Theodor Ambrose Hubert Schwann
- Schleiden-Schwann cell theory
- Schwann's cell unit
- Schwann's cells
- Schwann's sheath
Biography of Theodor Ambrose Hubert Schwann
The doctor and the botanist
Theodor Ambrose Hubert Schwann is remembered above all for his application of Mathias Schleiden’s cellular plant theories. He was the first of Johannes Müller's pupils to break with vitalism and work towards a physico-chemical explanation of life. He defined the cell as the fundamental unit of animal structure, that the animal body, like plants, is made up of single cells.
Schwann is considered the founder of modern histology. He is also credited as the originator of the theory that corruption and fermentation are processes of life. In this he gave some hint of the germ theory of disease. "For 20 years I have been travelling along some of the paths opened up by you", Louis Pasteur wrote to Schwann in 1878.
Schwann was not the discoverer of the animal cell, but rather the founder of the call theory. Before him, others had partly seen and described the morphological elements of animal tissue, now called cells, and recognised that the cell was the smallest, basic unit of animal structure. They were Francois-Vincent Raspail (1794-1878), René-Joachim-Henri Dutrochet (1776-1847), Gottfried Reinhold Treviranus (1776-1837), Friedrich Arnold (1803-1890), Johannes Peter Müller (1801-1858), Friedrich Gustav Jacob Henle (1809-1885), Johannes Evangelista Ritter von Purkinje (1787-1869) and Robert Brown (1773-1858). Robert Brown had discovered the cell nucleus in 1832 in orchids. The name cell had been used before by Raspail and Dutrochet, the latter coming very close to Schwann.
In 1837 the botanist Matthias Jakob Schleiden (1804-1881) had viewed and stated that new plant cells formed from the nuclei of old plant cells. When Schwann and Schleiden dined the following year, the conversation turned on the nuclei of plants and animal cells. Schwann remembered seeing similar structures in the cells of the notochord, as had been shown by Johannes Müller, and instantly realized the importance of connecting the two phenomena. The resemblance was confirmed without delay by both observers, and the results soon appeared in his famous Microscopic Investigations on the Accordance in the Structure and Growth of Plants and Animals, in which he declared that "All living things are composed of cells and cell products that are reproduced".
The boy from Neuss
Theodor Schwann was born in Neuss near Düsseldorf, then a part of Prussia. His father was a bookseller and strict Catholic. To his teachers and fellow pupils in primary school and at the progymnasium, Schwann was a cooperative child, diligent and modest. Little tempted by the delights of society, lacking self-confidence, and excessively shy, he withdrew into study, family life, and piety. Equally brilliant in all branches of learning, he showed a particular inclination for mathematics and physics. Given his lack of interest in the outside world, it was accepted that his vocation should be directed toward the church when he, in 1826, left his native town to enter the Jesuit College of the Three Crowns in Cologne.
Here Schwann came under the influence of an exceptional religious teacher, Philipp Karl Joseph Anton Johann Wilhelm Smets (1796-1848). To Schwann, Smets’ teaching was a revelation and it was from him that Schwann learned the lesson of the elevation of man by personal perfection.
Inreasingly enamored with reason, Schwann renounced theology to take up medical studies. His philosophical position became that of a christian reationalist whose personal philosophy was in the tradition of René Descartes (1596-1650) and Gottfried Wilhelm Leibniz (1646-1716).
In October 1829 Schwann entered the University of Bonn, where he enrolled in the premedical curriculum and obtained his bachelor’s degree in 1831. He had ample opportunity to let himself be influenced by the giants of his time. At Bonn he attended Johannes Peter Müller’s (1801-1858) lectures on physiology and began to assist him in the laboratory. In the autumn of 1831 Schwann moved to Würzburg, where he studied for three semesters, attending clinical lectures. Here he was a pupil of Johann Lukas Schönlein (1794-1864), whose academic appointment was rescinded in 1832 for political reasons.
In April 1833 Schwann left Würzburg for Berlin, where Johannes Müller had been appointed to teach anatomy and physiology. In Berlin, Schwann attended clinical demonstrations and prepared his dissertation, on the necessity of air for the development of chicken eggs. It was Müller who suggested the theme for the dissertation, and guided Schwann in the work that made him doctor of medicine on May 31, 1834. He passed the state examination on July 26, and immediately became one of Müller’s assistants at the anatomical museum of Berlin, remaining in that position until 1835.
In Berlin during this period, Müller was working on the Handbuch der Physiologie, which introduced into Germany Magendie’s experimental method in medical studies. Müller, however, remained a convinced vitalist until his death. Restricted in his chemical and physical background, Müller progressively detached himself from physiology and and devoted himself entirely to comparative morphology, in which field he acquired fame. Schwann, on the other hand, from the beginning of his career took a completely different position, which inaugurated the quantitative period of physiology.
Müller’s Handbuch was not merely a compilation; he critically examined all the notions that he printed. Repeating the experiments of others, suggesting new ones, opening avenues not yet explored, this treatise is as unique in its conception as in its realization. In the section entrusted to him, Schwann enriched Müller’s Handbuch with the results of extensive work and contributed numerous new notions. This books also contains an account of a study clearly showing Schwann’s innovating tendency; his first experiments can be dated on the basis of his laboratory notebooks, at April 16, 1835.
Schwann envisaged experiments in which it would be possible to subject the physiological properties of an organ or of a tissue to physical measurement. One such method involved measuring the secretion of a gland. But it was the muscle that seemed to him likely to furnish the most rewarding results. He planned to measure the length of a muscle contracted by the action of the same stimulus for different loads or, further, to compare the intensity of the contraction with that of the stimulus. He accomplished this experiment by means of the «muscular balance» and in a sense established the first tension-length diagram. It was in 1837 he made the classic experiment showing that the tension of a contracting muscle varies with its length.
Parallel with his experiments on muscle, Schwann pursued the researches that led to his discovery of pepsin. In 1836, while investigating the digestive process, Schwann isolated a substance responsible for for digestion in the stomach and named it pepsin, the first enzyme prepared from animal tissue. He coined the term metabolism to describe the chemical changes that take place in animal tissue. In 1841, using an artificial biliary fistula in a dog, he showed that bile is essential for digestion.
Life is in the air
About 1835 Joseph-Louis Gay-Lussac’s (1778-1850) observations, prompted by Nicolas Apert’s (1749-1841) experiments, made acceptable the notion that oxygen was the agent of both fermentation and putrefaction. Apert was the inventor of airtight food preservation. He observed that neither infusorians nor the smell of putrefaction appeared in a maceration of meat that had been boiled, and noted the appearance of both these phenomena when he used an unboiled maceration or unheated air. Convinced that it was the destruction of germs that prevented the development of infusorians and molds, and that the prevented putrefaction, Schwann wished to make a counterproof by showing that the heating of air did not prevent the operation of a chemical process to which it contributed oxygen, and not germs. He demonstrated that a frog breathes normally in previously heated air, and he investigated alcoholic fermentation, which also depended, in the current opinion, on the presence of oxygen. To his great astonishment, Schwann observed that heating the air he bubbled through a boiled suspension of yeast in a sugary solution prevented fermentation in certain experiments. In january 1836 he noted in his laboratory notebook the conclusion that alcoholic fermentation is the work of a live organism.
The description of the multiplication of yeast cells appears in Schwann’s laboratory notebook under the date of February 16, 1836. The first public announcement of the relationship between alcoholic fermentation and the life cycle of yeast was by Cagniac de la Tour, who described the multiplication of yeast in the issue of L’Institut for November 25, 1836. Schwann’s paper of 1837, however, independently demonstrated the living nature of the agent of fermentation and presented arguments of a new sort.
In the period of 1839-1848, while he was professor of physiology at the University of Louvain, Belgium, he identified the role of microorganisms in the process of decay, as he observed the formation of yeast spores and concluded that the fermentation of sugar and starch was the result of life processes. The fact that this process is one of living organisms, however, was not accepted until the time of Louis Pasteur, who wrote to him in 1878: "for 20 years I have been travelling along some of the paths opened up by you". Schwann also formulated the basic principle of embryology by observing that the egg is a single cell that eventually develops into a complete organism.
In 1839 Schwann published his monograph Mikroskopische Untersuchungen über die Übereinstimmung in der Struktur und dem Wachstum der Thiere und Pflanzen (Microscopic Researches into Accordance in the Structure and Growth of Animals and Plants), which was translated into English for the Sydenham Society in 1847 by Henry Smith. In this monoghraph he described cells to support the thesis that the cell nucelus and its protoplasm form a universal structure. In it he described and illustrated with beautiful drawings, the structure of nerve cells and muscle cells.
The Mikroskopische Untersuchungen is composed of three parts. The first is devoted to a microscopic study of the chorda dorsalis in frog larvae. Studying that structure, Schwann found that it consists of polyhedral cells that have in or on the internal surface of their wall a structure corresponding to the nucelus of the plant cells. He also found the structure of cartilage to be in accordance with the tissues of plants. It was not until 1830 that the perfecting of the microscope permitted Robert Brown to recognize the presence of the nucleus as the essential characteristic of the plant cell.
In the second part Schwann presented a findings that the varied forms of the «elementary parts» of tissues – be they epithelium, hoof, feather, crystalline lens, cartilage, bone, tooth, muscle tissue, fatty tissue, elastic tissue, nerve tissue – are products of cellular differentiation.
In the third part, of a philosophical nature, Schwann, on the basis of his cell theory expounded in the first two parts, developed a theory of the cells that he presented as purely hypothetical. He stated that according to the cell theory, one may suppose that an organised body is not produced, as was accepted by theological theories, by a fundamental power guided in its operation by a definite idea, but is developed, according to blind laws of necessity, by powers that, like those of inorganic nature, are established by the very existence of matter. He believed that the source of life phenomena resided in another combination of the materials of the inorganic world, whether it be in a peculiar mode of the atoms to form molecules, or in the arrangement of these conglomerate molecules to form parts of an organism.
Before publishing his Mikroskopische Untersuchungen, Schwann asked the bishop of Mecklingen, then head of the clergy at his home town, whether his discovery was contrary to the doctrine of the Church, in which case he would have doubts regarding publication.
Schwann’s cellular theory was a concept of great importance for the development of Virchow's cellular pathology.
Schwann was a quiet, deeply religious man who always avoided conflicts, and maybe this lack of aggressive drive prevented him from succeeding in pursuing a career in German academic medicine, this despite the fact that as early as in 1839 he had made two significant contributions to science. Not succeedeing in achieving an academic appointment in Germany, he eventually accepted the chair of anatomy at the free Catholic University of Louvain, succeeding Charles-Joseph Windischmann (1807-1839). In 1848 he moved to the State University of Liège (Lüttich), where he was professor of phsyiology and comparative anatomy until his retirement in 1880.
However, in 1839, when he became profesor of anatomy at Louvain, his mainspring of enthusiasm and discovery was broken. Like Pascal before him, he abandoned rationalism to return to the God of his childhood, the «God of the heart, not of reason.» A conscientious professor at Louvain and at Liège (from 1848), Schwann spent the rest of his life in a solitary existence darkened by episodes of depression and anxiety.
Before he went to Liège in 1848, Schwann had been approached by his friend Joseph Antion Spring 1814-1872), who presented the proposals of the Belgian government, including a substantial increase of salary and the promise, never fulfilled, of the construction of an institute of anatomy. When Schwann was appointed, he first received the chair of anatomy, which previously had been held by Spring, who also taugh physiology. In 1858 Spring became professor of general pathology and clinical medicine, and Schwann of physiology as well as of general anatomy and embryology. In 1872 he abandoned general anatomy and in 1877 embryology, teaching only physiology until he retired in 1879.
During his stay at Louvain (1839-1848) Schwann developed a method of utilizing the biliary fistula for the study of the role of bile in digestion, and concluded that a lack of bile secretion in the digestive tract is incompatible with survival. He received the Sömmering Medal in 1841; and in 1847 the Sydenham Society published an English version of his Mikroskopische Untersuchungen, translated by Henry Smith, who in his introduction presented the following judgement: «The treatise has now been seven years before the public, has been most acutely investigated by those best competent to test its value, and the first physiologists of our day have judged the discoveries which it unfolds as worthy to be ranked among the most important steps by which the science of physiology has ever been advanced.»
The papers of 1844 and 1845 that record Schwann’s work on the biliary fistula were his last physiological works. After that time, although he never ceased to work in the laboratory, his scientific inquiry lost its impact. Following his arrival in the prosperous industrial region of Liège, he became more of an inventor, developing a number of instruments used in mining technology, including pumps for the aspiration of water in coal mines and a respiratory apparatus for rescue operations. This instrument is the ancestor of the apparatus for measuring metabolism in man and of the devices used by divers.
All of Schwanns fundamental research occured while he was with Johannes Müller, and there he had fellow students like Friedrich Gustav Jacob Henle (1809-1885), Theodor Ludwig Wilhelm Bischoff (1807-1882), and Robert Remak (1815-1865.
Only once was Schwann involved in a controversy, about his faith, because the catholic priest had quoted him as agreeing to the authenticity of the tomfoolery of a young woman who claimed to have been inspired by the Holy Ghost; an incidence called the Louise-Lateau case. Schwann disputed this in a pamphlet. He remained a bachelor.
Schwann is said to have been a very amiable, pleasant person, of middle height, with lively eyes.
It was only after his death it became known that Germany repeatedly had tried to regain its lost and famous son. Schwann had been discussing positions at Breslau (1852), Munich (1854), Würzburg (1854), and Giessen (1855), but remained faithful to his dear adopted fatherland, Belgium. However, he died in Germany. During a Christmas visit to a brother and sister living in Cologne, Schwann suffered a stroke and died on January 11, 1882, after two weeks of agony.