preemption \pre-'emp-sh3n\ U.S. policy that allowed the first settlers, or squatters, on public land to buy the land they had improved. Since improved land, coveted by speculators, was often priced too high for
squatters to buy at auction, temporary preemptive laws allowed them to acquire it without bidding. The Pre-Emption Act (1841) gave squatters the right to buy 160 acres at $1.25 per acre before the land was auctioned. The Homestead Act (1862) made preemption an accepted part of U.S. land policy. See also Homestead Movement.
prefabrication Assembly of standardized building components at a location other than the building site. Units may include doors, stairs, win¬ dow walls, wall panels, floor panels, roof trusses, room-sized components, and even entire buildings. Prefabrication requires the cooperation of archi¬ tects, suppliers, and builders regarding the size of basic modular units. In the U.S. building industry, the 4-by-8-ft (1.2-by-2.4-m) panel is a stan¬ dard unit; the architect’s drafted building plans and the supplier’s pre¬ fabricated wall units are based on multiples of that module. Advantages of prefabrication include the cost savings of mass production, the oppor¬ tunity to use specialized equipment to produce components, and stan¬ dardization of parts for quick assembly and erection. The major drawback is in assigning responsibility for quality control. See also precast concrete.
prefect In ancient Rome, any of various high officials with primarily judicial and administrative responsibilities. In the early republic, a prefect of the city (praefectus urbi ) took over the consul’s duties during their absence from Rome. The office lost some importance after the introduc¬ tion of praetors (mid 4th century bc). Augustus revitalized the office when he appointed five prefects to supervise the city government, the fire bri¬ gade, the grain supply, and the Praetorian Guard. The praetorian prefects acquired great power and often became virtual prime ministers.
pregnancy Process of human gestation that takes place in the female’s body as a fetus develops, from fertilization to birth (see parturition). It begins when a viable sperm from the male and egg from the ovary merge in the fallopian tube (see fertility; fertilization). The fertilized egg (zygote) grows by cell division as it moves toward the uterus, where it implants in the lining and grows into an embryo and then a fetus. A placenta and umbilical cord develop for nutrient and waste exchange between the cir¬ culations of mother and fetus. A protective fluid-filled amniotic sac encloses and cushions the fetus. Early in pregnancy, higher estrogen and progesterone levels halt menstruation, cause nausea, often with vomiting (morning sickness), and enlarge the breasts and prepare them for lacta¬ tion. As the fetus grows, so does the uterus, displacing other organs. Nor¬ mal weight gain in pregnancy is 20-25 lbs (9-11.5 kg). The fetus’s nutritional needs require the mother to take in more calories and espe¬ cially protein, water, calcium, and iron. Folic-acid supplements are rec¬ ommended during early pregnancy to prevent neural tube defects. Smoking, alcohol, and many legal and illegal drugs can cause congenital disorders and should be avoided during pregnancy. Ultrasound imaging is often used to monitor structural and functional progress of the growing fetus. The due date is estimated as 280 days from the time of last menstruation; 90% of babies are born within two weeks of the estimated date. See also amniocentesis; preeciampsia and eclampsia; premature birth. See illustration on opposite page.
prehistoric religion Religious practices and beliefs of prehistoric peoples, as inferred from archaeological findings. The oldest burials that attest to a belief in life after death date from 50,000-30,000 bc. Corpses were buried with goods such as stone tools and parts of animals, sug¬ gesting an attempt to placate the dead or equip them for the next world. The Middle Paleolithic Period provides the first evidence of animal sacri¬ fices, which may have been offerings to the dead, to a higher power, or to the fertility of the animal species. Prehistoric human sacrifices have also been found, usually of women and children. From the Bronze Age on, weapons and jewelry were often thrown into springs, wells, and other bodies of water as sacrifices (probably of war booty). Animals such as bears were important in prehistoric religion from the Upper Paleolithic Period on, probably seen as guardian spirits and associated with magical powers. Fertility rites were also practiced, as evidenced by small, corpu¬ lent female figures, known as Venus statuettes, with highly emphasized breasts and buttocks.
prelude Musical composition, usually brief, generally played as an introduction to another piece. The prelude originated as short pieces that were improvised by an organist to establish the key of a following piece or to fill brief interludes in a church service. Their improvisatory origins were often reflected in rhythmic freedom and virtuosic runs. A section in this style would often lead to a closing fugal section; in time this turned into a separate movement, and preludes came to be paired with fugues.
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premature birth ► prerogative court I 1543
chorionic villi
decidua
basalis
placenta
intervillus space
umbilical
arteries
umbilical cord
chorion amnion
uterus
amniotic cavity
mucus plug
Full-term fetus in the uterus. The amnion, formed from the inner embryonic mem¬ brane, encloses the fetus. The space between the amnion and fetus (amniotic cavity) is filled with the watery amniotic fluid. The outermost embryonic membrane, the chorion, has developed fingerlike projections (villi) on its outer surface, which have enlarged and penetrated the decidua basalis layer of the uterus. The chorionic villi and the decidua basalis form the placenta. Maternal blood fills the spaces around the villi (intervillous spaces); oxygen and nutrients diffuse into the villi and pass on to the fetus via the umbilical vein. Waste materials that leave the fetus via the umbilical arteries diffuse out of the villi into the mother's blood.
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In the 17th century, preludes began to be frequently written for lute or harpsichord. In later years the term came to be used for short piano pieces, often in sets, by composers such as Frederic Chopin, Aleksandr Scriabin, and Claude Debussy.
premature birth Birth less than 37 weeks after conception. Infants bom as early as 23-24 weeks may survive but many face lifelong dis¬ abilities (e.g., cerebral palsy, blindness, deafness). Premature infants account for 8-9% of live births but two-thirds of infant deaths. 40-50% of cases have no explanation; other cases can be attributed to such causes as maternal hypertension or diabetes, multiple pregnancy, or placental separation. With good care, about 85% of live-born premature infants should survive. Infants born very early (before 32-34 weeks) lack fully developed lungs and often develop respiratory distress syndrome. They also have problems maintaining body temperature and fighting infection. Most deaths result from breathing problems, infections, and brain or lung hem¬ orrhages. Premature infants are characterized by low birth weight, small size, irregular breathing, absence of subcutaneous fat, and thin skin.
premenstrual syndrome (PMS) Variable group of symptoms occurring before menstruation in 40% of women, severe in about 10% of those. Physical symptoms may include headache, cramps, bloating, and constipation or diarrhea. Emotional symptoms range from irritability, leth¬ argy, and mood swings to hostility, confusion, and depression. Theories as to the cause centre on hormones, nutrition, and stress (known to affect severity). Depending on the symptoms, treatment may involve exercise, stress management, nutritional therapy, or drugs. Dietary measures include low sodium and high protein and complex carbohydrate intake and avoid¬ ance of xanthines (including caffeine). Increasing calcium intake has been shown to prevent or reduce cramps, which are best treated with ibuprofen.