Karen Hill

If you were born in the United States in the year 1900 and you were a male, you could probably expect to live only to the age of 46. A female born at the same time could expect to live slightly longer until the age of 49. But if you were born in the 1970s, … Read more

All human beings have reactions, or feelings, to situations or to their own thoughts. These reactions are called emotions. Emotions can be positive ones that make a person happy, love, happiness, pleasure, and pride. But emotions can also be negative ones that make a person unhappy, anger, fear, sadness, hate, disappointment, and pain. Many doctors … Read more

Most people have fears of some sort, at some times in their lives. That is natural. But people who have a fear that stays with them constantly, or keeps coming back over and over again, are said to have a phobia. Phobias can be fears of certain places, certain situations, or certain objects. Examples of … Read more

A newborn baby responds to noise by an automatic action, a reflex action. His eyes are open, but during his first month of life he can see only light and dark. By the second month, he can follow an object with his eyes. As the nerves between his eyes and brain develop, the baby begins … Read more

Most everyone is able to speak normally without realizing just what a complicated procedure it really is and what amazing coordination is required by your larynx, cheeks, tongue, and lips to get the words out. It is when this coordination is not working properly that a person stutters or stammers. In one form of stuttering, … Read more

The kind of voice you have depends on the size and position of your vocal chords. Vocal chords can be long or short, stretched or relaxed. Boys and girls have the same short, stretched vocal chords during their early years, and so have similar high-pitched voices. As a boy grows older and reaches his teens, … Read more

If you put your fingers on your throat and say a word, you will get a “buzzing” feeling, or vibration, on your fingers. These vibrations come from the voice box, or larynx, inside your throat. Your larynx is a box-shaped organ between the back of your tongue and trachea, or wind pipe. As you breathe, … Read more

Deafness and hard-of-hearing are not the same thing. Deafness means a total or near-total loss of hearing, along with an inability to understand speech. A person can be born deaf, or be born with normal hearing and become deaf because of an accident or illness. People who lose some ability to hear during their life … Read more

Sound waves are movements, or vibrations, in the air made by sounds. When these sound waves enter the canal of your outer ear, they hit your ear N drum, a thin, tough sheet of tissue stretched tightly along the canal that separates your outer ear from your middle ear. As the sound waves hit, the … Read more

If you know the functions of tools such as scissors, forks, nutcrackers, and grinders, you will understand how marvelously specialized your teeth are. Although your 20 primary, or baby, teeth first appeared when you were about six months old, your permanent teeth (32) started to grow out when you were about six or seven years … Read more

Actually calories have nothing to do with food! They are really measurements of heat energy your body needs. The food you take into your body can be considered a “fuel,” much like car runs on fuel. The breaking down of the food in the body tissues is a form burning that fuel and giving off … Read more

The cells of your body use the food you eat to do three important jobs: provide energy, make new cells, and repair cells that wear out. The carbohydrates, fats, proteins, vitamins, and minerals in the food you eat are broken down into tiny particles, or molecules, which are the materials your body needs to perform … Read more

As soon as food enters your mouth, it begins a long trip through your body. This trip is called digestion. At each stop along the way, parts of your body receive the food and each performs its specialized job before sending the food on to its next stop in the digestion trip. First, your teeth … Read more

You usually have your meals at the same time each day. Your stomach becomes accustomed to this schedule and produces its acids and enzymes with a churning activity according to that schedule. With no food going into your stomach to absorb these juices produced by the peristaltic waves, it “talks,” or “gurgles,” or “rumbles.”

Hunger begins when substances like glucose (sugar), vitamins, minerals, and amino acids are missing from your blood. Nerves in your body send a message to the hunger center in your brain telling it of the shortage. The hunger center then reacts by making the stomach and intestines more active.

When you eat, food from your mouth goes down a tube called the esophagus and into your stomach, where it is stored temporarily, then later digested. As the food arrives, the stomach wall starts its glands working. One type of gland gives off a mucus that lubricates the food. Other glands give off acids which … Read more

The human body contains about 50 quarts of water. But this body fluid is not pure water. It is actually a salt solution. Why is this so? According to one scientific theory, all land animals, including man, are descendants of organisms that once lived in the sea and arose from it. The body fluid of … Read more

A human being can live without food for more than a month, but no one can stay alive for more than a week without water! All living things need water for their bodies to function. When you take in food, water helps to dissolve it and, along with certain chemicals in your body, it turns … Read more

Your spinal cord, or spinal column, a column of bones that runs from your brain all the way down your back. Not only do these bones, or vertebrae, support you body, but they also house nerve cells which carry messages on their way to and from your brain. These vertebrae are held in place by … Read more

A “Charley Horse” is not a person or an animal. It is a thing, a cramp in your arms or legs. If you have ever exercised too much and hours later felt that you couldn’t move without your muscles aching, you’ve gat a “Charley Horse.” A “Charley Horse” is actually a strain or soreness in … Read more

If you didn’t have muscles, you wouldn’t be able to move. A muscle is a bundle of tissue cells that tighten up and get shorter when they are at work. This tightening up of a muscle is what makes a part of you move. When that part of you stops moving, the muscle relaxes and … Read more

There is a “sleep center” in your brain which regulates the sleeping and waking of your body. When this sleep center goes to work, it does two things: it blocks off part of your brain so that it goes to sleep and you no longer have the will to do anything. It also blocks off … Read more

The feeling of “needles and pins” sticking in your feet after you have been sitting with your leg curled up in one position for a long time is called “falling asleep.” What actually happens is this. Your blood usually flows freely through the blood vessels in your leg, just as water can flow freely through … Read more

There are some activities your body automatically continues whether you’re awake or asleep. Without them, you could not go on living. For example, your heart beats and you breathe; your blood continues to flow, bringing food and oxygen to all the cells in your body. Sleep is also the time when those body cells that … Read more

Most dreams are based on events that happened to you that day. Others involve deep fears you might have had since you were very young. In still others, wishes you’ve had for a long time are granted in your dreams. Sometimes, these are wishes you didn’t even know you had. As you dream, you are … Read more

The white spots that are often scattered on your nails are simply signs that the nail has been bruised or injured. However, before this was known as a medical fact, superstitious people gave other meanings to these spots. On the thumbnail, they meant you would receive a gift. On the index finger, the spots represented … Read more

“Throw them away, of course!” would probably be your answer. And that is exactly what most people do. But in some societies, where superstitions are strong, fingernail cuttings are believed to be used by sorcerers for casting evil spells against their owners. Therefore, the cuttings are carefully guarded or hidden. Another old superstition claims that … Read more

Just think what a world of long-nailed people we’d have if cutting, biting, or filing nails caused people pain. But none of these acts hurts the human body because nails are made up of hardened dead skin cells, actually a form of dead protein, much like the dead protein that forms the horns on deer, … Read more

You drop a hot potato long before you actually feel the pain that comes from burning your hand. That’s because as soon as you touched it, your nerves quickly sent a message saying, “too hot” to your spinal cord. The nerves in your spinal cord answered this message right away, they didn’t even wait for … Read more

Your hair can and will change color when you are old, but this does not happen overnight. Different hair colors, from blonde to black, are determined by the melanin, the coloring matter, in your hair cells. This melanin becomes part of your hair cells as they form in the roots. Gray hair starts to appear … Read more

Your hair is made of the same material as your nails, a horse’s hoof, a reptile’s scales and as a bird’s claws and feathers. If your hair or any parts of these animals is cut, there is no pain because your brain only receives “pain messages” from parts of your body that have nerve endings. … Read more

The hair on your head grows about half an inch each month. Even when your body stops growing taller, your hair will still keep growing. Hair grows faster in summer than in winter, and faster during the day than at night. When each strand, or shaft, of hair reaches a certain length, it stops growing … Read more

All mammals have some hair, and man is a mammal. In some mammals, that hair covers the whole body, but in man, it grows only in certain parts. Your hair has two main purposes on your body: to provide warmth and to protect your skin and body openings. While the hair on an adult’s body … Read more

Your kidneys are two purplish-brown, flat, bean-shaped organs that lie on each side of your spine near your waistline. These fist-sized organs are among the most important in your body. The kidneys’ most important function is the production of urine, which carries waste materials out of your body. It is just as important for your … Read more

The largest gland inside your body is your liver. It weighs from 3 to 4 pounds, and is a reddish-brown mass. The liver has to be large because of the complicated work that it does. It is almost like a miniature chemical laboratory in your body. Here how it works. As blood enters your liver, … Read more

Although not all scientists agree on the answer, many believe that most people’s brains develop more on one side than on the other. And since the left side of your brain controls the muscles on the right side of your body, and the right side of your brain controls the muscles on the left side … Read more

When you were born, sometimes a mole, or nevus, appeared on your skin. This is called a “birthmark” because it was present at birth. Moles are soft, dark, raised spots that can appear on almost every part of the body. They can differ from each other in what they are made of. Some moles consist … Read more

You probably figured that because an adult is bigger, he would have more bones in his body. But that isn’t so! An infant has 300 bones in its body, while an adult has only 206. What happens to them as the child grows? Do they just disappear? No! As the child grows, two or three … Read more

Scientists can’t say for certain what the man of the future will look like. But they do predict that he will have a smaller face and a bigger nose. He’ll have less hair than he does now, in fact, he might even be bald! Man’s face has been gradually getting smaller since cave-man days. In … Read more

Yes, indeed! When you were being formed inside your mother’s uterus, you were connected from your abdomen to her body by a rope-like tube called the umbilical cord. Everything you needed to live and grow during the nine months before you were born, oxygen and food from your mother’s blood, came to you from your … Read more

Even though you are not aware of it, there are tears in your eyes all the time even when you’re not crying. These tears are washing your eyes constantly, bathing them in a salty fluid made by the lachrymal, or tear, glands. Normally, this amount of fluid is so small, it can drain off into … Read more

When you feel embarrassed or upset, tiny blood vessels under the skin in your face and neck grow larger, and more blood flows close to the surface. The skin then has more color in it than usual, and feels warmer because this extra blood brings extra heat along with it. No one knows exactly why … Read more

Athlete’s foot is really a fungus infection of the foot, and not a special kind of foot. Anyone at all is liable to get this highly contagious infection, whether he is an athlete or not. In athlete’s foot, the skin between the toes becomes scaly, cracked, and itchy. Athlete’s foot can be spread by walking … Read more

Boy’s muscles are usually bigger than girls’, but bigger is not necessarily better! Boys’ muscles tend to be bigger because boys usually use them more in sports and other physical activities. This also makes their muscles harder. Later, when boys reach their teens, or the period called adolescence, their glands produce special chemicals, or hormones, … Read more

A bruise is an injury on the surface of your body. It is usually caused by a blow or a fall. Even though your skin is not broken, the small blood vessels under your skin are. As more blood rushes to the damaged tissues, your skin becomes swollen and red. The bruised area later turns … Read more

Usually when you sneeze, you are trying to get rid of an irritation or harmful object in the air passage of your nose. Sneezing is a reflex action, an automatic reaction of your body without your controlling or willing it. The irritation stimulates the nerve cells in your nose to send a message to your … Read more

When you get sick, your white blood cells fight the harmful germs with special germ killers called antibodies. White cells manufacture antibodies for each particular sickness, so if you have chicken pox, your white blood cells make chicken pox antibodies. After you are recovered, these antibodies stay in your blood and keep killing any chicken … Read more

Your body has the ability to resist or overcome a disease by a process called immunity. Your body acquires this immunity in several ways. For example, if you had a disease such as yellow fever and had recovered from it, you would never get it again. This is because your body has produced antibodies to … Read more

Attached to one end of your large intestine is a narrow tube-shaped sac called the appendix. It is about the size of your longest finger. Scientists feel that at one time, thousands of years ago, this appendix may have served a purpose in early man’s digestive system. Now, however, it seems to be of no … Read more

Your tonsils are small masses of tissue located at the back of your mouth in your throat. Because this tissue manufactures germ-fighting white blood cells, it is able to trap harmful bacteria that may enter your nose and mouth when you breathe. Fighting infection is the normal work of your tonsils, since they are the … Read more

The most common contagious disease in the world is the common cold. Colds are actually infections of the mucous membranes of your nose and throat, but sometimes they spread to your air passages and lungs. The cold germs, or viruses, that cause these infections and make you cough or sneeze travel through the outside air … Read more

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