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Theodor Schwann (; 7 December 181011 January 1882) was a German physician and
physiologist Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemica ...
. His most significant contribution to
biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary ...
is considered to be the extension of cell theory to animals. Other contributions include the discovery of
Schwann cell Schwann cells or neurolemmocytes (named after German physiologist Theodor Schwann) are the principal glia of the peripheral nervous system (PNS). Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory en ...
s in the
peripheral nervous system The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brai ...
, the discovery and study of pepsin, the discovery of the
organic Organic may refer to: * Organic, of or relating to an organism, a living entity * Organic, of or relating to an anatomical organ Chemistry * Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
nature of
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
, and the invention of the term "
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run ...
".


Early life and education

Theodor Schwann was born in
Neuss Neuss (; spelled ''Neuß'' until 1968; li, Nüss ; la, Novaesium) is a city in North Rhine-Westphalia, Germany. It is located on the west bank of the Rhine opposite Düsseldorf. Neuss is the largest city within the Rhein-Kreis Neuss district. It ...
on 7 December 1810 to Leonard Schwann and Elisabeth Rottels. Leonard Schwann was a
goldsmith A goldsmith is a metalworker who specializes in working with gold and other precious metals. Nowadays they mainly specialize in jewelry-making but historically, goldsmiths have also made silverware, platters, goblets, decorative and servicea ...
and later a printer. Theodor Schwann studied at the
Dreikönigsgymnasium The Dreikönigsgymnasium ("Tricoronatum", meaning "Three Kings School", sometimes called in English the College of the Three Crowns) is a regular public Gymnasium located in Cologne, Germany. Founded in 1450 by the city of Cologne, it is the ol ...
(also known as the Tricoronatum or Three Kings School), a Jesuit school in
Cologne Cologne ( ; german: Köln ; ksh, Kölle ) is the largest city of the German western state of North Rhine-Westphalia (NRW) and the fourth-most populous city of Germany with 1.1 million inhabitants in the city proper and 3.6 millio ...
. Schwann was a devout
Roman Catholic Roman or Romans most often refers to: * Rome, the capital city of Italy *Ancient Rome, Roman civilization from 8th century BC to 5th century AD * Roman people, the people of ancient Rome *'' Epistle to the Romans'', shortened to ''Romans'', a let ...
. In Cologne his religious instructor , a priest and novelist, emphasized the individuality of the human soul and the importance of
free will Free will is the capacity of agents to choose between different possible courses of action unimpeded. Free will is closely linked to the concepts of moral responsibility, praise, culpability, sin, and other judgements which apply only to ac ...
. In 1829, Schwann enrolled at the
University of Bonn The Rhenish Friedrich Wilhelm University of Bonn (german: Rheinische Friedrich-Wilhelms-Universität Bonn) is a public research university located in Bonn, North Rhine-Westphalia, Germany. It was founded in its present form as the ( en, Rhine ...
in the premedical curriculum. He received a bachelor of philosophy in 1831. While at
Bonn The federal city of Bonn ( lat, Bonna) is a city on the banks of the Rhine in the German state of North Rhine-Westphalia, with a population of over 300,000. About south-southeast of Cologne, Bonn is in the southernmost part of the Rhine-Ru ...
, Schwann met and worked with
physiologist Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemica ...
Johannes Peter Müller Johannes Peter Müller (14 July 1801 – 28 April 1858) was a German physiologist, comparative anatomist, ichthyologist, and herpetologist, known not only for his discoveries but also for his ability to synthesize knowledge. The paramesonephri ...
. Müller is considered to have founded scientific medicine in Germany, publishing his ''Handbuch der Physiologie des Menschen für Vorlesungen'' in 1837–1840. It was translated into English as ''Elements of Physiology'' in 1837–1843 and became the leading physiology textbook of the 1800s. In 1831, Schwann moved to the
University of Würzburg The Julius Maximilian University of Würzburg (also referred to as the University of Würzburg, in German ''Julius-Maximilians-Universität Würzburg'') is a public research university in Würzburg, Germany. The University of Würzburg is one of ...
for clinical training in medicine. In 1833, he went to the
University of Berlin Humboldt-Universität zu Berlin (german: Humboldt-Universität zu Berlin, abbreviated HU Berlin) is a German public research university in the central borough of Mitte in Berlin. It was established by Frederick William III on the initiative ...
, where Müller was now Professor of Anatomy and Physiology. Schwann graduated with an M.D. degree in medicine from the University of Berlin in 1834. He did his thesis work in 1833–1834, with Müller as his advisor. Schwann's thesis involved a careful study of the necessity for oxygen during the embryonic development of the chicken. To carry it out, he designed and built an apparatus that enabled him to pump the gases oxygen and hydrogen out of the incubation chamber at specific times. This enabled him to establish the critical period in which the eggs needed oxygen. Schwann passed the state examination to practice medicine in the summer of 1834, but he chose to continue to work with Müller, doing research rather than practicing medicine. He could afford to do so, at least in the short term, because of a family inheritance. His salary as an assistant was only 120 taler. For the next five years, Schwann would pay the other three-quarters of his expenses out of his inheritance. As a long-term strategy, it was not sustainable.


Career

From 1834 to 1839, Schwann worked as an assistant to Müller in at the Anatomisch-zootomische Museum at the University of Berlin. Schwann carried out a series of microscopic and physiological experiments focused on studying the structure and function of nerves, muscles and
blood vessels The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away f ...
. In addition to performing experiments in preparation for Müller's book on
physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemic ...
, Schwann did research of his own. Many of his important contributions were made during the time that he worked with Müller in Berlin. Schwann used newly powerful microscopes to examine animal tissues. This enabled him to observe animal cells and note their different properties. His work complemented that of Matthias Jakob Schleiden in plants and was informed by it; the two were close friends. Described as quiet and serious, Schwann was particularly gifted in the construction and use of apparatus for his experiments. He was also able to identify important scientific questions and design experiments to systematically test them. His writing has been described as accessible, and his logic as a "clear progression". He identified the question that he wanted to answer and communicated the importance of his findings effectively to others. His co-worker Jakob Henle spoke of him as having an "inborn drive" to experiment. By 1838, Schwann needed a position with a more substantial salary. He hoped to return to Bonn, a Catholic city. He attempted to gain a professorship there in 1838 and again in 1846, but was disappointed. Instead, in 1839, Schwann accepted the chair of anatomy at the
Université Catholique de Louvain The Université catholique de Louvain (also known as the Catholic University of Louvain, the English translation of its French name, and the University of Louvain, its official English name) is Belgium's largest French-speaking university. It ...
in
Leuven Leuven (, ) or Louvain (, , ; german: link=no, Löwen ) is the capital and largest city of the province of Flemish Brabant in the Flemish Region of Belgium. It is located about east of Brussels. The municipality itself comprises the historic c ...
, Belgium, another Catholic city. Schwann proved to be a dedicated and conscientious professor. With his new teaching duties, he had less time for new scientific work. He spent considerable time perfecting experimental techniques and instruments for use in experiments. He produced few papers. One exception was a paper in 1844 that reported on a series of experiments on dogs and established the importance of
bile Bile (from Latin ''bilis''), or gall, is a dark-green-to-yellowish-brown fluid produced by the liver of most vertebrates that aids the digestion of lipids in the small intestine. In humans, bile is produced continuously by the liver (liver bi ...
in digestion. In examining processes such as muscle contraction, fermentation, digestion, and putrefaction, Schwann sought to show that living phenomena were the result of physical causes rather than "some immaterial vital force". Nonetheless, he still sought to reconcile "an organic nature" with "a divine plan." Some writers have suggested that Schwann's move in 1838, and his decreased scientific productivity after that, reflect religious concerns and perhaps even a crisis relating to the theoretical implications of his work on cell theory. However, other authors regard this as misrepresenting his thinking, and reject the idea that Schwann went through an existential crisis or a mystical phase. Ohad Parnes uses Schwann's laboratory notebooks and other unpublished sources along with his publications to reconstruct his research as a unified progression. Florence Vienne draws on unpublished writings to discuss the ways in which cell theory, as a "unifying principle of organic development", related to the philosophical, religious, and political ideas of various proponents including Schwann. In 1848, Schwann's compatriot
Antoine Frédéric Spring Antoine Frédéric Spring (8 April 1814 in Gerolsbach, Bavaria – 17 January 1872) was a German-born, Belgian physician and botanist. He studied botany and medicine at the University of Munich, obtaining his PhD in 1835 and his medical doctorat ...
convinced him to transfer to the
University of Liège The University of Liège (french: Université de Liège), or ULiège, is a major public university of the French Community of Belgium based in Liège, Wallonia, Belgium. Its official language is French. As of 2020, ULiège is ranked in the ...
, also in Belgium. At
Liège Liège ( , , ; wa, Lîdje ; nl, Luik ; german: Lüttich ) is a major city and municipality of Wallonia and the capital of the Belgian province of Liège. The city is situated in the valley of the Meuse, in the east of Belgium, not far fro ...
, Schwann continued to follow the latest advances in anatomy and physiology but did not himself make major new discoveries. He became something of an inventor. One of his projects was a portable respirator, designed as a closed system to support human life in environments where the surroundings cannot be breathed. By 1858 he was serving as professor of physiology, general anatomy and embryology. In 1863, the
American Philosophical Society The American Philosophical Society (APS), founded in 1743 in Philadelphia, is a scholarly organization that promotes knowledge in the sciences and humanities through research, professional meetings, publications, library resources, and communit ...
elected him an international member. As of 1872, he ceased to teach general anatomy, and as of 1877, embryology. He retired fully in 1879. Schwann was deeply respected by his peers. In 1878, a festival was held to celebrate his years of teaching and his many contributions. He was presented with a unique gift: a book containing 263 autographed photographic portraits of scientists from various countries, each of them sent by the scientist to be part of the gift for Schwann. The volume was dedicated "To the creator of the cell theory, the contemporary biologists." Three years after retiring, Schwann died in
Cologne Cologne ( ; german: Köln ; ksh, Kölle ) is the largest city of the German western state of North Rhine-Westphalia (NRW) and the fourth-most populous city of Germany with 1.1 million inhabitants in the city proper and 3.6 millio ...
, on 11 January 1882. He was buried in the family tomb in Cologne's
Melaten Cemetery Melaten is the central cemetery of Cologne, North Rhine-Westphalia, which was first mentioned in 1243. It was developed to a large park, holding the graves of notable residents. Name The name "Melaten" refers to a hospital for the sick and ...
.


Contributions

When viewed in the context of his unpublished writings and laboratory notes, Schwann's research can be seen as "a coherent and systematic research programme" in which biological processes are described in terms of material objects or "agents", and the causal dependencies between the forces that they exert, and their measurable effects. Schwann's idea of the cell as a fundamental, active unit then can be seen as foundational to the development of microbiology as "a rigorously lawful science".


Muscle tissue

Some of Schwann's earliest work in 1835 involved
muscle contraction Muscle contraction is the activation of tension-generating sites within muscle cells. In physiology, muscle contraction does not necessarily mean muscle shortening because muscle tension can be produced without changes in muscle length, such a ...
, which he saw as a starting point for "the introduction of calculation to physiology". He developed and described an experimental method to calculate the contraction force of the muscle, by controlling and measuring the other variables involved. His measurement technique was developed and used later by Emil du Bois-Reymond and others. Schwann's notes suggest that he hoped to discover regularities and laws of physiological processes.


Pepsin

In 1835, relatively little was known about digestive processes. William Prout had reported in 1824 that the digestive juices of animals contained
hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the dige ...
. Schwann realized that other substances in digestive juices might also help to break down food. At the beginning of 1836, Schwann began to study digestive processes. He conceptualized digestion as the action of a physiological agent, which, though not immediately visible or measurable, could be characterized experimentally as a "peculiar specific substance". Eventually Schwann found the enzyme pepsin, which he successfully isolated from the stomach lining and named in 1836. Schwann coined its name from the Greek word ''pepsis'', meaning "
digestion Digestion is the breakdown of large insoluble food molecules into small water-soluble food molecules so that they can be absorbed into the watery blood plasma. In certain organisms, these smaller substances are absorbed through the small intest ...
" (from ''peptein'' "to digest"). Pepsin was the first enzyme to be isolated from animal tissue. He demonstrated that it could break down the
albumin Albumin is a family of globular proteins, the most common of which are the serum albumins. All the proteins of the albumin family are water- soluble, moderately soluble in concentrated salt solutions, and experience heat denaturation. Album ...
from egg-white into
peptones Peptides (, ) are short chains of amino acids linked by peptide bonds. Long chains of amino acids are called proteins. Chains of fewer than twenty amino acids are called oligopeptides, and include dipeptides, tripeptides, and tetrapeptides. A ...
. Even more importantly, Schwann wrote, by carrying through such analyses one could eventually "explain the whole developmental process of life in all organized bodies." During the next year, he studied both
decomposition Decomposition or rot is the process by which dead organic substances are broken down into simpler organic or inorganic matter such as carbon dioxide, water, simple sugars and mineral salts. The process is a part of the nutrient cycle and ...
and respiration, constructing apparatus that he would later adapt for the study of yeast.


Yeast, fermentation, and spontaneous generation

Next Schwann studied
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
and
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food p ...
. His work on yeast was independent of work done by Charles Cagniard de la Tour and
Friedrich Traugott Kützing Friedrich Traugott Kützing (8 December 1807 in Ritteburg – 9 September 1893) was a German pharmacist, botanist and phycologist. Despite his limited background in regard to higher education, Kützing made significant scientific contribution ...
, all of whom published work in 1837. By 1836, Schwann had carried out numerous experiments on alcohol fermentation. Powerful microscopes made it possible for him to observe yeast cells in detail and recognize that they were tiny organisms whose structures resembled those of plants. Schwann went beyond others who simply had noted the multiplication of yeast during alcoholic fermentation, first by assigning yeast the role of a primary causal factor, and then by claiming it was alive. Schwann used the microscope to carry out a carefully planned series of experiments that contraindicated two popular theories of fermentation in yeast. First he controlled the temperature of fluid from fermenting beer in a closed vessel in the presence of oxygen. Once heated, the liquid could no longer ferment. This disproved Joseph Louis Gay-Lussac's speculation that oxygen caused fermentation. It suggested that some sort of
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in old ...
was necessary for the process to happen. Next, Schwann tested the effects of purified air and unpurified air. He sterilized the air by passing it through heated glass bulbs. Fermentation did not occur in the presence of purified air. It did occur in the presence of unpurified air, suggesting that something in the air started the process. This was strong evidence against the theory of spontaneous generation, the idea that living organisms could develop out of nonliving matter. Schwann had demonstrated that fermentation required the presence of yeasts to start, and stopped when the yeasts stopped growing. He concluded that sugar was converted to alcohol as part of an organic biological process based on the action of a living substance, the yeast. He demonstrated that fermentation was not an inorganic chemical process like sugar oxidation. Living yeast was necessary for the reaction that would produce more yeast. Although Schwann was correct, his ideas were ahead of most of his peers. They were strongly opposed by
Justus von Liebig Justus Freiherr von Liebig (12 May 1803 – 20 April 1873) was a German scientist who made major contributions to agricultural and biological chemistry, and is considered one of the principal founders of organic chemistry. As a professor at th ...
and
Friedrich Wöhler Friedrich Wöhler () FRS(For) Hon FRSE (31 July 180023 September 1882) was a German chemist known for his work in inorganic chemistry, being the first to isolate the chemical elements beryllium and yttrium in pure metallic form. He was the fi ...
, both of whom saw his emphasis on the importance of a living organism as supporting
vitalism Vitalism is a belief that starts from the premise that "living organisms are fundamentally different from non-living entities because they contain some non-physical element or are governed by different principles than are inanimate things." Wher ...
. Liebig, in contrast, saw fermentation as a series of purely chemical events, without involving living matter. Ironically, Schwann's work was later seen as being a first step away from vitalism. Schwann was the first of Müller's pupils to work towards a physico-chemical explanation of life. Schwann's view furthered a conceptualization of living things in terms of the biological reactions of
organic chemistry Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, and reactions of organic compounds and organic materials, i.e., matter in its various forms that contain carbon atoms.Clayden, J ...
, while Liebig sought to reduce biological reactions to purely
inorganic chemistry Inorganic chemistry deals with synthesis and behavior of inorganic and organometallic compounds. This field covers chemical compounds that are not carbon-based, which are the subjects of organic chemistry. The distinction between the two disci ...
. The value of Schwann's work on fermentation eventually would be recognized by
Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named afte ...
, ten years later. Pasteur would begin his fermentation research in 1857 by repeating and confirming Schwann's work, accepting that yeast were alive, and then taking fermentation research further. Pasteur, not Schwann, would challenge Liebig's views in the Liebig–Pasteur dispute. In retrospect, the
germ theory The germ theory of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or "germs" can lead to disease. These small organisms, too small to be seen without magnification, invade h ...
of
Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named after ...
, as well as its
antiseptic An antiseptic (from Greek ἀντί ''anti'', "against" and σηπτικός ''sēptikos'', "putrefactive") is an antimicrobial substance or compound that is applied to living tissue/skin to reduce the possibility of infection, sepsis, or putre ...
applications by Lister, can be traced to Schwann's influence.


Cell theory

In 1837, Matthias Jakob Schleiden viewed and stated that new plant cells formed from the nuclei of old plant cells. Dining with Schwann one day, their conversation turned on the nuclei of plant and animal
cells Cell most often refers to: * Cell (biology), the functional basic unit of life Cell may also refer to: Locations * Monastic cell, a small room, hut, or cave in which a religious recluse lives, alternatively the small precursor of a monastery w ...
. Schwann remembered seeing similar structures in the cells of the
notochord In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consi ...
(as had been shown by Müller) and instantly realized the importance of connecting the two phenomena. The resemblance was confirmed without delay by both observers. In further experiments, Schwann examined notochordal tissue and cartilage from toad larvae, as well as tissues from pig embryos, establishing that animal tissues are composed of cells, each of which has a nucleus. Schwann published his observations in 1838 in the ''Neue notisen geb. nat.-heilk''.Schwann T. Ueber die Analogie in der Structur und dem Wachsthum der Thiere und Pflanzen. ''Neue Not Geb Nat Heil'', 1838;Jan:33–36; 1838;Feb:25–29; 1838;Apr:21–23. This was followed in 1839 by the publication of his book ''Mikroskopische Untersuchungen über die Uebereinstimmung in der Struktur und dem Wachsthum der Thiere und Pflanzen'' (Microscopic investigations on the similarity of structure and growth of animals and plants). It is considered a landmark work, foundational to modern biology. In it Schwann declared that "All living things are composed of cells and cell products". (English translation by Henry Smith, for the Sydenham Society, 1847) He drew three further conclusions about cells, which formed his cell theory or cell doctrine. The first two were correct: # The cell is the unit of structure, physiology, and organization in living things. # The cell retains a dual existence as a distinct entity and a building block in the construction of organisms. By the 1860s, these tenets were the accepted basis of cell theory, used to describe the elementary anatomical composition of plants and animals. Schwann's theory and observations created a foundation for modern
histology Histology, also known as microscopic anatomy or microanatomy, is the branch of biology which studies the microscopic anatomy of biological tissues. Histology is the microscopic counterpart to gross anatomy, which looks at larger structures v ...
. Schwann claimed that "there is one universal principle of development for the elementary parts of organisms, however different, and this principle is the formation of cells." Schwann supported this claim by examining adult animal tissues and showing that all tissues could be classified in terms of five types of highly differentiated cellular tissues. # cells that are independent and separate, e.g. blood cells # cells that are independent but compacted together in layers, e.g. skin, fingernails,
feather Feathers are epidermal growths that form a distinctive outer covering, or plumage, on both avian (bird) and some non-avian dinosaurs and other archosaurs. They are the most complex integumentary structures found in vertebrates and a premie ...
s # cells whose connecting walls have coalesced, e.g. cartilage, bones, and
tooth enamel Tooth enamel is one of the four major tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the crown. The other major tissues are dentin, ...
# elongated cells forming fibers, e.g. tendons and ligaments # cells formed by the fusion of walls and cavities, e.g. muscles, tendons and nerves His observation that the single-celled
ovum The egg cell, or ovum (plural ova), is the female reproductive cell, or gamete, in most anisogamous organisms (organisms that reproduce sexually with a larger, female gamete and a smaller, male one). The term is used when the female gamete i ...
eventually becomes a complete organism, established one of the basic principles of
embryology Embryology (from Greek ἔμβρυον, ''embryon'', "the unborn, embryo"; and -λογία, '' -logia'') is the branch of animal biology that studies the prenatal development of gametes (sex cells), fertilization, and development of embr ...
. Schwann's third tenet, speculating on the formation of cells, was later disproven. Schwann hypothesized that living cells formed in ways similar to the formation of crystals. Biologists would eventually accept the view of pathologist
Rudolf Virchow Rudolf Ludwig Carl Virchow (; or ; 13 October 18215 September 1902) was a German physician, anthropologist, pathologist, prehistorian, biologist, writer, editor, and politician. He is known as "the father of modern pathology" and as the founder ...
, who popularized the maxim ''Omnis cellula e cellula''—that every cell arises from another cell—in 1857. The epigram was originally put forth by
François-Vincent Raspail François-Vincent Raspail, L.L.D., M.D. (25 January 1794 – 7 January 1878) was a French chemist, naturalist, physician, physiologist, attorney, and socialist politician. Biography Raspail was born in Carpentras, Vaucluse. A member of th ...
in 1825, but Raspail's writings were unpopular, partly due to his republican sentiments. There is no evidence to suggest that Schwann and Raspail were aware of each other's work.


Specialized cells

Schwann was particularly interested in nervous and muscular tissues. As part of his efforts to classify bodily tissues in terms of their cellular nature, he discovered the cells that envelope the
nerve fiber An axon (from Greek ἄξων ''áxōn'', axis), or nerve fiber (or nerve fibre: see spelling differences), is a long, slender projection of a nerve cell, or neuron, in vertebrates, that typically conducts electrical impulses known as action p ...
s, which are now called
Schwann cell Schwann cells or neurolemmocytes (named after German physiologist Theodor Schwann) are the principal glia of the peripheral nervous system (PNS). Glial cells function to support neurons and in the PNS, also include satellite cells, olfactory en ...
s in his honor. How the fatty
myelin Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can ...
sheaths of peripheral nerves were formed was a matter of debate that could not be answered until the
electron microscope An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
was invented. All axons in the peripheral nervous system are now known to be wrapped in Schwann cells. Their mechanisms continue to be studied. Schwann also discovered that muscle tissue in the upper
esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to t ...
was
striated Striations means a series of ridges, furrows or linear marks, and is used in several ways: * Glacial striation * Striation (fatigue), in material * Striation (geology), a ''striation'' as a result of a geological fault * Striation Valley, in ...
. He speculated that the muscular nature of the esophagus enabled it to act as a pipe, moving food between the mouth and the stomach. In examining teeth, Schwann was the first to notice " cylindrical cells" connected to both the inner surface of the enamel and the pulp. He also identified fibrils in the dentinal tubes, which later became known as "
Tomes's fibers An odontoblast process (also called Tomes's fibers or Tomes fibers, or by a dated term Tomes's fibrils) is an extension of a cell called an odontoblast, which forms dentin in a tooth. The odontoblast process is located in dentinal tubules. It for ...
". He speculated on the possible structural and functional significance of the tubes and fibrils.


Metabolism

In his ''Microscopical researches'', Schwann introduced the term "metabolism", which he first used in the German adjectival form "metabolische" to describe the chemical action of cells. French texts in the 1860s began to use ''le métabolisme''. ''Metabolism'' was introduced into English by Michael Foster in his ''Textbook of Physiology'' in 1878.


References


Further reading

* * * * * * * * * * * * * * *


External links

*
Schwann, Theodor and Schleyden, M. J. 1847. Microscopical researches into the accordance in the structure and growth of animals and plants. London: Printed for the Sydenham Society
* {{DEFAULTSORT:Schwann, Theodor 1810 births 1882 deaths People from Neuss 19th-century German biologists German Roman Catholics People from the Rhine Province Recipients of the Copley Medal University of Bonn alumni University of Würzburg alumni Humboldt University of Berlin alumni Catholic University of Leuven (1834–1968) faculty University of Liège faculty Members of the Royal Swedish Academy of Sciences Foreign Members of the Royal Society Recipients of the Pour le Mérite (civil class) German physiologists