A worksheet function that is called by Excel can call back into Excel using the C API. An XLL command that is called by Excel can call the C API. DLL and XLL functions and commands that are called by VBA when VBA has itself been called by Excel can call the C API.
Cell Theory. The discovery of the cell was made possible by the invention of the microscope, which was made possible by improved lens-grinding techniques.Antoni van Leeuwenhoek (1632-1723), a Dutch tradesman, learned to grind lenses and assemble them into simple microscopes.nspired by Hooke's work, Leeuwenhoek began making microscopic examinations of his own. In 1678, he reported to the Royal Society that he had discovered little animals -- bacteria and protozoa -- in various samples. The society asked Hooke to confirm Leeuwenhoek's findings, and he did.
By 1838 his methods had led him to propose the cell theory for plants. Schleiden was the first to recognize the importance of cells as fundamental units of life. In his most well-known article, Schleiden described Robert Brown's 1832 discovery of the cell nucleus (which he renamed cytoblast).Schleiden knew that the cell nucleus must somehow be connected with cell division, but he mistakenly believed that new cells erupted from the nuclear surface like blisters.n his most well-known article, Schleiden described Robert Brown's 1832 discovery of the cell nucleus (which he renamed cytoblast). Schleiden knew that the cell nucleus must somehow be connected with cell division, but he mistakenly believed that new cells erupted from the nuclear surface like blisters.