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Protococcus ► Proudhon I 1557
Protococcus \,pro-t3-'ka-k9s\ or Pleurococcus Genus of green algae. Popularly called moss though not actually classified as such, it is found as a thin, green covering on the moist, shaded side of trees, rocks, and soil. The spherical cells, either solitary or clumped together forming short false filaments, have heavy cell walls that protect them against excessive water loss. Each cell contains a large dense chloroplast. The position of Protococcus in classification systems is uncertain.
protocol In computer science, a set of rules or procedures for transmit¬ ting data between electronic devices, such as computers. In order for computers to exchange information, there must be a preexisting agree¬ ment as to how the information will be structured and how each side will send and receive it. Without a protocol, a transmitting computer, for example, could be sending its data in 8-bit packets while the receiving computer might expect the data in 16-bit packets. Protocols are estab¬ lished by international or industrywide organizations. Perhaps the most important computer protocol is OSI (Open Systems Interconnection), a set of guidelines for implementing networking communications between computers. The most important sets of Internet protocols are TCP/IP, HTTP, and FTP.
proton Stable subatomic particle (one of the baryons) with a unit of posi¬ tive electric charge and a mass 1,836 times that of the electron. Protons are found in the atomic nucleus along with neutrons. For every nucleus of a given element, the number of protons is always the same; this num¬ ber is the element’s atomic number. A single proton is the nucleus of an atom of ordinary hydrogen; as such, it is identical to the hydrogen ion (H + ). Protons have antimatter counterparts (antiprotons), with the same mass but a negative charge. Protons are used as projectiles in particle accelerators to produce and study nuclear reactions. They are the chief constituent of primary cosmic rays and are among the products of radio¬ active decay (see radioactivity) and nuclear reactions.
protozoal X.pro-ts-'zo-slV diseases Diseases caused by protozoans. These organisms may remain in the human host for their entire life cycle, but many carry out part of their reproductive cycle in insects or other hosts. For example, mosquitoes are vectors of Plasmodium, the cause of malaria. See also entamoeba; Giardia lamblia; sleeping sickness.
protozoan N.pro-ts-'zo-siA Any of a group of small (usually micro¬ scopic) single-celled protists. They are found in most soils, fresh water, and oceans. While most are solitary individuals, various colonial forms exist. The taxonomic relationships of protozoans to one another and to other protists continue to be revised. The smallest known protozoans are tiny blood parasites less than 2 microns long; the largest may be 16 mm long and visible to the naked eye. Protozoan shapes vary, but all share such eukaryotic features as lipid-protein membranes and membrane- enclosed vacuoles and organelles (see eukaryote). They show wide varia¬ tion in modes of movement, nutrition, and reproduction. Various classification systems exist to group the protozoans. The major phyla include Sarcomastigophora (flagellated forms and forms possessing cyto¬ plasmic extensions called pseudopodia), Ciliophora (ciliated forms), and Apicomplexa, Microspora, and Myxozoa (spore-producing forms). Api- complexa and Microspora are sometimes included in the single phylum Sporozoa. Commonly known protozoans include dinoflagellates, amoebas, and paramecia (see Paramecium). See illustration opposite.
protractor Instrument for constructing and measuring plane angles. The simplest protractor is a semicircular disk marked in degrees from 0° to 180°. A more complex protractor, for plotting position on navigation charts, is called a three-arm protractor, or station pointer, and consists of a circular scale connected to three arms. The centre arm is fixed, while the outer two can be rotated to any desired angle relative to the centre one. A related instrument is the course protractor, which allows naviga¬ tors to measure the angular distance between north and the course plot¬ ted on a navigation chart.
Proudhon \pru-'do n \, Pierre-Joseph (b. Jan. 15, 1809, Besangon, France—d. Jan. 19, 1865, Paris) French journalist and socialist. After working as a printer, he moved to Paris in 1838 and joined the socialist movement. His What Is Property? (1840) created a sensation with such phrases as “property is theft.” While working in Lyon (1843-48), he encountered the Mutualists, a weavers’ anarchist society whose name he later adopted for his form of anarchism. His System of Economic Contra¬ dictions (1846) was attacked by Karl Marx and initiated the split between anarchists and Marxists. In Paris in 1848, Proudhon published radical newspapers; imprisoned (1849-52), he was harassed by the police after
phylum Sarcomastigophora
subphylum Mastigophora
phylum
Ciliophora
cavity
undulating
membrane
-cilium
Tetrahymena
membranes
myoneme (contractile filament)
Vorticella
phylum
Apicomplexa
class Sporozoa
Representative protozoans. The zooflagellate Trypanosoma brucei is the causative agent of African sleeping sickness. The phytoflagellate Gonyaulax is one of the dinoflagellates responsible for the occurrence of red tides. The amoeba is one of the most common sarcodines. Other members of the subphylum Sarcodina, such as the radiolarians, heliozoans, and foraminiferans, usually possess protective coverings. The heliozoan Pinaciophora is shown covered with scales. The subphylum Cilio¬ phora, which includes the ciliated Tetrahymena and Vorticella, contains the greatest number of protozoan species but is the most homogeneous group. The malaria- causing Plasmodium is spread by the bite of a mosquito that injects infective spores (sporozoites) into the bloodstream.
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1558 I Proulx ► Prusiner
his release and fled to Belgium in 1858. On his return in 1862, he gained influence among the workers, including some of the founders of the First International.
Proulx \'prii\, (Edna) Annie (b. Aug. 22,1935, Norwich, Conn., U.S.) U.S. writer. She studied at the University of Vermont. She began profes¬ sional writing with commissioned nonfiction books on cooking, garden¬ ing, and country living. She founded and edited (1984-86) Behind the Times, a rural Vermont newspaper, and published stories in men’s out¬ door magazines. Her first novel, Postcards (1992), depicting the decline of the small farm, received the PEN/Faulkner Award. It was followed by The Shipping News (1993, Pulitzer Prize, National Book Award) and Accordion Crimes (1996). Her story collections Heart Songs (1988) and Close Range (1999) also won high praise.
Proust Vpriist\, Marcel (b. July 10, 1871, Auteuil, near Paris, France—d. Nov. 18, 1922, Paris)
French novelist. Bom to a wealthy family, he studied law and literature.
His social connections allowed him to become an observant habitue of the most exclusive drawing rooms of the nobility, and he wrote social pieces for Parisian journals. He pub¬ lished essays and stories, including the story collection Pleasures and Days (1896). He had suffered from asthma since childhood, and c. 1897 he began to disengage from social life as his health declined. Half- Jewish himself, he became a major supporter of Alfred Dreyfus in the affair that made French anti- Semitism into a national issue.
Deeply affected by his mother’s death in 1905, he withdrew further from society. An incident of invol¬ untary revival of childhood memory in 1909 led him to retire almost totally into an eccentric seclusion in his cork-lined bedroom to write A la recherche du temps perdu (1913-27; In Search of Lost Time, or Remembrance of Things Past). The vast seven- part novel is at once a kind of autobiography, a vast social panorama of France in the years just before and during World War I, and an immense meditation on love and jealousy and on art and its relation to reality. One of the supreme achievements in fiction of all time, it brought him world¬ wide fame and affected the entire climate of the 20th-century novel.