Eyelashes protect our eyes. They help keep small particles and dust out of our eyes, especially when the wind is blowing. Eyelashes are also super-sensitive, and they alert the eyelids to shut when something touches them. If you rub your finger against your eyelashes, you will find that your eyelid automatically shuts.
But be careful not to rub too hard—if you lose a lash it will take about four to eight weeks to grow back! Fortunately, your upper eyelid has between 100 and 150 lashes.
The brain is the body’s command center; everything we do—eating, talking, walking, thinking, remembering, sleeping—is controlled and processed by the brain. As the most complex organ in the human body, the brain tells us what’s going on outside our bodies (whether we are cold or hot, for instance, or whether the person we see coming toward us is a friend or a stranger) as well as what’s going on inside our bodies (whether we have an infection or a broken bone, or whether we feel happy or sad).
The key to the body’s nervous system, the brain contains between 10 billion and 100 billion nerve cells, or neurons. Neurons combine to form the body’s nerves, thin cords that spread from head to toe and all parts in between. Neurons take in and send out electrical signals, called impulses, that control or respond to everything your body does and feels. The brain is like a very busy, high-speed post office, constantly receiving messages and sending them out all the time; it handles millions of nerve impulses every second.
Seven astronauts were aboard Challenger flight STS-51L when it exploded during liftoff on January 28, 1986. Christa McAuliffe was a Concord, New Hampshire, high school social studies teacher. She and the other six crew members were killed when a solid-fuel booster rocket leak led to a massive fuel tank explosion during liftoff from its launch pad.
NASA’s next flight was Discovery, which was launched on September 28, 1988. After the Challenger disaster, NASA’s three remaining shuttles— Atlantis, Discovery, and Columbia—were rebuilt, each with more than 250 modifications improving safety and performance.
Euclid’s Elements is a series of 13 geometry and mathematics books written by the Greek mathematician Euclid in Alexandria about 300 B.C.E. It is a collection of definitions, postulates (axioms), theorems, and mathematical proofs of the propositions. The 13 books cover Euclidean geometry and the ancient Greek version of elementary number theory. Along with the Greek mathematician Autolycus’s On the Moving Sphere, the Elements is one of the oldest Greek mathematical treatises to have survived, and is the world’s oldest continuously used math textbook.
Historians do not know a lot about Euclid’s life, but his work has proven important to the development of logic and modern science. Most of the theorems in the Elements were not discovered by Euclid himself, but were the work of earlier Greek mathematicians such as Pythagoras, Hippocrates of Chios, Theaetetus of Athens, and Eudoxus of Cnidos. However, Euclid is credited with arranging these theorems in a logical manner.
Unlike the fragrant blossoms that attract bees, carrion flowers simulate the odor of a rotting animal carcass and attract carrion beetles and different types of flies, including blowflies, flesh flies, and midges. The stapelia flower, which is shaped like a starfish and grows in Africa, has fine hairs around its petals, perhaps to imitate the appearance of a small dead animal. When the bloom opens it gives off a rotting smell, imitating dead animal meat.
The smell attracts flies, which collect pollen before they fly away. Some carrion flowers, such as the European and Brazilian Dutchman’s pipe, lure insects into dark openings that lead to the foul-smelling interior where they become trapped. When the flower “releases” the insect, it is coated with fresh pollen to be taken to a different plant. The lantern stinkhorn, a fungus that releases a feces-like odor, attracts green bottle flies to spread its spores.
Animal specialists believe that cats purr to show contentment. Cats are born with the ability to purr; kittens make tiny rumbling sounds when they are nursing. Scientists think that purring starts out as a form of communication between a mother cat and her kittens. The purr lets the mother cat know that her babies are happy and feeding well, and she may purr back in response. Later, cats continue to purr when they are in a contented mood or as a friendly greeting. But scientists aren’t really sure how cats purr. Many think that it comes from the vibration of blood in a large vein in the cat’s chest, caused when surrounding muscles repeatedly squeeze and release the blood vessel.
Air in a cat’s lungs and windpipe increase the sound of the vibrations that can be heard (although sometimes the purring is silent and can only be felt). Other scientists think that cats purr when membranes called false vocal chords, located in a cat’s throat near the real ones, start to vibrate.
Sometime during the sixteenth century, British farmers moved from sleeping on the ground to sleeping in beds. These beds were little more than straw-filled mattress tied to wooden frames with ropes.
To secure the mattress before sleeping, you pulled on the ropes to tighten them, and that’s when they began saying, “Goodnight, sleep tight.”
Known for its cold, desert-like conditions, Arctic tundra is located in the Northern Hemisphere, encircling the North Pole. The stark landscape is frozen for most of the year, and water is unavailable. Temperatures during the arctic winter can dip to –60 Fahrenheit (–51 Celsius).
In the summer the ground thaws for just a few weeks, and the region’s plants and animals—which include geese, sea birds, polar bears, caribou, and shrews—fight for survival. Because the tundra is not usually exposed to human activity it is most susceptible to change and damage from human use or pollution. Oil spills damage the plants, land, and animals that live along the coast.
Growing old is part of being a living thing. Every plant and animal must go through a cycle of life that involves a beginning, a middle, and an end. Actually, as soon as we are born we begin aging or growing older. But when we talk of growing old we think of the physical changes that occur when bodies cannot grow and repair themselves as they once did.
At about age 30 the signs of aging start to appear, though for most people the physical changes are not really obvious until many years later.
In 1865, Robert Lincoln rushed to his father’s deathbed. Sixteen years later, as Garfield’s secretary of war, he was with that president when he was shot by an assassin. In 1901, Robert arrived in Buffalo for the American Exposition just in time to see President McKinley murdered.
After that, Robert Lincoln vowed never again to be in the presence of an American president.