post-traumatic stress disorder (PTSD), mental disorder that follows an occurrence of extreme psychological stress, such as that encountered in war or resulting from violence, childhood abuse, sexual abuse, or serious accident. The stressful event is usually followed by a period of emotional numbness and denial that can last for months or years. After that period, symptoms such as recurring nightmares, "flashbacks," short-term memory problems, insomnia, or heightened sensitivity to sudden noises may begin. In some cases outbursts of violent behavior have been observed. The usual treatment for PTSD is individual psychotherapy, including anxiety management, or group psychotherapy with others who have the disorder. Some antianxiety and antidepressant drugs are being studied for their effectiveness.

Certain traits (a history of depression, shyness, impulsivity) appear to heighten a person's risk of experiencing PTSD after a traumatic event. In those who do experience it, there is growing evidence that actual physical changes occur in the brain. The hippocampus, a structure that lies deep in the brain and that is associated with memory, has been found to be smaller in PTSD victims. It has been hypothesized that excesses of cortisol, a steroid hormone released during periods of extreme stress, may damage nerve fibers in the area or actually kill the nerve cells. However, the role of cortisol is not completely understood; studies of concentration camp survivors found abnormally low levels of cortisol rather than abnormally high levels.

Post-traumatic stress disorder was referred to as "shell shock" after World War I and as "battle fatigue" after World War II and was traditionally thought of as a condition of war veterans. Studies of Vietnam veterans and Nazi concentration camp survivors have added greatly to the knowledge of PTSD. The National Vietnam Veterans Readjustment Study (1988) estimated that 31% of the males and 27% of the females who served in the Vietnam War had symptoms of PTSD. Estimates of civilian populations put the rate of PTSD at 10% (women) and 5% (men) in the 15 to 54 age group. Childhood sexual abuse, sexual abuse, and assault are common causes of PTSD in both military and nonmilitary women. In 1989 the U.S. Congress created the National Center for Post-Traumatic Stress Disorder for the study and treatment of PTSD.

post-mortem examination or autopsy, systematic examination of a cadaver for study or for determining the cause of death. Post-mortems use many methodical procedures to determine the etiology and pathogenesis of diseases, for epidemologic purposes, for establishment of genetic causes, and for family counsel. Post-mortems may be performed at the request of the authorities in cases of unexplained and suspicious death or where death was not attended by a physician. In other circumstances post-mortem examination may be performed only with the consent of the deceased's family or with permission granted by the person himself before death. These examinations are more frequently being used for the acquiring of organs and tissues for transplantation. Valuable medical information can be learned from a post-mortem examination. Legionnaire's disease, for example, was discovered as a result of autopsies, and improved safety standards have resulted from the examination of the bodies of crash victims.

post office: see postal service.

parcel post, sending of packages through the mail service. At the congress of the Universal Postal Union in Paris in 1878, an international parcel-post system was established. The British parcel-post bill, passed in 1882, put into effect the following year domestic, colonial, and foreign services. Various other countries established such systems; the United States entered into conventions with other governments to convey parcels sent into the country but delayed instituting a domestic service until the Parcel Post Act of 1912. A water route for parcel post was started in 1917, and a fleet of trucks was put into operation in the East the next year. Parcel-post delivery on rural routes was established in 1919, making it possible for farmers to ship eggs and other produce direct to the consumer. Small animals that do not require food or water while in transit are accepted as parcel post. Extra fees provide for the special handling, insurance, and special delivery of parcels. In 1948 an air parcel-post service was established. Under treaty arrangements the United States is able to exchange parcel post with most countries of the world. Private freight companies (such as Federal Express and United Parcel Service) compete with the U.S. Postal Service for domestic and international delivery.

Post, Wiley, 1899-1935, American aviator, b. Grand Plain, Tex. He won fame in 1931 when he and Harold Gatty flew around the northern part of the earth in 8 days 15 hr 51 min. In 1933 he made a second flight alone. Post was killed with Will Rogers in an airplane crash near Point Barrow, Alaska.

Post, George Browne, 1837-1913, American architect, b. New York City, grad. New York Univ., 1858, in civil engineering, and studied architecture with R. M. Hunt. He was one of the leaders in a notable group that helped regenerate American architecture in the period from 1875 to 1890. A member of the National Commission of Fine Arts, he was a medalist and president (1876-99) of the American Institute of Architects. He designed, among other buildings, the Produce Exchange, the Stock Exchange, the buildings of the College of the City of New York, and the World building, all in New York City, and the Wisconsin state capitol.

Post, Emily Price, 1873-1960, American authority on etiquette, b. Baltimore. Born into a wealthy family, Post began her literary career as a novelist. Her best-known book, however, is Etiquette (1922), a practical guide to proper social behavior, written in a lively style. Etiquette gained wide popularity and sold over a million copies; the 12th and subsequent revised editions were edited by Post's granddaughter-in-law, Elizabeth L. Post. Emily Post broadcast on the radio after 1931 and produced a daily column on good taste that was syndicated in more than 200 newspapers. Also an authority on interior decoration, she wrote The Personality of a House (1930).

Hubbell Trading Post National Historic Site: see National Parks and Monuments (table).

Arkansas Post, community on the Arkansas River, SE Ark. Founded by the French in 1686 as a trading post, it is the oldest white settlement in the state; it became the capital of the Arkansas territory in 1819. Once an important port, Arkansas Post was a Confederate stronghold during the Civil War until it was captured by Union troops in 1863. Arkansas Post National Memorial is there (see National Parks and Monuments, table).

Psychological reaction occurring after a highly stressful event and typically characterized by flashbacks, recurrent nightmares, and avoidance of reminders of the event; depression and anxiety are often present. Traumatic events that can lead to PTSD include automobile accidents, rape or assault, military combat, torture, and such natural disasters as floods, fires, or earthquakes. Long-term effects can include marital and family problems, difficulties at work, and abuse of alcohol and other drugs. Antidepressant medication and psychotherapy, including group therapy, are used in treating the disorder.

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In building construction, a system in which two upright members, the posts, hold up a third member, the beam, laid horizontally across their top surfaces. In Britain it is called post-and-lintel system, but in the U.S. “lintel” is usually reserved for a short beam that spans a window or door opening. The post and beam formed the basis of architecture from prehistoric to Roman times, and is illustrated by such ancient structures as Stonehenge. All structural openings evolved from this system, which is seen in pure form only in colonnades and in framed structures, the posts of doors, windows, ceilings, and roofs usually being hidden in walls. The beam must bear loads that rest on it as well as its own load without deforming or breaking. Post-and-beam construction has largely been supplanted by the modern steel frame.

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