Why do dogs always put out their tongues and pant?

Q Why are the aborigines of America called Red Indians and not Red Americans?-- Appoorva Naravan Shenvi, MumbaiAs you might have read in you...

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Q Why are the aborigines of America called Red Indians and not Red Americans?

— Appoorva Naravan Shenvi, Mumbai

As you might have read in your textbooks, Columbus had set out to find a western route to India. When he reached Central America, he thought he had reached India. Hence, the local people were referred to as Indians. When these people went to war, they often applied red paint on their bodies and hence, the word Red Indians.

But now no one refers to these peoples as Red Indians. They are called American Indians. Yes, the name Indian has remained stuck to them.

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Q How do the small intestine and the large intestine help in the digestion of food?

— Vikram B Deshmukh, Nasik

You will be surprised to learn that the small intestine is about 7 mt (23 ft) long. The digestion begins in the mouth with the saliva acting on the carbohydrates. A tiny gland in the stomach secretes gastric juices which helps digest the food. But most of the digestion takes place in the smallintestine. The liver, pancreas and many tiny glands in the intestinal wall pour secretions into the food here. The digested food passes through it in two or three hours. The large intestine is about one-and-a-half mt long but is about six cm wide. This is a clearing house for waste material in the food. The chyme coming down from the small intestine into the large intestine is liquid, when it enters the large intestine. Here the water is absorbed and the matter that passes from here into the anus is semi-solid.

Q Why do dogs always put out their tongue and pant?

— P Vinay, Borivli (west)

Observe carefully. Dogs do not put out their tongues all the time. It is only in summer or after running fast that they put their tongues out.

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Human beings have sweat glands in the pores of their skin. After the sweat evaporates, it takes away a lot of heat, from our body, as the latent heat of vapourisation. The dogs have no such sweat glands in their skin. If they feel warm, they try to cool down thebody temperature by putting out their tongues and permitting the moisture in their tongues to evaporate.

Q Why do some people have black moles on their body?

— Prashant & Pradnya Joshi, Nasik

Q Why are most foreigners very fair?

— Ganesh Iyer, Navi Mumbai

The colour of the human skin is due to pigments in the colour cells called chromatophores. Red coloured chromatophores are called erythrophores. Black coloured chormatophores are called melanophores. The dark-coloured melanophores contain a pigment called melanin. People living in Africa develop a dark colour because of dense melanophores — which contain the melanin pigment — in their skin. This protects them from ultraviolet rays of the sun. People of North America and Europe have a fair skin. The sun does not shine brightly in those areas; so, they don’t need the extra protection. Sometimes the melanophore cells get crowded at certain point. This is how black moles are formed.