In early England, one man would challenge another to a duel by slapping his face with a glove. The challenge was a serious matter of honour, and if the slapped man did not accept it, he would be branded a coward. Having a chip on your shoulder was kind of an early Wild West equivalent of the glove slap, though generally less mortal in nature.
Boys and men would place a woodchip on their shoulder, challenging anyone who dared knock it off to a fistfight. So, if a man had a “chip on his shoulder,” he was clearly in an aggressive mood and spoiling for a fight.
Babies grow in their mother’s uterus, a special organ that houses the baby until it is born. At the start of pregnancy, a mother’s egg is fertilized, which makes a new cell. The cell divides quickly into many more cells. At about one week, this tiny mass, called an embryo, sticks to the wall of the uterus, and begins to grow. From the moment of conception, 46 chromosomes and tens of thousands of genes combine to determine a baby’s physical characteristics—the sex, facial features, body type, and color of hair, eyes, and skin. At the eighth week, the embryo is called a fetus.
By the end of the twelfth week, the fetus is completely formed and is able to make a fist, can turn his or her head, and can squint and frown. Until the baby is ready to come out, it grows inside its mother’s uterus. When the baby is ready to be born, at about 40 weeks, the mother starts to feel labor contractions. The uterus squeezes and pushes the baby out of the uterus and into the world.
Substance abuse means taking drugs (other than those prescribed by a doctor for a specific illness) in amounts that are dangerous or that prevent a person from doing everyday things, like going to school or work. The substance being abused can be alcohol, marijuana, pills called tranquilizers that make people feel very tired or relaxed, household products that are inhaled, or a number of other drugs.
Drug abuse happens all over the world, to all kinds of people, young and old. It frequently causes terrible damage to a person’s body, to relationships with family and friends, and to career or education. In some cases, substance abuse leads to death, because the abuser gets involved in an accident or because he or she overdoses, or takes enough of the substance to cause the body to completely shut down.
A popular summer-camp rhyme is “Leaves of three, let it be.” Poison ivy, the threeleaved plant that grows wild in all regions of the United States, is aggravating to the skin, though not lethal if swallowed unless you are very allergic. After brushing up against the poison ivy plant, a red rash usually develops.
Rubbing the rash will not spread poison ivy to other parts of the body (or to another person) unless urushiol oil—the sticky, resin-like substance that causes the rash—has been left on your hands. Other plants that usually irritate the skin upon contact include cowhage, poison oak, poison sumac, rengas tree, and trumpet vine.
Yes and no. Bones are hard connective tissue, made up of bone cells, fat cells, and blood vessels, as well as nonliving materials, including water and minerals. Some bones have a very hard, heavy outer layer made out of compact bone. Under this layer is a lighter layer called spongy bone, which is located inside the end, or head, of a long bone.
Spongy bone is tough and hard, but light, because it has lots of irregularly-shaped sheets and spikes of bone (called trabeculae) that make it porous (full of tiny holes). The soft, jelly-like inner core of bone is called the bone marrow. It is where red blood cells, certain white blood cells, and blood platelets are formed. The jawbone is the hardest bone in your body. Although bones are hard, they are not the hardest substance in the human body: the enamel on your teeth is harder.
A fruit is the part of the plant that nourishes and protects new seeds as they grow. The plant’s ovaries develop into fruit once the eggs inside have been fertilized by pollen. Some plants produce juicy fruit, such as peaches, pears, apples, lemons, and oranges.
Others produce dry fruit, such as nuts and pea pods. If an animal doesn’t eat the fruit, or a human doesn’t pick it off, it falls to the ground and decays and fertilizes the soil where a new seed will grow.
The femur, or thighbone, is the biggest bone in the body. The average femur is 18 inches (45.72 centimeters) long. The longest bone ever recorded was 29.9 inches (75.95 centimeters) long. It was from an 8-foot-tall (2.45 meters) German who died in 1902 in Belgium.
The stirrup (also called the stapes) in the middle ear is the smallest bone in the body. A tiny, U-shaped bone that passes vibrations from the stirrup to the cochlea, it weighs about 0.0004 ounces (0.011 grams) and can measure just one-tenth of an inch.
In the United States you are considered a grown-up when you reach the age of 18. You are no longer legally connected with your parents, and you are entitled to the rights—and expected to fulfill the duties—of an adult American citizen. (You may vote and be called for military service, for instance.)
There is a good chance, though, that when you are 18 your body has not yet reached full maturity. Many people continue to grow for a few more years. Most are fully grown—at least in height—by the time they are 20 years old, though boys may keep on growing until they are 23.
An allergic reaction is a reaction to a substance that is normally harmless to most other people. Allergies happen when a person’s immune system overreacts to a normally harmless substance that the person has breathed in, touched, or eaten. Allergens— the antigens that bring on an allergic reaction—may be foods, medications, plants or animals, chemicals, dust, or molds. Some common allergic reactions are hay fever, allergic conjunctivitis (an eye reaction); asthma, pet-dander allergies, and skin reactions, such as hives.
A common cause for allergies are dust mites, a large part of household dust. If they are breathed in by an allergic person, the body parts of the dead mites can trigger asthma, a lung condition that causes a person to have difficulty breathing. Cat and dog dander, or skin flakes, can cause an allergic reaction, such as sneezing, wheezing, and running eyes and nose. Common food allergy triggers are the proteins in cow’s milk, eggs, peanuts, wheat, soy, fish, shellfish, and tree nuts.
1. We should never put anything in or near our eyes, unless we have a reason to use eye drops. We would only do that if our doctor or parent told us to use them.
2. If the lens in our eye doesn’t work quite right, we can get glasses to help us see. Glasses have lenses in them that work with our eye’s own lens to help us see better.
3. Just behind the pupil is a lens. It is round and flat. It is thicker toward the middle.
4. Over the front of our eye is a clear covering called the “conjunctiva.”
5. Blinking helps to wash tears over our eyeballs. That keeps them clean and moist. Also, if something is about to hit our eye, we will blink automatically.
6. Some people start to sneeze if they are exposed to sunlight or have a light shined into their eye.
7. The highest recorded speed of a sneeze is 165 km per hour.
8. Our eyes have many parts. The black part on the front of our eye is called the “pupil.” It is really a little hole that opens into the back part of our eyes.
9. Our body has some natural protection for our eyes. Our eyelashes help to keep dirt out of our eyes. Our eyebrows are made to keep sweat from running into our eyes.
10. The most common injury caused by cosmetics is to the eye by a mascara wand.
11. It is impossible to sneeze with your eyes open.
12. Around the pupil is a colored muscle called the “iris.” Our eyes may be BLUE, BROWN, GREEN, GRAY OR BLACK, because that is the color of the iris.
13. Our eyes are very important to us, and we must protect them. We don’t want dirt, sand, splinters or even fingers to get in our eyes.
14. The reason why your nose gets runny when you are crying is because the tears from the eyes drain into the nose.
15. The space between your eyebrows is called the Glabella.
16. The white part of our eye is called the “sclera.” At the front, the sclera becomes clear and is called the “cornea.”
17. We don’t want our eyes to get scratched or poked. That could damage our sight!
18. Babies’ eyes do not produce tears until the baby is approximately six to eight weeks old.
19. Inside our eye, at the back, is a part called the “retina.” On the retina are cells called “rods” and “cones.” These rods and cones help us to see colors and light.
20. Your eyes blinks over 10,000,000 times a year!
21. The study of the iris of the eye is called iridology.
22. The shark cornea has been used in eye surgery, since its cornea is similar to a human cornea.
23. The number one cause of blindness in adults in the United States is diabetes.
24. The eyeball of a human weighs approximately 28 grams.
25. The eye of a human can distinguish 500 shades of the gray.
26. The cornea is the only living tissue in the human body that does not contain any blood vessels.
27. The conjunctiva is a membrane that covers the human eye.
28. Sailors once thought that wearing a gold earring would improve their eyesight.
29. Research has indicated that a tie that is on too tight cam increase the risk of glaucoma in men.
30. People generally read 25% slower from a computer screen compared to paper.
31. Men are able to read fine print better than women can.
32. In the United States, approximately 25,000 eye injuries occur that result in the person becoming totally blind.
33. All babies are colour blind when they are born.
34. A human eyeball weighs an ounce.