Why are some insects attracted towards light?

Generally animals and plants are attracted towards light. This tendency is termed phototropism or phototaxis. Animals which towards the source of light are known as positively phototropic and others that shun light are called negatively phototropic. Most of the insects are positively phototropic but the degree of attraction differs. And some are negatively phototropic. Bed bug shows negative phototropism. Mosquitoes shun intense light, but in dim light they display positive phototropism. This behaviour differs in different species of insects with the exhibition of the following traits.

Insects without eyes also exhibit phototropism. The photosensitivity is distributed or diffused throughout the dorsal surface of insects so photo stimulation can occur even if the insect does not possess any eyes. Some insects are more sensitive to light rays. Their surface cells and eyes are more refined to perceive and follow light sources.

Some are attracted towards yellow light and some towards mercury light etc. Well illuminated areas are used as mating grounds by male insects, full of matured sperms and females with matured eggs.

Why don't we have hair on our palms?

In humans hair is present in the skin of nearly every part of the body excepting the palms of hands, the soles of the feet, the flexor surface of the digits. The structural components of the skin alone decide the generation of the appendages of the skin. Structurally the skin has two layers: the Epidermis and Dermis. Among these two layers, the epidermis has a high capacity for regeneration after damage. It continually replaces the outer dead cells and also generated the appendages of the skin, like hairs, nails, sweat and sebaceous glands.

In the two parts of the hair, namely the root and shaft, the root is the structure which emerges first during development and is called the hair follicle. It is set in between the epidermis and the superficial part of the dermis. Each hair follicle commences on the surface of the skin with a funnel shaped opening. From this opening the follicle passes inwards in an oblique or curved direction.

As the deep end of each hair follicle there is a small conical vascular eminence called papilla, which is continuous with the dermal layer of the skin. The capillaries of the papilla provide nutrients to the hair.

When any one of the layers of epidermis and dermis gets abnormal development it affects the formation of the hair follicle and also becomes an unfit layer to support the hair.

For example, in the skin of palm and soles the stratum cornium of the keratinization zone of epidermis and reticular layer of dermis are comparatively thicker than in the skin of other parts of our body.

Such a thick keratinization zone will not allow the formation of hair follicles and the thick dermis is not the ideal structure to support the germinal matrix of the hair follicles. That is why hairs do not grow on our palm of the hands and the soles of the feet.

Ants do not get hurt when they fall. Why?

The fall of a body is controlled mainly by gravitational attraction of the Earth. The gravitational force depends on the mass of the falling object-a heavier object is attracted more than a lighter object. This attractive force is opposed by an upward thrust (resistance) offered by air on the body. This resistance also depends on the surface area of the object. That is, if the surface area is more, the resistance is also more. Thus in any falling object, these two forces compete with each other.

In the case of an ant, the force of gravity is almost balanced by air resistance and so it is able to land safely. If there is a wind blowing, ants also float away. However, if a cluster of ants or a big ant is forcibly hurled to the ground, they will get hurt. Anyway, it will be difficult to know whether the ant gets hurt or not.

Why does our hair change its colour as we age?

Hairs are the appendages of the skin generated from the epidermal layer. Hair is made up of Keratin, a highly insoluble and mechanically stable fibrous protein. This Keratin is not only found in hairs but also in the skin. Actually Keratin is produced from the Keratinisation zone of the epidermis, which is the outer most layer of the skin. In the skin it provides water proofing quality.

The Keratin is generally pigmented. It is intensively pigmented in the hair. The dark black colour of the hair is due to the presence of high concentration of melanin pigments in it. The skin colour is also due to the presence of this pigment in the keratinocytes.

The Keratin gets its melanin pigments from melanocytes, which are found in the inner layer of the epidermis, which is found just beneath the keratinizing layer. The melanocytes have lond processes which extent between and under the cells of the epidermis. The melanin granules formed in the melanocytes pass along their branches and are secreted at their tips. The granules are subsequently engulfed by the keratinocytes, which make up 90 percent of the epidermal cells.

Melanin is a protein like polymer of the amino acid tyrocin. In its biosynthesis tyrocin is converted in to dihydroxy phenyl alanine (DHPA) by oxidative enzymes amongst which tyrocin is particularly important. Then a series of reactions take place during which polymerisaton occurs to form the final melanoprotein.

The hair grows only from the keratinocytes of the germinal matrix of the hair follicle. This germinal matrix lies in the proximal enlargement of the root hair, called the hair bulb. The hair shaft, which projects from the surface, consists of an inner medulla, an intermediate cortex and an outer cuticle. All these parts are made up of cornified cells.

The medulla is composed of polyhedral cells; the cortex consists of elongated cells with inner lumen. These cells are united to form flattened fusiform fibers. The lumens of these cells contain pigmented granules in dark hair and air space in white hair.

The development of white hairs because of the absence of melanin pigments, may be due to the absence of one or more enzymes, necessary for the DHPA path way. It will lead to the failure of melanin accumulation in the keratinocytes, found in the hair bulb, from which hair is growing.

Usually such physiological disorder occurs in the old age, which results in the growing of gray and white hairs in the body.

Why do our arms move to and fro when we walk?

To keep our torsos stable and conserve energy, we swing our arms backwards and forwards while walking. When you swing, say, your right leg forward to take a step, you provide a rotational moment about the central vertical axis of your torso. By the principle of conservation of angular momentum, an opposite reactionary moment is felt by your torso. By swinging your right arm backwards and your left arm forwards, you counterbalance this moment. Just try running without swinging your arms at all. Or worst still, try running while swinging your arms in the opposite directions to normal: that is: swing your left arm forward when you swing your left leg forward and so on. You will find that your torso rotates from side to side in an uncomfortable and unnatural manner.

Of course, legs are heavier than arms, so as to ensure that the moments are the same, evolution has ensured that our arms are further from the central axis of our bodies than our legs are. This allows the moments from our legs and our arms to be roughly equal.

Two-legged walking animals balance themselves by synchronising the movement of the backbone to the side of the leg that stays in contact with the ground. This keeps their gravitational centre close to the standing leg. It is seen in chicken and, to better effect, in penguins.

Why do runners run in anti-clockwise direction?

As the heart is on the left side, for humans and animals, running anticlockwise makes the centrifugal force in the body to act from left to right. Whereas it is from right to left for clockwise running.

Superior venecava ( the principal vein carrying blood to the heart) takes blood to the heart aided by heart suction. This vein carries blood from left to right.

Centrifugal force due to anticlockwise running helps this suction. If we run clockwise, the centrifugal force impedes suction. That is why, in olden days, health officers ensured that all carnival merry-go-rounds were run only in the anti-clockwise direction.

Racing tracks, animal shows in circuses, bullock-drawn pelton wheels, all mostly have only left turns. Stairways in temple towers have only left turns for going up. Clockwise running tires people, especially, children, easily.

Why do we blink our eyes?

The objective of blinking of our eyelids is to keep the front of the eyeball clean. Blinking is done by means of muscles in the eye lids and the cleansing by tears. The tears are secreted in a little gland and carried along to the eye and when our eyelids open and close, the tears are poured over the front of the eye and they wash away any particles of dust or any other harmful substances.

Some animals like the snake for example, do not have eyelids and hence cannot blink. But there is a hard film or scale over the eyes to protect them from dust and injury.

Why are water drops spherical?

Liquid drops tend to be in a state of minimum surface energy which is directly related to the surface area. The force, surface tension, which is trying to hold the droplet together, therefore tries to reduce the surface area of the drop. Mathematically only a sphere has the smallest surface area for a given volume, compared to other geometric shapes. Hence, in the absence of external forces, liquid drops tend to be spherical.

How does antidandruff shampoo work?

Dandruff is thought to be caused by overgrowth of yeast such as Pityrosporum ovale which live on normal skin. This overgrowth causes local irritation resulting in hyperproliferation of the cells (keratinocytes) forming the outer layer of the skin. These form scales which accumulate and are shed as dandruff flakes.

Antidandruff shampoos work by three mechanisms. Ingredients such as coal tar are antikeratostatic and they inhibit keratinocyte cell division. Detergents in the shampoo are keratolytic: they break up accumulation of scale. Finally, antifugal agents such as ketoconazole inhibit growth of the yeast itself. Other components such as selenium sulphide also inhibit yeast growth and therefore scaling.

What is dandruff?

Dandruff is a condition of excessive scaliness of the scalp. There are two varieties - dry and greasy. In the dry variety, the scales are fine, thin, white or greyish, and dry or slightly greasy. Such type of hair lacks lusture. People with this type of hair will have mild to moderate itching. The scales will fall freely on the shoulders.

This dandruff will be more common in winter than in summer. It signifies exaggeration of normal exfoliation of the horny layer of the epidermis, It usually affects people with dry integument and scalp. Such people are rather reluctant to use oil, on their scalp. In the greasy variety both the scalp and the integument are oily. It diffuses all over the scalp. Later the condition also extends to other hairy regions. It may extend typically to the eyebrows, eyelids, beard and other regions. The basic defect in this case is over production and/or change in composition of the sebaceous secretion. Dandruff is common at puberty and it occurs due to endocrine disorders, familial predisposition, unbalanced diet and constipation. Effective treatments for these conditions are prescribed, in siddha medicine, based on commonly available plant products.

How are mummies made?

Mummies are embalmed bodies that have been preserved for thousands of years. The dead have been mummified with the help of good drying agents applied all over the body.

Drying agents are other materials were stuffed inside the body to maintain its shape after removing internal organs. The word mummy is derived from the Persian word mummia meaning bitumen because the black resin used for embalming the dead looked like bitumen.

Three techniques of mummification have been discovered by Greek historians. The methodology was the same in all three cases and the differences lie in the process of extraction of internal organs. Mummies belonging to 1570-1070 BC are still found to be in good condition.

Actually in the process of mummification embalmers removed all the internal organs except the heart and kidneys. The brain was removed through the nostril using a hook. They soaked them in natron (a mixture of salt, sodium bi-carbonate and sodium carbonate). It was then bandaged and kept in jars. The internal cavities were stuffed with linen bags of sawdust, natron bags, and resin coated materials.

The nostrils and eyes were stuffed with linen rolls. Cedar oil, natron and purgatives were then smeared were then smeared on the body to close the pores. After this, the body was wrapped in long sheets of fine linen. Toes, fingers and limbs were separately wrapped in long sheets of fine linen. Toes, fingers and limbs were separately wrapped and then the torso was wrapped up in several layers.

A mask revealing the external features, made of pliable linen treated with resin was fixed on the face. According to ancient texts, a complete treatment could take about 70 days. Though resin has burnt the skin of the dead body in many cases, the hairs were seen to be intact.

Why does boiling milk overflow but boiling water does not?

The major component of milk is water (83-87%). Its other constituents are protein (3.5%) , sugar (5%), and fat (4-7.4%). When heated, fat being lighter than water, floats as a creamy layer on the top and water vapor, in the form of steam bubbles, is trapped under it. Further heating results in the formation of more number of bubble. These bubbles expand and lift the creamy layer causing it to overflow. In the case of water, the steam bubbles break as they reach the surface.

Is there any significance in using gravel on railway tracks?

Yes. Gravel used on railway tracks is known as ballast. It is used to dissipate the vibration produced by trains traveling at high speeds. In effect, the gravel layer acts as a cushion and damps the vibrations so that they do not travel long distances. If the rails are laid on a solid base, these vibrations can travel long distances and lead to cracks on the base as well as on nearby buildings.

The ballast provides a foundation for the sleepers, distributes the pressure on to the formation and helps in diverting the rain water. In a typical ballast, voids constitute 20 to 30 percent of the volume.

How fast is the Earth moving through space?

The Earth is speeding like a top and like a merry-go-round horse on a carousel that is itself riding on a larger carousel, and the whole amusement park is moving through space.

The Earth rotates on its axis at about 460 meters per second at the equator. The speed of a trip around the Sun is about 30 km per second. Meanwhile, the solar system is in a more-or-less circular orbit around the center of the galaxy at an average velocity of about 220 kilometers a second, according to Facts on File Dictionary of Astronomy, and the galaxy is moving at about 19.4 kilometers a second, toward a point in the constellation Hercules called the solar apex. Some authorities believe that there is also a general drift by the Milky Way and some neighboring upper clusters towards the Southern Cross at a speed of more than a million miles an hour.

Why do we sneeze?

It is a reflex mechanism initiated by irritation of the nasal outer membrane (epithelium). The irritants stimulate pain fibers in the trigeminal nerve supplying the nasal epithelium, which transmit afferent nerve fibers (going towards) the medulla oblongata. Efferent (coming from) neve fibers from the medulla oblongata initiate a strong inspiratory effort where in about 2.5 litres of air is inspired. This is followed by strong contraction of the respiratory muscles (including abdominal muscles) building up a high intrapulmonary pressure of about 100 mm Hg. This leads to an explosive outflow of air at velocities reaching upto 965 km/hr.

How does a lie detector work?

Lie detector, also known as polygraph, is generally used during interrogation by police.

The instrument works by recording our physiological functions such as blood pressure, heartbeat, respiration and perspiration. A pneumograph tube is fastened around the subject's chest and a blood-pressure-pulse cuff is strapped around the arm. Psycho-galvanic skin reflex (electro-dermal response) and flow of current between different parts of the body are also measured.

Sensitive electrodes are used to pick up the impulses which are recorded on a moving graph paper. The parameters are recorded when a suspect answers questions put to him by an operator. The data is then used as a basis for deciding whether the person is lying or not.

While most of the questions asked are interrelated, some are included to improve the test's accuracy. The questions are usually answered in 'yes', 'no' mode only.

The modern polygraph was first constructed in 1921 by John A.Lagoon, a medical student at the University of California, along with a police officer. His instrument was capable of continuously recording blood pressure, pulse and respiration. As it recorded these conditions simultaneously it was called a polygraph. Though this has been in use since 1924, it has not developed into a complete fool-proof system and is yet to be accepted judicially.

Why does boiled water lose taste?

Naturally occurring water contains quite a few substances dissolved in it. For example, it contains gases such as oxygen and carbon dioxide, sulphates and carbonates of calcium and magnesium, and other elements such as iron depending on the nature of the soil. These constitutes impart not only taste but also hardness to the water. Due to boiling, the dissolved gases are released and hardness is removed. Insoluble carbonates and hydroxides are formed which get deposited on the surfaces and the bottom of the vessel as scales. Their separation from water deprives it of its taste.

What causes pimples in teenagers?

Clinically pimple is called acne vulgaris. It is a chronic inflammatory dermatosis affecting the hair follicle. It is universal in the middle-to-late teenage years affecting both males and females. Pimple in adolescents is believed to occur as a result of physiological hormonal variations and alterations in hair follicle maturation. Pimples may be induced by drugs containing hormones lime corticosteroids, testosterone, gonadotropins, contraceptives and chemicals like iodides and bromides. Occlusive conditions like heavy clothing and tropical climate are also responsible for acne vulgaris. Some families seem to be particularly affected by acne, suggesting a heritable factor.

It has also been found that bacterial lipases of Propioni bacterium acnes break down sebaccous glands in the surface of face, liberating oil containing highly irritating fatty acids. This results in earliest inflammatory phases of acne.

Pimples are divided into non-inflammatory and inflammatory although both may co-exist. Histologically the non-inflammatory and inflammatory although both may co-exist. Histologically the non-inflammatory pimple is an expanding mass of lipid and Keratin within the mid portion of the hair follicle. This results in the dilation of follicles and follicular epithelium and also sebaccous glands atrophy. Inflammatory pimples are characterised by erythematous papules, nadules and postules. In such inflammatory acne administration of antibiotics like tetracycline is advised. This inhibits the lipase production by bacteria and gives better relief.

The synthetic Vitamin A derivative namely B-cis retinoic acid has brought about remarkable clinical improvement in cases of severe acne.

Persons with pimples are advised to wash th e face twice a day with soap and hot water. Sunshine helps to clear pimples. They are also advised to drink a lot of water and get enough sleep.

Why does nose get blocked while crying?

When a person cries tear fluid is secreted by a lacrimal gland seen bulging the conjunctiva (muscous membrane covering the eyeball and lining the eyelids). This tear passes through numerous ducts into the conjunctive sac, aided by ocular muscle contraction. From there it reaches the lacrimal sac and through the lacrimal duct it is drained into the nasal cavity. (Lacrimal duct is an anatomical drainage canal which connects the corner of the eye to the lower surface of the nasal cavity.) When there is a sudden discharge of tear, as while crying, the fluid is pooled resulting in congestion.

Another interesting fact is that Nature has provided a flap valve at the terminal part of the canal to prevent tear fluid from being pushed back by air, while sneezing or blowing.

Why do wisdom teeth emerge later than other teeth?

Third molars or wisdom teeth usually do not appear until after the age of 17 because until there is not enough room in the jaw to allow their growth.

Sometimes, even in adulthood, there is not enough room for third molars, which is why many people have them removed. Indeed, only a minorities of the population have properly developed third molars in good alignment.

Can anyone throw some light on Bermuda Triangle?

Bermuda Triangle is a section of the Western Atlantic, off the southeast coast of the U.S, forming triangle extending from Bermuda in the north to southern Florida and then east to a point through the Bahama past puerto Rico to about 40 degrees west longitude and then back again to Bermuda.

In this mysterious place, a large number of planes and ships have vanished into thin air, most of them since 1945. Interestingle, of the thousands of lives lost in the past, not a single body or a piece of wreckage from the vanishing planes and ships have been found.

Many varied and imaginative explanations have been offered and seriously considered to account for the continuing disappearances and assumed (because no bodies have been recovered) fatalities.

These include sudden tidal waves caused by earthquakes, fireballs which explode the planes, attacks by sea monsters, a time-space warp leading to another dimension, electromagnetic or gravitational vortices which cause planes to crash and ships to lose themselves at sea, capture and kidnapping by flying or submarine UFOs (Unidentified Flying Objects) manned by entities from surviving cultures of antiquity, outer space, or the future looking for specimen of currently existing earth inhabitants.

One single common thread which unites them is the fact that ships and planes have completely vanished or that the ships have been found without their crews and passengers. While isolated mysteries of this nature could be explained by unusual circumstances or coincidences of weather and human error, so many of the Bermuda Triangle incidents have happened in clear weather, near to port, shore or landing base, that they seem unexplainable according to presently held concepts.

How is it that blind men have better listening and feeling capabilities? Is it true that if there is a handicap, other faculties work better?

Scientists have found that the brain is plastic - meaning, the brain can rewire itself. This has proved beneficial to the handicapped. For example blind people can learn to process touch signals from their fingertips using brain regions normally devoted to vision.

Researchers have demonstrated the process of brain rewiring using a technique called transcranial magnetic stimulation in which they apply a magnetic field to the skull and induce electric currents on the brain. They found that the visual cortex ( the part of the brain which handles signals from the eye) of a blind person's brain does not remain idle - other senses use it. In a typical experiment they asked ten blind and five sighted volunteers to identify Braille letters or raised Roman letters by touch. As they did so, the researchers used magnetic pulses to disrupt various regions of their brains. When they gave pulses to the visual cortex at the back of the head, the blind subjects felt extra dots or had trouble making out the Roman letters. The same stimulation had no effect on sighted readers. The researchers believe that blind people almost certainly use the visual cortex for hearing, tast and smell as well.

It is believed that this applies to persons having other types of impairment.

How to verify the purity of honey?

Honey is adulterated by way of adding jaggery syrup. To verify whether honey is pure, take a glass of water and pour one tablespoon of honey in it. Gently shake the glass ( Note: do not stir ). If the honey completely dissolved in water, it is adulterated. On the other hand if it stays as a mass, it is pure honey.

How does scratching stop itching?

Itching is the result of damage to cells in our skin. As a result of the damage, substances like histamine ( the amine that causes widening of blood vessels and plays a role in allergic phenomena) are set free and irritate the nerve fibres in the skin. These send signals, similar to pain signals, to the central nervous system.

One can compare the nerve fibres to telephone lines and the central nervous system to a switchboard. The switchboard routes incoming telephone calls, and makes sure that only one line at a time is connected with each telephone number. By occupying the line you can prevent others from having a conversation with the same number. Likewise, the itch message can be blocked by occupying the central nervous system with another signal, for example, the one generated by scratching, which is less irritating.

Why is there a peculiar smell after a shower (rain)?

The peculiar smell immediately after a shower is due to certain volatile chemical compounds released by a group of soil-inhabiting bacteria called streptomycetes.

Streptomycetes, grouped as actinomycetes, are abundant in dry warm soil, a million of them can be detected in a gram of the soil. They release compounds such as geosmin and 2 methyl isoborneol when wetted by rain water after a long dry spell. That is why we get the musty odour only after the first rain of the rainy season. The smell can be felt in newly ploughed lands also.

How do honey bees find their way back to their hives

Bees live in colonies called hives. Each colony has one queen bee, a few drones (males) and thousands of workers (females). The queen manipulates the behaviour of the workers through various pheromones. A successful forager bee communicates information about the source of food discovered by them to the others upon returning home. This they do by means of a round dance or a waggle dance.

During a round dance, the forager runs in small circles clockwise and anticlockwise, alternately. In the case of waggle dance the bee dance tracing a figure of eight. The round dance is performed if the food is within a short distance of say 100 m and the waggle dance, if the food is far away. The waggle dance is said to convey information on the distance between the colony and the food, the direction in which the food is located and the quantity is available. The dancer also carries the smell of the pollen and/or nectar that it recently came across.

Thus by this peculiar dance the bees find their way to the sources of food and the way back to the hive. This dance was first found by an Austrian zoologist Karl Von Frisch which got him the Nobel Prize in 1973.

How do certain beverages give a feeling of freshness?

Most of the beverages contain alkaloids which act as mild stimulants. Caffeine, for example, is found in coffee, tea, cocoa, milk chocolate and also in cola drinks. Tea has a trace of theophylline. Cocaine is found in cocoa products. These alkaloids are collectively referred to as methyl xanthines. They share a number pharmacological actions of much therapeutic interest: they relax, smoothen the muscles (notable bronchial muscle), and stimulate the central nervous system and cardiac muscle. They induce the kidneys to excrete more urine, stimulate mental activity, quicken the reflexes, increase vigilance and decrease motor reactions time in response to both visual and auditory stimuli. They increase stamina and reduce fatigue. They give the users a feeling of confidence and power. They even induce euphoria in some users. These stimulant effects are short lived: they last for about an hour. They are then subsequently followed by depression. Overdose or repeated use may lead to paranoia, psychosis or hallucinations.

Can a fridge, left open in a closed room, be used to cool the room?

No. Instead it will heat the room. Under normal circumstances, the heat from inside the fridge is taken out by the compressor and let out in the air behind the fridge. As a result, the space inside is cooled. If the fridge is kept open in a closed room, the chillness coming out through the front door of the fridge is canceled by the heated air coming from behind.

Apart from this, in any electrical appliance, a part of the electricity supplied is wasted as heat because of the principles of thermodynamics. This heat will raise the temperature of air inside the room.

How long can we survive without oxygen?

Humans can survive only for a few minutes without oxygen. This is because of the susceptibility of the brain cells. Though the brain is only about 2 percent of the body's weight, it consumes about 20 percent of the oxygen we breathe in.

Hence if oxygen supplied (by the blood) is stopped for a few minutes, the brain ceases its function resulting in death. We will lose consciousness in 8-10 seconds after the blood supply to the brain is cut.

Brain cells can survive for long periods without oxygen at very low temperatures, as oxygen consumption is reduced. This technique, induced hypothermia, is made use of during major surgeries. Other tissues can survive for long periods without oxygen and that is why it is possible to remove organs, from brain dead persons, for transplantation.

Why do moles form on the human body?

The scientific name of mole is Nevus. Medically the moles or nevi are instructive tumors of the skin. The term nevus denotes any congenital lesion of skin. Common acquired nevi are tan-to-brown, uniformly pigmented solid regions of elevated skin with well defined rounded borders. They are usually less than 6mm across. They are formed when single cells which are normally interspersed among basal Keratinocytes are transferred in to round to oval melanocytes called nevus cells that grow in aggregates or nests along the dermal-epidermal junction.

The nuclei of nevi cells are uniform and rounded, contain inconspicuous nucleoli and show little or no mitotic activity. The early developmental stage in nevi are called junctional nevi. When they grow in to underlying dermis as nests or cords of cells they are called compound nevi. When they are still further. Now they are called dermal nevi. Clinically, compound and dermal nevi are often more elevated than junctional nevi. Although nevi are common, their clinical and histological diversity necessitates thorough knowledge of their appearance and natural evolution. Otherwise they become confused with other skin conditions notably malignant melanoma (skin cancer tumor). There are numerous clinical and histological types of nevi. The following are important ones:

1. Congenital nevi: These are present at birth and are called acquired nevi.

2. Spindle and epithelioid cell nevi: They are red-pink nodules and contain large plump cells with pink blue cytoplasm.

3.Blue nevi: These are black blue nodules and are dendritic with heavily pigmented nevus cells.

4. Halo nevi: These are identical to ordinary acquired nevi but provided with lymphocytic infiltration surrounding nevus cells. So they have host immune response.

Is it true that a red flag agitates a bull?

It is generally believed that anything red makes a bull angry and causes it to attack. Therefore, the bull fighter has to have a bright red cape and use a red cloth.

The truth is that if the bull fighter had any other colored cloth he would be able to accomplish the same reaction from the bull. Bulls are color blind.

Many experiments were conducted where they used white cloth and got the bulls to behave in the same way as with the red cloth.

The reason is the movement of the cape and not the color of the cloth that brings about the reaction in the bull. Anything waved in front of a bull would excite it.

What is the black box (in planes) made of? Normally what does it do?

Black boxes which usually hold the clues to a plane's crash, are built strong enough to survive bomb blasts, violent impacts and intense fires. They measure approximately 4 by 6 by 8 inches and weigh about 30kg and are kept in a case which can withstand 30 minutes of 1100 degrees C at 50,000 (Btu's) British Thermal Units per square foot per hour.

They are actually orange in color and a very high quality heat resistant paint is used, so that they can be spotted easily even at dimly lit crash sites. They are always placed in the tail end of the flight.

The black box records voice and flight data. The cockpit voice recorder continuously collects data and retains a record of the most recent 30 minutes, the conversation between the pilot and the Ground Control Room.

The flight data recorder keeps a record of the most recent 25 hours of a plane's operating data, including altitude, air speed, vertical acceleration and heading.

Flight data are recorded either by magnetic tape or in solid-state memory. Modern data recorders can log more than 200 different parameters and transmit data either 64 times or 128 times a second. Thus when recovered from the airplane crash sites the black box helps to reconstruct a clear picture of the crash.