Thiomargarita is a genus which includes the vacuolate sulfur bacteria species Thiomargarita namibiensis, Candidatus Thiomargarita nelsonii, Ca. Thiomargarita joergensii. Representatives of this genus can be found in a variety of environments that are rich in hydrogen sulfide, including methane seeps, mud volcanoes, brine pools, organic-rich sediments such as those found beneath the Benguela Current and Humboldt Current; these bacteria are considered to be chemolithotrophs that utilize reduced inorganic species of sulfur as metabolic electron donors to produce energy for the fixation of carbon into biomass. Carbon fixation occurs via the Calvin Benson Bassham cycle and the reverse Krebs cycle
Enzymes are macromolecular biological catalysts. Enzymes accelerate chemical reactions; the molecules upon which enzymes may act are called substrates and the enzyme converts the substrates into different molecules known as products. All metabolic processes in the cell need enzyme catalysis in order to occur at rates fast enough to sustain life. Metabolic pathways depend upon enzymes to catalyze individual steps; the study of enzymes is called enzymology and a new field of pseudoenzyme analysis has grown up, recognising that during evolution, some enzymes have lost the ability to carry out biological catalysis, reflected in their amino acid sequences and unusual'pseudocatalytic' properties. Enzymes are known to catalyze more than 5,000 biochemical reaction types. Most enzymes are proteins; the latter are called ribozymes. Enzymes' specificity comes from their unique three-dimensional structures. Like all catalysts, enzymes increase the reaction rate by lowering its activation energy; some enzymes can make their conversion of substrate to product occur many millions of times faster.
An extreme example is orotidine 5'-phosphate decarboxylase, which allows a reaction that would otherwise take millions of years to occur in milliseconds. Chemically, enzymes are like any catalyst and are not consumed in chemical reactions, nor do they alter the equilibrium of a reaction. Enzymes differ from most other catalysts by being much more specific. Enzyme activity can be affected by other molecules: inhibitors are molecules that decrease enzyme activity, activators are molecules that increase activity. Many therapeutic drugs and poisons are enzyme inhibitors. An enzyme's activity decreases markedly outside its optimal temperature and pH, many enzymes are denatured when exposed to excessive heat, losing their structure and catalytic properties; some enzymes are used commercially, in the synthesis of antibiotics. Some household products use enzymes to speed up chemical reactions: enzymes in biological washing powders break down protein, starch or fat stains on clothes, enzymes in meat tenderizer break down proteins into smaller molecules, making the meat easier to chew.
By the late 17th and early 18th centuries, the digestion of meat by stomach secretions and the conversion of starch to sugars by plant extracts and saliva were known but the mechanisms by which these occurred had not been identified. French chemist Anselme Payen was the first to discover an enzyme, diastase, in 1833. A few decades when studying the fermentation of sugar to alcohol by yeast, Louis Pasteur concluded that this fermentation was caused by a vital force contained within the yeast cells called "ferments", which were thought to function only within living organisms, he wrote that "alcoholic fermentation is an act correlated with the life and organization of the yeast cells, not with the death or putrefaction of the cells."In 1877, German physiologist Wilhelm Kühne first used the term enzyme, which comes from Greek ἔνζυμον, "leavened" or "in yeast", to describe this process. The word enzyme was used to refer to nonliving substances such as pepsin, the word ferment was used to refer to chemical activity produced by living organisms.
Eduard Buchner submitted his first paper on the study of yeast extracts in 1897. In a series of experiments at the University of Berlin, he found that sugar was fermented by yeast extracts when there were no living yeast cells in the mixture, he named the enzyme that brought about the fermentation of sucrose "zymase". In 1907, he received the Nobel Prize in Chemistry for "his discovery of cell-free fermentation". Following Buchner's example, enzymes are named according to the reaction they carry out: the suffix -ase is combined with the name of the substrate or to the type of reaction; the biochemical identity of enzymes was still unknown in the early 1900s. Many scientists observed that enzymatic activity was associated with proteins, but others argued that proteins were carriers for the true enzymes and that proteins per se were incapable of catalysis. In 1926, James B. Sumner crystallized it; the conclusion that pure proteins can be enzymes was definitively demonstrated by John Howard Northrop and Wendell Meredith Stanley, who worked on the digestive enzymes pepsin and chymotrypsin.
These three scientists were awarded the 1946 Nobel Prize in Chemistry. The discovery that enzymes could be crystallized allowed their structures to be solved by x-ray crystallography; this was first done for lysozyme, an enzyme found in tears and egg whites that digests the coating of some bacteria. This high-resolution structure of lysozyme marked the beginning of the field of structural biology and the effort to understand how enzymes work at an atomic level of detail. An enzyme's name is derived from its substrate or the chemical reaction it catalyzes, with the word ending in -ase. Examples are alcohol dehydrogenase and DNA polymerase. Different enzymes that catalyze the same chemical reaction are called isozymes; the International Union of Biochemistry and Molecular Biology have developed a nomenclature for enzymes, the EC numbers. The first number broadly classifies the enzyme based on its mechanism; the top-level classification is: EC 1, Oxidoreductases: catalyze oxidation/reducti
The nucleolus is the largest structure in the nucleus of eukaryotic cells. It is best known as the site of ribosome biogenesis. Nucleoli participate in the formation of signal recognition particles and play a role in the cell's response to stress. Nucleoli are made of proteins, DNA and RNA and form around specific chromosomal regions called nucleolar organizing regions. Malfunction of nucleoli can be the cause of several human conditions called "nucleolopathies" and the nucleolus is being investigated as a target for cancer chemotherapy; the nucleolus was identified by bright-field microscopy during the 1830s. Little was known about the function of the nucleolus until 1964, when a study of nucleoli by John Gurdon and Donald Brown in the African clawed frog Xenopus laevis generated increasing interest in the function and detailed structure of the nucleolus, they found that such eggs were not capable of life. Half of the eggs had one nucleolus and 25% had two, they concluded. In 1966 Max L. Birnstiel and collaborators showed via nucleic acid hybridization experiments that DNA within nucleoli code for ribosomal RNA.
Three major components of the nucleolus are recognized: the fibrillar center, the dense fibrillar component, the granular component. Transcription of the rDNA occurs in the FC; the DFC contains the protein fibrillarin, important in rRNA processing. The GC contains the protein nucleophosmin, involved in ribosome biogenesis. However, it has been proposed that this particular organization is only observed in higher eukaryotes and that it evolved from a bipartite organization with the transition from anamniotes to amniotes. Reflecting the substantial increase in the DNA intergenic region, an original fibrillar component would have separated into the FC and the DFC. Another structure identified within many nucleoli is a clear area in the center of the structure referred to as a nucleolar vacuole. Nucleoli of various plant species have been shown to have high concentrations of iron in contrast to human and animal cell nucleoli; the nucleolus ultrastructure can be seen through an electron microscope, while the organization and dynamics can be studied through fluorescent protein tagging and fluorescent recovery after photobleaching.
Antibodies against the PAF49 protein can be used as a marker for the nucleolus in immunofluorescence experiments. Although only one or two nucleoli can be seen, a diploid human cell has ten nucleolus organizer regions and could have more nucleoli. Most multiple NORs participate in each nucleolus. In ribosome biogenesis, two of the three eukaryotic RNA polymerases are required, these function in a coordinated manner. In an initial stage, the rRNA genes are transcribed as a single unit within the nucleolus by RNA polymerase I. In order for this transcription to occur, several pol I-associated factors and DNA-specific trans-acting factors are required. In yeast, the most important are: UAF, TBP, core binding factor ) which bind promoter elements and form the preinitiation complex, in turn recognized by RNA pol. In humans, a similar PIC is assembled with SL1, the promoter selectivity factor, transcription initiation factors, UBF. RNA polymerase I transcribes most rRNA transcripts 28S, 18S, 5.8S) but the 5S rRNA subunit is transcribed by RNA polymerase III.
Transcription of rRNA yields a long precursor molecule which still contains the ITS and ETS. Further processing is needed to generate 5.8 S and 28S RNA molecules. In eukaryotes, the RNA-modifying enzymes are brought to their respective recognition sites by interaction with guide RNAs, which bind these specific sequences; these guide RNAs belong to the class of small nucleolar RNAs which are complexed with proteins and exist as small-nucleolar-ribonucleoproteins. Once the rRNA subunits are processed, they are ready to be assembled into larger ribosomal subunits. However, an additional rRNA molecule, the 5S rRNA, is necessary. In yeast, the 5S rDNA sequence is localized in the intergenic spacer and is transcribed in the nucleolus by RNA pol. In higher eukaryotes and plants, the situation is more complex, for the 5S DNA sequence lies outside the Nucleolus Organiser Region and is transcribed by RNA pol III in the nucleoplasm, after which it finds its way into the nucleolus to participate in the ribosome assembly.
This assembly not only ribosomal proteins as well. The genes encoding these r-proteins are transcribed by pol II in the nucleoplasm by a "conventional" pathway of protein synthesis; the mature r-proteins are "imported" back into the nucleus and the nucleolus. Association and maturation of rRNA and r-proteins result in the formation of the 40S and 60S subunits of the complete ribosome; these are exported through the nuclear pore complexes to the cytoplasm, where they remain free or become associated with the endoplasmic reticulum, forming rough endoplasmic reticulum. In human endometrial cells, a network of nucleolar channels is sometimes formed; the origin and function of this network has not yet been identified. In addition to its role in ribosomal biogenesis, the nucleolus is known to capture and immobilize proteins, a process known as nucleolar detention. Proteins that are detained in the nucle
An acid is a molecule or ion capable of donating a hydron, or, capable of forming a covalent bond with an electron pair. The first category of acids is the proton donors or Brønsted acids. In the special case of aqueous solutions, proton donors form the hydronium ion H3O+ and are known as Arrhenius acids. Brønsted and Lowry generalized the Arrhenius theory to include non-aqueous solvents. A Brønsted or Arrhenius acid contains a hydrogen atom bonded to a chemical structure, still energetically favorable after loss of H+. Aqueous Arrhenius acids have characteristic properties which provide a practical description of an acid. Acids form aqueous solutions with a sour taste, can turn blue litmus red, react with bases and certain metals to form salts; the word acid is derived from the Latin acidus/acēre meaning sour. An aqueous solution of an acid has a pH less than 7 and is colloquially referred to as'acid', while the strict definition refers only to the solute. A lower pH means a higher acidity, thus a higher concentration of positive hydrogen ions in the solution.
Chemicals or substances having the property of an acid are said to be acidic. Common aqueous acids include hydrochloric acid, acetic acid, sulfuric acid, citric acid; as these examples show, acids can be solutions or pure substances, can be derived from acids that are solids, liquids, or gases. Strong acids and some concentrated weak acids are corrosive, but there are exceptions such as carboranes and boric acid; the second category of acids are Lewis acids. An example is boron trifluoride, whose boron atom has a vacant orbital which can form a covalent bond by sharing a lone pair of electrons on an atom in a base, for example the nitrogen atom in ammonia. Lewis considered this as a generalization of the Brønsted definition, so that an acid is a chemical species that accepts electron pairs either directly or by releasing protons into the solution, which accept electron pairs. However, hydrogen chloride, acetic acid, most other Brønsted-Lowry acids cannot form a covalent bond with an electron pair and are therefore not Lewis acids.
Conversely, many Lewis acids are not Brønsted-Lowry acids. In modern terminology, an acid is implicitly a Brønsted acid and not a Lewis acid, since chemists always refer to a Lewis acid explicitly as a Lewis acid. Modern definitions are concerned with the fundamental chemical reactions common to all acids. Most acids encountered in everyday life are aqueous solutions, or can be dissolved in water, so the Arrhenius and Brønsted-Lowry definitions are the most relevant; the Brønsted-Lowry definition is the most used definition. Hydronium ions are acids according to all three definitions. Although alcohols and amines can be Brønsted-Lowry acids, they can function as Lewis bases due to the lone pairs of electrons on their oxygen and nitrogen atoms; the Swedish chemist Svante Arrhenius attributed the properties of acidity to hydrogen ions or protons in 1884. An Arrhenius acid is a substance that, when added to water, increases the concentration of H+ ions in the water. Note that chemists write H+ and refer to the hydrogen ion when describing acid-base reactions but the free hydrogen nucleus, a proton, does not exist alone in water, it exists as the hydronium ion, H3O+.
Thus, an Arrhenius acid can be described as a substance that increases the concentration of hydronium ions when added to water. Examples include molecular substances such as acetic acid. An Arrhenius base, on the other hand, is a substance which increases the concentration of hydroxide ions when dissolved in water; this decreases the concentration of hydronium because the ions react to form H2O molecules: H3O+ + OH− ⇌ H2O + H2ODue to this equilibrium, any increase in the concentration of hydronium is accompanied by a decrease in the concentration of hydroxide. Thus, an Arrhenius acid could be said to be one that decreases hydroxide concentration, while an Arrhenius base increases it. In an acidic solution, the concentration of hydronium ions is greater than 10−7 moles per liter. Since pH is defined as the negative logarithm of the concentration of hydronium ions, acidic solutions thus have a pH of less than 7. While the Arrhenius concept is useful for describing many reactions, it is quite limited in its scope.
In 1923 chemists Johannes Nicolaus Brønsted and Thomas Martin Lowry independently recognized that acid-base reactions involve the transfer of a proton. A Brønsted-Lowry acid is a species. Brønsted-Lowry acid-base theory has several advantages over Arrhenius theory. Consider the following reactions of acetic acid, the organic acid that gives vinegar its characteristic taste: CH3COOH + H2O ⇌ CH3COO− + H3O+ CH3COOH + NH3 ⇌ CH3COO− + NH+4Both theories describe the first reaction: CH3COOH acts as an Arrhenius acid because it acts as a source of H3O+ when dissolved in water, it acts as a Brønsted acid by donating a proton to water. In the second example CH3COOH undergoes the same transformation, in this case donating a proton to ammonia, but does not relate to the Arrhenius definition of an acid because the reaction does not produce hydronium. CH3COOH is
In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center of the animal cell, as well as a regulator of cell-cycle progression. The centrosome is thought to have evolved only in the metazoan lineage of eukaryotic cells. Fungi and plants lack centrosomes and therefore use structures other than MTOCs to organize their microtubules. Although the centrosome has a key role in efficient mitosis in animal cells, it is not essential in certain fly and flatworm species. Centrosomes are composed of two centrioles arranged at right-angles to each other, surrounded by an amorphous mass of protein termed the pericentriolar material; the PCM contains proteins responsible for microtubule nucleation and anchoring including γ-tubulin and ninein. In general, each centriole of the centrosome is based on a nine triplet microtubule assembled in a cartwheel structure, contains centrin and tektin. In many cell types the centrosome is replaced by a cilium during cellular differentiation.
However, once the cell starts to divide, the cilium is replaced again by the centrosome. The centrosome was discovered by Edouard Van Beneden in 1883, described and named in 1888 by Theodor Boveri. Centrosomes are associated with the nuclear membrane during the prophase stage of the cell cycle. In mitosis the nuclear membrane breaks down and the centrosome nucleated microtubules can interact with the chromosomes to build the mitotic spindle; the mother centriole, the older of the two in the centriole pair has a central role in making cilia and flagella. The centrosome is copied only once per cell cycle so that each daughter cell inherits one centrosome, containing two structures called centrioles; the centrosome replicates during the S phase of the cell cycle. During the prophase in the process of cell division called mitosis, the centrosomes migrate to opposite poles of the cell; the mitotic spindle forms between the two centrosomes. Upon division, each daughter cell receives one centrosome. Aberrant numbers of centrosomes in a cell have been associated with cancer.
Doubling of a centrosome is similar to DNA replication in two respects: the semiconservative nature of the process and the action of CDK2 as a regulator of the process. But the processes are different in that centrosome doubling does not occur by template reading and assembly; the mother centriole just aids in the accumulation of materials required for the assembly of the daughter centriole. Centrioles however, are not required for the progression of mitosis; when the centrioles are irradiated by a laser, mitosis proceeds with a morphologically normal spindle. Moreover, development of the fruit fly Drosophila is normal when centrioles are absent due to a mutation in a gene required for their duplication. In the absence of the centrioles, the microtubules of the spindle are focused by motors allowing the formation of a bipolar spindle. Many cells can undergo interphase without centrioles. Unlike centrioles, centrosomes are required for survival of the organism. Cells without centrosomes lack radial arrays of astral microtubules.
They are defective in spindle positioning and in the ability to establish a central localization site in cytokinesis. The function of centrosome in this context is hypothesized to ensure the fidelity of cell division because it increases the efficacy; some cell types arrest in the following cell cycle. This is not a universal phenomenon; when the nematode C. elegans egg is fertilized the sperm delivers a pair of centrioles. These centrioles will form the centrosomes which will direct the first cell division of the zygote and this will determine its polarity. It's not yet clear whether the role of the centrosome in polarity determination is microtubule dependent or independent. Theodor Boveri, in 1914, described centrosome aberrations in cancer cells; this initial observation was subsequently extended to many types of human tumors. Centrosome alterations in cancer can be divided in two subgroups, structural or numeric aberrations, yet both can be found in a tumor, they appear due to uncontrolled expression of centrosome components, or due to post-translational modifications which are not adequate for those components.
These modifications may produce variations in centrosome size. In addition, because centrosomal proteins have the tendency to form aggregates centrosome-related bodies are observed in ectopic places. Both enlarged centrosomes and CRBs are similar to the centrosomal structures observed in tumors. More, these structures can be induced in culture cells by overexpression of specific centrosomal proteins, such as CNap-1 or Nlp; these structures may look similar, yet detailed studies reveal that they may present different properties, depending on their proteic composition. For instance, their capacity to incorporate γ-TuRC complexes can be variable, so their capacity to nucleate microtubules, therefore affecting in different way the shape and motility of implicated tumor cells; the presence of an inadequate number of centrosomes is often linked to the appearance of genome instability and the loss of tissue differentiation. However, the method to count the centrosome number is not precise, because it is assessed using fluorescence microscopy, whose optical resolution is not high enough to resolve centrioles that are close to each other.
It is clear that the presence of an excess of centrosomes is a common event in human tu
Fluid statics or hydrostatics is the branch of fluid mechanics that studies "fluids at rest and the pressure in a fluid or exerted by a fluid on an immersed body". It encompasses the study of the conditions under which fluids are at rest in stable equilibrium as opposed to fluid dynamics, the study of fluids in motion. Hydrostatics are categorized as a part of the fluid statics, the study of all fluids, incompressible or not, at rest. Hydrostatics is fundamental to hydraulics, the engineering of equipment for storing and using fluids, it is relevant to geophysics and astrophysics, to meteorology, to medicine, many other fields. Hydrostatics offers physical explanations for many phenomena of everyday life, such as why atmospheric pressure changes with altitude, why wood and oil float on water, why the surface of still water is always level; some principles of hydrostatics have been known in an empirical and intuitive sense since antiquity, by the builders of boats, cisterns and fountains. Archimedes is credited with the discovery of Archimedes' Principle, which relates the buoyancy force on an object, submerged in a fluid to the weight of fluid displaced by the object.
The Roman engineer Vitruvius warned readers about lead pipes bursting under hydrostatic pressure. The concept of pressure and the way it is transmitted by fluids was formulated by the French mathematician and philosopher Blaise Pascal in 1647; the "fair cup" or Pythagorean cup, which dates from about the 6th century BC, is a hydraulic technology whose invention is credited to the Greek mathematician and geometer Pythagoras. It was used as a learning tool; the cup consists of a line carved into the interior of the cup, a small vertical pipe in the center of the cup that leads to the bottom. The height of this pipe is the same as the line carved into the interior of the cup; the cup may be filled to the line without any fluid passing into the pipe in the center of the cup. However, when the amount of fluid exceeds this fill line, fluid will overflow into the pipe in the center of the cup. Due to the drag that molecules exert on one another, the cup will be emptied. Heron's fountain is a device invented by Heron of Alexandria that consists of a jet of fluid being fed by a reservoir of fluid.
The fountain is constructed in such a way that the height of the jet exceeds the height of the fluid in the reservoir in violation of principles of hydrostatic pressure. The device consisted of an opening and two containers arranged one above the other; the intermediate pot, sealed, was filled with fluid, several cannula connecting the various vessels. Trapped air inside the vessels induces a jet of water out of a nozzle, emptying all water from the intermediate reservoir. Pascal made contributions to developments in both hydrodynamics. Pascal's Law is a fundamental principle of fluid mechanics that states that any pressure applied to the surface of a fluid is transmitted uniformly throughout the fluid in all directions, in such a way that initial variations in pressure are not changed. Due to the fundamental nature of fluids, a fluid cannot remain at rest under the presence of a shear stress. However, fluids can exert pressure normal to any contacting surface. If a point in the fluid is thought of as an infinitesimally small cube it follows from the principles of equilibrium that the pressure on every side of this unit of fluid must be equal.
If this were not the case, the fluid would move in the direction of the resulting force. Thus, the pressure on a fluid at rest is isotropic; this characteristic allows fluids to transmit force through the length of tubes. This principle was first formulated, in a extended form, by Blaise Pascal, is now called Pascal's law. In a fluid at rest, all frictional and inertial stresses vanish and the state of stress of the system is called hydrostatic; when this condition of V = 0 is applied to the Navier-Stokes equation, the gradient of pressure becomes a function of body forces only. For a barotropic fluid in a conservative force field like a gravitational force field, pressure exerted by a fluid at equilibrium becomes a function of force exerted by gravity; the hydrostatic pressure can be determined from a control volume analysis of an infinitesimally small cube of fluid. Since pressure is defined as the force exerted on a test area, the only force acting on any such small cube of fluid is the weight of the fluid column above it, hydrostatic pressure can be calculated according to the following formula: p − p = 1 A ∫ z 0 z d z ′ ∬ A d x ′ d y ′ ρ g = ∫ z 0 z d z ′ ρ g, where: p is the hydrostatic pressure, ρ is the fluid density
Lazzaro Spallanzani was an Italian Catholic priest and physiologist who made important contributions to the experimental study of bodily functions, animal reproduction, animal echolocation. His research of biogenesis paved the way for the downfall of preformationism theory, though the final death blow to preformationism was dealt by Pasteur. Spallanzani was died in Pavia, Italy, he was educated at the Jesuit College and started to study law at the University of Bologna, which he gave up soon and turned to science. Here, his famous kinswoman, Laura Bassi, was professor of physics and it is to her influence that his scientific impulse has been attributed. With her he studied natural philosophy and mathematics, gave great attention to languages, both ancient and modern, but soon abandoned them. In 1754, at the age of 25, he became professor of logic and Greek in the University of Reggio. In 1762 he was ordained as a priest, 1763 he was moved to Modena, where he continued to teach with great assiduity and success, but devoted his whole leisure to natural science.
He declined many offers from other Italian universities and from St Petersburg until 1768, when he accepted the invitation of Maria Theresa to the chair of natural history in the University of Pavia, being reorganized. He became director of the museum, which he enriched by the collections of his many journeys along the shores of the Mediterranean Sea. In June 1768 Spallanzani was elected a Fellow of the Royal Society and in 1775 was elected a foreign member of the Royal Swedish Academy of Sciences. In 1785 he was invited to Padua University, but to retain his services his sovereign doubled his salary and allowed him leave of absence for a visit to Turkey where he remained nearly a year and made many observations, among which may be noted those of a copper mine in Chalki and of an iron mine at Principi, his return home was a triumphal progress: at Vienna he was cordially received by Joseph II and on reaching Pavia he was met with acclamations outside the city gates by the students of the university.
During the following year his students exceeded five hundred. While he was travelling in the Balkans and to Constantinople, His integrity in the management of the museum was called in question, with letters written across Europe to damage Spallanzani's reputation. A judicial investigation speedily cleared his honour to the satisfaction of some of his accusers, but Spallanzani got his revenge on his principal accuser, a jealous colleague, by planting a fake specimen of a composite "species". When his colleague published the remarkable specimen Spallanzani revealed the joke, resulting in wide ridicule and humiliation. In 1788 he visited Vesuvius and the volcanoes of the Lipari Islands and Sicily, embodied the results of his researches in a large work, published four years later, he died from bladder cancer on 12 February 1799, in Pavia. After his death, his bladder was removed for study by his colleagues, after which it was placed on public display in a museum in Pavia, where it remains to this day.
His indefatigable exertions as a traveller, his skill and good fortune as a collector, his brilliance as a teacher and expositor, his keenness as a controversialist no doubt aid in accounting for Spallanzani's exceptional fame among his contemporaries. Yet greater qualities were by no means lacking, his life was one of incessant eager questioning of nature on all sides, his many and varied works all bear the stamp of a fresh and original genius, capable of stating and solving problems in all departments of science—at one time finding the true explanation of stone skipping and at another helping to lay the foundations of our modern volcanology and meteorology. Spallanzani researched in 1768 the theory of the spontaneous generation of microbes. At the time, the microscope was available to researchers, using it, the proponents of the theory and Needham, came to the conclusion that there is a life-generating force inherent to certain kinds of inorganic matter that causes living microbes to create themselves if given sufficient time.
Spallanzani's experiment showed that it is not an inherent feature of matter, that it can be destroyed by an hour of boiling. As the microbes did not re-appear as long as the material was hermetically sealed, he proposed that microbes move through the air and that they could be killed through boiling. Needham argued that experiments destroyed the "vegetative force", required for spontaneous generation to occur. Spallanzani paved the way for research by Louis Pasteur, who defeated the theory of spontaneous generation a century later. Spallanzani discovered and described animal reproduction, showing that it requires both semen and an ovum, he was the first to perform in vitro fertilization, with frogs, an artificial insemination, using a dog. Spallanzani showed that some animals newts, can regenerate some parts of their body if injured or surgically removed. Spallanzani is credited with the classification of tardigrades, which are one of the most durable extremophiles still to this day. Spallanzani is famous for extensive experiments on the navigation in comple