Dutch lens grinders Hans and Zacharias Janssen make the first microscope by placing two lenses in a tube.
Robert Hooke studies various object with his microscope and publishes his results in Micrographia. Among his work were a description of cork and its ability to float in water.
Anton van Leeuwenhoek uses a simple microscope with only one lens to look at blood, insects and many other objects. He was first to describe cells and bacteria, seen through his very small microscopes with, for his time, extremely good lenses.
Several technical innovations make microscopes better and easier to handle, which leads to microscopy becoming more and more popular among scientists. An important discovery is that lenses combining two types of glass could reduce the chromatic effect, with its disturbing halos resulting from differences in refraction of light.
in 1828 Robert Brown first recognized the cell nucleus. It shows about twenty orchid epidermal cells, and the nucleus can clearly be seen within each cell. Three stomata can also be clearly seen - these are the breathing pores through which a plant exchanges gases with the atmosphere. He used a microscope do discover these things
Matthias Schleiden became the first to formulate what was then an informal belief as a principle of biology equal in importance to the atomic theory of chemistry
The German biologist Theodor Schwann (1810-1882) is considered a founder of the cell theory. He also discovered pepsin, the first digestive enzyme prepared from animal tissue, and experimented to disprove spontaneous generation.
born March 27, 1817, Kilchberg, Switz.—died May 10, 1891 He noted what he called transitory cytoblasts, which later were identified as chromosomes. He also witnessed cell division and investigated the process of osmosis in unicellular algae.
Rudolf Virchow born October 13, 1821—died September 5, 1902,his application of the cell theory to explain the effects of Disease in the organs and tissues of the body. He emphasized that diseases arose, not in organs or tissues in general, but primarily in their individual.
Ernst Ruska develops the electron microscope. The ability to use electrons in microscopy greatly improves the resolution and greatly expands the borders of exploration.