My Science School

Humans have 2,000,000 to 5,000,000 eccrine sweat glands, with an average distribution of 150 to 340 per square centimetre. They are most numerous on the palms and soles and then, in decreasing order, on the head, trunk, and extremities. Some individuals have more glands than others, but there is no difference in number between men and women.

The specific function of sweat glands is to secrete water upon the surface so that it can cool the skin when it evaporates. The purpose of the glands on the palms and soles, however, is to keep these surfaces damp, to prevent flaking or hardening of the horny layer, and thus to maintain tactile sensibility. A dry hand does not grip well and is minimally sensitive.

The glands on the palms and soles develop at about 3 1/2 months of gestation, whereas those in the hairy skin are the last skin organs to take shape, appearing at five to 5 1/2 months, when all the other structures are already formed. This separation of events over time may represent a fundamental difference in the evolutionary history of the two types of glands. Those on palms and soles, which appear first and are present in all but the hooved mammals, may be more ancient; those in the hairy skin, which respond to thermal stimuli, may be more recent organs.

 

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Gustatory sweating is sweating that occurs on the forehead, scalp, neck, and upper lip while eating, talking, or thinking about food.

Gustatory sweating can occur for no apparent reason or as a result of an underlying condition, such as diabetes or Parkinson’s disease. These diseases can also cause damage to the nerves in the mouth. When the nerves become injured, they can become confused and cause sweating.

Gustatory sweating may cause some people distress, as thinking about food can trigger the reactions of sweating. Since there is often an underlying cause, a person should talk to their doctor to find out what may be causing the sweating.

People do not necessarily need to see a doctor after sweating from eating food. Those who only sweat while eating either very hot or spicy foods have no reason to be concerned.

Some people who experience Frey’s syndrome may consider it to be a nuisance but do not consider it significant enough to seek help.

 

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A body has between two and four million sweat glands lying deep in the skin. They are connected to the surface by coiled tubes called ducts. You perspire constantly, even without exercise. Sweat is a liquid made from 99% water and 1% salt and fat. Up to a quart of sweat evaporates each day.

When your body becomes overheated, you sweat more. The evaporation of sweat from your skin cools your body down.

When you're frightened or nervous (imagine being pinned under heavy weights) you also sweat more. Your palms and forehead begin to sweat. So do the soles of your feet and your armpits. These are sites where sweat glands are most abundant.

So why do you smell when you sweat? You may notice the smell mostly comes from our pits (hence why we put deodorant there). This is because the apocrine glands produce the bacteria that break down our sweat into “scented” fatty acids.

“Apocrine sweat by itself does not have an odor, but when the bacteria that lives on our skin mixes with apocrine secretions, it can produce a foul-smelling odor,” Haimovic says.

 

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Perspiration, also known as sweating, is the production of fluids secreted by the sweat glands in the skin of mammals.

Two types of sweat glands can be found in humans: eccrine glands and apocrine glands. The eccrine sweat glands are distributed over much of the body and are responsible for secreting the watery, brackish sweat most often triggered by excessive body temperature. The apocrine sweat glands are restricted to the armpits and a few other areas of the body and produce an odorless, oily, opaque secretion which then gains its characteristic odor from bacterial decomposition.

Sweat contributes to body odor when it is metabolized by bacteria on the skin. Medications that are used for other treatments and diet also affect odor. Some medical conditions, such as kidney failure and diabetic ketoacidosis, can also affect sweat odor. Areas that produce excessive sweat usually appear pink or white, but, in severe cases, may appear cracked, scaly, and soft.

 

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You know that all birds have feathers. Some feathers are quite beautiful. But what are feathers for? Feathers help most birds to fly, but they are important for other reasons, too.

In cold weather, a bird’s feathers make a warm winter coat. The bird fluffs up its feathers to keep its body warm. For some birds, waterproof feathers act like a raincoat. These birds can swim and dive without getting too wet and sinking.

The colours of feathers can be important, too. Bright colours help some birds attract mates. Other colours make birds blend in with their habitat so they are hard to see. Then hungry enemies won’t notice them.

All birds have wings. Wings are for flying, of course, and most birds can fly.

A bird’s wings are thin and very light. They are nothing but a few little bones and small muscles covered with thin skin and feathers.

Bird wings aren’t all the same, however. The kind of wings a bird has depends mainly on the bird’s way of life.

Inside an egg, a tiny baby bird is curled up in a ball. Its head is bigger than its body. Its eyes are closed. All the food it needs is inside the egg. The baby bird has grown so much that it fills up the egg. It is ready to hatch.

The baby bird begins to move inside the egg. The eggshell cracks, the crack grows bigger, and bits of the shell fall off. Soon there is a big hole. The baby bird wiggles through the hole. A new life has begun.

When some kinds of birds hatch, they are helpless. Their eyes are still closed and they have no feathers. They can’t stand on their tiny, weak legs. Birds such as robins and nuthatches are helpless for weeks after they hatch. They need their mothers to feed them and keep them warm. But other kinds of birds can see, walk, and hunt for food soon after they hatch, even though they cannot fly yet. Two days after hatching, a duckling can run, swim, and find food.

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It’s springtime. A bird flies by with a piece of red string in its mouth. Soon it flies by again with a twig. What is it doing? The bird is getting ready to build its nest. The nest is where the mother bird will lay her eggs. After the chicks hatch, they will stay in the nest until they grow up.

Different kinds of birds build different kinds of nests. Many birds make nests in trees. Some of these are layers of twigs piled together. Others are like bowls made of mud and grass. Nests can also be holes in tree trunks, or hanging pouches or sacs made of woven twigs and grass.

Some water birds make nests that float on water. They make the nests out of weeds and sticks and fasten them to rushes.

Some birds don’t make nests at all. Some sea birds lay their eggs on a ledge on the side of a cliff. Other birds lay their eggs in holes in the ground. And some birds lay their eggs in the nests of other birds.

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Not its wings. Some other animals have wings, too.

Not its bill. Some other animals have bills, too.

Not its eggs. Many other animals lay eggs.

Not the fact that it can fly. Some birds can’t fly.

Give up?

Feathers! All birds have feathers. In fact, birds are the only animals that have feathers.

So if it has feathers, it’s a bird!

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The Largest Mammals

A humpback whale swims near the top of the water. From time to time, it comes up for fresh air, filling its lungs. Then the whale dives down again. A few minutes later, it surfaces once more, and whoosh! the whale blows used air through the blowhole on top of its head. It breathes in again and dives.

Whales live in the water and look like fish, but they are really mammals. They are warm-blooded and feed their babies with mother’s milk. They don’t have gills like fish - they have lungs. That’s why they must come to the surface for air.

Big whales eat big things, right? Well, not all whales do. The throats of many whales are too small to swallow anything bigger than an orange! And many whales have no teeth. Baleen whales, such as right whales, gray whales, and rorquals, strain food from the water through hundreds of thin plates in their mouths. These whales eat plankton, which is made up of tiny plants and animals.

Toothed whales include sperm whales, belugas, and narwhals; dolphins and porpoises; and killer whales. These whales are meat eaters. Favorite meals include squid, crabs, lobsters, sharks, cod, and skates.

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Mammals in the Sea

Most kinds of mammals live on land. But seals, whales, and a few other mammals live in the sea. They can stay underwater for a long time, but these mammals breathe air through their lungs. They rise above the water to breathe.

Whales look so much like fish that many people think they are fish. But they are mammals. They have hair, they are warm-blooded, and their babies drink mother’s milk. Dolphins and porpoises are small whales.

Seals, sea lions, and walruses are mammals that spend much of their time in the water and some time on land. When they come onto land, they waddle about on their fins.

Another group of sea mammals includes dugongs and manatees, which are sometimes called sea cows. These animals look a bit like walruses without tusks. Instead of hind flippers, each of these animals has a wide, flattened tail.

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Flying Mammals

Here they come! And seeing those black shapes flutter against the darkening sky could give you goose-bumps.

Bats are the only mammals that can fly. Their two leathery wings are supported by arm bones and spread-out finger bones. When bats are resting, their wings fold up like umbrellas.

Most bats live in caves, usually in large groups called colonies. But sometimes they live in barns, trees, or attics, where they hang upside down by their toes!

Bats are nocturnal animals. They sleep during the day and come out to eat at night. Some people think bats are blind, but they really have good eyesight. They have to find their food in the dark. They do this by squeaking as they fly. The squeaks bounce off objects, and the bats hear the echoes.

Most bats eat moths and other insects. Some bats eat only fruit. The famous vampire bat of South America drinks blood. It bites the skin of a sleeping animal with its teeth and then laps up the blood.

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Mammal Homes

The winter wind howls. Snow falls in thick flakes. Rain soaks the ground. Hungry animals prowl. Some mammals don’t need a house of any kind. Whales don’t. Neither do many mammals with hoofs, such as elk and moose.

Some mammals look for shelter only at night or when they are giving birth. Most monkeys, for example, sleep in trees. The elephant looks for a hidden spot in which to have her baby.

But some mammals make houses to keep out the sun, wind, snow - or other animals. A beaver’s house of branches and twigs is often built in a pond. The top of the house freezes in winter, keeping out the cold and the other animals. But the bottom of the house doesn’t freeze. The beaver can go in and out to get the food it has stored there. Every animal’s house is just right for the animal that lives in it.

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Babies in Pouches

A newborn kangaroo is smaller than a grown-up person’s thumb. A newborn koala is even smaller. A newborn opossum is smaller yet - no bigger than a bee.

How do such tiny creatures stay safe? After they are born, they spend months in a pouch on the mother’s body. They don’t even peek out. They just drink milk and grow.

            Then, for a while, they spend part of the day outside the pouch. But they jump back in again when something scares them.

Even after they leave the pouch, the babies stay close to the mother. An opossum rides on its mother’s back when she looks for food. A koala baby rides piggyback as its mother moves through the treetops eating eucalyptus leaves.

A kangaroo baby is called a joey. It outgrows its pouch at about 8 months old. Then it hops along beside its mother.

All these young are tiny and weak at first, but they grow into big, strong animals. A full-grown opossum is about as big as a cat. A full-grown koala is a bit larger. An adult kangaroo is nearly as tall as an adult person.

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Mammal Food

The newborn lion cub is hungry. It pushes its way past all its brothers and sisters. Latching onto its mother’s nipple, it drinks her warm, sweet milk.

As the lion cub grows, its jaws become strong. Its baby teeth fall out, and stronger, sharper teeth grow in. The lion cub learns to bite and tear and gnaw and chew. Now it needs more than milk when it is hungry. It needs meat.

Some young animals just follow their mother around and eat whatever she eats. But others need to be taught how to eat grown-up food.

The lion cub follows its mother when she hunts. She lets it play with the animal she has killed. The cub tastes the meat. The young lion finds it likes this kind of food.

Every baby mammal drinks milk for awhile after it is born. But mammals learn to eat the kind of food their parents eat.

Baby antelopes, horses, cows, elephants, and giraffes grow up to eat plants. Lion cubs, wolf pups, and baby walruses grow up to eat other animals. Bears row up to eat both plants and animals. But they all started out drinking mother’s milk.

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Animals Can Be Your Friend

When you think of pets, what do you think of? Many people think of dogs, cats, birds, hamsters, or fish. Other people think of snakes, insects, monkeys, pigs, or even llamas. Still others think of tarantulas or iguanas.

All around the world, people love animals as pets. In Japan, children train pet mice to dance, and some people keep pet jellyfish. Mongooses are common pets in India. Large sea birds called cormorants are popular pets in China.

What kind of pet is right for you? Kittens and puppies are fun to play with. Birds and fish are fun to watch. Cats, fish, and snakes are quiet pets.

Dogs and birds can be quite noisy, but they can be trained to do tricks. If you want an unusual pet, how about a hedgehog, a tropical fish, or a mouse?

Getting a new pet is fun and exciting. But remember—your pet probably will be with you as long as it lives. So will your responsibility to your pet! Make sure that you and your pet are a perfect match.

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