How Come?

Archive for the ‘human body’ Category

People say that if you go outside in cold weather without a jacket, you will “catch a cold.”  Assuming that is true, how come?  I always thought you “catch a cold” by coming into contact with a virus, writes Michael Green, of Seaford, NY.

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.

How come humans can’t use sonar in the dark, like bats?  asks Kevin Guan, via email.

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.