Pump
A pump is a device that moves fluids, or sometimes slurries, by mechanical action. Pumps can be classified into three major groups according to the method they use to move the fluid: direct lift and gravity pumps. Pumps operate by some mechanism, consume energy to perform mechanical work moving the fluid. Pumps operate via many energy sources, including manual operation, engines, or wind power, come in many sizes, from microscopic for use in medical applications to large industrial pumps. Mechanical pumps serve in a wide range of applications such as pumping water from wells, aquarium filtering, pond filtering and aeration, in the car industry for water-cooling and fuel injection, in the energy industry for pumping oil and natural gas or for operating cooling towers. In the medical industry, pumps are used for biochemical processes in developing and manufacturing medicine, as artificial replacements for body parts, in particular the artificial heart and penile prosthesis; when a casing contains only one revolving impeller, it is called a single-stage pump.
When a casing contains two or more revolving impellers, it is called a double- or multi-stage pump. In biology, many different types of chemical and biomechanical pumps have evolved. Mechanical pumps may be placed external to the fluid. Pumps can be classified by their method of displacement into positive displacement pumps, impulse pumps, velocity pumps, gravity pumps, steam pumps and valveless pumps. There are two basic types of pumps: centrifugal. Although axial-flow pumps are classified as a separate type, they have the same operating principles as centrifugal pumps. A positive displacement pump makes a fluid move by trapping a fixed amount and forcing that trapped volume into the discharge pipe; some positive displacement pumps use an expanding cavity on the suction side and a decreasing cavity on the discharge side. Liquid flows into the pump as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses; the volume is constant through each cycle of operation.
Positive displacement pumps, unlike centrifugal or roto-dynamic pumps, theoretically can produce the same flow at a given speed no matter what the discharge pressure. Thus, positive displacement pumps are constant flow machines. However, a slight increase in internal leakage as the pressure increases prevents a constant flow rate. A positive displacement pump must not operate against a closed valve on the discharge side of the pump, because it has no shutoff head like centrifugal pumps. A positive displacement pump operating against a closed discharge valve continues to produce flow and the pressure in the discharge line increases until the line bursts, the pump is damaged, or both. A relief or safety valve on the discharge side of the positive displacement pump is therefore necessary; the relief valve can be external. The pump manufacturer has the option to supply internal relief or safety valves; the internal valve is used only as a safety precaution. An external relief valve in the discharge line, with a return line back to the suction line or supply tank provides increased safety.
A positive displacement pump can be further classified according to the mechanism used to move the fluid: Rotary-type positive displacement: internal gear, shuttle block, flexible vane or sliding vane, circumferential piston, flexible impeller, helical twisted roots or liquid-ring pumps Reciprocating-type positive displacement: piston pumps, plunger pumps or diaphragm pumps Linear-type positive displacement: rope pumps and chain pumps These pumps move fluid using a rotating mechanism that creates a vacuum that captures and draws in the liquid. Advantages: Rotary pumps are efficient because they can handle viscous fluids with higher flow rates as viscosity increases. Drawbacks: The nature of the pump requires close clearances between the rotating pump and the outer edge, making it rotate at a slow, steady speed. If rotary pumps are operated at high speeds, the fluids cause erosion, which causes enlarged clearances that liquid can pass through, which reduces efficiency. Rotary positive displacement pumps fall into three main types: Gear pumps – a simple type of rotary pump where the liquid is pushed between two gears Screw pumps – the shape of the internals of this pump is two screws turning against each other to pump the liquid Rotary vane pumps – similar to scroll compressors, these have a cylindrical rotor encased in a shaped housing.
As the rotor orbits, the vanes trap fluid between the rotor and the casing, drawing the fluid through the pump. Reciprocating pumps move the fluid using one or more oscillating pistons, plungers, or membranes, while valves restrict fluid motion to the desired direction. In order for suction to take place, the pump must first pull the plunger in an outward motion to decrease pressure in the chamber. Once the plunger pushes back, it will increase the pressure chamber and the inward pressure of the plunger will open the discharge valve and release the fluid into the delivery pipe at a high velocity. Pumps in this category range from simplex, with one cylinder, to in some cases quad cylinders, or more. Many reciprocating-type pumps are triplex cylinder, they can be either single-acting with suction during one direction of piston motion and discharge on the other, or double-acting with suction and discharge in both directions. The pumps can be powered manually, by air or steam
Kashrut
Kashrut is a set of Jewish religious dietary laws. Food that may be consumed according to halakha is termed kosher, from the Ashkenazi pronunciation of the Hebrew term kashér, meaning "fit". Among the numerous laws that form kashrut are prohibitions on the consumption of certain animals, mixtures of meat and milk, the commandment to slaughter mammals and birds according to a process known as shechita. There are laws regarding agricultural produce that might impact the suitability of food for consumption. Most of the basic laws of kashrut are derived from the Torah's Books of Deuteronomy, their details and practical application, are set down in the oral law and elaborated on in the rabbinical literature. Although the Torah does not state the rationale for most kashrut laws, some suggest that they are only tests for man's obedience, while others have suggested philosophical and hygienic reasons. Over the past century, many rabbinical organizations have started to certify products and restaurants as kosher using a symbol to indicate their support.
About a sixth of American Jews or 0.3% of the American population keep kosher, there are many more who do not follow all the rules but still abstain from some prohibited foods. The Seventh-day Adventist Church, a Christian denomination, have a health message that expects adherence to the kosher dietary laws. Jewish philosophy divides the 613 commandments into three groups—laws that have a rational explanation and would be enacted by most orderly societies, laws that are understood after being explained but would not be legislated without the Torah's command, laws that do not have a rational explanation; some Jewish scholars say that kashrut should be categorized as laws for which there is no particular explanation since the human mind is not always capable of understanding divine intentions. In this line of thinking, the dietary laws were given as a demonstration of God's authority, man must obey without asking why. However, Maimonides believed; some theologians have said that the laws of kashrut are symbolic in character: Kosher animals represent virtues, while non-kosher animals represent vices.
The 1st-century BCE Letter of Aristeas argues that the laws "have been given... to awake pious thoughts and to form the character". This view reappears in the work of the 19th century Rabbi Samson Raphael Hirsch; the Torah prohibits "seething the kid in its mother's milk". While the Bible does not provide a reason, it has been suggested that the practice was perceived as cruel and insensitive. Hasidic Judaism believes that everyday life is imbued with channels connecting with Divinity, the activation of which it sees as helping the Divine Presence to be drawn into the physical world; these sparks of Holiness are released. The Hasidic argument is that animals are imbued with signs that reveal the release of these sparks, the signs are expressed in the biblical categorization of ritually clean and ritually unclean. According to Christian theologian Gordon J. Wenham, the purpose of kashrut was to help Jews maintain a distinct and separate existence from other peoples. Wenham argued that since the impact of the food laws was a public affair, this would have enhanced Jewish attachment to them as a reminder of their distinct status as Jews.
There have been attempts to provide empirical support for the view that Jewish food laws have an overarching health benefit or purpose. One of the earliest is that of Maimonides in The Guide for the Perplexed. In 1953, David Macht, an Orthodox Jew and proponent of the theory of biblical scientific foresight, conducted toxicity experiments on many kinds of animals and fish, his experiment involved lupin seedlings being supplied with extracts from the meat of various animals. At the same time, these explanations are controversial. Scholar Lester L. Grabbe, writing in the Oxford Bible Commentary on Leviticus, says "n explanation now universally rejected is that the laws in this section have hygiene as their basis. Although some of the laws of ritual purity correspond to modern ideas of physical cleanliness, many of them have little to do with hygiene. For example, there is no evidence that the'unclean' animals are intrinsically bad to eat or to be avoided in a Mediterranean climate, as is sometimes asserted."
The laws of kashrut can be classified according to the origin of the prohibition and whether the prohibition concerns the food itself or a mixture of foods. Biblically prohibited foods include: Non-kosher animals and birds: mammals require certain identifying characteristics, while birds require a tradition that they can be consumed. Fish require fins. All invertebrates are non-kosher apart from certain types of locust, on w
Jugular vein
The jugular veins are veins that take deoxygenated blood from the head back to the heart via the superior vena cava. There are two sets of jugular veins: internal; the left and right external jugular veins drain into the subclavian veins. The internal jugular veins join with the subclavian veins more medially to form the brachiocephalic veins; the left and right brachiocephalic veins join to form the superior vena cava, which delivers deoxygenated blood to the right atrium of the heart. The internal jugular vein is formed by the anastomosis of blood from the sigmoid sinus of the dura mater and the common facial vein; the internal jugular runs with the common carotid artery and vagus nerve inside the carotid sheath. It provides venous drainage for the contents of the skull; the external jugular vein runs superficially to sternocleidomastoid. There is another minor jugular vein, the anterior jugular vein, draining the submaxillary region; the jugular venous pressure is an indirectly observed pressure over the venous system.
It can be useful in the differentiation of different forms of lung disease. In the jugular veins pressure waveform, upward deflections correspond with atrial contraction, ventricular contraction, atrial venous filling; the downward deflections correspond with the atrium relaxing and the filling of ventricle after the tricuspid opens. Components include: The a peak is caused by the contraction of the right atrium; the av minimum is due to relaxation of the right closure of the tricuspid valve. The c peak reflects the pressure rise in the right ventricle early during systole and the resultant bulging of the tricuspid valve—which has just closed—into the right atrium; the x minimum occurs as the ventricle contracts and shortens during the ejection phase in systole. The shortening heart—with tricuspid valve still closed—pulls on valve opens, the v peak begins to wane; the y minimum reflects a fall in right atrial pressure during rapid ventricular filling, as blood leaves the right atrium through an open tricuspid valve and enters the right ventricle.
The increase in venous pressure after the y minimum occurs as venous return continues in the face of reduced ventricular filling. The jugular vein is the subject of a popular idiom in the English language, deriving from its status as the vein most vulnerable to attack; the phrase'to go for the jugular', means to attack decisively at the weakest point - in other words, to attack at the opportune juncture for a definitive resolution, or coup-de-grace. An alternate explanation for the phrase suggests "to go for the jugular" means to attack without restraint; the jugular vein system is essential but not weak or vulnerable, because this venous system is found deep in the body. Chronic cerebrospinal venous insufficiency
Vein
Veins are blood vessels that carry blood toward the heart. Most veins carry deoxygenated blood from the tissues back to the heart. In contrast to veins, arteries carry blood away from the heart. Veins are less muscular than arteries and are closer to the skin. There are valves in most veins to prevent backflow. Veins are present throughout the body as tubes. Veins are classified in a number of ways, including superficial vs. deep, pulmonary vs. systemic, large vs. small. Superficial veins are those closer to the surface of the body, have no corresponding arteries. Deep veins have corresponding arteries. Perforator veins drain from the superficial to the deep veins; these are referred to in the lower limbs and feet. Communicating veins are veins. Pulmonary veins are a set of veins. Systemic veins deliver deoxygenated blood to the heart. Most veins are equipped with valves to prevent blood flowing in the reverse direction. Veins are translucent, so the color a vein appears from an organism's exterior is determined in large part by the color of venous blood, dark red as a result of its low oxygen content.
Veins appear blue because the subcutaneous fat absorbs low-frequency light, permitting only the energetic blue wavelengths to penetrate through to the dark vein and reflect back to the viewer. The colour of a vein can be affected by the characteristics of a person's skin, how much oxygen is being carried in the blood, how big and deep the vessels are; when a vein is drained of blood and removed from an organism, it appears grey-white. The largest veins in the human body are the venae cavae; these are two large veins which enter the right atrium of the heart from below. The superior vena cava carries blood from the arms and head to the right atrium of the heart, while the inferior vena cava carries blood from the legs and abdomen to the heart; the inferior vena cava is retroperitoneal and runs to the right and parallel to the abdominal aorta along the spine. Large veins feed into these two veins, smaller veins into these. Together this forms the venous system. Whilst the main veins hold a constant position, the position of veins person to person can display quite a lot of variation.
The pulmonary veins carry oxygenated blood from the lungs to the heart. The superior and inferior venae cavae carry deoxygenated blood from the upper and lower systemic circulations, respectively; the portal venous system is a series of venules that directly connect two capillary beds. Examples of such systems include hypophyseal portal system; the peripheral veins carry blood from feet. Microscopically, veins have a thick outer layer made of connective tissue, called the tunica externa or tunica adventitia. During procedures requiring venous access such as venipuncture, one may notice a subtle "pop" as the needle penetrates this layer; the middle layer of bands of smooth muscle are called tunica media and are, in general, much thinner than those of arteries, as veins do not function in a contractile manner and are not subject to the high pressures of systole, as arteries are. The interior is lined with endothelial cells called tunica intima; the precise location of veins varies much more from person to person than that of arteries.
Veins serve to return blood from organs to the heart. Veins are called "capacitance vessels" because most of the blood volume is contained within veins. In systemic circulation oxygenated blood is pumped by the left ventricle through the arteries to the muscles and organs of the body, where its nutrients and gases are exchanged at capillaries. After taking up cellular waste and carbon dioxide in capillaries, blood is channeled through vessels that converge with one another to form venules, which continue to converge and form the larger veins; the de-oxygenated blood is taken by veins to the right atrium of the heart, which transfers the blood to the right ventricle, where it is pumped through the pulmonary arteries to the lungs. In pulmonary circulation the pulmonary veins return oxygenated blood from the lungs to the left atrium, which empties into the left ventricle, completing the cycle of blood circulation; the return of blood to the heart is assisted by the action of the muscle pump, by the thoracic pump action of breathing during respiration.
Standing or sitting for a prolonged period of time can cause low venous return from venous pooling shock. Fainting can occur but baroreceptors within the aortic sinuses initiate a baroreflex such that angiotensin II and norepinephrine stimulate vasoconstriction and heart rate increases to return blood flow. Neurogenic and hypovolaemic shock can cause fainting. In these cases, the smooth muscles surrounding the veins become slack and the veins fill with the majority of the blood in the body, keeping blood away from the brain and causing unconsciousness. Jet pilots wear pressurized suits to help maintain their venous blood pressure; the arteries are perceived as carrying oxygenated blood to the tissues, while veins carry deoxygenated blood back to the heart. This is true of the systemic circulation, by far the larger of the two circuits of blood in the body, which transports oxygen from the heart to the tissues of the body. However, in pulmonary circulation, the arteries carry deoxygenated blood from the heart to the lungs, veins return blood from the lungs to the heart.
The difference between veins a
Domestic pig
The domestic pig called swine, hog, or pig when there is no need to distinguish it from other pigs, is a domesticated large, even-toed ungulate. It is variously considered a subspecies of a distinct species; the domestic pig's head-plus-body-length ranges from 0.9 to 1.8 m, adult pigs weigh between 50 and 350 kg, with well-fed individuals exceeding this weight range. The size and weight of a hog depends on its breed. Compared to other artiodactyls, its head is long and free of warts. Even-toed ungulates are herbivorous, but the domestic pig is an omnivore, like its wild relative; when used as livestock, domestic pigs are farmed for the consumption of their flesh, called pork. The animal's bones and bristles are used in commercial products. Domestic pigs miniature breeds, are kept as pets; the domestic pig has a large head, with a long snout, strengthened by a special prenasal bone and a disk of cartilage at the tip. The snout is used to dig into the soil to find food, is a acute sense organ; the dental formula of adult pigs is 3.1.4.33.1.4.3.
The rear teeth are adapted for crushing. In the male the canine teeth can form tusks, which grow continuously and are sharpened by being ground against each other. Four hoofed toes are on each foot, with the two larger central toes bearing most of the weight, but the outer two being used in soft ground. Most domestic pigs have rather a bristled sparse hair covering on their skin, although woolly-coated breeds such as the Mangalitsa exist. Pigs possess both apocrine and eccrine sweat glands, although the latter appear limited to the snout and dorsonasal areas. Pigs, like other "hairless" mammals, do not use thermal sweat glands in cooling. Pigs are less able than many other mammals to dissipate heat from wet mucous membranes in the mouth through panting, their thermoneutral zone is 16 to 22 °C. At higher temperatures, pigs lose heat by wallowing in water via evaporative cooling. Pigs are one of four known mammalian species which possess mutations in the nicotinic acetylcholine receptor that protect against snake venom.
Mongooses, honey badgers and pigs all have modifications to the receptor pocket which prevents the snake venom α-neurotoxin from binding. These represent four independent mutations. Domestic pigs have small lungs in relation to their body size, are thus more susceptible than other domesticated animals to fatal bronchitis and pneumonia; the domestic pig is most considered to be a subspecies of the wild boar, given the name Sus scrofa by Carl Linnaeus in 1758. However, in 1777, Johann Christian Polycarp Erxleben classified the domestic pig as a separate species from the wild boar, he gave it the name Sus domesticus, still used by some taxonomists. Archaeological evidence suggests that pigs were domesticated from wild boar as early as 13,000–12,700 BC in the Near East in the Tigris Basin, Çayönü, Cafer Höyük, Nevalı Çori being managed in the wild in a way similar to the way they are managed by some modern New Guineans. Remains of pigs have been dated to earlier than 11,400 BC in Cyprus; those animals must have been introduced from the mainland, which suggests domestication in the adjacent mainland by then.
There was a separate domestication in China which took place about 8000 years ago. DNA evidence from subfossil remains of teeth and jawbones of Neolithic pigs shows that the first domestic pigs in Europe had been brought from the Near East; this stimulated the domestication of local European wild boar, resulting in a third domestication event with the Near Eastern genes dying out in European pig stock. Modern domesticated pigs have involved complex exchanges, with European domesticated lines being exported, in turn, to the ancient Near East. Historical records indicate that Asian pigs were introduced into Europe during the 18th and early 19th centuries. In August 2015, a study looked at over 100 pig genome sequences to ascertain their process of domestication, assumed to have been initiated by humans, involved few individuals, relied on reproductive isolation between wild and domestic forms; the study found that the assumption of reproductive isolation with population bottlenecks was not supported.
The study indicated that pigs were domesticated separately in Western Asia and China, with Western Asian pigs introduced into Europe, where they crossed with wild boar. A model that fitted the data included a mixture with a now extinct ghost population of wild pigs during the Pleistocene; the study found that despite back-crossing with wild pigs, the genomes of domestic pigs have strong signatures of selection at DNA loci that affect behavior and morphology. The study concluded that human selection for domestic traits counteracted the homogenizing effect of gene flow from wild boars and created domestication islands in the genome; the same process may apply to other domesticated animals. The adaptable nature and omnivorous diet of the wild boar allowed early humans to domesticate it readily. Pigs were used for food, but early civilizations used the pigs' hides for shields, bones for tools and weapons, bristles for brushes. In India, pigs have been domesticated for a long time in Goa and some rural areas, for pig toilets.
Though ecologically logical as well as economical
The Path of Totality
The Path of Totality is the tenth studio album by American nu metal band Korn, released on December 2, 2011 in Europe and December 6, 2011 in the US. The album was produced by various electronic music producers such as Skrillex, Noisia and various other independent producers. "Get Up!", is one of three tracks produced by Skrillex, was released as a digital download on May 6, 2011. "Narcissistic Cannibal" was released as the second single on October 18, 2011. Regarding the album, vocalist Jonathan Davis stated: "I want to trail-blaze. I want to change things. I want to do things. I want to create art and not conform to what's going on. We didn't make a dubstep album. We made a Korn album." The album was made available for pre-order on Amazon and iTunes on October 21, 2011. Revolver has named The Path of Totality album of the year in their 100th issue. Korn was inducted into the Kerrang! Hall of Fame during the 2011 Kerrang! Awards; the album features production by Skrillex, Feed Me, Excision, 12th Planet, Kill the Noise, Noisia.
Monti, Datsik contributed to the mixing process. The band recorded The Path of Totality with electronic producers back in Davis's home studio in Bakersfield during inspired sessions, it was revealed by Jonathan Davis that vocals were tracked in the singer's home theater or in closets and hotels everywhere from Korea to Japan. The Path of Totality is claimed by the band to be a fusion of their traditional sound with dubstep and drum and bass. Korn collaborated with a number of producers for the album with each producing their own individual tracks. Roadrunner released the following statement: Korn frontman Jonathan Davis describes the new album as "very well-rounded, with a mix of mellow, upbeat tracks. In a new biography on Roadrunner Records' official website, Jonathan Davis declares The Path of Totality as "future metal." "We're mixing metal and electro music, you're not supposed to do that. Since day one, Korn has always been all about going against the grain and trying to take music different places."
The album title was revealed as The Path of Totality. "The title The Path of Totality refers to the fact that in order to see the sun in a full solar eclipse, you must be in the exact right place in the exact right time," says Jonathan Davis, explaining the story behind the name. "That's. I think. I'm not sure it could happen again."Munky stated. "A shadow is cast on the earth. The moon has to be aligned with the sun to create this flawless shadow that covers the sun from the earth. All of the producers and writers had to come together at the perfect time to cast these songs onto tape."The album is a standard 11-track album, with the deluxe edition featuring extra songs and The Encounter as a bonus DVD. The band's website is offering special pre-order packages that include a Path of Totality T-shirt and signed lithograph as well as the CD/DVD deluxe combo. Hot Topic offered a signed lithograph with pre-orders for a limited time. Korn commenced a world tour to promote the album named The Path of Totality Tour, which offers special VIP packages.
"Get Up!" was released as a promotional single, becoming a top ten hit on Billboard's Mainstream Rock Songs chart and would be featured in the soundtrack for EA Sports video game Madden NFL 12. The digital single has sold over 200,000 downloads in the US according to Nielsen SoundScan. A lyric video for the single was released on YouTube which accumulated over 3 million views and more than 35,000 likes; the second single, "Narcissistic Cannibal", was released to radio stations and digital music outlets on October 18 and 24, respectively. A number of new songs have been added to the tour's setlist, including "Kill Mercy Within", "My Wall", "Way Too Far". "Narcissistic Cannibal" leaked onto YouTube on October 11. It was released for free download on Korn's official website as a WAV file. A lyric video was released on both Korn's official YouTube channel and Roadrunner's channel as well, it has since accumulated 6,200 likes. Hot Topic premiered a new track, "Sanctuary", on November 16. Roadrunner Records and Korn started streaming the album in full on December 1, as well as offering lead single "Get Up!" as a free download.
"Way Too Far" and "Chaos Lives in Everything" were released as the album's third and fourth singles, respectively. The album received polarizing reviews. Rock Sound gave the album an 8/10 rating, remarking that "It may not be perfect, but Korn have thrown caution to the wind and set out an impressive template for a future sound, for a band doing that nearly 20 years into their career, they deserve your respect", they do note however. Spin gave the album a 7/10, saying "Thing is, dubstep's slithering textures suit Davis' demented croon". Henry Northmore from The List gave the album a rating of 4/5 saying that "the purists will hate it, but if you are willing to have your brain assaulted from every direction by a new Frankensteinian metal/beats hybrid, you’ll find an album packed with pure adrenaline". Allmusic gave the album 4/5 saying that "despite all the electronics, there’s no mistaking The Path of Totality as a Korn album...and one of their better ones to boot". Alistair Lawrence from BBC Music criticized the album saying that "onc
Poultry
Poultry are domesticated birds kept by humans for their eggs, their meat or their feathers. These birds are most members of the superorder Galloanserae the order Galliformes. Poultry includes other birds that are killed for their meat, such as the young of pigeons but does not include similar wild birds hunted for sport or food and known as game; the word "poultry" comes from the French/Norman word poule, itself derived from the Latin word pullus, which means small animal. The domestication of poultry took place several thousand years ago; this may have been as a result of people hatching and rearing young birds from eggs collected from the wild, but involved keeping the birds permanently in captivity. Domesticated chickens may have been used for cockfighting at first and quail kept for their songs, but soon it was realised how useful it was having a captive-bred source of food. Selective breeding for fast growth, egg-laying ability, conformation and docility took place over the centuries, modern breeds look different from their wild ancestors.
Although some birds are still kept in small flocks in extensive systems, most birds available in the market today are reared in intensive commercial enterprises. Together with pig meat, poultry is one of the two most eaten types of meat globally, with over 70% of the meat supply in 2012 between them. All poultry meat should be properly handled and sufficiently cooked in order to reduce the risk of food poisoning; the word "poultry" comes from the West & English "pultrie", from Old French pouletrie, from pouletier, poultry dealer, from poulet, pullet. The word "pullet" itself comes from Middle English pulet, from Old French polet, both from Latin pullus, a young fowl, young animal or chicken; the word "fowl" is of Germanic origin. "Poultry" is a term used for any kind of domesticated bird, captive-raised for its utility, traditionally the word has been used to refer to wildfowl and waterfowl but not to cagebirds such as songbirds and parrots. "Poultry" can be defined as domestic fowls, including chickens, turkeys and ducks, raised for the production of meat or eggs and the word is used for the flesh of these birds used as food.
The Encyclopædia Britannica lists the same bird groups but includes guinea fowl and squabs. In R. D. Crawford's Poultry breeding and genetics, squabs are omitted but Japanese quail and common pheasant are added to the list, the latter being bred in captivity and released into the wild. In his 1848 classic book on poultry and Domestic Poultry: Their History, Management, Edmund Dixon included chapters on the peafowl, guinea fowl, mute swan, various types of geese, the muscovy duck, other ducks and all types of chickens including bantams. In colloquial speech, the term "fowl" is used near-synonymously with "domesticated chicken", or with "poultry" or just "bird", many languages do not distinguish between "poultry" and "fowl". Both words are used for the flesh of these birds. Poultry can be distinguished from "game", defined as wild birds or mammals hunted for food or sport, a word used to describe the flesh of these when eaten. Chickens are medium-sized, chunky birds with an upright stance and characterised by fleshy red combs and wattles on their heads.
Males, known as cocks, are larger, more boldly coloured, have more exaggerated plumage than females. Chickens are gregarious, ground-dwelling birds that in their natural surroundings search among the leaf litter for seeds and other small animals, they fly except as a result of perceived danger, preferring to run into the undergrowth if approached. Today's domestic chicken is descended from the wild red junglefowl of Asia, with some additional input from grey junglefowl. Domestication is believed to have taken place between 7,000 and 10,000 years ago, what are thought to be fossilized chicken bones have been found in northeastern China dated to around 5,400 BC. Archaeologists believe domestication was for the purpose of cockfighting, the male bird being a doughty fighter. By 4,000 years ago, chickens seem to have reached the Indus Valley and 250 years they arrived in Egypt, they were regarded as symbols of fertility. The Romans used them in divination, the Egyptians made a breakthrough when they learned the difficult technique of artificial incubation.
Since the keeping of chickens has spread around the world for the production of food with the domestic fowl being a valuable source of both eggs and meat. Since their domestication, a large number of breeds of chickens have been established, but with the exception of the white Leghorn, most commercial birds are of hybrid origin. In about 1800, chickens began to be kept on a larger scale, modern high-output poultry farms were present in the United Kingdom from around 1920 and became established in the United States soon after the Second World War. By the mid-20th century, the poultry meat-producing industry was of greater importance than the egg-laying industry. Poultry breeding has produced strains to fulfil different needs. Male birds are unwanted in the egg-laying industry and can b
