CELL AND CELL THEORY

Z Janssen and H. Janssen were the first to the construct properly working compound microscope in 1590.Leeuwenhoek made notable improvements in the lenses of compound microscope. In 1665, Robert Hooke cut a thin section of cork and observed it under the microscope. He found that cork was made of large number of chambers similar to those of beehive. Hooke referred to these chambers as cells. In fact the cork cells were dead, and loving cells were never empty but they were filled with cytoplasm.
In 1824, Dutrochet concluded that all biological tissues are composed of cells and that these cells are attached with each other due to some adhesive compound. A few years later, in 1838, Schlieden published his studies on the structure of plant tissues and concluded that all plant tissues were made up of cells. In the next year, in 1839, Schwann concluded the same thing for animal tissues on the basis of his studies. Thus in 1839, conclusive evidence was presented to prove that all cell is a structural unit in both plants and animals, and it was postulated that cell is also a functional unit of all living organisms. These conclusions are popularly known as the Cell Theory, and it is credited to Schlieden and Schwann. In 1846, Nageli provided the logical extension of cell theory; he postulated that all the cells originate from preexisting cells. Virchow, in 1855, presented an elaborate version of this hypothesis alongwith considerable evidence in its support; it is referred to as Cell lineage theory and is credited to Virchow.