Your Body

More people get tooth decay, or cavities, than any other disease. Almost everyone in the world has a cavity sometime during his life. How, then, do you get cavities? After you eat, tiny bits of food are left in your teeth. Bacteria that live on your teeth cause these bits of food to form an … Read more

When you cut your finger, blood flows from tiny vessels in your skin. This blood helps wash out the dirt and germs that may be there from the object that did the cutting. However, the bleeding soon stops because the blood thickens, or clots. The clots keep out harmful bacteria and soon form a scab. … Read more

Headaches can start for any of hundreds of reasons. A headache is not a sickness or a disease itself; rather it is a symptom that indicates a possible sickness or disease somewhere in your body. Severe headaches can be the beginning of pneumonia or infections of the ears, nose, or throat. Others, less severe, can … Read more

You know what is going on in the world through your senses: sight, smell, taste, touch, and hearing. But some people believe that there is another way for people to know things. That way is called ESP, or extrasensory perception. It means “outside the senses.” Scientists studying the effects on a person of happenings that … Read more

The places in your body where two or more bones are joined together are called joints. Some joints are fixed, they do not move, and some joints are movable. Fixed joints are found where one bone lies against another, sometimes with a thin layer of tissue separating them. Joints like these do not move at … Read more

Just as most people are right-handed or left-handed, they are also either right-eyed or left-eyed. That means that one eye is dominant, or stronger than the other. Actually, when you look at an object with both eyes open, your brain sees only the image picked up by your dominant eye. To determine whether you are … Read more

Yes, but it is nothing to be alarmed about. A blind spot is simply a point at which you might hold a small object and cannot see it. This happens because there is one point on your retina where the optic nerve leaves your eye, just below the center of the back of your eye, … Read more

Your eyes blink, or close the eyelids rapidly, for any of several reasons. It might be to protect themselves from an irritating substance or to protect themselves against a bright light or to keep themselves clean. Every time you blink your eyes, you are really crying, or producing tears. Under your upper eyelids are tear … Read more

You may have heard someone say, “I bumped my head so hard, I saw stars!” What he thought were stars was really a flash of bright light, a trick played on him by the optic nerve, which goes from all parts of the eye to the brain. A hard bump on the head stimulates the … Read more

A camera has a diaphragm, an opening that gets bigger or smaller to let in the right amount of light for a clear picture. In your eye, the iris does the same thing. The iris is a thin layer of tissue at the front of your eyeball. A camera has a lens that focuses the … Read more

If you can’t see clearly without glasses, you might need them. Or when you get to be about 45 and your eyes lose some of their ability to focus, you might need glasses then. There are three common eye problems that require glasses: nearsightedness, farsightedness, and astigmatism. Nearsighted people see things clearly only if these … Read more

Absolutely not! Touching the skin of a toad has nothing whatsoever to do with the cause of warts. The belief that it does is just a superstitious old tale. In reality, these growths on the surface of the skin are infections caused by tiny germs called viruses. These viruses live in cells on the outer … Read more

A person whose body cannot produce pigment, or coloring matter, in its organs is called an albino. Albinism is most easily recognized in the skin, hair, and eyes. True albinos have very pale white skin, white hair, and pink eyes. An albino’s eyes show up as pink because the tiny red blood vessels in the … Read more

You sweat, or perspire, to cool off the extra heat your body makes. If you could not sweat, your temperature would be so high that it could kill you. Your body lets this heat escape through your skin by sweating. Your sweat glands, all 2,000,000 of them, are spread out all over the surface of … Read more

The same pigment, or melanin, which determines your skin color causes freckles, but in a slightly different way. When you are out in the sun for a long time, your skin makes more melanin than when you are indoors. Sometimes your skin may turn an even brown. But other times, if the melanin is grouped … Read more

When you were first born, your skin was too big for your tiny body. It took six months before your skin really “fit.” Then, your skin became stretchable, like a rubber band. When you grow much older, the muscles in your skin will become weak, and your skin will lose some of its stretch. It … Read more

The tiny oil glands below the surface of your skin are constantly producing small amounts of oil to keep your skin soft and flexible. These glands have tiny openings, or pores, on the surface of your skin to permit this oil to escape. Sometimes, however, these pores become clogged with wastes from skin cells and … Read more

Goose pimples are little bumps that appear on your skin when you are frightened or cold. At the center of each bump is a hair in a tiny tube. This tube goes inside your skin. Near the bottom of the tube is a tiny muscle which tightens up and pushes against the tube if you … Read more

There is no such thing as anyone having skin as white as snow, as black as night, or as yellow as a canary. All skin, no matter what color it is, has an outer layer called the epidermis. The epidermis contains pigments, or coloring matter, which are responsible for the color of your skin. The … Read more

Wouldn’t you look strange walking around with your insides showing? Your skin is your body’s covering, but because it has a more important function than just covering your body, your skin is considered an organ of your body, the largest organ, at that! The most important function of your skin is to keep your body … Read more

If you look down at the tips of your fingers and toes, you will see patterns of circles and swirls on the ridges of your skin. No other person in the world, living or dead, has exactly the same pattern as you, nor will anyone yet to be born. Even though your body grows and … Read more

People who cannot tell all colors apart are said to be color blind. Most color-blind people can see yellows and blues, but confuse reds with greens. It is very rare for a person to be blind to all colors, but those who are see everything in shades of black, white, and gray. It is interesting … Read more

Of all the blind people in the world, only about 5% were born blind; the other 95% became blind as a result of diseases or injuries to the eyes or the brain. Although there are about 14 million people in the world who are called “blind,” there are actually many degrees of blindness. Those who … Read more

The terms midget and dwarf both refer to any adult human being, animal, or plant that is considerably smaller than the ordinary size of its species. Midgets usually have normal body proportions even though they are small, but dwarfs have abnormal body proportions in the spine or in the arms and legs. Dwarfism is usually … Read more

Besides your sense of sight, there is another sense that tells you what position your body is in. That sense is called your muscle sense. Suppose, for example, you wanted to climb a tree. Your eyes would tell you how high up the first branch is, but then your muscle sense takes over and decides … Read more

You are made aware of the world around you by your senses. At one time, it was believed that human beings had only five senses: sight, hearing, touch, smell, and taste. But modern scientists have added to the list the senses of hunger, pain, and thirst. All your senses are divided into two groups, external … Read more

You can’t hold your breath for more than a few minutes, because when you stop breathing, you begin to store up a gas called carbon dioxide, which your body cells produce as a waste product. Since your breathing is controlled by the respiratory center in your brain, an increase of carbon dioxide in your blood … Read more

You have to breathe in order to stay alive. When you breathe in, or inhale, you draw air, which contains a gas called oxygen, into your lungs. You cannot live without oxygen, for oxygen changes the food you have eaten into energy. Your body uses this energy to keep you warm, to make new cells, … Read more

You breathe in oxygen from the air. There is oxygen in water too, but the human body cannot take this oxygen from the water. If you tried to take a breath underwater, your lungs would quickly fill up with water and you wouldn’t be able to breathe. Fish and other sea creatures, however, can breathe … Read more

All body cells need air, or oxygen, to perform their different functions. Without oxygen, these functions would stop completely. Throughout your life you breathe in oxygen continuously and automatically without saying, “I will breathe,” or “I won’t breathe.” Once this oxygen reaches your lungs, it enters small air sacs called alveoli through the alveoli’s very … Read more

Although onions taste really delicious on hamburgers or in a stew, the person cutting and cooking them usually sheds a great many tears first. This happens because onions contain a strong smelling oil. When the onion is peeled and cut, this oil escapes into the air in the form of vapor, or tiny particles of … Read more

When you are asleep and relaxed, and breathing through your mouth rather than through your nose, the air coming out causes your soft palate, the tissue at the back and top of your mouth, to flutter back and forth. This fluttering, or vibration, makes a sound called a snore. Often this vibration causes the cheeks, … Read more

Your sense of smell is very closely related to your sense of taste. To see how this works, think of a chocolate ice cream cone at your lips. You taste the sweetness of the chocolate with the taste buds at the tip of your tongue. But the smell of the chocolate is a job for … Read more

The inside of your nose is like a chemical laboratory for smelling. It has the power to smell even extremely small amounts of an odor. Odors are actually tiny particles, or molecules, of gas that travel through the air and into your nose. In the highest part of your nose, these molecules touch a group … Read more

Because your tongue is made up of muscles which you can control, it helps you chew and swallow your food. These muscles run in many directions so you can move the front part of your tongue in many different ways. Your tongue can push food between your teeth, move it about from side to side, … Read more

Look in the mirror and stick out your tongue. See the little bumps on the surface of it? Inside each of these little bumps, or papillae, are about a dozen tiny organs called taste buds. There are also taste buds in three places in your throat. Not all tastes are detected by the same taste … Read more

Your brain contains memory centers where millions of old memories are stored away in an orderly manner according to subjects: music you have heard, sights you have seen and tastes and smells you have experienced. Because of this orderly arrangement, it is possible for one section of a person’s brain to be damaged or destroyed … Read more

It is not the size of the brain that makes one person brilliant and another backward, for most adults have the same size brain about three pounds. Rather, it is the way the brain develops. Your brain stores information from your past experiences, helping you to remember, learn, and think. But people differ in how … Read more

A computer is a complicated electronic or mechanical machine invented by man to solve difficult problems. But a computer can only carry out instructions that the human brain gives it. The computer has no ability to think or reason for itself. However, it could take a man a lifetime to solve some of the problems … Read more

When you are lightly touched on any part of your body, nerve cells inside your skin respond to that touch and send a message to your brain. Your brain can receive that message in two different ways. If it receives a “tickle message” and decides that the tickle should be scratched, it will send a … Read more

Valentine hearts come in all sizes, but a real heart, the one inside the human body, doesn’t look anything like them. Make a fist with your hand. That’s about the size and shape of your heart. Your heart is not very large, but it is very important, for it keeps you alive by pumping blood … Read more

Anyone who has ever hurt his “funny bone” knows that there is nothing funny about this bone at all. In fact, this “bone” is not really a bone at all; it is actually a nerve located at the back of your elbow above your bone and near the surface of your skin. When you hit … Read more

When you are breathing normally, your diaphragm, a large, powerful muscle in your chest, tightens and relaxes to pull in the air and push it out. However, when organs near your diaphragm become irritated, they cause the diaphragm to contract suddenly in a kind of spasm as it takes in a breath of air. At … Read more

In some cases, yes. The Indians of the Andes Mountains, on the west coast of South America, have developed bodies which are different from ours in order to survive where they live. At 17,000 feet above sea level, where these Indians live, we would find it very hard to breathe, but they do not. The … Read more

There were two special chromosomes in you when you were just beginning life as a fertilized egg. These are called sex chromosomes. Scientist have named them the X chromosome and Y chromosome. A woman’s egg cell contains only an X chromosome, while a man’s sperm cell Y contains either an X or a Y. If … Read more

Every parent, human, animal, or plant, passes down certain characteristics to their children so that these offspring will resemble them, but not be exactly like them. This passing down of characteristics is called heredity. When you began life as an egg produced by your mother and fertilized by your father, you came with a pre-packaged … Read more

Girls reach their full height when they are about 18 years old, but boys keep growing taller for a few more years. There are two periods in your life when you grow very rapidly. The first period began right after you were born and lasted until you were about six months old. The second period … Read more

When you eat, your food is broken down and sent to the cells of your body. These cells take in the food and grow bigger. Then each cell divides and becomes two cells exactly like itself. Each cell divides again, making four cells, and so on. This cell division goes on day and night. As … Read more

About nine months before you were born, you started to grow from just two cells. One cell, a sperm cell, came from your father. The other cell, an egg cell, came from your mother. These two cells joined together inside your mother’s body and formed a new cell called a fertilized egg. This cell was … Read more

When you feel hot or cold, you are actually feeling the temperature of your blood. Since you are considered a warm-blooded animal (along with birds and other mammals), your body maintains an average temperature of 98.6° Fahrenheit (37.0° Celsius), no matter what the temperature is around you. Each species of warm-blooded animals has its own … Read more

Everyone’s blood isn’t exactly the same, but this important fact was not known to scientists until 1900. Before then, blood transfusions were given from person to person without any thought to blood types. When it was discovered that in about half the cases, the patient got worse after a transfusion, and sometimes even died, scientists … Read more

When you cut yourself, blood flows out of the wound. That blood contains, in addition to red blood cells and white blood cells, tiny structures called platelets. These platelets pile up around the wound, then combine with other substances in the blood plasma (liquid) and chemicals in the damaged tissue to form long sticky threads … Read more

Your blood has special cells in it that fight disease and infections. These cells, called white blood cells, are produced in your bone marrow, the, soft tissue that fills the inside of your bones. White blood cells work like an army to attack and kill harmful germs that get into your body. When an infection … Read more

Blood looks as if it is solid red, but it really is not. If you look at blood under a microscope, you will see that it is made up of four different parts: plasma, red blood cells, white blood cells, and platelets. The plasma, which is the actual fluid, is a yellowish-white liquid. It contains … Read more

Your heart is a kind of pump which sends blood to all parts of your body, since none of your cells can work or grow without it. Blood has three main functions: it carries food and oxygen to permit your body’s cells to work and grow; it carries wastes from these cells to organs which … Read more

The amount of blood in a person’s body depends on how big he or she is, and surprisingly enough, on where that person lives. For example, if you weigh about 80 pounds, you have about 2.5 quarts of blood in your body, while your 160-pound father has about five quarts, or twice as much. When … Read more

The billions of cells whose job it is to keep your body informed of conditions outside and inside it are called nerve cells, or neurons. Neurons transmit messages throughout the body by passing signals, or impulses, from one to the other. Sensory neurons are nerve cells which carry impulses from the eyes, ears, nose, mouth, … Read more

All living things on earth, plants or animals, have one thing in common they are all made up of cells. Your entire body, your bones, your muscles, your skin, your blood, your teeth, your nerves, your hair, contains more than 10 million million (10,000,000,000,000) cells! Most of these cells are so tiny that you can … Read more