A book is a set or collection of written, printed, illustrated, or blank sheets, made of paper, parchment, or other material, usually fastened together to hinge at one side. A single sheet within a book is called a leaf, and each side of a leaf is called a page. A book produced in electronic format is known as an e-book.
Books may also refer to a literature work, or a main division of such a work. In library and information science, a book is called a monograph, to distinguish it from serial periodicals such as magazines, journals or newspapers. The body of all written works including books is literature.
In novels, a book may be divided into several large sections, also called books (Book 1, Book 2, Book 3, etc).
A lover of books is usually referred to as a bibliophile, a bibliophilist, or a philobiblist, or, more informally, a bookworm.
A store where books are bought and sold is a bookstore or bookshop. Books can also be borrowed from libraries.
When writing systems were invented in ancient civilizations, nearly everything that could be written upon—stone, clay, tree bark, metal sheets—was used for writing. Alphabetic writing emerged in Egypt around 1800 BC. At first the words were not separated from each other (scriptura continua) and there was no punctuation. Texts were written from right to left, left to right, and even so that alternate lines read in opposite directions. The technical term for this type of writing is 'boustrophedon,' which means literally 'ox-turning' for the way a farmer drives an ox to plough his fields.
Papyrus, a thick paper-like material made by weaving the stems of the papyrus plant, then pounding the woven sheet with a hammer-like tool, was used for writing in Ancient Egypt, perhaps as early as the First Dynasty, although the first evidence is from the account books of King Neferirkare Kakai of the Fifth Dynasty[3] Papyrus sheets were glued together to form a scroll. Tree bark such as lime (Latin liber, from there also library) and other materials were also used.[4] (about 2400 BC).
According to Herodotus (History 5:58), the Phoenicians brought writing and papyrus to Greece around the tenth or ninth century BC. The Greek word for papyrus as writing material (biblion) and book (biblos) come from the Phoenician port town Byblos, through which papyrus was exported to Greece.[5]τόμος) which originally meant a slice or piece and from there it became to denote "a roll of papyrus". Tomus was used by the Latins with exactly the same meaning as volumen (see also below the explanation by Isidore of Seville). From Greeks we have also the word tome (Greek:
Whether made from papyrus, parchment, or paper in East Asia, scrolls were the dominant form of book in the Hellenistic, Roman, Chinese and Hebrew cultures. The more modern codex book format form took over the Roman world by late antiquity, but the scroll format persisted much longer in Asia.
Viruses are found wherever there is life and have probably existed since living cells first evolved.[32] The origin of viruses is unclear because they do not form fossils, so molecular techniques have been the most useful means of investigating how they arose.[33] These techniques rely on the availability of ancient viral DNA or RNA, but, unfortunately, most of the viruses that have been preserved and stored in laboratories are less than 90 years old.[34][35] There are three main hypotheses that try to explain the origins of viruses:[36][37]
The virophage 'sputnik' infects the mimivirus and the related mamavirus, which in turn infect the protozooan Acanthamoeba castellanii.[47] These viruses that are dependent on other virus species are called satellites and may represent evolutionary intermediates of viroids and viruses.[48][49] Prions are infectious protein molecules that do not contain DNA or RNA.[50] They cause an infection in sheep called scrapie and cattle bovine spongiform encephalopathy ("mad cow" disease). In humans they cause kuru and Creutzfeldt-Jakob disease.[51] They are able to replicate because some proteins can exist in two different shapes and the prion changes the normal shape of a host protein into the prion shape. This starts a chain reaction where each prion protein converts many host proteins into more prions, and these new prions then go on to convert even more protein into prions. Although they are fundamentally different from viruses and viroids, their discovery gives credence to the idea that viruses could have evolved from self-replicating molecules.[52]
Computer analysis of viral and host DNA sequences is giving a better understanding of the evolutionary relationships between different viruses and may help identify the ancestors of modern viruses. To date, such analyses have not helped to decide on which of these hypotheses are correct. However, it seems unlikely that all currently known viruses have a common ancestor and viruses have probably arisen numerous times in the past by one or more mechanisms.[53]
Opinions differ on whether viruses are a form of life, or organic structures that interact with living organisms. They have been described as "organisms at the edge of life",[54] since they resemble organisms in that they possess genes and evolve by natural selection,[55]and reproduce by creating multiple copies of themselves through self-assembly. However, although they have genes, they do not have a cellular structure, which is often seen as the basic unit of life. Additionally, viruses do not have their own metabolism, and require a host cell to make new products. They therefore cannot reproduce outside a host cell (although bacterial species such as rickettsia and chlamydia are considered living organisms despite the same limitation). Accepted forms of life use cell division to reproduce, whereas viruses spontaneously assemble within cells, which is analogous to the autonomous growth of crystals. Virus self-assembly within host cells has implications for the study of the origin of life, as it lends further credence to the hypothesis that life could have started as self-assembling organic molecules.[1A virus (from the Latin virus meaning toxin or poison) is a microscopic infectious agent that can reproduce only inside a host cell. Viruses infect all types of organisms: from animals and plants, to bacteria and archaea.[1] Since the initial discovery of tobacco mosaic virus by Martinus Beijerinck in 1898,[2] more than 5,000 types of virus have been described in detail,[3] although most types of virus remain undiscovered.[4] Viruses are ubiquitous, as they are found in almost every ecosystem on Earth,[5] and are the most abundant type of biological entity on the planet.[6] The study of viruses is known as virology, and is a branch of microbiology.
Viruses consist of two or three parts: all viruses have genes made from either DNA or RNA, long molecules that carry genetic information; all have a protein coat that protects these genes; and some have an envelope of fat that surrounds them when they are outside a cell. Viruses vary in shape from simple helical and icosahedral shapes, to more complex structures. They are about 1/100th the size of bacteria.[7] The origins of viruses in the evolutionary history of life are unclear: some may have evolved from plasmids—pieces of DNA that can move between cells—while others may have evolved from bacteria. In evolution, viruses are an important means of horizontal gene transfer, which increases genetic diversity.[8]
Viruses spread in many ways; plant viruses are often transmitted from plant to plant by insects that feed on sap, such as aphids, while animal viruses can be carried by blood-sucking insects. These disease-bearing organisms are known as vectors. Influenza viruses are spread by coughing and sneezing, and others such as norovirus, are transmitted by the faecal-oral route, when they contaminate hands, food, or water. Rotaviruses are often spread by direct contact with infected children. HIV is one of several viruses that are transmitted through sexual contact.
Not all viruses cause disease, as many viruses reproduce without causing any obvious harm to the infected organism. Viruses such as hepatitis B can cause life-long or chronic infections, and the viruses continue to replicate in the body despite the hosts' defence mechanisms. In some cases, these chronic infections might be beneficial as they might increase the immune system's response against infection by other pathogens.[9] However, in most cases viral infections in animals cause an immune response that eliminates the infecting virus. These immune responses can also be produced by vaccines that give immunity to a viral infection. Microorganisms such as bacteria also have defences against viral infection, such as restriction modification systems. Antibiotics have no effect on viruses, but antiviral drugs have been developed to treat both life-threatening and more minor infections. Unlike antibiotics however, antiviral drugs do not destroy their target pathogen but inhibit their development.
