Cytoplasm
In cell biology, the cytoplasm is all of the material within a cell, enclosed by the cell membrane, except for the cell nucleus. The material inside the nucleus and contained within the nuclear membrane is termed the nucleoplasm; the main components of the cytoplasm are cytosol – a gel-like substance, the organelles – the cell's internal sub-structures, various cytoplasmic inclusions. The cytoplasm is about 80% water and colorless; the submicroscopic ground cell substance, or cytoplasmatic matrix which remains after exclusion the cell organelles and particles is groundplasm. It is the hyaloplasm of light microscopy, high complex, polyphasic system in which all of resolvable cytoplasmic elements of are suspended, including the larger organelles such as the ribosomes, the plant plastids, lipid droplets, vacuoles. Most cellular activities take place within the cytoplasm, such as many metabolic pathways including glycolysis, processes such as cell division; the concentrated inner area is called the endoplasm and the outer layer is called the cell cortex or the ectoplasm.
Movement of calcium ions in and out of the cytoplasm is a signaling activity for metabolic processes. In plants, movement of the cytoplasm around vacuoles is known as cytoplasmic streaming; the term was introduced by Rudolf von Kölliker in 1863 as a synonym for protoplasm, but it has come to mean the cell substance and organelles outside the nucleus. There has been certain disagreement on the definition of cytoplasm, as some authors prefer to exclude from it some organelles the vacuoles and sometimes the plastids; the physical properties of the cytoplasm have been contested in recent years. It remains uncertain how the varied components of the cytoplasm interact to allow movement of particles and organelles while maintaining the cell’s structure; the flow of cytoplasmic components plays an important role in many cellular functions which are dependent on the permeability of the cytoplasm. An example of such function is cell signalling, a process, dependent on the manner in which signaling molecules are allowed to diffuse across the cell.
While small signaling molecules like calcium ions are able to diffuse with ease, larger molecules and subcellular structures require aid in moving through the cytoplasm. The irregular dynamics of such particles have given rise to various theories on the nature of the cytoplasm. There has long been evidence, it is thought that the component molecules and structures of the cytoplasm behave at times like a disordered colloidal solution and at other times like an integrated network, forming a solid mass. This theory thus proposes that the cytoplasm exists in distinct fluid and solid phases depending on the level of interaction between cytoplasmic components, which may explain the differential dynamics of different particles observed moving through the cytoplasm, it has been proposed that the cytoplasm behaves like a glass-forming liquid approaching the glass transition. In this theory, the greater the concentration of cytoplasmic components, the less the cytoplasm behaves like a liquid and the more it behaves as a solid glass, freezing larger cytoplasmic components in place.
A cell's ability to vitrify in the absence of metabolic activity, as in dormant periods, may be beneficial as a defence strategy. A solid glass cytoplasm would freeze subcellular structures in place, preventing damage, while allowing the transmission of small proteins and metabolites, helping to kickstart growth upon the cell's revival from dormancy. There has been research examining the motion of cytoplasmic particles independent of the nature of the cytoplasm. In such an alternative approach, the aggregate random forces within the cell caused by motor proteins explain the non-Brownian motion of cytoplasmic constituents; the three major elements of the cytoplasm are the cytosol and inclusions. The cytosol is the portion of the cytoplasm not contained within membrane-bound organelles. Cytosol makes up about 70% of the cell volume and is a complex mixture of cytoskeleton filaments, dissolved molecules, water; the cytosol's filaments include the protein filaments such as actin filaments and microtubules that make up the cytoskeleton, as well as soluble proteins and small structures such as ribosomes and the mysterious vault complexes.
The inner and more fluid portion of the cytoplasm is referred to as endoplasm. Due to this network of fibres and high concentrations of dissolved macromolecules, such as proteins, an effect called macromolecular crowding occurs and the cytosol does not act as an ideal solution; this crowding effect alters. Organelles, are membrane-bound structures inside the cell that have specific functions; some major organelles that are suspended in the cytosol are the mitochondria, the endoplasmic reticulum, the Golgi apparatus, lysosomes, in plant cells, chloroplasts. The inclusions are small particles of insoluble substances suspended in the cytosol. A huge range of inclusions exist in different cell types, range from crystals of calcium oxalate or silicon dioxide in plants, to granules of energy-storage materials such as starch, glycogen, or polyhydroxybutyrate. A widespread example are lipid droplets, which are spherical droplets composed of lipids and proteins that are used in both prokaryotes and eukaryotes as a way of storing lipids such as fatty acids and sterols.
Lipid droplets make up much of the volume of adipocytes, which are specialized lipid-st
Antiseptic
Antiseptics are antimicrobial substances that are applied to living tissue/skin to reduce the possibility of infection, sepsis, or putrefaction. Antiseptics are distinguished from antibiotics by the latter's ability to safely destroy bacteria within the body, from disinfectants, which destroy microorganisms found on non-living objects; some antiseptics are true germicides, capable of destroying microbes, while others are bacteriostatic and only prevent or inhibit their growth. Antibacterials include antiseptics. Microbicides which destroy virus particles are called antivirals. Antifungals known as an antimycotics, are pharmaceutical fungicides used to treat and prevent mycosis; the widespread introduction of antiseptic surgical methods was initiated by the publishing of the paper Antiseptic Principle of the Practice of Surgery in 1867 by Joseph Lister, inspired by Louis Pasteur's germ theory of putrefaction. In this paper, Lister advocated the use of carbolic acid as a method of ensuring that any germs present were killed.
Some of this work was anticipated by: Ancient Greek physicians Galen and Hippocrates and Sumerian clay tablets dating from 2150 BC that advocate the use of similar techniques. Medieval surgeons Hugh of Lucca, Theoderic of Servia, his pupil Henri de Mondeville were opponents of Galen's opinion that pus was important to healing, which had led ancient and medieval surgeons to let pus remain in wounds, they advocated draining and cleaning the wound edges with wine, dressing the wound after suturing, if necessary and leaving the dressing on for ten days, soaking it in warm wine all the while, before changing it. Their theories were bitterly opposed by Galenist Guy de Chauliac and others trained in the classical tradition. Oliver Wendell Holmes, Sr. who published The Contagiousness of Puerperal Fever in 1843 Florence Nightingale, who contributed to the report of the Royal Commission on the Health of the Army, based on her earlier work Ignaz Semmelweis, who published his work The Cause and Prophylaxis of Childbed Fever in 1861, summarizing experiments and observations since 1847 Alcohols, including ethanol and 2-propanol/isopropanol are sometimes referred to as surgical spirit.
They are used to disinfect the skin. Chlorhexidine gluconate is used as a skin antiseptic. Hydrogen peroxide is used as a 6 % solution to deodorize wounds and ulcers. More 3% solutions of hydrogen peroxide have been used in household first aid for scrapes, etc. However, the strong oxidization causes scar formation and increases healing time during fetal development. Iodine is used in an alcohol solution or as Lugol's iodine solution as a pre- and postoperative antiseptic; some studies do not recommend disinfecting minor wounds with iodine because of concern that it may induce scar tissue formation and increase healing time. However, concentrations of 1% iodine or less have not been shown to increase healing time and are not otherwise distinguishable from treatment with saline. Novel iodine antiseptics containing povidone-iodine are far better tolerated, do not negatively affect wound healing, leave a deposit of active iodine, thereby creating the so-called "remnant", or persistent, effect; the great advantage of iodine antiseptics is their wide scope of antimicrobial activity, killing all principal pathogens and, given enough time spores, which are considered to be the most difficult form of microorganisms to be inactivated by disinfectants and antiseptics.
Octenidine dihydrochloride increasingly used in continental Europe as a chlorhexidine substitute. Polyhexanide is an antimicrobial compound suitable for clinical use in critically colonized or infected acute and chronic wounds; the physicochemical action on the bacterial envelope prevents or impedes the development of resistant bacterial strains. Balsam of Peru is a mild antiseptic. Dakin's solution is a sodium hypochlorite solution also containing boric acid to lower pH, it is used on live tissues for cleaning wounds of bacteria and viruses. Because of practicality of preparation and lower cost, it is used in Veterinary Medicine treatments, it does not stain the animal's fur or affect it's aesthetic or commercial value. Super-oxidized solutions contain hypochlorous acid and are stabilised at a neutral pH. SOS are acting, broad spectrum antiseptics that are clinically effective at non-cytotoxic concentrations that in contrast to many cytotoxic antiseptics, support wound healing There is now growing consensus that modern SOS are more effective for healing wounds faster After continued exposure to antibiotics, bacteria may evolve to the point where they are no longer harmed by these compounds.
Bacteria can develop a resistance to antiseptics, but the effect is less pronounced. The mechanisms by which bacteria evolve may vary in response to different antiseptics. Low concentrations of an antiseptic may encourage growth of a bacterial strain, resistant to the antiseptic, where a higher concentration of the antiseptic would kill the bacteria. In addition, use of an excessively high concentration of an antiseptic may cause tissue damage or slow the process of wound healing. Antiseptics are mo
Vincent van Gogh
Vincent Willem van Gogh was a Dutch post-impressionist painter, among the most famous and influential figures in the history of Western art. In just over a decade he created about 2,100 artworks, including around 860 oil paintings, most of them in the last two years of his life, they include landscapes, still lifes and self-portraits, are characterised by bold colours and dramatic and expressive brushwork that contributed to the foundations of modern art. However, he was not commercially successful, his suicide at 37 followed years of mental illness and poverty. Born into an upper-middle-class family, Van Gogh drew as a child and was serious and thoughtful; as a young man he worked as an art dealer travelling, but became depressed after he was transferred to London. He spent time as a Protestant missionary in southern Belgium, he drifted in ill health and solitude before taking up painting in 1881, having moved back home with his parents. His younger brother Theo supported him financially, the two kept up a long correspondence by letter.
His early works still lifes and depictions of peasant labourers, contain few signs of the vivid colour that distinguished his work. In 1886, he moved to Paris, where he met members of the avant-garde, including Émile Bernard and Paul Gauguin, who were reacting against the Impressionist sensibility; as his work developed he created a new approach to still lifes and local landscapes. His paintings grew brighter in colour as he developed a style that became realised during his stay in Arles in the south of France in 1888. During this period he broadened his subject matter to include series of olive trees, wheat fields and sunflowers. Van Gogh suffered from psychotic episodes and delusions and though he worried about his mental stability, he neglected his physical health, did not eat properly and drank heavily, his friendship with Gauguin ended after a confrontation with a razor when, in a rage, he severed part of his own left ear. He spent time including a period at Saint-Rémy. After he discharged himself and moved to the Auberge Ravoux in Auvers-sur-Oise near Paris, he came under the care of the homeopathic doctor Paul Gachet.
His depression continued and on 27 July 1890, Van Gogh shot himself in the chest with a Lefaucheux revolver. He died from his injuries two days later. Van Gogh was unsuccessful during his lifetime, was considered a madman and a failure, he became famous after his suicide, exists in the public imagination as the quintessential misunderstood genius, the artist "where discourses on madness and creativity converge". His reputation began to grow in the early 20th century as elements of his painting style came to be incorporated by the Fauves and German Expressionists, he attained widespread critical and popular success over the ensuing decades, is remembered as an important but tragic painter, whose troubled personality typifies the romantic ideal of the tortured artist. Today, Van Gogh's works are among the world's most expensive paintings to have sold at auction, his legacy is honoured by a museum in his name, the Van Gogh Museum in Amsterdam, which holds the world's largest collection of his paintings and drawings.
The most comprehensive primary source on Van Gogh is the correspondence between him and his younger brother, Theo. Their lifelong friendship, most of what is known of Vincent's thoughts and theories of art, are recorded in the hundreds of letters they exchanged from 1872 until 1890. Theo van Gogh was an art dealer and provided his brother with financial and emotional support, access to influential people on the contemporary art scene. Theo kept all of Vincent's letters to him. After both had died, Theo's widow Johanna arranged for the publication of some of their letters. A few appeared in 1906 and 1913. Vincent's letters are eloquent and expressive and have been described as having a "diary-like intimacy", read in parts like autobiography; the translator Arnold Pomerans wrote that their publication adds a "fresh dimension to the understanding of Van Gogh's artistic achievement, an understanding granted us by no other painter". There are more than 600 letters from around 40 from Theo to Vincent.
There are 22 to his sister Wil, 58 to the painter Anthon van Rappard, 22 to Émile Bernard as well as individual letters to Paul Signac, Paul Gauguin and the critic Albert Aurier. Some are illustrated with sketches. Many are undated. Problems in transcription and dating remain with those posted from Arles. While there Vincent wrote around 200 letters in Dutch and English. There is a gap in the record when he lived in Paris as the brothers lived together and had no need to correspond. Vincent Willem van Gogh was born on 30 March 1853 into a Dutch Reformed family in Groot-Zundert, in the predominantly Catholic province of North Brabant in the southern Netherlands, he was the oldest surviving child of Theodorus van Gogh, a minister of the Dutch Reformed Church, Anna Cornelia Carbentus. Van Gogh was given the name of his grandfather, of a brother stillborn a year before his birth. Vincent was a common name in the Van Gogh family: his grandfather, who received a degree in theology at the University of Leiden in 1811, had six sons, three of whom became art dealers.
This Vincent may have been named after a sculptor. Van Gogh's mother came from a prosperous family in The Hague, his father was the youngest son of a minister; the two
Red blood cell
Red blood cells known as RBCs, red cells, red blood corpuscles, erythroid cells or erythrocytes, are the most common type of blood cell and the vertebrate's principal means of delivering oxygen to the body tissues—via blood flow through the circulatory system. RBCs take up oxygen in the lungs, or gills of fish, release it into tissues while squeezing through the body's capillaries; the cytoplasm of erythrocytes is rich in hemoglobin, an iron-containing biomolecule that can bind oxygen and is responsible for the red color of the cells and the blood. The cell membrane is composed of proteins and lipids, this structure provides properties essential for physiological cell function such as deformability and stability while traversing the circulatory system and the capillary network. In humans, mature red blood cells are oval biconcave disks, they lack most organelles, in order to accommodate maximum space for hemoglobin. 2.4 million new erythrocytes are produced per second in human adults. The cells develop in the bone marrow and circulate for about 100–120 days in the body before their components are recycled by macrophages.
Each circulation takes about 60 seconds. A quarter of the cells in the human body are red blood cells. Nearly half of the blood's volume is red blood cells. Packed red blood cells are red blood cells that have been donated and stored in a blood bank for blood transfusion. All vertebrates, including all mammals and humans, have red blood cells. Red blood cells are cells present in blood; the only known vertebrates without red blood cells are the crocodile icefish. While they no longer use hemoglobin, remnants of hemoglobin genes can be found in their genome. Vertebrate red blood cells consist of hemoglobin, a complex metalloprotein containing heme groups whose iron atoms temporarily bind to oxygen molecules in the lungs or gills and release them throughout the body. Oxygen can diffuse through the red blood cell's cell membrane. Hemoglobin in the red blood cells carries some of the waste product carbon dioxide back from the tissues. Myoglobin, a compound related to hemoglobin, acts to store oxygen in muscle cells.
The color of red blood cells is due to the heme group of hemoglobin. The blood plasma alone is straw-colored, but the red blood cells change color depending on the state of the hemoglobin: when combined with oxygen the resulting oxyhemoglobin is scarlet, when oxygen has been released the resulting deoxyhemoglobin is of a dark red burgundy color. However, blood can appear bluish when seen through skin. Pulse oximetry takes advantage of the hemoglobin color change to directly measure the arterial blood oxygen saturation using colorimetric techniques. Hemoglobin has a high affinity for carbon monoxide, forming carboxyhemoglobin, a bright red in color. Flushed, confused patients with a saturation reading of 100% on pulse oximetry are sometimes found to be suffering from carbon monoxide poisoning. Having oxygen-carrying proteins inside specialized cells was an important step in the evolution of vertebrates as it allows for less viscous blood, higher concentrations of oxygen, better diffusion of oxygen from the blood to the tissues.
The size of red blood cells varies among vertebrate species. The red blood cells of mammals are shaped as biconcave disks: flattened and depressed in the center, with a dumbbell-shaped cross section, a torus-shaped rim on the edge of the disk; this shape allows for a high surface-area-to-volume ratio to facilitate diffusion of gases. However, there are some exceptions concerning shape in the artiodactyl order, which displays a wide variety of bizarre red blood cell morphologies: small and ovaloid cells in llamas and camels, tiny spherical cells in mouse deer, cells which assume fusiform, lanceolate and irregularly polygonal and other angular forms in red deer and wapiti. Members of this order have evolved a mode of red blood cell development different from the mammalian norm. Overall, mammalian red blood cells are remarkably flexible and deformable so as to squeeze through tiny capillaries, as well as to maximize their apposing surface by assuming a cigar shape, where they efficiently release their oxygen load.
Red blood cells in mammals are unique amongst vertebrates. Red blood cells of mammals cells have nuclei during early phases of erythropoiesis, but extrude them during development as they mature; the red blood cells without nuclei, called reticulocytes, subsequently lose all other cellular organelles such as their mitochondria, Golgi apparatus and endoplasmic reticulum. The spleen acts as a reservoir of red blood cells. In some other mammals such as dogs and horses, the spl
Tissue (biology)
In biology, tissue is a cellular organizational level between cells and a complete organ. A tissue is an ensemble of similar cells and their extracellular matrix from the same origin that together carry out a specific function. Organs are formed by the functional grouping together of multiple tissues; the English word "tissue" is derived from the French "tissu", meaning something, "woven", from the verb tisser, "to weave". The study of human and animal tissues is known as histology or, in connection with disease, histopathology. For plants, the discipline is called plant anatomy; the classical tools for studying tissues are the paraffin block in which tissue is embedded and sectioned, the histological stain, the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of medical diagnosis and prognosis.
Animal tissues are grouped into four basic types: connective, muscle and epithelial. Collections of tissues joined in structural units to serve a common function compose organs. While all eumetazoan animals can be considered to contain the four tissue types, the manifestation of these tissues can differ depending on the type of organism. For example, the origin of the cells comprising a particular tissue type may differ developmentally for different classifications of animals; the epithelium in all birds and animals is derived from the ectoderm and endoderm, with a small contribution from the mesoderm, forming the endothelium, a specialized type of epithelium that composes the vasculature. By contrast, a true epithelial tissue is present only in a single layer of cells held together via occluding junctions called tight junctions, to create a selectively permeable barrier; this tissue covers all organismal surfaces that come in contact with the external environment such as the skin, the airways, the digestive tract.
It serves functions of protection and absorption, is separated from other tissues below by a basal lamina. Connective tissues are fibrous tissues, they are made up of cells separated by non-living material, called an extracellular matrix. This matrix can be rigid. For example, blood contains plasma as its matrix and bone's matrix is rigid. Connective tissue holds them in place. Blood, tendon, ligament and areolar tissues are examples of connective tissues. One method of classifying connective tissues is to divide them into three types: fibrous connective tissue, skeletal connective tissue, fluid connective tissue. Muscle cells form the active contractile tissue of the body known as muscle tissue or muscular tissue. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle tissue is separated into three distinct categories: visceral or smooth muscle, found in the inner linings of organs. Cells comprising the central nervous system and peripheral nervous system are classified as nervous tissue.
In the central nervous system, neural tissues form spinal cord. In the peripheral nervous system, neural tissues form the cranial nerves and spinal nerves, inclusive of the motor neurons; the epithelial tissues are formed by cells that cover the organ surfaces, such as the surface of skin, the airways, the reproductive tract, the inner lining of the digestive tract. The cells comprising an epithelial layer are linked via tight junctions. In addition to this protective function, epithelial tissue may be specialized to function in secretion and absorption. Epithelial tissue helps to protect organs from microorganisms and fluid loss. Functions of epithelial tissue: The cells of the body's surface form the outer layer of skin. Inside the body, epithelial cells form the lining of the mouth and alimentary canal and protect these organs. Epithelial tissues help in absorption of water and nutrients. Epithelial tissues help in the elimination of waste. Epithelial tissues hormones in the form of glands; some epithelial tissue perform secretory functions.
They secrete a variety of substances such as sweat, enzymes, etc. There are many kinds of epithelium, nomenclature is somewhat variable. Most classification schemes combine a description of the cell-shape in the upper layer of the epithelium with a word denoting the number of layers: either simple or stratified. However, other cellular features, such as cilia may be described in the classification system; some common kinds of epithelium are listed below: Simple squamous epithelium Stratified squamous epithelium Simple cuboidal epithelium Transitional epithelium Pseudostratified columnar epithelium Columnar epithelium Glandular epithelium Ciliated columnar epithelium In plant anatomy, tissues are categorized broadly into three tissue systems: the epidermis, the ground tissue, the vascular tissue. Epidermis - Cells forming the outer surface of the leaves and of the young plant body. Vascular tissue - The primary components of vascular tissue are the xylem and phloem; these transport nutrients internally.
Ground tissue - Ground tissue is less differentiated than other tissues. Ground tis
Histology
Histology microanatomy, is the branch of biology which studies the tissues of animals and plants using microscopy. It is studied using a light microscope or electron microscope, the specimen having been sectioned and mounted on a microscope slide. Histological studies may be conducted using tissue culture, where live animal cells are isolated and maintained in an artificial environment for various research projects; the ability to visualize or differentially identify microscopic structures is enhanced through the use of staining. Histology is one of the major preclinical subjects in medical school. Medical students are expected to be familiar with the morphological features and function of all cells and tissues of the human body from an early stage of their studies, so histology stretches over several semesters. Histopathology, the microscopic study of diseased tissue, is an important tool in anatomical pathology, since accurate diagnosis of cancer and other diseases requires histopathological examination of samples.
Trained physicians licensed pathologists, are the personnel who perform histopathological examination and provide diagnostic information based on their observations. The trained personnel who prepare histological specimens for examination are histotechnicians, histotechnologists, histology technicians, histology technologists, medical scientists, medical laboratory technicians, or biomedical scientists, their support workers, their field of study is called histotechnology. In the 17th century, Italian Marcello Malpighi invented one of the first microscopes for studying tiny biological entities. Malpighi analysed several parts of the organs of bats and other animals under the microscope. Malpighi, while studying the structure of the lung, noticed its membranous alveoli and the hair-like connections between veins and arteries, which he named capillaries, his discovery established how the oxygen enters the blood stream and serves the body. In the 19th century, histology was an academic discipline in its own right.
The French anatomist Bichat introduced the concept of tissue in anatomy in 1801, the term "histology" first appeared in a book of Karl Meyer in 1819. Bichat described twenty-one human tissues, which can be subsumed under the four categories accepted by histologists; the usage of illustrations in histology, deemed as useless by Bichat, was promoted by Jean Cruveilhier. During the 19th century, many fixation techniques were developed by Adolph Hannover, Franz Schulze and Max Schultze, Alexander Butlerov and Benedikt Stilling. In the early 1830, Purkynĕ invented a microtome with high precision. Mounting techniques were developed by Rudolf Heidenhain, Salomon Stricker, Andrew Pritchard and Edwin Klebs. Koelliker's laboratory developed haematoxylin staining, in 1870s, Vysockij introduced eosin as a double or counter staining; the 1906 Nobel Prize in Physiology or Medicine was awarded to histologists Camillo Golgi and Santiago Ramon y Cajal. They had conflicting interpretations of the neural structure of the brain based on differing interpretations of the same images.
Cajal won the prize for his correct theory, Golgi for the silver staining technique he invented to make it possible. There are four basic types of animal tissues: muscle tissue, nervous tissue, connective tissue, epithelial tissue. All tissue types are subtypes of these four basic tissue types. Epithelium: the lining of glands, bowel and some organs like the liver and kidney Endothelium: the lining of blood and lymphatic vessels Mesothelium: the lining of pleural and pericardial spaces Mesenchyme: the cells filling the spaces between the organs, including fat, bone and tendon cells Blood cells: the red and white blood cells, including those found in lymph nodes and spleen Neurons: any of the conducting cells of the nervous system Germ cells: reproductive cells Placenta: an organ characteristic of true mammals during pregnancy, joining mother and offspring, providing endocrine secretion and selective exchange of soluble, but not particulate, blood-borne substances through an apposition of uterine and trophoblastic vascularised parts Stem cells: cells with the ability to develop into different cell typesThe tissues from plants and microorganisms can be examined histologically.
Their structure is different from animal tissues. For plants, the study of their tissues is more called as plant anatomy, with the following main types: Dermal tissue Vascular tissue Ground tissue Meristematic tissue Chemical fixatives are used to preserve tissue from degradation, to maintain the structure of the cell and of sub-cellular components such as cell organelles; the most common fixative for light microscopy is 10% neutral buffered formalin. For electron microscopy, the most used fixative is glutaraldehyde as a 2.5% solution in phosphate buffered saline. These fixatives preserve tissues or cells by irreversibly cross-linking proteins; the main action of these aldehyde fixatives is to cross-link amino groups in proteins through the formation of methylene bridges, in the case of formaldehyde, or by C5H10 cross-links in the case of glutaraldehyde. This process, while preserving the structural integrity of the cells and tissue can damage the biological functionality of proteins enzymes, and
Post-Impressionism
Post-Impressionism is a predominantly French art movement that developed between 1886 and 1905, from the last Impressionist exhibition to the birth of Fauvism. Post-Impressionism emerged as a reaction against Impressionists' concern for the naturalistic depiction of light and colour. Due to its broad emphasis on abstract qualities or symbolic content, Post-Impressionism encompasses Les Nabis Neo-Impressionism, Cloisonnism, Pont-Aven School, Synthetism, along with some Impressionists' work; the movement was led by Paul Cézanne, Paul Gauguin, Vincent van Gogh, Georges Seurat. The term Post-Impressionism was first used by art critic Roger Fry in 1906. Critic Frank Rutter in a review of the Salon d'Automne published in Art News, 15 October 1910, described Othon Friesz as a "post-impressionist leader". Three weeks Roger Fry used the term again when he organized the 1910 exhibition and the Post-Impressionists, defining it as the development of French art since Manet. Post-Impressionists extended Impressionism while rejecting its limitations: they continued using vivid colours thick application of paint, real-life subject matter, but were more inclined to emphasize geometric forms, distort form for expressive effect, use unnatural or arbitrary colour.
The Post-Impressionists were dissatisfied with what they felt was the triviality of subject matter and the loss of structure in Impressionist paintings, though they did not agree on the way forward. Georges Seurat and his followers concerned themselves with Pointillism, the systematic use of tiny dots of colour. Paul Cézanne set out to restore a sense of order and structure to painting, to "make of Impressionism something solid and durable, like the art of the museums", he achieved this by reducing objects to their basic shapes while retaining the saturated colours of Impressionism. The Impressionist Camille Pissarro experimented with Neo-Impressionist ideas between the mid-1880s and the early 1890s. Discontented with what he referred to as romantic Impressionism, he investigated Pointillism, which he called scientific Impressionism, before returning to a purer Impressionism in the last decade of his life. Vincent van Gogh used colour and vibrant swirling brush strokes to convey his feelings and his state of mind.
Although they exhibited together, Post-Impressionist artists were not in agreement concerning a cohesive movement. Yet, the abstract concerns of harmony and structural arrangement, in the work of all these artists, took precedence over naturalism. Artists such as Seurat adopted a meticulously scientific approach to composition. Younger painters during the early 20th century worked in geographically disparate regions and in various stylistic categories, such as Fauvism and Cubism, breaking from Post-Impressionism; the term was used in 1906, again in 1910 by Roger Fry in the title of an exhibition of modern French painters: Manet and the Post-Impressionists, organized by Fry for the Grafton Galleries in London. Three weeks before Fry's show, art critic Frank Rutter had put the term Post-Impressionist in print in Art News of 15 October 1910, during a review of the Salon d'Automne, where he described Othon Friesz as a "post-impressionist leader". Most of the artists in Fry's exhibition were younger than the Impressionists.
Fry explained: "For purposes of convenience, it was necessary to give these artists a name, I chose, as being the vaguest and most non-committal, the name of Post-Impressionism. This stated their position in time to the Impressionist movement." John Rewald limited the scope to the years between 1886 and 1892 in his pioneering publication on Post-Impressionism: From Van Gogh to Gauguin. Rewald considered this a continuation of his 1946 study, History of Impressionism, pointed out that a "subsequent volume dedicated to the second half of the post-impressionist period": Post-Impressionism: From Gauguin to Matisse, was to follow; this volume would extend the period covered to other artistic movements derived from Impressionism, though confined to the late 19th and early 20th centuries. Rewald focused on such outstanding early Post-Impressionists active in France as van Gogh, Gauguin and Redon, he explored their relationships as well as the artistic circles they frequented, including: Neo-Impressionism: ridiculed by contemporary art critics as well as artists as Pointillism.
Pont-Aven School: implying little more than that the artists involved had been working for a while in Pont-Aven or elsewhere in Brittany. Symbolism: a term welcomed by vanguard critics in 1891, when Gauguin dropped Synthetism as soon as he was acclaimed to be the leader of Symbolism in painting. Furthermore, in his introduction to Post-Impressionism, Rewald opted for a second volume featuring Toulouse-Lautrec, Henri Rousseau "le Douanier", Les Nabis and Cézanne as well as the Fauves, the young Picasso and Gauguin's last trip to the South Seas. Rewald wrote that "the term'Post
