American CivilWar • Slavery
• Underground Railroad
Strawberry
Strawberries are red, heart-shaped fruits.
They are eaten fresh, often with cream.
They are also used as a filling for pastries,
pies, and cakes. Strawberries are
rich in vitamin C, and they also contain
iron and other minerals.
Strawberry plants grow in mild regions
all over the world. The United States
and Canada are leading producers of
strawberries. Many countries have developed
their own strawberry varieties to
suit their climate.
Strawberry plants grow close to the
ground. At the top of the plant is the
crown, from which the leaves sprout.
Harriet Beecher Stowe
Flowers and strawberries grow on a strawberry
plant.
BRITANNICA STUDENT ENCYCLOPEDIA Strawberry 195
The leaves have three hairy parts with
jagged edges. White flowers grow in
small groups on slender stalks. As the
plant gets older, the crown sends out
vines that spread over the ground.
Botanists (people who study plants) do
not consider strawberries to be true berries.
A true berry, such as a blueberry, is
a single fruit that forms from a single
flower. Strawberries are actually groups
of small fruits that form from a single
flower.
Strawberries need to be stored in a cool
and dry place after they have been
picked. But they still do not stay fresh
for very long. Some are frozen or canned
to make them last longer.
#More to explore
Berry • Fruit
Strep Throat
Strep throat is an infection of the throat
caused by bacteria (germs) called streptococci.
Anyone can get strep throat, but
the illness is most common in children.
People develop strep throat between two
and five days after coming into contact
with the bacteria. The illness usually
begins suddenly, with a fever. Other
symptoms, or signs, include a severe sore
throat, chills, and problems swallowing.
There also may be thick white or yellow
spots at the back of the throat.
Streptococci live in the nose and throat
of an infected person. Sneezing, coughing,
sharing dishes, and touching can
pass the bacteria to others.Washing
hands often may help to prevent the
spread of streptococci.
Doctors check for strep throat by swabbing
the back of the throat, or wiping it
with a special stick. The stick is then
tested for the presence of bacteria. Doctors
treat strep throat with medicines
called antibiotics, which kill bacteria. If
strep throat is not treated, it can lead to
scarlet fever or a more serious disease
called rheumatic fever.
#More to explore
Antibiotic • Bacteria • Scarlet Fever
Submarine
A submarine is a vessel, or ship, that can
go underwater. Submarines are called
subs for short. Militaries and scientists
use submarines to travel deep under the
ocean.
Militaries use submarines to patrol
ocean waters and to attack enemy ships
during wartime. Military submarines are
usually very large. They may carry more
A doctor checks a girl’s throat for signs of
strep throat.
196 Strep Throat BRITANNICA STUDENT ENCYCLOPEDIA
than 100 people. They have separate
rooms for working, eating, and sleeping.
They also carry such weapons as missiles
and torpedoes.
Scientific researchers and explorers usually
use smaller submarines. These submarines
may have mechanical arms,
cameras, and other tools to help scientists
study the underwater world.
Parts of a Submarine
A submarine has huge tanks, called ballast
tanks, that allow it to dive and to
surface. The tanks fill with water to give
the submarine the weight it needs to
sink. When the submarine is ready to
surface, the ballast tanks release the
water and fill with air. This lightens the
vessel enough for it to float.
For power, submarines use engines, batteries,
nuclear power sources, or a combination
of these. Propellers push
submarines through the water.
A submarine’s crew uses complex equipment
to find the way through deep, dark
oceans. To find enemy submarines or
other targets, submarines may use sonar.
Sonar equipment locates objects by
picking up sound waves. Other onboard
equipment provides clean air and fresh
water to the crew.
History
A Dutch inventor named Cornelis
Drebbel built the first working submarine
in 1620. It was a leather-covered
rowboat that could reach a depth of 15
feet (4.5 meters).
The U.S. inventor David Bushnell built
a submarine that he ran in 1776 during
the American Revolution. In 1800 the
famous U.S. inventor Robert Fulton
built the Nautilus. This was a small submarine
that could attach explosives to
ships.
A nuclear-powered U.S. submarine runs on
the surface of the water. The upright structure
on the submarine is called the conning
tower.
David Bushnell built a submarine for the
United States during the American Revolution
(1775–83). The operator ran it by turning
a crank that was attached to a propeller.
BRITANNICA STUDENT ENCYCLOPEDIA Submarine 197
Other inventors experimented with gas-,
steam-, and battery-powered submarines.
By the early 1900s submarines had
both a diesel engine (a type of internalcombustion
engine) and batterypowered
electric motors. The diesel
engine ran the submarine on the surface.
The electric motors ran it underwater.
Militaries used these diesel-electric submarines
