Theodor Schwann (; 7 December 181011 January 1882) was a German physician and physiologist. and the invention of the term "metabolism".

Early life and education

Theodor Schwann was born in Neuss on 7 December 1810 to Leonard Schwann and Elisabeth Rottels.

In 1829, Schwann enrolled at the University of Bonn in the premedical curriculum. He received a bachelor of philosophy in 1831. While at Bonn, Schwann met and worked with physiologist Johannes Peter Müller. 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 for clinical training in medicine. He could afford to do so, at least in the short term, because of a family inheritance.

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.

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". As of 1872, he ceased to teach general anatomy, and as of 1877, embryology. He retired fully in 1879.

Muscle tissue

Some of Schwann's earliest work in 1835 involved muscle contraction, which he saw as a starting point for "the introduction of calculation to physiology". Schwann's notes suggest that he hoped to discover regularities and laws of physiological processes.

Pepsin was the first enzyme to be isolated from animal tissue.

He demonstrated that it could break down the albumin from egg-white into peptones.

Even more importantly, Schwann wrote, by carrying through such analyses one could eventually "explain the whole developmental process of life in all organized bodies."

By 1836, Schwann had carried out numerous experiments on alcohol fermentation.

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 was necessary for the process to happen. Next, Schwann tested the effects of purified air and unpurified air.

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. Ironically, Schwann's work was later seen as being a first step away from vitalism.

The value of Schwann's work on fermentation eventually would be recognized by Louis Pasteur, ten years later. 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".

He drew three further conclusions about cells, which formed his cell theory or cell doctrine. The first two were correct:

  1. The cell is the unit of structure, physiology, and organization in living things. 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.

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, 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 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. How the fatty myelin sheaths of peripheral nerves were formed was a matter of debate that could not be answered until the electron microscope 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 was striated.

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". 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

  • 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