Current Affairs 12th Class

(1) Population density : Population density is the number of individuals present per unit area or volume at a given time. For instance, number of animal per square kilometer, number of trees per area in a forest, or number of plank tonic organism per cubic meter of water. If the total number of individuals is represents by letter N and the number of units of space by Letter S, the population density D can be obtained as \[D=N/S.\] Space is indicated in two dimensions \[({{m}^{2}})\] for land organisms, and in three dimensions \[({{m}^{3}})\] for aquatic organisms and for the organisms suspended in space. (2) Birth rate or Natality : The birth rate of a population refers to the average number of young ones produced  by birth, hatching or germination per unit time (usually per year). In the case of humans, it is commonly expressed as the number of births per 1000 individuals in the population per year. The maximum birth rate of a species can achieve under ideal environmental conditions is called potential natality. However, the actual birth rate under the existing conditions is much less. It is termed realised natality. (3) Death rate or mortality : The death rate of a population is the average number of individuals that die per unit time (usually per year). In humans it is commonly expressed as the number of death per 1000 persons in a population per year. Lowest death rate for a given species in most favourable conditions is called potential mortality, while the actual death rate being observed in existing conditions is called realized mortality. (4) Survivorship curve : The death rate of population can be easily represented by survivorship curve. In this curve time is plotted against number of survivors. There are three kind of survivorship curves. (i) Diagonal curve : If death rate of different age group organism are equal then the curve is represented or plotted as a straight line. Example : Hydra, mice and many adult birds. (ii) Convex curve : When organism completed their potential life spawn and died in old age then the curve is convex, the curves goes horizontal till potential life spawn and then decline rapidly. Example : Men, rabbit and many mammals. (iii) Concave curve : This kind of curve most found in such organism who die before their potential life spawn. Example : Fish, Oysters and Invertibrates.     (5) Vital index : The percentage ratio of natality over mortality is known as vital index i.e. natality / mortality \[\times 100.\] It determines the growth of a population. (6) Immigration : It is permanent entry of additional person into the existing population of a country or region from out side. Example; Many Nepalese and Chinese come to settle in India. (7) Emigration : It is the permanent departure of some persons from the existing population of a region to a different state or a foreign country. Example; Many Indians go to Western more...

Meaning : The regulation of conception by preventive methods or devices to limit the number of offspring  is called birth control. Methods : A variety of methods are known for birth control. The birth control methods which deliberately prevent fertilization are referred to as contraception. These methods are of 2 main types : temporary and permanent. (1) Temporary  Methods : These  are  further  of  many types : (i) Safe Period (Rhythm Methods) : A week before and a week after menses is considered the safe period for sexual intercourse. The idea is based on the following facts- (a) Ovulation occurs on about the 14th day (may be 13 th to 16th day) of menstruation. (b) Ovum survives for about 1-2 days. (c) Sperms remain alive for about 3 days. This method may reduce the chances of pregnancy by about 80 percent. However, a great care is needed in its use. Rhythm method is also called natural family planning. i.e., a few days before and a few days after ovulation. Changes in cervical mucus and body temperature during the menstrual cycle mark the ovulation time. Thus, the natural family planning requires adequate knowledge of these physiological signs. Some couples use the natural family planning method of increase the chances of conception so that unplanned pregnancies are avoided. (ii) Coitus Interruptus : This is the oldest method of birth control. It was in use over 2,000 years ago. It involves withdrawal of the penis from the vagina by the male before ejaculation so that semen is not deposited in the vagina and there is no fertilization. (iii) Spermicides : Foam, tablets, jellies, pastes and creams, if introduced into the vagina before sexual intercourse, adhere to the mucous membrane and immobilise and kill the sperms. These contain seprmicides such as lactic acid, citric acid, boric acid, potassium permanganate and Zinc sulphate. (iv) Mechanical Means : These are of 3 types : (a) Condom (Nirodh) is a thin sheath, usually made of rubber, to cover the erect penis. It is the most widely used contraceptive by males in India as it is cheap and easily available. It is given free also by government. It checks pregnancy by preventing deposition of semen in the vagina. Condom is also a safeguard against infection of AIDS and sexual diseases. (b) Diaphragm and cervical cap are dome-shaped rubber plastic covers that are fitted on the cervix in the female's vagina, and check the entry of sperms into the uterus. These must be kept fitted for at least six hours after sexual intercourse. They are smeared with a spermicidal jelly or cream each time they are used. The diapharm and cervical cap are the counterparts of condoms in the female (c) Intrauterine devices (IUDs) are plastic or metal object placed in the uterus by a doctor. These include loop, copper-T, spiral, ring, bow, shield, etc. They prevent the fertilization of the egg or implantation of the embryo. Their presence perhaps acts as a minor irritant and this makes the more...

Population growth refers to the increase in its size. It is determined by the number of individuals added to the population and the number of individuals lost from the population. Addition occurs by births and immigration. Loss results from deaths and emigration. If more individuals are added than are lost i.e., the vital index is more than 100, the population will increase or show positive growth. If more individuals are lost than are added i.e., the vital index is less than 100, the population will decrease or show negative growth.  If addition and loss are balanced, i.e., the vital index is 100, the population will become stationary or show zero growth. Malthus Theory of Human Population Growth : Thomas Malthus, a British political economist, put forward a theory of human population growth in 1778. Malthus in his "Essay on the principle of population" pointed out that population tends to increase in geometric progression while food supply increase only in arithmetic progression. Faster growth of population than of its requirements causes an imbalance between the two. When this imbalance reaches a certain limit, environmental factors like famine, epidemic of a disease, earth quake, flood, war etc reduce the population to a size, the available resources can support. The factors that control the population size were called positive checks by Malthus. Natural Control of Population Growth : Growth of a population is controlled by an interaction between three factors: biotic potential, environmental resistance and carrying capacity of environment. (1) Biotic or reproductive potential : Biotic potential is the natural capacity of a population to increase at its maximum rate under ideal environmental conditions and stable age and sex ratios. The biotic potential for all animals is very high. If unchecked, the numbers of any species will quickly over run the world. Biotic potential in the human female is estimated to be about 12 per female during its reproductive period between the puberty and the menopause period. (2) Environmental Resistance : In nature full biotic potential of an organism or population is never realized, since conditions are rarely ideal. Various harmful environmental (abiotic) factors like non-availability of food and shelter, natural calamities like drought, cloud bursts, floods, fires, temperature fluctuations, accidents, etc. and certain biotic factors like pathogens, parasites, predators etc. check the biotic potential from being realized. The sum of all these inhibitory factors is called environmental resistance. (3) Carrying capacity : It is defined as “Feeding capacity of an environment of  an ecosystem for a population of a species under provided set of conditions”. When a population reaches the carrying capacity of its environment, the population has zero growth rate. So the population generally stabilizes around the carrying capacity. The carrying capacity of the earth for human population is considered to be about 8 to15 billions. Carrying capacity of the environment for a population depends upon three major components : (i) Productive systems which produce food and fibre e.g. croplands, orchards, etc. (ii) Protective systems which buffer air and water cycles more...

Aim : It is a technique to determine : (1) Sex of the developing baby. (2) Genetically controlled congenital diseases. (3) Metabolic disorders in foetus. So amniocentesis is a pre-natal diagnostic technique. Procedure : It involves following steps : (1) Location of the foetus is determined by a technique called sonography (using high frequency ultrasound waves) to prevent accidental damage to the foetus. (2) A fine hollow needle is passed through the abdominal and uterine wall of a pregnant female (about 14th to 15th week after conception) into the amniotic cavity.     (3) A small amount of amniotic fluid is withdrawn. It contains foetal skin cells and a number of proteins, especially enzymes. The cells can be cultured in vitro for further examination.   Significance (1) Sex determination : The somatic cells of foetal skin drawn with the amniotic fluid are stained to determine the presence of sex chromatin (barr body). Presence of barr body indicates that the developing foetus in female as female is with 2 X-chromosomes out of which one X-chromosome is active, while other X-chromosome is heterochromatised into a darkly stained barr body. (2) Congential disease : By Karyotypic studies of somatic cells, abnormalities due to changes in chromosome number like Down's syndrome, Turner's syndrome, Klinefelter's syndrome etc. can be determined. (3) Metabolic disorder : By the enzyme analysis of amniotic fluid, different types of inborn metabolic disorders like phenylketonuria, alcaptonuria etc. can be detected. These inborn errors are caused by the absence or inactivity of specific enzymes due to gene mutations. So with the help of amniocentesis, if it is confirmed that the child is likely to suffer from some incurable, congenital defect, the mother can go for abortion. (4) Drawback : However, these days, the amniocentesis is being misused also. Mothers even get their normal foetus aborted if it is a female. This is just equivalent to killing of a normal child. So Govt. of India enforced the Pre-natal Diagnostic Techniques (Regulation and Prevention of Misuse) Act, 1994, since January 1, 1994 under which all genetic counselling centres and laboratories are required to apply for registration. The violation of this Act can bring a fine of Rs. 50,000 and imprisonment for two years. The doctor's registration is also cancelled till the complaint is disposed of. (5) Chorionic Villus Sampling (CVS) : Amniocentesis is possible without a chance of injuring the foetus with the needle only after the sixteenth week of pregnancy. At this time, abortion is not safe. A new technique, named Chorionic Villus Sampling (CVS), can be done during the eighth to tenth week of pregnancy when abortion is safe for the woman. For CVS, cells are sucked into a catheter passed through the cervix. CVS technique provides a mass of rapidly dividing foetal cells, thus facilitating the examination of chromosomal disorders.  

The environment is the aggregate of all those things and set of conditions which directly or indirectly influence not only the life of organisms but also the communities at a particular place. Any external force or influence, which surrounds and affects the life of a plant in any way, becomes a factor of its environment. These factors are called environmental factors and may be living (biotic) as well as non-living (abiotic). The abiotic factors affect the structure, life history, physiology and behaviour of organisms. The biotic factors mostly influence growth and reproduction. The environmental conditions which influence the life and development of plants, each part of the environment is called ecological factors. Ecological factors are grouped into four main classes (ecological factors) which are as follows : Climatic factors : The study of climatic factor is known as climatology. The chief climatic factors are : (1) Water : Rainfall is the chief source of soil moisture. Water exchange between earth surface and atmosphere is called hydrological cycle. Humidity of the air is expressed in terms of relative humidity. It is measured by hygrometer (Psychrometer). Epiphytes and cryoptogamic plants grow in those regions where relative humidity is high. (2) Light : Light (solar radiations) is a very important ecological factor as it is the source of energy to the whole biosphere. It enters the biosphere through the process of photosynthesis performed by green plants and other autotrophs. Here organic food is manufactured from inorganic raw materials. Solar energy is changed into chemical energy of food. The radiant energy of sunlight carries out all important functions, without this life except few bacteria would disappear. On this basis of relative light requirements and the effect of light on the overall vegetative development, plants are classified ecologically into following categories : (i) Heliophytes are popularly called sun plants because they grow in open in full sunlight. They possess a number of characteristics like. (ii) Sciophytes are shade plants which grow in areas having moderate to low intensity light, as below the shade of other plants. Optimum growth occurs with light of 10-30% of full sunlight. The plants grow in total darkness are called etiolated (Long, thin, weak and yellow in colours). (3) Temperature : Temperature influences every reaction and activity of organisms. Temperature shows daily as well as annual variations. The phenomenon of change of temperature between day and night and in different seasons of the year is called thermoperiodicity. It is of two types, diurnal (or daily) and seasonal (or annual). Thermoperiodicity determines periodical phenomena like seed germination, stem growth, flower formation, fruiting, dispersal, maturation of gonads, breeding, egg laying, etc. Low night temperature is suitable for seed germination in many plants, e.g., Rumex, Asclepias. Cooler nights also help in increasing size of tuber in Potato and fruit setting in Tomato. Organisms adapted to live at relatively constant temperature during the whole year are known as stenothermal, e.g., many palms, corals, snakes and some fishes. The organisms which can tolerate large changes of more...

Out of about 3,50,000 known plants at this time, a few i.e., about 100. Scientists are in search of less known and underutilized crop plants, which can be used for food and other purposes and thus exploitation of traditional plants can be reduced. Such under-utilized and under-exploited plants are known as new crops. Some of these new and underutilized crops are as follows : (1) Triticale : Triticale is the first man made cereal or crop,  which has been produced by intergeneric hybridization between common wheat (Triticum aestivum) and European rye (Secale cereale) with a view to combine characters of these two parent plants. Triticale is hexaploid, i.e, \[2n=6x=42\] (tetraploid Durum wheat × diploid Rye) or octaploid, i.e., \[2n=8x=56\] (hexaploid Bread wheat × diploid Rye). Triticale is the first new man-made plant to join the rank of cereals which have long evolutionary plants are being used for fulfilling man's daily requirements history. Triticale or triticosecale is not suitable for purpose of bread making due to low gluten content, but it is a good forge crop. Triticale is grown all over world, mainly in USSR. (2) Winged bean (Psophocarpus tetragonolobus family Leguminosae) : This is a herbaceous plant, which has capacity of nitrogen fixation. The tuberous roots, leaves, shoots, long pods with prominent wings and seeds are highly nutritious due to rich source of proteins and edible for humans as well as livestock. When green, the pods, leaves and shoots are used as vegetables, unripe seeds may be used as soups and ripe seeds can be roasted. The ripe seeds contain about 34% proteins and 18% oils (similar to soybean). Further this plant can be used as a green-manure plant, fodder plant and also as a cover crop. (3) Jojoba or Hohoba (Simmondsia chinensis) : This is a shrub, which is native of Mexican deserts. It is important drought desert plant, because it can survive under poor soil and low moisture conditions and hence is being grown in deserts. The seeds of this plant contain about 50% liquid wax, which is similar to sperm whale oil (spermaceti). This liquid wax was originally used in cosmetics, but now is also being used in high performance lubricants. (4) Guayule (= Wayule, Parthenium argentatum family Asteraceae) : It is commonly known as carrot grass or congress grass. This is native of America and nowadays it is most troublesome terrestrial weed in India and is present in almost all states of India. The roots of this plant secret transcinnamic acid, which inhibits the growth of other plants (allelopathy). This is a shrub and can grow on poor desert soils. This plant is nowadays used in obtaining rubber, which is called guayule rubber, which is similar to para rubber or hevea rubber. The body of this plant contains caotchouc granules, which are ingredient of rubber. The plant contains 12- 20% rubber on dry wt. basis. This plant can be a natural source of rubber in future. (5) Leucaena or Subabul/Loo-See-na/Loo-kee-na (Leucaena leucocephala family Leguminosae) : This more...

Study of use of living organisms and the substances produced due to their activities is called biotechnology. Mostly micro-organisms are used in many industries as alcohol, enzymes, vaccines, vitamins, antibiotics, organic acids, etc. So biotechnology is controlled use of microbes for benefit of human beings. In this science, principles of biochemistry, molecular biology and microbiology are mostly used. Some important examples of biotechnology products are : Alcohol : It is the result of yeast fermentation, which is the incomplete oxidation of complex organic compounds with the help of enzymes produced by yeast (Invertase and Zymase) \[\underset{(\text{Sucrose})}{\mathop{{{C}_{12}}{{H}_{22}}{{O}_{11}}}}\,+{{H}_{2}}O\underset{\text{Invertase}}{\mathop{\xrightarrow{\text{Yeast}}}}\,\underset{(\text{Glucose})}{\mathop{{{C}_{6}}{{H}_{12}}{{O}_{6}}}}\,+\underset{(\text{Fructose})}{\mathop{{{C}_{6}}{{H}_{12}}{{O}_{6}}}}\,\] \[{{C}_{6}}{{H}_{12}}{{O}_{6}}\underset{\text{Zymase}}{\mathop{\xrightarrow{\text{Yeast}}}}\,\underset{(\text{Ethyl}\,\text{alcohol})}{\mathop{2{{C}_{2}}{{H}_{5}}OH}}\,+2C{{O}_{2}}\] In the middle of the 19th century, Louis Pasteur reported that alcohol, beer and butter milk are the result of yeast fermentation. Yeast fermentation is the basis of baking as well as brewing industries, besides preparation of fermented foods like idli, dosa etc. Types of yeasts (1) Baker’s yeast : These include the selected strains of Saccharomyces cerevisiae and Torulopsis utilis grown on molasses. They are available in the form of powder or cakes. These yeasts have ability to ferment the sugar in the dough. The carbon dioxide produced during fermentation is responsible for the leavening (i.e., raising the dough). Both \[C{{O}_{2}}\] and alcohol escape during baking so that the bread and other baked products become porous and soft. The baker's yeast is manufactured by growing the 'stock' strain on molasses and then collected after centrifugation and washing. These are used to flavour the food, as nutrient ingredients, to ferment and raise dough in bread making (leavening agent). (2) Brewer’s yeast : Brewing industry produces alcoholic beverages of several types depending upon the fermenting agent and the medium. Fermenting agents are Saccharomyces cerevisiae, S. sake, S. ellipsoidens (wine yeast) and S. pireformis (ginger yeast) is a saprophytic unicellular ascomycetes fungus. Molasses is dark coloured syrup left after extraction of sugar. It still contains 30% sucrose and about 32% invert sugar (mixture of glucose and fructose). Some other common products of yeast fermentation are : Beer : It is produced from Hordeum vulgare (barley) malt and alcohol content is 4-8%. Wine : Produced from grapes by fermentation and alcohol content is 10-20%. Brandy : Produced by distillation of wine and alcohol content is 43-57%. Gin : Produced from fermented European rye, i.e., Secale cereale. Rum : Produced from molasses of sugarcane and alcohol content is 40%. Industrial production of alcohol : Although industrial fermentations to produce alcohol are performed almost exclusively with S. cerevisiae, the bacterium Zymomonas mobilis is a potentially useful organism for the commercial production of alcohol. Zymomonas can permit glucose, fructose and sucrose, thus producing relatively high yields of alcohol.  Organic acids : Microbes are useful in the manufacture of a number of organic acids as follows : (1) Acetic acid (Vinegar) : It is most important acid being produced by two step fermentation of sugarcane juice by yeast and Acetobacter aceti bacteria. \[{{C}_{6}}{{H}_{12}}{{O}_{6}}\underset{\text{Anaerobic}}{\mathop{\xrightarrow{\text{Yeast}}}}\,\underset{\text{(Ethyl}\,\text{alcohol)}}{\mathop{2{{C}_{2}}{{H}_{5}}OH+2C{{O}_{2}}}}\,\] \[{{C}_{2}}{{H}_{5}}OH+{{O}_{2}}\underset{Aerobic}{\mathop{\xrightarrow{Acetobacter\,aceti}}}\,\underset{\text{(Acetic}\,\text{acid)}}{\mathop{C{{H}_{3}}COOH+{{H}_{2}}O}}\,\] (2) Lactic acid : It was the first organic acid to be produced from microbial fermentation more...

Pacemakers (1) Pacemaker is a device that supplies electrical impulses to the heart to maintain the heartbeat at a regular rate. (2) The artificial pacemaker was introduced by Chardack in 1960. (3) Pacemakers are life saving when the normal heart rate 72-80 drops to abnormally low levels like \[30-40\] due to diseases.             (4) Pacemaker consists of a pulse generator and an electrode. (5) The pulse generator is hermetically sealed box; it contain lithium halide cells to provide power for over 10 years. (6) The electrode is a fine metallic spring ensheathed in a thin layer of biocompatible plastic; the special tip remains in contact with the interior of right ventricle. (7) An artificial pacemaker is implanted when a person's sinu-atrial node is not functioning properly. (8) Two basic types of pacemakers are fixed-rate and demand type. (9) Fixed-rate pacemaker discharges impulses at a steady rate, irrespective of the heart's activity. (10) Demand pace maker discharges impulses only when the heart-rate slows or a beat is missed. A normal heart-rate and beat suppresses the pacemaker.            (11) A pacemaker may be external (worn on belt) or internal (implanted in the chest). (12) There are two main types of implantation, transvenous implantation and epicardial implantation. (13) Modern pacemakers are comparatively insensitive to interference, but may be affected by powerful electromagnetic pulses. (14) Anyone fitted with a pacemaker should avoid powerful radio or radar transmitters and should not pass through security screens at airports. (15) Pacemakers are likely to be influenced by microwave ovens, electric shavers, automobile ignition and cellular phones.  

Major advancements in the medical sciences have been the development of new imaging techniques that provide detailed pictures of internal organs.        (1) X-rays (i) Following their discovery by Wilhelm Roentgen, a German physicist in 1895, X-ray became an important tool for medical diagnosis. (ii) X-ray are a form of electromagnetic radiation of extremely short wavelength. (iii)  When a beam of X-rays is directed at a part of the body such as chest, the rays are absorbed more by dense structures such as the ribs or heart muscles than by less dense structures such as the skin or lungs. (iv) This causes shadows of variable intensity to be cast on a photographic film. (v) X-rays cause no sensation when passed through body tissues. (vi) Large or frequent radiation doses may damage the skin and internal organs and may cause cancer in later life. (vii) The study of X-rays for detection and treatment of disease is called radiology. (viii) X-ray imaging in the simplest form is commonly employed for diagnosing diseases of the heart, lungs and detection of bone and joint injuries. (ix) Nowadays, the risk involved in having X-rays is extremely small; radiation doses are kept to a minimum.       (2) Computed Tomographic Scanning (CT) (i) CT scanning was developed by Godfrey Hounsfield of Britain in 1968 (Nobel Prize in 1979). (ii) This technique combines the use of X-rays with computer technology to produce a two or three-dimensional clear cross-sectioned image of an area. (iii)  Computed tomographic scanning is also known as CAT (Computed Axial Tomography). (iv) CT scanning provides clearer and more detailed information than X-rays. (v)  Another advantage of CT scanning is that it tends to minimize the amount of radiation exposure. (vi) CT scanning can be used to obtain images of any part of the body. (vii) CT scanning helps in the diagnosis of diseases of brain, spinal cord, chest and abdomen. (viii) This technique is also extremely useful in detecting tumour and monitoring the extent of their spread to surrounding tissues and organs.     (3) Positron Emission Tomographic Scanning (PET) (i) PET scanning was developed by Louis Sokoloff of USA in 1985. (ii)   PET is a diagnostic technique based on detection of positrons (positively charged electrons) emitted by radio isotopes such as carbon 11, nitrogen 13 or oxygen 15 generated by the cyclotron. (iii)  These radio isotopes are then incorporated by chemical methods into biological molecules such as glucose, amino acids, carbon dioxide and ammonia. (iv) These positron emitting compounds are injected into the blood-stream and are taken up in greater concentration by areas of tissues that are more metabolically active. (v)  PET scanning provides three- dimensional images that reflect the metabolic and chemical activity of tissues beings studied. (vi) PET scanning is particularly valuable for measurement of regional cerebral blood volume, blood flow, metabolic rates of glucose and oxygen in humans. (vii) PET scanning is used for detecting tumours, for locating the origin of epileptic activity within brain more...

(1) Sphygmomanometer   (i) Sphygmomanometer, commonly called B.P. Apparatus, is an instrument for measuring blood pressure. (ii) This instrument consists of a rubber cuff attached by a rubber tube to a compressible hand pump or bulb. (iii)  Another tube attaches to the cuff and to a column of mercury or pressure dial marked off in millimeters. (iv) Blood pressure is usually taken in the left brachial artery. (v) Blood pressure is recorded by giving the systolic pressure and diastolic pressure expressed as millimeters of mercury (mm Hg). (vi) A healthy young adult male has blood pressure reading of about 120/80 (i.e. 120 mm Hg systolic and 80 mm Hg diastolic). (vii) The difference between systolic and diastolic pressure is called Pulse pressure. (viii) Blood pressure often rises normally with age to about 130/90 at age 60. (ix) Abnormally high blood pressure is known medically as hypertension; abnormally low blood pressure is termed hypotension. (2) Electrocardiograph (i) The abbreviation ECG stands for electrocardiogram, a record of myoelectrical changes that immediately precede contraction of heart muscle. (ii) Electrocardiograph is the instrument used to record ECG. (iii)  Leads from this instrument are attached to the chest, wrists and ankles using conducting jelly. (iv) The waves produced in ECG are known as P, Q, R, S and T. (v) An ECG is helpful for diagnosing pathological disorders of the heart like coronary artery disease, coronary thrombosis, pericarditis, cardiomyopathy and myocarditis.

• Multi-channel monitors measure and display the ECG, blood pressure in various heart chambers and other physiological data.
• Echocardiography is a method of obtaining an image of the structure of heart using ultrasound.
• Doppler echocardiography is a technique which allows the indirect measurement of the flow of velocity as it passes through the heart.

    (3) Electroencephalograph (i) The electrical activity of the exposed animal brain was discovered by Satton in 1875. (ii) Hans Berger (1929) was the first to record Electro-Encephalo-Gram (EEG). (iii)  Electroencephalography is done by attaching a number of small electrodes to the scalp. (iv) The electrodes are connected to an instrument that measures the brain's impulses in microvolts and amplifies them for recording purposes. (v) Electroencephalography is painless, produces no side-effects and to record it takes about 45 minutes. (vi) An EEG records the minute electrical impulses produced by the activity of brain. (vii) EEG is useful to find out whether the person is alert, awake or asleep. (viii) EEG can help in diagnosing certain conditions such as epilepsy, encephalitis, dementia and brain tumour. (ix) Electroencephalography can also be used to monitor the condition of patients during surgery and to assess the depth of anaesthesia. (x) EEG is also used as a test for brain death. (xi) The weaker magnetic fields from the brain can be studied with the help of SQUID (Super conducting Quantum Interference Device). (xii) Magnetoencephalography (MET) is useful for studying the disease associated with the brain and spinal cord.