Theodor Schwann

Friedrich Theodor Schwann (7 December 1810 in Neuss - 11 January 1882 in Cologne) was a Prussian naturalist, physiologist and anatomist, considered one of the founders of cell theory. In addition, fermentations and nerve fibers, in which he described the Schwann sheath, Schwann cell and contributed significantly to histology.

Biography

Theodor Schwann was born in Neuss, near Düsseldorf, on December 7, 1810. He met Johannes Müller, a physiologist, whom he helped in his experiments. Schwann continued his medical studies at the University of Wurzburg and later at the University of Berlin, from which he graduated in 1834. His doctoral thesis was on the respiration of the chick embryo.

In 1839 Schwann was appointed professor of anatomy at the University of Leuven, Belgium, where he remained until 1848, when he accepted a professorship at the University of Liège. He there he remained until his retirement in 1880. After leaving the influence of Müller, Schwann's productivity practically ceased: in Belgium he made only one publication on the use of bile. He was an excellent teacher, conscientious, loved and appreciated by his students.

Schwann's work was actually recognized by scientists in other countries, and in 1879 he was made a Fellow of the Royal Society and also of the French Academy of Sciences. In 1845 he received the Copley Medal. He died on January 11, 1882, at the age of 71, in Cologne.

Contributions

Physiology

At the University of Berlin, Schwann again came into contact with Müller, who convinced him to pursue a scientific career. Very shortly after starting to work with Müller, he had his first success. Using extracts from stomach linings, Schwann demonstrated that a factor other than hydrochloric acid was at work in digestion. Two years later, in it, he succeeded in isolating the active principle, which he called "pepsin".

Between 1834 and 1838 Schwann conducted a series of experiments designed to resolve the question of the truth or falsity of the concept of spontaneous generation. His method consisted of exposing a sterilized (boiled) broth only to hot air in a glass tube. The result he obtained was the impossibility of detecting microorganisms and the absence of chemical change (putrefaction) in the broth. He was convinced that the idea of spontaneous generation was false. His 1836 studies of sugar fermentation also led to his discovery that yeast caused the chemical process of fermentation.

At Müller's suggestion, Schwann also began research on muscle contraction and discovered striated muscles in the upper part of the esophagus. He also identified the delicate sheath of cells that surround peripheral nerve fibers, now called the Schwann sheath.

Cell theory and metabolism

In 1839, Schwann became acquainted with Matthias Schleiden's microscopic investigation of plants. He described the plant cell and proposed a theory of the cell that he was sure held the key to plant growth and anatomy. Following this line of research on animal tissues, Schwann not only verified the existence of cells, but traced, in the development of adult tissues, many of the stages of the early embryo. This investigation and the cell theory that followed were summarized in Mikroskopische Untersuchungen über die Uebereinstimmung in Le vide of plante (1839; Microscopic Investigations into the Similarity in Structure and Growth of Fauna and of flora). In this work, Schwann demonstrated that "the great barrier between the animal kingdom and the vegetable kingdom, namely the diversity of ultimate structure, disappears," establishing the cell theory. Schwann then proposed three generalizations about the nature of cells:

• animals and plants are formed by cells plus the secretions of cells;
• these cells have an independent life;
• are subject to the life of the organism.

On the other hand, he realized that the phenomena of individual cells can be summarized into two classes: «those that refer to the combination of molecules to form a cell, called plastic phenomena», and «those that result from chemical changes, either in the component particles of the cell itself, or in the cytoplastema (today cytoplasm), called metabolic phenomena». Thus, Schwann coined the term "metabolism", which became generally adopted for the set of chemical processes and by which energy changes occur in living things.

Histology

Schwann also contributed to the understanding and classification of adult animal tissues. He classified tissues into five groups: separate, independent cells, like blood; compaction of independent cells, such as skin; cells whose walls have joined together, such as cartilage, bone, and teeth; elongated cells that form fibers, such as tendons and ligaments; and finally, cells formed by the fusion of their walls and cavities, such as muscles. His conclusions were also the basis for the modern concept of embryology, which described embryonic development as a succession of cell divisions.

This generalization of the essential structural relationship of all living beings had been denied for centuries by the ancient Aristotelian doctrine of plant and animal souls. Perhaps Schwann's findings were more disturbing than he would have liked to admit, since he realized that he supported a physical rather than a theological explanation. Schwann saw the consequences of his discoveries, and the idea of the world of life as nothing more than a machine horrified him. He found refuge in the Catholic faith, choosing, as he said, a God "more sensitive to the heart than to reason."