

The Dream Encyclopedia, Second Edition © 2009 Visible Ink Press®. All rights reserved.


A dense, more or less round, white or light-colored concretion having various degrees of luster formed within or beneath the mantle of various mollusks by deposition of thin concentric layers of nacre about a foreign particle.
Rounded masses of concentrically arranged squamous epithelial cells, seen in some carcinomas.
Mucous casts of the bronchi or bronchioles found in the sputum of asthmatic persons.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


June. [Am. Gem Symbolism: Kunz, 319–320]


emblem of discreet shyness. [Gem Symbolism: Kunz, 69]
See: Modesty
Allusions—Cultural, Literary, Biblical, and Historical: A Thematic Dictionary. Copyright 2008 The Gale Group, Inc. All rights reserved.


2. a pale greyish-white colour, often with a bluish tinge
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005


(language, mathematics)
A language for constructive mathematics developed by Constable at Cornell University in the 1980s.


(language, real-time)


(language, education)
One of five pedagogical languages based on Markov algorithms, used in "Nonpareil, a Machine Level Machine Independent Language for the Study of Semantics", B. Higman, ULICS Intl Report No ICSI 170, U London (1968). Compare Brilliant, Diamond, Nonpareil, Ruby.


A multilevel language developed by Brian Randell ca 1970 and mentioned in "Machine Oriented Higher Level Languages", W. van der Poel, N-H 1974.


(language, tool, history)
An obsolete term for Larry Wall's PERL programming language, which never fell into common usage other than in typographical errors. The missing 'a' remains as an atrophied remnant in the expansion "Practical Extraction and Report Language".

["Programming Perl", Larry Wall and Randal L. Schwartz, O'Reilly & Associates, Inc. Sebastopol, CA. ISBN 0-93715-64-1].
This article is provided by FOLDOC - Free Online Dictionary of Computing (


(Practical Extraction Report Language) A programming language written by Larry Wall that combines syntax from several Unix utilities and languages. Introduced in 1987, Perl is designed to handle a variety of system administrator functions and provides comprehensive string handling functions. It is widely used to write Web server programs for such tasks as automatically updating user accounts and newsgroup postings, processing removal requests, synchronizing databases and generating reports. Perl has also been adapted to non-Unix platforms. See mod_perl and LWP. See also PURL.
Copyright © 1981-2019 by The Computer Language Company Inc. All Rights reserved. THIS DEFINITION IS FOR PERSONAL USE ONLY. All other reproduction is strictly prohibited without permission from the publisher.
References in periodicals archive ?
CLINICAL PEARL: The iron level should be compared to the total RBC count and the hemoglobin, hematocrit, TIBC and percentage saturation and the serum ferritin for most thorough iron-indices investigations.
Clinical pearl. If a patient is not comfortable consenting to a rectal exam, a lubricated Q-tip can be used to palpate the vagina to minimize patient discomfort.
The "clinical pearls" for dialysis hypotension are given for each level of the case.
Interspersed throughout are personal asides, clinical pearls, and lengthy tutorials on basic science topics, such as DNA replication and gene splicing.
"Our goal is to make it easier for readers to quickly obtain clinical pearls and practice management insights from articles and put them into use," the company said.
This was one of several clinical pearls he shared about how to effectively manage patients taking opioids and other medications with drug abuse liability.
Haynes shares the fruits of his wide experience, and he has distilled a great deal of complex and rapidly changing information into clinical pearls that we can all put to immediate use.
He uses the style of his lecture material with many boxes of clinical pearls or key points, boldface type, and ECG diagrams.
An entirely different view of the world is seen by clinicians who move knowledge horizontally: journal articles, consultation among providers, the latest treatments, clinical pearls, what diagnostic tests and therapeutic treatments work and which don't.
Clinical pearls on the drugs that cause dementia, drugs intended to "cure it
OCTOBER 6-7: WANP ANNUAL CONFERENCE "Clinical Pearls in Daily Practice" in Lynnwood, Washington (near Seattle).
For each they include basics, diagnosis, treatment, ongoing care, and clinical pearls. More detailed areas include epidemiology, etiology and pathophysiology, commonly associated conditions, physical exam, diagnostic tests and interpretation, medication, diet, patient education, complications, and code.

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