AIDS is a serious disease. The name
stands for acquired immunodeficiency
syndrome. Millions of people have died
from AIDS since the 1980s. Scientists
have not yet found a cure, but they can
treat the disease effectively.
Causes
Tiny particles called viruses cause many
diseases. The particular virus that causes
AIDS is called human immunodeficiency
virus (HIV). HIV enters the body
through contact with infected blood or
other body fluids. Coughing, sneezing,
and handshaking do not spread the
virus.
HIV kills helper T cells in the body.
Helper T cells are a type of white blood
Some farmers use special irrigation systems
to water their crops.
The AIDS Memorial Quilt is displayed in
Washington, D.C. The quilt honors people
who have died of the disease.
BRITANNICA STUDENT ENCYCLOPEDIA AIDS 49
cell. They are part of the bodys immune
system, which fights off disease. The
body loses its ability to fight off disease
when its helper T cells die.
Symptoms
A new HIV infection often causes symptoms,
or signs, that are similar to those
of influenza (flu). They usually last only
a week or two. After they clear up, an
infected person may show no signs of
illness for years. However, such a person
can still pass the virus to other people.
Because of their weak immune systems,
most HIV-infected people eventually
come down with other infections. A
person who has these infections is said
to have AIDS.
The most common infections include
tuberculosis and a certain type of
pneumonia. People with AIDS also
frequently develop a cancer called Kaposi
sarcoma. The AIDS virus may also attack
the nervous system and cause brain and
eye damage. Death often follows.
Prevention and Treatment
People can prevent HIV infection. The
main way to do this is to keep out of
contact with possibly infected blood or
body fluids.
If a person is infected, certain drugs can
stop HIV from doing damage. Drug
treatment has added years to the lives of
many people with HIV infections.
#More to explore
Disease, Human Immune System
Virus
Ailey, Alvin
Alvin Ailey was a famous modern
dancer. He was also a highly respected
choreographera person who creates
dances and directs dancers. His dance
company toured around the world,
bringing recognition to African Americans
in dance.
Ailey was born in Rogers, Texas, on
January 5, 1931. His family moved to
Los Angeles when he was 12. Ailey
began to study modern dance at the
Lester Horton Dance Theater in 1949.
He became the companys director and
choreographer in 1953.
In 1954 Ailey moved to New York City,
where he studied with modern dance
pioneer Martha Graham and others. He
created the Alvin Ailey American Dance
Theater in 1958. The troupe performed
many kinds of works, but Ailey particularly
wanted to bring African American
culture to modern dance.
Members of the Alvin Ailey American
Dance Theater rehearse a scene from the
dance called Revelations.
AIDS exists
everywhere in
the world.
However, the
disease is a
particularly
big problem in
parts of
Africa.
50 Ailey, Alvin BRITANNICA STUDENT ENCYCLOPEDIA
In 1958 Ailey achieved his first big success
as a choreographer with Blues Suite.
One of his most famous dances is Revelations
(1960), which is set to African
American spirituals. His works combine
ballet and modern dance.
In 1965 Ailey retired from dancing, but
he continued choreographing. He died
in New York City on December 1,
1989. His company remained in operation
after his death.
#More to explore
Dance Graham, Martha
Air
All living things need air to breathe.
Animals and plants would die without
it. Air also holds airplanes and kites
above the ground, and it is used to
inflate tires and balloons. Air surrounds
Earth as the atmosphere. Air has no
color, taste, or odor. Although air is
invisible, people can hear air when the
wind howls. And they can feel air brush
against their skin when the wind blows.
Air consists of a mixture of gases. These
gases consist of tiny particles called molecules.
They are so small that they cannot
be seen. Molecules are combinations
of different chemical elements. In air the
most common of these elements are
nitrogen and oxygen. Oxygen is an
important component of air because
humans and other animals need it to
survive. In addition to nitrogen and
oxygen, air consists of small amounts of
the gases argon, neon, helium, and
methane. Besides gases, air also contains
water vapor, dust, pollen, and bacteria.
The water vapor in air is the source of
rain and snow.
The oxygen in air comes from plants.
Through a process called respiration, or
breathing, humans and other animals
take in oxygen and force out carbon
dioxide. Carbon dioxide is a molecule
made of oxygen and carbon. Plants take
in the carbon dioxide and use it to make
food. This is part of the process known
as photosynthesis. Plants break down
the molecule, use the carbon, and then
release the oxygen into the air. In this
way the carbon dioxide and oxygen in
the air are constantly used and replaced.
#More to explore
Atmosphere Molecule Photosynthesis
Air Force
An air force is the part of a countrys
military that conducts warfare in the
skies. Its pilots fly airplanes and other
aircraft armed with weapons. They use
these aircraft to attack enemy aircraft as
A kite takes flight on a windy day.
BRITANNICA STUDENT ENCYCLOPEDIA Air Force 51
well as targets on the ground and in the
water, mostly during wars.
An air force is usually one of several
branches of a countrys military. In the
United States the other major branches
are the Army and the Navy (which
includes the Marine Corps).
Basic Functions and Aircraft
Most air forces perform a variety of military
functions, or jobs. During wars an
air force uses aircraft to observe the
enemys activities. It also gathers information
about possible battlefields and
targets.
Another basic job of an air force is to
gain control of the air over a particular
area. To do this, it uses aircraft called
fighters to drive away or destroy enemy
aircraft. Fighters are jet airplanes
designed to fly very fast. They can also
change direction quickly. Fighters carry
missiles, machine guns, or other weapons
on board.
An air force also uses aircraft to drop
bombs. It often uses large aircraft called
bombers to bomb targets in an enemys
country. It uses attack aircraft to help its
countrys troops fighting on the ground.
Pilots fly attack aircraft close to the
ground while bombing or shooting at
enemy troops below. Attack aircraft are
smaller and lighter than bombers.
Another duty of an air force is to move
troops and military supplies from place
to place. It normally uses helicopters or
large transport planes to do this.
History
Inventors created the first successful
airplanes in the early 1900s. Several
European countries used fighter aircraft
and bombers duringWorldWar I, from
1914 to 1918. Air warfare was a major
part ofWorldWar II in the 1940s.
Air forces have used many new inventions
to improve their aircraft and weapons