medical school at New York University
and became a doctor in 1939.
Salk began studying vaccines in 1942.
By the 1950s he had developed a
vaccine against polio. He tested the
polio vaccine on large numbers of
people, including himself and his own
family. The vaccine worked. In 1955
the U.S. government agreed that Salk’s
vaccine was safe. Millions of children
soon received the vaccine. Salk’s success
made him a hero. He received the
Presidential Medal of Freedom and
other awards.
Salk died in La Jolla, California, on June
23, 1995. Today polio has been nearly
wiped out in the United States and
Dr. Jonas Salk vaccinates a girl against
polio in 1953.
BRITANNICA STUDENT ENCYCLOPEDIA Salk, Jonas 21
many other countries. However, it still
occurs in places where children have not
received the vaccine.
#More to explore
Polio • Vaccine
Salmon
Salmon are fish that are known for making
long, difficult journeys in order to
breed. Salmon belong to the scientific
family Salmonidae, which also includes
trout.
There is one species, or type, of Atlantic
salmon. There are six species of Pacific
salmon: coho, chum, king, pink, sockeye,
and cherry.
Where Salmon Live
The Atlantic salmon lives mainly in the
North Atlantic Ocean. It breeds in the
rivers of North America and Europe.
Pacific salmon are found in the waters of
the North Pacific. They breed in rivers
near both the North American and
Asian coasts.
Physical Features
Salmon come in a range of sizes. The
Atlantic salmon weighs about 12 pounds
(5.5 kilograms). The pink salmon usually
weighs 3 to 6 pounds (1.4 to 2.7
kilograms). The king salmon may weigh
25 pounds (11 kilograms) or more.
While in the ocean, salmon have a silver
color and spots on their back and fins.
During the breeding season, they
undergo changes in color that vary by
species.
Life Cycle
After being born in freshwater, salmon
travel to the ocean. They live there for
one to three years. Then they travel back
to where they hatched in order to breed.
For some salmon, this can mean a trip of
more than 2,000 miles (3,200 kilometers).
Salmon may leap over waterfalls
and cut through churning rapids to
reach their home waters again.
Once in freshwater, salmon stop eating
and live off their body fat. The males
fight for a mate. After a male and a
female are paired, the female digs a pit
and lays thousands of eggs. Most Pacific
salmon die shortly after mating. Many
Atlantic salmon, however, return to the
sea and may breed again.
#More to explore
Fish • Trout
Salmon make difficult journeys,
including leaping up waterfalls,
to reach the place where they
mate and produce offspring.
22 Salmon BRITANNICA STUDENT ENCYCLOPEDIA
Salt Lake City
Population
(2000 census),
city, 181,743;
(2007 estimate)
180,651
Salt Lake City is the capital of the U.S.
state of Utah. It is the world headquarters
of the Church of Jesus Christ of
Latter-day Saints, or the Mormons. The
church strongly influences the city’s
political, social, and economic life.
Salt Lake City lies in a valley at the foot
of theWasatch Range of the Rocky
Mountains. Several ski areas are located
nearby. Salt Lake City hosted the 2002
Winter Olympics.
Many people in Salt Lake City work for
the government or in health care, trade,
tourism, or other service industries. Factories
in the city make computers, software,
and other high-technology
products.
Mormon pioneers founded Salt Lake
City. In 1847 a church leader named
Brigham Young led a group of
Mormons westward from Illinois. They
were looking for a place where they
would be free to practice their religion.
They settled in a valley near the Great
Salt Lake. The Mormons turned the
bare land into a beautiful, well-planned
city.
In 1856 Salt Lake City became the capital
of the Utah Territory. Utah became a
U.S. state in 1896. Salt Lake City was
the state capital.
..More to explore
Mormon • Rocky Mountains • Utah
A view of Salt Lake City, Utah, includes the state Capitol (left) and the Wasatch Range.
BRITANNICA STUDENT ENCYCLOPEDIA Salt Lake City 23
Samoa
Samoa is a small island country in the
southern Pacific Ocean. Samoa’s capital
and largest town is Apia, on the northern
coast of Upolu Island.
Samoa is in Polynesia, which is part of
the region called Oceania. There are two
main islands, Upolu and Savai’i, and
seven smaller islands. Six islands east of
Samoa are controlled by the United
States. They are called American Samoa.
The islands of Samoa are rocky and
mountainous. They are surrounded by
coral reefs. The weather is hot and
humid all year.
Rain forests cover much of Samoa. The
wildlife includes bats, lizards, snakes,
scorpions, centipedes, and many birds.
Polynesians make up almost all of the
country’s people. These people and their
language are called Samoan. Many
people also speak English. Christianity is
the main religion.
Tourism, fishing, and farming are
important parts of Samoa’s economy.
Farmers grow coconuts, bananas, pineapples,
mangoes, and taro.
Polynesians settled in Samoa in about
1000 BC. Europeans first arrived in the
1700s. In 1899 the United States and
Germany divided the islands between
themselves. The United States took the
