Theodor Ambrose Hubert Schwann
Theodor Ambrose Hubert Schwann
Theodor Schwann was a German physiologist who is credited with publishing the most influential work on cell theory. He made significant findings in the study of digestion, fermentation, and tissues.
Schwann originally left his hometown of Neuss to study religion in Cologne. Instead, he gave up theology to enroll in premedical studies at the University of Bonn. Later, in Berlin, he prepared a dissertation under the guidance of Johannes Müller (1801-1858). Following his graduation, Schwann became Müller's assistant and devoted his time to research.
Having become interested in digestive processes, Schwann isolated from the lining of the stomach a chemical that was responsible for the digestion of protein. This chemical, which he called pepsin, was the first enzyme to be isolated from animal tissue.
Interested in disproving the theory of spontaneous generation (the production of living organisms from nonliving material), which was experiencing a resurgence in popularity among the German scientific community, Schwann began to research fermentation. He demonstrated that yeast consists of plant-like organisms and that the fermentation of sugar is the result of the life processes of yeast cells. Schwann later used the term "metabolism" to describe the chemical changes that occur in living tissue. His findings, however, received so much adverse criticism that he left Germany for Belgium, where he worked as a professor at the universities of Liege and Louvain. (His findings on fermentation would later be confirmed by Louis Pasteur.)
Previous to Schwann, no one had thought that an organism was composed solely of cells, although cells had been observed in both plants and animals under the microscope. While assisting Müller, he observed small units containing nuclei in animal tissue; he realized that these units were the animal equivalent to the plant cells studied by researcher Matthias Schleiden (1804-1881). Schwann also noticed that the fertilized egg from which an animal grows contains a nucleus and is surrounded by a membrane similar to the nucleus and membrane of animal tissue.
In 1839, one year after Schleiden presented his cell theory, Schwann published his own version of cell theory. While Schleiden's theory only applied to plants, Schwann offered a more precise theory that he extended to animals. This work, whose title in English is Microscopical Researches on the Similarity in the Structure and Growth of Animals and Plants, began with a presentation of Schwann's study of frog larvae. He asserted that the cells of the frog's notochord (the structure providing dorsal support) and cartilage are like plant cells; all contain a nucleus, membrane, and vacuoles. He then proceeded to argue that all organisms are made up entirely of cells or of the products of cells. The lives of individual cells, in turn, are subordinate to the life of the organism. Schwann also described the egg as a single cell that eventually develops into a complex organism. The cell, he maintained, is the basic unit of all life and the smallest unit capable of independent reproduction.
In his book Schwann wanted to supercede the religious view of living things being shaped by a divine plan with a scientific vision in which organisms are products of natural forces. Interestingly, Schwann eventually abandoned the pursuit of science for religious and mystical studies. Nevertheless, cell theory soon became widely accepted and is now considered one of the fundamental concepts of biology.