Lecture 6 - Cells & Germs

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History and Philosophy of Science and Technology
Chen- Pang Yeang

HPS211 Lecture 6 MAY31/2012 Cell th Studies of Living Organisms before late 18 Century - Natural History was focused on: fieldwork, observe, collect, classify species - Medicine was focused on form and functions of human body  Studies of animals and plants as by-products - Faculties of medicine, private collections (Linnaeus, Buffon) Transformation in the Late 18 Century - Shift focus from species in wild to the bodies of organisms - Rise of morphology (i.e. Cuvier’s comparative anatomy)  concerns the study of structure and forms of animals and plants  Morphology done in laboratories (indoors) - Museums of natural history as research centers th I. Transformation of Life Science in the 19 century - Shift focus from morphology to physiology  Physiology  the study of the functions of organs in a body  It emphasizes function (structure vs. function  morphology vs. physiology)  It became a dominant type of biological studies; replaced natural history, morphology, etc. - Emphasis on experimental method, laboratory science (i.e. microscope, vivisection, tissue culture) - New institutions in France and Germany  Collège de France: François Magendie and Claude Bernard  Teaching Laboratories at research centers  University of Berlin: Johannes Müller, Carl Ludwig, Emil DuBois-Reymond, Hermann Helmholtz - “Biology” as the denotation of life science th - Cell was discovered in the 17 century by Robert Hooke  Hooke got hold of a microscope and he improved the resolution and magnification, leading to his discovery of cells  Hooke wrote a book called Micrographia (1665) – an account of his observation - After Hooke, more and more natural scientists observed cells using microscope - Antonie van Leeuwenhoek: talented artisan  Improved the image quality of the microscope  Saw something Hooke didn’t  saw cells moving, and therefore they are LIVING cells - Using powerful microscopes other scientists observe more new things  Nucleus discovered inside the cells (Robert Brown)  Identified egg cells from animal ovaries (Karl Ernst von Baer)  Sperm cells in animal semen (Antonie van Leeuwenhoek) II. Schleiden and Schwann’s Cell Theory - Jakob Matias Schleiden (Jena)  lawyer turned botanist - Theodore Schwann (Berlin)  received education in a Jesuit college, assisted Müller - Their proposals came independently regarding cells - Schleiden and Schwann’s observations: 1. Cells are present in almost all plant and animal tissues 2. A cell comprises a body and a nucleus within - Schleiden and Schwann’s Cell Theory (1838-39) 1. All tissues of living beings are made of cells (structural claim) 2. Cells are basic units of life; they are lively themselves and are responsible for lively phenomena of an organism (functional claim) - Schleiden and Schwann’s Theory of Cell Formation 1. A new cells emerges from its mother cell 2. Chemical substance of mother cell’s nucleus spills out to form a granule in the mother cell body 3. Granule grows as more nuclear substance deposits on it 4. When the granule is large enough, it separates from mother cell and grows further into a full cell 5. A process similar to crystallization; inorganic chemical reaction 6. Free cell formation III. Remak and Virchow’s Theory of Cell Formation: Division - Schleiden and Schwann’s view on cells was disagreed by a number of biologists, especially Robert Remak (Berlin) and Rudolph Virchow (Berlin)  Virchow, professor of medicine  trained lots of students - Remak and Virchow’s Theory of Cell Formation  A new cell is formed through division from an existing cell  this is the only way of cell formation  Virchow’s slogan (1855): omnis cellula e cellula (every cell is from a pre-existing cell) - Context: Vitalism vs. Materialism  Materialism – Organisms are like machines; life can be reduced to physical and chemical effects  Descartes, Boerhaave, Buffon, Helmholtz, Schleiden, etc.  Vitalism – organisms require some vital forces or agents; life cannot be reduced to physical and chemical effects  Stahl, Linnaeus, Müller, Remak, etc  “Spontaneous generation” at the center of the debate  Free cell formation was considered spontaneous generation. Hence its replacement with cell division was considered a victory of vitalism over materialism IV. New Directions of Researches and Thoughts - Cells with a simple structure  Hooke cells (1655) – cells as empty boxes  no structural significance  Schwann cells (1850s) – includes nucleus, cytoplasm, and membrane - Cell as a mini-organism  Many organelles discovered in 1850s-1900s  Has lots of microscopic entities (i.e. mitochondria, ribosomes, etc.)  Each organelles/ microscopic entity has functions that is important for the growth of cell  2 half of 19 c., scientists discovered unicellular organisms (i.e. slime molds, amoeba, bacteria)  can cause disease, chemical reaction, etc. - Made possible by technological progress  Compound-lends microscope to overcome spherical and chromatic aberrations  Staining techniques  Microtome techniques (making thin sections of tissue)  Tissue culture - Theory of Cell State a. A sociological metaphor of life – an organism as a “state” of individual cellular organisms b. “Division of labor” developed as number multiplies c. The whole organism reduced to the sum of individual cells d. Counterpoint: holism – the whole is more than the sum of individuals; organism as a complex integrated system; homeostasis and teleology - Embryology and Heredity  Cell theory and microscopy enabled biologists to follow the development of an organism from a fertilized ovum to an embryo and eventually to an adult  Significance of nucleus in ce
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