Mothers and grandmothers have traditionally raised the cold-weather alarm:  Bundle up, change wet socks and shoes, don’t sit in a draft and get chilled.  The idea that sneezing, sniffling, stuffy noses, fever, and body aches are caused by getting chilled is a very old one.  People have talked about catching “colds” since at least the 1500s.  The common sickness was called a “cold” because its cause, people thought, was miserably cold weather.

We now know that colds (and flu) are the result of infection–an overwhelming of the body’s defenses by tiny, invading viruses.  The first viruses were discovered in the late 1800s.  By the 1930s, scientists suspected that viruses were to blame for colds; proof came in the 1940s.  Since then, we’ve learned that colds can be caused by some 200 different viruses, often from the rhinovirus group.

But the billion or so colds we catch in the U.S. each year do tend to cluster in the colder months of fall and winter.  Why?  One reason is that we spend more time indoors in winter, in close contact with other people.  The low humidity of winter weather may also help cold viruses flourish, especially in our dried-out noses.

And scientists studying the flu, a much more serious respiratory infection, have found evidence that cold, dry weather plays an important part in the yearly winter outbreaks. Researchers exposed guinea pigs to a flu virus under different combinations of temperature and humidity.  No healthy animals were infected when the humidity was held at a steamy 80 percent, or when the temperature hovered at a summery 86 F.  But flu transmission soared when humidity dropped to below 35 percent, and when the temperature was lowered to about 41 F.

According to researchers, winter’s cold dryness helps the flu virus survive in air longer, and get a foothold in the nose, where protective mucus dries out.  (There is little flu in the tropics, where the weather is warm and humid all year long.)

Another study in the U.K. connects cold with colds.  Volunteers who plunged their feet into chilly, 50-degree F. water for 20 minutes were more likely to develop cold symptoms over the following week than those whose feet stayed warm.  Researchers say that when the body harbors a cold virus, held in check by the immune system, chilled, wet feet may predispose us to a full-blown illness.

Some scientists think that there’s another piece of the summer/winter puzzle:  Vitamin D.  In summer, when UV radiation from the Sun peaks, our Vitamin D levels rise.  As days grow shorter, Vitamin D levels fall, reaching their lowest levels in late winter, the peak of cold and flu season.  Since Vitamin D plays an important role in the immune system, making sure our levels are adequate in winter may help us fight off the viruses that cause colds and flu.

Listening for the echoes of their own rapid-fire, high-pitched calls, bats navigate the night, while snatching tiny insects from the air.  Dolphins (along with many whales and shrews) are also skilled “echolocaters.”  And it turns out that we humans, too, are capable of using a kind of sonar, and getting better with practice.  In fact, in the 1800s, one blind man used a kind of echolocation as he traveled the world, mostly on foot, writing about his adventures in a series of books.

Bats are the experts at traveling — and hunting — by listening.  Like submarines in the murky ocean depths, bats move through a sea of echoes, “picturing” objects in their way.

Bats emit high-pitched sounds through their mouths or noses, using their big, oddly-shaped ears to listen for sound reflections.  A bat may sweep your dark yard with sound at 10 blips a second.  When the sounds echo off an insect, the bat increases the rate, giving it a better sense of the bug’s size and location.  As the bat zeroes in, it chirps faster and faster, up to 200 times a second.

While human beings would lose a sonar throwdown with bats, some sight-impaired people do develop the ability to echolocate.  The simplest form of echolocation is tapping a cane or stick while listening for the echoes.  This gives the walker a sense of the changing terrain, as well as objects along the path.  But some people also use clicking or other sounds, much like bats, to determine the location, size, shape, and composition (hard or soft) of objects around them.

California teenager Ben Underwood, blind since he was a toddler, navigates using a series of fast tongue clicks.  Underwood says he began using clicking as a young child, and can even sink baskets by listening for echoes from the basketball pole and backboard.  One scientist estimated that Ben’s sonar clocks in at about 120 clicks a second.

Daniel Kish, a California psychologist who is also blind, practices and teaches echolocation.  His students have even learned to mountain-bike using the human form of sonar.

The first well-known human practitioner of echolocation was James Holman, born in 1786 with normal vision.  James was only 12 years old when he enlisted in the British navy, rising to lieutenant by his 20s.  Then, after an illness involving severe joint pain, Holman lost his vision at 25.

Holman decided to travel the world, using a walking stick and listening for resounding clicks as he trekked through Europe, Asia, Africa, and South America.  The books he wrote about his sometimes-perilous journeys were bestsellers in the 1800s.  After his death in 1857, the so-called “Blind Traveler” was gradually forgotten.  His story is recounted in the book “A Sense of the World:  How a Blind Man Became History’s Greatest Traveler,” by Jason Roberts.

For more on Holman, listen to an interview with Roberts at www.npr.org/templates/story/story.php?storyId=5675082.  For more on Ben Underwood and Daniel Kish, go to  http://abcnews.go.com/Primetime/story?id=2283048.

It’s how we decode dinner: Scientists say there are at least four basic tastes — sweet, salty, sour and bitter. (Some add a fifth, umami, the savory taste provided by an amino acid in food called glutamate.) While we have generally pleasant reactions to sweet and salty tastes, it’s a different story with “bitter” and “sour.” “Bitter” may mean poison, so our brain is hard-wired to reactive negatively to the taste. “Sour” may mean a food is spoiled, and full of harmful bacteria.

When given a taste of something bitter, newborn babies make an immediate expression of disgust, and turn their faces away. But when tasting something sour, like lemon juice, an infant’s reaction is usually slower and milder. The lips purse and pucker, the nose wrinkles, the eyes narrow. Over a period of seconds, the baby may close her mouth and retract her lips, or frown.

But as babies get a few months older, some may actually smile at the taste of lemon juice. Human beings seem to have a love/hate relationship with sour tastes, even at 4 months old. Which is why some of us enjoy endless varieties of sour candy — and lemons — even as we pucker our lips and scrunch up our face.

Until the last few years, scientists hadn’t found the sour-taste receptors they suspected were lurking on our tongues. Then, in 2006, researchers announced that they had narrowed down the search to tongue cells containing two proteins, PKD1L3 and PKD2L1.

The proteins combine to create “ion channels,” allowing electrically charged calcium atoms (ions) to flow in and out of cells. This flow of ions, in turn, allows signals to travel to the brain, where they are decoded as different tastes. In the experiments, sweet, salty, and bitter solutions caused the channels to stay closed. But when sour-tasting acids were introduced, the channels opened.

The studies also uncovered a fascinating connection: One of the tongue’s sour-sensing proteins, PKD2L1, is also lurking in a group of neurons on the spinal cord. There, the protein may monitor the acidity of cerebrospinal fluid that bathes the spinal cord and brain. In a sense, the protein lets the spinal cord “taste” the fluid. (Scientists say the protein is a good example of evolution’s multitasking ways.)

A recent study by scientists at the Monell Chemical Senses Center in Philadelphia found that our reaction to sour tastes may lie in our genes. Researchers gave water with varying amounts of citric acid to pairs of identical as well as fraternal twins. (Fraternal twins are no more closely related than any two siblings in a family.) They found that some people were a thousand times as sensitive as others at detecting a slightly sour taste. Identical twins, who share the same genes, were much more similar in sour sensitivity to each other than were fraternal twins. The conclusion: Our reaction to sour tastes — where we fall on the Pucker Index — is “highly inherited.”

If you’ve ever hit your funny bone, you know that the only amusement comes from the faces, gestures, and sounds you make as you grab your elbow and dance around the room. The vibrating pain, extending to your fingers, seems to start in the knobby bone on the inner elbow. Actually, the bone is an innocent bystander; it’s a nearby nerve that’s causing all the excruciating commotion.

It should be called the Funny Nerve, but its official name is the ulnar nerve (after the ulna bone in the forearm). Stretching from neck to hand, the ulnar nerve sends impulses back and forth from the spine.

The pain from hitting the ulnar nerve is no laughing matter. Smaller nerves running through the skin allow us to sense heat and cold, or to feel the prick of a thorn before it pierces the skin. These nerves are relatively unprotected, so that we can perceive the world around us. But the ulnar nerve is a big nerve. Its main function is to control muscles in the forearm and hand, as well as enabling our pinky and ring fingers to feel sensations.

Other large nerves are protected by bone and fat. But the ulnar nerve is almost completely exposed. The ulnar nerve runs in a bony groove (the “cubital tunnel”) through the elbow, where all that stands between desktop and nerve is an thin layer of fat and skin.

Bump your inner elbow, and this large, exquisitely sensitive nerve is slammed between your solid bone and, say, the top of your desk. The result is a searing, tingling, electric pain that starts in your elbow, shoots down your arm, and ends in the fourth and fifth fingers of your hand. Youch.

It’s easy to see why people thought the elbow bone was the painful culprit, instead of a nerve no one could see or feel. But hitting your ulnar nerve is about as funny as a toothache. So what’s the amusing part? Some say the spot is called the funny bone because the ulnar nerve runs along the “humerus” bone in the upper arm. (Get it? Humorous?) But the real reason is probably because the feeling is so odd-unlike the pain from a bump anywhere else on the body. “Funny,” in this case, probably just means “peculiar.”

While the pain from hitting your funny bone only lasts a few seconds, the ulnar nerve can become irritated from simple daily activities. The telltale signs: burning pain in the elbow, and tingling and numbness in the pinky and ring fingers, and in the outside of the hand. Known as cubital tunnel syndrome, the symptoms are a result of the nerve being stretched and held against the bony bump of the elbow for long periods. Sleeping with your arm bent, holding a phone to your ear for hours, and leaning on your elbow can all annoy the ulnar nerve.

For more on the ulnar nerve and cubital tunnel syndrome, visit

www.muschealth.com/gs/HealthTopic.aspx?action=showpage&pageid=P00908.

The appendix. Can’t live with it, can’t live without it.

Oh, wait.

Actually, the appendix is one of the body’s most unobtrusive organs. No painful protests, like the ungrateful stomach after Thanksgiving dinner. No gasping after a sprint to the finish line, courtesy of the overworked lungs. And no ominous rumbling, like intestines encountering the wrong restaurant tomato. And not only can we live nicely with an appendix, we can also live happily without one, if need be.

Did nature simply get sloppy and produce a worm-like cave on the large intestine? Recently, researchers at Duke University in North Carolina unveiled a new explanation for the appendix’s existence. Hint: Rather like the fire extinguisher that usually sits unused on the wall, this tiny organ may be good in a crisis.

The 2- to 4-inch-long appendix juts from the right side of the large intestine like the tail on a dog. Only about a third of an inch in diameter, the narrow appendix has an opening nearly as small as the tip of a mechanical pencil. The one-way door at the exit is called Gerlach’s valve. Mucus made in the appendix flows through this valve and into the bowel.

Trouble starts when something – such as a bit of dried feces — blocks the opening. The result can be infection and inflammation, along with pain, vomiting, and fever. The appendix can swell and even burst, causing a deadly infection called peritonitis. Fortunately, appendicitis is usually easily treated. The infected organ is removed, and antibiotics stop infection from spreading.

When the ailing appendix is removed, the digestive system seems to function just as well without it. So what’s it for? Researchers had suggested that the appendix is part of the immune system, fighting infections by secreting antibodies into the intestines.

The Duke researchers also think that the appendix is a part of the body’s defenses. But its main role, they say, may be as a sanctuary for helpful bacteria, a place where friendly organisms can hang out until they’re urgently needed.

The intestines run on “good” bacteria, colonies which break down food and occupy space desired by not-so-friendly microorganisms. But when we come down with a serious intestinal disease involving diarrhea, the supply of good bacteria quickly dwindles. The researchers note that diarrheal diseases like cholera and dysentery still plague much of the underdeveloped world, and were common throughout human history.

The human appendix sits in a relatively protected place, away from infections raging in the rest of the gut, near the immune system’s lymph glands. Inside this “safe house,” in the mucus behind the one-way door, helpful bacteria can grow and multiply. When diarrhea has run its course, the intestines are denuded of bacteria both good and bad. The appendix can then “re-inoculate” the colon with a ready-made colony. Since people in the developed world are less likely to suffer from diseases like dysentery, the appendix can be removed without apparent harm.

While nearly everyone gets pruny fingers after a long bath, their exact cause is still a mini scientific controversy.

Part of the explanation involves how skin responds to water. While skin is a good protective covering for our bones and organs, it isn’t waterproof. In fact, skin is nourished and plumped up by water, even absorbing it from the air around us.

The skin’s outer layer, the epidermis, is attached to the thicker layer underneath, called the dermis, but there is some “give” between the two. Hair follicles in the dermis pump out sebum, an oil that protects and lubricates the skin. But the undersides of fingers and toes (as well as palms and soles) don’t have hair, and don’t have as much protective oil.

Meanwhile, the skin on hands and feet is quite thick. Submerge your hands in warm water for awhile, and the oil that protects the skin (and makes it a bit waterproof) washes away. So as you soak in the tub, the keratin protein of the extra-thick epidermis on your hands and feet will soak up 6 to 10 times its own weight in water, like an absorbent paper towel. As the epidermis swells with water, it pulls away from the dermis and folds up into ridges and furrows. (On palms and soles, the epidermis is so tightly anchored to the dermis that it can’t crimp up.)

Interestingly, researchers have found that people with Parkinson’s disease, diabetes, and other diseases that damage the nervous system or blood vessels often show reduced or absent finger wrinkling.

How come? In a study published in 2006, researchers in Taiwan compared ordinary fingers to reattached fingers, in which nerves had been severed in the past. In normal fingers, immersion in water reduced blood flow by more than 27 percent, and the fingers pruned up nicely. But when the reattached fingers soaked in water, blood flow actually increased by nearly 23 percent, and the fingers remained smooth and wrinkle-free. This suggests, the researchers say, that wrinkling is due more to the actions of nerves signaling the constriction of blood vessels, rather than to a property of the skin itself.

So what’s the whole story behind wrinkled digits? One explanation: Water kicks off the wrinkling process by seeping in and altering the balance of electrolytes (liker sodium and potassium) in the skin. This changes the functioning of nerve fibers (if they are intact), which in turn triggers a narrowing of the blood vessels leading to fingers. As the vessels deflate, the negative pressure tugs the plumped-up epidermis down into wrinkles. (Sufferers of Raynaud’s phenomenon, in which blood flow to the fingers is sharply reduced in cold temperatures, also report getting mildly pruny fingers, even when their hands are dry.)

Meanwhile, doctors can test the health of nerves in the hand and fingers after an injury by submerging the fingers in water. If the tips get wrinkly, it’s a good sign.

Open a new box of crayons, and your mind is flooded with scenes from the first day of kindergarten. The smell of a snuffed-out candle can evoke memories of birthdays past. And a whiff of the right perfume can bring back times spent with a long-gone grandmother.

More than sight and sound and touch, smell is the sense most linked to both memory and emotion. Scientists say this is probably because scent is so important to survival. Just think of kittens, eyes closed, learning who their mother is by her unique scent. Smelling and remembering smells help animals find edible food and avoid danger.

The brain’s olfactory cortex, which decodes odors received from the nose, is linked closely to the amygdala, the brain’s seat of emotion, and to the hippocampus, where memories are consolidated for storage. Research shows that memories evoked by odors are among the most vivid.

And recent studies show that we can use the smell connection to improve our memories-say, on the morning of a big test. Researchers have known for some time that “sleeping on it” is good advice when it comes to learning, since sleep helps the brain process new memories. So studying and then sleeping may help us remember more the next morning, when faced with that blank answer sheet.

But what if sleeping could be combined with smelling, for a one-two memory punch? Researchers in Germany devised an experiment to find out. Neuroscientists had student volunteers play card-matching games on a computer. As they located pairs of cards, players received a puff of rose-scented air.

Afterwards, the students went to sleep for the night, sporting electrodes that allowed researchers to track their sleep stages. Meanwhile, the scientists sent gusts of rose fragrance to students during different sleep stages. The next morning, those who had inhaled rose-petal scent during deep-sleep stages were much better at remembering the locations of card pairs. The scent-primed group got 97 percent right, versus the scent-free group’s 86 percent average.

To see how the smell/memory connection worked in the brain, the researchers repeated the experiment using an MRI machine. When a student – asleep in the scanner — got a precisely-timed whiff of roses, the MRI revealed activation of the brain’s cortex and hippocampus. In fact, the hippocampus was busier when the students were asleep and smelling roses than when they were awake, trying to recall card locations. The MRI provided a visual picture of the brain connecting the dots of smell and memory.

But we don’t need to stop and smell roses while studying; occasional whiffs of any single strong scent can help. Of course, we won’t have a bedside machine wafting the scent of Cram at us as we fall into a deep slumber. Still, the next morning, we can try bringing the chosen scent with us to the exam – say, by spraying it on our pencil. Studies show that such scent-linking may trigger some handy memories.

Have you avoided wearing a hat on a sub-zero day, afraid of the bad-hair aftermath? After scuffing across the carpet in your slippers, have you approached doorknobs warily? Do you pull masses of stuck-together socks out of the dryer? Does rustling your blanket at night produce tiny, crackling sparks?

The culprit, of course, is static electricity, the same phenomenon behind brilliant flashes of lightning in July. Static electricity is a build-up of negative or positive charges.

Most atoms in a material are electrically balanced, or neutral. The positively charged protons at the center (nucleus) are balanced by an equal number of negatively charged electrons whizzing around them. Losing one or more of its negative electrons will make an atom positively charged. Gaining an extra electron or two will make an atom negatively charged.

When you rub a balloon against your head, electrons transfer from atoms in your hair to atoms on the surface of the balloon. Since electrons have a negative charge, the extra electrons have built up a negative charge on the balloon. Meanwhile, in losing electrons, your hair has built up a positive charge.

Since electrical opposites attract, your hair clings to the balloon as you move it away from your head. But since like charges repel each other, your positively-charged strands separate from one another, producing that Bride-of-Frankenstein look.

Sparks sometimes fly when atoms rebalance themselves. When you rub your shoes on the carpet and then touch a metal doorknob, electrons make a tiny leap, with a spark and a zap.

In a list of materials that easily lose electrons, human skin and hair are near the top. So are glass, nylon, and wool. Materials that easily gain electrons include PVC plastic, silicon, and Teflon. While everyday static electricity is annoying, it’s also useful. Electrical attraction is what makes plastic wrap cling. And inside a Xerox machine, the attraction between a charged plastic drum and toner powder helps produce printed copies.

On the down side, static electricity can be dangerous at the gas pump. Gasoline vapors can ignite from sparks produced by sliding in and out of your car seat while the gas is pumping. Can’t avoid re-entering your car? Gas producers recommend touching metal on your vehicle, away from the pump, with your bare hand, to discharge the electron build-up.

Static electricity can even be hazardous on the Moon, where there aren’t any gas pumps in sight. For a few days each month, the Moon sweeps through the Earth’s magnetic field. During the pass, energetic electrons caught in the field strike the lunar surface, charging the moon dust. Much like static-y hair, charged moon dust can actually levitate. Scientists say that when astronauts next visit the Moon, projected to occur in 2020, dust could clog equipment, and sparks could damage delicate electronics.

For more on static electricity, visit www.sciencemadesimple.com/static.html. Rub a balloon on your head and make a soda can race across the room?  See how at www.exploratorium.edu/science_explorer/roller.html.

Have you ever climbed into a cast-iron tub before it’s filled, and touched your bare back to the metal? Even in a warm room, the tub will make you flinch. Or stepped barefoot on marble tiles after walking across a carpet? Common sense tells you that the carpet and the marble are probably at the same temperature. But your bare feet, acting as a handy thermometer, tell a different story: The marble feels much cooler.

While your skin may not be the most accurate thermometer, it is sensing a real difference between materials. It all comes down to the movement of heat between one object and another.

While heat and temperature are related, they’re actually two different things. Temperature measures the average amount molecules are moving in a substance, or their average kinetic energy. Heat is the energy a substance has because of the energy of all of its molecules. So while a mug and a bathtub full of water may be at the same temperature—say, 100 degrees F.—the big tub of water has much more stored heat.

Put two objects of different temperatures together, and heat energy will be transferred from hotter object to cooler. Pour boiling water into a room-temperature mug, and the mug warms up, even as the water loses heat energy. Eventually, both will reach the same temperature.

What does all this have to do with objects around the house that feel oddly cool (or strangely warm) to the touch? Your body, a substantial reservoir of heat energy, maintains a temperature of about 98.6 degrees F. So your own temperature is, on average, more than 20 degrees higher than that of the room air’s air and the objects in it. Making you a walking, talking oven.

As we’ve seen, heat flows from a hotter object to a cooler object. Which is why we bundle up in winter, to help the body maintain its nearly 100-degree internal temperature even in frigid 15-degree air.

So when you touch an object at 72 degrees—say, your wooden desk—you are transferring heat energy from your very warm fingertips to the cooler wood. As they gain energy, molecules in the wood begin moving more energetically. And as heat energy is transferred from your hand at the point of contact, the temperature in you fingertips drop, and your skin senses coolness. (But since your body’s metabolic furnace works hard to maintain your high temperature, you and your desk will never reach temperature equilibrium.)

Why does metal (and marble) feel extra-cool? Different materials conduct heat energy more or less easily. Metal is an especially good conductor of heat, losing and gaining heat quickly. So when you touch a metal cake pan at room temperature, heat flows swiftly from your hand into the pan. With the quicker, steeper drop in your fingertip temperature, you sense that the pan is cooler than, say, your wooden desk. Besides wood, other slow heat conductors, like carpeting and clothing, also feel warmer to the touch.

Sniff sniff sniff. You can actually see a dog’s nose hard at work, picking up a scent wafting through the air, following the invisible trail a rabbit left in the yard, or investigating your pants leg for evidence of a secret meeting with a cat.

No one knows for sure how much more scent-sensitive dogs are than humans: A thousand times? Ten thousand? But what is known is that a dog’s nose has many more odor receptors, and an olfactory (smell) center that takes up much more room in the brain.

Human beings have about 5 million odor receptors, while dogs, depending on the breed, may have more than 220 million. The small human nose devotes only a postage stamp-sized area to odor receptors. The average dog nose has a mucous-y scent receptor area which, if spread out, would cover a Kleenex tissue. A dog’s nose—moist on the outside, as well as the inside—acts as a magnet to scent molecules in the air and on the ground.

Sniffing—a string of quick inhales and exhales—helps a dog rapidly identify a scent. Each deliberate sniff widens the dog’s nostrils, allowing him to pull in more scent-laden air. According to researchers, a sniff also temporarily straightens the dog’s nasal cavity, allowing odor molecules to proceed directly to receptors deeper in the nose. The contact between molecules and receptors generates nerve impulses, which travel along the olfactory nerves to the brain’s huge smell center. Presto: Scent decoded.

(Meanwhile, Jacobson’s organ, a special chamber above the roof of a dog’s mouth, has its own scent receptors. These transmit nerve impulses to the brain’s hypothalamus, an area associated with social and mating behavior.)

The average dog’s ability to detect a few scent molecules in a trillion others has created a whole industry built on canine noses. Dogs sniff for hidden drugs in cars and planes, follow the trails of hikers missing in the woods, and find the remains of people in the rubble left behind by earthquakes and bombings. Now, scientists are testing the ability of dogs to detect the distinctive smell markers of various cancers.

So far, it seems that dogs are good at detecting melanoma, the deadliest skin cancer. Dogs have also been trained to detect the waste products of lung and breast cancer cells, simply by sniffing a patient’s breath. And some dogs can identify people with bladder or prostate cancer, by picking up on odors in urine. Dogs trained to detect certain cancers, scientists say, might someday help screen whole villages of people in remote areas without easy access to lab tests.

A dog’s sensitivity to scents can even be used to calm her down, in a kind of canine aromatherapy. Researchers in Northern Ireland found that dogs riding in a car filled with the odor of lavender spent more time sitting quietly, less time racing from window to window and yapping in the driver’s ear.

To watch a dog’s nose at work, visit www.sciencentral.com/articles/view.php3?article_id=218391249&cat=3_3.