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In biology, cell theory is a scientific theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction. With continual improvements made to microscopes over time, magnification technology advanced enough to discover cells in the 17th century. This discovery is largely attributed to Robert Hooke, and began the scientific study of cells, also known as cell biology. Over a century later, many debates about cells began amongst scientists. Most of these debates involved the nature of cellular regeneration, and the idea of cells as a fundamental unit of life. Cell theory was eventually formulated in 1838. This is usually credited to Matthias Schleiden and Theodor Schwann. However, many other scientists like Rudolf Virchow contributed to the theory. Cell theory has become the foundation of biology and is the most widely accepted explanation of the function of cells. The three tenets to the cell theory are as described below: # All living organisms are composed of one or more cells. # The cell is the basic unit of structure and organization in organisms. # Cells come from preexisting cells. == Microscopes== The discovery of the cell was made possible through the invention of the microscope. In the first century BC, Romans were able to make glass, discovering that objects appeared to be larger under the glass. In Italy during the 12th century, Salvino D’Armate made a piece of glass to fit over one eye, allowing for a magnification effect to that eye. It was not until the 1590s when a Dutch spectacle maker Zacharias Jansen began to test lenses that progress had been made to microscopes. Jansen was able to obtain about 9x magnification, but the objects appeared to be blurry. In 1595, Jansen and his father built the first compound microscope. While simple glasses were able to magnify objects, they were not considered to be a microscope. A compound microscope was defined by having two or more lenses in a hollow tube.〔(【引用サイトリンク】url=http://www.history-of-the-microscope.org/history-of-the-microscope-who-invented-the-microscope.php )〕 In 1665, Robert Hooke used a microscope about six inches long with two convex lenses inside and examined specimens under reflected light for the observations in his book Micrographia. Hooke also used a simpler microscope with a single lens for examining specimens with direct transmitted light, because this allowed for a clearer image.〔 However, the first real invention and use of a microscope was by Anton van Leeuwenhoek. He was a Dutch draper that took interest in microscopes after seeing one while on an apprenticeship in Amsterdam in 1648. At some point in his life before 1668, he was able to learn how to grind lenses. This eventually led to Leeuwenhoek making his own microscope. His were instead simple powerful magnifying glasses, rather than a compound microscope. This was because he was able to use a single lens that was a small glass sphere but allowed for a magnification of 270x. This was a large progression since the magnification before was only a maximum of 50x. After Leeuwenhoek, there was not much progress for the microscopes until the 1850s, two hundred years later. Carl Zeiss, a German engineer who manufactured microscopes, began to make changes to the lenses used. But the optical quality did not improve until the 1880s when he hired Otto Schott and eventually Ernst Abbe.〔 These microscopes could focus on objects the size of a wavelength or larger, giving restrictions still to advancement in discoveries with objects smaller than a wavelength. Later in the 1920s, the electron microscope was developed, making it possible to view objects that are smaller than a wavelength, once again, changing the possibilities in science.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「cell theory」の詳細全文を読む スポンサード リンク
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