Karen Hill

Itching, which doctors call pruritic, can have many causes, and the exact mechanism is still a matter of controversy. Most researchers believe the common itch starts with the release of a substance called histamine, and possibly other chemicals, from special cells called mast cells in the skin. The release can be triggered by allergies, contact … Read more

A trace of mosquito saliva is injected when the mosquito bites. The saliva contains an enzyme that prevents the victim’s blood from clotting while the mosquito feeds. In humans, the enzyme prompts an immune reaction that brings mast cells to the wound. The mast cells release histamine, which produces the itching and red rash. There … Read more

Depending on variables like the size of the troop and the type of terrain, the Indians may have been able to hear the troops from quite a distance. There are many factors involved in the seismology of such a phenomenon, and only individual experiments would determine how much energy would be coupled into the ground … Read more

The heart health benefits of aspirin are unique to the drug, and is often recommended to help prevent heart attacks. Aspirin may have multiple effects, but it is likely that its impact in cutting the stickiness of blood platelets is its major role in preventing heart attacks. Acetaminophen had no effect on the stickiness of … Read more

Cyanide kills by asphyxiating the cells of the body. Cyanide competes with oxygen in the body’s cells. The enzyme responsible for using oxygen has more affinity for cyanide than it does for oxygen, so the presence of cyanide starves a cell for oxygen. Cells’ respiratory pathways use the oxygen in a complex process to break … Read more

There are two basic kinds of reaction to a bee sting, one requiring immediate care in the emergency room and the other less serious. In the less serious local reaction, the chemicals in bee venom cause an immediate redness and swelling near the site of the sting and perhaps a fat, red, warm arm that … Read more

The risk associated with smoking three or four cigarettes a day is less than for someone who smokes forty cigarettes a day. But for a particular person, it can be very hazardous indeed, a bigger environmental hazard than almost anything you can name. Even one cigarette a day raises the risk of cardiovascular disease and … Read more

According to exercise physiologists, there are ways to accelerate elimination of the lactic acid that builds up in muscles. Lactic acid is removed most effectively from muscle by having an active recovery period, like walking after running, rather than a passive recovery, like lying down after the end of exercise. Lactic acid is a product … Read more

Depending on the severity of the allergy and the willingness of owner and cat to carry out elaborate hygiene routines, it may be possible to keep both pet and spouse. In fact, most veterinarians the cat’s own hygienic standards are a big part of the problem. A specific protein in its saliva and skin glands … Read more

In a car crash, it makes no difference whether you are relaxed or tense. In fact, drunken drivers have a greater chance of being injured or killed. Checking the National Highway Traffic Safety Administration accident files, researchers compared survival rates and serious injury rates in serious crashes for drinkers and nondrinkers and found that the … Read more

Night terrors are sudden feelings of terror, for no particular reason, that strike during sleep, with no dream or frightening scene recalled. They are most common in children three to eight years old, and it is estimated that about 1 to 4 percent of the entire population has had an attack. During and after a … Read more

The dream about an exam echoes the first time such an anxiety emerged in your thinking, many psychologists and psychoanalysts believe. This is a dream that everyone has at some time in some form. Both Freud and Adler talked about the examination dream, and though they had different interpretations, they recognized it as one of … Read more

Lots of people outgrow their food allergies. Many people avoid foods to which their allergies are long gone, experts say, and many allergies disappear by the age of four. The reason is not known, but many immune conditions are outgrown with time, possibly because the immune system needs time to mature. Actually, only a minority … Read more

A condition doctors call vasomotor rhinitis produces a runny, stuffy, sneezy nose even when no true allergy or infection is present. Many people are sensitive to things like perfume or dust, but a very common factor is cold, dry air. Although the exact cause of vasomotor rhinitis is not known, doctors suspect it is chiefly … Read more

In general, just putting your hand on or touching lead won’t hurt you. There are exceptions, like some cosmetics used in the Middle East that are absorbed through the skin, but mere skin contact is generally not a danger, unless you put your hands in your mouth or unless the lead touches something else and … Read more

Blood released from capillaries and trapped under the skin and breakdown products of hemoglobin in the blood are chiefly responsible for the coloration of black eyes and other bruises. In the case of black eyes, old blood is never really black, but dark purple and green. The color of the pooled blood is magnified by … Read more

The way a person feels when waking up from sleep, day or night, depends largely on the sleep stage the person was in just before waking up. This “sleep inertia” affects how someone feels for a little while after waking. Waking from what is called slow-wave sleep, a deep sleep without rapid eye movement, a … Read more

The presence of nipples and other breast tissue in men exemplifies the fact that the basic body plan of men and women is similar. There are exaggerations in each sex based on early development and later hormonal influence. The nipple happens to be one of the features whose full development has been restricted in the … Read more

You don’t lose fat cells when you lose weight, the fat cells simply become smaller. In people who have an excess number of fat cells, the fat cells may be even smaller than normal when they get down to a normal weight. That may be one reason it is so easy to regain weight. The … Read more

A hiccup involves the diaphragm, the sheet of muscles in the chest that controls breathing and separates the chest from the abdomen, and the vocal cords in the voice box. When a sudden involuntary contraction of the diaphragm is accompanied by a quick closure of the vocal cords, the “hiccup” sound occurs. The phrenic nerves, … Read more

A vast majority of snorers are in fact men, and may be waking up hundreds of times a night without remembering it in the morning. Snoring in its worst form is a symptom of obstructive sleep apnea, in which a person’s breathing passage is blocked in the relaxation of sleep, so that he cannot breathe … Read more

The heart muscle is a special hardworking kind found nowhere else in the body, though it can get very tired when deprived of oxygen in a heart attack and can get stronger through exercise. The other types of muscle are skeletal or striated muscle, the kind that lets the body move voluntarily, and smooth muscle, … Read more

It is true that men don’t have as much of the hormone estrogen as women. But the male hormone androgen, which normal men have in considerable supply, appears to exert similar protective effects on the skeleton. Men who have an insufficient supply of androgen do get osteoporosis, the loss of bone mass that often occurs … Read more

Tears contain a variety of different salts, most of which probably come from the blood and, ultimately, from the diet. Salt in food is absorbed by the intestines and enters the bloodstream. The salt probably enters tears as blood flows through the lachrymal glands, where tears are formed. The first known chemical analysis of tears, … Read more

Fingernail growth averages out to about a tenth of a millimeter a day. Toenails are about a half to a third slower, and drugs or disease can change the growth rate. There are differences from finger to finger. The middle and fourth finger tend to grow a little faster than the fifth and the thumb. … Read more

The notion of ambidexterity is valid, and some people do show equal proficiency in various manual skills with both hands. However, hand-use preferences are on a continuum, and a mere three categories of left-handed, right-handed and ambidextrous are artificial divisions. One researcher calls ambidextrous people ambilateral, and further divides them into the ambidextral, those with … Read more

About 10 percent of identical twins have different dominant hands. Nobody knows the causes of handedness. Left-handedness tends to run in families, but because many identical twins have different handedness, we know that is not the whole story. Other factors are presumed to be involved, such as perhaps position in the womb, but there are … Read more

There is no relationship between breast size and volume of milk. The female breast contains fifteen to twenty lobes of milk-secreting glands embedded in various amounts of fatty tissue, which is not involved in milk production. Instead, it is controlled by hormones produced during and after pregnancy that stimulate the milk-secreting glands, and the nursing … Read more

Blood inside the body is either bright red or dark red, depending on whether it is arterial blood or venous blood. Red blood cells carry oxygen from the lungs to the tissues, where the oxygen is exchanged for carbon dioxide. Each red blood cell is packed with hemoglobin, a protein that contains iron. Hemoglobin combines … Read more

The larynx, like many other body parts, is under hormonal control during development. Male hormones encourage the growth of the larynx, and the Adam’s apple is the prominence made by the cartilage that creates the housing for the larynx. The larger male larynx, the longer vocal cords and the bigger box that resonates when the … Read more

The body may sweat during swimming, with the moisture dissipating unnoticed in the water. You do not necessarily sweat when you swim, but if you swim long enough and hard enough so that the exercise raises the internal body temperature, then you will sweat. This can be proven by measuring body weights before and after … Read more

People are indeed top-heavy, and balance, the ability to stand upright and move around without falling over, is not as simple as it feels. It requires constant tiny adjustment of muscles as the weight shifts on the feet, much as a juggler maneuvers to balance a plate on a stick. The adjustments become unconscious and … Read more

It is a complex question, made even more complex by factors like the prior activity of each individual and how long each has been in the room. Assuming that both people have become acclimatized to the room and that neither is running a fever, there are two important factors. One is the percentage of body … Read more

Human eyes do grow, but most of the growth takes place early in life. For the retina, a vast majority of growth takes place before the age of two. For the eyeball, most growth occurs before the age of six, and there is supposedly no growth at all after puberty. Nearsightedness, which is tied to … Read more

A pregnant woman can pass on some kinds of immunity to the baby, whether she has been immunized or not. These maternal antibodies are very powerful, and babies are protected for several months. That is why the measles vaccine is delayed until the age of nine to fifteen months. At earlier ages, the antibodies interfere … Read more

On average, a healthy young person can hold his breath about three minutes. With training, that might be extended some, but beyond that, a person might start to lose consciousness, because the body does not store a lot of oxygen. What triggers breathing is not a lack of oxygen, but a buildup of carbon dioxide … Read more

One reason babies sleep so much is that human growth factor, made by the pituitary gland, is secreted during sleep in higher concentrations than when the baby is awake. How the body and brain coordinate the process is not fully known, but for the first few months of life, a baby sleeps most of the … Read more

Just as an animal’s fur stands on end when cold, hair stands on end as a response to threatening noises or sights. This bristling is thought to occur to make the animal look larger, and therefore more formidable, to an opponent. Bristling fur as a response to cold keeps the animal warmer by increasing the … Read more

Squinting your eyes often makes objects appear sharper, even more so if you’re shortsighted. It’s because the rays are focused on the retina more than a change in the shape of the eyeball. Ideally, the eye receives rays of light and bends them so that an image is resolved on a small point of the … Read more

Humidity can make it seem like hair has a mind of its own, by affecting its natural curl pattern. Any change in relative humidity can make the hair fiber assume or exaggerate its natural state. As each hair fiber is formed in the follicle, the sac it grows from, it emerges with a distinct curl … Read more

The bones and the series of ligaments that form the knuckles and many other joints have a little elasticity. In cracking a joint, what basically happens is that you separate the two bones by pulling or bending. This abruptly creates a space between the bones, a vacuum. Then the fluids normally present in the surrounding … Read more

It is believed the watering of the eyes when you yawn may result from pressure on the main tear glands. These gland are at the outer margins of the eye sockets, and may produce tears because of the facial contortions involved in yawning. The involuntary act of yawning usually includes opening the mouth very wide … Read more

The brain’s activities do expend energy, and fuel is burned, but in very small amounts. In the sense of actually breaking down fatty tissue so that one might lose weight, thinking would play a very minor role. Extensive studies of brain function have been made and the varying levels of energy use at different levels … Read more

Whether humans are getting taller or not depends on what people you’re talking about. In a given population, physical anthropologists and public health experts believe, the trend could go either way. Physical anthropologists point to a trend toward increasing height over time, which they call the “secular trend.” The trend is borne out by measurements … Read more

New research has shown that there is a significant reduction in stomach capacity when someone reduces food intake. However, stomach capacity can also be increased by someone who eats more, which has implications for someone facing a big Thanksgiving dinner. The research involved obese people on a formula diet of six hundred calories a day, … Read more

“Sand” and scratchy eyes are not cause and effect but are both the result of irritation. The so-called sand, or “sleep” that builds up at the corners of the eyes is actually dried mucus. If the eyes are irritated for any reason, pollution or dryness, for example, more mucus is secreted, and the longer the … Read more

People stop growing at many different ages, but for most people the age limit is about eighteen or nineteen. Thus, a person who continued to grow right after high school would be well within the normal range. In some unusual cases, people can continue to grow until about the age of twenty, and in people … Read more

Most wild tomatoes are relatively small and are found close to the equator. The tomato is a New World plant, but comes from South America and Mexico, not North America. There are thousands of varieties, and new wild varieties are still being sought out in South America to enrich the limited genetic pool of the … Read more

Butter spoils less quickly than milk because of the amount of free water or available water in the food. The microbes involved in spoilage require water to live and multiply. Milk has a huge amount of available water, 93 or 94 percent, and butter has much less, so bacteria, yeast and molds are less able … Read more

Some members of the deadly nightshade family, Solanaceae, produce chemicals called glycoalkaloids, which are toxins. Normal amounts of the parts of these plants that are normally consumed are not ordinarily toxic to human beings, though the potato plant itself is very toxic, as is the tomato plant. Consuming very large quantities of potato skins, 2.4 … Read more

The modern commercial pineapple is seedless, thanks to English greenhouse breeders of the early 1700s who turned a small, seedy tropical fruit into a large, fleshy object. Over generations of breeding, most of the reproductive organs of the pineapple’s tight cluster of flowers were persuaded to clump into one sterile mass called a syncarp. It … Read more

Compounds containing cyanide can be found in some fruit pit kernels and some other foods as well. Even cabbage, broccoli and cauliflower contain cyanide compounds, but not enough to make them unsafe. Too many fruit pits can add up to a real risk, however. Apricot pits, for example, contain a compound called amygdalin, the supposedly … Read more

The mold that normally produces blue cheese produces traces of toxic substances, but not enough to hurt a human being in the quantities normally consumed. Almost all blue cheeses are ripened by the mold Penicillium roqueforti, which does make about six alkaloid toxins, called mycotoxins. However, two of the six, the most potentially harmful, are … Read more

The chemicals in hot peppers that cause the burning sensation may protect them from animals so they get eaten by birds. Any plant, whether it is a shrub like a pepper, a tree or an herb, that has bright red or orange fruit with a number of small seeds in it, and in which the … Read more

There is not a perfect correlation between the amount of hot foods eaten and the warmth of the climate. In Honduras, for example, hot pepper is not a major part of the cuisine, as it is in nearby Mexico and Thailand. A regional fondness for pepper may simply arise because meat and other foods tend … Read more

With cold soup, the fault may not be in the salt but in the absence of heat to volatilize the other flavorings so they ascend to the nose. Flavor is both taste and smell, and most spices are also perceived with the nose, so that the perceived concentration increases as the volatiles, the gaseous form … Read more

Cans of spoiled food may swell, and it is usually taken as a sign of spoilage, but canned food may be spoiled even if the can does not swell. If cans do swell, it can be for two reasons, one chemical and one biological. Acid foods, like tomato juice, canned pineapple or almost any canned … Read more

The change in color in a green pepper is the same kind that occurs in any other ripening fruit that changes color. Chlorophyll breaks down or degrades, and other pigments are exposed or formed. The complex ripening process is under the control of plant hormones like ethylene, a growth regulator that makes chlorophyll break clown, … Read more

Peaches spoil faster than fruits like apples or pears for several reasons. First, they have a different surface structure, with no natural waxy coating or thick epidermis to protect them from bruises. Second, unless a fruit is completely dried out, normal metabolism continues and the fruit burns up sugar reserves; the peach respires at a … Read more

It might be difficult, but it is not impossible for the child of strict vegetarians to get enough calcium from a diet that does not include eggs, meat, fish or milk products. The recommended daily allowance of calcium for children is 600 to 1,000 milligrams, depending on age. Many fruits and vegetables contain significant and … Read more

Any vitamin or mineral taken in excess could interfere with the absorption, metabolism or storage of some other component of the diet, but interactions are usually not a problem. Nutritionists basically recommend that people should derive their nutrition from food, not food supplements, and that they should choose a well-balanced diet including a variety of … Read more

The problem is oligosaccharides, or “several-unit” sugars, which are produced by legumes, especially in the final stages of seed development. The oligosaccharides, called raffinose, stachyose and verbascose, are used by the seeds to store energy. The human body lacks enzymes to break them down, and so cannot digest and absorb them as it does the … Read more

Vitamin E is an antioxidant, interfering with the chemistry of oxygen interacting with other chemicals. Both human bodies and food are degraded by oxidation, so the same chemistry that helps protect humans can protect foods. Vitamin E is a broad term for a member of a group of chemicals called tocopherols, which have vitamin E … Read more

Gelatin is a tasteless, odorless substance extracted by boiling collagen, a jelly-like fibrous protein found in animal bones, tendons, hoofs and connective tissues. When dried gelatin is mixed in warm water, the fine-grained particles do not actually dissolve, but rather become evenly dispersed and remain suspended in the liquid. When cooled to 95 degrees Fahrenheit … Read more

Spinach often grows well in sandy soil, and unless it is very well rinsed it may feel gritty. Spinach contains some oxalic acid. Rhubarb, which is sour enough to set your teeth on edge, owes its sour taste to oxalic acid, which can be gritty. However, the variety of spinach that accumulates the most oxalic … Read more

It is possible to get a toxic dose of vitamin A, but not from carrots. Probably the worst thing that would result from eating a large number of carrots is an alarming-looking yellowing of the skin called carotenemia. It is apparently harmless. Carrots contain an orange pigment, called beta carotene, that the human body converts … Read more

Some but not all vitamins are lost in cooking, and the amount varies widely. Minerals are fairly stable in cooking, but different vitamins are susceptible in different degrees to various factors, including heat, light and air. Generally, water-soluble vitamins like riboflavin, thiamine and especially vitamin C are more susceptible to losses in heat and water … Read more

The waxy film or coating on fruits and vegetables is a natural protective substance secreted by cells in or near the skin of the fruits. Composed of many kinds of waxes and lipids, the film helps waterproof the fruit. It prevents cracking because of moisture loss and also prevents moisture from entering the fruit from … Read more

Storing eggs small end down keeps eggs fresh somewhat longer. An egg’s freshness is judged by candling, using a light to see the position of the yolk. The nearer the yolk is to the center, the fresher it stays, because the surrounding albumin, or egg white has antibacterial properties to protect the embryo, or the … Read more

Varieties of fruits and vegetables can differ widely in nutrition. For example, a New York State McIntosh apple would have about 3 milligrams of ascorbic acid, or vitamin C, per 100 grams, while a Cortland would have 11 milligrams, a Jonathan would have 17 and a Cox orange would have 19. One kind of winter … Read more

Tonic water, also known as Indian tonic water, is a carbonated soft drink with dissolved quinine. The amount of quinine in tonic water would not be much help against its original target, the fever of malaria. Quinine, derived from the bark of the cinchona tree, must be administered in very high doses to reduce fevers. … Read more

A person who can taste the very few molecules of plasticizer that might escape from a food container probably has an extra-sensitive sense of taste but need not worry about being harmed. The plasticizers used to make the plastics flexible in containers intended for food are very slightly soluble in water and slightly more soluble … Read more

The National Institute on Alcohol Abuse and Alcoholism of the National Institutes of Health estimates that alcohol is cleared at a rate of approximately one hundred milligrams per kilogram of body weight per hour. That’s about half an ounce of pure alcohol every two hours. So if a person ingested approximately three drinks in a … Read more

Kudzu, often called the vine that ate the South, is a Chinese and Japanese fodder and cover crop with an edible root. The original Japanese pronunciation was kuzu. The Latin name is Pueraria lobata, but it was called Pueraria thunbergiana until 1947. An American consul in Japan in the late nineteenth century, Thomas Hogg, exported … Read more

Popcorn pops because of a delicate balance between a moist interior and a dry coating. The exterior cells, the pericarp, are hard and relatively impermeable. The interior cells are soft and contain moisture. When the seed is heated, the moisture turns to steam. The pressure builds up to the point where the hard outside pops, … Read more

Don’t count on either safety or succulence when it comes to white mushrooms in the woods. It is probably a harmless but not so tasty mushroom, but the squirrel is probably no better judge of its safety than a layman. The squirrel’s physiology is close enough to ours that if a mushroom is deadly to … Read more

Most experts say it is possible for ivy to damage walls both physically and chemically. But botanical gardeners usually advise that the chief danger is to masonry that is already in bad shape. There are two schools of thought. One sees ivy as a likely threat to a wall. The other believes that if the … Read more

Water and dissolved minerals are taken up through cells called the xylem, and food manufactured in the leaves is distributed to the rest of the plant through cells called the phloem. The rise of sap is essentially concerned with the xylem. It is a system of very fine tubes that continuously connect the extremities of … Read more

Many tress along the street don’t live very long. The average life of a street tree surrounded by concrete and asphalt is seven to fifteen years. Many do survive, but decline rapidly. Many factors underground determine whether a tree will make it. If the soil is so compacted that the roots can’t get in, it … Read more

Oleander is extremely toxic, one of the most toxic plants on anyone’s list. Even a few oleander leaves falling into a small ornamental pool could poison a dog who lapped water from the pool. All parts of the oleander plant are considered toxic, with the seeds usually the most toxic, the leaves a little less … Read more

There are several types of poison associated with different kinds of poisonous mushrooms. The chief mechanism is the destruction of the liver, the filtering system for poisons in the body. The toadstool toxin inhibits an enzyme called RNA polymerase, which synthesizes the genetic material messenger RNA. Without the messenger KNA, the liver cells stop synthesizing … Read more

Sometimes there are nice correlations between an organism’s defenses and its enemies, but in the case of poison ivy, any such connection is a puzzle. Poison ivy is toxic to humans and a few higher primates and that’s it. As close a relative as the rhesus monkey, for example, is normally not sensitive to it. … Read more

It is possible to grow a coconut palm from a coconut, if it is an unhusked coconut. The ones usually sold as food have had their tough fibrous outer coating removed. The hairy kernel of Cocos nucifera encloses an insignificant embryo amid a large endosperm of meat and liquid. An unhusked coconut, still filled with … Read more

A tall palm tree called Lodoicea maldivicia, which grows only in the Seychelles in the Indian Ocean, produces the largest single seed in the world known in the plant kingdom. The two-lobed seed can be twenty inches long. It grows in huge fruits that look something like two coconuts joined together in an almost heart-shaped … Read more

All plant functions, from germination to photosynthesis to blooming, can be accomplished under light in wavelengths ranging from 300 to 700 manometers, or billionths of a meter. Therefore, indoor gardeners need either incandescent “grow lights” or a combination of “cool” and “warm” fluorescent bulbs that give off light in that range. Regular incandescent lights give … Read more

Viruses attack living cells like soldiers taking over a factory. The processes a plant relies on to survive, like growth, metabolism and photosynthesis, take place in cells. Viruses can subvert the cells’ functions to their own ends, eventually killing the tissues that the cells make up. First, the virus attaches itself to the external wall … Read more

Strings of lights do not harm a tree unless it is brought inside in a pot and exposed to warm dry air and then suddenly taken back outside into the cold, or unless the lights are actually hot enough to cause burns. Light does affect the growth cycle of trees, but chiefly in combination with … Read more

Honeybees collect the nectar secreted by flowers to attract pollinating insects and convert it to honey through two chemical changes and one physical change. The changes add up to a product that is digestible by bees or humans, easy for the bees to store and free of microorganisms that can cause spoilage, like bacteria or … Read more

The leaf color changes of autumn result from a complex interplay of factors of temperature, sunlight and moisture, all dependent on timing. Not all the processes are predictable, but it is known that sunny days and cool nights in late summer and early autumn make for a particularly bright display of reds. The yellow display … Read more

The deer tick, which often carries the Lyme disease microbe, requires very humid surroundings and would probably not survive longer than forty-eight hours in the dry air of a house. The deer tick belongs to the hard-bodied tick group, but certain other kinds of ticks can live for long periods under adverse conditions. Deer ticks … Read more