Category Kids Queries

Scientists have several ideas why humans can high-five each other instead of, say, high – four or high – six. One theory suggests four fingers and a thumb on each hand are the perfect number and length to grip objects firmly. (Another study suggests we can grasp most things with just our thumb and index finger if necessary; the other four fingers are spares.)

The process of evolution determined the most beneficial number of fingers and toes for our survival. Pandas, after all, have thumb like digits to help them grasp bamboo shoots, while some birds have quadruple digits for perching and tucking away during flight. Occasionally, babies are born with extra fingers and toes (a condition known as polydactyly), but those additional digits have never offered enough of an edge to survive to later generations. In other words, evolution determined that five fingers per hand are just right for humans.

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Your eyes are amazing machines, but it takes only one small imperfection in the shape of your cornea or the lens of cause fuzzy focusing. Doctors call these imperfections astigmatisms, and they’re often inherited from parents. Glasses and contact lenses (or corrective surgery) can fix the problem.

Glasses or contact lenses correct vision because they allow the eye to focus light in the right spot on the retina — the spot that produces the clearest image. Because everyone’s eyes are different, a pair of glasses that makes one person see wonderfully may look terribly blurry to someone else. You know this if you’ve ever tried on somebody else’s glasses!

If you need glasses or contact lenses, your doctor will write you a prescription. In this case, a prescription doesn’t mean medicine you’ll pick up at the drugstore. A vision prescription is a piece of paper with numbers on it. The people who will make your glasses for you need these numbers to create lenses that will correct the way your eye bends light. Remember, the target is right in the center of the retina.

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Humans blink automatically to flush away the stream of cleansing tears produced by ducts in the corners of our eyes. Adults blink about 15 times per minute, but our rate of blinking slows when we read (which is why our eyes tire after tackling a long book) or focus on a distant object. No matter how hard we try not to blink, the need to flush the eyes eventually trumps our willpower – as anyone who’s lost a staring contest will tell you.

Every time you blink, your eyelids spread a cocktail of oils and mucous secretions across the surface of the eye to keep your globes from drying out. Blinking also keeps eyes safe from potentially damaging stimuli, such as bright lights and foreign bodies like dust.

Scientists have found that the human brain has a talent for ignoring the momentary blackout. The very act of blinking suppresses activity in several areas of the brain responsible for detecting environmental changes, so that you experience the world as continuous.

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That depends on the kind of crying you’re talking about. Our eyes produce tears of three types…

Basal tears flow constantly to keep our eyes from drying out. Our bodies produce about five to ten ounces (148 to 295 ml) of basal tears each day.

Reflex tears protect our peepers from irritants in the air, such as smoke and dust.

Emotional tears flow when our brain registers sadness or stress, which triggers the release of body chemicals called hormones that turn on the waterworks. Some scientists believe that emotional tears help rid our body of bad chemicals that build up during stress – which is why you feel better after ‘’having a good cry’’. With the possible exceptions of elephants and gorillas, humans are the only animals that shed tears of this type.

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Because sea water contains about three times more salt than your tears. The higher concentration of salt can cause a mild stinging in your eyes even if you wear a mask.

There is a tiny amount of salt in your tears, but its minor compared to the amount of salt present in salt water. Your tears contain about 0.9% sodium chloride, while salt water in the ocean contains 3.5%! That means the oceans is almost four times saltier than tears.

Opening your eyes in a swimming pool exposes them to dirt and other debris that might be floating in the water that could cause an irritation of the eye. It also exposes them to germs and to other bacteria in the water that could cause an eye infection.  A brief exposure to say, swim down and pick something up off the bottom of the pool is probably not going to be harmful, if the water is clear and reasonably well-maintained.

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Sodium chloride – the most common type of salt – is in all your body’s fluids: blood, sweat, and (yep) tears. Your tears contain a little less than one percent salt.

Tears contain greater quantities of water along with other organic and inorganic chemical components like mucin, lipids, lysozyme, lactoferrin, lipocalin, lacritin, sodium and potassium. The salinity of tears is attributed to the presence of salts of sodium and potassium.

This salinity of tears along with the presence of enzymes like lysozyme is responsible for their antimicrobial activity. Basal tears have a salt content similar to blood plasma. The salinity of basal tears disturbs the osmotic balance of bacteria and keeps the cornea in a healthy microbial-free environment. The mineral content of tears also nourishes the tissues associated with eyes. Saline nature of tears also indicates our evolutionary descent from marine organisms.

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